I don't really know much about entropy but I learned recently that the entropy in the universe is constantly increasing and that perhaps someday we will reach maximum entropy and the universe will end in heat death. In order for this to be true there are two prerequisites:
- Heat must constantly be created.
- There must be no way to destroy heat (at least no way that turns it into a more useful form of energy).
1 is certainly true. Every process creates some heat. When a person walks his/her feet hit the ground with kinetic energy and the friction creates heat.
But I don't see how 2 can be true. For one thing, heat never even leaves its place of origin (earth, another planet or a star). In order for heat to travel in requires air (or some other conductor/convector). Since there is no air in space there is also no heat. Heat leaves things only in the form of electromagnetic radiation (light) (in the case of earth, infrared).
So conversion from heat to light is certainly possible and is even found in nature. Now how do we get from light to other forms of energy? Well, photosynthesis. Solar panels. So this is possible too. If so, why will we ever run out of useful energy? Even if the rest of the universe does, can't we still reharness our own energy by converting the heat to light and light to other forms of energy?
Suppose the sun died (and leave aside the fact that it would first destroy earth with a supernova), can't we just put up a huge solar panel around earth to pick up all the infrared and convert it back to useful energy?