So begins Stardust, Brian Cox’s second instalment of the wonderful Wonders of the Universe on BBC One. I highly recommend it and if you have missed it, all three episodes are still available on iPlayer.
The premise of Stardust is that we are all born from the destruction of stars, which sounds far-fetched. But it’s not at all. Brian Cox’s starting point in Wonders of the Universe is also that of Uma Jakobsdóttir in The Human Race: that every atom in our bodies was once part of something else, be it a dinosaur, a dormouse or a tree. Everything is made from the same basic ingredients and chemical elements, which are the building blocks of everything on earth. When living things die, their physical elements are released back into the world so they can continue the cycle of creation, usually as something else. So far, so good?
In The Human Race, Uma explains how we are comprised at an atomic level. Her theory is a critical cog in her explanation of her “creation”, which she believes has the power to halt global warming. Brian Cox takes this premise in a slightly different, but no less interesting direction, by explaining where the elements of which we are composed actually come from. His premise in Wonders of the Universe is that “we are based entirely on physics of cosmology…we are made by the Universe…every atom in our bodies was created out in deep space”.
It’s not as crazy as it sounds. His hypothesis is that the earth is comprised of just 92 chemical elements and that everything beyond earth is made of those same 92 elements. The moon is rich in helium, silver and water. Mars is rich in iron, hence its red colour. Venus’ atmosphere is thick with sulphur and Neptune is rich in organic molecules like methane. We know this and we can prove it. It is even the case in places we haven’t been able to travel to, such as the star Proxima Centauri, which is 4.2 light years away from earth; or the nearest galaxy, Andromeda, which is a staggering 2.5 million light years away.
Science we can measure
The reason we know all of this is because we can test it. When you burn an element, it gives off light containing its own unique set of colours. For example, sodium is yellow, potassium is lilac and copper is blue. Each element also absorbs light of the same colour. This property tells us what stars are made of. We are able to do this by analysing the spectrum of light emitted by whatever we are looking at in the night sky. The colour markers tell us what elements are being emitted and are therefore included in the makeup of the star. This is the case for every star in the sky.
However, Brian Cox takes this principle even further. In Wonders of the Universe he examines how these elements were created in the first place and in doing so, gives us a crash course in nuclear fusion. His great gift is his ability to make such a complex subject accessible and understandable. His focus is subatomic particles, such as quarks, which bond together to form neutrons and protons. These are the building blocks of all atomic nuclei and elements, and are at the heart of all atoms. Within the atom, protons and neutrons are assembled to build up the elements. As Brian Cox explains, it’s very simple. In fact it’s child play!
A “simple and beautiful” process
The simplest structure is a single proton, the nucleus of the simplest chemical element, hydrogen. From this starting point you can create the other elements. The first stage is to fuse two protons together. One of the protons then becomes a neutron and that is deuterium. Take two deuterium atoms and we get helium, the second-simplest element. Then it is a question of adding more protons and neutrons in order to build more complex elements, eventually forming the most complex elements in the universe. Brian Cox describes this process as both “simple and beautiful”.
However there is only one place where this process can happen. A star. Stars are the only furnaces sufficiently hot and dense to fuse atoms together. Interestingly, the Sun is 6,000 °C at its surface and this is not nearly hot enough to power the fusion of atoms. Towards the core of the Sun, temperatures reach 15,000,000 °C and this is where simple fusion occurs. This process converts one element into another and generates all of the Earth’s heat and light. For all its power, however the Sun can only convert hydrogen into helium. Other elements, such as carbon – upon which all life is dependent – are far too complex and require something so powerful that it can generate temperatures in excess of 100,000,000 °C.
That “something” is the death of a star.
The final moment of a star’s existence can produce upwards of 26 of the basic elements including hydrogen, helium, carbon and oxygen. As a result, the fusion of atoms and our consequent existence is all down to the final death throes of a star.
It fits nicely in with the cycle of life with which we are all so familiar. Except, of course, that this is played out on a celestial scale, in which our life comes from the dying breath of a star.
Brilliant stuff. I will be definitely be buying the Wonders of the Universe book that accompanies this series.