Sean Carroll

I had an easy question.

You threw me a softball there.

Look, you know, back in my day, when Neil and I were young, it was perfectly okay to think that maybe dark matter didn't exist.

In other words, there were absolutely things going on in galaxies and clusters of galaxies, things like that, that looked like dark matter, looked like there's more matter in a galaxy than we could attribute, account for just by counting the stars and the gas and the dust.

But maybe there was something weird going on with gravity.

You know, maybe Isaac Newton and Albert Einstein didn't have the last word.

We've long since passed that phase of the development of cosmology.

And I think a lot of people haven't caught up because we've learned so much more from the leftover radiation from the Big Bang, the cosmic microwave background, from gravitational lensing with clusters of galaxies, from the growth of structure of galaxies and clusters and things like that.

Dark matter exists.

It's really there in some form or another.

Now, maybe gravity is also modified.

That's perfectly okay.

But yeah, there's something called dark matter.

Is it a particle?

Well, we got to admit we don't know what it is.

The range of possibilities goes from, you know, some tiny fraction of the mass of an electron to the mass of the moon or something like that, right?

I mean, there's a very, very large range of possible masses that dark matter could have if it's a particle.

Could it be something beyond a particle?

It always could be like this.

Anything is possible.