I think what Orac was saying wasn't what you read. I think he meant there is no perpetual motion even in space.

Now I will give my take on perpetual motion in space.

Imagine a universe with just 2 perfect masses in it. That is they are point source masses. Assume they are in a circular orbit around their common center of mass. I believe this is one stable solution to the 2 body problem. Under these conditions I believe you would have a system in perpetual motion. They would circle each other for eternity.

Now let's look at the real universe. If we start with 2 bodies circling each other we will have something that at first looks like the system in the first example. But in the real universe there are a lot of other factors involved. For one thing the 2 bodies aren't perfect point sources. They are extended bodies and they aren't perfectly inelastic. So there will be tidal effects. The tidal effects will remove energy from the 2 masses and dissipate it as heat. Therefore the orbits will change. Also there are other bodies in the universe and gravitational effects from the other bodies will cause the orbits to be perturbed. So due to energy exchanges with the other bodies the orbits will once again be perturbed. So in the real universe there is no real perpetual motion.

Face it, the people who have tried over and over to build perpetual motion machines have come up against the same problem. Losses due to friction cause the machine to slow and eventually stop.

I suppose that the universe as a whole might represent a sort of perpetual motion, but that depends on the overall evolution of the universe. That is far beyond anything I am prepared to speculate on. I do figure that that really gets into the realm of speculation.

Bill Gill

C is not the speed of light in a vacuum.
C is the universal speed limit.