[seanflyon]

a) Mars.Your notion that humans cannot survive for long in 1/3 gravity is interesting. While it has not been proven that we can live long and healthy lives in 1/3 G, many very intelligent and informed people believe we can. Do you have a particular reason to believe we cannot?

b) You have to pay the energy cost but that is not the hard part. Fossil fuels are finite, but we don't need to use fossil fuels and even if we did setting up a civilization on mars would take a tiny portion of earth's fossil fuels. We are not going to run out of hydrogen as long as we have the energy to split water and plenty of energy hits the earth in the form of sunlight every day, not to mention fission or fusion.

So no, the laws of thermodynamics are not the problem. We "just" need to make it cheaper.