Can light collide with light?

If two electromagnetic waves intersect, what happens? Is light 'immaterial' or without density, is light weightless?

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orksecurity7 years ago
Light has mass (relativistic mass only, no rest mass). Gravitational lensing is one example of that; websearch will find you details about that. However, for all practical purposes light has no density, and will not collide with another light beam.
"collision" is perhaps a bit emotive, but light can of cource constructively, and destructively interfere with itself, that's how diffraction gratings work for example.
nepheron (author)  steveastrouk7 years ago
So is this like that whole light-through-slits experiment? When a beam of light it aimed through 2 slits, and it separates into a bunch of bars?
Yes, but along will come Kelsey to point out the single photon version.
Valid point. Two beams crossing in midair won't noticeably affect either beam farther on, but at the intersection you can get interference effects.
Unless of course the place where the beams intersect is not "midair", but instead a non-linear optical medium, then one beam can affect the future travel (phase, frequency, amplitude, etc) of the other beam.
Also a valid point.
Kryptonite7 years ago
I would say that no, it cannot collide, even though it indeed does have mass (as proved below).
nickodemus7 years ago
This looks like a question for Kelsey! :D
My layman's guess, is yes. I don't think light could be weightless, since it can't escape a black hole. I can't wait to see what all the science majors think. :-)