What is Occam’s Razor?

Question

I see this term float around the internet a lot but to this day the Google definitions have done nothing but confuse me further

EDIT: OMG I didn’t expect this post to blow up in just a few hours! Thank you all for making such clear and easy to follow explanations, and thank you for the awards!

In: 12004

Answer 1

Occam’s Razor says that when trying to explain an observation, you should go with the simplest explanation first. “Simplest” usually meaning “whatever requires the fewest assumptions”.

Say you notice that the name of an old film wasn’t you remembered it being. Maybe you notice a poster for the first Avengers movie and see it’s called “Avengers Assemble”. That can’t be right, you think, you’re sure it was just called The Avengers.

Two explanations occur to you

1) you misremembered it

2) you come from another universe where it was called The Avengers and you somehow jumped dimensions

The second one requires more assumptions, namely that other universes exist and that its possible to travel between them. The first one doesn’t require any new assumptions on top of how you already understand reality, so you go with that one.

But then you gather new evidence–another poster where it was called The Avengers. So what now–your first theory now doesn’t work, so what do you do? Immediately adopt the second theory?

No, because someone suggests a different theory. The film was released under different titles in different regions, and you saw a poster made for the UK. This isn’t as simple as that first theory, but it’s still simpler than the multiverse theory, so you change to that theory. And in this case that is the actual answer.

So, it doesn’t mean “the simplest explanation is always true”, just that it’s usually an easier process of arriving at the truth if you start at the simplest answer and work up

Edit: I should add, the important part is that if you have to theories that explain observations *equally well* then you should assume the simpler is true. It does not apply when one theory explains observations better. For example, quantum mechanics is far more complicated than Newtonian mechanics, but it explains certain observations better, so Occam’s razor doesn’t apply