Wendy Freedman

There's a Hubble constant.

There are Hubble galaxies and different qualities in classification and so on.

And everything rests on the PL relation.

Well, it's signaling a discrepancy.

between what we're measuring locally when we use these stars like Cepheids or red giant stars and supernovae to measure the Hubble constant, the current expansion rate today.

And when we compare that method with what you infer from the cosmic microwave background, the background radiation from the Big Bang,

you can measure these very small fluctuations in the temperature and also the polarization of the background radiation and fit those with the spectrum with what we call the standard cosmological model.

And that's been now in place for a quarter of a century.

And when you do that, this is a predictive model.

It tells you how the universe will evolve.

And it tells you that the expansion rate today would have a value of 67%.

with a very small uncertainty of less than 1%.

And when we use Cepheids with HST, we get values more like 73.

And so that's a rather small difference compared to 50 and 100 where we started off.

I think it would have been appropriate to relax a little bit and have at least a day to celebrate closer.

And, you know, there are always crises in cosmology.

And I think.

It was a very rare time around 2001, 2003.

So our HST key project results came out in 2001.

We got a value of 72 with an uncertainty of 10%.