On the torque thing you're speaking to someone with 5 years Physics, Engineering background who topped mathematics at Sydney University and I just don't see it.
Try as I might I see the Earth following curved spacetime with the centre of the curve where we see the Sun, that is moving with our galaxy towards the great attractor at roughly 600km per second. Depending on your perspective you are probably travelling aboput 900 km / sec right now through space - so what?
Back to the Earth and the Sun, I think the mathematics of a regressed Sun causing significant torque once you consider GR is either wrong or vastly overstated. From th einitial link in the advanced physics forum I gave you, my POV was:
http://www.advancedphysics.org/forum/showthread.php?t=3001
Quote:But in any stable system geometry saves you. As the point of suspension of a stable system is the balance point between the two bodies - like a see-saw with different weights on both end - there will be a clear point of suspension.
Now add a propagation delay speed, it equally affects both bodies so by symmetry. Lets consider the simplest case - two equal massive bodies orbiting in a perfect circle.
Given the bodies have equal mass, they are both equally recessed in where they see the balance point is. So body A sees B as being at B minus x degrees and A sees B as being at A minus x degrees, so retract this equal vector from each and re adjust the balance point (and simply you have a circle centred on an origin, move two opposite points one forward x degrees and one backwards x degrees and your centre is still the balance point). That is the simplest case. It works rather nicely.
Now consider most objects in the Universe orbit their suns if stably in an ellipsoid, bound by Kepler's laws of motion. I wonder if the same effect applies? The recession vector is the same for each body as the distance is the same - each sees the other as x degrees behind its true position. So the suspension point is still stable.
From my perspective we see the Sun as it was about 8.5 minutes ago, and given gravity propogates at the same speed as light, we are falling directly towards what we are seeing. If gravtiy was instaneous with the right equipment you should be able to see a noticeable deflection in where we are falling vs where the Sun appears to be.
Xerxes from Columbia University who administers these boards replied
Quote:Xerxes314
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I looked up the "technical reference" at the end of the FAQ (T. Damour, in Three Hundred Years of Gravitation) and can vouch for the fact that the explanations are extremely technical. There is no particularly good intuitive way of understanding these effects. To briefly sum up current understanding:
1) The gravitation field is retarded.
2) The effects of that field on a body are modified in such a way that it appears Newtonian in the weak-field, low-velocity limit.
3) There is an effect due to the bodies moving around: gravitational radiation. This comes in as velocity to the fifth or something.
To the Earth Sun rotation we fall towards what we are seeing. The Sun isn't moving that fast relative to our Solar system, its too heavy to be influenced much by all the planets gavity combined acting on its mass. This is where this torque arguement breaks down as the gravitational forces we project on our massive Sun are rather miniscule from its perspective. A bowling ball held in you arm has a greater gravitiational effect on you than the Sun, so what are you supposing all our combined planets are doing to change the Sun's point of gravitational suspension? Do you think they change the balance point more than a tiny astronomical unit? Jupiter is 500 million miles away from the Sun and 1/1000th the mass, its the Sun's mass that totally dominates our motion though space.
From
http://www.fortunecity.com/emachines/e11/86/solarsys.html page 143, sentence 4 under Reduced Mass "The Sun and the Earth are both rotating about their common centre of mass. From a great distance this would not be very obivious since the centre of Mass is inside the Sun".
Read that again, the centre of rotational mass for the Earth / Sun argument is inside the Sun. Inside the largely gaseous / plasma, rotating Sun. Earth shifts the point of gravitational suspension of the Sun about 150 km towards us (well within its 695,000km diameter)! Account for that in your torque model and see how it breaks everything down.
Remember also that our solar system is an n-body problem and hence inherently chaotic and unstable to some extent. And it exists as just 1 star and 10 planets in a galaxy of 200 billion stars that is gravitational trapped and rotating - measuring purposed angular deflection would be absurbly challenging given all the variables.
http://www.fortunecity.com/emachines/e11/86/solarsys.html
Instanteous gravity folk looking at the Sun fail to realise they purpose a problem without account to the n-body problem, which Laplace showed can't be integrated (generally solved) - so technically nuts to them for their poor mathematics!
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Finally the simplest way to show that gravity isn't instanteous is to see we exist and so does our Universe. From big bang physics it is extremely obivious this couldn't occur unless the Big Bang's shock front, and most of unfolding spacetime, actually out-raced its own gravity wave (which due to inflation it did for the first 10 ^ -35 of a second, then eventually galaxies started to clump gravitational together.) However today most of space is gravitational dis-connected from the rest of space!
But take you back to why does the Big Bang disprove instantenous gravity? Well the Schwarzchild radius for just our Sun alone is 3km, compess it to under that and you have a black hole. For a bigger Sun its considerably larger. For the Universe itself say 10^26 stars at 10^30 kg each the Scharzchild radius is = 2GM/c^2 = 2 * 10 ^-11 * 10^26 * 10^30/10^16 = 2* 10^29 meters or 10^14 light years. (We believe the Universe is 13.8 billion years old).
So if gravity was instantaneous then a second after the Universe was created its gravity propogated to create a black hole of radius about 10^14 light years, and we are inside it - yet I don't feel crushed to a singularity myself right now. The Big Bang wouldn't have lasted a second - it would have been the Big crunch if gravity was instantenous!
During inflation for a trillionith of a trillionith of a trillionith of a second spacetime blew apart at around 50,000 lightspeed until a phase change occurred and relativity kicked in. At this point given gravity propogates only at lightspeed the gravity wave / field from each of the universe's pieces couldn't catch up to each other and we avoided a big crunch. If gravity was instanteous it would have caught all the pieces whilst the Universe was smaller than a basketball, that's how big it was when inflation stopped.
As it is the expansion of the Universe is actually accelerating, something that can't happen with gravity travelling faster than light. But it cetrainly can through geometry alone (forget even dark matter or energy) if gravity travels at c and more of the Universe is past us then it is towards our original epicentre and we are experiencing more of its residual receding gravity shock wave too!
