special theory of relativity

1. Einstein showed that light travels in bundles called quanta, which are at
the heart of the light-emitting diode. When electrons in a semiconductor-based diode move from one side to another, they shift to a less excited state, releasing energy in the form of photons. Channel these, and you get a bright, long-lasting light source.

2. In 1917 Einstein demonstrated that when a photon comes into contact with an atom, it can trigger a chain-reaction release of additional photons from

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When H.G. Wells sent the hero of The Time Machine into what Wells called "futurity," it was on a grim 30-million-year round-trip to pretty much the end of Earth time, when the last, poorest excuses for life were flopping around like squid under a darkening sun. Wells wasn't the first writer to imagine time travel, but he advanced the idea that a machine, rather than an angel or a bonk on the head, could accomplish it, and he pushed his machine to the limit.