My professor today told us to think about the following situation: If there is a 99% reflecting mirror, then if a beam of light shines on the mirror 99% of the light is reflected and 1% is transmitted. Now he says that if a second 99% reflecting mirror is placed behind the original mirror, 100% of the light is transmitted. This sounds impossible to me. The first mirror still reflects 99% of the light incident on it regardless of the presence or absence of the second mirror. My only guess is that the 1% transmitted through the first mirror reflects back and forth between the mirrors and then 1% of that is reflected, giving the apparent result that light "appears" when a second mirror is placed behind the first. If this is not the case then wouldn't conservation of energy be violated by the "appearance" of light? Thanks.