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It might be possible to detect gravitons after all

quantamagazine.org

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Re: It might be possible to detect gravitons after all

#21

Post by yarg »

ta93754829 wrote: post #10

So I thought gravity was basically the curvature of spacetime. But if there's a "gravity" particle, those two things seem mutually exclusive? Can someone who understands this please explain it to me, thanks!

To my understanding (not the best) there's a huge disconnect between the physics of the very small (quantum mechanics and the standard model) and that of the very large (general relativity).

The disconnect seems to be unresolvable (I don't understand this part at all) and so efforts are being made to quantise gravity and incorporate it into the standard model.

Re: It might be possible to detect gravitons after all

#22

Post by LeoPanthera »

ta93754829 wrote: post #10

So I thought gravity was basically the curvature of spacetime. But if there's a "gravity" particle, those two things seem mutually exclusive? Can someone who understands this please explain it to me, thanks!

In theory, if gravitons exist, they should reproduce the same effects as the curvature of spacetime at larger scales. So, while they seem contradictory, they're actually complementary. Gravitons would be the "quantized" particles that, in large numbers, create the effect we observe as curved spacetime.

The problem is that nobody has successfully combined these two views into a single unified theory, known as "quantum gravity". General Relativity and quantum mechanics don't naturally fit together, and that's why we don't yet fully understand gravity in a way that reconciles both the spacetime curvature and graviton perspectives.

Re: It might be possible to detect gravitons after all

#23

Post by 1024core »

ta93754829 wrote: post #10

So I thought gravity was basically the curvature of spacetime. But if there's a "gravity" particle, those two things seem mutually exclusive? Can someone who understands this please explain it to me, thanks!

Sort of like how light is both a wave and a particle...?

Re: It might be possible to detect gravitons after all

#24

Post by [deleted] »

Willingham wrote: post #18
gary_0 wrote: post #15

Earlier quoted context omitted.

Electromagnetism is both a continuous wave and a discrete particle, so it makes sense to me that a continuous spacetime curvature could also be a discrete particle at the same time. (Keeping in mind we're not talking about tangible shapes but mathematical models that describe aspects of reality that are hard for humans to intuitively conceptualize.) Of course, our idea of how to reconcile quantum gravity with general…

When you mention nuclear forces, are you referencing weak force and strong force? Do we understand these forces at the same level that we understand electromagnetism?

[deleted]

Re: It might be possible to detect gravitons after all

#25

Post by whatshisface »

sharikous wrote: post #19
whatshisface wrote: post #3

I'm with the debaters on this one, the energy levels of a bound quantum system are predetermined to change in quantized intervals irrespective of if they are coupled to a classical or quantum field. What theory of gravity is this experiment intended to falsify? It would be great to have an independent gravitational wave detector though.

the statistics would be different. Check out Rabi oscillations (classical EM) vs Jaynes-Cummings model (quantized EM) and phenomena like quantum antibunching (only possible for quantized EM)

How would mergers produce antibunched gravity?

Re: It might be possible to detect gravitons after all

#26

Post by ajkjk »

ta93754829 wrote: post #10

So I thought gravity was basically the curvature of spacetime. But if there's a "gravity" particle, those two things seem mutually exclusive? Can someone who understands this please explain it to me, thanks!

Not an expert, but: the curvature of spacetime is modeled as a tensor field (the metric tensor). That field can have (classical) waves in it, which is what LIGO detects (I believe). Then you can certain hypothetically quantize that field, in which case it definitely has to be a spin-2 particle and it seems likely that there will be a way to do it since all the rest were.

The "geometry" comes from the fact that the way we measure distances (or, well, experience time) uses the metric tensor field to do it. But it is still ultimately just a value attached to every point like any other field.

Re: It might be possible to detect gravitons after all

#27

Post by btilly »

Willingham wrote: post #18
gary_0 wrote: post #15

Earlier quoted context omitted.

Electromagnetism is both a continuous wave and a discrete particle, so it makes sense to me that a continuous spacetime curvature could also be a discrete particle at the same time. (Keeping in mind we're not talking about tangible shapes but mathematical models that describe aspects of reality that are hard for humans to intuitively conceptualize.) Of course, our idea of how to reconcile quantum gravity with general…

When you mention nuclear forces, are you referencing weak force and strong force? Do we understand these forces at the same level that we understand electromagnetism?

Yes. The Standard Model has completely explained all experiments involving them for around 50 years now.

In fact the outstanding success of the Standard Model has posed its own problems - the lack of deviations from it makes it hard for experiments to point in a useful direction for better theories to be developed along.

Re: It might be possible to detect gravitons after all

#28

Post by JumpCrisscross »

Vecr wrote: post #20
JumpCrisscross wrote: post #11

Earlier quoted context omitted.

You’re mixing up general relativity with quantum gravity.

I'm not exactly sure what you're saying. I know you can have gravitons without "quantum gravity" (as incomplete theories). I'm responding to a commenter on applications. In a global position finding system, gravitational effects could be used, as could be quantum effects. Maybe even both in the same system. It seems really doubtful to me a practical system would depend on anything graviton related.

You buried your lede. The “tricks” you describe relate to GR. I missed that you’re essentially saying “no.”

Re: It might be possible to detect gravitons after all

#29

Post by gradschoolfail »

whatshisface wrote: post #17
ta93754829 wrote: post #10

So I thought gravity was basically the curvature of spacetime. But if there's a "gravity" particle, those two things seem mutually exclusive? Can someone who understands this please explain it to me, thanks!

Our ability to solve integrals is much more limited when the dx represents a slight change in a function, rather than a small change in a real number. As a result, a lot of things that are easy to say in English such as "quantized curvature in spacetime," or "strongly coupled gauge theory," turn into a big mess when they're written down more precisely. One of the consequences of this limitation is that we have a mode…

This needs to be emphasized more, by the TFA too — most (theoretical) physicists think that detecting gravitons is an engineering exercise that has no implications* for quantum gravity (as understood by the public)

>The model of non-self-interacting gravity is a particle we call a "graviton,"

This needs to be emphasized even more, because it has

>when the dx represents a slight change in a function

*see the discussion around sharikous’ comment below

https://news.ycombinator.com/item?id=42003116

Re: It might be possible to detect gravitons after all

#30

Post by dcl »

ta93754829 wrote: post #10

So I thought gravity was basically the curvature of spacetime. But if there's a "gravity" particle, those two things seem mutually exclusive? Can someone who understands this please explain it to me, thanks!

Yes. I've seen lots of twitter/X posts lately about how Gravity is not actually a force. But how can that be true if there is a force carrying "gravity" particle? Or is the word 'force' being used loosely here?
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