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Space-time is deformed by the presence of gravitational or electromagnetic forces. I don't know if it's right to say that the elasticity itself is a force, it's more of a property.5hot6un":3qkhy2jk said:...what force acts as the elasticity of space-time?
Really? My understanding is that the deformation of space-time is how gravity acts at a distance. This is supposed to be one of the most profound things that Einstein proposed. This concept moved us beyond Newton's explanations of gravity. It eliminates the need for a "graviton" particle and preserves the speed limit of particles to the speed of light. Space-time deforms in the presence of mass. Observations of gravitational lensing have confirmed this.ramparts":1fnkuezk said:Spacetime doesn't have "elasticity" - you're stretching the analogy way too far. Words like "warping" are terms used to explain relatively complicated concepts to the general public, not exact scientific definitions.
The paths of moving objects are curved by the presence of mass. It is convenient to see this as a curving of space-time. But it could also be seen as a direct action (possibly by interaction with gravitons) on a object which curves its path.5hot6un":mk87p670 said:... My understanding is that the deformation of space-time is how gravity acts at a distance. This is supposed to be one of the most profound things that Einstein proposed. This concept moved us beyond Newton's explanations of gravity. It eliminates the need for a "graviton" particle...
Thanks undidly!undidly":1ougs8uh said:The funnel is real.
The gradient at any point is the escape velocity at that point,divided by C ,multiplied by 90 degrees.
Try the limits.
Zero mass should calculate to zero gradient.
Zero mass has zero escape velocity.
Zero /C *90 degrees = zero gradient ,flat .
A black hole should have the maximum gradient.
A black hole escape velocity is C (at the event horizon).
C/C * 90 degrees = 90 degrees ,straight down.
Earth is between these limits,less than a twentieth of a degree at the surface.Work it out.
The depth of the funnel (G well) for Earth is less than a metre.
This is GR stuff.There are no gravitons.
Hi weeman. Credit must go to Jeters_boy, who posted it in another thread. I plan to watch it again, I liked it that much. I'm afraid I'm drawing incorrect conclusions from this lecture that was intended for laymen like me. Oh well. I have no plans to go back to college to study it!weeman":3r5rmfkm said:Thanks for posting that vid, FlatEarth! Very good stuff. I just watched the whole thing at 1 o'clock in the morning :mrgreen:
Why does ST spring back to flat?.5hot6un":29kautgp said:undidly":29kautgp said:The funnel is real.
These simple equations state quite clearly (to me at least) that ST is elastic-like. Now I need someone with a deep understanding of GT to explain how ST's tenancy to be flat in the absence of matter affects the universe.
Let me try to say this in a different way.
ST alone is flat. Add mass and ST warps. Take mass away, ST flattens back out. This tendency to move towards flat is a force and MUST have some influence on the universe as a whole. Maybe it is known and accounted for. I would like to know how.
Einstein's GT does not say gravity is a field. Newton suggested that. Einstein explained that gravity is the deformation of space-time.Jerromy":169uyp50 said:"Waves" implies a variance in a field. If there were some type of waves to the force of gravity I'm sure we'd have figured it out by now. Newton may not have had the insight but Einstien did and he determined that gravity is a field, not a "wave of gravitons".
Right, so... yes, spacetime curvature is how gravity acts. That is the rather beautiful concept underlying what Einstein did. However, the analogy of spacetime as some higher-dimensional rubber sheet is just a useful tool to communicate that to the public. You were talking about elasticity, and forces behind that, and even though those things do exist on a rubber sheet, none of that stuff is in the theory of general relativity.5hot6un":2b73y0ui said:Really? My understanding is that the deformation of space-time is how gravity acts at a distance. This is supposed to be one of the most profound things that Einstein proposed. This concept moved us beyond Newton's explanations of gravity. It eliminates the need for a "graviton" particle and preserves the speed limit of particles to the speed of light. Space-time deforms in the presence of mass. Observations of gravitational lensing have confirmed this.ramparts":2b73y0ui said:Spacetime doesn't have "elasticity" - you're stretching the analogy way too far. Words like "warping" are terms used to explain relatively complicated concepts to the general public, not exact scientific definitions.
It sounds like a lot more than a nifty way to explain stuff to us common folk.
And since we know ST deforms, we also know it exists in a non deformed state. Right?
Therefore it would seem correct to state that ST had a tendency to be non deformed in the absence of mass.
If it did not, we would see deformed ST all over the universe where massive objects have once been.
So how far in the opposite direction from "deformed" does ST go? To continue the fabric analogy; does ST move more towards a loose mesh in the absence of matter? Or is there a pervasive steady state?
If ST does "loosen" the further away from mass it is, could this be a source of inflation?
Surely someone smarter than me must have wondered this.
Having read the rest of this thread, I would humbly suggest that you change your approach. You came into this thread asking questions because you don't know something about science, and then in the rest of your posts act as if you already know all of the science. It is quite clear that you don't; that's fine, there's nothing wrong with that, but you shouldn't be off asserting things like "Einstein's GT does not say gravity is a field" which are simply untrue. In GR, gravity is a field - it's a tensor field, to get all jargon-y. A tensor is just a type of mathematical object, and these particular tensors describe the curvature of spacetime at each point. It's a different field than the one used in Newtonian physics, but it's still written in the language of fields.5hot6un":29fmnglf said:Einstein's GT does not say gravity is a field. Newton suggested that. Einstein explained that gravity is the deformation of space-time.Jerromy":29fmnglf said:"Waves" implies a variance in a field. If there were some type of waves to the force of gravity I'm sure we'd have figured it out by now. Newton may not have had the insight but Einstien did and he determined that gravity is a field, not a "wave of gravitons".
That's kind of the point of this tread. Einstein's deformed ST implies it is a medium.
There is an active search for gravity waves.
http://www.spacedaily.com/news/gravity-05f.html
The term gravity waves is wrong in my opinion. They are space-time waves. Ripples in the ST medium.
I appreciate the feedback. I certainly do not mean to act as if I know all the science. But I do understand some of it.ramparts":20il72sj said:Having read the rest of this thread, I would humbly suggest that you change your approach. You came into this thread asking questions because you don't know something about science, and then in the rest of your posts act as if you already know all of the science. It is quite clear that you don't; that's fine, there's nothing wrong with that, but you shouldn't be off asserting things like "Einstein's GT does not say gravity is a field" which are simply untrue. In GR, gravity is a field - it's a tensor field, to get all jargon-y. A tensor is just a type of mathematical object, and these particular tensors describe the curvature of spacetime at each point. It's a different field than the one used in Newtonian physics, but it's still written in the language of fields.
Also, a minor thing, it's hurting my head to read "ST" all the time No one uses that - just write "spacetime", it'll make your posts easier to read.
I have more questions. Please read them as if written in the tone of an inquisitive child.ramparts":3oi7c9mg said:Right, so... yes, spacetime curvature is how gravity acts. That is the rather beautiful concept underlying what Einstein did. However, the analogy of spacetime as some higher-dimensional rubber sheet is just a useful tool to communicate that to the public. You were talking about elasticity, and forces behind that, and even though those things do exist on a rubber sheet, none of that stuff is in the theory of general relativity.
There is a "non-deformed" state of spacetime - it's called Minkowski space, or flat space. Of course, it doesn't exist anywhere in the universe, since the universe has matter - even the places that don't have matter are affected by matter elsewhere - but any region of spacetime on small enough scales looks pretty similar to it, in the same way that even though the Earth is curved, on small scales the surface looks flat. Minkowski space is just like the flat surface, but in higher dimensions (and with some funny stuff to account for the time dimension).
Also (slightly unrelated?): this picture doesn't eliminate the need for a graviton particle. In fact, this came before we knew what a graviton was. In something called quantum field theory, forces become particles - for example, the electromagnetic force becomes a photon. The same things happen when you quantize gravity. These different pictures - forces, spacetime, particles - equally "right" ways of looking at the same thing. It just depends how you look at it.
I can answer the last one. Right now the last measurements had gravity propagating at the speed of light, give or take. Since gravity is the deformation of spacetime (or is it space-time ?) you can say changes in this deformation (gravity waves) move at the speed of light. I note that there was some dispute that Kopeikin's experiement actually measured the "speed of gravity". I don't know if that dispute was ever resolved.5hot6un":3npnbvk9 said:I have more questions. Please read them as if written in the tone of an inquisitive child.
By what mechanism does a section of spacetime return to a less deformed state when a massive object moves further away?
In my mind, this question conjurers up visions of spacetime acting as a physical thing.
I also wonder if the section of spacetime moves back to a less deformed state at the speed of light or at some other rate?
It seems to me that there is only one useful interpretation of GR- the one that sees spacetime as something real, not just a measure of distance and motion. For all his brilliance, Einstein had difficulty with some of the key precepts of quantum mechanics, but we know that the only way to explain the very large is to understand the very small. QED explains what spacetime is, and it cannot be ignored.ramparts":3bkphcun said:It is possible there is more to it; we're hoping that a fuller understanding of GR on the quantum level will help elucidate the precise nature of spacetime. There are still two fields of philosophical interpretation of GR - one which sees spacetime as an actual, physical manifold upon which all physics happens, and the other which sees it as just a useful mathematical construct to describe something entirely different.