Terence Tao

And so over time, we had to realize that the Earth was round,

that it spins, it goes around the solar system, the solar system goes around the galaxy, and so on and so forth.

And the universe is expanding.

Expansion is self-expanding, accelerating.

And in fact, very recently in this year or so, even the acceleration of the universe itself is evidence that it's non-constant.

And the explanation behind why that is... It's catching up.

It's catching up.

I mean, it's still, you know, the dark matter, dark energy, this kind of thing.

Yes.

We have a model that sort of explains, that fits the data really well.

It just has a few parameters that you have to specify.

But so, you know, people say, oh, that's fudge factors.

You know, with enough fudge factors, you can explain anything.

But the mathematical point of the model is that you want to have fewer parameters in your model than data points in your observational set.

So if you have a model with 10 parameters that explains 10 observations, that is a completely useless model.

It's what's called overfitted.

But like if you have a model with two parameters and it explains a trillion observations, which is basically, so yeah, the dark matter model, I think it has like 14 parameters and it explains petabytes of data that the astronomers have.

You can think of a theory, like one way to think about a physical mathematical theory is it's a compression of the universe and a data compression.

So, you know, you have these petabytes of observations.

You'd like to compress it to a model which you can describe in five pages and specify a certain number of parameters.