> even earthly nuclear energy reserves may become strained on a thousand year time horizon No, they won't. Even if we restrict to just fission power, on a thou

> even earthly nuclear energy reserves may become strained on a thousand year time horizon No, they won't. Even if we restrict to just fission power, on a thousand year time horizon we can expect thorium reactors and extraction of uranium from seawater, which multiplies the available energy by a factor of at least a thousand. Furthermore, on that time horizon we can expect fusion to be available, and deuterium from seawater multiplies the available energy by a factor of about a billion. Not to mention that on a thousand year time horizon, we should be making full use of the available solar energy in Earth's vicinity by means of orbital power stations, in which case we won't even need any other energy source on that time horizon except for specialized uses like fast spacecraft. > On a thousand year time horizon it's entirely plausible that maintaining a purely renewable economy makes the production of certain materials impractically expensive And it also makes it practically certain that any material that's that expensive to produce won't be needed anyway, since cheaper substitutes will be found. "Limited resources" by itself simply doesn't strike me as a plausible Great Filter.