Gravitons: Explaining Need & Function in Relation to GR

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Discussion Overview

The discussion centers on the role and necessity of gravitons in the context of general relativity (GR). Participants explore the implications of GR's description of gravity as the curvature of spacetime and how this relates to the concept of gravitons, particularly in light of quantum mechanics. The scope includes theoretical considerations and potential alternatives to GR.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • Some participants question the need for gravitons if GR posits that objects move along geodesics in spacetime, suggesting that gravitons may contradict GR's framework.
  • Others propose that gravitons could represent a mathematical tool or framework that complements the description of spacetime curvature.
  • One participant suggests that virtual gravitons can be analogized to elementary functions that describe spacetime curvature, indicating that both approaches may yield equivalent descriptions of particle motion.
  • There is mention of the challenges in reconciling GR with quantum mechanics, with some participants asserting that GR may be fundamentally flawed or that certain assumptions may need reevaluation.
  • Some argue that if gravitational waves exist as predicted by GR, then it follows that there must be a quantized entity associated with them, referred to as gravitons.
  • Concerns are raised regarding the lack of a known consistent quantization of full GR, with references to parts of GR that have been quantized and the existence of inconsistent quantizations.

Areas of Agreement / Disagreement

Participants express differing views on the necessity and implications of gravitons in relation to GR, with no consensus reached on whether gravitons are needed or how they fit within the framework of GR and quantum mechanics.

Contextual Notes

There are unresolved questions regarding the quantization of GR and the mathematical consistency of proposed models. The discussion highlights the complexity and ongoing debates surrounding the integration of quantum mechanics with general relativity.

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If general relativity states that objects move along geodesics in spacetime, why is there a need for gravitons? What do they do? If they are passed back and forth between energetic objects to create the gravitational interaction, this seems to completely disregard GR, but if objects move along curved paths in spacetime as Einstein believed, I have a hard time understanding what need there is for gravitons.
 
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GR may be wrong ... or some of the assumptions may be wrong.
Gravitons form part of what a likely alternative to GR could look like.

We do know there are problems with GR in relation to quantum mechanics.
 
If general relativity states that objects move along geodesics in spacetime, why is there a need for gravitons?
Think of it as a purely mathematical tool.

I'm speaking informally here:

Spacetime curvature may be described as a function. Say, a polynomial. Virtual gravitons are like elementary functions that can be composed into more sophisticated functions.

You can imagine virtual gravitons as sinusoids of different period, that you can add and get any space curvature you like.

Let me say it again, it is only an analogy. In reality, things are quite different.

However, you can see that you can describe particle motion using spacetime curvature or virtual gravitons and these descriptions will be equivalent.

Elementary gravitons are of interest of quantum mechanics, because they should be quantized. That means, non-commutative. When you multiply two functions describing spacetime curvature, the result will depend on the multiplication order. How exactly, this can be deduced from gravitons. In the case of elementary gravitons, the commutation relation should take particulary simple form.
Note however, that there is no known quantization of full GR today. Parts of it have been however quantized. There are also "quantizations" of GR that are not mathematically consistent.

It may even turn out that full GR can not be quantized at all and decomposition of spacetime curvature into gravitons is meaningless.
 
copernicus1 said:
If general relativity states that objects move along geodesics in spacetime, why is there a need for gravitons? What do they do? If they are passed back and forth between energetic objects to create the gravitational interaction, this seems to completely disregard GR, but if objects move along curved paths in spacetime as Einstein believed, I have a hard time understanding what need there is for gravitons.

GR also predicts the existence of gravitational waves. According to QM, all waves are quantized (yes, all). If both of those tenets are correct than there exist a quanta of gravitational waves. Let's call it a graviton.
 
haael said:
Elementary gravitons are of interest of quantum mechanics, because they should be quantized. That means, non-commutative. When you multiply two functions describing spacetime curvature, the result will depend on the multiplication order. How exactly, this can be deduced from gravitons. In the case of elementary gravitons, the commutation relation should take particulary simple form.
Note however, that there is no known quantization of full GR today. Parts of it have been however quantized. There are also "quantizations" of GR that are not mathematically consistent.

Thanks! Can you elaborate and/or provide references regarding the parts of GR that have been quantized?
 

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