Why are perpetual motion machines impossible according to the laws of physics? In particular, how do perpetual motion machines violate the laws of thermodynamics? https://www.youtube.com/watch?v=A-QgGXbDyR0

NASA has made news in recent years due to its development of the controversial EmDrive, an "impossible" engine that could make interstellar travel possible. Address the implications of this drive and why it should, in theory, not work according to the principles forbidding the operation of perpetual motion machines. Give your opinion on whether or not you think the EmDrive is a real, operating engine. For an overview you may enjoy the following video: https://www.youtube.com/watch?v=gTEMMiQXXVg