Photons vs Gravitons

[TouchuvGrey]

TL;DR

Photons vs (hypothetical) gravitons

Hello Everyone:

New member Mike from Australia.

If i posted in the wrong forum please tell me.

Light is made up of photons. photons obviosly travel at c. photons are affected by gravity.
Gravity is (possibly) made up of gravitons.

Photon and the hypothetical gravitons both travel at c. They are the only things
we know of that travel at that speed.

Gravity affects light. Does light affect gravity ?

Is there any known or theoritical relationship between photons and gravitons ?

Mike
No degree or studies, just curious.

 

[PeterDonis]

If i posted in the wrong forum please tell me.

That depends. It seems like your question is not specifically about any quantum aspects of light or gravity, but just about this:

Gravity affects light. Does light affect gravity ?

The answer, in classical GR, to this question is yes: light has energy, and everything that has energy produces gravity. More specifically, everything that has energy produces spacetime curvature via the Einstein Field Equation of GR.

However, you use the terms "photon" and "graviton", which are not part of classical physics; they are quantum terms. If you're specifically interested in quantum aspects of light and/or gravity, please start a separate thread in the Quantum Physics forum. For the discussion here, instead of "photon" and "graviton", the simple terms "light" and "gravity" should be sufficient.

Also, welcome to PF!

 

[PeterDonis]

Is there any known or theoritical relationship between photons and gravitons ?

Classically, fhe field equations for light and gravity are similar, yes; both of them have the basic form of a differential equation whose LHS describes the field and its derivatives and the RHS describes the source--what produces the field. For light, the field is described by the EM field tensor and the source is the charge-current 4-vector. For gravity, the field is described by the Einstein tensor and the source is the stress-energy tensor.

Again, if you are asking specifically about similarities between the quantum aspects of light and gravity (which is what the terms "photon" and "graviton" refer to), please start a separate thread in the Quantum Physics forum.

 

[anuttarasammyak]

Hello.
Neutrinos (had been thought to) also travel at c. But recent study suggests almost c due to their not zero mass.
[edit] ( ) added. An example of experiments measuring neutriono speedhttps://arxiv.org/abs/1109.4897 Only mass zero particles travel at c by SR.

 

[PeterDonis]

Neutrinos also travel at c.

No, they don't:

But recent study suggests almost c due to their not zero mass.

Please don't post contradictory statements. Also, nonzero neutrino masses do not "suggest" that they do not travel at $c$; they require it.

 

[Matterwave]

To be fully technical, it is still possible that one of the neutrino mass eigenstates is 0. All we constrain with oscillation tests are mass splittings and not absolute mass. The other neutrino mass tests that I'm aware of simply give upper bounds to the mass eigenstates. I'm not aware of a publication that has ruled out 0 rest mass for the lightest mass eigenstate.

 

[PeterDonis]

To be fully technical, it is still possible that one of the neutrino mass eigenstates is 0.

Technically, yes, this is possible. My understanding is that it's considered extremely unlikely, because whatever mechanism makes the neutrino masses nonzero in the first place would be expected to apply to all of the mass eigenstates.

 

[Ibix]

Gravity affects light. Does light affect gravity ?

I think it's worth pointing out that light is analogous to gravitational waves, while gravity in the sense of the more-or-less static field holding us to the Earth is analogous to an electric and/or magnetic field.

But there is an asymmetry here. A gravitational field, including a gravitational wave, will deflect light and other gravitational waves (the latter is theoretical - I don't think lensing of gravitational waves has actually been observed yet). An electromagnetic field, including light, however, doesn't. What it does do is generate a gravitational field (again, theoretically - the energy needed to test this is absurdly large) that then deflects light and gravitational waves.

 

[jedishrfu]

Wheeler once posited the notion of a geon, a ring of light held together by the gravity of its own field energy. Geons have never been observed, and I believe there's some debate on whether they are stable, but theoretical physics entertains such notions in the search for quantum gravity and dark matter.

https://en.wikipedia.org/wiki/Geon_(physics)