You can't yet make energy out of thin air, but that doesn't mean there isn't untapped juice out there. Grad students at MIT have an idea to harness and transform a human stampede at, say, an office, train station, or mall into volts. They call such technology, which would take form as flooring made to turn physical vibration or movement into electricity, "crowd farming". James Graham and Thaddeus Jusczyk's idea wouldn't work in smaller settings:
a single human step can only power two 60W light bulbs for one flickering second. But get a crowd in motion, multiply that single step by 28,527 steps, for example, and the result is enough energy to power a moving train for one second.