The Nobel Prize in physics has been awarded to a group of astronomers whose research revealed that the universe is expanding at an increasing rate.
The Nobel Prize in Physics 2011 was awarded “for the discovery of the accelerating expansion of the Universe through observations of distant supernovae” with one half to Saul Perlmutter and the other half jointly to Brian P. Schmidt and Adam G. Riess.
The trio of astronomers’ key discovery lay in the observation of light from distant supernovae. In 1998, two teams one lead by Perlmutter and the other by Schmidt (with Reiss), announced that the light from these stars was fading. The finding indicated that – contrary to theories at the time – the universe was accelerating in its expansion, rather than slowing down.
The Canadian, UK and Australian Science Media Centres have collect the following commentary from the recipients and and notable physicists.
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Dr. Adam Reiss, Johns Hopkins University, winner (along with Brian Schmidt and Saul Perlmutter) of the 2011 Nobel Prize in Physics for the discovery that the expansion of the universe is accelerating (from teleconference):
“Brian and I were grad students together – I was from 1992 -1996. We were working on how to measure distant supernovae, and at the same time find more distant supernovae and find the expansion rate of the universe. We expected it was slowing down.
“We thought this would be an interesting experiment to do, but we didn’t know it would be this interesting.
“In 1997, I was analyzing data on what the team had found. I kept getting a funny error that wouldn’t go away.
“I asked Schmidt to check my work and he couldn’t figure it out. At some point we decided, maybe this was where the universe was, it wasn’t slowing down, it was speeding up.
“There was a team at Lawrence Berkeley getting the same signal, and then over the years it’s been confirmed by many other teams.
“I want to draw a distinction between what the Prize is for and what it’s not for.
“The universe is accelerating. This observation doesn’t depend on why it’s accelerating. Dark energy is the biggest candidate for why, but that hasn’t been confirmed. But this observation that the universe is expanding is what the prize was awarded for.”
Professor Suzanne Cory, President of the Australian Academy of Science, said:
“On behalf of all his colleagues at the Australian Academy of Science, I offer my warmest congratulations to Brian Schmidt and his colleagues for this richly deserved accolade. This is a great day for Australian science.
“Over just a few short years in the 1990s, Brian and his American colleague Professor Adam Riess discovered through their study of exploding stars – supernovae – that the expansion of the universe is accelerating. Racing to the same discovery was Professor Saul Perlmutter in the United States, who shares the Nobel Prize with Schmidt and Riess. This discovery had a profound and immediate effect on cosmology. Previously it had been thought that the expansion of the universe was slowing, or proceeding at a steady rate. Astrophysicists say the finding that the expansion is in fact accelerating has completely altered our understanding of the universe and opened up important new fields in the study of time and dark energy.
“For his part in this astounding discovery, Brian Schmidt was made a Fellow of the Australian Academy of Science in 2008. He is an energetic and highly respected member of the Australian National University’s astronomy and astrophysics team.”
Dr Marc Duldig is President of the Australian Institute of Physics, said:
“They discovered that the Universe isn’t just expanding. The rate of expansion is increasing. Their discovery transformed astronomy. Today scientists are searching for dark energy – in part to explain their discovery.”
Prof Michael Rowan-Robinson, Professor of Astrophysics at Imperial College London, said:
“The two astrophysics teams, one led by Saul Perlmutter, the other by Brian Schmidt and Adam Riess, found evidence of the accelerated expansion of the Universe at approximately the same time using data from exploding white dwarf stars in distant galaxies.
“The signals were somewhat fainter than expected, suggesting the galaxies were further away than originally predicted. This suggested that galaxies are being pushed apart by some mysterious repulsive force, the so-called dark energy. A repulsive force acting on large scales in the universe was first proposed by Einstein in 1916, when he was trying to construct a static model of the universe. There is still no consensus among physicists on the nature of this dark energy.
“The impact of this finding on cosmology has been huge. The dominant role of dark energy in the universe has been confirmed by the WMAP mission, analysing fluctuations in the microwave background radiation left over from the earliest stages of the Big Bang.
“I have a particular interest as I was part of a group that looked for other reasons to explain how the Universe can appear to be expanding at an ever-faster rate. We were unable to undermine the findings of the two teams and it’s now momentous to see the research which indicated the existence of dark energy being rewarded so prestigiously.
“These astrophysicists’ research revolutionised our common perception of the Universe and unveiled an array of mysteries that we are still trying to fathom.”
Professor Carlos Frenk, Director of the Institute for Computational Cosmology, at Durham University, said:
“This Nobel Prize recognises one of the most unexpected and dramatic discoveries in Physics in recent decades.
“It is unexpected because it shows that the expansion of our Universe is accelerating, not decelerating as physicists thought 15 years ago.
“It is dramatic because it implies that we do not inhabit a simple, elegant Universe made only of matter but a Universe that, in addition to matter, contains a strange substance, so bizarre that we call it “dark energy”.
“We have no idea of what the dark energy revealed by the supernovae data is – unravelling its identity ranks as one the great scientific challenges of the 21st Century.”
Prof Roger Davies, President of the Royal Astronomical Society & Philip Wetton Professor of Astrophysics, Department of Physics, University of Oxford, said:
“It is wonderful to see the award of the Nobel prize in Physics to the supernova cosmology teams. This recognises a transformative discovery in astrophysics that was a huge surprise at the time. The discovery set the direction for work over the last decade or so and stimulated some of the most ambitious proposals for future space missions and ground based surveys.
“The surprise is perhaps best illustrated by the fact that before the discovery of the accelerating universe astronomers had been attempting to measure it’s deceleration hypothesised to be caused by the mass of galaxy halos slowing the universal expansion. The discovery led to the realisation that empty space exerts a pressure that pushes the galaxies apart – something that demands new physics and a new understanding of space-time.”
Lord Martin Rees, Astronomer Royal & Emeritus Professor of Cosmology and Astrophysics at the University of Cambridge, said:
“This award recognises an important and surprising discovery. Even empty space contains energy and exerts a kind of ‘antigravity’ which causes cosmic expansion to accelerate. It will be a long time before theorists understand this force — it is part of the bedrock nature of space and time. This discovery has been subsequently strengthened and corroborated by other advances: the evidence from the cosmic microwave background (especially the Boomerang and WMAP experiments) that the geometry of the universe is ‘flat’, and an accumulation of evidence from observations with large telescopes that atoms and ‘dark matter’ amount to no more than 30 percent of density needed to make it so.
“I think, however, that this is one of the increasingly frequent instances when the Nobel Committee is damagingly constrained by its tradition that a prize can’t be shared between more than three individuals. The key papers recognised by this award were authored by two groups, each containing a dozen or so scientists. It would have been fairer, and would send a less distorted message about how this kind of science is actually done, if the award had been made collectively to all members of the two groups.”
Professor Bryan Gaensler is Australian Laureate Fellow at The University of Sydney and Director of the ARC Centre of Excellence for All-sky Astrophysics (CAASTRO):
“Most science is incremental. Even the Nobel Prize often goes to what might seem to the general public to be an obscure or technical discovery. But in 2011, the Nobel Prize for Physics has recognised one of the most jaw-dropping, unexpected, craziest results in the history of science – the Universe is accelerating! The prize deservedly goes to the leaders of the teams who first measured this effect – Australia’s Brian Schmidt, and Americans Saul Perlmutter and Adam Riess.
“It’s hard to overstate the profound fundamental change that this discovery wrought on all of cosmology and discovery. In barely more than a decade, we have gone from a comfortable picture of a mainly empty, gently decelerating, Universe, to broad acceptance that we live in a bizarre cosmos, suffused with as-yet-unexplained Dark Energy, tearing itself apart as it gains speed in all directions.
“The underlying concept was simple enough – that distant supernova explosions could be used as ‘standard candles’ to measure the distance scale of the Universe. But the brilliance of Schmidt, Perlmutter and Riess was in the execution: these supernovae are rare and faint, and even just finding them right after they occur is a feat in itself. But then one needs to carefully calibrate and correct for a myriad of obfuscating and subtle effects in order to tease out the faint signal of the accelerating Universe. It is a testament to the expertise and skill of these astronomers that not only were they able to convince themselves of this weak effect to a level such that they were comfortable in publishing their work, but that after publication, the results were quickly accepted and applauded by the community rather than questioned or queried. The combination of brilliance, exquisite care and dogged determination that Schmidt, Perlmutter, Riess and their teams applied to their work has been rewarded by a Nobel Prize.
“Beyond the celebration of these three Laureates, special acknowledgement must also go to Professor Robert Kirshner of Harvard University. Bob Kirshner was the PhD advisor and mentor for both Schmidt and Riess, and was very much the initial inspiration and motivation behind the team’s search for the supernovae that led to this momentous discovery. The Nobel limit of three Laureates per year means some tough calls inevitably need to be made. Kirshner’s key contribution and involvement in this work should not be overlooked.
“Australia has much to celebrate by the award going to our own Brian Schmidt. Media reports might claim Schmidt as an ‘American-Australian’ or an ‘adopted Australian’, but make no mistake: despite his Montanan/Alaskan twang, Schmidt is an Australian scientist who did his Nobel-prize work in Australia, and is still very much an active researcher, leader and mentor within Australian astronomy. Beyond his outstanding research record as recognised by the Nobel committee today, what sets Brian apart is his unstinting commitment to Australian science – he is extraordinarily generous with his time for students, public events, review panels and committees; he often takes sides in debates that are to the detriment of his own interests but represent what’s best for the community; and he has even funded research activities at ANU out of his own personal funds when no other money was available. A devoted family man, a talented viniculturist, a good friend to many within Australian astronomy, and now a Nobel Laureate – congratulations to Brian Schmidt!”
Declaration of conflict of interest: Brian Schmidt and Bryan Gaensler are collaborators within the ARC Centre of Excellence for All-sky Astrophysics (CAASTRO)
Dr Mark Sullivan, Department of Physics, University of Oxford, said:
“I think this is fantastic news, and thoroughly well-deserved. Their direct discovery of the accelerating universe in the late 1990s, using distant cosmic explosions known as supernovae, has rewritten textbooks, and was one of the landmark breakthroughs of 20th Century physics. The nature of the dark energy that propels this accelerating universe remains a mystery, preoccupying physicists ever since, and is at the forefront of modern astrophysical research – it’s the motivation for many ongoing, and future, ground and space-based experiments.”
Professor Sir Peter Knight, President of the Institute of Physics, said,
“The recipients of today’s award are at the frontier of modern astrophysics and have triggered an enormous amount of research on dark energy. These researchers have opened our eyes to the true nature of our Universe. They are very well-deserved recipients.”
Dr. Ray Carlberg, Professor of Astronomy at the University Of Toronto and Fellow of the Royal Society of Canada. (not yet confirmed)
What exactly did the two teams who were awarded the Nobel Prize discover?
“They discovered that the expansion of the universe – against every expectation that gravitational pull would gradually slow the expansion, and to the huge surprise of everyone – that the expansion of the universe is speeding up.
“They did this in some beautifully simple but powerful experiments where they looked at supernova and built upon the work of others, showing that if you could measure the brightness accurately – then you could tell how far away it was.
“What the Nobel winners had found was truly astonishing. Beforehand, there were some people who were looking at distant supernova and said that it didn’t look like the acceleration was expanding.
“Then analysis improved. There were two groups … who discovered that at a given expansion speed, which was seen by the redshift of the light, the supernovae were dimmer than expected. They knew if there was some error they might be brighter than expected, but they were dimmer. So expansion was accelerating.
“I know these guys quite well. One fellow is Saul Perlmutter at the Lawrence Berkeley lab in California, which is basically a physics lab. At about that time, they started getting bigger imagers, bigger cameras they were putting on telescopes that meant you could point it at the sky and get a big enough picture you were basically sure you would get supernovae.
“The group Adam Reiss and Brian Schmidt were involved with was based at Harvard, and they were basically students at the time. Now they made observations from an astronomy standpoint, and Saul was physics, so they made slightly different measurements. The brightness of a supernova rises and falls a bit, and so they had to find the peak brightness. Each team developed different techniques to find the peak brightness, and these 2 individual teams – one California-based and one Harvard-based – converged on the answer together, which is really great, to have two different approaches.
How does your work fit into this?
“This accelerating expansion was confirmed by a group I helped to create. I was working with the Canada-France collaboration, the Supernova Legacy Survey. Our work wasn’t just to confirm their measurements, but to take the next step and to measure the properties of what’s speeding up the expansion. The word that’s been coined to describe it is ‘dark energy’. We don’t know anything about it, but at least it’s some words we can use to describe what we are measuring.
“What we found was that dark energy was consistent with an idea that Einstein had called the cosmological constant.
“We had big new cameras installed on the Canada-France telescope in Hawaii – which is jointly operated by Canada and France with Hawaii as a partner. And we did a series of systematic pictures of the sky. The discovery of accelerated expansion was in 1999, and in 2000 a group of us said, the next thing is to find out about ‘dark energy’, that’s driving the acceleration. The program was approved, and scientists around the world including some in California and Europe joined us to do follow-up observations. They realized we were building a superb database of supernova measurements, and we published a paper in 2006, and presented our final results. It’s the best measurement of ‘dark energy’.
How does this relate to Einstein’s cosmological constant?
“Einstein developed the general theory of relativity, which is a theory of gravity. He did that around 1912 or so. He realized you could apply it to the whole universe, so he did, and discovered the universe had to be either expanding or contracting. So he asked his astronomer friends which one it was, and they said, as far as we know, the stars are just moving around, they aren’t expanding or contracting.
“At that time, we didn’t know anything about galaxies, what they were looking at was just the Milky Way galaxy. Then Edwin Hubble in California started looking at distant galaxies, and discovered they were moving away. So he discovered the expansion of the universe.
“But Einstein, in order to make the universe neither expanding nor contracting, put in a ‘cosmological constant’ in the equations. Then it was pointed out by some folks that the cosmological constant didn’t actually fix the problem, you could have a balance for a while, but in the end the universe had to start expanding or contracting. At that point, Einstein said, well, darn, I shouldn’t have put that in.
“But there’s a saying in physics that anything that’s not disallowed will happen. And the cosmological constant wasn’t disallowed, it seemed to exist in nature, and it seems to exist as ‘dark energy’.”
“All scientists bow down before Einstein, he was our greatest thinker. What he called his ‘greatest blunder’ was probably his greatest prediction.”