Wendy Freedman

Well, I think astronomy is different than physics.

Astrophysics is different than physics.

We don't have a laboratory where we can go in and we can work with the equipment and we understand the equipment and do tests that we set.

We're working with these stars that are far away that have metals in their atmospheres, pulsating stars, exploding stars.

If we look at the supernovae,

We don't understand yet, although there's some interesting hints that maybe we understand one of the mechanisms for exploding supernovae.

But there's scatter in the relation for supernovae.

And the supernova magnitude, supernova luminosity depends on

the color of the star, how fast the supernova, how fast it's declining, the mass of the galaxy, which, you know, truly has nothing to do with the supernova itself.

It's a proxy for something else.

And then there's additional leftover scatter.

And different groups have different calibrations of the supernovae.

And so when we're comparing our local observations with the cosmic microwave background, where it's clean and what is referred to as linear physics,

And there are different groups that are getting the same answers.

And with a precision, again, of better than 1%.

The onus is on us, I believe, locally to really show that we have overcome the systematics in using these stars.

The Hubble constant refers to a Hubble parameter at the current time, T equals zero, H zero.

And actually, the Hubble parameter, the parameter that describes, governs the evolution of the universe, changes with redshift or with time.

Yeah, it's confusing.

It is the value of the Hubble parameter at the current time.