Image copyright PAImage captionWeiss (L) takes half the prize; Thorne (C) and Barish (R) share the other half
The 2017 Nobel prize in physics has been awarded to three US scientists for the detection of gravitational waves.
Rainer Weiss, Kip Thorne and Barry Barish will share the nine million kronor (£831,000) prize.
The ripples were predicted by Albert Einstein and are a fundamental consequence of his General Theory of Relativity.
The winners are members of the Ligo-Virgo observatories, which were responsible for the breakthrough.
The winners join a prestigious list of 204 other Physics laureates recognised since 1901.
Prof Weiss gets half of the prize money, while Barish and Thorne will share the other half.
Gravitational waves describe the stretching and squeezing of space-time that occurs when massive objects accelerate.
The warping of space resulting from the merger of two black holes was initially picked up by the US Ligo laboratory in 2015 – the culmination of a decades-long quest.
Three more examples have been detected since then.
Gravitational waves – Ripples in the fabric of space-time
Image copyrightIGO/CALTECH/MIT/SONOMA STATEImage captionArtwork: Two coalescing black holes spinning in a non-aligned fashion
Gravitational waves are a prediction of the Theory of General Relativity
It took decades to develop the technology to directly detect them
They are ripples in the fabric of space-time generated by violent events
Accelerating masses will produce waves that propagate at the speed of light
Detectable sources ought to include merging black holes and neutron stars
Ligo/Virgo fire lasers into long, L-shaped tunnels; the waves disturb the light
Detecting the waves opens up the Universe to completely new investigations
Speaking at a press conference, Olga Botner, from the Royal Swedish Academy of Sciences, said: “The first ever observation of a gravitational wave was a milestone – a window on the Universe.”
The US Ligo and European Virgo laboratories were built to detect the very subtle signal produced by these waves.
Even though they are produced by colossal phenomena, such as black holes merging, Einstein himself thought the effect might simply be too small to register by technology.
But the three new laureates led the development of a laser-based system that could reach the sensitivity required to bag a detection.
The result was Ligo, a pair of widely separated facilities in North America: one observatory is based in Washington State, while the other is in Livingston, Louisiana.
The European side of the gravitational wave collaboration is based in Pisa, Italy. On 14 August this year, just after coming online, it sensed the most recent of the four gravitational wave events.
Speaking over the phone at the Nobel announcement in Stockholm, Rainer Weiss said the discovery was the work of about 1,000 people.
He explained: “It’s a dedicated effort that’s been going on for – I hate to tell you – it’s as long as 40 years, of people thinking about this, trying to make a detection and sometimes failing in the early days, then slowly but surely getting the technology together to do it. It’s very, very exciting that it worked out in the end.”
Nonetheless, the Nobel trio’s contribution is also regarded as fundamental.
Weiss set out the strategy that would be needed to make a detection.
Thorne did much of the theoretical work that underpinned the quest.
And Barish, who took over as the second director of Ligo in 1994, is credited with driving through organisational reforms and technology choices that would ultimately prove pivotal in the mission’s success.
Image copyrightS.OSSOKINE/A.BUONANNO (MPI GRAVITATIONAL PHYSICS)Image captionA computer simulation of gravitational waves radiating from two merging black holes
The Astronomer Royal, Sir Martin Rees, said the three leaders honoured by the Nobel Committee were “outstanding individuals whose contributions were distinctive and complementary”.
But he added: “Of course, Ligo’s success was owed to literally hundreds of dedicated scientists and engineers. The fact that the Nobel committee refuses to make group awards is causing them increasingly frequent problems – and giving a misleading and unfair impression of how a lot of science is actually done.”
Many commentators had gravitational waves down as a dead cert to win last year, but the Nobel committee has always been fiercely independent in its choices and has made everyone wait 12 months.
Had the prize been awarded last year, it is very likely that the Scottish physicist Ron Drever would have shared it with Weiss and Thorne.
The trio won all the big science prizes – apart from the Nobel – in the immediate aftermath of the first detection in 2015.
The Scotsman developed some of the early laser systems at Glasgow University before taking this knowledge to Caltech in California, which manages the Washington State Ligo facility.
Glasgow remains the UK hub for the big British contribution to Ligo. Its Institute for Gravitational Research designed and built the suspension system that holds the ultra-still mirrors used in the US and Italian labs.
Catherine O’Riordan, interim co-chief executive of the American Institute of Physics (AIP), said: “Weiss, Barish and Thorne led us to the first detection of gravitational waves and laid the foundation for the new and exciting era we officially entered on September 14, 2015 – the era of gravity wave astronomy.”
This is actually the second Nobel prize to involve gravitational waves. In 1993, Americans Russell Alan Hulse and Joseph Hooton Taylor were awarded the physics prize for work that provided indirect evidence for the warping of space.
A NASA camera on the Deep Space Climate Observatory satellite captured its first view of the entire sunlit side of the spherical planet Earth, on July 6, 2015.
Credit: NASA
The amount of carbon dioxide that humans will have released into the atmosphere by 2100 may be enough to trigger a sixth mass extinction, a new study suggests.
The huge spike in CO2 levels over the past century may put the world dangerously close to a “threshold of catastrophe,” after which environmental instability and mass die-offs become inevitable, the new mathematical analysis finds.
Even if a mass extinction is in the cards, however, it likely wouldn’t be evident immediately. Rather, the process could take 10,000 years to play out, said study co-author Daniel Rothman, a geophysicist at the Massachusetts Institute of Technology. [7 Iconic Animals Humans Are Driving to Extinction]
However, slashing carbon emissions dramatically in the coming years may also be enough to prevent such global catastrophe, said Lee Kump, a geoscientist at Pennsylvania State University who was not involved in the study.
Carbon and death
Over Earth’s 4.5-billion-year history, life has seen a lot of boom and bust times. In the past half-billion years alone, five major extinctions have wiped out huge swaths of life: the Ordovician-Silurian mass extinction, the Late Devonian mass extinction, the Permian mass extinction, the Triassic-Jurassic mass extinction and the Cretaceous-Tertiary mass extinction that wiped out the dinosaurs. The most severe was the Permian extinction, or “The Great Dying,” when over 95 percent of marine life and 70 percent of land-based life died off.
All these major extinctions have one similarity.
“Every time there’s been a major mass extinction — one of the big five — there’s been a serious disruption of the global carbon cycle,” Rothman said. It could be a direct link between CO2 and death due ocean acidification or an indirect link, as carbon dioxide emissions can warm a planet to unlivable temperatures and have even been linked with volcanic eruptions and the related cooling of the atmosphere.
For instance, at the end of the Permian period, about 252 million years ago, ocean carbon dioxide levels skyrocketed, marine rocks reveal. (Carbon dioxide that is in the air gradually dissolves into the ocean’s surface and eventually enters the deep ocean.) However, carbon doesn’t always equal assured doom for the planet. It’s possible that a change in carbon levels in the atmosphere and oceans are markers for rapid environmental change, which could be the underlying cause of extinctions. In addition, rocks from the past reveal many other “carbon excursions” — or rises in atmospheric or ocean levels of carbon — that did not result in mass extinctions, Rothman said. [Ocean Acidification: The Other Carbon Dioxide Threat]
Fast time and slow time
So what distinguishes the deadly carbon excursions from the ones that don’t cause mass dying?
In the new study, which was published Sept. 20 in the journal Science Advances, the scientists assumed that two factors may play a role: the rate at which carbon levels increase, and the total amount of time that change is sustained, Rothman said.
To calculate those values, Rothman looked at data on carbon isotopes, or versions of the element with differing numbers of neutrons, from rock samples from 31 geologic periods over the past 540 million years. Determining the length and magnitude of rises in atmospheric carbon can be tricky because some periods have thorough rock samples while others are sparsely represented, Rothman said.
From that data, Rothman and his colleagues identified the rates of carbon change and total carbon input that seemed to be correlated to extinctions in the geologic record. Then, they extrapolated to the present day, in which humans are adding carbon to the atmosphere at a furious rate.
Rothman calculated that adding about 310 gigatons of carbon to the oceans was enough to trigger mass extinctions in the past, although there is huge uncertainty in that number, Rothman said.
“Most every scenario that’s been studied for how things will play out, as far as emissions are concerned, suggest on the order of 300 gigatons or more of carbon will be added to the oceans before the end of the century,” Rothman said.
What happens the day after that threshold is reached?
“We run the risk of a series of positive feedbacks in which mass extinction could conceivably be the result,” Rothman said.
Of course, those effects wouldn’t be felt immediately; it could take 10,000 years for the die-off to result. And there’s a lot of uncertainty in the estimates, Rothman added.
“I think it’s a really useful approach, but there are always limitations when we’re working in deep time,” Kump told Live Science. “One of the limitations is that Rothman had to accept the state of our understanding of the timing and duration of these disturbances.”
But even with that uncertainty, “clearly the rate of fossil fuel burning today rivals, if not exceeds, the rate of carbon cycle perturbation in the past” associated with mass extinctions, Kump said.
Because the rate of carbon rise is so steep currently, the best option for preventing eventual catastrophe is to ensure the duration of the carbon increase is short, he said.
“If we can rein ourselves in, we can avoid the Permian catastrophe,” Kump said.
