We would have the same (if not higher) energy consumption per capita on any other planet. And unless that planet is humongously large (which would also increase its surface-level gravity, thus rendering it uninhabitable), the relation between surface temperature and energy consumption will be similar[0]. Now there's only a finite number of planets in our solar system and leaving our solar system, say in the direction of Proxima Centauri (the star nearest to the Sun), amounts to traveling ~4.2 light-years. At a velocity of 0.1c (which is a lot – especially if you're trying to move an entire species[1]) that means a travel time of 42 years (as seen from our current frame of reference). Any velocity lower than that and we're getting into hundreds-of-years territory, so we'll be needing space ships across we can live for generations.
Also, a space ship is not that different from a planet, in that it also has to obey thermodynamics. So the surface temperature issue there is just the same. (In fact it's worse, since our space ship will likely be smaller and we also need to factor in additional waste energy of the space ship's propulsion engine or whatever we're using.)
[0]: https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law
[1]: Or, say, half the species (or whatever amount necessary to make the total energy consumption on the planets we already inhabit drop to levels such that the planets' surfaces don't start to boil).
We can barely speculate about such a world, but interstellar travel would not be much of a challenge with that sort of energy abundance. We'll find a way.
The argument in the UCSD blog post linked above will apply to any finite system if you assume exponential growth in power use, and exponential beats cubic for expansion to other worlds (I’m assuming no FTL for a cubic limit to expansion).
Abundant power — be it from fusion or solar or quantum magic — does not actually need to guarantee eternal exponential growth of power use, but the absence of such growth would necessarily lead eventually to the absence of economic growth.
We can still have a SciFi future without that, it will just look different in a way our current society can’t properly envision (which I think is an unsurprising a claim to make even in the absence of the rest of this argument).
I don't think I agree.
1) The extremely high (but still finite) amount of energy required to evaporate the Pacific Ocean is still much less than the infinite energy you need to accelerate even one single space traveler to the speed of light. Infinity is weird.
Of course we won't be trying to reach the speed of light but the energy (and fuel) required to move half the species (so that the other half can stay on Earth/Mars/…) will still be significant.
2) My second argument was that the Stefan-Boltzmann law is just the same on board the space ship. And if we live there for generations, chances are our energy consumption per capita will be similar as on the planet we left, and so we will be running into similar issues with Stefan-Boltzmann's law. Sure, we can split up the passengers across multiple space ships and make each ship much bigger (to increase surface size) but not only will this increase the total mass and thus fuel required for the trip but we would probably still not achieve the (rather high) surface area per capita ratio that we have on Earth.
Thinking a bit further, just because we can produce a high amount of energy that doesn't necessarily mean we can automatically convert it into kinetic energy for a space ship very well. Most propulsion systems in space still require expelling a propellant and conservation of momentum means this is unlikely to change. (Sure, one could imagine solar sails but the little momentum exchanged there won't get half of humanity to Proxima Centauri very fast.) So while we might have unlimited energy we might still be constrained by momentum requirements.
The only way I can see to solve this conundrum would be producing enough propellant on board the space ship, e.g. (lots of) photons, using a laser. Definitely not impossible (especially not at these energy levels) but it'll be interesting to see what these propulsion systems will look like exactly. :)
Ideally, we would of course try to use the propellant to also get rid of the waste heat mentioned earlier but I'm not sure whether this would work entropy-wise.
True, but how many tons of space junk can you accellerate to 95% of light speed for the same amount of energy?
On an interstellar ship far from a star, I think you're more likely to freeze to death, because temperature in space is near zero Kelvin.
Inside the solar system however, you could reflect away the received radiation (and heat) using mirrors.
We're talking about a civilization on board an interstellar ship that had to leave their home planet because they were consuming so much energy that the resulting waste heat ended up making the oceans boil. So the assumption that they'll keep on consuming lots of energy (and producing lots of waste heat) on board such a ship sounds rather reasonable to me.
> Inside the solar system however, you could reflect away the received radiation (and heat) using mirrors.
The discussion is about getting rid of heat produced on board the space ship, not heat that's received from elsewhere.
