Friday, March 16, 2018

Stephen Hawking 1942-2018

I met Stephen Hawking a few times over the years -- the most memorable was in the early 1980s when I was a grad student at the University of Chicago. Stephen was visiting the university, but he also wanted to take a side trip out to Fermilab -- a one-hour drive outside of Chicago. This being the days before GPS (back when we had to navigate by the stars) I was assigned by my Ph.D. adviser to ride along with Stephen and his driver and direct them to Fermilab.

I showed up at the hotel in Hyde Park at the appointed hour and went to the lobby, but Stephen was nowhere to be seen. What to do? Had this been an ordinary theoretical physicist, I would simply have asked the hotel clerk to phone his room. But this was Stephen Hawking -- one does not simply go and knock on his door. So I just waited in the lobby, assuming that Stephen would make his appearance when he wished. After quite a bit of time had passed, Stephen's assistant/driver popped into the lobby and asked, "Why didn't you call up to our room? We've been waiting up there for you!"

Meanwhile (I learned later) one of the senior scientists in the astrophysics group at Fermilab was pacing back and forth, muttering that if anything happened to Hawking, he would "send Scherrer to Tuscaloosa" -- presumably a form of internal exile. But Stephen Hawking, his driver, and I finally did make it out to Fermilab (late) and all was forgiven.

Many years later, I finally got a chance to visit Tuscaloosa to speak at the University of Alabama. It's really a very nice town.

Friday, March 9, 2018

Was the Early Universe Lumpy?

When the universe was only a few minutes old, was it smooth, like Cream of Wheat (yum!), or was it lumpy, like oatmeal? (Yuk!)  British cosmologist John Barrow and I explored this question in this paper, posted yesterday. Most cosmologists think that the matter in the early universe was smooth, not lumpy, and there's no compelling reason to believe otherwise, but it's always important to look at alternatives.

How can we even say anything intelligent about the universe when it was only a few minutes old? Our best probe is the production of elements in the early universe, which goes under the tongue-twisting name of "primordial nucleosynthesis." Most of the atomic nuclei on Earth were made in stars, but a small number, including helium, deuterium, and lithium, were manufactured in the first few minutes of the universe. And the amount of each element produced is exquisitely sensitive to the density of protons and neutrons when the universe was just a few minutes old. If the universe were lumpy rather than smooth, then the element abundances would fluctuate up and down in a predictable way, and we can average these out to get a prediction for what we would see today.