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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

#41

Post by whatshisface »

NitpickLawyer wrote: post #39
cryptonector wrote: post #34

Earlier quoted context omitted.

That gravity is curvature of spacetime is one view of two equivalent views, but it is the standard view. The other view is that you have flat spacetime with different distortions (of things other than spacetime) than the distortions you get in curved spacetime. The Schwarzschild metric essentially lets you do exactly that projection of curved spacetime to flat, and vice-versa. When you watch an animation like https:/…

I last took a physics course when Pluto was a planet, so excuse my possibly outdated question, but isn't the detection of gravitational waves proof of gravity being a force? I follow a few educators/communicators in this field and I have a feeling they're using this "gravity isn't really a force" to bridge the gap between their deep understanding and us mortals that don't poses the language / understanding to get the…

It's a bit of an internet meme, gravity can take momentum away from one object and transfer it to another, and that's what Newton said a force was. The meme is that the way it happens makes "changing momentum" (3-momentum, the one Newton was talking about) and "going straight" (geodesically, in curved space-time) hard to separate in English.

Re: It might be possible to detect gravitons after all

#42

Post by stouset »

NitpickLawyer wrote: post #39
cryptonector wrote: post #34

Earlier quoted context omitted.

That gravity is curvature of spacetime is one view of two equivalent views, but it is the standard view. The other view is that you have flat spacetime with different distortions (of things other than spacetime) than the distortions you get in curved spacetime. The Schwarzschild metric essentially lets you do exactly that projection of curved spacetime to flat, and vice-versa. When you watch an animation like https:/…

I last took a physics course when Pluto was a planet, so excuse my possibly outdated question, but isn't the detection of gravitational waves proof of gravity being a force? I follow a few educators/communicators in this field and I have a feeling they're using this "gravity isn't really a force" to bridge the gap between their deep understanding and us mortals that don't poses the language / understanding to get the…

My naïve understanding is that you can model gravity as a force in a flat, static spacetime. Equivalently you can model gravity as a forceless distortion of curved spacetime. Both models can be translated faithfully into one another, so you can solve problems related to gravity in either domain.

Re: It might be possible to detect gravitons after all

#43

Post by ruthmarx »

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!

> So I thought gravity was basically the curvature of spacetime.

That's just part of the picture.

I always thought that Veritasium video did more harm than good.

Re: It might be possible to detect gravitons after all

#44

Post by Aardwolf »

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…

> The model of non-self-interacting gravity is a particle we call a "graviton," and it probably describes reality very well when the gravitation involved is so weak that its self-interaction is undetectable.

Can you please elaborate, the first part of the sentence says graviton is for non-self-interacting gravity, the second part of the sentence says graviton is for self-interacting (if 'its' in 'its self-interaction' refers to the graviton).

I don't intend to nitpick the sentence, just trying to understand the theory and I don't even know if particle means self interaction or the opposite and can't parse it here either...

If the answer is graviton is for non-self-interacting: what is the model for the other case (where gravity does self interact) and what would cause that self interaction if not the graviton?

Re: It might be possible to detect gravitons after all

#45

Post by Wololooo »

NitpickLawyer wrote: post #39
cryptonector wrote: post #34

Earlier quoted context omitted.

That gravity is curvature of spacetime is one view of two equivalent views, but it is the standard view. The other view is that you have flat spacetime with different distortions (of things other than spacetime) than the distortions you get in curved spacetime. The Schwarzschild metric essentially lets you do exactly that projection of curved spacetime to flat, and vice-versa. When you watch an animation like https:/…

I last took a physics course when Pluto was a planet, so excuse my possibly outdated question, but isn't the detection of gravitational waves proof of gravity being a force? I follow a few educators/communicators in this field and I have a feeling they're using this "gravity isn't really a force" to bridge the gap between their deep understanding and us mortals that don't poses the language / understanding to get the…

So the main issue here is how people were presenting it, in Quantum field theory, as stated by other people, each force is associated with a field and has at least one force carrier, the exact number is linked to the specifics of the mathematical framework underlying it

To that extent you can build 3 fundamental forces, electro magnetic, weak (that are called together electroweak) and the strong force. You have an extra force carrier through the Higgs that allows you to give mass to everyone.

Now you need to consider gravity because you know that gravity exist and since everything under the sub is quantised, well so should gravity.

The main issue with gravity is that it is interpreted so far as a curvature of space time, it's mainly fine for big items, but the implications for quantum field theory is that you should modify the small integral element that you use (space shouldn't have the same size) except that you look locally at space that is mainly flat... And changing the integral does not lead to well behaved behaviours.

You can start to introduce new fields but doing so also causes an issue...

Funnily enough even in the standard model something is missing, everything mostly fits, but that's the trick, mostly, neutrinos have mass and this in itself is a problem because the Higgs mechanism doesn't provide mass to them ...

Long story short, people take shortcut when explaining the messy gritty part of it, which is "fine" but not really, and from a simple standpoint one would like to have a simple field from which gravity is born, which might be but so far, to my simpleton understanding, this hasn't been too successful, unless some form of string theory is realised. But the pre requisite for this is a form of supersymmetric theory existing which is currently disfavored, but could exist in the unproved energy scales from here to the plank energy scale.

Sorry this ended being a tad long and I'm not sure this is clarifying things.

Re: It might be possible to detect gravitons after all

#46

Post by choilive »

itishappy wrote: post #14
choilive wrote: post #4

> physicists are debating what it would really prove. Well, if we can detect the graviton before we have a working quantum theory of gravity, it would mean that gravity is in fact quantized and that we just need to figure it out. This would be a very big deal.

They can detect an interaction, but they can't prove that it's quantized without (I believe) sub-Poissonian statistics[0], which requires detecting enough events and with enough certainty that it would require planet-scale machinery. > Now graviton chasers find themselves in a peculiar position. On the main facts, everyone is in agreement. One, detecting a quantum event sparked by a gravitational wave is — surprising…

It sounds like the article is saying we could detect many events without using a planetary scaled detector It mentions a single detector being a 15kg Be bar chilled to near absolute zero. Certainly very very difficult, but not in the realm of sci-fi.

Re: It might be possible to detect gravitons after all

#47

Post by FeepingCreature »

Aardwolf wrote: post #44
whatshisface wrote: post #17

Earlier quoted context omitted.

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…

> The model of non-self-interacting gravity is a particle we call a "graviton," and it probably describes reality very well when the gravitation involved is so weak that its self-interaction is undetectable. Can you please elaborate, the first part of the sentence says graviton is for non-self-interacting gravity, the second part of the sentence says graviton is for self-interacting (if 'its' in 'its self-interaction…

> Can you please elaborate, the first part of the sentence says graviton is for non-self-interacting gravity, the second part of the sentence says graviton is for self-interacting (if 'its' in 'its self-interaction' refers to the graviton).

The point is, we know gravitation does self-interact. But our best model, the graviton, doesn't model self-interaction. So the model is probably accurate in regimes where you'd expect little self-interaction anyways.

Re: It might be possible to detect gravitons after all

#48

Post by hhdhdbdb »

whatshisface wrote: post #8
ars wrote: post #7

I don't understand what a graviton is . The article implies that it's something that communicates changes in gravity? Is that correct? How does it communicate the magnitude of the change? By having lots of gravitons? Or does it have something akin to a frequency?

A graviton is the smallest possible unit of a gravitational wave. The amplitude of the wave corresponds to the number of gravitons, like you said, and its frequency to their frequency (quantum particles have frequencies that are related to their momenta). We're aware that light, at least, works like that.

A gravitational wave requires an event like a black hole merger, or basicially somerhing to move and change the field, right?

In this case, how does the fact that a big object is still influencing space/time around it communicate that fact when it is not moving. Is that still gravitrons?

Re: It might be possible to detect gravitons after all

#49

Post by Iolaum »

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…

Even with gravity being "self interactive" can't we have stable particles ("gravitons"?) that behave like solitons do?

https://en.wikipedia.org/wiki/Soliton

Re: It might be possible to detect gravitons after all

#50

Post by renegade-otter »

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!

I just watched this a few days ago on the Space Matters channel about gravitational waves: https://www.youtube.com/watch?v=9bg2NINW8a0

Not just some dumbed down Discovery show - it pushes the limits of what a layperson can understand.

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