We spoke briefly last time the equivalence of mass and energy, which is governed by Einstein’s most famous equation;

E = mc²

In this equation the conversion of mass to energy is eloquently expressed and unlocks the secret behind the atom bomb’s power and nuclear power here on Earth. These are examples of nuclear fission, the process whereby a nucleus is split into smaller constituents (by destabilising it with neutrons). The mass of these smaller constituents is lower than the initial mass – which we now know, thanks to the above equation is a result of the conversion of the mass into energy. You can understand by looking at the above equations why this is such a powerful process.It is staggering to think that we can just throw this fact around now – but once upon a time this would have been a great mystery – well in fact the power was not being harnessed.

Say I have a mass of 1kg; if I convert this *all *into energy, then I have;

E = c² = (9.00 x 10^16)J

The above can be expressed more eloquently as 90,000 TJ with the T representing terra – so 1 terra joule is equivalent to 1,000,000,000,000 J. These numbers are huge and all of this just comes from one kilogram. Imagine the untapped potential existing in every day objects. Now I must stress, before you tout these facts – we are speaking about perfect energy conversion here. What we have when we are talking about the nuclear fission, is the splitting of one thing into two things that are *slightly *lighter – so the actual mass that has been converted is the difference rather than the amounts in totality. Even so, the conversion factor is **huge **– the speed of light squared. This is why an atom bomb can melt a city and a small amount of uranium can power it. I cannot currently give every day real life examples of perfect energy conversion in action, like I can for fusion and fission – although to call the sun every day might be a stretch in itself. That is for another post.

So what of nuclear fusion? This is a slightly different process but for the basic understanding of energy-mass conversion it is the same. Here you take a nucleus and you fuse it with other constituents – the resulting product is lighter than the original components and therefore energy is released. While the process is different, when you think just about energy transfer you can strip it away to the basic start out with a mass – finish with a lighter one plus energy. The core difference is if you end up with fewer larger atoms (larger in the atomic number sense) or many smaller atoms. The really exciting thing about fusion conversion is it is this that powers the stars – all the stars are are giant nuclear fusion reactors. We cannot yet replicate this energy conversion on Earth even though we know how it works.

In our local star the sun, helium is fused together to create hydrogen. The temperatures reached by this process are astonishing with just the surface reaching 5,778 K. The power of this process fuels life everywhere in the universe as we know it, from the bottom of the ocean to the corners of space where its light penetrates; its energy is huge and far reaching. Nothing could exist on Earth today without it – and while we talk about fossil fuels and solar power, in a very indirect way they are both solar power. When the sun has converted all of its helium it will die – unlike some more massive stars in the universe which have the temperature to fuel themselves with hydrogen. Using this you can consider the mass of a sun and start to play around… if I have a star with twice the mass which is 100 times as bright relative to the sun I expect it to have 1/50th of the life. Make sense? In fact it is the same with all such conversions – you can work out how much there is to convert and you can consider the power or the rate of conversion and make comparisons.

This is just a quick example of how you can take an equation and think things through in your mind. Start to understand what it means and how it applies to the world around you, why it is important and what it can do for you.