The nuclear fusion startup Helion, which announced recently that it has raised $500 million, says it has developed new technologies that may make nuclear fusion viable — practically, economically and environmentally.

It is too early to tell if its claims will pan out, but there have been so many breakthroughs lately that they cannot be dismissed.

The possibility of carbon-free energy generation raises a seldom discussed question: Just how much would it change the world if cheap and clean energy sources were truly abundant?