photons

[einsteinsdog]

If two photons collide , does anything happen?

[fo3nix]

they either scatter, or possibly at high enough energy, will create other photons (maybe). not 100% sure on the latter.

[einsteinsdog]

its probably too small an effect to study

[gary baldy]

You should have taken more of interest in what experiments your master was doing instead of licking your own bottom! In fact i'm being to doubt whether you really are Einstein's dog at all!

[mibn2cweus]

Depending on the energy of the collision they might simply bounce off each other or at higher energies create particles or matter and antimater. This is how matter is believed to have been created in the early stages of the 'big bang'.

[rojash]

They discuss is calmly, decide it's "knock for knock" and each claim on their own insurance.

[jake-the-peg]

Too small an effect to study?

Better tell these guys

http://hep-proj-photon2001.web.cern.ch/hep-proj-photon2001/

They held their 14th Anual workshop on photon-photon collisions 4 years ago!

[Clanad]

Parenthetically, it's important to understand that photons are not particles that can collide, like motes of dust, but, rather, they are wave like and apparently exist in packets of waves. If and when they do collide, they are analogous to waves of water meeting. That is, they pass through each other and can interfere with each other during the passing phase, but they come out the same. Actually, the wave interference physics of photons enables the basis for forming holograms, among other applications. I fully realize this is an extreme oversimplification of a complex subject, but illustrative, nevertheless...

[Hippy]

OK Clanad (Mr. D. Advocate here), if the light photons are wave packets like the ripples on a pond etc., why do we see light from distant stars? Waves in space? When space is largely a vacuum so nothing there to transmit the waves. We don't see ripples in the pond when the water has gone! That is, ripples in the emptiness where the water used to be. Throw a stone into the empty pond; go on. Look! no splash. Not a single ripple.

Maybe those eggheads have been meeting for 14 years to figure out where their ripples went.

[wacky racer]

electromagnetic waves!!!

The sort that radio telescopes see when looking at the universe - not your average swimming pool stuff. Clanad is spot on.

[Clanad]

I'm not aware of who Mr. D is hippy... having said that, protons, neutrons, electrons, and neutrinos are fermions, and photons and gravitons are bosons. Having said that, I explained in the previous answer that I was attempting to keep the discussion, interesting as it is, at a level that we (including myself) can all relate to. Fact is, one can not make waves on a pond and wave packets of photons totally analogous. My attempt was to simply paint a visual picture that could be relative. Physicists tell us, and our own observations concur, that electromagnetic waves do travel through the relative vacuum of space. In fact, early scientists believed that, just like water or sound waves, light waves needed something through which to propagate. Thus began their fruitless search for what they termed the Ether (Aether). That has been abandoned long ago, since we know now that space is pretty much empty.
Having said all that, full understanding of why light (and other electromagnetic phenomena) travels through empty space at a constant speed has not been achieved, thus far...

[wacky racer]

constant speed Clanad?? Now that is a separate discussion altogether.

[fo3nix]

OK let's clear some things up.

First of all, photons (as with all other particles) can be both particles and waves at the same time; its just two different ways of interpreting the same thing. In fact, particles don't strictly exist, as they are mathematically objects with no size.

Photons travel from the sun to us because they can be interpreted as being waves, and have two components: the electromagnetic component and the magnetic component. It can be shown quite easily that the magnetic part creates the electric part, which in turn creates the magnetic part, ad infinitum. It kind of hop-skips its way here.

Photons travel (in vacuum) at constant speed (the speed of light), because they are massless.

[Hippy]

Devil's Advocate, dear boy.

[Clanad]

Did you not mean electric and magnetic components of photons, fo3nix? The resultant (electromagnetic) radiation, in space, can be seen as a self propagating transverse oscillating wave of electric and magnetic fields which oscillate at right angles to each other and to the direction of propagation.

[fo3nix]

Oh crap, yea I did ;)
electric and magnetic components. jumping ahead of myself there.

[mibn2cweus]

Electromagnetic wave propagation, Java applet here.