I mentioned these in class, so here's some links if you're curious.
The original link on how much would it cost to build a "death star" is here. One of the many follow-ups was one I wrote that we'd have that much money in less than 500 years. Of course, a death star would also have a lot of power, but getting that much growth is much less realistic.
I also babbled about how enough economic growth at current rates will lead us to Dyson Spheres in ... hmm ... not that many centuries. These ideas are related to the Kardashev Scale, and our civilization's position on that scale.
Another idea that is staring to intrude on macroeconomics is extreme life expectancy. Here's the piece by Aubrey de Gray; in class I paraphrased this quote from that article: "I think the first person to live to 1,000 might be 60 already." If that's even barely possible, then Medicare is pretty much the only government program that we should even be thinking about (which is why there's all these posts about Medicare on this blog). Don't forget that 75 years ago, Auntie Em was Hollywood's version of how old the aunt of a 14 year old girl should look.
I don't make this stuff up. I just report it. If you want to explore more, the macroeconomist who's really out there is Robin Hanson. Check out his website (which isn't maintained that well) or his blog overcomingbias.