# Why Does E=MC2?

16:37 Mon 24th May 2010 The AnswerBank

Whenever anybody brings up Albert Einstein one of the first things which is usually mentioned is his well known equation of E=MC2. In fact this equation is probably the most well known in the world, but what does it actually mean?

Energy and Mass

First things first, what do the ‘E’ and ‘M’ in the equation actually refer to? Well, as you may have guessed from the subtitle, they represent ‘energy’ and ‘mass’. One of Einstein’s great realisations was that essentially energy and matter were different forms of the same thing. Thus energy can become mass and vice versa.

So, what are energy and mass? Well energy is fairly easy; it is basically the amount of ‘power’ stored within something. For example by burning a log on a fire you will be releasing the energy stored inside it. This is measured in joules.

‘Mass’, on the other hand, is a measure of an objects resistance to acceleration (known as inertia); In other words the amount of ‘matter’ that an object is composed of. This should not be confused with weight, which represents the effect of gravity on an object. Mass is measured in kilograms.

The Missing Letter

Right, so now we know what ‘E’ and ‘M’ mean what about that final ‘C’? Confusingly enough ‘C’ actually refers to the speed of light. Now, as you may remember from science at school, at 300,000 kilometres per second nothing travels faster than light.

You may wonder why exactly the speed of light is involved in this equation. The simple answer is that it basically represents a constant, i.e. something which can be used to demonstrate the relationship between mass and energy.

Bringing it all Together

Those are the letters then, but what the hell does it all mean? Ultimately Einstein’s great equation is a method of establishing how much energy can potentially be released from a certain amount of mass. Generally this is a huge amount, for example from 1kg of a substance it would be possible to generate a massive 90,000,000,000,000,000 joules of energy. Enough to power a standard light bulb for 28,519,279 years!

So why aren’t scientists doing this now to solve the energy crisis I hear you cry. Well, there’s the problem – actually doing this is very difficult. To release this energy the atoms within the substance must be utterly annihilated. The only way of doing this is by using ‘antimatter’ - an atom which has a negative charge. This has been created in laboratories but quickly destroys itself, meaning actually reacting it with a substance isn’t possible, at least not yet..

Einstein’s theory is however observable in radioactive substances. Elements like Uranium are highly unstable and have atoms which are constantly falling apart, creating new more stable elements which have fewer protons around their nucleus than they originally did. Thus any extra mass is released as energy, usually as heat.

This process was also used in the most famous demonstration of E=MC2: the atomic bomb. It is known as ‘nuclear fusion’ and also used in nuclear power plants. ‘Nuclear fusion’, put simply, involves using the energy released from the conversion of mass in a radioactive element, usually Plutonium, to either release a huge amount of energy all at once, as in a bomb, or alternatively slowly to produce heat, as in a nuclear plant.

Well, hopefully, you’re now a little bit more clued up on what exactly E=MC2 actually means. So, next time there’s a question about it during the local pub quiz you’ll be well equipped to answer and impress your friends!