What keeps things moving isn’t actually energy, but low entropy or high orderliness. To answer that, we need to return to the concept of entropy. But here’s a quandary – if energy is always conserved, why do we constantly have to resupply it? That effectively means energy is always conserved. Secondly, energy can’t be created or destroyed, only transferred – for example, into heat. First off, everything we do requires energy. Without heat, in other words, nothing would move, and past, present and future would be little more than an indistinguishable mass!Įinstein demonstrated that time changes with speed and gave us a new notion of time and space.Ĭhances are, you had these two core concepts drummed into you in your high school physics classes. And if you really get down to it, motion is simply heat – the movement of molecules at a microscopic level. But change is only possible if there’s motion. The past is distinguished from the future by change. But here’s where things get really interesting – we can only tell the past and future apart because of heat. In both cases, reversing that movement is impossible. Time moves from past to future, while heat always moves from hotter to colder objects. In fact, heat and time share a fundamental similarity – they can both only travel in one direction. That, to put it in simple terms, was the central insight of Albert Einstein’s theory of general relativity.Īs if that weren’t baffling enough, heat also plays a part in this dynamic. That’s because times are relative to one another. It sounds impossible, but there’s no such thing as one objective or “true” measure of time that can be applied both in the mountains and at sea level. Even his houseplants will have grown more! The result? The mountain-dweller will have aged more and lived longer than his pal from the flatlands. One of them goes to live on a beach and the other at the top of a mountain. Take a simple thought experiment – two friends of the same age part company. It’s not just time that slows down when measured at a lower level – all processes do.

Placing one clock on the floor and another on a table has the same effect: the differences are minuscule, and you’d need a precision timepiece to prove it, but the second timepiece will always run faster. Compare two clocks, where one is placed at sea level and the other high up in the mountains, and you’ll find the latter runs faster. In reality, time passes at different speeds in different places. In everyday life, we see time as a uniform forward movement – something that just happens, like the ticking of an eternal clock entirely beyond our control. After all, if you trust your eyes alone, you’re likely to end up believing the world is flat. That’s one of the first lessons of the sciences.

Carlo rovelli the order of time review