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Message thread on the nature of Gravity
The following are messages on Gravity's Mechanism that were sent on CompuServe's
AstroForum between November 18 and December 8, 1989. The subject line and
date/time lines have been deleted to save space. A few messages were lost due to
scrolling before capture. A few others were deleted either because they were
personal in nature or were not related to the topic. - Dan Ward
#: 51966 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Tom VanFlandern/DC 71107,2320 (X)
Interesting about the non-displacement of the Sun's gravity, and the
resultant theory that it is faster than light. Now, how to test?
I kinda like my annihilation of a massive body into energy, via a nuke, and
test for resultant perturbations in the positions of nearby bodies.
* Reply: 51992
#: 51992 S11/Cosmology
Fm: Jeff Heleen 76545,501 To: Paul Burke/CA 74656,2333 (X)
Query: but even if you did blow up a thingy in space with a nuke, assuming the
nuke was at the center and the thingy blew up with matter (atoms) spewing out
equally in all directions, wouldn't the center of mass for the thingy still be
where it was before therefore still able to perform its role as if it were
still there?
Jeff
* Reply: 52002
#: 52002 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Jeff Heleen 76545,501 (X)
The idea is to convert as much mass as possible into energy, Jeff, with the
expectation of observing an alteration in the orbital paths of numerous
objects surrounding the thingy.
If gravity is instantaneous, before the light burst hits any of the others,
there SHOULD be something measurable in the paths of the orbiters.
* Reply: 52034
#: 52034 S11/Cosmology
Fm: Emory Kimbrough 72777,1553 To: Paul Burke/CA 74656,2333 (X)
Unfortunately, the energy is also a source of gravity. Besides, if you are
only invoking mass-energy conversion, why did you include the asteroid?
* Replies: 52157, 52288
#: 52157 S11/Cosmology
Fm: Jeff Heleen 76545,501 To: Emory Kimbrough 72777,1553 (X)
Ah. You've anticipated my question. I wondered whether or not energy had
gravity, it being equivalent to matter. Have they taken that into account when
hypothesizing about the 'missing mass' in the universe?
* Reply: 52185
#: 52185 S11/Cosmology
Fm: Emory Kimbrough 72777,1553 To: Jeff Heleen 76545,501 (X)
Yes, that has been taken into account. Notice, though, that E=mc^2 tells you
that mass ties up quite a lot of energy. For that reason, if you are going on
a dark-matter safari, you had best hunt for more matter, not for more momentum
carried by existing matter.
* Reply: 52458
#: 52458 S11/Cosmology
Fm: Jeff Heleen 76545,501 To: Emory Kimbrough 72777,1553 (X)
And here I thought I was on to something (sigh). Guess I'll just have to keep
thinking. Thanks. (grin)
#: 52288 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Emory Kimbrough 72777,1553 (X)
Me, invoke an asteroid? Not on THIS forum!
To my simple direct method of cogitation, since gravity 'appears' to have
something to do with mass, I speculated that eliminating a lot of mass
quickly just might have a gravitational effect on nearby objects. The time
relative to the start of the nuking and dissolution of the asteroid,
changing its mass to energy, and the detection of the change at a remote
location would possibly give a value to the speed of gravitation detection.
Could be I'm wrong.
* Replies: 52307, 52358
#: 52307 S11/Cosmology
Fm: Emory Kimbrough 72777,1553 To: Paul Burke/CA 74656,2333 (X)
None of the asteroid's mass will change to energy. The asteroid is absorbing
energy from the explosion, not releasing more energy. It will actually get
heavier as the bomb (rapidly) gets lighter.
On the other hand, if you use a tritium-lithium asteroid......
* Reply: 52346
#: 52346 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Emory Kimbrough 72777,1553 (X)
Emory, I'd use anything at all to eliminate as much mass as possible as
rapidly as possible to get a nice 'step' function in the position readings
of the monitoring objects.
Even if the mass conversion to energy is slow, I'd expect to see a
'ramping' effect on the position monitors before the spike representing the
arrival of the light wave from the explosion reaches the same sensors. That
is, IF gravity is faster than light.
If the position monitors don't show any ramping or other effects until the
light wave passes, then gravity is slower or at least not as fast as light.
#: 52358 S11/Cosmology
Fm: Dick DeLoach, Sysop 76703,303 To: Paul Burke/CA 74656,2333 (X)
If gravity propagates faster than light, then you could be in the same
position as the Classical Greeks who first attempted to measure the speed of
light. They put one guy on a hill-top with a lanturn fixed with a shutter and
another guy on the valley floor below, with a timing device of some sort. The
guy at the top opens the shutter and shouts, "NOW!" ....
--- Dick
* Reply: 52380
#: 52380 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Dick DeLoach, Sysop 76703,303 (X)
And the guy at the bottom of the hills says, "What??". His companion
recorder says "He said NOW". "Ok, got it."
And that's how we know light travels 6 pendulicalars per stadia.
* Reply: 52473
#: 52473 S11/Cosmology
Fm: Dick DeLoach, Sysop 76703,303 To: Paul Burke/CA 74656,2333 (X)
Actually, I was being serious. I think that *was* the first technique used to
measure the speed of light. The reported speed was something like: "If not
instantaneous, then very fast". This from an obscure monograph on the history
of attempts to measure the speed of light, which I recall browsing years ago.
--- Dick
* Reply: 52536
#: 52536 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Dick DeLoach, Sysop 76703,303 (X)
I remember seeing the picture of a similar time experiment after the
'invention' of electricity. A line of monks, somewhere in the neighborhood of
a mile? was assembled, and one touched the positive pole of a battery, while
holding hands with another, who linked with another, until the chain was
complete back to the battery, at which time the last monk in line touched the
negative pole.
They all leaped into the air simultaneously.
And never repeated THAT experiment!
* Replies: 52641
#: 52641 S11/Cosmology Fm: Peter Lipschutz 71651,71 To: Paul Burke/CA 74656,2333
Hello...haven't been here for months...
I seem to recall something in my physics classes about the INSTANTANEOUS
"communication" between electron-pair components REGARDLESS of
the distance......this implies some sort of superluminal property yes???
I guess we'll just have to wait for the Super Collider to see if there is a
viable connection between gravity and everything else..
In the mean time.......keep 'em flying, Peter
#: 52101 S11/Cosmology
Fm: Lenny Abbey 72277,566 To: Tom VanFlandern/DC 71107,2320 (X)
Tom, if strange theorums are not to be dismissed just because they sound like
alchemy, we will need to drop back and check out Velikovsky before progressing
to gravitons.
* Reply: 52110
#: 52110 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Lenny Abbey 72277,566 (X)
Lenny,
As nearly as I can tell from what little I have read of him, Velikovsky
does not strike me as a crackpot at all (which is certainly his reputation
among astronomers), but rather as an intelligent man who was mistaken about
most of the conclusions he drew because of a few bad premises. Even so, he
had a few worthwhile ideas; and the effort to disprove his central thesis,
which only took place a generation after he published, was time well spent,
revealing some unanticipated weaknesses in accepted astronomical theories.
In other words, arguing against the conclusion implicit in your message,
I think that every idea proposed by sane minds deserves some consideration on
its merits. It has been my experience that even wrong hypotheses provide some
useful insights. I mean, it *could* perfectly well turn out the the whole Big
Bang idea is way off the mark, and that some other cosmology is correct. But
it would seem rash to conclude that the time spent in developing the theory
and its implications was wasted effort.
When the professionals stop making major blunders of their own, maybe
I'll be quicker to dismiss peculiar new ideas. Even then, I wouldn't dismiss
everything a man ever wrote without inspection, even if his name is
Velikovsky. -|Tom|-
* Reply: 52133
#: 52133 S11/Cosmology
Fm: Lenny Abbey 72277,566 To: Tom VanFlandern/DC 71107,2320 (X)
My argument is that if every idea proposed by sane minds should be considered
on its merits, who decides which ideas we are going to investigate first, and
their priority?
Isn't it out of place to devote time to gravitons and Velikovsky when we have
not yet fully discussed the works of Heraclitus and Senna?
At some point we are forced to use personal opinion and prejudice (a much
misunderstood and unjustly maligned word) in order to prevent our orderly
progression from ignorance to enlightenment being mired down with
investigations of the rantings of theorists who sometimes seem "sane" (another
poor word) to some people.
* Reply: 52142
#: 52142 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Lenny Abbey 72277,566 (X)
Lenny,
Yours is a valid argument I would not care to disagree with. The choice
of priorities is a personal one, and should not be dictated by anyone else.
Fortunately there are enough minds around eager for understanding that ideas
with merit can usually be considered by *someone* when the time is right. The
tragedy would be if we all decided the same ideas were meritorious, and worked
redundantly to check out the same ones.
I used to make a more conservative selection of ideas to investigate
myself. But then I found that a small percentage of the really radical ideas
turned out to have merit. Although most of them do not have merit, it is
worthwhile (in my priority system) to constantly check out radical ideas
because the few that pan out pay off *big* (just because they are radical
ideas, and usually restructure a whole edifice of knowledge).
I started looking at models of gravitation when I asked some of the same
questions DDL did earlier in this thread. Why do masses attract each other?
Why inverse square? Why independent of density, composition, etc? Why does
gravity *appear* to act instantaneously, while light suffers a delay? Why
always attractive, never repulsive? What *really* would happen (a black
hole?!) if the strength of gravity exceeded the ability of neutrons to resist
further compression?
If you are satisfied with the answers you now have to these questions,
then new models are not for you. I'm extremely dissatisfied, and am actively
seeking new explanations which make sense. To me, it's worth the investment,
even if these or other discussions eventually show me that the C-graviton
model is not viable. You can be sure I'll keep looking. I have a drive to
find answers which make sense. -|Tom|-
* Reply: 52293
#: 52293 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Tom VanFlandern/DC 71107,2320 (X)
Your explanations of the way the Sun's real position versus the perceived
position illustrate the instantaneous effect of gravity are quite easy to
follow. Makes sense to me. But brings up this further question.
As the Sun IS leading the Earth, and the Earth does not spiral out, (or in)
if gravity IS constrained by relativistic limits, what else is there out
there, to explain the orderliness of orbits?
* Reply: 52366
#: 52366 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Paul Burke/CA 74656,2333 (X)
Paul,
You ask the key question, what constrains orbits NOT to spiral out given
a component of force which should cause just that. Not to duck your question,
but there is no use speculating just yet about solutions which necessarily
must be outside of the domain of presently accepted physics or dynamics.
Let's first see if anyone is successful in shooting down the argument that we
do have a dilemma. Only if people reach the conclusion that NO solution
exists within the domain of accepted physics/dynamics, are they willing to
consider going outside of that domain for solutions.
Of course there will be some who will not accept an argument just
*because* it allows no solution within the accepted framework. That is
carrying scientific conservatism too far in my view. Obviously some of the
most interesting things waiting to be discovered will require extension and/or
revision of the accepted framework.
If we reach the point where no more arguments can be made about how to
solve this problem within conventional physics, I will be glad to add my
speculations to those of others here about what solutions might then work.
-|Tom|-
* Reply: 52381
#: 52381 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Tom VanFlandern/DC 71107,2320 (X)
The problem I see is that the right theory has yet to be formed to explain
gravity, given the anomalies in the current observations.
The g-model has those light fast thingys rounding off large objects, from
the outside. I see no reason to believe such efforts would always result in
a spherical object, with the heavy stuff in the middle, every place we
look. The occasional pointy thing should be out there also.
I look to find gravity operating from the inside out, pulling not pushing
objects into spheres.
* Reply: 52395
#: 52395 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Paul Burke/CA 74656,2333 (X)
Paul,
I certainly agree that the "right theory" has yet to be formed. *Any*
existing theory leaves a host of unanswered questions. We're just trying to
make some progress here. If we don't keep trying out new models, we'll never
find the right one. I personally am sorry to see the trend in science of
asking everyone to be satisfied with operational descriptions without pressing
the questions of how it all works fundamentally.
Since C-gravitons give (to a first approximation) EXACTLY the same forces
inside and outside of bodies as Newton's law gives, I am still having trouble
understanding how there can be a difference which rounds off bodies in one
case and leaves them pointy in the other. Point-for-point everywhere in the
universe, the forces are essentially the same in the two constructs.
You say you are looking for an explanation of gravity which pulls from
within instead of pushing from without. Two questions: (1) Why? The pulling
model seems to offer nothing of special value except familiarity. It's the way
we've been taught since childhood. That doesn't strike me as a good enough
reason to prefer it. Is there another reason?
(2) Looked at fundamentally, how can *anything* exert a "pulling" force?
"Pushing" is intuitive and easy to understand at the fundamental level:
whenever two entities collide, a "pushing force" seems to result. But what
could possibly cause any one entity to "pull" another? I guess this is tied
up with the question of whether or not "action at a distance" is possible.
Can anything affect anything else without the effect being carried between the
two things by means of some sort of agents? These are tough questions, but
worth asking, and thinking about. -|Tom|-
* Reply: 52413
#: 52413 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Tom VanFlandern/DC 71107,2320 (X)
Tom, I prefer the 'pulling' to 'pushing' for shaping big objects, as all
the big objects we see *are* spherical, while the little, asteroids,
comets, small moons, etc are not. The implication that it takes a fairly
large internal 'puller' to round off things 'appears' to satisfy the
observations.
If gravitons did the rounding off, then there seems to be no reason to
expect anything other than spherical for all bodies. As this does *not*
satisfy the observations, then more questions arise about the external
shaper vs the internal type.
* Reply: 52420
#: 52420 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Paul Burke/CA 74656,2333 (X)
Paul,
Finally, I am starting to see what you mean by your reference to the
shaping of bodies being different in the two models. I'm sorry to be so slow,
but I just couldn't see your image until this last message. Thanks for
sticking with it until we communicated. Now that I have at least a partial
image of your objection, let me try again to respond to it.
Larger masses tend to become round because of the weight of their surface
layers. The larger the mass, the heavier the surface layers, resulting in
smaller mountains which can withstand the extra weight without being squashed.
Now where does this weight come from? In the Newtonian description, all
of the atoms inside the mass tend to *pull* the mountains downward, keeping
them from getting too high. In the C-graviton model, the greater number of
impacts by C-gravitons from above than from below causes the surface layers
and mountains to be heavier. The larger the planet below, the more
C-gravitons which don't get through the planet, making the pushing force of
C-gravitons coming from above more effective.
Either way, the force is the same. In the Newtonian case, atoms inside
the mass somehow reach out, and by a poorly understood process, pull the
surface layers downward. In the C-graviton model, the surface layers are
pushed in all directions by C-gravitons coming from all directions; but *not*
equally. The bigger the mass below, the greater the excess of C-gravitons
pushing from above than pushing from below. Hence the surface layers are
still pushed downward, and by just the same amount as in the Newtonian case.
Mountains on big planets get squashed; those on asteroids don't because there
are almost as many C-graviton impacts from below as from above. Does this
clarify the picture at all for you? -|Tom|-
* Replies: 52457, 52462
#: 52457 S11/Cosmology
Fm: Jeff Heleen 76545,501 To: Tom VanFlandern/DC 71107,2320 (X)
If I may with a question. What about small massive bodies like neutron stars
or the like? They would have a small Surface area for the C-gravitons to be
pushing down on. Wouldn't there be less effect from them then? All the force
for rounding the object would have to come from inside.
* Reply: 52494
#: 52494 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Jeff Heleen 76545,501 (X)
Jeff,
Neither surface area nor density of a body has any effect on the
C-graviton force (ignoring extreme densities where shielding sets in, as
discussed in another message). Ordinary masses are almost totally transparent
to the C-gravitons. So there is NO tendency for the C-gravitons that hit an
atom and bounce back, to hit one *near the surface*. Atoms anywhere
throughout the mass are equally likely to be struck. That is why area and
density don't matter, just mass (which is a measure of the number of particles
in the body which C-gravitons can strike).
Now despite the condition that almost all C-gravitons pass right through
a mass without taking any notice of it, there are still enough C-gravitons
which do strike atoms to hit every single atom repeatedly, and from all
directions. If you have that picture now in mind, the next step is to ignore
the *direct* action of a C-graviton strike (to push the atom), because these
strikes and pushes come from all directions, and so cancel each other out.
Concentrate your attention on the indirect effect of a C-graviton
striking a particular atom and bouncing back. Since that particular
C-graviton does not continue its journey through the mass, the atoms further
along its original pathway are not subject to collision from that C-graviton,
but are "shadowed" from it. Meanwhile, those atoms are continuing to be
struck from all other directions, but less often from the direction of the
original atom, which keeps bouncing some C-gravitons back. So all the other
atoms feel a slight net push toward the original atom because of the
shadowing. In all, every atom feels a net push toward every other atom with a
strength which depends upon the distance between them. So it is JUST AS IF
every atom "pulled" on every other atom. The pushes from outside behave
EXACTLY the same as would pulls from inside. -|Tom|-
* Reply: 52501
#: 52501 S11/Cosmology
Fm: Jeff Heleen 76545,501 To: Tom VanFlandern/DC 71107,2320 (X)
Oh okay now I see. I was only considering the surface before.
But now, you said that where sufficient mass is present there would be a net
effect on, say, an orbiting body since so many more would be shielded from one
side (the neutron stars' or whatever) so that the satellite would be pushed
into orbit. Even tho the mass of the satellite may be small, there are so many
c-gravitons floating around that the satellite is still struck enuf times that
it enters orbit, and with a satellite with much larger mass the proportional
amount of c-gravitons striking it is so much larger (by a proportional amount)
that it too enters orbit. So like you said, everything depends on mass. Am I
finally on the right track? I think I can understand it all conceptually. It
all seems to make sense. By the way, does anyone have any idea what the mass
density (or should I say energy density) of these c-gravitons would be (if, of
course, we could detect them)?
.....Jeff
* Reply: 52516
#: 52516 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Jeff Heleen 76545,501 (X)
Jeff,
The energy density of the C-gravitons is measured indirectly by the
Universal Gravitational Constant. Since we don't know the mean velocity of
the C-gravitons, nor the "transparency factor" (e.g. what percentage pass
through mass of a given density without noticing it), we can't yet derive the
physical density. But some assumptions are possible. For example, the model
potentially provides a whole new way of discovering a unified theory for all
the forces of nature. If we make some assumptions and develop new models for
the E-M, strong, and weak forces, some very interesting numbers come out.
But the enjoyment of examining such speculative results can only accrue
to those who conclude there is a need for the C-graviton model, or something
like it, to explain gravitation. -|Tom|-
#: 52462 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Tom VanFlandern/DC 71107,2320 (X)
That certainly handles the objection to shaping effect, Newton vs C-g. Why is
the core heavier than the crust? How do the densest metals stay in the crust?
Tungsten, uranium, etc?
* Reply: 52495
#: 52495 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Paul Burke/CA 74656,2333 (X)
Paul,
The core of a planet is not *heavier* than the crust. Gravity is zero at
the center of mass, because the forces from all directions balance perfectly.
But the matter at the center is *denser* than matter in the crust because of
the weight of layers above. The more mass a planet accumulates, the more
weight that mass puts on the layers beneath as each layer presses down on the
ones below it. The matter at the center simply gets squeezed the most.
Again, there is no difference between the two models: C-gravitons pushing more
from above than from below have EXACTLY the same effect as matter below
pulling down in Newtonian fashion.
Whether heavy metals stay in the crust or not (aside from their re-supply
from meteoritic accretion) is a function of whether or not the planet melts,
and in general the strength and viscosity of the matter the planet is made
from. Most of the heavy metals are depleted from the Earth's crust (compared
with cosmic abundances), which is why there is a lot of iron in the core, and
a magnetic field. This indicates the Earth was melted quite early in its
evolution. Still, no difference between models, since the forces are exactly
the same, whether provided by C-gravitons or Newtonian gravitation. When I
refer to "atoms" for simplicity, of course I really mean particles of matter.
A proton would reflect 1836 times as many C-gravitons as an electron, because
it is that much more massive. It doesn't matter whether those particles
assemble themselves into tungsten, or remain as hydrogen. It's just the mass
that counts in either model. -|Tom|-
* Reply: 52541
#: 52541 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Tom VanFlandern/DC 71107,2320 (X)
Gonna make it VERY difficult to set up and perform an experiment to find
the existence of C-gs. If the little guys zip thru everything from all
directions, what would make a C-g deflector, and since that would probably
be a massive thingy, how to seperate the effect of its mass from the effect
of the C-gs?
This is getting strange.
* Reply: 52561
#: 52561 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Paul Burke/CA 74656,2333
Paul,
The *only* difference, to my knowledge, between the C-graviton model and
the Newtonian model of gravitation with any hope of detection is the
"shielding" effect. If you used matter so dense that 100% of the C-gravitons
were reflected, with none getting through, then the interior matter is no
longer contributing to the gravitational field outside the mass (because it
isn't reflecting any C-gravitons; so it isn't creating an apparent pull toward
itself).
Neutron stars might be getting "close" to that point. If you could find
one which was reflecting all C-gravitons, you could experiment. Drop a large
but accurately-known mass onto the star so that it accretes and becomes part
of the star. In the Newtonian model, the mass just went up by the amount of
mass you added. In the C-g model, the mass remained constant, because you
can't reflect more than 100% of the gravitons. This should clearly
distinguish the two models. -|Tom|-
#: 52151 S11/Cosmology
Fm: Jeff Heleen 76545,501 To: Tom VanFlandern/DC 71107,2320 (X)
Pardon the interruption, but even if the earth were moving towards the
apparent direction of the sun (20 acr-sec from the real location) that
apparent location is always moving off therefore at any time t the earth is
still being pulled toward the sun hence not spiraling off into space. Is this
not so or am I missing something?
* Reply: 52188
#: 52188 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Jeff Heleen 76545,501 (X)
Jeff,
See my simultaneous reply to Tom LeCompte for more details. If you don't
see that the apparent Sun has a small component of force always pulling the
Earth forward and accelerating it, then just imagine that it is a large angle
instead of a small one. If the apparent Sun were displaced, say, 45 degrees
instead of 20 arc secs, and it was *always* at a 45-degree forward angle to
the Earth's direction of motion, can you then visualize that there would
always be an acceleration of the Earth's velocity?
Central forces must always be at exactly 90 degrees to the velocity
vector, on average. Any displacement of a central force ahead of a 90-degree
angle will result in an acceleration of the body in orbit. In elliptical
orbits in real dynamics (where gravity IS assumed to act instantaneously), the
central force lags a 90-degree angle exactly as much as it leads one,
averaging exactly 90 degrees. In the example we are discussing wherein
gravity propagates with a delay, the Sun would always be 20 arc seconds ahead
of the position it would otherwise occupy, producing an acceleration which
would cause the Earth's orbit to spiral. This is not an easy concept, but do
you see the difference? -|Tom|-
* Reply: 52450
#: 52450 S11/Cosmology
Fm: Jeff Heleen 76545,501 To: Tom VanFlandern/DC 71107,2320 (X)
Oh, okay. I think I see. Only when gravity is considered to be delayed does
the force from the apparent sun come into effect. Okay, I see where that might
produce an acceleration of the earth if it was over and above total gravity of
the system but wouldn't that small force actually be the WHOLE force of
gravity? Since we're considering gravity to be delayed then there would be NO
force felt coming from where the sun actually is (since it's delayed) and ALL
the force would be felt from the apparent sun (since it is then just
arriving). I mean, it seems to me kind of like adding apples and oranges.
Sure, the apparent sun will produce an acceleration seeming to spiral out but
once the apparent sun moves to a new location it will produce a new
acceleration in a new direction (ie towards its new location) thereby bringing
the spiral in to a circle (or ellipse or whatever). Or am I still missing
something here?
* Reply: 52497
#: 52497 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Jeff Heleen 76545,501 (X)
Jeff,
Others here have been arguing that the force of the Sun comes from its
apparent position, not its true position. I have been arguing the opposite
viewpoint.
IF the force did come from the apparent position, then we have the
following problem. The apparent position ALWAYS leads the focus of the
elliptical orbit by a bit; so it ALWAYS accelerates the Earth.
To see that more easily, let the Sun be more massive just so the Earth
can move much faster in its present orbit. I want to get the Earth moving
close enough to lightspeed that the apparent Sun is way out in front of the
Earth, instead of off to one side. Then no matter which direction the Earth
moves at that high speed, the Sun's image is out in front (not precisely at
the apex of the Earth's motion, but near it).
If the *force* on the Earth comes from the true Sun, there is no problem.
If it comes from the apparent Sun, which is always out in front, then the
Earth is always accelerated faster and faster. No force ever acts to slow it
down. The orbit spirals outward, eventually to leave the solar system
forever. -|Tom|-
* Reply: 52502
#: 52502 S11/Cosmology
Fm: Jeff Heleen 76545,501 To: Tom VanFlandern/DC 71107,2320 (X)
Tom
I don't think I agree, at least not totally. True, if the for gravity is
felt from the true sun (gravity is instantaneous) then no problem.
But if from the apparent sun (gravity at c) then yes, it will accelerate
toward the apparent sun out near its apex but that apparent sun is also
orbiting the true sun (since where else does the apparent sun get its image
from) thereby pulling the earth around the true sun with it. Therefore no
spiralling into space. Isn't that how it should go?
.....Jeff
* Reply: 52517
#: 52517 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Jeff Heleen 76545,501 (X)
Jeff,
If the apparent Sun leads the Earth, and if the force of gravity comes
exclusively from it, then it causes the Earth to speed up, period. Even
though the Earth may remain in orbit for thousands or millions of revolutions
while it is speeding up (depending on how much acceleration it does get), the
acceleration is continuous, and the end result inevitable.
We are comparing two situations: (1) force is from true Sun, implying
orbit of Earth is a circle. (2) force is from apparent Sun, which can be
resolved into two force components: one toward true Sun, trying to keep the
Earth in a circular orbit; and one in the direction of motion, trying to
accelerate the Earth. The result in case (2) is an outward spiral orbit.
-|Tom|-
* Reply: 52564
#: 52564 S11/Cosmology
Fm: Jeff Heleen 76545,501 To: Tom VanFlandern/DC 71107,2320 (X)
Tom
That's where you're losing me, with point 2. If force is from apparent sun
why is it broken into two parts, one toward true sun and one toward apparent
sun? That's the whole purpose of the apparent sun, ie gravity proagates at c
so it arrives at earth with the sunlight meaning solely from the apparent sun.
And also, now that I think of it, okay the earth will accelerate toward the
apparent sun more and more but since this is a gradual process wouldn't the
earth just shift to a higher orbit (not spiral out of the system totally) in
order to conserve momentum?
.....Jeff
* Replies: 52584, 52600
#: 52584 S11/Cosmology
Fm: Jeff Heleen 76545,501 To: Jeff Heleen 76545,501 (X)
Oops! I keep thinking in non-relativistic terms. You're right. Since the earth
is already moving at almost light speed then if it already hasn't gone out of
orbit then with a little more acceleration it will. The only thing that could
keep it in orbit would be a black hole, I guess. Okay, that makes sense for
relativistic speeds but I still think that at normal speeds with the apparent
sun providing the sole force it would still stay in orbit.
#: 52600 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Jeff Heleen 76545,501 (X)
Jeff,
The 2-body central force problem requires that the source of the force be
located at the focus of the elliptical orbit. The true Sun resides at the
focus the the Earth's elliptical orbit; the apparent Sun leads the focus.
This changes the equations of motion, and an acceleration results.
You seem to see that the Earth must accelerate. Yes, it is a gradual
process, and yes, the Earth would "shift to a higher orbit ... in order to
conserve momentum". But the process continues forever, because there is still
an acceleration even in the higher orbits.
If gravity propagated at velocity c, the "acceleration" the Earth would
feel would be similar to that from a roughly Saturn to Uranus-sized planet
permanently leading the Earth in its orbit at a distance of 1 astronomical
unit. You didn't ask this question, but perhaps you might be wondering how
this case differs from that of a body stationed at the L5 Lagrangian Point in
a another planet's orbit, trailing the planet by roughly 60 degrees in the
same orbit. This case is stable because it does not change the total energy,
or the semi-major axis, of the body. Such a change in total energy can only
be avoided by a so-called "conservative force", which is one that obeys the
special constraint that percentage changes in distance from the Sun are always
accompanied by minus twice the same percentage change (on average) in the
velocity. The case we are dealing with obeys no such relationship; and in
fact the total energy of the Earth would be continually increased. [Ignore
this argument if it is not related to the objection you had in mind.] -|Tom|-
* Reply: 52652
#: 52652 S11/Cosmology
Fm: Jeff Heleen 76545,501 To: Tom VanFlandern/DC 71107,2320
Tom
Sorry if I seem a bit slow to catch on. Let's see if I've got this right.
Due to the fact that we don't see any such acceleration on the part of the
earth then this whole thing points toward gravity being instantaneous,
otherwise our instruments would have picked up changes in the orbital path. Am
I finally getting close? Thanks for the patience.
.....Jeff
#: 52230 S11/Cosmology
Fm: Hal Finney 74076,1041 To: Tom LeCompte 73667,1120 (X)
If I may jump in here...
The "apparent" Sun is the place the sun's light seems to come from. As Tom VF
points out, if the Sun were so massive that the Earth's speed approached the
speed of light, the apparent Sun would be far displaced from the true Sun's
location. As Earth's speed approaches c, the apparent Sun approaches the
Earth's orbit, 90 degrees ahead of the Earth.
This doesn't have anything to do with the real Sun orbiting the center of
mass. For that case, making the real Sun more massive reduces its motion.
However, it increases the motion of the apparent Sun by requiring Earth's
orbital speed to increase.
The apparent Sun moves continually as the Earth goes through its orbit. If
the Earth is moving very fast the apparent Sun will also move very fast,
always leading the Earth. Furthermore, the "apparent center of mass" will
also move in a circle, near the apparent Sun and leading the Earth around its
orbit.
Thus it doesn't make sense (semantically) to say that the Earth orbits the
apparent Sun, nor the apparent center of mass. Neither of these is a fixed
point. An orbit "around" something should be described with respect to a
fixed point.
The Earth actually orbits the true center of mass, as we would have expected
initially. That is the only fixed point in the Earth-Sun system, by
conservation of momentum if nothing else.
How, then, does gravity propagate? Is it infinite? No. Both gravitational
fields and electric fields have an interesting property. They propagate
outwards at the speed of light. But as the field propagates it does so in
such a way that the apparent center of the field shares the constant linear
velocity which the object had at the point when that "piece" of field
originated.
In other words, the field "points" at where the attractor _actually is now_,
as long as the attractor (the Sun in this case) hasn't changed velocity in the
last (distance/c) seconds. If it has, that effect won't be noticed until
speed of light delay has elapsed. Meanwhile, the field points at where the
attractor
Also, consider the following thought experiment. Imagine the Sun as moving
in a circular orbit eastward around the Earth. The direction we see the Sun in
is always where it actually was 500 seconds ago; but the direction of its
gravitational force is where the Sun actually is now, which is where we will see
it 500 seconds in the future. Now imagine that the Sun ceases to exist. Light
and (in your description) gravitation emitted before the end should continue
their journeys to Earth over the next 500 seconds. When they arrive, we will see
the Sun's light extinguished. Simultaneously, we will feel a force toward a
direction where the Sun would be now if it had continued to exist; but which the
Sun never actually occupied. This "spirit force" from a body which no longer
exists and a place it never occupied is a problem for me. What do you think?
-|Tom|-
* Replies: 52322, 52326
#: 52322 S11/Cosmology
Fm: Hal Finney 74076,1041 To: Tom VanFlandern/DC 71107,2320 (X)
Tom - Look at things in a frame comoving with the Sun. The grav field extends
outwards from the center of the stationary Sun. Now if the Sun changes
direction, use the new comoving frame. Once again the grav field will be
centered around the Sun in the new frame. However, special relativity
prevents the change from propagating outward faster than c. Meanwhile, from
the point of view of this new frame, the part of the field beyond c*t from
here is pointing at an "old" image of the Sun. The Sun was never there,
though, from the point of view of this new frame.
That's the resolution of the paradox you mention where you made the Sun
vanish. Things are attracted to where it "never was" only in a certain frame.
In the Sun's own frame, things are still attracted to where it always was -
right in the center. One might as well complain that in the Sun's frame
aberration lets the Earth see a "ghost" image of the Sun where it never was;
while in the Earth's frame they are just pointing their telescopes at where
the Sun really was 8 minutes ago.
I don't see this as an argument from analogy with EM. Rather, it's just the
application of basic principles of special relativity to a central force
problem. I'm doing some research to find out whether general relativity
modifies this simple analysis, such as in a binary system. But certainly it
isn't going to have gravity propagating faster than light, I can guarantee
that!
* Reply: 52368
#: 52368 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Hal Finney 74076,1041 (X)
Hal,
There was nothing in my thought example which required the Sun to be the
dominant mass. I could have given the Earth the Sun's mass and vice versa,
and nothing else would change. This legitimizes looking at the problem from
the "Earth-stationary" perspective. From the "Earth-stationary" view, the
Sun's photons never appear to come from fictitious places. We see the Sun
only in places it ACTUALLY occupied 500 seconds ago. There are no ghost
images, only images from the past. But as I explained, in the thought
experiment gravity would appear to arrive at a stationary Earth from a
location which the Sun never occupied. Most peculiar!
If you insist I look from the Sun-frame perspective, then the Earth
*must* be taken as moving, and I would make the following argument. The force
which propagates out from the Sun with velocity c must first be felt on the
sunward side of the Earth, then by Earth's center, and finally by the night
side. While this force is transiting through the Earth, Earth is moving
forward in its orbit at 30 km/s or 1.0E-4 c. The resultant of the two
velocity vectors (force propagating radially out from Sun, and Earth's orbital
motion) is that the force must APPEAR to act with a displacement of 20 arc
seconds or 1.0E-4 radians as it transits the Earth, just as vertically falling
rain appears to fall at an angle when seen from a moving train, and just as
photons following the same path at the same speed as the gravitational force
from the Sun are seen to do.
So from either perspective, I still see a dilemma, despite your clever
solution, which had me doing a double-take for a while. Or am I still missing
something? -|Tom|-
* Reply: 52445
#: 52445 S11/Cosmology
Fm: Hal Finney 74076,1041 To: Tom VanFlandern/DC 71107,2320 (X)
Tom - Yes, in the Earth-centered frame the visible position of the Sun is not
a "ghost". And in the Sun-centered frame the gravitational attraction of the
Earth is never towards a "ghost". However, in the opposite frames the "ghosts"
exist. That doesn't bother me in either case. You seem bothered in just one
case.
You are proposing a sort of gravitational equivalent to stellar aberration. I
think Tom LC has occasionally proposed the same thing. But a gravitational
field is different from a bunch of particles (photons) flying out from a
central location. It is the curvature of spacetime. And in the Sun-centered
frame it's not in motion. It is a stationary structure which surrounds the
Sun. There is no "flow" of gravity out from the center which mixes with the
Earth's velocity to cause aberration of the direction of gravitational force.
I haven't been able to find a description of a binary star system at a level
which I can understand. What I do have are descriptions of infinitisimal test
masses orbiting stars. I think the Earth-Sun system can be modelled OK by
that. Would you mind if we made the Earth infinitisimally small? That doesn't
change your aberration argument but makes the relativity predictions easier to
state.
Simply put, in the Sun-centered frame, the Earth orbits around the Sun in a
stable orbit, one example being a circle. I'm sure this comes as no surprise.
This prediction requires that in the Earth-centered frame the force is towards
the actual location of the Sun, rather than a "lagging" location. This does
not imply that gravity travels faster than c.
* Replies: 52489, 52490
#: 52489 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Hal Finney 74076,1041 (X)
Hal,
In my thought experiment, gravitational attraction from a direction
toward which no mass exists, has ever existed, or ever will exist is a
conceptual problem for me, but not for you; so let's move on to the
Sun-centered frame, which you seem more comfortable with.
This curvature of spacetime: is it *caused* by the Sun? If so,
instantaneously, or with some delay? If the Sun ceased to exist, would
spacetime stay curved at the Earth's orbit for 500 seconds, or go away
immediately? If the Sun comes back into existence, does spacetime at the
Earth's orbit curve immediately? Or does *something* propagate out from the
Sun, establishing the spacetime curvature as it goes?
If you vote for instantaneous, you have an "action at a distance" and a
"causality" problem, because information (in the form of spacetime curvature)
was communicated faster than light. The information in this case is that
light from the Sun is going to reappear in 500 seconds.
If you agree with most relativists that the spacetime curvature is
re-established at the speed of light by something propagating outward from the
Sun, then why can't I presume that same something *maintains* the spacetime
curvature by continuing to propagate outward at velocity c? But if the
curvature is continually regenerated by something propagating at c, then my
dilemma remains. We have two velocity vectors, one from the Sun and the other
being the Earth's orbital motion, the vector sum of which gives a displaced
direction of origin.
Let me try a slightly different perspective. Gravitation creates a
potential, different at every distance. Force occurs only where there is a
gradient (a change) in that potential; i.e. radially. Let's look at the
gradient in the potential of the Sun near the Earth's orbit, which causes the
force the Earth feels toward the Sun. The gradient or "slope" in the
potential toward the Sun is exactly analogous to the curvature of spacetime,
which also "slopes" toward the Sun. The following remarks apply to either.
If the slope toward the Sun simply exists statically, then it is
reasonable for it to point toward the true Sun. But if it is continually
recreated by something propagating outward at velocity c, then it must point
toward the apparent Sun. Imagine a single "gravity wave" doing this
propagating. The gravity wave continually recreates the Sun's potential. Then
it is the weakening of this wave in inverse square fashion as it moves
radially outward which causes the gradient in the potential. But as the
Earth, moving at 30 km/s, encounters this single wave, Earth must see the wave
(as it sees everything) shifted forward by 20 arc seconds. The wave must
first act on the sunward side of the Earth, then its center, then its
nightside, with a finite time delay. This slopes the gradient in the
direction of the Earth's motion during that small time interval as the wave
passes.
It's okay with me to take the Earth's mass as negligible for these
examples. I also understand that the relativistic equations, just as for the
Newtonian, have the Earth moving in a closed orbit, not spiraling outward. I
just don't understand your last remark, "This does not imply that gravity
travels faster than c." It seems to me that the instantaneous propagation
assumption IS implicit in deriving those equations. That's what the present
CIS discussion is all about. -|Tom|-
* Reply: 52526
#: 52526 S11/Cosmology
Fm: Hal Finney 74076,1041 To: Tom VanFlandern/DC 71107,2320 (X)
Tom - To some extent we are perhaps just dealing with different "mental
models" of what is going on. You seem to feel that something must be
propagating out from the Sun to maintain the potential field. I use the old
"rubber sheet" model where the Sun distorts space near it, and these
distortions are spread out through spacetime due to the equivalent of tension
in a rubber sheet. There is nothing physical to propagate out; it is just a
pattern of stresses. There is nothing which is a candidate for aberration.
We can choose whatever frame we want for our analysis, and the physics will be
the same whichever frame we use. That's why orbits analyzed in the Sun's
frame allow us to predict what will happen in the Earth's frame as well. From
the fact that the Earth is attracted towards the Sun in the Sun frame, we can
deduce that in the Earth frame it is attracted to the true rather than
apparent Sun.
This doesn't require any assumption that gravity propagates faster than light.
Suppose that the Sun were to suddenly increase its mass. Analyze it in the
Sun frame. The curvature of space will increase in response, first near the
Sun, then propagating outwards (at c) as successive pieces of spacetime
outwards from the Sun increase their curvature. But both before and after the
change the Earth will still be attracted towards the Sun.
Thus, relativity doesn't make gravitation propagate faster than light.
Rather, the Earth's attraction to the true Sun is a consequence of the fact
that physics has to be the same in both the Earth and the Sun frames, combined
with predictions about the Earth's orbit made in the Sun's frame.
* Replies: 52560, 52644
#: 52560 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Hal Finney 74076,1041 (X)
Hal,
It is quite true that, in the Sun frame, the gravity gradients point
toward the true Sun, just as the paths of photons are directly away from the
true Sun. I have no problem with your setup. But when you observe or
encounter things eminating from the Sun, and you are travelling quite fast,
this causes a displacement in the *apparent* direction from which those things
come (called aberration). The angle of that displacement in radians is just
v/c, where v is the Earth's velocity in the Sun frame. How can this NOT
affect gravity in the same way it affects light?
You say that "there is *nothing* physical to propagate out". This
strikes me as playing with words. You seem to agree that increases in mass
"spread out through spacetime", but are not allowing me to use the word
"propagate". But if the Sun does not maintain its field at the Earth's
distance instantly, but must keep regenerating the spacetime curvature by
somehting spreading out from the Sun, then this is all that is required for
aberration to exist.
Remember the analogy of the moving train, with vertical rain falling on
the windows? The faster the train moves forward, the greater the angle to the
horizontal the rain makes as it streaks down the windows. If the train goes
fast enough, the rain may even appear to streak from the forward side of the
window to the rear side.
To draw an analogy with light and gravity, the rain suffers aberration
due to the train's motion just as light does due to the Earth's motion. You
seem to be proposing another substance falling vertically besides the rain, **
at the same velocity as the rain **, which somehow appears to streak the
windows of the moving train vertically, with no aberration. I do not see this
as possible. -|Tom|-
* Reply: 52595
#: 52595 S11/Cosmology
Fm: Hal Finney 74076,1041 To: Tom VanFlandern/DC 71107,2320 (X)
Tom, suppose we take the Schwarzschild metric, which describes the curvature
of space around a static, spherically symmetric mass like the Sun. Now we
transform to a frame co-moving with the Earth, following a geodesic path. We
analyze the curvature to find its tidal components, and we calculate what
direction those tidal forces are symmetric around. This would tell us, in
effect, what direction the source of gravity is in.
(Note that since we are following a geodesic path we can't really calculate
our own (Earth's) acceleration, since geodesics are the non-accelerated paths
in general relativity! But we should be able to measure a direction
associated with the tidal forces.)
Now, if we do this math, do you think the answer will come out as pointing at
the true sun? Or do you think it will point at the apparent sun? If general
relativity is consistent, it would have to point at the true sun.
I am trying to understand whether your position is "Yes, the math works out
OK, but still it doesn't make sense because it seems like there should be some
aberration of the gravitational force." Or is it "Fine, it works OK in the
sun centered coordinates, but when we go to an Earth based frame the math will
show that there's aberration, hence general relativity is inconsistent."
If it's the latter, I will try to work through the math and calculate just
what really does happen. I assume that the tidal forces will point at the
true sun because that's what seems to be required by consistency. But I
haven't done the calculation so maybe it wouldn't hurt to check.
On the other hand, if you share my confidence that the math will come out as
pointing at the true sun, and you just find that that doesn't square with your
intuition as to what should happen, then I won't bother working it out.
* Reply: 52642
#: 52642 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Hal Finney 74076,1041
Hal,
The relativistic equations of motion are not independently derived, but
rather they *assume* the Newtonian law of gravitation as a starting point.
Specifically, they assume the explicit points in the law as stated:
acceleration is directly proportional to mass, and inversely proportional to
the square of distance. They also assume the implicit points in that law:
that the acceleration is directed along the line joining the *true* positions
of the masses at any given moment, and that the effect occurs instantly,
without light-time or any other delay.
We know that the relativistic equations of motion are conservative (there
is an energy integral), and that they represent the observed motions very
well. There are no accelerations, as indeed there could not be under the
starting assumptions. The central force problem has periodic solutions even
with very strange power laws.
So in answer to your question, I conclude that the math *must* show that
the gradient is toward the true Sun, or the Earth would accelerate. (If you
worked through the math and found the gradient pointed at the apparent Sun, I
would be forced to conclude that I do not understand the origin of the
equations of motion after all, and that there is apparently a way out of the
logical dilemma we are discussing that I haven't thought of.)
A general problem in science, in my opinion, is a failure to review the
assumptions underlying theories when using them. I think this "speed of
gravity" business may be another example. The assumption of instantaneous
propagation was put into the law of gravity because it is required for the law
to work. So much time has not elapsed since this assumption was a topic of
regular debate that many people now deny that it is an underlying assumption.
But I don't think I am mistaken that it is. -|Tom|-
#: 52644 S11/Cosmology
Fm: Ken Hill 71336,1074 To: Hal Finney 74076,1041
Hal, et. al.,
I've been reading this thread with great interest, but slight comprehension.
It seems that your argument that the laws of physics must be consistent in all
frames, including the solar frame is the easiest to follow. I know from my
time programming inertial nav systems that it often takes backing out to an
easily understood frame to make things clear. Trying to understand the
arguments from the moving earth frame had my mind, quite frankly, in knots. I
had a couple of questions.
Does this argument explain the results of the Earth/Moon gravitaion data?
(Gravitation vector points at the true sun.) It seems to.
Also, this thread made it's way over to the Science forum and a statement was
made that an experiment could be done involving a binary pulsar to determine
the speed of gravity. Any ideas of what that might involve? Thought I'd ask
here first. (I haven't given it a great deal of consideration at this point.)
Note: My background is just popular stuff with a bit of a grasp of
transforming frames and VERY basic dynamics.
Ken
#: 52326 S11/Cosmology
Fm: Hal Finney 74076,1041 To: Tom VanFlandern/DC 71107,2320 (X)
Tom - I'm still looking into it, but I did have one other thought about how
gravity might propagate. You are right that in a binary system, if the
direction of attraction is based on a linear extrapolation of where the body
"would be" now, the system is unstable. It's not as bad as your case where
the attraction is towards the apparent image of the attracting body, but the
tendency would exist.
However, in general relativity a linear extrapolation is rather unnatural.
Rather, by the equivalence principle, you should use a freely falling frame.
The gravitational field, then, would point towards where the object would be
now if it were influenced solely by gravitational attraction. This
formulation then includes the earlier one (a linear extrapolation) as a
special case where the attracting object is effectively not influenced by
gravitation.
That solves the problem for a binary system. Since both objects are in fact
falling freely, an extrapolation of position based on a free-fall frame should
in effect take into consideration the gravitational acceleration of the
attracting object. Thus even in a binary system objects in effect are
attracted to where the other object is "now", with no lag, assuming no other
forces enter the picture.
I don't know whether this approach is right, but it seems more in keeping with
the flavor of general relativity. I'll keep digging.
* Reply: 52369
#: 52369 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Hal Finney 74076,1041 (X)
Hold up there a minute on this one, Hal. You suggest using a freely
falling frame to extrapolate the direction gravity will be coming from by the
time it reaches out to a close binary companion. Another clever idea, and one
I haven't heard before. But I have two difficulties with it.
First, I should be able to examine the problem from a frame in which one
of the stars is stationary and the other is orbiting around it. Then aren't
we back to an "Earth-Sun" problem, since one of the stars has no motion in
this frame?
Second, I can understand how a propagating gravity wave might be imagined
to "remember" the linear velocity of its source in some reference frame (even
though light does not "remember" the velocity of its source). But how can it
"remember" an acceleratiom of its source which hadn't occurred yet when the
wave began its journey? In fact, since the occurrence of that acceleration is
dependent upon the continued existence of the companion star, which might have
recently ceased to exist for all the wave knows when it starts off, maybe the
source star will never undergo the acceleration at all. Whether the source
accelerates or doesn't accelerate, how can the wave "know" what the source
star did once the wave is half way to the companion? [If the masses are
equal, the gravity wave itself should be in flat space-time and unaccelerated
when it is at the center of mass; so it has only its "memory" of its source's
motion to go by.]
Are we still sinking, or starting to swim toward a resolution? <grin>
-|Tom|-
* Reply: 52446
#: 52446 S11/Cosmology
Fm: Hal Finney 74076,1041 To: Tom VanFlandern/DC 71107,2320 (X)
Tom - Yeah, I may be a little off base on that idea. I agree with you that it
seems a little far-fetched to imagine distant gravity responding to
accelerations which the source hadn't experienced yet.
However, in general relativity, there is no such thing as gravitational
acceleration. A body following an orbit or otherwise moving solely under the
influence of gravity is actually following a geodesic path, a straight line
through spacetime. So perhaps that makes it more plausible.
An example is a satellite orbiting the Earth, which itself follows a curved
path around the Sun. I think it's plausible that the satellite is attracted
towards the position which the Earth is at now, even though that position is
farther along the "curved path" (actually a straight line in spacetime) the
Earth is following. I still hope to learn enough to verify this.
* Reply: 52514
#: 52514 S11/Cosmology
Fm: Emory Kimbrough 72777,1553 To: Hal Finney 74076,1041 (X)
The geodesic path through spacetime is actually a path of maximum proper time.
That's not necessarily a straight line.
#: 52237 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Tom LeCompte 73667,1120 (X)
Tom,
I am unfamiliar with the concept of "apparent center of mass". Since the
apparent Sun is always seen 20 arc seconds west of the physical center of
mass, it would seem to follow that the center of the circular path followed by
the apparent Sun in the course of a year IS the physical center of mass.
I don't see how to clarify my previous example intended to prove that
there is a problem, but perhaps you can ask a clarifying question. If the
displacement angle approached 90 degrees instead of 20 arc seconds due to a
high orbital velocity, then at every instant the apparent Sun pulls forward on
the Earth. How can this fail to accelerate it? I am simply taking the
familiar Sun-Earth example to its logical extreme to clarify the point we are
debating.
In Eddington's "Space, Time & Gravitation", in which he argues for a
speed-of-light propagation rate for gravity based on analogy with what happens
between two electric charges, Eddington explains the dilemma for classical
gravitation with these words:
"If the Sun attracts Jupiter towards its present position S, and Jupiter
attracts the Sun towards its present position J, the two forces are in the
same line and balance. But if the Sun attracts Jupiter toward its previous
position S', and Jupiter attracts the Sun towards its previous position J',
when the force of attraction started out to cross the gulf, then the two
forces give a couple. This couple will tend to increase the angular momentum
of the system, and, acting cumulatively, will soon cause an appreciable change
of period, disagreeing with observations if the speed is at all comparable
with that of light."
Do you see that there is a problem needing resolution? -|Tom|-
* Replies: 52342, 52343
#: 52342 S11/Cosmology
Fm: Tom LeCompte 73667,1120 To: Tom VanFlandern/DC 71107,2320 (X)
You can ignore my previous argument about "apparent center of mass". I
started doing the real math, and now that I know the "real" answer I can see
that that picture only accidentally works.
The crux of the matter is the "headlight" effect. If I take a quickly
moving light bulb, special relativity modifies its uniform distribution of
radiation to one that points in the direction of motion. (Like a headlight)
The inverse also occurs. If I am in a spaceship moving quickly, I see
everything shift towards the forward window. (c.f. "The Visual Appearance of
Objects at Relativistic Speeds", T.J. LeCompte, MIT Thesis (1985) available
from the Massachusetts Institute of Technology) This occurs not only with the
appearance of objects, but also their field lines. (c.f. "Classical
Electrodynamics" J.D. Jacksom, p. 555 Fig 11.9. 2d edition (1975) Wiley)
Let me talk about the hydrogen atom first, so there is no dispute to
the speed of the field: it travels at c. The electon is whizzing around the
proton. Because of the delay in the field, the proton appears behind it's real
position. This causes a longitudinal component of force. However, the motion
of the electron causes objects to appear to move forward. This moves the
"image" of the proton by the EXACT AMOUNT that the delay in light travel time
moved it back. Likewise, the longitudinal component of the force is canceled,
so the force is again transverse. This is accurate to terms of order (v/c). I
suspect that it is true for all orders, but to calculate the (v/c)^2 terms,
magnetism becomes important, and the work doubles.
I hope to catch up and reply to your message about simultaneity over this
weekend. For the moment let me address your "headlight" analogy for the
hydrogen atom.
As I understand your analogy (which I think I don't yet), the forward
displacement of the proton due to the motion of the electron (the
"aberration") just exactly cancels the backwards displacement of the proton
due to light-time delay, resulting in the apparent image and true position of
the proton coinciding. This is certainly not the case for planets and stars:
the images are displaced from their true positions. Why should it be
different for atoms?
The precise point at which I start to lose your picture is when you say,
"Because of the delay in the field, the proton appears behind it's real
position." Visualizing the atom as oriented the same way as the Earth
orbiting about the Sun (i.e. electron orbiting counter-clockwise as seen from
above), the delay in the arrival of light or gravity from the proton should
cause the proton's image to be seen somewhat westward, to the right, or in the
direction of the electron's motion relative to its true position. This is
exactly the same displacement, and in the SAME direction, as that caused by
the forward motion of the electron. In astronomy, the "headlight" effect and
the retarded position due to light-time delay are one and the same, simply
seen from the fixed frame or the moving frame. They do not cancel, as I
understood you were proposing.
So you see I don't yet have your picture, perhaps because I can't shake
the astronomical analog which I am so familiar with. Can you see my
difficulty? If so, can you help me out of it? -|Tom|-
* Reply: 52430
#: 52430 S11/Cosmology
Fm: Tom LeCompte 73667,1120 To: Tom VanFlandern/DC 71107,2320 (X)
I think that you think a certain quantity is invarient, when it is not.
Imagine just a flat piece of paper, that is being illuminated by a infinite
plane of light - all light rays parallel, and all that. The light stricks the
paper at some angle. Observers moving in different frames will disagree as to
this angle. Likewise, if we are talking about lines of force, or field lines,
or whatever, the angle they make with the paper changes as well, so the
observers disagree as to the direction in which the force is applied. However,
the observers also disagree about the position of the field source and the
time it takes the field lines to propagate: between these two effects, all
observers agree on the future motion of the object acted on by the field.
In the case of the sun-moon system, (Speed of gravity = speed of light;
you can substitute sun=proton, earth=electron if you wish) the sun's image
moves westward because of the delay in light travel time. However, the image
moves forward because of angle difference (the Earth is moving with respect to
the sun) in the light rays - the photons aren't hitting the earth exactly
perpendicular in our frame. (The are in the *sun's* frame) This moves the
image of the sun eastward, by the same amount it was moved eastward by the
delay. Likewise with gravity - it now acts on a line between the Earth and the
"real sun", because the real sun and the image sun line up. (If this still
isn't clear, you might take a look at the picture in Jackson I mentioned)
I'm not sure that this doesn't work for other stars and planets? Why do
you say it doesn't?
* Replies: 52447, 52448, 52449
#: 52447 S11/Cosmology
Fm: Hal Finney 74076,1041 To: Tom LeCompte 73667,1120 (X)
Tom - I'm afraid I share Tom VF's confusion about your argument exactly. And
this talk about "westward", etc. hasn't helped me any, without knowing which
part of the Earth's orbit you are talking abut.
Let me restate Tom's objections. You speak of the Sun's image moving due to
light travel time delay. You must be using an Earth-based frame. For that
case, if the Earth is moving Westward, (implying that it is at the "North" or
12 o'clock part of its orbit if you draw it on a plane), the Sun's relative
motion appears to be Eastward. Light travel time delay means that we see it
where it was 8 minutes ago. Since it's moving East, that displaces it towards
the West, the same direction as Earth is moving.
In Earth's frame, these photons travel on a straight line from this old
position of the Sun to the Earth. That's why telescopes have to be tilted
Westward. From the Sun's frame, though, the photons travelled exactly
straight North from Sun to Earth. In this frame, the Westward tilt of Earth's
telescopes is intepreted as due to the relative motion of the Earth and these
North-travelling photons (stellar aberration - the opposite of the "headlight
effect").
With Tom VF, I don't see that these two effects would cancel each other.
(Rather, they are really the same effect seen in two different frames.) And I
don't think you think so either - it's hardly in doubt that the effect exists!
Do you think that they do cancel for gravity, though? Could you clarify what
part of your argument applies to fields like EM or gravity, and what part
applies to photons? And of course, do you now think the Earth is attracted
towards the apparent Sun, or to the true Sun?
* Reply: 52464
#: 52464 S11/Cosmology
Fm: Tom LeCompte 73667,1120 To: Hal Finney 74076,1041 (X)
I think that your argument is better than mine. I started looking in a
bunch of "dead Russian" books, and they all focus not on the fields but the
potential. (The field is the gradient of the potential) So, casting your
argument in potential form, we get:
The sun sets up a gravitational potential. In a frame comoving with the
sun, the potential is static (time-independent) and extends to infinity. In
this potential, you "inject" a moving Earth, and it will follow Keplerian
orbits.
Now, we could argue about the field at any given point, but it's not
necessary: we found a frame in which the potential is 1/r, so we know the
solutions in this frame. (Keplerian orbits) Furthermore, becuase the field is
static, the fact that it's due to to retarded potentials as opposed to
instantaneous potentials doesn't matter.
Part of the confusion is that the apparent motion of the sun is due not
to the revolution of the Earth, but rather it's rotation. This caught me for a
bit, and I think the idea of picking a coordinate system where it's at rest is
a good idea.
* Reply: 52498
#: 52498 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Tom LeCompte 73667,1120 (X)
Tom,
Please see my earlier messages to Hal Finney, in which I raise the same
objection to the "gradient of the potential" viewpoint. In one of the
messages I argue that the retarded, not the static, potential must be
considered, as becomes evident if one turns the source off or on.
The Earth's rotation, about 0.5 km/s, can be neglected in comparison with
Earth's orbital velocity, 30 km/s. Let's pretend to look from the Earth's
center to avoid that difficulty.
In case I've added confusion with my compass directions, I've used
"north" in the sense of pointing toward the north celestial pole,
perpendicular to the Earth's orbital plane. In messages from others north was
used in the sense of 12 o'clock in the orbit plane. I just wanted to clarify
the picture I was describing, since getting the other guy's picture seems to
be the hardest part of this dialog.
I am holding back on the discussion of simultaneity and causality, hoping
that we could either agree that gravity CAN travel at c, in which case my
"speed of sound" analogy is quite useless; or else we could agree that gravity
must travel faster than c, in which case maybe you, Emory, and everyone else
in this discussion can help me with the analogy, or think of something else,
so we don't have models which violate causality. -|Tom|-
* Reply: 52507
#: 52507 S11/Cosmology
Fm: Tom LeCompte 73667,1120 To: Tom VanFlandern/DC 71107,2320 (X)
I agree that you need to use the retarded potential. That's the
advantage of picking a frame comoving with the sun; in this case the potential
is static, so the retarded potential is the instantaneous potential.
I agree that there is a whole lot of confusion with "norths" and so on.
That's another reason to work in this frame: the whole potential is
spherically symmetric.
#: 52448 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Tom LeCompte 73667,1120 (X)
Tom,
Everything is fine until we get to the specifics. Looking at the Sun
from the Earth with our heads pointing northward, west is to the *right* (not
the left, as on a geographic map; sky directions are a reversed *mirror* image
of ground directions). West and right are the same as "forward" for the
Earth's orbital motion. Light-time delay causes the Sun's apparent image to
be westward, to the right, or forward of its true position. This image is
what an observer at the center of the Earth sees who imagines that the Earth
is stationary and the Sun moves eastward around it.
If the Earth as taken as moving forward around a stationary Sun, then the
Sun's image is displaced westward, to the right, or forward from its true
position. It's the same displacement, just viewed from a moving instead of a
stationary perspective. Check it out in the almanacs (or see the Explanatory
Supplement to the American Ephemeris): the right ascension or longitude of the
apparent Sun is 20 arc seconds *less* (westward on the celestial sphere) than
its true r.a. or longitude.
My reference to stars is planets was just to point out that they move on
the celestial sphere around their mean places in little mini-ellipses
reflecting the Earth's orbital motion. This displacement is called
aberration. The displacement is observed; it isn't cancelled by light-time
delay or anything else. The amount of aberration for the Sun or a star in the
Sun's direction is the same.
This subject has been of interest to me, and quite bothersome as well, for
quite some time. One of the experiments I did while at the US Naval Observatory
(my specialty is Celestial Mechanics) was the following.
Picture the Moon as in orbit around a stationary Earth. To a crude
approximation, that orbit is an ellipse, heavily perturbed by the Sun. I
posed the following question: in precisely what direction does the body
perturbing the Moon's orbit lie? I presumed that reasonable answers were: (a)
toward the true Sun, which lies at the focus of the Earth's elliptical orbit;
(b) toward the apparent Sun, the direction photons from the Sun come from; ©
somewhere in between. The difference between (a) and (b) is 20 arc seconds,
an astronomically large and easily-detected angle.
After removing the effects of the planets, the Earth's and Moon's lack of
sphericity, and other perturbations, I solved for the direction of the major
perturbing body. The result was that the perturbing force was coming from the
direction of the true Sun, and not from the apparent Sun. The accuracy of the
observations was such as to give a mean error of plus or minus one arc second
in this determination (i.e. statistically significant to 20 sigma).
Since the mean direction of the Sun's gravitational force differed from
the mean direction of its photons, a simple model might suggest that the
gravitation and photons were not propagating at the same speed. Coincidence
of the gravitational force with the Sun's true place would seem to imply
instantaneous propagation of gravity; but allowing for the possible error of
the determination, plus/minus one arc-sec out of a possible 20, this only
constrains gravitation to propagate at least 20 times faster than light in
this simple, non-relativistic interpretation. Ever since then I've been
looking for help finding the "right" interpretation. -|Tom|-
* Replies: 52463, 52527
#: 52463 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Tom VanFlandern/DC 71107,2320 (X)
Might you have been finding some effect similar to that of the tides on the
Earth, which lag the perturbing body (Moon) by several hours? The direction of
the perturber is not evident from the high/low tides themselves.
* Reply: 52493
#: 52493 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Paul Burke/CA 74656,2333 (X)
Paul,
Sorry, the tidal analogy is not applicable to the orbital dynamics of the
Earth-Moon-Sun problem. We understand why the tides lag by varying amounts,
because the tug of the Moon causes the water to flow horizontally; and the
"piling up" of that water depends upon geography of coastlines, weather, and
factors unrelated to gravitation.
One of the great triumphs of Celestial Mechanics is its ability to
represent the motions of the planets accurately to so many significant figures
over such long periods of time. The motions of the centers of mass of the
Sun, Earth, and Moon follow the laws of dynamics to the precision of the
optical observations. And even radar and spacecraft data of far greater
precision have little difficulty.
It is assumed in the laws of dynamics that gravity propagates instantly.
When comparing dynamical predictions to observations, it is assumed that the
light from these bodies suffers a delay, or aberration. My little test using
the Sun-Moon-Earth data simply confirms that the assumptions we are presently
using do in fact allow the theory to represent the observations. If gravity
propagated with a delay, and nothing compensated for that effect, there would
be both periodic and secular effects visible in the Moon's motion, neither of
which are present.
I am quite comfortable with the conclusion that gravity propagates faster
than light, and that the accepted opinion about this is wrong, because I have
seen this failure to re-examine underlying assumptions corrupt whole schools
of thought before. On the other hand, I am comfortable being shown that, in
this particular case, I've overlooked something, and propagation at velocity c
is allowed by the data. My strongest interest is in a clear resolution of the
question, not in "being right" myself. -|Tom|-
* Reply: 52540
#: 52540 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Tom VanFlandern/DC 71107,2320 (X)
I agree, Tom. Finding the cause of the discrepancy in the speed of
gravitational effects will be quite interesting, no matter which way it
goes.
I've spent the day and a few $$$ experimenting with a couple of the more
common graphics programs, and Generic CADD, to find a simple method of
building .GIF files to upload/download.
Deluxe Paint uses an .LBM file format, and I can't locate a GIFFER for that
type. PC PaintBrush IV saves in .PCX format. I have found a couple of PD
programs at the $3.00 place that will convert those to .GIF.
Generic CADD saves .DWG files, and there are no converters for those, but,
another PD program, SCRCAP will take the image off the screen into a .SCR
file. Then, SCR2GIF makes that into a nice .GIF file, even better looking
than the graphics programs output.
Sometimes a picture enhances the words.
#: 52527 S11/Cosmology
Fm: Hal Finney 74076,1041 To: Tom VanFlandern/DC 71107,2320 (X)
Tom - Hunting through the library, I found a book by Lightman et al, something
like "Problems and Exercises in Relativity". One of their problems was about
a sensitive tide-measuring meter which could measure the Sun's position.
Would it measure the Sun as being at the same spot as its visual position?
This is your very question, of course.
Their answer was no, but unfortunately they didn't give much analysis. They
did go through the numbers to see what would happen if the answer were yes,
and as you know it turns out that the orbit is unstable, and rather quickly
too (a few hundred years).
#: 52343 S11/Cosmology
23-Nov-89 20:48:08
Sb: #52237-Gravity's mechanism
Fm: Tom LeCompte 73667,1120
To: Tom VanFlandern/DC 71107,2320 (X)
Now, let's go to the gravitational case. If gravity travelled at the
speed of light, the situation is analogous to the hydrogen atom, and orbits
are stable. If gravity travelled faster (or slower!) than light, the
longitudinal components of the force would not cancel, and as you point out,
orbits would be unstable. So, your observation shows that the speed of gravity
must be the same as the speed of light (assuming only special relativity and
Newton's laws of motion and gravitation: you don't even need General
Relativity) or the planetary orbits would be unstable.
#: 52238 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Tom LeCompte 73667,1120 (X)
Tom,
Yes, I agree that the bending of light by gravity must occur at the point
where the field is. But then both images, the Sun and the displaced star (or
QSO) travel on towards Earth, where both suffer aberration (displacement by 20
arc seconds) due to the Earth's orbital velocity (or equivalently, due to the
500-second propagation delay).
Recall that every image on a photographic plate of the sky is displaced
by a like amount of aberration. So gravity acts instantly or with a delay (it
wouldn't matter which) to bend the light beams froms stars or QSO's. Then
those light beams propagate to Earth along with the Sun's rays, and both are
displaced equally due to the *Earth's* orbital motion. (If the Earth were
motionless relative to the Sun, there would be no displacement for either
image.)
The gravitational lens example differs because the central object (the
galaxy) is in rapid motion. So if gravity acted instantly and the central
galaxy suddenly came into existence, the galaxy and the 4 QSO images it
generated would begin sending light toward the Earth at the same moment; and
all five images would undergo the same displacements, keeping the galaxy in
the apparent center. If gravity acted with a speed-of-light delay, then the
galaxy would send its gravity outward in the plane of the sky until it reached
the distance where the QSO images are generated. Then as light from those
images began moving toward Earth, the galaxy and light from it would no longer
be in the center position.
We seem to be getting slightly repetitive on this point. If I am missing
something elementary in your argument, please be patient and try again in new
words. I'm really trying to see it your way, but so far without success.
-|Tom|-
* Reply: 52344
#: 52344 S11/Cosmology
Fm: Tom LeCompte 73667,1120 To: Tom VanFlandern/DC 71107,2320 (X)
You're right. I was confusing the gravity propagation time with the
light propagation time. The existance of a gravitational lensing body actually
gives no information about the speed of gravity. (Instead, it shows that the
speed of light is independent of position - a useful thing to know, but has
nothing to do with the discussion) I goofed.
#: 52290 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Tom VanFlandern/DC 71107,2320 (X)
I hadn't seen such an explicit explanation of the 'shadowing' graviton,
Tom, thanks.
Now that I have seen it, I'll have to sleep on it. I have trouble 'seeing'
how randomly directed particles can generate a directional force on
everything. Stuff ALWAYS falls down. (Small stuff near massive stuff).
I can accept neutrinos whipping thru the earth without noticing it, etc,
and photons zooming all over the cosmos.
The 'shadow' effect doesn't make it thru my 'truth accepter', for some
reason.
* Reply: 52367
#: 52367 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Paul Burke/CA 74656,2333 (X)
Paul,
I keep hoping there might be some way to communicate better with your
"truth accepter". You may need to keep challenging it to "put up or shut up".
Let me give it a slightly different picture of the same phenomenon to chew on.
Do you recall Olbers' Paradox? If the universe were infinite, the night
sky should be bright because every line from an observer out into space will
eventually run into the surface of a star. Hence photons should be arriving
from every direction at once, making the sky bright.
Various resolutions exist, the easiest of which is that the universe is
NOT infinite. But suppose for the sake of argument that the universe were
infinite and filled densely with photons, as the Paradox suggests. Further
suppose that this imaginary universe had no gravitation.
Now wouldn't the photons make a sort of "substitute gravity"? They
couldn't penetrate masses; but light pressure would press people against the
surfaces of their planets. Moreover two bodies nearby each other would shadow
each other from some photons, and would feel a force exactly toward each
other, even though the photons were moving randomly in all directions. This is
because even though the actual photons are moving randomly, the "shadows"
where photons are missing are not at all random, but are strictly
center-to-center "inverse square" cones. So it's not those random photons
which cause the apparent attraction so much as the missing photons.
If you can see it happening for the photons, it is a very easy step from
there to the C-graviton model. The model may turn out to have nothing to do
with reality. Its value for now is to help answer those gnawing questions
about WHY everything has this amazing property, gravity. -|Tom|-
* Reply: 52382
#: 52382 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Tom VanFlandern/DC 71107,2320 (X)
That's the explanation of gravitons I understand, Tom.
Diverting into photonic substitution, if photons had that property, then
we'ed all tilt as the Milky Way passed overhead. When it rose, it would
push us to the west, then slowly mash us into the ground, and then push us
east, as it journeyed around. It overwhelms the random photonic bombarbment
of the other photon manufacturers.
Back to g's, the same effect should be evident, if the Earth 'shadows' us
from the g's entering in Australia, but not from every spot above a
particular density value. Shouldn't something shielded from above by a very
dense plate, of depleted uranium, or tungsten, be lighter than in the
unshielded state, if g's are absorbed by dense stuff? (How to seperate out
the attraction of the dense material to the test stuff, under the current
gravitation 'law'?)
And there should be a 'shadow' tail near the Earth, where the g's absorbed
by it leave an area not populated by them, with all the other little guys
there, resulting in a delta-g area, where stuff is lighter. (Wrong! I keep
forgetting the sphericity of the situation.)
How can a Voyager do a gravity-assist orbital change, if the gravitrons hit
it from all sides away from the surface of a planet? There's no 'reason' to
expect an assist from them, while there is every evidence of such from the
mass generated property of gravity.
* Reply: 52396
#: 52396 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Paul Burke/CA 74656,2333 (X)
Paul,
To answer your objection about the Milky Way exerting extra force in the
"photonic" universe, the hypothesis was that, whatever direction one looked,
there would be a photon visible. Hence one could not see the Milky Way above
the background because there are already a maximum possible number of photons
arriving from every unit area on the sky.
In the gravitational analog, the question has often been asked, "Is there
an anisotropy to universal gravitation?" This is a fancy way of asking the
question you indirectly posed: Could there be more gravitation in one
direction than another in the universe? This might happen because of an
unequal distribution in the distant mass of the universe, or perhaps because
the gravitational constant is not, after all, the same everywhere. It is
assumed until observations tell us otherwise that the answer to these
questions is "no". [C-gravitons are also assumed to be "isotropic".]
What about gravitational shielding? In the C-graviton model, extremely
dense matter might indeed shield some matter behind it from some C-graviton
impacts. Matter of ordinary density, even mercury or uranium or tungsten,
would be quite transparent to C-gravitons. There would be no detectable
shielding. But when you start approaching the limits of density for any
matter, as in a neutron star, shielding may very well come into play. In
fact, if the density of a neutron star increased even more, one must soon
reach the point where the shadowing effect is total (i.e. 100% of the
C-gravitons are blocked), after which no further increases in density, or the
strength of the star's gravitational field, would be possible.
Your Voyager example fails to recall that the force is nearly the same
from C-gravitons or Newtonian gravity. Voyager is in Jupiter's graviton
shadow, so it can still get a gravity assist.
Keep up the good discussion! -|Tom|-
* Reply: 52414
#: 52414 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Tom VanFlandern/DC 71107,2320 (X)
If it takes a very dense -neutron star quality- mass to inhibit a
graviton, then there is no reason to expect that the mass of the earth
between me and Australia would have any effect on g's. So, the amount of
gravitons hitting me come equally from *all* directions, no shadow/shield.
But I still fall down when I stumble.
I'm gonna try to make a picture of the way I see this, with a Paint
program, and upload it, if I can get it into a .GIF format.
* Reply: 52419
#: 52419 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Paul Burke/CA 74656,2333 (X)
It takes a very dense mass, such as a neutron star, to inhibit a large
enough fraction of the C-gravitions to allow secondary effects, such as
shielding, to occur. But every single atom reflects *some* C-gravitons,
thereby contributing its share to the body's overall field. However for every
C-graviton reflected by an atom, an extremely large number pass transparently
right through without taking notice of the atom.
Even though each atom reflects extremely few of the C-gravitons which
pass by it, in the whole Earth there are in excess of 1E50 [10 to the 50th
power] atoms. So there is a slight imbalance between the number of
C-gravitons striking you from above and from below; and it is these which (if
the model is right) cause you to "feel" the weak force we call gravity.
It will be nice when, one day soon, CIS will have a "fax" mode which will
allow us to view pictures easily. -|Tom|-
* Reply: 52461
#: 52461 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Tom VanFlandern/DC 71107,2320 (X)
Now we're both talking the same effect. The effect of gravity is therefore
(graviton model) relative to the amount of material in the body.
Density/volume is important. The depleted uranium mass-counter balance we
used on the Tristar control column has more 'stuff' per cc than I do.
(Thank God!) So it can intercept more g's than I do. So it will have a
greater response to the more numerous g's, and fall faster, when I
drop it on the floor.
It won't, you know.
(ref: Apollo Lunar experiment, Hammer and feather)
* Reply: 52496
#: 52496 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Paul Burke/CA 74656,2333 (X)
Whoa, Paul. First, I assume that "g's" refer to C-gravitons, not to
"g's" of acceleration. Secondly, there is still a law of inertia, even in the
C-graviton universe. It takes a greater force to accelerate a large mass than
a small one. [Force = mass times acceleration]
A larger mass intercepts more C-gravitons, so the net force acting on it
is larger. But NOT the net acceleration, which is the same for hammer and
feather. It's EXACTLY the same for both models. The C-graviton model is
constructed to give the same force as Newtonian gravitation on all bodies, and
at all points within all bodies (except super-dense ones where total shielding
sets in, which is never the case for Earth). -|Tom|-
* Reply: 52591
#: 52591 S11/Cosmology
Fm: Jeff Heleen 76545,501 To: Tom VanFlandern/DC 71107,2320 (X)
That sounds to me like a difference between C-g's and Newton. In the C-g model
the more massive object feels more force with the acceleration being the same
as the less massive object. But in Newtonian the force and acceleration would
be different because of the different masses. Actually, I think I read
somewhere that due to better technology and more sensitive equipment, along
with new mathematical models, they've now claimed that different masses
actually do fall at different rates. (in a vacuum).
I've only seen the one article about it (and I don't remember where). Has
anyone else seen it?
.....Jeff
* Reply: 52596
#: 52596 S11/Cosmology
Fm: Emory Kimbrough 72777,1553 To: Jeff Heleen 76545,501 (X)
Reports of different masses falling at different rates are, at best,
controversial. Earlier this year, a reasearch team that published one of the
best and most highly publicized claims of observing this effect retracted
their claim, saying that they could not rule out more mundane explanations of
their results.
#: 52305 S11/Cosmology
Fm: Dick DeLoach, Sysop 76703,303 To: Bill Forcade 74746,604 (X)
For reasons which will be clear before too long, I'll say that yours is an
incredibly timely message, Bill. Forgive the aire of mystery attached to the
lack of further clarification at this time, but that's all I can say for now.
<grin>.
--- Dick
* Reply: 52418
#: 52418 S11/Cosmology
Fm: Bill Forcade 74746,604 To: Dick DeLoach, Sysop 76703,303 (X)
Thanks Dick, I don't mind the mystery at all. I assume that the things "which
will be clear before too long", will become clear by reading the messages on
this forum, if some other source of information is implied please let me know
in the future where I should look.
#: 52175 S11/Cosmology
Fm: Dick DeLoach, Sysop 76703,303 To: Tom VanFlandern/DC 71107,2320 (X)
Here's why I don't think the "graviton" model works: If gravitational forces
could be explained in terms of this particle "rain", coming from all
directions in space, then as the earth orbits the sun, the "front half" of the
earth would encounter more of these hits per unit time than the "back half"
just due to its motion through this rain; the "back half" is running away from
the hits and the front half is running into them. So there would be a net
retarding force on anything that moves through this graviton rain, and all
orbiting bodies would eventually slow down and their orbits would decay. I
don't think that happens, and that's why I don't think the graviton model
works.
--- Dick
* Reply: 52189
#: 52189 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Dick DeLoach, Sysop 76703,303 (X)
Dick,
The argument you cite, the slowing of all velocities of bodies moving
through a medium, is one of several arguments against the existence of a
classical aether. Besides the problem you cite, it would also provide a frame
for measuring absolute motion, thereby making it irreconcilable with
Relativity theory.
The way around your objection is to make the "drag" of the medium
negligible. The way around the Relativity problem is, paradoxically, to make
the C-graviton velocities much faster than light, which also has the effect of
diminishing the amount of the expected "drag" effect. It turns out that if
you simply hypothesize C-gravitons moving fast enough to make the acceleration
of the Earth in its orbit [which we have been discussing elsewhere in this
thread] too small to be observed, this also makes the "drag" effect
negligible, because the Earth's velocity is so many orders of magnitude slower
than the C-graviton velocities.
If faster-than-light motion gives you heartburn, then jump ahead to that
part of the thread. I am trying out an analogy with sound waves to maintain
that such a thing would not violate causality, despite Relativistic
predictions to the contrary. If I or someone cannot support the viability of
such an idea, then this objection to the C-graviton model is indeed fatal, as
far as I can see. But I am still operating under the delusion that I may have
proposed a loophole allowing faster-than-light motion to co-exist with Special
Relativity without violating causality. Join in and welcome back! -|Tom|-
* Reply: 52345
#: 52345 S11/Cosmology
Fm: Dick DeLoach, Sysop 76703,303 To: Tom VanFlandern/DC 71107,2320 (X)
I'd like to archive this outstanding discussion in the libraries, Tom. Thank
you for your leadership role and thanks too to all the others who are making
such fine contributions.
About graviton drag and the objection it raises: Sorry, but I am not persuaded
by the "gravitons-go-fast-compared-to-orbital-speeds" argument. That just
addresses the *rate* at which orbits decay. But certainly if there are
gravitons then there is a drag effect, however small, and this must ultimately
have an effect if enough time passes. I take it that you are implying that
gravitons move fast enough that drag effects have not become measurable in the
X billion years that everything has been slogging through this soup. I ask
then, how much more time do you predict will pass before we start to lose
orbits to the graviton drag? (That sounds like a Roaring 20's dance or a
Southern California motor sports event, I can't decide which. <grin>)
--- Dick
* Reply: 52557
#: 52557 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Dick DeLoach, Sysop 76703,303 (X)
Dick,
I'm sorry, but in reviewing messages I just realized this one of yours
was not replied to. I don't know how I overlooked it.
Optical observations are sufficiently accurate that we can rule out any
acceleration or deceleration of the Earth's orbital motion as great as one arc
second per century squared. On the one hand, this seems to set a lower limit
to the speed of propagation of gravitation (which if finite should accelerate
the Earth) of 1.E8 c (100,000,000 times the speed of light), unless someone
can devise a clever way out of that implication. [Contact binaries suggest a
limit of about 1.E10 c.] On the other hand, it sets an upper limit to any
possible drag effect which might exist from the C-gravitons.
Drag ought to be proportional to mass and independent of cross-sectional
area in this case because of the hypothesized transparency of matter to
C-gravitons. So only relative velocity is left in determining how much drag
can occur. The Earth moves at 1.E-4 c, the C-gravitons at, say, 1.E+8 c. The
12 orders of magnitude difference in velocity allow very little room for
significant drag even over the life of the solar system, since the amount will
be smaller than other unknown effects, such as tidal friction, collision drag,
etc.
If we are faithful to the model, drag is a negligible effect. It is not
clear that it ever could become great enough to overcome the outward spiraling
effect, which should dominate the long-term motion of bodies. -|Tom|-
* Reply: 52571
#: 52571 S11/Cosmology
Fm: Dick DeLoach, Sysop 76703,303 To: Tom VanFlandern/DC 71107,2320 (X)
Prety good -- I give it an 8. <grin>
Seriously, the reason gravitons don't work for me is that the drag effects,
while small, are nontheless persistent and unidirectional; that is, they
*always* act to retard the motion of orbiting bodies. For gravitons to work,
there must be a force which is *always* present and which *never* has any
non-negligible effect. That's more than I can swallow.
Changing gears slightly, have the general properties of gravitons been
described in this discussion? So far I understand that they must propagate at
speeds exceeding the speed of light by 12 orders of magnitude, but I don't
know what else they have to do and I'd like to know. Do they have mass? Are
they part of the electromagnetic spectrum and if so, what frequency range?
Does it depend on the energy of individual gravitons as in the case of
photons? How do you characterize their energy states? Are they assumed to be
descretized, and if so, is there some particular scheme required for the rest
of the model to be internally consistent? Does the concept of "momentum
transfer" have any meaning in the graviton model? What else can you tell me
about these beasties?
--- Dick
* Reply: 52601
#: 52601 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Dick DeLoach, Sysop 76703,303 (X)
Dick,
You're not going to believe this, but using a new photographic technique
I invented, I actually obtained a rare photo of a C-graviton which I was going
to convert to GIF and upload; but the dog ate it before I could. <smirk>
The next best thing I can do is try to answer all your questions about
what they look like.
Average speed: greater than 1.E8 c. [That's 12 orders of magnitude
faster than *Earth*, not *lightspeed*.]
Mass: they certainly have "substance"; but they do not meet the criteria
for either of the two kinds of mass (inertial and gravitational) which are
presently defined. We may have to define a new class of mass to cover such
cases.
Electromagnetism: no. I can imagine ways in which a couple of different
classes of C-graviton-like entities could account for all four fundamental
forces of nature, including electromagnetism. But they are not themselves
part of that spectrum. They may instead provide a medium for the propagation
of E-M phenomena.
General: individual gravitons probably vary in speed and momentum, though
there would be little room for variation in their statistical aggregate
behavior. I imagine them as discrete, more particle-like than wave-like, and
as responsible for inertia as well as gravity.
The value of C-gravitons, if the model contradicts nothing that we
already know, is that they aid understanding and enable predictions to be
made. Will you continue to withhold your belief until I get another photo?
<grin> -|Tom|-
* Replies: 52610, 52613
#: 52610 S11/Cosmology
Fm: Dick DeLoach, Sysop 76703,303 To: Tom VanFlandern/DC 71107,2320 (X)
Hahahaha! When you reassure me that I don't have to accept that gravitons
travel 12 orders of magnitude faster than light -- that it's really only EIGHT
orders of magnitude, I'm reminded of the man who almost panicked at the news
that the sun would explode in X billion years, thinking for a moment that he
had heard X *million* years. <grin>.
Let me say at the outset that I am not opposed to gravitons on principal, nor
do I seek to either establish or overthrow that model. To explain how I feel
about this, let me say that I am rather uncomfortable with the notion of
scientists "searching for the grand unification theory which links all
forces". I do not think it is the business of science to search for
unification theories. It is the business of science to find out how nature
works. If nature can be explained by a single entity of which other forces
are special cases, that would be quite elegant and beautiful. But the task
should be to find out what nature *IS*, not to prove that nature acts in a way
which we a priori think is beautiful.
A frustrating limitation of this sterile medium is the fact that it is
difficult to make the point I just tried to make without sounding accusatory.
<grin>. So let me hasten to add explicitly that while we've never discussed
this subject directly, my guess is that you feel essentially the same as I do
on the above point; it wasn't my intent to imply that you take the opposite
view. I'm simply trying to illustrate that at the core I am philosophically
neutral about the graviton model and quite willing to be persuaded. But the
game is over when I find a contradiction with experiment -- there can be no
glossing of observational evidence to service a model, no matter how beautiful
it might be. I'm sure you feel the same way about it. Right now we have a
force that has been applied to absolutely everything in the universe for over
15 billion years with no effect, and I'm having some trouble with that.
<grin>.
I was avoiding mentioning the implied velocity of C-Gravitons because there
is no question that entities which cross the known universe in 150 years or less
are implausible with mainstream cosmologies, which require that the size of the
universe be quite limited. On a later occasion I might try to make the case
that there are other viable cosmologies which do not create this plausibility
problem.
I do indeed echo your sentiments about models and experiments. Our goal
is to understand nature, not to find simple and beautiful descriptions of it.
<we have a force that has been applied to absolutely everyting in the
universe for over 15 billion years with no effect.>
No effect? Gravitation is pretty significant for "no effect", don't you
think? But I assume you mean again that the secondary effect, drag on moving
bodies, is smaller than tides, collisions, and several other forces over the
lifetime of the universe. Still, I can't seem to see much significance in
that. A lot of secondary effects are negligibly small. Remember that nearly
every pair of gravitationally-interacting bodies suffers some acceleration
from tidal friction, which evolves orbits gradually. The C-graviton drag is
just a smaller effect. -|Tom|-
#: 52613 S11/Cosmology
Fm: Dick DeLoach, Sysop 76703,303 To: Tom VanFlandern/DC 71107,2320 (X)
<Concluded from previous msg>
Perhaps you can help me out of this by commenting further on what you mean by
saying that gravitons have "substance" different from "mass". What properties
does this substance have at 1E8*C? Can gravitons "stop"? How do their
properties change at non-relativistic speeds? Can you propose an experiment
which might give direct observational evidence of these rascals?
--- Dick
* Reply: 52650
#: 52650 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Dick DeLoach, Sysop 76703,303
Dick,
I use the term "substance" to indicate anything which exists. It could
be matter or energy, particle or wave, or none of the above. C-gravitons
cannot have gravitational mass because they cannot have gravity in the
ordinary sense. [In this model, it is the absence of C-gravitons where they
would otherwise occur which gives rise to the force we call gravity.] They
would not have inertial mass if inertia itself is a property of masses
*caused* by C-gravitons.
Still, these particle-like entities fulfill some intuitive concept which
we associate with mass. This is why I hinted at some new type of mass which
is neither of the two recognized types.
The chief property which C-gravitons have is the ability to transfer some
of their momentum to ordinary mass. A C-graviton could presumably stop
relative to something else; there would be no meaning to an "absolute" stop. I
think of the medium -air- as an analogy: individual air molecules can "stop"
or drop below the speed of sound without any special significance. The rms
speed of all molecules would remain the same.
The experiment I proposed to Paul on 11-27 involved looking for the
shielding effect in sufficiently dense matter, perhaps a neutron star. It is
*possible* that subtle effects could show up in the solar system, but I am
doubtful. For example, during a lunar eclipse, the Earth might not exert its
normal gravity on the Moon because the Sun is already shielding both bodies
from some of the gravitons which would otherwise strike them.
Of course, no experimental evidence will ever be quite as good as the
picture from my special camera. <grin> -|Tom|-
#: 52348 S11/Cosmology
Fm: Paul Burke/CA 74656,2333 To: Tom VanFlandern/DC 71107,2320 (X)
Seems to me, if gravitrons affect all the other slower particles in the
universe, they should play hell with photons. We should never get a
coherent image of anything fairly far out, as the G's will push the photons
forming the image all over the place.
What happens at the edge of the universe, where there are a universe of g's
missing on one side of every thing on the edge? Shouldn't that force the
edge out at a super-luminal speed?
* Reply: 52393
#: 52393 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Paul Burke/CA 74656,2333 (X)
Paul,
When it comes to propagating through space, photons no longer act like
particles; they have wave properties. That's why C-gravitons don't push them
all over the place. In the C-graviton model we are examining fundamental
questions: the WHY of gravity, rather than HOW it operates. At the WHY level,
all wave phenomena need a medium in which to propagate, so far as we know.
Operationally, the aether was rejected as a hypothetical medium for light to
propagate in. But IF faster-than-light C-gravitons can be shown not to
violate causality, they would provide an ideal medium for the propagation of
light which would not contradict the experimental results showing that no
aether exists. So C-gravitons could solve two "WHY" puzzles at once: why
there is gravity, and why light propagates as waves.
You also asked "What happens at the edge of the universe?" That will
lead to some additional discussion, but require me to develop a few more
concepts here first. The *short* answer (which just leads to more questions)
is that the C-graviton model has no edges. Please be patient on this one. We
need to develop the discussion one step at a time to make sure we are still
doing something useful. To jump ahead with speculations which may turn out to
be unnecessary is just frustrating for everyone trying to follow this dialog.
-|Tom|-
#: 52549 S11/Cosmology
Fm: Dick DeLoach, Sysop 76703,303 To: ALL
I've been reviewing all the files we have over in the Space Forum as part of a
major overhaul there, in which many new discussion sections and libraries are
being added, and I ran across a little item by Stephen Goodfellow which bears
on discussions we've had here recently. It's an essay in which Goodfellow
proposes that vacuum is the source of gravity. He offers thought experiments
to support this idea plus commentary on the shortcomings of conventional
thinkers who do not grasp the essence of his thesis. Since we're hot and
heavy into discussions here of models of graviational mechanisms, I thought
I'd port this one over for your review. It's in LIB 17's preview area and Dan
will make it public soon. (GRVITY.TXT).
I also relayed Susan Kruest's upload of a humorous article revealing certain
astounding discoveries about light. See LIGHT.TXT in LIB 17 as soon as Dan
processes it.
--- Dick
#: 52958 S11/Cosmology
Fm: Steve Moshier 71211,51 To: Steve Moshier 71211,51 (X)
> Is that problem now resolved? No, as far as I can tell. He specifies
"isotropic" and gives a reference to C. M. Will.
Do you know how the Astronomical Almanac defines a heliocentric orbit, or
someone I could ask about this?
* Reply: 53007
#: 53007 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Steve Moshier 71211,51 (X)
Steve,
Having worked in the Nautical Almanac Office for 20 years, I'm familiar
with the basis of their calculations. When you ask if I know <how the
Astronomical Almanac defines a heliocentric orbit>, it is with respect to the
true or geometric Sun, not the apparent Sun, and not the solar system
barycenter, if that is what you mean. If you were looking for something else,
I'll try to help. -|Tom|-
* Reply: 53064
#: 53064 S11/Cosmology
Fm: Steve Moshier 71211,51 To: Tom VanFlandern/DC 71107,2320 (X)
> Heliocentric orbit
I'm using the positions and velocities of the planets, as given by the
DE200, and subtracting the DE200 position and velocity of the Sun. But the
orbits don't come out quite the same as the orbits given in the Almanac.
There are discrepancies here and there of more than 1 unit in the last
tabulated decimal.
How do they get the mean distance? I'm using the DE200 mass ratios for
this. Does the Almanac use the masses of the Sun and planet in its
calculation?
* Reply: 53127
#: 53127 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Steve Moshier 71211,51 (X)
Steve,
The almanacs usually use the masses and other astronomical constants
adopted by the International Astronomical Union. DE200 used a set of masses
and constants derived by JPL. That difference probably accounts for the
differences you are seeing. But you didn't say which decimal place (other
than "the last") that difference occurs in.
"Mean distance" usually refers to the semi-major axis of the elliptical
orbit. There is an osculating (changing) value which represents the perturbed
ellipse from moment to moment. And there is a *mean* mean distance which is
the average semi-major axis over some period of time, and is usually
invariant.
If I am not getting to the root of your question, just supply more
specifics, and I'll try again. -|Tom|-
* Reply: 53287
#: 53163 S11/Cosmology
Fm: Hal Finney 74076,1041 To: Tom VanFlandern/DC 71107,2320 (X)
Tom - Sorry, I guess I missed the point on your question about aberration of
acceleration.
I've been thinking about aberration and how it might relate to gravity, and
I've decided there is a relationship. This is how I think it would work.
From the Earth's viewpoint, aberration is caused by the velocity of the Sun.
Due to the time it takes for the light from the Sun to get here, we see the
Sun where it was earlier, which will be "forward" in the direction of Earth's
motion.
If the Sun were varying its grav field strength, a similar effect would occur.
The change in grav field will spread out in a wavefront just like a light
wavefront. This wavefront of grav field change will be aberrated just like
light. From the Earth's perspective this wavefront comes in perpendicular to
the direction to the "old" Sun.
However, although in the Sun's frame the grav field itself is always
perpendicular to this "change" wavefront, that perpendicular relationship is
not held in the Earth's frame. In the Earth's frame, the "change" wavefront
gets rotated by aberration, but the acceleration is still radially directed
towards the Sun itself. It's because the force lines don't stay perpendicular
to the "change" wavefront that the direction of gravity isn't subject to
aberration despite the speed of light limitation on propagation of changes.
I know this isn't really adding anything to my argument; I'm still just
describing the phenomena that I think will happen. But I do think there is a
place for aberration in gravitational propagation so I thought it might help
to make clear what that place is. Probably the loss of perpendicularity
between the change wavefront and the direction of force will seem to you to be
just another way of restating the paradox.
* Reply: 53217
#: 53217 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Hal Finney 74076,1041 (X)
Hal,
This doesn't prove anthing either; but I checked a couple of references
about how relativity is introduced into the dynamics, and they say things such
as "Newton's law is modified so that the equation of the orbit becomes ...",
and terms in GM/c^2 are added to Newton's equations. Just to make sure we
agree about precisely where the problem arises, do you in fact agree that the
velocity of action of gravity is instantaneous in *Newton's* equations?
Because if you do agree, then I will argue that all of the relativistic
corrections to Newton's equations are of order v^2/c^2, or 1E-8 in the case of
the Earth; whereas aberration is of size 1E-4 for the Earth. On the other
hand, if your "compensation" for the finite propagation time of gravity is
already in Newton's equations, then I would concentrate my argument on the
derivation of those pre-relativistic relationships.
About your "dual perpendicularity" argument, let's try this. I'm in a
spaceship and I see a star up ahead approaching at near the speed of light. If
it's really the star which is moving so fast, it's gravity and light should be
felt in synch. It can't exert a force on me from one side because it has
never been to that location in space before, and it will take the same amount
of time for it to curve spacetime at my distance from it, as it will take for
the light from it to reach me. But if it's *me* that is moving fast past a
slow star, then I'll feel the gravity from a 90-degree angle while the star
still appears to be out in front of me (analogous to Earth moving very fast
around the Sun). This let's me judge a sort of "absolute motion", because you
have hypothesized something (gravity) which doesn't aberrate or obey vector
addition laws, and so is "absolute" in some non-relativistic sense. Is that
not a paradox for you?
And let's not forget the contact binary example. Static fields don't
explain how these can be stable. All in all, it's still looking mighty
difficult to maintain that gravity propagates at c. -|Tom|-
* Reply: 53238
#: 53238 S11/Cosmology
Fm: Hal Finney 74076,1041 To: Tom VanFlandern/DC 71107,2320 (X)
Tom - I had drawn a diagram the other day of pretty much the situation you are
describing. Unfortunately, it is in MacPaint and I don't have a program to
convert to GIF. Would you be able to view it in that format? If so I will
upload it.
It shows a planet moving at .866 c past a Sun which just sprang into
existance. The timing of the passage is such that the planet first feels the
grav pull of the Sun just as it is at right angles to the lines of force, in
the Sun's frame.
In the planet's frame, the area influenced by the Sun's grav field is a circle
expanding at the speed of light, just as it is in the Sun's frame. Such
expanding circles are preserved by Lorentz transformations. Due to aberration
and such effects, though, when the planet first encounters this circle it sees
the Sun, not at a 90 degree angle as in the Sun's frame, but at only a 30
degree angle from the direction it is going. Furthermore, due to time
dilation the "circle of grav influence" at the time of "first gravity" on the
planet is twice as big as it is in the Sun's frame. The center of this
expanding circle is at the location of the "apparent Sun".
The planet does agree, though, that at this time the true Sun is at a 90
degree angle to the direction of its motion. And the field lines of the grav
field, which have been carried along with the Sun, also point in that 90
degree angle.
As for Newtonian gravity, I certainly agree that it is instantaneous. The
explanations I have seen of relativistic modifications to Newtonian gravity
usually include a step where they introduce some retarded effects due to speed
of light limitations. Then they promptly drop them since they are doing a
static-field analysis.
I can't resist adding a spaceship thought experiment of my own.
I am the captain of a spaceship, parked a few light-hours outside the Solar
system. A futuristic display shows the gravitational field of the Sun
spreading out into space radially in front of us. I tell the helmsman to
accelerate us to 0.5 c with respect to the Sun. We quickly reach that speed,
protected from the acceleration by inertial dampers.
"Whoa!" I say. "Helmsman, I wanted you to start us moving with respect to the
Sun, not its gravitational field. Look at that field! It's heading towards
us at 0.5 c! I didn't tell you to do that!"
"But Captain," he protests nervously. "I didn't try to make that happen. I
just accelerated us and the field started moving towards us all by itself!"
"What? That's impossible!" I argue. "Look at that field! It's exactly
tracking the position of the true Sun - moving towards us at 0.5 c just as the
Sun is. But that's impossible since gravity only moves at the speed of light.
The outer field shouldn't have started moving for hours. How could it 'know'
that the true Sun has started moving with respect to us? There must be some
kind of faster-than-light communication from the Sun out to this outer field
for it to have 'known' to start accelerating towards us just at the very
moment that the true Sun did!"
The captain is wrong. The point of this story is that the gravitational field
is a real physical object that surrounds the Sun. The captain should not have
been surprised that it moves with and points towards the true Sun. That does
not require faster-than-light communication among parts of the field. It's
just the way extended physical objects work when you move with respect to
them.
* Replies: 53353, 53354
#: 53287 S11/Cosmology
Fm: Franklin Antonio 76337,1365 To: Tom VanFlandern/DC 71107,2320 (X)
I saw you mention DE200, so i figured you'd be a reasonable person to ask a
question that's been on my mind. The Astro. Almanac mentions the JPL
DE200/LE200 integration. How does one get a copy of this data? Can one order
up a tape from JPL?
* Replies: 53368, 53413, 53536
#: 53352 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Steve Moshier 71211,51 (X)
Steve,
Documentation? In the Almanac Office? I think it's still forbidden! <g>
I worked there until 1983, Steve. I've been through this calculation
comparison many times, especially since the various national ephemeris offices
never got the identical answers, either; and we always had to track down the
discrepancies. The suggestions I made before were our first-line technique
for figuring out what it was *this time*.
I vaguely recollect a problem of definition of the ecliptic plane at the
0.1 arc sec level. It seems it makes a difference whether you average the
osculating or the Newcombe-defined mean ecliptic at that level of precision,
and no approved choice was part of the definitions. JPL chose one way, the
NAO chose the other.
Another point to remember is *consistency* of precision. In a
near-circular orbit, the perihelion is poorly-defined; so fewer decimal places
are needed to represent the same precision in that angle. The same for a low
inclination orbit: the node is not well-defined, so fewer decimal places are
in order. As a rule of thumb, the four quantities e sin w, e cos w, sin i sin
O, and sin i cos O should all have the same target precision. [w =
perihelion, O = nodes] This means that if i is 0.1 radians, consistency
requires you to drop one decimal place from O. -|Tom|-
* Reply: 53408
#: 53353 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Hal Finney 74076,1041 (X)
Hal,
Sorry, I have no access to Mac-compatible computers. Aren't there
on-line GIF converters available for nearly everything?
If you come across one of those references again, in which retarded
effects proportional to v/c (as opposed to v^2/c^2) are developed, please let
me know. I would love to see a consistent, understandable development showing
how to avoid paradoxes in relativity due to the "instantaneous" nature of
gravity.
In your new example, you propose in effect that the Sun's gravitational
field is like an extension of the Sun's surface: a physical part of the Sun.
In your drama, you are in the role of captain giving orders to your helmsman.
[That seems to leave open the role of science officer. I just wanted to
stress that I do not have pointed ears!] <g>
We have already agreed, I think, that if something continually streams
out of the Sun to produce its field, that something must travel faster than
light. But you now describe the Sun's field as static and unchanging; not
like the falling rain in previous examples, but rather like a roller or
skateboard rink, with walls curving down toward the rink center. Then the
skateboarder always feels a force toward the center no matter how fast he is
moving because the walls he skates on are fixed, not constantly regenerated.
But even this example fails, I maintain. You simply cannot have a force
without an action; and an action requires "moving parts", if you will. In the
case of the skateboarder, the vertical force driving him toward center is
provided by gravity, and must still interact with his speed: if gravity acts
at speed c, then a skateboarder approaching c will feel the force coming from
in front of himself.
The only way to avoid the problem of the Earth's speed interacting with
gravity's speed is to posit that gravity and the Earth do not interact. This
is because, as soon as they interact, they must do so at a certain rate, which
creates the paradox.
You also did not address the secondary paradox that starship Captain can
tell it is his ship which moves and not the Sun because the direction of the
Sun's force and its light do not coincide. The other side of the coin is that
it could have been the Sun which was accelerated to 0.5 c, which would have
left its field behind. Or would it? This gets to the nitty-gritty of the
picture you are trying to construct. If the Sun is suddenly accelerated to
0.5 c, is its field accelerated instantly as if it were rigidly attached? Or
does the field follow, but with some lag? Or does the field get left behind
completely, and begin to die out at the same time the moving Sun starts
generating a new field? Any way you call it, I've got a fatal paradox because
of the basic, underlying problem: gravity and light do not come from the same
direction!
[Aside question: I honestly do not yet see the weakness in the argument
for faster-than-light gravity at the moment, despite the commendable
tenaciousness of your replies. I'm curious to know if your vigorous defense
of the mainstream view is more motivated by conviction that it is correct, or
by the conviction that such a fundamental error could not have gone on
undetected for so long. If it is the latter, I'm prepared to produce a number
of other examples, both historical and present.] -|Tom|-
* Reply: 53385
#: 53360 S11/Cosmology
Fm: Ken Hill 71336,1074 To: Tom VanFlandern/DC 71107,2320 (X)
Tom,
Regarding your statement "So I would conjecture that the same C-gravitons are
indirectly responsible for the property of inertia also." Is this solely
because of the equivalence of gravitational and inertial mass, or have you
thought of mechanisms by which C-gravitons can exhibit the phenomenon of
inertia? This may have been covered before and I just missed it through my own
density and inertia. <grin>
Ken
* Reply: 53372
#: 53368 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Franklin Antonio 76337,1365 (X)
Franklin,
Yes, the DE200 integration is available via JPL. I don't have current
ordering instructions, but perhaps Franklin O'Donnell of JPL, who also
frequents this forum and SPACEFORUM, can help out there. His CIS address is
75006,3573. Be forewarned, however, the integration is for the whole solar
system for a few centuries; so it's a massive amount of data. Be prepared to
specify your exact needs to keep the amount of data manageable (and
affordable). -|Tom|-
#: 53372 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Ken Hill 71336,1074 (X)
Ken,
My conjecture about C-gravitons being responsible for inertia is
partially derived from the equivalence of gravitational and inertial mass,
which cannot be coincidence. But I also have some ideas in mind about how
that might happen, geometrically. My thoughts on this are evolving as a
result of the current discussion; so let me wait until I've got a coherent
picture again before going into detail. -|Tom|-
#: 53385 S11/Cosmology
Fm: Hal Finney 74076,1041 To: Tom VanFlandern/DC 71107,2320 (X)
Tom - Let me sum up my position.
First, I am still unclear about your position! Specifically, I'm not sure
whether you believe that gravity propagates at faster than c in general
relativity. This is not an empirical question, it is a mathematical one about
the consequences of Einstein's field equations. I thought you agreed with me
that gravity would _not_ propagate at faster than the speed of light in that
theory.
Similarly, when you ask things like "what would happen if the Sun suddenly got
accelerated" I'm not sure whether you are asking an empirical question (that
is, what would actually happen in reality if the Sun _really did_ get
accelerated), or whether you are again asking what my understanding is of what
general relativity would predict in that situation. I don't think anyone can
claim to know the answer with certainty to what would _really_ happen, so I
assume you again are asking about the presently accepted theory.
Assuming that we agree that this is what we have been arguing about (!), I am
confused about your question about my motivations. You ask whether I am
convinced that "such a fundamental error could not have gone on undetected for
so long". The "error" would be, in the context I've presented here, that
gravity actually propagates faster than c in the theory of general relativity.
That's why I'm confused. I thought we agreed a few days ago that general
relativity would not predict faster-than-light gravity. And now it seems like
you're asking about it. I must be missing something.
What about your paradox? The problem is that I haven't really been able to
grapple with it in terms of general relativity. Your fundamental premise,
that gravity's finite speed of propagation ought to make it subject to
aberration, I simply don't believe. I have tried to give you all kinds of
different examples to show that finite speeds of propagations don't lead to
aberration. I've talked about trees in the forests, about elastic materials
being deformed under stress, and about the gravitational field as an "extended
object" around the Sun. That is the best I can do to cast doubt on your
premise, which is really an assumption which I don't share.
Furthermore, I think your paradox applies with equal force to the case of the
electric field surrounding a moving object. Shouldn't such fields be directed
towards the "old" position of the object? Well, electromagnetism is much
simpler than general relativity. I've looked in several books in the last few
days and all agree that the electric field tracks the "current" position of
the moving object. Are you prepared to argue forcefully that electric fields
must therefore propagate faster than c?
As for your argument that the standard theory leads to some kind of preferred
frame of reference: In the Sun's frame, the Earth sees light aberrated due to
the speed of the photons. But it feels no aberration for gravity since that's
just static curved space. Light and gravity are not parallel. In the Earth's
frame, we see light from the "old" position of the Sun, but we feel gravity
from the "current" position. They are not parallel. Both frames predict the
same observations, on my understanding, so this does not provide a standard to
judge whether you are moving or not.
I would add that I've enjoyed this discussion very much, even though it's
frustrating that we haven't quite been able to get onto the same "wavelength".
It's motivated me to go back and study some physics that I haven't looked at
in quite a long time. I suppose that if we can't make progress we might have
to just agree to disagree. I would feel better, though, if I was confident
that we agreed about what we disagreed about!
* Replies: 53439, 53440
#: 53408 S11/Cosmology
Fm: Steve Moshier 71211,51 To: Tom VanFlandern/DC 71107,2320 (X)
> Almanac
Tom, we should have guessed that the most sacred, deified book since the
Vedic hymns would turn out to be a complete shambles behind the scenes.
Wonderful!
I'll do some more cursing and swearing on it over the weekend and contact
you later. I have been ruminating on exactly the same points that you mention
-- although the question of where the ecliptic is seems in fact to have been
settled, by vote of the IAU.
#: 53439 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Hal Finney 74076,1041 (X)
Hal,
Let me clarify my position. The speed of light is an explicit parameter
in Einstein's field equations. It comes in through E = m c^2. But Einstein
takes from Newton (1) action proportional to mass, (2) action inverse square
with distance, (3) action along the line of centers, (4) action which is
instantaneous. These Newtonian considerations are then modified by Special
Relativity (space and time contract with velocity) which bring in the concept
of "rest mass", and the equivalence principle, to yield the field equations of
General Relativity. Nowhere does the speed of light enter the process to the
first power, as would be required if propagation delay was considered. It's
always v^2/c^2, never v/c. So it is my position that, despite using Special
Relativity and its requirements that light and all electromagnetic phenomena
must propagate at velocity c or less, nonetheless General Relativity has
gravity operating along the line of centers with "current" positions of the
masses, instantaneously.
I think it is not in dispute that the General Relativity field equations
do in fact represent gravity operating instantaneously along the line of
centers with "current" (not "retarded") positions. My understanding of your
position is that somehow the propagation delays cancel out of the field
equations, permitting you to have it both ways: i.e. gravity really only
propagates at velocity c, but due to some fortuitous cancellations in the
equations, they happen by chance to look exactly like the instantaneous
propagation equations. If you believe the instantaneous propagation equations
in G.R. would look in any way different from those we actually use, I am
unaware of this. If we agree that the equations we use are the same as the
instantaneous ones, then our difference of opinion is over the question of
whether one can get the same equations with gravity propagating at velocity c.
I maintain you cannot. Earlier in the discussion I professed ignorance about
how physicists make electric fields track current positions without action at a
distance and without faster-than-light travel. It seems "magical" to my mind:
how can one body react to the "current" position of another unless it can
communicate instantly with it? It surely must react only to some forward
projection of a retarded position. But as you already know, in the
gravitational analog, orbits are unstable with such projected retarded
positions.
So how do physicists do it? I don't know the answer, and have been
asking that question repeatedly, because astronomers are always deferring to
electromegnetism as an example of how forces can, despite logic or intuition,
operate based on "current" positions. Wouldn't it be ironic if physicists
used dynamicists to justify to other physicists the confidence they espouse
that their models do not present paradoxes? So in answer to your question,
until someone can show me how electric forces can accomplish this seemingly
magical feat, I maintain that they too must be caused by some hypothetical
faster-than-light actions. I will drop this opinion in a flash when I am
shown "the light" <g>.
I, too, have found this exchange enjoyable. You have a logical mind, and
I hate to admit that two motivated people cannot reach an agreement; but it
does happen. Sometimes the passage of time allows new insights or
perspectives. So feel free to continue this discussion now or at any time an
idea occurs. In the meantime, my next message will make yet one more effort
to impart my viewpoint, from yet another angle. Maybe *this* time
.. ?! -|Tom|-
* Reply: 53463
#: 53441 S11/Cosmology
Fm: Tom VanFlandern/DC 71107,2320 To: Hal Finney 74076,1041 (X)
Consider an observer, E, and a rapidly approaching mass with a
substantial gravity field, S. Let S be approaching E at 99% of the speed of
light, c. Then from the observer E's perspective, mass S follows closely
behind the light waves it emits. For example, if S emits a signal when it is
still 1000 light years away, when that signal finally arrives at E the mass S
will have travelled 990 light years and be only 10 light years away. S will
itself arrive about 10.1 years after the signal arrives.
When S judges that it is really just 10 light years away from E, S makes
a decision to accelerate either up or down a bit, as a consequence of which it
will pass one light year to either the north or to the south of E about 10
years later. [From the perspective of S, it is simply trying to avoid a
collision with the approaching E.]
Now here is the paradox: it will be 10 years before the first light
following the acceleration reaches E, so that E can see for himself that S has
moved, and which way. But E can tell instantly which way S moved as soon as
it happens because E can sense the change in the gravity field of S instantly.
From E's view, mass S deflected its essentially linear motion to one side.
But S in your construction carries its static gravitational field with it at
all times as a sort of extended self; so that gravitational field will reach E
well before the light from S will reach E. The part of the gravitational
field of S which has already reached E when S is still 10 light years away
will immediately begin to show a bias to the north or south as S itself begins
to move off to the north or south. And at every later moment for 10 years,
the part of S's gravitational field at E will be biased in the same direction
as S, even though no light from S since the acceleration has yet reached E.
This is therefore a form of faster-than-light communication. -|Tom|-
* Reply: 53462
#: 53462 S11/Cosmology
Fm: Hal Finney 74076,1041 To: Tom VanFlandern/DC 71107,2320 (X)
Tom - The description of a gravitational field as something that moves along
with the Sun really only applies to the steady-state case. I've decided that
my starship analogy was somewhat misleading in that respect.
When the Sun changes its motion, the gravitational field changes as well, now
pointing to the new position of the Sun. However, this change only propagates
out from the Sun in a spherical shell at the speed of light. Outside that
shell the gravity field continues to track the old motion of the Sun. This is
your "ghost Sun" effect, which I maintain is real although perhaps surprising.
Thus, when your mass S veers up or down, E doesn't find out about it for ten
years. The gravitational field at E will continue to track what E would view
as S's continued motion straight towards him. After the ten years has
elapsed, the gravitational field near E will change and begin tracking the new
current position of the mass S.
Let me add a couple of complications that I don't think are important. First,
in E's frame this all happens about 70 years before they would hit, rather
than 10 years, based on a relative speed of 0.99.
The other is that mass S can't really just decide to veer off. Conservation
of momentum is going to keep its center of mass going in the same direction it
was before. It would have to eject some mass "south" to make itself go
"north". So after the change the gravitational field is going to be more
complex than that surrounding a star. But the basic point remains, that the
change in the gravitational field will only spread out at c. Within that
circle of radius c*t the field will be that of S heading north plus its
ejected mass heading south, and I don't really know what such a field would be
like.
I downloaded a GIF converter program, but I wasn't able to get it to work!
I'll have to try another. I have a picture showing the grav field around a
moving star that is somewhat helpful, I think.
* Replies: 53468, 53495
#: 53463 S11/Cosmology
Fm: Hal Finney 74076,1041 To: Tom VanFlandern/DC 71107,2320 (X)
Tom - Let me try another image to try to make the "forward projection of
retarded position" concept seem more reasonable.
Surround the Sun by a radial network of steel girders that extends out a
light-day or so. The natural elasticity of the steel would limit how quickly
any change at the center could propagate outward, even if speed of light
limitations didn't exist.
Now subject the Sun to small perturbations of position. Such a change
propagates outward through the girders as the stress pattern travels out from
the Sun. After a while things settle down with the girders aligned on the new
position.
The same thing happens if the Sun changes velocity slightly (I say "slightly"
because of the limited strength and elasticity of the steel). The girders on
the outside are still going to be aligned with the old position of the Sun
until the stresses from the center get propagated out to them. Again there
may be a period of oscillation but then things settle down again with the
girders aligned on and travelling with the Sun.
Now, from the perspective of a traveller moving through the system, the outer
girders are aligned with the current, rather than retarded, position of the
Sun.
Yet he knows that there is a limited rate at which changes to the Sun's
position will propagate outward through this network. So, in a sense, the
outer girders really are tracking the forward projection of a retarded
position. Indeed, the Sun could have undergone another of its pertubations a
few light-hours ago, and the outer girders may not know about it yet. They
could be tracking a position that the Sun will never occupy (your "ghost
Sun").
There is nothing magical about the mechanics of this situation. I haven't
shown here that gravity (or electromagnetism) works this way, but I hope to
have shown that tracking a projected retarded position is actually a very
natural phenomenon that doesn't require faster-than-light action.
#: 53464 S11/Cosmology
Fm: Hal Finney 74076,1041 To: Tom VanFlandern/DC 71107,2320 (X)
Tom - I can't agree about relativity inheriting that much from Newtonian
gravity. Einstein's field equations are essentially second-order PDE's
relating the metric coefficients "g" to the stress-energy tensor "T" (which is
0 in empty space). The metric measures the degree to which spacetime departs
from flatness.
So, specifically: (1) The source of the field is not "mass", but the
stress-energy tensor, which includes things that were not counted as mass in
Newtonian gravity.
(2) Action is not inverse square with distance. Calculating what it _is_
isn't easy but it comes out to be stronger than that when you are close to a
gravitating body. That's why Mercury has more precession, because it has to
"fight harder" to get away from the Sun than in Newton's theory so it spends
more time there.
(3) Action may be along the lines of centers; it is in the simple case of a
small test particle orbiting a spherical, static star. That's going to be
true of any curvature-based theory because the curvature obviously has to be
spherically symmetric for that case, and curvature determines particle paths.
However, it is by no means obvious what the forces are in a more complicated
case; certainly this assumption is not "built into" the theory at all. In
fact, since the theory only relates changes in the metric to what the metric
is in _local_ spacetime, there is no way that the "distant position" of the
body could be mentioned in the equations.
(4) The speed with which the action travels again has to be discovered by
solving the field equations, which include space and time derivatives. Thus
gravitational waves, for example, can be shown to travel at c. Given the
local nature of the equations there is no way even to express the idea that a
remote body "instantaneously" affects a local one. Rather, the equations just
describe how quickly the metric can propagate changes in itself that are
driven by the stress-energy tensor T.
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