Originally Posted by Bah Humbug

Maybe I should have made it explicit, but that's part of what I meant in "meaningful". Sure, once you slip the surly bonds of gravity you can just coast to your destination if everything's calculated correctly (and of course you need to carry enough fuel to decelerate upon arrival), but when I wrote of "just get in your rocket and go" I didn't mean "and your grandchildren will arrive". Hong Kong is on the other side of the world and I can fly out there in a day, turn around, and come back. That's incomprehensible for just a century ago, and is the sort of progress that's nothing compared to what we need to even take a trip to Mars and return. The best-case scenario with unlimited free energy is constant 1G acceleration to the halfway point, then turning around and using the engine to brake, and... well even that's years to get to and from Alpha Centauri, and it's the sort of energy cost where we might as well just be playing make-believe anyway.

An analogy I sometimes use is, imagine if the only landmasses on the world are Cuba and Taiwan, and humans evolve on Cuba. Even if they invent boats, the chances of them being able to build a large enough ship to get to Taiwan, and get back, are basically zero. And that's on a scale that is much, much smaller than going interplanetary. It's much smaller again than interstellar, by factors we're really bad at internalizing. And it rains on the ocean, and there are fish, and there's wind. Space is basically empty. Outside of magical functionally-unlimited free energy (amounts of which would make that trip to HK take a few minutes and too cheap to charge for, and building or removing mountain ranges easy) we're stuck here. Unfortunately.

This also basically puts the kibosh on aliens, which doesn't stop my nightmares.