PERPETURL MOTION MACHINES 271
amount of energy is probably too small to be used as a source of usable energy. There are vast amounts of dark energy between the galaxies, but the amount that can be found on the Earth is tiny. But the
embarrassing thing is that no one knows how to calculate this energy,
or where it came from.
My point is that the conservation of energy arises from deep, cosmological reasons. Any violation of these laws would necessarily
mean a profound shift in our understanding of the evolution of the universe. And the mystery of dark energy is forcing physicists to confront
this question head-on.
Because creating a true perpetual motion machine may require us to
reevaluate the fundamental laws of physics on a cosmological scale, I
would rank perpetual motion machines as a Class III impossibility;
that is, either they are truly impossible, or we would need to fundamentally change our understanding of fundamental physics on a cosmological scale in order to make such a machine possible. Dark
energy remains one of the great unfinished chapters in modern science.