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Q & A: Momentum of photons

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Most recent answer: 04/21/2008
I have read that light has momentum.If this is true,what would it take to aim a laser at a small object, say a small rock or pebble, and actually move it? What kind of laser would this be? Also, do you know of a practical reference that discusses this problem? There is a lot of stuff on the Internet that discusses the momentum of light but it all seems very abstract. Thanks.
- Harry Clarkson (age 19)
Medford, Mass.
Yes, light does carry momentum.  This has been experimentally observed in the laboratory. Unfortunately, the amount of momentum in even the most powerful lasers is tiny.  No practical applications like moving rocks are feasible with current day lasers.   There is one Buck Rogers kind of idea that has been around for a long time, that is of interplanetary travel using a huge sail that is driven by the momentum of light from the sun. Take a look at Wikipedia's


(published on 04/21/2008)

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