The last domino

About this video

Sam has set up a hundred dominoes in a long, winding line across the floor. Before he tips the first one, his sister Mei looks at the line and says, "The last one will fall right next to the chair leg." She is right. Once the dominoes are in place, everything that happens after the first push is fixed. Could the whole world be like that?

Causes make chains: the knock caused the fall, and the fall caused the break. Now suppose everything that happens has causes like that, and that the causes always work by the same rules - what scientists call the laws of nature. Then each moment of the world is fixed by the moment before, as each domino is fixed by the one before it. The idea that everything that happens is fixed by what came before, together with the laws of nature, is called determinism. It means the whole future, down to the last detail, already follows from how the world is right now.

In 1814 the French scientist Pierre-Simon Laplace put it this way. Imagine a mind that knew, at one moment, where every tiny bit of the world was and how it was moving, and every law of nature. If it were clever enough to work it all out, nothing would be uncertain for it: it could tell the whole future and the whole past. No real mind could do that. The point is that if determinism is true, there would be a future there to know, already fixed.

For determinism: for hundreds of years science has found causes for things that once seemed to happen for no reason - eclipses, illnesses, earthquakes. Against it: many physicists think that at the very smallest scale some events are not fixed by what came before, and the laws say only how likely they are; others disagree, and the question is still open. Either way it leads to a big question about our own choices. This video goes with the A World Like Clockwork lesson of Metaphysics Level 1 on Knaph.

Transcript

1. 0:00Sam lines up a hundred dominoes. Mei says where the last will fall.
2. 0:05She's right. After the first push, everything is fixed.
3. 0:11Determinism says every moment is fixed by the one before, and the laws of nature.
4. 0:17Laplace imagined a mind that knew everything now. It could tell the whole future.
5. 0:23Science keeps finding causes. But some tiny events may not be fixed.
6. 0:29Is the world like clockwork?