Can particles and geometry coexist in gravitational theory?

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    Gravitons Relativity
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Discussion Overview

The discussion revolves around the relationship between particles and geometry in gravitational theory, particularly in the context of General Relativity (GR) and the concept of gravitons. Participants explore whether space can be considered as geometry and how this relates to the existence of gravitons, which are posited by some theories but not yet observed.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant expresses confusion about how geometry in GR can coexist with the concept of gravitons, which are suggested to be real by some theories, including string theory.
  • Another participant points out that while the geometry changes in GR are observable, gravitons have not been detected, indicating a potential divide between theoretical predictions and empirical evidence.
  • A participant mentions their professor's belief that many agree on the existence of gravitons, but questions whether this is a widely held view, given the lack of experimental confirmation.
  • Discussion includes the idea that gravitational waves, which are effects of geometry, may be more observable than gravitons, suggesting a distinction in the nature of these phenomena.
  • A reference is made to a field theoretic approach that starts with particles and leads to a conclusion about the unobservability of flat metrics, emphasizing the transition from particle theory to a geometric understanding of gravity.

Areas of Agreement / Disagreement

Participants express differing views on the coexistence of particles and geometry in gravitational theory, with some supporting the reality of gravitons while others highlight the lack of empirical evidence for them. The discussion remains unresolved regarding the compatibility of these concepts.

Contextual Notes

There are limitations in the understanding of how gravitons fit within the framework of GR, and the discussion reflects uncertainty about the definitions and implications of both particles and geometry in this context.

mewmew
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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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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.
 
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.
 
Last edited:
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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