in the picture predicting the pendulum’s behaviour where a small change in the initial position of the pendulum wouldn’t cause it to end up at a different magnet. And it’s the same with the weather. Think of the large black region in the picture as the weather in a desert: it’s always going to be hot there, however hard a butterfly flaps its wings. And similarly for the arctic, which is like the magnet staying in a white region. But the weather for the UK is like the pendulum starting at a place where the colours in the picture change rapidly with just a small shift in the pendulum’s position.
If we knew the precise positions and speeds of all the particles in the universe, we could predict the future with certainty. The trouble is that if you get one of those starting positions even slightly wrong, the future can turn out to be completely different. The universe may behave like clockwork, but we’ll never know the positions of the cogs accurately enough to take advantage of its deterministic nature.
Heads or tails?
The 1968 European Football Championship was held before penalties were introduced as a way of deciding a drawn match. So when Italy and the Soviet Union were still goalless after extra time in their semi-final, a coin was tossed to decide which of them would go through to the final. It has been universally acknowledged since Roman times that a coin is a fair way to decide a dispute. After all, it’s impossible to tell as it spins through the air how it will land. Or is it?