Wonders of the Universe - Brian Cox [100]
Once the last remnants of the last stars have decayed away to nothing and everything reaches the same temperature, the story of our universe will finally come to an end. For the first time in its life the Universe will be permanent and unchanging. Entropy finally stops increasing because the cosmos cannot get any more disorganised. Nothing happens, and it keeps not happening forever.
This is known as the heat death of the Universe, an era when the cosmos will remain vast, cold, desolate and unchanging for the rest of time. There’s no way of measuring the passing of time, because nothing in the cosmos changes. Nothing changes because there are no temperature differences, and therefore no way of moving energy around to make anything happen. The arrow of time has simply ceased to exist. This is an inescapable fact, written into the fundamental laws of physics. The cosmos will die; every single one of the hundreds of billions of stars in the hundreds of billions of galaxies in the Universe will expire, and with them any possibility of life in the Universe will be extinguished
A VERY PRECIOUS TIME
The fact that the Sun will die, incinerating Earth and obliterating all life on our planet, and that eventually the rest of the stars in the Universe will follow suit to leave a vast, formless cosmos with no possibility of supporting any life or retaining any record of the living things that brought meaning to its past, might sound a bit depressing to you. You might legitimately ask questions about the way our universe is put together. Surely you could build a universe in a different way? Surely you build a universe such that it didn’t have to descend from order into chaos? Well, the answer is ‘no’, you couldn’t, if you wanted life to exist in it.
The arrow of time, the sequence of changes that will slowly but inexorably lead the Universe to its death, is the very thing that created the conditions for life in the first place. It took time for the Universe to cool sufficiently after the Big Bang and for matter to form; it took time for gravity to clump the matter together to form galaxies, stars and planets, and it took time for the matter on our planet to form the complex patterns that we call life. Each of these steps took place in perfect accord with the Second Law of Thermodynamics; each is a step on the long road from order to disorder.
The arrow of time has created a bright window in the Universe’s adolescence during which life is possible, but it’s a window that won’t stay open for long. As a fraction of the lifespan of the Universe, as measured from its beginning to the evaporation of the last black hole, life as we know it is only possible for one-thousandth of a billion billion billionth, billion billion billionth, billion billion billionth of a per cent.
And that’s why, for me, the most astonishing wonder of the Universe isn’t a star or a planet or a galaxy; it isn’t a thing at all – it’s a moment in time. And that time is now.
Around 3.8 billion years ago life first emerged on Earth; two hundred thousand years ago the first humans walked the plains of Africa; two and a half thousand years ago humans believed the Sun was a god and measured its orbit with stone towers built on the top of a hill. Today, our curiosity manifests itself not as sun gods but as science, and we have observatories – almost infinitely more sophisticated than the Thirteen Towers – that can gaze deep into the Universe. We have witnessed its past and now understand a significant amount about its present. Even more remarkably, using the twin disciplines of theoretical physics and mathematics, we can calculate what the Universe will look like in the distant