The article probably should be titled "World's tiniest steam engine uses a laser as a piston". That's the part that's interesting. The source of the energy - t

The article probably should be titled "World's tiniest steam engine uses a laser as a piston". That's the part that's interesting. The source of the energy - the laser's ultimate power source might be a coal burning power plant - is not at issue. Otherwise we'd have to hope it's "lasers all the way down".