> The speed of light is an actual hard speed limit; various sci-fi tricks like warp drive and traveling through wormholes have immense practical and theoretical barriers to being usable and I don’t think they’ll ever be overcome.
It probably is, but so what?
> Time travel into the past actually is impossible, which is why no one has ever come back to tell us about it.
And why is that significant?
> Even if we achieve speeds on the order of (say) 10% of the speed of light, which we almost certainly can’t for simple relativity reasons, traveling to potentially habitable stars will take hundreds of years; we have no reason to believe that cryofreeze/stasis/etc technologies are actually achievable; multigenerational interstellar travel is likely impossible for all the reasons Kim Stanley Robinson lays out here; we will therefore never colonize the stars and in the exceedingly unlikely event that we survive to see it, we’ll die when our sun expands to become a red giant; we might mine or colonize planets or moons in our solar system, but that won’t fundamentally change human life.
Chemical / Fission / Fusion and Antimatter rocket concepts are limited not because of relativistic effects but energy density and the capacity to handle waste heat[1]. The Helical engine concept is claimed to be limited to 0.99c taking advantage of relativistic effects instead of being limited by them[2]. All these engine concepts are theoretically possible to build. Building them is an engineering problem, not prohibited by any law of physics. Interstellar travel is hard not impossible, see a relevant episode of PBS spacetime[3]. There are over 50 stars that are closer than 20 light years[4]. The closest is only 4 light years away, at 10% light speed that's 40 years not hundreds. Not only that but as far as we can tell there probably is a planet in the stars habitable zone.
> There’s very likely other life in the universe, even intelligent life, but given that the cosmic speed limit will apply to them too, we’ll never meet with any of them physically, and given the distances involved synchronous communication is essentially impossible
That statements assumes too much of alien biology. There are organisms on earth that live hundreds of years. Tortoise live up to 150, whales up to 200, Greenland sharks between 300 and 500, there are jellyfish that are effectively immortal. For a Greenland shark a trip to Wolf 359 is between a third and a fifth of it's lifetime. There could be species out there that could live for hundreds or thousands of years as a matter of their biology.
hmm..a smaller exponent is still exponential growth