Listen Now Download as mp3 from the show Naked Science Q&A and the Edinburgh Science Festival
Stephen James asked:
If I put lights in a perfectly sealed box with mirrors inside it, would the light bounce around inside for eternity?
Dave: It depends on your mirrors. Normal mirrors which you use at home actually only reflect about 80% of the light so by the time itís gone backwards and forwards a few times every time youíre going to lose 20% of what youíve got left. Light moves at about 300 million metres per second so itís going to bounce backwards and forwards in your box very quickly. Even the best possible mirrors we make will lose about 1% of light every time you do it. So the answer is yes but in practicality, no.