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Astronomy with an online telescope
Astronomy with an online telescope

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3.1 The most famous equation in the world

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Figure 6 Albert Einstein, who in 1905 formulated the theory of relativity.

Perhaps the most famous and well-known equation in the whole of physics is Albert Einstein’s cap e equals m postfix times c squared.

This simple-looking equation holds the key to the source of the Sun’s energy. The equation is a direct consequence of Einstein’s theory of relativity and essentially states that energy cap e and mass m are equivalent and that under certain circumstances, such as during nuclear reactions, an amount of matter can be converted into energy.

The other term in the equation, c squared , sets an exchange rate for this conversion. The c here is the speed of light: at 300 000 km per second this is already a very large number and in Einstein’s equation it is squared – multiplied by itself – making a vast number. This huge conversion factor means that a small amount of mass is equivalent to an extremely large amount of energy.

As a result of this conversion factor, nuclear reactions are immensely more powerful than chemical reactions. The Drax power station that you saw in Section 2 consumes over 9 million tonnes of coal every year, yet nuclear power stations such as Sizewell B run on just 30 to 40 tonnes of nuclear fuel. Even in nuclear reactions, only a small fraction of the mass of the fuel is converted into energy using cap e equals m postfix times c squared. Of the 30 to 40 tonnes of nuclear fuel used at Sizewell every year, just over one kilogram of that mass is converted to energy.