Where would it come from? Nuclear? Even with nuclear, how do you get launch costs down so low the average person can afford space travel? There's more to launch costs than just the energy cost. How do you get rockets to be as "cheap as dirt"? Rockets don't just appear when they're needed. And how long it'd take to get even one other planet up to snuff for moving vast quantities of people there? It could be a hundred years or more before we get any of that stuff done. Consider how slowly advances have been in space travel over the last few decades. E.g. the fastest space probe we have launched is not much faster than the Voyager probes of 30 years ago. And that's just a robot. Manned missions have been really limited, too. To make a dent in population we're gonna need to get to massive, cheap, common spaceflight for millions and millions of people -- a "space fleet" with numerous massive vessels. Such a revolution doesn't seem possible "overnight". I'd wager a hundred years or more to get to this level unless something extremely revolutionary comes along (do you want to bet on that? Especially considering how incremental technological change seems to be.).
The problem is not whether or not X is possible, the problem is
how fast can we do it -- can we race the clock to avoid a crunch of some kind (and this doesn't mean going to the stone age or whatever TFian says. Things like this are
not black and white. It's
not a choice where the only options are "just keep going as usual" and "stone age", or even worse, "extinction".)? Because of that, it'd seem that as a simple matter of reason, we should at the very least get serious trying to de-exponentialize growth in population/resource consumption somehow
right now, instead of letting it balloon while we wait on these huge things that could take a century, two centuries, even, to get going. That would give us
more time to implement additional measures, not to mention help getting us on to a smarter course overall (which
doesn't, by the way, mean "back to the stone age".). It just seems rational that we should try and get a handle on growth and we should take that seriously! That
is not the same thing as "oh ◊◊◊◊, we're gonna be extinct!!!!!!!!" apocalypticism!
Energy is far form the only problem here insofar as mass spaceflight is concerned. Heck, if we want to even have a shot at it we're gonna need to get our politics straight. Like in the USA, we spend $700 billion a year on military -- wouldn't it be much better to spend that on space travel instead? If we really need space travel then our priorities are really screwed up to heck with that! ($700G/year to make things (weapons) to give us the
opposite of survival (death).)That's another factor: political will, and also common people's will (to limit their breeding, to be more responsible with energy, etc.). Indeed, I think the problem of
will is probably the most significant one here. Not some idea that "civilization itself is fundamentally unsustainable". So far, our progress toward getting to sustainable civilization (
not an oxymoron like TFian paints it to be) does not seem at all adequate, given our continuing high level of dependency on fossil fuels and continuing exponential growth.
