B Can gravitons be detected?

[Josiah]

TL;DR Summary

Can gravitons be detected

Hi, would gravitons kick electrons into a higher energy level? If so can that change by electron be detected, moving from one energy level to the next?
Josiah

 

[DrChinese]

1. Hi, would gravitons kick electrons into a higher energy level?

2. If so can that change by electron be detected, moving from one energy level to the next?

1. Assuming gravitons exist: the answer is no. Electrons require a minimum amount of energy to jump to a higher level. A graviton would be many orders of magnitude too low to provide that.

2. Yes, that can definitely be detected. Normally the electron will drop to a lower level within some characteristic time span. When it does, you'd expect a photon to be emitted. So look for that.

 

[PeterDonis]

A graviton would be many orders of magnitude too low to provide that.

Not a sufficiently energetic gravition. In other words, if we assume that gravitons actually exist, i.e., that there is a valid quantum theory of gravity that, on some level, can be described as containing massless spin-2 particles that mediate the gravitational interaction, then such a particle could in principle induce an energy level transition of an electron in an atom, if it had the right energy.

The real issue is, first, that unlike photons, we don't know that the "if" in my statement above is actually the case--we don't have a quantum theory of gravity that we've actually tested experimentally, and while theoretically speaking, there does exist a quantum field theory of a massless spin-2 field, we don't know if that theory actually works as a model for gravity in the real world on any level.

 

[Demystifier]

According to the theory we have, graviton of right energy, of course, can be absorbed by the electron in the atom. The reason why we don't observe it is because gravity is a much weaker force than the electromagnetic force, so the probability of such graviton absorption is much lower than that of photon absorption.

 

[Josiah]

1. Assuming gravitons exist: the answer is no. Electrons require a minimum amount of energy to jump to a higher level. A graviton would be many orders of magnitude too low to provide that.

2. Yes, that can definitely be detected. Normally the electron will drop to a lower level within some characteristic time span. When it does, you'd expect a photon to be emitted. So look for that.

Hi, you said that gravitons don't change the level of the electron. But they obviously get absorbed by matter. Is this possible to detect?

 

[PeterDonis]

you said that gravitons don't change the level of the electron.

He was mistaken. See post #3.

they obviously get absorbed by matter.

Very, very, very, very,.....(lots more veries here)...weakly.

Is this possible to detect?

In principle, yes. In practice, don't hold your breath.

 

[Josiah]

Also, if gravitons get abosbed by matter, wouldn't it there be a difference in gravity, depending on what is in the way? For example if a moon is in the way of the the sun, wouldn't the earth experience less of a gravitational pull from the sun, because some got absorbed by the moon?

He was mistaken. See post #3.


Very, very, very, very,.....(lots more veries here)...weakly.


In principle, yes. In practice, don't hold your breath.

 

[Josiah]

How would you do it in principle?

 

[renormalize]

Also, if gravitons get abosbed by matter, wouldn't it there be a difference in gravity, depending on what is in the way? For example if a moon is in the way of the the sun, wouldn't the earth experience less of a gravitational pull from the sun, because some got absorbed by the moon?

No, propagating gravitons have nothing to do with the slowly-varying gravitational fields that attract the moon to the earth or the planets to the sun. It's exactly analogous to the fact that propagating photons make no contribution to the electrostatic fields that bind electrons to an atomic nucleus. Moreover, ordinary celestial bodies are predicted to be almost perfectly transparent to gravitons, just like they are to neutrinos, only more so.

 

[DrChinese]

[DrChinese] was mistaken. See post #3.


Very, very, very, very,.....(lots more veries here)...weakly.


In principle, yes. In practice, don't hold your breath.

This is a B level thread, n'est pas? I'll stand by my answer, until someone demonstrates otherwise - a very, very, very, very long time from now.

 

[PeterDonis]

This is a B level thread, n'est pas?

Yes, but that doesn't mean you can misstate what the actual physics, as best we know it, says.

I'll stand by my answer, until someone demonstrates otherwise

You're assuming that your "no" answer is somehow the default answer unless someone demonstrates otherwise. It's not. The default answer is whatever is implied by our best current theories, and that's not the unqualified "no" answer you gave.

 

[PeroK]

Hi, you said that gravitons don't change the level of the electron. But they obviously get absorbed by matter. Is this possible to detect?

If gravitons are emitted by one object and absorbed by another in the way you suppose, then wouldn't gravity be a repulsive force?

The first object would recoil due to momentum of the emitted graviton etc?

Perhaps the graviton isn't what you suppose it to be?

 

[PeroK]

I found this, which perhaps highlights that a B-level answer is unrealistic.
https://www.nature.com/articles/s41467-024-51420-8

 

[Josiah]

If gravitons are emitted by one object and absorbed by another in the way you suppose, then wouldn't gravity be a repulsive force?

The first object would recoil due to momentum of the emitted graviton etc?

Perhaps the graviton isn't what you suppose it to be?

But doesn't the magnetic force do the same thing? It emits photons which transfer the force to the other object. In the case of two magnets repelling each other.

 

[snorkack]

Is it then electrons which are detected, though?
Bells routinely ring in frequency range of common astronomical gravitational waves.
The vibrations of a ringing bell, like all confined vibrations, are necessarily quantized.
If you detect a bell rung by transition due to the bell absorbing of a single graviton, you have detected a graviton.
But has the graviton then excited an electron, or rather the nuclei the bell consists of?
The bell, being a chunk of conductive metal, is also a LC oscillator. Which means that you might set the electrons in the bell in vibration relative to the nuclei.
However, a thick chunk of conducting metal has a fairly low capacitance and inductance, and thus high oscillation frequency. Much higher than the oscillation frequency of its nuclei. Which means that a bell that is a good receiver of gravitons into the ringing mode of the movement of nuclei might be a poor receiver of the electric oscillation modes of electrons moving relative to nuclei.

How commonly are the quanta of audible sound measured? Like, by microphones?
How many quanta of sound does man need to hear sound?

 

[PeroK]

But doesn't the magnetic force do the same thing? It emits photons which transfer the force to the other object. In the case of two magnets repelling each other.

The same would apply to the electrostatic force. It could only be repulsive if charged particles fired photons at each other. But, of course, opposite charges attract each other.

 

[DrChinese]

I found this, which perhaps highlights that a B-level answer is unrealistic.
https://www.nature.com/articles/s41467-024-51420-8

Thanks for the link. From the abstract of your reference, published only a few months ago: "But [graviton] detection has so far been considered impossible." And that's assuming the graviton even exists. Yes, it is possible that some signatures of the graviton may be detected "soon". But I question the idea that single electron will be experimentally demonstrated to be excited to a higher orbital by a graviton - ever.

You can't answer a B-level question reasonably with recent, advanced cutting edge papers requiring deep theory. It's like someone asking if quantum mechanics says my baseball can suddenly appear on the moon, or be thrown through a solid wall... and you always answer that it can, it just doesn't happen "often". Should every nuance of deep physics be presented as answer for every question?

If you answer every B-level question with an A-level answer, what's the point of even marking a level?

Yes, but that doesn't mean you can misstate what the actual physics, as best we know it, says.

And I would certainly contest that there is a single accepted theory (what you call "actual physics") of the graviton anyway, despite its existence being assumed by many. A lot of variants out there, with a lot of different concepts at play.

On the other hand: GR is generally accepted today as the theory of gravity, and does not feature gravitons. I would personally call that the "best we know it", which to date is pretty much batting 100% against all attempts to replace or amend it.

I would agree with you that we'd expect a successful theory of quantum gravity to feature some vanishingly small chance that the graviton could excite a bound electron (in the current stage of our universe). But isn't this discussion far away from what should be discussed in a B-level thread? You're the Mentor/Moderator, so I defer to your answer. Or if you think this is better discussed in the Advisor Lounge or elsewhere, that's fine too - just split it off.

And repeating my question above: If you answer every B-level question with an A-level answer, what's the point of even marking a level?

 

[PeterDonis]

I would agree with you that we'd expect a successful theory of quantum gravity to feature some vanishingly small chance that the graviton could excite a bound electron (in the current stage of our universe).

Which is a perfectly acceptable "B" level answer, and is not an unqualified "no".

 

[PeterDonis]

The same would apply to the electrostatic force. It could only be repulsive if charged particles fired photons at each other. But, of course, opposite charges attract each other.

It's worth noting that the quantum field theory lurking underneath all this is fairly subtle, and also full of land mines waiting to explode underneath the unwary. The PF Insights articles on virtual particles and the limitations of that concept might be a good place for the OP to start getting acquainted with all that.

 

[Josiah]

He was mistaken. See post #3.


Very, very, very, very,.....(lots more veries here)...weakly.


In principle, yes. In practice, don't hold your breath.

If gravitons can be detected in principle, how would you go about doing that?

 

[Josiah]

No, propagating gravitons have nothing to do with the slowly-varying gravitational fields that attract the moon to the earth or the planets to the sun. It's exactly analogous to the fact that propagating photons make no contribution to the electrostatic fields that bind electrons to an atomic nucleus. Moreover, ordinary celestial bodies are predicted to be almost perfectly transparent to gravitons, just like they are to neutrinos, only more so

But don't gravitons act the same way as photons act in transmitting the magnetic force between 2 magnets?

 

[PeroK]

But don't gravitons act the same way as photons act in transmitting the magnetic force between 2 magnets?

Gravitons are the hypothetical quantum particle of the gravitational field. Photons are the quantum particle of the electromagnetic field. The magnetic force is not transmitted by photons. I think this misunderstanding has already been pointed out several times.

 

[PeterDonis]

If gravitons can be detected in principle, how would you go about doing that?

In principle, you would set up an experiment that would test for quantum interference effects--for example, if you had the gravitational equivalent of beam splitters for photons, you could arrange them in a Mach-Zehnder interferometer.

 

[Josiah]

https://www.quantamagazine.org/it-might-be-possible-to-detect-gravitons-after-all-20241030/

 

[DrChinese]

https://www.quantamagazine.org/it-might-be-possible-to-detect-gravitons-after-all-20241030/

The source article is: Detecting single gravitons with quantum sensing

It is ingenious to correlate the detection events between this experiment and LIGO, since these use 2 different mechanisms of action. Their concept depends on gravitons having varying frequencies* and therefore carrying larger energy when coming from large-scale cosmological events (such as compact binary spiral/mergers). (Of course, those events are not too frequent.)

The authors include some interesting comments/calculations made by Weinberg and Dyson. Those indicate the extreme difficulty of graviton detection from close background sources such as the Earth or the Sun. Presumably, those emit gravity waves of insufficient strength to trigger the transition needed for detection.


*And other parallels to photons.

 

[Josiah]

Hi, in reference to the article about a method of detecting gravitons, using the beryllium bar at absolute zero, the gravitons would get absorbed making the beryllium resonate as the result of gravitational waves. Hence would it be possible to block or stop gravitons?

 

[JimWhoKnew]

It's an old thread, but since it was revived,

The same would apply to the electrostatic force. It could only be repulsive if charged particles fired photons at each other. But, of course, opposite charges attract each other.

The attraction between objects with same charge sign is one of the reasons why the graviton, if exists, is expected to have spin 2. A nice discussion can be found in Feynman's "Lectures on Gravitation".
(Additional reason, more restrictive, is the return of the gravitational wave's polarization "to itself" under a rotation by ##\pi## )