Nobel Prize Goes to Germantown Friends Alum Who Discovered the Universe’s Expansion is Accelerating

Being a science reporter is like getting private lessons in science. I often tell people I learned ten times as much in the five years I covered physics and cosmology for Science than I ever learned taking courses in college.

One of the scientists who spent hours helping me understand big bang cosmology was Saul Perlmutter of U.C. Berkeley and the Lawrence Berkeley Laboratory, though, ironically, he subsequently turned the field upside.  He led one of two teams of astronomers that independently discovered our universe was not only expanding but accelerating. They announced their findings in 1998.

Perlmutter, who attended Germantown Friends School, was awarded the Nobel Prize in physics today, along with two other astronomers, Adam Riess and Brian Schmidt.

There’s a nice write-up on Perlmutter here at

Back in the 1990s, scientists had plenty of evidence that the universe was expanding, but they didn’t know whether it would expand forever or turn around and collapse. They favored a theory that had the universe right on the edge, expanding but every more slowly. There were also questions about the age of the universe, with estimates ranging from 8 to 16 billion years.

Perlmutter and the other Nobel winners both tried chart the universe’s expansion using what they call “standard candles” – astronomical bodies of known brightness. For this, they used a certain type of supernova. Like flashlights of known wattage, these exploding stars were supposed to have the same intrinsic brightness, so the astronomers could measure their distances by how bright they appeared.

They could also measure how fast they were moving away from us through the way their light was distorted or “red-shifted”.

Perlumutter and the other Nobel winners commissioned telescopes around the world to observe supernovae in galaxies millions of light years away.

What they found was something nobody had predicted – the expansion of the universe was accelerating, rather than slowing down. To explain that, physicists have proposed something called dark energy, which could be driving the acceleration.  

I’ll have more on the ways cosmologists are explaining the cosmic acceleration in a future post, and my colleague Tom Avril is writing a story about the initial discovery and Perlmutter’s years here in Philadelphia.