The second law of thermodynamics, which gives us an arrow of time, is routinely violated at the smallest scales – an insight that is already yielding fresh clues to some of biology’s great mysteries
9 June 2021
SITTING with a friend in a cafe, you order a cappuccino and your buddy orders a milkshake. But as you go to take a sip of your coffee, you see a roiling boil, steam rising from the mug at an increasing rate. Astonished, you look up to tell your friend, then stop dead: his tongue is stuck to the now-frozen milkshake. Terrified and confused, you both run to your car and start the engine, but then notice the fuel gauge going up – your engine is sucking in heat and exhaust fumes and turning them into petrol and air.
This has never happened and almost certainly never will. But the key word here is “almost”. Although processes that involve the exchange of energy don’t behave like this at the scale of our everyday experiences, at the level of atoms and molecules they can and do run backwards.
Physicists first acknowledged the possibility of this kind of violation of the forward flow of time more than a century ago. Yet it is only recently that we have started to get to grips with what this might mean for the many critical processes that underpin life itself.
Our growing understanding of what drives – and limits – these processes, is not only upending traditional notions of energy, but also exposing new clues relating to perplexing questions about human biology, including how some neurological diseases take hold. Now, researchers have even set their sights on applying these ideas to understanding one of the greatest mysteries of all, the origin of life.
The industrial revolution of the 18th and 19th centuries saw hard graft increasingly replaced by …