What happens when two photons collide?

[Elite Engineer]

If photons are pure energy, if they collide won't they just double their energy (i.e. increase in light intensity) rather than cancel each other out because they have no mass?

 

~EE

[Strange]

In general, photons don't interact at all, as far as I know.

 

I think that under high energy conditions photons can collide and produce matter: http://en.wikipedia.org/wiki/Two-photon_physics

 

Edit: I wouldn't say photons are pure energy; they have other attributes, the most obvious being spin and momentum.

Edited July 17, 2014 by Strange

[imatfaal]

you can search on gamma-gamma interactions or "two photon physics". Photons do not normally interact - but at very high energy and in certain circumstances higher order interactions mean that two photons can interact and if the energy is high enough create stuff. A very high energy photon can through quantum fluctuations be seen as a fermion pair - the other photon can interact with one of these matter particles. They investigate gamma gamma interaction at the Large Positron Electron Collider at Cern

 

http://en.wikipedia.org/wiki/Large_Electron%E2%80%93Positron_Collider

[swansont]

If photons are pure energy, if they collide won't they just double their energy (i.e. increase in light intensity) rather than cancel each other out because they have no mass?

 

~EE

 

They aren't pure energy, and they don't cancel each other out rather than combine. Nothing in that sentence is correct if you are talking about some kind of photon-photon interaction.

 

If you are talking about interference, then that's what you see. The intensity will add or cancel depending on the relative phase.

[EdEarl]

So what happens after two virtual photons are created spontaneously? Do they later annihilate together?

[Sensei]

So what happens after two virtual photons are created spontaneously? Do they later annihilate together?

 

Annihilation is process in which matter is converted to photons...

 

For proton-antiproton annihilation might be much more complicated.

p+ + p- -> pion0 + pion0 + pion0

or

p+ + p- -> pion+ + pion-

or

p+ + p- -> kaon+ + kaon-

(up to 9 mesons were observed in p+p- annihilation, with theoretical 13 mesons possible)

pion0 typical decay mode is 2 gamma photons.

[swansont]

So what happens after two virtual photons are created spontaneously? Do they later annihilate together?

 

Virtual photons do not need to be created in pairs, and do not need to annihilate.

[RobertMD]

In particle physics, what MIGHT happen would be largely dependent on the relativity of each atom. Though photons don’t normally interact, whenever they’re simulated to give enough energy gain through an increase in velocity (like how they do it in the Large Hadron Collider), something will actually happen. So, the absolute answer to this question would be theoretical.

 

A good example of photon-photon interaction is made by colliding 2 beams of photons using the Large Hadron Collider. New particles will be formed as a result of a massive release of energy in the collision. These are Higgs boson particles, created by the hyper-excited photon decaying into electrons and hadron jets after an explosive collision.

[ajb]

So, the absolute answer to this question would be theoretical.

Sure, so we should formulate answers in forms of QED and maybe the standard model, which is exactly what others have done here.

 

 

A good example of photon-photon interaction is made by colliding 2 beams of photons using the Large Hadron Collider. New particles will be formed as a result of a massive release of energy in the collision. These are Higgs boson particles, created by the hyper-excited photon decaying into electrons and hadron jets after an explosive collision.

I don't know the details here, but indeed Higgs production via photon-photon interaction has been theoretically studied, including as possible tests of the MSSM. I have no idea about the experimental status of this. Do you have any information on this?

[Strange]

A good example of photon-photon interaction is made by colliding 2 beams of photons using the Large Hadron Collider.

 

I think you mean protons...

[elfmotat]

The lowest order scattering process where γ+γ → γ+γ is the following Feynman diagram:

 

 

 

Physically, what the diagram actually means is that a photon will fluctuate into a virtual electron-positron pair, one of them will absorb a nearby photon, the other one will emit a photon, and then they will annihilate to form another photon.

 

This diagram has four vertices, which means the probability for the process to occur is [math]P \propto \alpha^4 \approx 10^{-9}[/math]. I would calculate the full amplitude for the process, but it involves integrating over d⁴p for each internal line, which doesn't sound like too much fun. But without even calculating the full amplitude, it's still easy to see from the vertex factors above that the probability for the process to occur is going to be very very tiny.

 

Of course, there are even higher order diagrams which contribute, but each vertex will contribute a factor [math]\alpha \approx \frac{1}{137}[/math] to the probability of that process occurring.

Edited November 16, 2014 by elfmotat

[RobertMD]

I think you mean protons...

 

I stand corrected. Thank you, sir!

 

Sure, so we should formulate answers in forms of QED and maybe the standard model, which is exactly what others have done here.

 

Noted. I'll try to do better next time.

 

I don't know the details here, but indeed Higgs production via photon-photon interaction has been theoretically studied, including as possible tests of the MSSM. I have no idea about the experimental status of this. Do you have any information on this?

 

CERN hasn't posted any substantial updates yet since their November 2013 update about finding evidences of Higgs bosons decaying into tau particles and fermions. Since its discovery in 2012, physicists in the LHC have been poring over LHC's collision data for more evidence of interaction involving the Higgs boson. The latest article published in the journal Nature Physics on June 2014 stated the confirmation that Higgs bosons indeed decay into bosons and fermions. I've read somewhere that LHC is preparing for a "big run" which is set on mid-2015. They're expecting to produce several times more than the existing data sample by making higher-energy proton collisions, thus producing Higgs bosons at higher rates. Ahh, I should be reading more. Sorry, but this is all I can contribute for now. Cheers!

[Mitch Bass]

there is a rule when two objects of equal energy collide head to head to the two objects cancel each other

[ajb]

there is a rule when two objects of equal energy collide head to head to the two objects cancel each other

A better rule would be conservation of the quantum numbers of the standard model.

[davidivad]

photons can occupy the same space unless they have enough energy together to equal the wavelength of a particle (very generic version of the truth there is more to it).

also, arent photons thier own particle pair?

[swansont]

there is a rule when two objects of equal energy collide head to head to the two objects cancel each other

 

There is no such rule in physics.

[davidivad]

what happens when you take two different colored beams of light and intersect them at 90 degrees.

if you measure at the convergence, then you are taking a single measurement of both waveforms together.

the beams do not stay the same color once they diverge again.

take a lazer pointer and shine it through a flashlight beam onto a wall...

does it change color?

[Гера�им]

 

Two photon will collide and interact,as everything in nature cooperates,for examle occurring chemical,nuclear,thermonuclear reactions and the stars merge in order interacted photons to each other,of cours,need a lot of energy and density of photons.Can be to use interferencial maxima of a laser beam in the small volume as the greatest number of photons gets to the central maxima and the probability of collisions is more.

[elfmotat]

what happens when you take two different colored beams of light and intersect them at 90 degrees...

the beams do not stay the same color once they diverge again.

 

Yes they do.

 

 

take a lazer pointer and shine it through a flashlight beam onto a wall...

does it change color?

 

No.

 

 

Two photon will collide and interact,as everything in nature cooperates,

 

That's simply wrong. Photons do not couple directly to the electromagnetic field because electromagnetism is linear. I.e. there are no direct self-interactions. Photons do not "collide." At most, a photon can fluctuate into an electron+positron pair and interact with other photons, or some higher order version of that.

[davidivad]

 

Yes they do.

i think you may have misread what i was saying.

the beams do not affect each other at all.

you percieve the additive of those two beams where they converge only.

i hope this clarifies what i said.

[elfmotat]

i think you may have misread what i was saying.

the beams do not affect each other at all.

you percieve the additive of those two beams where they converge only.

i hope this clarifies what i said.

 

Okay, sorry I misread you. What you say is true.

[RanaMoh]

A good example of photon-photon interaction is made by colliding 2 beams of photons using the Large Hadron Collider. New particles will be formed as a result of a massive release of energy in the collision. These are Higgs boson particles, created by the hyper-excited photon decaying into electrons and hadron jets after an explosive collision.

[swansont]

A good example of photon-photon interaction is made by colliding 2 beams of photons using the Large Hadron Collider. New particles will be formed as a result of a massive release of energy in the collision. These are Higgs boson particles, created by the hyper-excited photon decaying into electrons and hadron jets after an explosive collision.

 

The LHC collides protons, not photons.

[Theoretical]

Two photon will collide and interact,as everything in nature cooperates,for examle occurring chemical,nuclear,thermonuclear reactions and the stars merge in order interacted photons to each other,of cours,need a lot of energy and density of photons.Can be to use interferencial maxima of a laser beam in the small volume as the greatest number of photons gets to the central maxima and the probability of collisions is more.

There are bunch of articles on this and supposedly experiments to back it up. So it seems that two gamma ray photons can be converted into an electron-positron pair in a vacuum. Perhaps the probability deceases with photon energy? For example, an electron neutrino with less than 0.0000022 MeV/c^2, which is about the energy of a visible green photon of 564 nm. Will any electron neutrino & anti electron neutrino pair be created by two crossing perpendicular beams of 564 nm photons?

Edited December 10, 2014 by Theoretical

[swansont]

There are bunch of articles on this and supposedly experiments to back it up. So it seems that two gamma ray photons can be converted into an electron-positron pair in a vacuum. Perhaps the probability deceases with photon energy? For example, an electron neutrino with less than 0.0000022 MeV/c^2, which is about the energy of a visible green photon of 564 nm. Will any electron neutrino & anti electron neutrino pair be created by two crossing perpendicular beams of 564 nm photons?

 

A problem with this scenario is that photons undergo electromagnetic interactions while neutrinos undergo weak interactions.

 

edit: if you look at the Feynman diagram elfmotat posted in #11, I think you could have the electrons and positrons doing this, but that makes the interaction that much more unlikely — it's one order removed.