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Instant Gravity : Proof

baron said:
Yeah, all that could have been avoided if he'd realised gravity isn't some kind of repeated pulse sent out from the same point, rather a distortion of space-time. If the central object flickered in and out of existence then what he suggests would happen, otherwise not so much.
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So, the number keeps rising in the sciences. Wonderful.
 
Ziggurat said:
This is one of those cases where somebody stumbles upon an actually interesting problem, with some deep and important physics behind it, but then totally and completely screws up the answer.

It's absolutely true that Newtonian gravity (which propagates instantly) will give you stable orbits for binary pairs. Furthermore, it's even true that if the propagation speed for gravity is not infinite, as in General Relativity, you cannot have stable orbiting pairs. But none of the rest of the argument follows. The gravitational fields of moving bodies are not simple. You can't get them by just looking at the time-delayed position of where the object was. This isn't controversial either, the exact same effect is readily observable with moving electric charges, and leads directly to magnetism. Similar stuff happens with gravity. But if you do the calculations right (and they haven't even come close to doing so), the orbits aren't unstable because they spiral outwards, they're unstable because they spiral inwards.

And again, these effects are observable with electric charges (where we know the propagation speed of the field quite well). They're even observable with gravity. Binary orbits decay. They shouldn't, if Newtonian gravity was correct. But it isn't, so they do.

None of this is controversial. None of it is even mysterious. But it does require actually knowing more than high school physics. And the author obviously doesn't.
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Quelle surprise!!!
 
smartcooky said:
The OP (and the crank in his link) have fallen at the first step, by proceeding under the premise that gravity is a force acting between two bodies... it isn't

Massive objects cause a distortion in space-time, which is perceived as gravity, objects orbit each other because they are affected by the distortion.

Go back to year 9 physics class (if you ever attended in the first place!)
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Wow, here it's year 11 or 12 depending which maths you have prior!! And normally the Physics at that point (unless AP) does not really cover such topics.
(As a (retired) teacher of the major sciences +, I know the topics being discussed here did not come up in high school except if the student interested wanted extra work/research assignments on his-her own!!! A year 9 version would be purely Newtonian, afaik!!! (The three systems I taught in primarily considered it but never went for it. There was an interest in the late 70s/early 80s but it never really got off the ground. And the systems were Nashville/Davidson Co., Tampa/ Hillsborough & Pasco Co. and Orlando/Orange Co.) ..........)
 
Loss Leader said:
My understanding is that space-time expanded at speeds far in excess of light during the early moments of the universe.
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Yep, but as far as I recall that is a change in the metric (the abstract notion of distance in the manifold) not a change in the local curvature of the manifold. That is, nothing actually travels trough (going from one location to another) the space-time (like a change in local curvature) faster than the speed of light but the space-time itself, locations in it that is, move further from each other at speeds far in excess of light.


Hope that makes sense.

ETA:

Or what baron said.
 
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Ziggurat said:
None of this is controversial. None of it is even mysterious. But it does require actually knowing more than high school physics. And the author obviously doesn't.
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Thanks for good answer. And the rest, think again .. it's not crank because 'gravity is not a force, but space distortion' .. both are equivalent approaches and should give you same answers. The force is derived from space curvature.
Space curvature can also travel at limited speed (and it does).
While most of the people ruled the OP arguments as nonsense, only Zigggurat used the correct arguments. Don't be afraid to say 'I don't know what is the correct answer' .. skepticism is based exactly on admitting that.
 
EHocking said:
Rather coincidentally I watched the telemovie "Einstein and Eddington" the other night.

Well worth the price of admission.
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Is that the one with Yahoo Serious as Young Einstein? It's an excellent example of cinematic art, and way better science than what usually appears on this thread.
 
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