Main Page | See live article | Alphabetical index Carnot's rule, states that you never get something for nothing. This thermodynamic law says there must be a degradation of energy in any machine that outputs free energy. External links Google cache New Scientist article on solar sails. Rebuttal letter This article is a stub. You can help Wikipedia by fixing it. This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.