This experiment was designed to explore what we know about causality, the relationship between causes and their effects. It was invented almost 300 years ago by the Scottish philosopher David Hume. Hume pointed out that something very peculiar was wrong with the way we viewed the world around us, a problem which has endured both for scientific and philosophical thinkers alike: “The Problem of Induction”.

The reason we believe that when the white ball strikes the red one it will send the latter forward is because, in the past, this is what has happened. Every time we’ve seen billiards, pool or snooker played, a collision between a moving ball and a stationary one has caused the stationary ball to move forward. As with billiards, so too with science. We assume that the movement of planets, the course of chemical reactions and even biological processes will continue to happen in the future the way they have in the past. For Hume, however, this isn’t enough. Just because we’ve observed uniform, predictable and periodic events in the past this doesn’t mean they will continue that way. Lets consider this argument:

In the past, every time the white ball hit the red one, the red ball moved.

Therefore, when the white ball hits the red one, the red one will move.

But this is where things get a little complicated. Hume points out that there is actually a hidden premise in this argument. The hidden premise is called the “principle of uniformity” which states that events in the future will resemble events we’ve seen in the past. In this way:

In the past, every time the white ball hit the red one, the red ball moved.

Principle of uniformity : events in the future will resemble events of the past

: events in the future will resemble events of the past Therefore, when the white ball hits the red one, the red one will move.

So far so good. But what justification do we have for the so called “principle of uniformity”? This is where the difficulty arrises, because according to Hume the principle is actually self justifying. In other words, the only reason we believe in the principle of uniformity is because of the principle of uniformity itself!

In the past, the principle of uniformity has been true.

Principle of uniformity : events in the future will resemble events of the past

: events in the future will resemble events of the past Therefore, the principle of uniformity will continue to be true.

What we are left with is a cyclical argument in which the principle self-justifies and is considered logically invalid.

So what exactly does that mean? It means things look pretty bleak. As it stands, this argument demonstrates that my prediction that the white ball will move the red ball is just as reasonable as saying the white ball will suddenly turn into an egg and hatch once it hits the red one. An astronomer’s prediction that a comet will pass by is just as likely as a prediction that the moon will suddenly vanish into a cloud of smoke. We can no longer logically guarantee that causes will result in particular effects. Anything can happen. Nothing is predictable.