How exciting it was to wake up to the news this morning that an Aussie astronomer had won the Nobel Prize for physics. Three cheers to Brian Schmidt and Australian science!
Brian Schmidt, professor of physics at the Australian National University, shares the prize with Saul Perlmutter and Adam Riess “for the discovery of the accelerating expansion of the Universe through observations of distant supernovae.”
Saul Perlmutter, Brian Schmidt and Adam Riess, winners of the 2011 Nobel Prize in physics.
This was, and still is, a mind shattering discovery for astronomy. One that I enjoy sharing with people at the Planetarium's Discover the Night Sky evenings each March and August.
The result was completely unexpected and has led to the concept of dark energy. We don’t know why the expansion of the Universe is accelerating, which is to say that it’s expanding faster now, than it was in the past. But this research puts us on the hunt for an answer and for now dark energy is just what we call it.
The journey to the Nobel Prize for these three astronomers began around 20 years ago. Saul Perlmutter was head of the Supernova Cosmology Project at Lawrence Berkeley National Laboratory, California, while Brian Schmidt headed up the High-z Supernova Search Team from Mt Stromlo Observatory, Canberra. Adam Reiss was an integral part of the High-z Supernova Search Team and based at John Hopkins University, Baltimore.
Oddly enough, the two teams were searching for the exact opposite of what they found. They were trying to measure how much the expansion of the Universe was slowing down not speeding up. The idea went like this. We know the Universe was given a big kick at the start of its life by the Big Bang. So since then everything has been expanding away from everything else. But the Universe is also filled with matter and that means gravity. Gravity works against the expansion, making objects in the Universe tug on each other.
Astronomers had counted up the mass of the Universe and found that there was just enough mass to slow down the expansion but not enough to stop it entirely. The Universe wasn’t going to end in a big crunch, but would likely drift along, forever slowing but never stopping.
That was now, but what about then? The thing about astronomy is that when you look at objects that are far away, it means you are looking into the past. By observing distant supernovae, the two teams were able to look back into the past, to measure how fast the Universe was expanding back then.
So it was assumed that gravity had been slowing things down, or in other words, the expansion of the Universe was decelerating. The HubbleSite, has a fantastic explanation of dark energy, where Adam Reiss, who analysed the data for the High-z Supernova Search Team says:
“I wrote a computer program to tell me, 'so what is the mass of the universe that is causing that much deceleration?', which I was assuming was going on. It reported that the universe had a negative mass. Now the universe can’t have a negative mass but what that really meant is ‘hey dummy you should look at the data!’ It’s not decelerating at all. It’s actually the negative of deceleration, that’s acceleration.”
Video: excerpt from Planetarium show that illustrates the expanding universe.
About 14 billion years ago the Universe began with the Big Bang. This initial expansion was slowed by matter in the Universe. However, around 7.5 billion years ago, when the Universe was half its current age, dark energy kicked in. We don't know the reason why but it makes the expansion of the Universe accelerate.
While the two teams had always had a friendly but competitive rivalry going on, they must have been thrilled to have had each other when this startling discovery first appeared. I've always loved Brian Schmidt's quote at that time which appeared in the New York Times:
"My own reaction is somewhere between amazement and horror. Amazement because I just did not expect this result and horror in knowing that it will likely be disbelieved by a majority of astronomers – who, like myself, are extremely sceptical of the unexpected.”
Each team independently came to the same fantastical conclusion. This meant that together they could convince the rightly sceptical science world that what they were seeing was correct.
Congratulations to everyone who worked on the two teams and produced this brilliant discovery. It’s your day to enjoy the time when you were amazed by the Universe.
Brian Schmidt describes the High-z Supernova Search