... years.¹

This article is an elaboration of a web page (http://www-formal.stanford.edu/jmc/future/mars.html) put up for my students in a class in Technological Opportunities for Humanity at Stanford University. It may change.

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...P²

This conclusion depends on regarding the solar system as isolated. If we consider a large system involving Alpha Centauri and our own solar system, we can imagine increasing our solar system's energy by taking energy from the Alpha Centauri system. It seems apparent that this would take a very long time. If it were determined to take more than (say) years, then we could regard the energy of our own system as essentially unchangeable. Actually it might take only tens or hundreds of thousands of years.

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