Is light matter, and how can it be affected by gravity and travel through vacuum?

[Dale]

Volcano, you already asked this in post 19 and I already answered in post 20. Stop repeating yourself.

 

[Hootenanny]

I am really asking, is there such an experiment?

I'm not sure what you're asking here. Clearly we can perform a gedanken experiment, whether or not we can perform an actual experiment is irrelevant here.

And second question; is there something has mass but not matter, what is it?

Yes, as has been said many times in this thread a photon pair resulting from the annihilation of an electron and positron pair has a non-zero mass, but is not considered matter.

Edit: DaleSpam beat me to it

 

[Dale]

So essentially you are saying that since an electron and a positron have mass, and they can annihilate to create two photons, those two photons have mass? I'm pretty sure this is entirely incorrect. Photons are massless.

This is entirely correct, individual photons are massless.
|(.511, .511,0,0) MeV/c|/c = 0 MeV/c²
|(.511,-.511,0,0) MeV/c|/c = 0 MeV/c²

But a system of photons can have mass if the photons are not traveling in the same direction.
(.511,.511,0,0) MeV/c + (.511,-.511,0,0) MeV/c = (1.022,0,0,0) MeV/c
|(1.022,0,0,0) MeV/c|/c = 1.022 MeV/c²

In general a system of particles will have a different mass than the sum of the masses of its constituent particles.

many bosons can occupy the same space. That space isn't necessarily zero. For example, a Bose-Einstein condensate of helium atoms.

You are correct. I was thinking only of elementary particles where elementary bosons do not take up space due to not obeying the Pauli exclusion principle.

I guess I would tentatively also say that any composite particle containing fermions is matter, even if the composite particle as a whole is a boson. Unfortunately, I haven't thought about it enough to catch any potential contradiction.

I think you are a bit confused. This is exactly what I am arguing AGAINST, and what you have been arguing in favor of until your last paragraph! I specifically stated that a hot gas does NOT have more matter then a cold gas. I stated "matter is anything that has mass".

If matter is anything that has mass and a hot gas has more mass than a cold gas then I don't see how you can consistently claim that a hot gas does not have more matter than a cold one.

When you posited that a hot gas has greater "mass" then a cold gas as an example to disprove my definition, I pointed out that your argument was flawed because the "relativistic mass" of a hot gas is not the same as rest mass.

I am using the usual definition of mass as being the invariant norm of the four-momentum, aka rest mass. I am certainly not talking about relativistic mass. The invariant rest mass of the hot gas is higher than that of the cold gas. A hot gas has more energy in its rest frame, it has more inertia as measured in its rest frame, and according to GR it has more gravity.

 

[QuantumPion]

This is entirely correct, individual photons are massless.
|(.511, .511,0,0) MeV/c|/c = 0 MeV/c²
|(.511,-.511,0,0) MeV/c|/c = 0 MeV/c²

But a system of photons can have mass if the photons are not traveling in the same direction.
(.511,.511,0,0) MeV/c + (.511,-.511,0,0) MeV/c = (1.022,0,0,0) MeV/c
|(1.022,0,0,0) MeV/c|/c = 1.022 MeV/c²

In general a system of particles will have a different mass than the sum of the masses of its constituent particles.,

I'll concede I don't know enough about general relativity to argue the point further. If a system of photons does have real mass then I guess my definition of matter is too broad after all.

 

[Volcano]

Sorry for two reason,

1. Couldn't distinguish DaleSpams's above reply
2. I guessed you talking about energy-mass differences. But you mean mass-matter difference.

But already want to learn thermal energy and mass relation. Please give me a link to read.

And, please think one more time before supposing someone repeating irrevelant. But, if really believe this, shortly, don't reply ;) I came here to ask, learn and share; not more.

Edit: Thought twice :)

 

[sungod]

I'm a sort of newcomer here, so this may have been answered elsewhere. But, as I understand, mass is tied to inertia. Isn't this why we're looking for Higgs? If so, are photons inertial? Then, the spacetime is Minkowskian. They themselves cannot create a non-Minkowskian spacetime that will affect nearby photons. If photons do have mass and can create a non_Minkowskian spacetime that can alter the parhs of nearby photons, then photons will interact. This gives rise to two further questions:
1. As I remember long-ago college, a fundamental result of QED is that photons cannot interact.
2. What mediates the interaction? If gravitons, then gravitons must be the quanta of still more elementary fields. Would this be correct?