Anaxagoras the physicist

Anaxagoras was one of the first people to suggest that the Sun was a fiery lump, and that the moon shone because it was illuminated by the sun. And, as you will now find out, he came up with a theory that was very similar to the idea of the conservation of energy, a very modern understanding of physical forces, it was Anaxagoras who came up the idea of, or at least a forerunner to, the Big Bang: the idea that all the stuff in the Universe expanded from a single point.

Anaxagoras’ argument

Firstly, Anaxagoras agreed with Parmenides, who thought that ‘nothing cannot be’. You might remember from when we studied Parmenides, the thought that you could not describe ‘nothing’ and therefore, it cannot exist. So, Anaxagoras thought, if ‘nothing cannot be’, then nothing cannot come into existence, and something cannot become nothing. Stuff doesn’t appear out of nowhere or disappear.

But, that’s a bit confusing, because stuff does seem to be created all the time. Things do appear to come in and out of existence. Anaxagoras argued, however, that stuff never just pops into existence, it is created when stuff (that already exists) changes – when bits of stuff join together or separate from one another.

But why does stuff join together or separate? What makes that happen? Again, Anaxagoras had an answer: Stuff joins together and separates because stuff is in motion – it moves.

But what causes something to move? Well another thing that is moving, of course? But what causes that to move? … something else… But does this chain just go on forever? No! Thought, Anaxagoras. There must be some kind of power that start the movement.

Nowadays, we’d call that power a ‘force’ like gravity, or electromagnetism, Anaxagoras called this first mover, ‘mind’.

This led Anaxogoras to speculate that, at the beginning of the universe, all the stuff in the world was in a big lump, but then this force (which he called ‘mind’) started rotating everything, and so everything started moving outwards in a disorderly fashion. Similar ideas to that of Anaxagoras have been going out of fashion and coming back in for the two and a half thousand years since he died. Nowadays, a version of the same idea is known as the ‘big bang’.

An outline of Anaxagoras’ argument

1. Nothing cannot be

2. Nothing cannot come into existence, and something cannot become nothing. Stuff never just pops into existence.

3. Instead, it is created when stuff (that already exists) changes – when bits of stuff join together or separate from one another.

4. Stuff joins together and separates because stuff is in motion – it moves.

5. Something moves when it is moved by something else.

6. But the chain of motion doesn’t go on forever, so there must be some kind of power that started the movement in the first place.

7. Anaxagoras called this first mover, ‘mind’.