This part of the long business cycle always produces a lot of arguments for austerity. So far they have always turned out to be spectacularly wrong.
"Nuclear fission is currently on decline."
Nuclear power, both fission and fusion, is currently in a renaissance and we appear to be laying the groundwork for the next stage of advances: gas- and metal-cooled reactors, superconductors, mechanical compression systems, reliable mode-locked lasers, dielectric wall and wake field particle accelerators, electronics that can do real-time gigahertz feedback, etc.
When the next long expansion gets into full swing, I predict that the nuclear logjam will break loose.
"There aren't any better energy source than oil available now, or in the foreseeable future."
There's a lot of solar power in space. A lot. And literal mountains of metal, richer than the best terrestrial ores and pre-smelted too. At some point technology will tip the profit margin positive on exploiting it.