Wonders of the Universe - Brian Cox [48]
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Look up into a clear blue sky and you are bathing in the energy of nuclear explosions on an unimaginable scale.
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To be completely accurate, we should mention that there are other factors than just the balance between the electromagnetic and nuclear forces that feed into the stability of the elements. These are to do with the shape of the nucleus itself and that the balance between protons and neutrons is favoured for quantum mechanical reasons. (If you are interested, google ‘Semi-empirical mass formula’ and enjoy!)
Here on Earth, fusion may seem the ultimate human technological achievement but actually it’s the most natural thing in the world. It didn’t only happen at the Big Bang; it’s a process that can be found occurring across the Universe as we speak. In fact, it illuminates the whole Universe and happens all the time millions of miles above our heads.
Fusion is the process that powers every star in the heavens, including our sun. Look up into a clear blue sky and you are bathing in the energy of nuclear explosions on an unimaginable scale. Deep in the Sun’s core, 800,000 kilometres (500,000 miles) below the surface (where temperatures reach fifteen million degrees Celsius), the Sun is busy fusing hydrogen into helium at a furious rate. In just one second the Sun converts 600 million tonnes of hydrogen into helium, releasing as much energy as the human race will use in the next million years. This is the energy that makes the stars shine and fills the Solar System with heat and light.
The shining Sun is one of the most natural demonstrations of the effect of fusion. It, and all the other stars in the heavens, are powered by the fusing of hydrogen and helium.
It is the process of turning hydrogen into helium that creates the energy that allows all life on Earth to exist, but for all its power the Sun only converts hydrogen, the simplest element, into helium, the next simplest. This process is repeated across the night sky; every star in the Universe began its life fuelled by hydrogen and powered by this reaction.
So the assembly of the second-simplest element, helium, is well understood. We know the stars can do it, we know it happened in the very early Universe, and we can even do it ourselves on Earth. But this doesn’t help to explain the origin of the other ninety-two naturally occurring elements. Clearly, somewhere in the Universe there must be a plentiful source of the other elements because they are everywhere, our whole planet is made from them. We are made of billions and billions of atoms; from magnesium, to zinc, to iron and, of course, the one atom that life is more dependent on than any other – carbon. Every human being on the planet is made from about a billion billion billion carbon atoms. That’s an unimaginable number of carbon atoms that simply didn’t exist in the early moments of the Universe. Where did they come from? The answer must be nuclear fusion, and the natural place to look is within the stars themselves
FROM BIG BANG TO SUNSHINE: THE FIRST STARS
The first stars formed around 100 million years after the Big Bang. The rate at which they burned their hydrogen fuel essentially depends on their mass. The more massive the star, the brighter it shines and the shorter its lifetime. The key to understanding how the heavier elements came into being lies in what happens to stars when they have exhausted their hydrogen fuel. For the most massive known stars, this may take only a few million years. For stars like our sun, it may take ten billion years – but the Universe has been around for plenty of time to allow generations of