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> You do realise there are probably more habitable planets than there are human beings right now? I don't realise that, for one. It certainly isn't part of the shared knowledge or common sense, so I don't think the way you have expressed yourself is fair. I thought we had only discovered a relatively small number of planets, most of which were relatively large gas giant types, and that claims to large numbers were based on speculation. That knowledge could be very much out of date by now. What is the current state of knowledge? What is the definition of a habitable planet? If it's just "an earth-size planet that is so close to a stable star", I don't think it's really fair to call that habitable. If there's no life on the planet already, it would be a great deal of effort to make it ready for human habitation, wouldn't it? There will be rock but no soil, so we need to start with simple life forms for a long time before we can get human food to grow. Is there any reason to suppose that a lifeless planet would have a breathable atmosphere? Or if the planet is Venusian or in a snowball phase, we probably couldn't do much on a useful timescale. Again, I don't actually know what the state of knowledge in that field is, so I'm betraying my ignorance rather than trying some kind of "gotcha". If we only need one planet at a time, I guess it's okay. But if we're talking about exponential growth, then we will need an exponential number of planets. We will "use up" the second one much faster than the first, and the third much faster than the second, and we'll probably need the fifth when we're starting the fourth and so on. There will come a time when we either need to slow down, or the difference between some technical and practical definition of "habitable planet" becomes relevant. |