Fusion for the uninitiated. Great promise, difficult to make happen. So far it costs billions and it’s unstable, too hot, hard to control. You can’t run it long enough get out more energy than you put in. When I was twelve it was 20 years away. The joke is that it always will be.

If we could make it happen it’d change everything. Nature even provides an example! But we’ve had brilliant minds on it for decades and no breakthroughs.