At a telescope at the south pole, scientists have been gathering information for the last few years. They have been studying the oldest light we can see, from the surface of last scattering: the Cosmic Microwave Background. And what they have found is absolutely stunning. The light shows polarization that provides evidence for gravity waves, rapid inflation of the early universe, and perhaps even the existence of gravitons.
How big is this? Really, really big.
From their press release:
First Direct Evidence of Cosmic Inflation
Almost 14 billion years ago, the universe we inhabit burst into existence in an extraordinary event that initiated the Big Bang. In the first fleeting fraction of a second, the universe expanded exponentially, stretching far beyond the view of our best telescopes. All this, of course, was just theory.
Researchers from the BICEP2 collaboration today announced the first direct evidence for this cosmic inflation. Their data also represent the first images of gravitational waves, or ripples in space-time. These waves have been described as the "first tremors of the Big Bang."
Since the cosmic microwave background is a form of light, it exhibits all the properties of light, including polarization. ...
"Our team hunted for a special type of polarization called 'B-modes,' which represents a twisting or 'curl' pattern in the polarized orientations of the ancient light," said co-leader Jamie Bock (Caltech/JPL).
Gravitational waves squeeze space as they travel, and this squeezing produces a distinct pattern in the cosmic microwave background. Gravitational waves have a "handedness," much like light waves, and can have left- and right-handed polarizations.
"The swirly B-mode pattern is a unique signature of gravitational waves because of their handedness. This is the first direct image of gravitational waves across the primordial sky," said co-leader Chao-Lin Kuo (Stanford/SLAC).
The Cosmic Background
Almost fourteen billion years ago, what we now know as the entire observable universe was in a space smaller than an atom. 10-37 seconds later — an almost immeasurable fraction of a second — space expanded to essentially the size it is today, in the blink of an eye. That's what scientists believe, and please understand this: it is nothing like an explosion. It was an incredibly rapid expansion of space itself, something cosmologists call "inflation".
But up until now, we didn't have direct evidence of inflation. It was inferred from the regularity, the smoothness of the cosmic microwave background (CMB). It is so smooth, its density only varies by about 1 part in 100,000. What is the background?
Just after inflation, space was filled with a hot plasma of particles and energy. It was so hot, atoms couldn't form, and so electrons and atomic nuclei were all floating around free. There was so much energy, if some enterprising hydrogen atom had tried to capture an electron, powerful photons would have immediately hit it with more than enough energy to rip that electron away from it again. As a result, space was filled with charged particles, and light couldn't travel freely.
The universe slowly cooled, and 380,000 years later it became cool enough for atoms to form, and so it became basically electrically neutral, and transparent to light. The light that was emitted then has been traveling every since. That moment, when the universe became transparent, is what is called the "surface of last scattering", and the light from it can be seen in every direction in the sky. It wasn't originally microwaves; it started out a lot hotter. But it has gradually cooled until it is only a fraction of a degree above absolute zero.
The South Pole
The BICEP (Background Imaging of Cosmic Extragalactic Polarization) experiment was designed to measure the polarization of the cosmic background. The telescope was placed at the Amundsen-Scott South Pole Station in November 2005 and studied the sky until the end of 2008. It was followed by the BICEP2 experiment which lasted from 2010 until 2012, whose results are coming out now. It will be followed by the BICEP3 experiment.
Why the south pole? The BICEP2 FAQ explains:
Water vapor in the atmosphere absorbs microwaves, making detailed studies of the CMB impossible from most places on earth. The South Pole is near the middle of the Antarctic plateau, the driest environment on the planet. At an effective altitude of over 10,000 feet ..., [with] stable weather patterns ..., the South Pole is the closest a ground-based telescope can get to being in space.
So for three years, from 2010 through 2012, they have studied the earliest light we can see, light from over 13 billion years ago, light that was emitted just 380,000 years after the big bang. Light that carries with it evidence of what happened just
10-37 seconds after the big bang.
And what message does that light carry about the early universe?
What They Found: Curled Light, Gravity Waves, and Inflation
That ancient light shows subtle swirls that may be caused by gravitational waves in the early universe. The light is polarized, and part of that polarization is called "B-mode" polarization, which the group's FAQ says is, "essentially the swirly part of that pattern (known mathematically as the ‘curl’)."
It is direct evidence for inflation. As they say, "We have detected B-mode polarization at precisely the angular scales where the inflationary signal is expected to peak with very high significance", adding, "[W]e are indeed directly observing a snapshot of gravitational waves through their imprints on matter and radiation over space."
This is not the first evidence of gravity waves, but this is the first time anyone has succeeded in taking a picture of them, and this is the most direct evidence of cosmic inflation to date.
Frank Wilczek put the magnitude of the discovery in context:
“If confirmed,” said Frank Wilczek, a Nobel Prize-winning physicist at the Massachusetts Institute of Technology, “it would be one of the absolute greatest discoveries in cosmology.”
As did one of the principal investigators, Jamie Bock:
“The implications for this detection stagger the mind,” said Jamie Bock, a physicist at Caltech and project co-leader. “We are measuring a signal that comes from the dawn of time.”
Quanta magazine explains the discovery in more detail:
Possible Echo of Big Bang Detected
The course-grained swirl pattern found in the light’s polarization matched the effects of giant buckles in space-time — gravitational waves that stretched to enormous proportions during inflation.
The ripples arose because, according to quantum mechanics, particles randomly pop in and out of existence, and gravity particles that arise in this way send cascades of ripples through space-time like pebbles striking the surface of a pond. When these particles arose during inflation, the ripples became imprinted and magnified as space-time expanded. The exact amount the ripples stretched, and the resulting size of the B-mode swirl pattern observed by Bicep2, reveals how energetically space-time inflated. This in turn helps theorists figure out why it did so.
Quanta goes on to give some hint at just how great the significance may be. You see, it isn't just gravitational waves and inflation, as if that weren't enough. It may also be evidence of the grand unification of three of the forces of nature (the electromagnetic force and the strong and weak nuclear forces), and the role they may have played in the inflation of the universe:
The size of the B-modes detected ... indicates that inflation occurred when the universe was approximately 10-37 seconds old and packed with 2 x 1016 giga-electron-volts of energy. [T]his energy scale ... is strikingly familiar. [T]hree of the forces of nature attain equal strengths and unite into a single force at exactly this energy scale, .... The coincidence is leading many physicists to wonder whether the breakup of this “grand unified” force into distinct types could have triggered inflation.
Is that not enough science for you? Well, there's more. You see, it may also provide evidence for the elusive particles that are thought to underlie the still-mysterious gravitational force. Gravitons are hypothetical particles that mediate the gravitational force, bosons that are the quantum of gravitation the way photons are the quantum of light, or the lesser-known gluons and W and Z bosons, which play the same role for the strong and weak nuclear forces. But are gravitons only hypothetical? Perhaps not for long:
the discovery of primordial gravitational waves would strongly suggest that the force of gravity really does come from quantum particles called gravitons. “If we can show these B-modes are due to gravitational waves and show they are due to inflation, then we can show that gravity is quantized,” said Lawrence Krauss, a theoretical physicist and cosmologist at Arizona State University, who detailed this possibility in a January paper co-authored by Wilczek. “Gravitons exist.”
Detecting primordial gravitational waves “would get us a lot closer to the origin of the universe,” said Wilczek. “It would be both a milestone and a platform for further exploration. But it’s important that it gets confirmed before we get carried away.”
Remaining level-headed
With inflation, gravitational waves, gravitons, and grand unification all on the table, you can see why some people might be feeling a little overexcited at this announcement. I must confess, despite Frank Wilczek's excellent advice, above, about not getting carried away, when I was reading these articles earlier today, I was feeling more than a little carried away. My feet were not quite touching the ground. Ebullient. Ecstatic. Giddy, even.
That's why Wilczek's advice is so good. A few other notes of caution were sounded, as in the article from Quanta:
Though there is little doubt that the microwaves exhibit the swirl pattern, called B-mode polarization, an independent observation is needed to rule out other possible sources for the signal and confirm that it comes from primordial gravitational waves.
And this comment from Matt Strassler:
Talking to and listening to experts, I’d describe the mood as cautiously optimistic; some people are worried about certain weird features of the data, while others seem less concerned about them... typical when a new discovery is claimed. I’m disturbed that the media is declaring victory before the scientific community is ready to. That didn’t happen with the Higgs discovery, where the media was, wisely, far more patient.
Thanks, all. Feet firmly back on the ground now. Still, one is justified at feeling a certain
frisson, no?
Physicists Matt Strassler and Sean Carroll have reactions to the news. Sean Carroll also wrote a great preview of the expected announcement before it was announced, with a lot of great detail. Phil Plait's article is highly informative, as always. Matt Strassler's web site in particular is a great one if you're looking for some background on what this all means, what the heck the big bang and inflation are (and aren't — hint: not an explosion), the history of the universe, and other cosmic topics. (He also has some great information on the Higgs boson.) His site is well worth taking some time on.
Notes:
The images come from the press release from Harvard. That site's policy states that their images "may be used for noncommercial and educational purposes. In other words, an Internet user may download a file and share it with others where no personal or commercial gain is involved." I believe that their use here meets that standard.
This is one experiment. Experiments have been wrong before. Confirmation is needed. The results here are really stunning, but until a second experiment has confirmed the results, some reservation is appropriate. Hopefully other groups will replicate what the BICEP team has done. The next few years may be really exciting. This has the potential to be a huge advance for cosmology.
I'm a computer programmer. I love this stuff, but I'm not qualified to tie Matt Strassler's shoelaces. If it weren't for the work, and the writing, of people like Strassler, Sean Carroll, Lisa Randall, Phil Plait, Steven Weinberg, Lawrence Krauss, Frank Wilczek, and others, I wouldn't even possess the partial understanding that enables me to write this diary.
A few other Kossacks have written diaries on the subject: Big Bang -- Gravity Wave Detection is Spectacular Evidence for Inflation and Smoking gun proof found of key Big Bang process