What effect do gravitons have on electrons?

[Josiah]

Hi,
what effect do gravitons have on electrons. I know with photons the electrons absorb the photons and leave the atom. Would gravitons have the same effect?

 

[anuttarasammyak]

We are not sure whether there exsits particle like graviton.

 

[PeroK]

Hi,
what effect do gravitons have on electrons.

As mentioned above, the graviton is a hypothetical particle in some prospective theories of quantum gravity. Until there is an established theory of quantum gravity, the gravitational interaction between electrons (or any elementary particles) is not understood.

 

[Demystifier]

Hi,
what effect do gravitons have on electrons. I know with photons the electrons absorb the photons and leave the atom. Would gravitons have the same effect?

Contrary to what people told you above, this is a well posed question in theoretical physics. It is well understood how electrons interact with gravitons in theory. So yes, in theory, an electron can absorb the graviton very much like it can absorb the photon.

 

[PeterDonis]

It is well understood how electrons interact with gravitons in theory.

More precisely, in the quantum field theory of a massless spin-2 field interacting with matter. In theoretical terms, yes, this theory is well understood. But we don't know whether it is actually realized in our universe, since we have no way of testing it now or in the foreseeable future because of the weakness of gravity as an interaction.

 

[Josiah]

Contrary to what people told you above, this is a well posed question in theoretical physics. It is well understood how electrons interact with gravitons in theory. So yes, in theory, an electron can absorb the graviton very much like it can absorb the photon.

If that is so, couldn't you use that method to detect gravitons? Given that in theory they get absorbed by electrons?

 

[renormalize]

If that is so, couldn't you use that method to detect gravitons? Given that in theory they get absorbed by electrons?

No, because the strength of gravitation is incredibly weak compared to that of electromagnetism. The scattering cross section (a measure of the interaction strength) for a graviton impacting an electron is $\sim10^{85}$ times smaller than for a photon striking that electron. (See https://ajsteinmetz.github.io/physics/2024/10/16/graviton-detector.html.) So you'd need a target of $\sim10^{85}$ electrons ($10^5$ more than the number in the whole universe) to get the same probability of observing single-graviton absorption as that for single-photon absorption by $1$ electron.

 

[Drakkith]

Per wiki: https://en.wikipedia.org/wiki/Graviton#Experimental_observation

Unambiguous detection of individual gravitons, though not prohibited by any fundamental law, has been thought to be impossible with any physically reasonable detector.[19] The reason is the extremely low cross section for the interaction of gravitons with matter. For example, a detector with the mass of Jupiter and 100% efficiency, placed in close orbit around a neutron star, would only be expected to observe one graviton every 10 years, even under the most favorable conditions. It would be impossible to discriminate these events from the background of neutrinos, since the dimensions of the required neutrino shield would ensure collapse into a black hole.[19]

 

[snorkack]

Another argument is - if you do observe gravitational wave as a change in the quantum state of your receiver, can you ascertain that it was the gravitational wave that was quantized, or only the gravitational wave receiver?

 

[timdavid]

Hi,
what effect do gravitons have on electrons. I know with photons the electrons absorb the photons and leave the atom. Would gravitons have the same effect?

Gravitons, if they exist, interact with electrons via gravity, not electromagnetism. Unlike photons, gravitons wouldn’t be absorbed by electrons or cause them to leave an atom. Instead, they would exert a tiny gravitational pull, but this effect is negligible at atomic scales.

 

[pines-demon]

I know this question is old and only resurfaced, but with such a question it is ok to just say "we do not know, we do not have a working theory yet". But also we should demand "under which mathematical model you want an answer?" because these questions have an answer under certain models and not others.

 

[snorkack]

Gravitons, if they exist, interact with electrons via gravity, not electromagnetism. Unlike photons, gravitons wouldn’t be absorbed by electrons or cause them to leave an atom.

It is not really a contrast between photons and gravitons. Note that ionizing atoms requires electromagnetic waves with frequency over 10¹⁵ Hz, unless in case of multiphoton excitations (inefficient if the photons must be very many). Reaching the quantized excited states of atoms also requires high frequency photons. The astronomical gravitational waves are detected at frequencies up to a few hundred Hz. Electromagnetic waves at a few hundred Hz do not excite atoms, either. However, they are absorbed by antennae, which have low energy collective excitation modes - inefficiently.
I see that there is a serious dispute as to whether gravitational wave detectors even absorb the waves they are detecting.

 

[PeterDonis]

I see that there is a serious dispute as to whether gravitational wave detectors even absorb the waves they are detecting.

Where do you see this?

 

[snorkack]

This
https://dcc.ligo.org/public/0099/P1200179/001/energy paper.pdf
describes:

A widely held viewpoint is if the masses are truly free, no energy is extracted from the wave. This free-mass approximation then leads to the idea that electromagnetically coupled gravitational wave detectors do not absorb energy from the passing wave.

last two sentences of the first section. Note that the "widely held viewpoint" is unattributed, and being refuted by the article - but described as "widely held viewpoint".

 

[PeterDonis]

the "widely held viewpoint" is unattributed, and being refuted by the article

No, the article is not refuting that viewpoint. It is just showing that a real interferometer, like LIGO, does not satisfy the premise of the viewpoint, that "the masses are truly free"; there are effects present in real interferometers like LIGO that are not present in the idealized case that the viewpoint applies to, and those effects allow the detector to absorb energy from the wave--a very small fraction of the wave's total energy, but not zero.

 

[Josiah]

No, because the strength of gravitation is incredibly weak compared to that of electromagnetism. The scattering cross section (a measure of the interaction strength) for a graviton impacting an electron is $\sim10^{85}$ times smaller than for a photon striking that electron. (See https://ajsteinmetz.github.io/physics/2024/10/16/graviton-detector.html.) So you'd need a target of $\sim10^{85}$ electrons ($10^5$ more than the number in the whole universe) to get the same probability of observing single-graviton absorption as that for single-photon absorption by $1$ electron.

Is it the electrons that absorb the gravitons, or is it the nucleus? (assuming gravitons exist)

 

[Josiah]

Is it the electrons that absorb the gravitons, or is it the nucleus? (assuming gravitons exist)

 

[Josiah]

No, because the strength of gravitation is incredibly weak compared to that of electromagnetism. The scattering cross section (a measure of the interaction strength) for a graviton impacting an electron is $\sim10^{85}$ times smaller than for a photon striking that electron. (See https://ajsteinmetz.github.io/physics/2024/10/16/graviton-detector.html.) So you'd need a target of $\sim10^{85}$ electrons ($10^5$ more than the number in the whole universe) to get the same probability of observing single-graviton absorption as that for single-photon absorption by $1$ electron.I

 

[Josiah]

I know the force of gravity is incredibly weak, but on the other hand there is a huge number of gravitons hitting the electron, so wouldn't this be detected. If you find the electron goes to a higher level, then you have detected the gravitons.

 

[PeterDonis]

I know the force of gravity is incredibly weak, but on the other hand there is a huge number of gravitons hitting the electron

These two things have nothing to do with each other.

Consider the analogy with electromagnetism: the number of photons hitting something, which corresponds to the intensity of light shining on that something, has nothing to do with the strength of the electromagnetic force. They're simply two different things.

wouldn't this be detected

You are trying to conflate different questions here.

If we assume that gravitons exist and that they are described by the QFT of the massless spin-2 field that I referred to before, then there is a nonzero probability for an electron to absorb a graviton. But that nonzero probability is astronomically tiny--many, many, many orders of magnitude smaller than the probability for an electron to absorb a photon. So tiny that, even if we had a whole universe full of nothing but electrons waiting to absorb gravitons, we would not expect to see even one such absorption for a time much longer than the lifetime of the universe. If such absorption were to happen, according to this theory, it would have an observable effect--but the if is a huge if.

However, as I've already commented, we don't know if gravitons actually exist, or if they exist, that they are correctly described by the massless spin-2 QFT I mentioned, in any physical regime that actually matters. And if that QFT does not correctly describe gravity in any physical regime that matters, then we have no way of even answering your question, because we have no theory to use to answer it.

In other words, we don't actually know that there are "a huge number of gravitons" flying around in the universe trying to hit things. We do know that we've never observed any.