General Relativity, Gravity, Help!!

JIM writes:

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Because in theory the universe has been estimated to have 12 dimensions total (the most common)

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Just because I'm being picky:Not twelve. Eleven.The common model from M-theory is that the universe has 11 dimensions...10 spatial and 1 temporal. There are the three dimensions we commonly deal with, six curled up dimensions which strings need if they are going to do what we want them to do, and a larger, cosmic dimension for M-theory to work in.This 11th dimension is what helps to explain why gravity is such a weak force compared to the other three. Previous models of string theory essentially had all strings as being closed loops. M-theory has most strings being non-loops where the ends are connected to the brane in which we exist, but gravity is a closed loop string. Thus, the other three forces are essentially trapped (for lack of a better term on my part) in this brane but gravitons can leave the brane.------------------
Rrhain
WWJD? JWRTFM!

Tsegamla writes:

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The cube model makes more sense to me, but considering the fact that both models seem to be valid/used a lot, I'm assuming that they really are compatible and that the problem is just my understanding of them.

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If I understand your description of the cube picture, these two representations are essentially identical. The trampoline model is sort of a two-dimensional way of looking at it while the cube method is a more three-dimensional model.The trampoline model, too, is more amenable to actual construction. That is, you can actually take a sheet of rubber, stretch it, place a heavy ball in it, and then roll a light ball along it and watch how the motion of the light ball curves around the heavy ball.To make the cube model, you'd have to find some way to fill the cube with a stretchy material and then uniformly pull all of it towards the center...and then find some way to move another object through all this material in order to see it curve around the point of pulling...not exactly an easy thing to do.The problem with the trampoline model is that it requires a third dimension to have work...and it also requires gravity. The trampoline model makes it look like space is curving into some other dimension and that some force is pulling it into that dimension when actual gravity doesn't work like that. It curves in on itself like the cube model.Does that help?------------------
Rrhain
WWJD? JWRTFM!

crashfrog writes:

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Of course, the gravitons themselves are particles

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Incorrect.Gravitons are strings. Strings are not particles. The problem with the standard model of quantum mechanics is that it defined things in terms of particles. At first, things like electrons and protons were particles. Then we discovered quarks and those were considered particles. But that didn't quite solve the problems. String theory does away with particles. At the very least, it claims that things like quarks are made up of strings which aren't particles.

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so they're also exhcanging gravitons.

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Incorrect.Gravitons do not emit gravitons.

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If they don't have mass, they're a pretty weird particle, and it wouldn't be clear how they could do their job at all.

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Since they're not particles at all....------------------
Rrhain
WWJD? JWRTFM!

JonF responds to me:

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Gravitons do not emit gravitons.

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But can we think of gravitons as splitting and recombining and all sorts of weird stuff as photons "do" on Feynman diagrams?

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I'm not sure. I may have to qualify my statement.More specifically, things with mass do not emit gravitons merely from their existence. It is the motion of the mass that causes the emission of the gravitons. Gravitons, however, are massless.When a charged particle moves, it emits photons. But static charges do not emit photons.------------------
Rrhain
WWJD? JWRTFM!

Tsegamla responds to me:

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Just one question about string theory, does it suggest that quarks are strings, or that quarks are made up of many strings?

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My understanding is that quarks are made of strings.One of the big problems with string theory is that it predicts strings to be so small that there would be no way to directly detect them. Thus, this makes it very difficult to produce a testable theory of strings. With quarks, there are ways to make testable predictions, even though we can't "see" the quarks in the common sense of the word. Strings, being so much smaller, are that much harder to deal with.The reason why we like string theory is that it is mathematically elegant and helps to combine what are seemingly conflicting aspects of physics. And that's a great way to get something studied, but that doesn't make it true.As one of the scientists on the recent Nova program on strings said, if string theory cannot be validated in the laboratory, then nobody should believe it.------------------
Rrhain
WWJD? JWRTFM!