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Any space, physics or all-around science geek can agree that Stephen Hawking is immortal, but now his work is being remembered on a coin that should last until all the black holes in the universe evaporate.
The UK Royal Mint has released the most appropriate coin ever to keep the late physicist’s memory alive forever, or at least as long as Earth is around. It’s kind of like an epitaph you can fit in your pocket. His name and the equation for the entropy of a black hole (more on that in a second) appear right above the event horizon of a conceptual drawing of a black hole.
"I wanted to fit a big black hole on the tiny coin and wish [Hawking] was still here chortling at the thought,” designer Edwina Ellis told the BBC about the 50p (about 72 cents) coin. She wanted it to embody how he “made difficult subjects accessible, engaging and relatable".
About those black holes evaporating—this is where entropy comes in. Entropy describes how a system loses energy at a certain temperature. Because nothing, not even light, can escape the extreme gravitational force of a black hole, Hawking started to wonder what that did to entropy. This is how the concept of Hawking radiation emerged. Black holes, he believed, must gradually lose and thus radiate matter from their surfaces.
The equation on the coin merges general relativity (laws of gravity) and quantum mechanics (laws of the tiniest particles) to explain how even black holes will dissipate into the ether over billions and billions of years.
"It is a great privilege to be featured on a coin,” said Hawking’s daughter Lucy, “and I hope my father would be pleased to be alongside Sir Isaac Newton and Charles Darwin as scientists who have made it on to money."
If you don’t live in the UK, that doesn't mean these are light-years away. Get one right now from the Royal Mint’s website and put a black hole in your pocket.