Question about photons

So if you have a lot of photons in one place, can they generate a gravity well?

I don't know the answer to your question but I do know that, despite photons having speed and momentum, they have no mass (which goes against the old Newtonian concept of the relationship between those things). So if the existence of mass is a necessary requirement for a gravity well, then the answer would be no. Else, I don't know.

Anyone?

But even if you CAN make a gravity well with just photons, you will need one hell of a lot of photons around one place to make any detectable gravity there!

@humy
Yeah, that was my conclusion also but there is the fact that even as a zero mass particle it still imparts momentum so there is SOME kind of connection to the world. Also photons RESPONDS to gravity, following the curves of spacetime.

An experiment should reveal the answer.
First suspend one million tons of antimatter iron in a magnetic field in a vacuum chamber somewhere on Earth.
Then set up a very sensitive and extremely fast reacting gravity detector next to the vacuum chamber so that its detecting the gravity of the one million tons of antimatter iron.
Then throw one million tons of ordinary matter into the vacuum chamber.
A picosecond after all that mass is converted into photons and just before those photons start to disperse too widely, if photons do create gravity then the gravity detector should detect no change else the gravity detector should detect within that picosecond a drop in gravity.
Then, for just one glorious moment just before all life on earth is wiped out via the Earth being completely obliterated, you can know the answer to the question.

@humy
Ah, about the time it takes for one molecule in a nerve ending to send a blip to the next molecule. I wonder what that would be in terms of megatons of nukes? How much matter and anti matter getting together would = 1 megaton of a conventional nuke?
Couldn't you just use two extremely powerful laser beams say a mm apart and track to see if they try to come together? Obviously a beam would be spreading by some amount, maybe that wouldn't work. What about a stream of individual photons a mm apart? They shouldn't self attract if they don't generate gravity so if they DO start approaching, that should say something about photons and gravity.

@sonhouse
Let's try an easy experiment: Construct a sphere with a mirror surface inside, and using a laser, start filling it with photons until it's packed to the max; then do your measurements.

@bunnyknight

That could work if the mirror was 100% reflective.

Do photons exist? I'm not convinced light is a particle.

@metal-brain said
Do photons exist? I'm not convinced light is a particle.

Some say that photons are just vibrations of some sub-ether or dark energy, which might explain why they're always on the move, and have wavy behavior. This would also mean that you could fit more photons in a volume if they had a higher frequency. How many could you fit? Who knows ... perhaps there is a saturation limit, like clipping of sound waves on a recording.

@bunnyknight said
Some say that photons are just vibrations of some sub-ether or dark energy, which might explain why they're always on the move, and have wavy behavior. This would also mean that you could fit more photons in a volume if they had a higher frequency. How many could you fit? Who knows ... perhaps there is a saturation limit, like clipping of sound waves on a recording.

Right. Photons are also said to not have mass. The term "mass-less particle" seems like a contradiction.

@metal-brain said
Do photons exist? I'm not convinced light is a particle.

Then you don't know the first thing about quantum physics.
Photons exist.
And it isn't "light is a particle" but "a photon is a particle at least some of the time".

It is always best not to form an opinion and then express it if it is about something you have very little or no knowledge about.
I do not form and then express an opinion about dentistry (other than it bloody well hurts), something I know little about, and, for the same reason, you shouldn't form and then express an opinion about physics, something you know little about. Better to just leave such things to the experts or semi-experts.

As I learned from my university quantum physics classes, science has established that a photon is both a particle and a wave and those two things don't contradict because which one it is at any given moment depends on how it is currently being measured and/or interacting; sometimes it behaves like a particle and thus is a particle by definition and sometimes it behaves like a wave and thus is a wave by definition. This effect is called "Wave–particle duality"

https://en.wikipedia.org/wiki/Wave%E2%80%93particle_duality

Photons are also said to not have mass.

That's because they don't have mass.

The term "mass-less particle" seems like a contradiction.

Why does "mass-less particle" "seems like a contradiction"? It doesn't to us science experts or any laypeople I know of until you said it. What does "mass-less particle" contradict?

@metal-brain said
Right. Photons are also said to not have mass. The term "mass-less particle" seems like a contradiction.

Magnetism and gravity apparently also have no mass, yet they're able to exert a force and move stuff, just like photons. Gosh, if only my tiny brain had a few more neurons so I could connect all the dots.

@humy said
Then you don't know the first thing about quantum physics.
It is always best not to form an opinion and then express it if it is about something you have very little or no knowledge about.
I do not form and then express an opinion about dentistry (other than it bloody well hurts), something I know little about, and, for the same reason, you shouldn't form and then express an o ...[text shortened]... nce experts or any laypeople I know of until you said it. What does "mass-less particle" contradict?

If there is no mass, how can it be a particle? Can you hold nothing in your hand and call it a particle?

@bunnyknight said
Magnetism and gravity apparently also have no mass, yet they're able to exert a force and move stuff, just like photons. Gosh, if only my tiny brain had a few more neurons so I could connect all the dots.

I'm not convinced light is bent by gravity. I am considering the possibility that the solar eclipse experiment was flawed that supposedly confirmed it. Why would gravity affect something without mass? I didn't see anything in Einstein's GR equations that indicated that. I have always been puzzled by that.

@metal-brain said
If there is no mass, how can it be a particle?

Why cannot it be a particle if it has no mass?

Can you hold nothing in your hand and call it a particle?

A particle having no mass doesn't make it "nothing" and ability to "hold" something "in your hand" is not what defines what a particle is.