LONDON – The sighting came from a small telescope on the roof of a laboratory sitting on the ice sheet three-quarters of a mile (1.3 kilometers) from the geographic South Pole.
First came the rumors. But then researchers at the Harvard-Smithsonian Center for Astrophysics went public.
Their telescope had spotted indirect evidence of gravitational waves, or ripples in space-time, from the earliest moments of the universe.
The scientists have not yet published their work, and no other team has confirmed the finding. Yet even without these mainstays of scientific rigor, excitement has swept through the community and into the world beyond.
If confirmed, the observation will rank among the greatest scientific discoveries of the past 20 years — and a Nobel Prize is all but guaranteed.
Einstein predicted gravitational waves in his 1916 theory of general relativity. His equations married space and time, and showed how the product, space-time, is warped by matter and energy, giving rise to the force of gravity.
Gravitational waves are tremors in space-time caused by intense gravitational forces. The Harvard team found evidence for primordial gravitational waves — those set in motion during the first trillionth of a second of the universe.
Primordial gravitational waves are seen as the smoking gun for a theory called cosmic inflation. Conceived in its original form more than 30 years ago by Alan Guth at the Massachusetts Institute of Technology, inflation says that the early universe experienced a terrific burst of expansion. The growth spurt lasted a mere fraction of a second but smoothed out irregularities in space and made the cosmos look almost the same in every direction.
The violent expansion had another effect, too. It amplified primordial gravitational waves, making them large enough for researchers to detect. Without inflation, the effects of these ripples in space-time would be too minuscule for today’s technology to spot.
Telescopes cannot see gravity, but they can see the effects of it. What the Harvard team spotted was the telltale signature that primordial gravitational waves imprinted on the faint light left over from the big bang. This ancient afterglow fills the universe, and is known as the cosmic microwave background.
Because gravitational waves squeeze space as they propagate, they make some patches slightly warmer than others. These warm spots polarize light waves that pass through, meaning the light waves vibrate in one direction more than others. In this case, the vibrations of light waves from the big bang are twisted, producing the distinctive pattern detected by Harvard’s Background Imaging of Cosmic Extragalactic Polarization telescope (BICEP2).
Here are some comments from a number of experts.
Paul Davies, physicist
When I was a student in London in the late 1960s, I attended a lecture on the early universe. The professor told us that the broad chemical makeup of the universe could be explained in terms of nuclear reactions that occurred in the first three minutes following the big bang. Everyone in the audience burst out laughing. It seemed utterly preposterous to claim that basic physics could be applied to the first few minutes of cosmic existence.
What a difference a generation makes!
Today we think nothing of using the first split second of the universe as a testing ground for fundamental physics. Yet I am still astonished that such a simple idea as inflation can account so well for the main features of the universe, and that we can push back our understanding of the cosmic birth to within a whisker of its murky beginnings.
By unveiling the role of gravitational waves in the primeval maelstrom, these results provide us with the first tantalizing glimpse of the cosmic birth pangs through an entirely new window on the universe. Gravitational wave astronomy has long been a dream for cosmologists. We now know these waves are out there, and encode priceless cosmic information unavailable to optical, radio or any other form of electromagnetic astronomy. Expect a boost for the decades-old program of perfecting Earth-based gravitational wave detectors.
Maybe in another generation we will be able to answer even more basic questions about the universe, such as whether the big bang was the ultimate origin of all physical existence, including space and time, or whether our universe, vast though it may be, is but an infinitesimal fragment of a stupendously larger ensemble of universes with no beginning or end.
Martin Rees, astronomer royal (a senior post in the U.K. royal household)
This is indeed an exciting result. It suggests that we really can infer what happened at 10 to the minus 36 seconds — when the universe was squeezed smaller than a tennis ball. And the polarization is big enough that the ESA Planck spacecraft will have it in the all-sky database that they’re analyzing and should be able to check it.
It is not a direct detection of gravitational waves (in the sense of measuring a “ripple” in space). It is an indirect detection. But inferences on the existence and strength of primordial gravitational waves are very important for cosmology and our understanding of the ultra-early universe.
The “inflation” theory suggests that the fluctuations that are seen in the background radiation, and which are the “seeds” for galaxy formation, are generated by quantum irregularities when the universe was expanding on a time scale of 10-36 seconds and the entire observable universe was smaller than a tennis ball.
But two distinct types of fluctuation could be generated in the very early universe — waves of density and gravitational waves. The relative amplitude of these two kinds of waves is a very important diagnostic of the physics of the inflationary era.
These waves both contribute to the variations in temperature observed in the background radiation (energy carrying information about the universe when it was roughly 300,000 years old). But these waves not only perturb the temperature, they also induce polarization in the microwave radiation.
And it has been realized for a long time that if the polarization could be measured, and correlated with the variations in temperature, it would be possible to separate out the contributions of the two types of wave.
But Planck wasn’t optimized for polarization measurements, and the best measurements have so far come from a succession of South Pole experiments — this one is the best so far. And what it’s detected is a large enough effect that it can indeed be followed up by Planck. It rules out some versions of “inflation” and really narrows down the options. It makes us hopeful that we will soon have more clues to the physics of this extreme era.
Ben Miller, actor and science author
Your whole world is wobbling. Every time something accelerates, it creates a ripple in the very fabric of the universe. That supernova on the far side of the galaxy, that pair of neutron stars orbiting one another in deep space, the tennis ball in the men’s final at Wimbledon — all of them create gravitational waves. Those waves spread out through the cosmos, stretching and compressing space and time like the ripples on a pond. Eventually, they will pass through you, and your space and time will wobble. Only a bit, of course. You will shrink and stretch in height, but imperceptibly. Your watch will run fast and slow, but by such a minute amount as to be unnoticeable. And then the wave will pass, and your space and your time will be still again.
At least, that was the conclusion of Albert Einstein. His general theory of relativity tells us that in most cases, the wobbling of space and time caused by gravitational waves will be so small as to be undetectable. To see the effects, you need to accelerate something really big. And the universe is pretty big. Just after the big bang, it had a rapid expansion, faster than the speed of light. And when you accelerate something as big as the universe as much as that, you are going to get some pretty big gravitational waves. It’s the aftereffects of these waves that BICEP2 has detected.
That’s the beauty of this discovery. If it turns out to be correct, it provides valuable evidence for two things. First, that gravitational waves really do exist. And second, that the universe we live in is a bubble that was born in an extremely rapid expansion just after the big bang. The rapid expansion produced gravitational waves, and those waves left an imprint on the first light.
So not only was Einstein right again, and accelerating objects produce gravitational waves, but even more incredibly, the thing we thought was the be-all-and-end-all, our universe, is just one tiny corner of creation. There’s a beautiful circularity to that. Once we believed that the Earth stood at the center of the cosmos. Copernicus then convinced us the Earth orbited the sun. Einstein showed us that there was no such thing as a center at all; what counts is relative motion. And now, the “smoking gun” of gravitational waves, imprinted in the primordial light of the universe, shows us that even the universe isn’t special. It’s just the place you happen to be reading this article.
Albert Zijlstra, director of Jodrell Bank Observatory, northwest England
This is an exciting announcement. The signal they have detected carries information about the earliest origin of the universe, and, in a way, opens up a new window on a hidden phase in the formation of the universe.
Several groups are currently trying to detect this signal. It is a very difficult experiment and is technically very well done. I congratulate them on the achievement.
To make full use of this signal will probably require a space satellite mission. There are limits to what can be done from the ground. The detection makes it more likely that such a space mission, by the ESA or by NASA, will eventually take place.
Some caution is still warranted. The result is preliminary, and the team has taken short cuts in the analysis, which they will have to fix before the results can be published. We will have to wait a bit longer to see whether their final result will change from what was announced last week. The detection seems fairly solid, but the nature of the detection could still change.
Jocelyn Bell, Burnell astrophysicist
This should be viewed as a provisional result — it has not yet been sent to a professional journal for publication, it has not been peer-reviewed, and it needs independent confirmation. Confirmation may well come from the Planck satellite data, possibly later this year, and its data is likely to be better in quantity and quality (and much more expensive!).
If this result is true, then it is another indirect confirmation of the existence of gravitational radiation (the first was 40 years ago from pulsar data). And it would be confirmation that what astronomers call “inflation” took place; this was a period of exceptionally fast expansion of space, over and above the big bang expansion, that took place in the early universe. So it would be reassurance that our current understanding is broadly correct.
However, this is very difficult data to work with. Extracting the signal is analogous to cleaning an old, dirty painting to better reveal the original underneath; one can over-clean (or under-clean). Here, the “picture underneath” is even more heavily obscured by unwanted effects, and removing them correctly is very tricky. I see this announcement as a place holder, and wait for independent confirmation.
Jim Al-Khalili, physicist and broadcaster
Although the BICEP2 results have yet to be reviewed and published, all indications are that this is a careful and thorough piece of research. Of course the results need to be verified and reproduced elsewhere, since “extraordinary claims require extraordinary evidence,” but I still believe this is a hugely significant — and possibly Nobel Prize-worthy — discovery.
BICEP2 detects the cosmic microwave background: the weak electromagnetic radiation pervading all space. This is the afterglow of the big bang, and it has been washing through the universe ever since. It seems the detected radiation carries within it the imprint of ripples in space-time known as primordial gravitational waves, which are the tremors of the creation of the universe itself.
Probably of more interest is what these results tell us about inflation theory, which suggests that within a tiny fraction of a second after it came into being, the universe underwent a period of exponential expansion, driven by a still mysterious dark energy that initiated the hot big bang and provided all the “stuff” of the universe, including the stars, planets and us.
These results provide strong support for inflation theory, and will allow us to work out how much dark energy drove inflation and just how hot the big bang was. It’s all very exciting.
Maggie Aderin-Pocock, space scientist and broadcaster
I love the scientific method: pose a question, do some research, create a theory, gather data/experiment to test the theory, draw conclusions and share the results. One hundred years ago Einstein came up with a theory describing gravitational interactions called general relativity. It predicted a number of phenomena but the one still outstanding was the detection of gravitational waves, ripples in the curvature of space-time. The BICEP2 experiment seems to have found an imprint of the primordial gravitation waves created in the very, very early universe.
The fact that these waves have been found could lead to the verification of another theory produced by Alan Guth in 1980. This theory predicted the rapid expansion of the early universe, termed “cosmic inflation,” a bit of fudge to explain early events after the big bang. One of the predictions of the theory was the generation of gravitational waves, with a distinctive signature. It seems that BICEP2 may have found the echoes of these waves.
Pending independent verification, if these results are found to be correct, work in cosmology continues apace. Converging on a grand unified theory of everything is still the holy grail, where we can understand the interaction of the universe at the subatomic, quantum mechanics scale as well as gravitational interactions that happen on a cosmic scale, all in a common framework.
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