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what makes two mirrors placed near each other attract?
- Sally (age 17)
You have an interesting question and, as frequently happens, 'It depends'. In this case it depends on whether or not there is a light source between the two mirrors. If there is a light source that radiates then some of the photons that strike the mirrors will be absorbed. Since photons carry momentum the net effect will be to push the mirrors apart. If there is no light source the problem becomes more complicated and you have go into the quantum regime to get the correct answer. Casimir and Polder, two Dutch physicists figured it out in 1948 by considering the fact that the quantization of electromagnetic fields would produce a tiny attractive force between two conducting plates. Their prediction was verified by precision experiments. See the 'Casimir Effect' article in Wikipedia for some gory details.
(published on 06/15/12)
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