As a guy who lives in a finite world where energy comes mainly from fossil fue in a way or another, I do not assume that any constant progress in energy supply is something achievable.
No, and traveling near lightspeed is likely hardly possible. However, fusion will likely become a reality within our lifetimes, and if we can build fusion powered spaceships, we could likely reach a fraction of the speed of light, say, 0.2c. I don't think it's that crazy to think we could do that a few centuries from now. That still means it would take over 1000 years to reach that planet.
Personally, I think that if humanity progresses that far technologically, without destroying itself, we probably won't care that much about habitable planets or planets with water. We'll just live in space and harvest the energy and resources that are available nearby. There are a lot of other planets much closer to us than K2-18b. We could just build bases in orbit around those stars, harvest asteroids for minerals and hydrogen for fusion power.
Alpha Centauri would "only" take 22 years to reach at 0.2c (plus some time for acceleration and deceleration). You could leave earth and live to see that solar system, and you could travel there on a ship that is basically a large city that will just park itself in orbit around the star on arrival, acquire resources, and start building something bigger.
Besides the incredible amount of energy you would need for 0.999c, which is physically difficult (impossible?) to bring on a ship, there's other physical constraints that make this difficult, such as the fact that the vacuum is actually not that empty. The faster you go, the more you have small particles hitting your ship at near lightspeed, micrometeorites, etc.
Why do you think that no state put significant effort into fusion research? You would imagine the first country to figure it out would dominate the world for decades to come.
Could you give some sources for that or explaing where exactly the problems in fusion technology lie and how it could be solved by throwing money at it?
ITER is planned to be completed in 2026 and it'll generate a net 0 of electricity at 300MW in/out.
It seems the issue with fusion is that it actually works much better at scale. But the same could be said about nuclear reactors - it obviously is much harder to build a compact one.
Does it work better at scale? The sun definitely produces a lot of energy in total. However, "the Sun's "power density" is "approximately 276.5 W/m3, a value that more nearly approximates that of reptile metabolism or a compost pile than of a thermonuclear bomb".
If, overlooking the details, we were able to build a cubic meter sized "fusion box" that outputs 276W, then it would take about 2 million of them to produce a reasonable output for a power plant of 600MW. And it would take up about half the volume of NASA's vehicle assembly building, ignoring any support structure needed. That's not unimaginably huge, but it's pretty large compared to other types of power plants, I would think.
So assuming we solve all the technical problems to capturing the power source of the stars using handwavium or perhaps generously donated alien widgets, I wonder if it might still be uneconomic.
Over any timeframe, the rate of progress between the beginning and ending of the timeframe can be phrased as exponential for some exponent. It's just a matter of accurately estimating what that exponent is.
I take your point though - hypergrowth cannot be sustained - and estimating that exponent is fairly valueless if volatility is too high. This is all just math fun that won't be valuable if we bump along for hundreds of years and then all of sudden make a massive discovery.
Thats true considering only two datapoints. It gets more interesting when more datapoints follow an exponential rule, say subsequent disruptions, no of transistors on processors or stock market indices.
