Wonders of the Universe - Brian Cox [93]
Boltzmann’s statistical definition of entropy is the key to understanding Eddington’s arrow of time. This is such a key concept with such profound consequences that it is worth repeating it once more in a slightly different way. If there are a million different ways of arranging a handful of sand grains, with 999,999 of the ways producing disordered sand piles but only 1 producing a beautifully ordered castle, then if you keep throwing the sand grains up in the air they will usually land in the form of a disordered pile. So, over time, if there is a force like the wind that acts to rearrange things, things will get more messy or disordered simply because there are more ways of being disordered than ordered. This means that there is a difference between the past and the future: the past was more ordered and the future will be less ordered, because this is the most likely way for things to play out. This is what Eddington meant by his statement that the future is more random than the past, and his description of the arrow of time as the thing that points in the direction of increasing randomness. And this is why entropy always increases.
Watching my carefully constructed sandcastle gradually disintegrate in the strong desert winds perfectly demonstrates how entropy increases, and the idea that the past is always more ordered than the future.
For the purposes of our story, this is sufficient; if you take a university physics degree, this is what you will learn about entropy and the arrow of time. But there is still a great deal of debate and research surrounding entropy, and it centres on something we have dodged slightly. We have only spoken about entropy differences; the past had a lower entropy than the future; ordered things become disordered as time ticks by, but one might legitimately ask where all the order in the Universe came from in the first place. In the case of our sandcastle, it’s obvious – I made it – but how did I get here? I’m very ordered. How did Earth get here? It’s very ordered too. And how did the Milky Way appear if it is composed of billions of ordered worlds orbiting around billions of ordered stars? There must have been some reason why the Universe began in such a highly ordered state, such that it can gradually fall to bits. The answer is that we don’t know why the Universe began with sufficient order in the bank to allow planets, stars and galaxies to appear. We understand how gravity can create local order in the form of solar systems and stars, but this must be at the expense of creating more disorder somewhere else. So there must have been a lot of order to begin with. In other words, the Universe was born in a highly ordered state, and there should be a reason for that. It is unlikely to have been chance, because by definition a highly ordered state is less likely to pop into existence than a less ordered one; a sandcastle is less likely to be formed by the desert winds than a pile of sand. Since the Universe is far less ordered today than it was 13.75 billion years ago, this means it is far more likely that our universe popped into existence a billionth of a second ago, fully formed with planets, stars, galaxies and people, than it is that the Universe popped into existence at the Big Bang in a highly ordered state. There is clearly something fascinating about the entropy of the early Universe that we have yet to understand
The sands of time are slowly and literally overrunning Kolmanskop, dismantling the highly crafted town and returning it to dust once more.
The arrow of time has been playing out dramatically in Kolmanskop since the mining facility was abandoned in 1954. In every building you can see the gradual transition from order to disorder; every room that was once full of structure is slowly being returned to a less-ordered state. This is the march of the arrow of time on Earth, but it is nothing compared to the grand journey that time’s arrow forces our universe to make.
THE LIFE CYCLE OF THE UNIVERSE
Our Universe follows