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Q & A: colliding light beams

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Most recent answer: 05/01/2012
Q:
Suppose there are two beams of light of the same wavelength traveling on an intersect course, and when they do intersect, what happens to the light? do they cancel each other out and the light disappears and becomes energy in some other form? does the light stop at that point and continue traveling on their courses?
- Kendall Piccolo (age 17)
Grand Coulee, WA, U.S.A.
A:
In classical physics, the equations describing the propagation of light were linear. That means the two beams would pass through each other with no effect.

Quantum mechanics allows some other processes, although they are rare under typical circumstances. The two light beams can create particle-antiparticle pairs, with the same total energy and the same total momentum and angular momentum as two photons, one from each beam, would have. Other processes involving more photons can also occur but even more rarely.

Mike W.

(published on 05/01/2012)

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