# Relativity and gravitons?

#### mewmew

I am doing some research this summer with a professor and we are learning GR. For the first time I am thinking about gravity actually in terms of geometry and started to ask my professor questions. He is a VERY smart man but I didn't get exactly what I was looking for with one question. I asked if space actually was geometry, as opposed to say just math that is geometry that explains how things work and he said it was actually geometry. I believe this to be true and I like it a lot, but he also said gravitons are real. I asked how can gravitons be real in GR and he seemed to slightly side step it and tell me that both are correct. He is very smart and perhaps just didn't have the time to explain to me how both can co exist or perhaps it is a question that doesn't have a clear cut answer. That is what I want to ask you guys! Thanks for any help.

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#### selfAdjoint

Staff Emeritus
Gold Member
Dearly Missed
The GR geometry changes are real; they have been observed. Your professor may be a string theorist; they believe gravitons are real, but no-one has ever detected one.

#### mewmew

Yes, as a matter of fact he is. He said that not many people however would disagree that gravitons are real, is this perhaps wrong? He also said we are quite far away from finding them and that he will most likely not live to see them discovered but may live to see gravitational waves discovered which are more an effect of the geometry. that is of course just a guess. Now, is it something like an electron where something can be a "wave" and a particle? I just don't see how gravitons and GR mesh together but only know part of the fundementals of both.

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#### pervect

Staff Emeritus
Science Advisor
You might take a look at

http://xxx.lanl.gov/abs/astro-ph/0006423

I don't really understand all the details, but this much I do understand:

You start out with a spin-2 field theory in flat space-time, then find out that because gravity couples to everything (well, everything with energy or pressure), this flat metric is not observable, and that observable space-time must have a non-Miskowskian geometry. So you start with "particles", and wind up with geometry in the end.

Or to quote from the abstract

Although this field theoretic approach, which has been advocated repeatedly by a number of authors, starts with a spin-2 theory on Minkowski spacetime, it turns out in the end that the flat metric is actually unobservable, and that the physical metric is curved and dynamical.

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