Sean Carroll

But boy, it really acts like particle like like we know a lot about where the dark matter is, how much of it there is, how fast it's moving.

It looks exactly like some massive, slowly moving particle that was sort of still stationary in the early universe and started moving ever since then.

So it's our job to go actually find it.

Then we'll know.

No, I think that's a perfectly good and fair distinction.

But I think that I would just be more conclusive about what we do know.

You know, like I said.

And you sounded very good there.

You sounded really good.

In the 80s, what we were discovering was there's more gravity at the edges of galaxies than there is that you would predict from the stars, et cetera, inside.

So, OK, maybe gravity is different.

But nowadays we see gravity where there is no ordinary matter to cause it.

So it's not just that the strength of gravity is different, but it's just pointing at something which we're not seeing.

So that's dark matter.

It is not sufficient to explain dark matter.

We need extra stuff out there.

And just to be super duper clear, because again, much like the notorious delayed choice quantum eraser experiments, sometimes people like...

to make things harder to understand rather than easier to understand.

There are people who have theories of modified gravity where they've changed Einstein's theory of gravity and they say, I can explain away the dark matter.

But when you look at their theory of gravity, in addition to changing gravity, they've also put new sources of gravity in there, which are just dark matter.