How to think about... Entropy

2019-03-15 04:17:01

Jose A. Bernat Bacete/Getty By Joshua Howgego PLACE 20 coins, heads up, on a tray and film it as you give it a shake. Then play the film backwards. From a jumbled mess, the coins all jump and come to rest with the same side up – an unreal, slightly creepy sequence. “It seems like a mundane observation, but actually this is very profound,” says physicist Sandu Popescu at the University of Bristol, UK. This little experiment illustrates the power of perhaps the most essential, implacable field within physics: thermodynamics, the science of heat, energy and, most crucially, entropy. The roots of thermodynamics lie in efforts to understand the steam engines that powered the industrial revolution of 18th and 19th-century Europe. The French engineer Sadi Carnot realised that their heat always tends to dissipate, moving to cooler regions. Anything that goes against this grain requires additional energy to power it. This movement from hotter to cooler is an expression of a more fundamental drive in the universe: disorder, as measured by entropy, always increases. The specifics don’t matter – heat always flows, flipped coins always jumble, burning logs always turn to ash. “If we discover a new force tomorrow, thermodynamics will be fine,” says Jonathan Oppenheim at University College London. Entropy increase is so universal that many physicists propose it is why we see time flowing (see “How to think about… Time”). It is certainly why our hearts must constantly pump blood,