The discussion centers on the interaction between hypothetical gravitons and electrons, highlighting that while theoretical physics suggests electrons can absorb gravitons similarly to photons, practical detection remains implausible due to the extreme weakness of gravitational interactions. The scattering cross section for gravitons is approximately 1085 times smaller than that for photons, necessitating an unfeasible number of electrons for observation. Current theories do not provide a working model for graviton detection, and the gravitational effects on electrons are negligible at atomic scales.
PREREQUISITESTheoretical physicists, researchers in quantum gravity, and anyone interested in the fundamental interactions of particles at the quantum level will benefit from this discussion.
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.Josiah said:Hi,
what effect do gravitons have on electrons.
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.Josiah said: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?
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.Demystifier said:It is well understood how electrons interact with gravitons in theory.
If that is so, couldn't you use that method to detect gravitons? Given that in theory they get absorbed by electrons?Demystifier said: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.
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.Josiah said:If that is so, couldn't you use that method to detect gravitons? Given that in theory they get absorbed by electrons?
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]
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.Josiah said: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?
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.timdavid said: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.
Where do you see this?snorkack said:I see that there is a serious dispute as to whether gravitational wave detectors even absorb the waves they are detecting.
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".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.
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.snorkack said:the "widely held viewpoint" is unattributed, and being refuted by the article