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If you look farther and farther away, you also look farther and farther into the past. The earlier you go, the hotter and denser, as well as less-evolved, the Universe turns out to be. The earliest signals can even, potentially, tell us about what happened prior to the moments of the hot Big Bang. This is the crux of the experiment that’s at the focus of ‘Losing the Nobel Prize.’ (NASA / STScI / A. Feild (STScI))
BICEP2 scientist Brian Keating’s new book is honest and insightful, but just as notable for what it fails to recognize.
NASA/ESA Hubble TelescopeBICEP 2 at the South Pole
BICEP 2 interior
Gravitational Wave Background from BICEP 2 which ultimately failed to be correct. The Planck team determined that the culprit was cosmic dust.
Imagine what it’s like to be a scientist working on a problem at the very frontiers of your field. You’ve got a new experiment that’s capable of measuring some property of the Universe to a degree it’s never been measured before. Maybe it’s a colder temperature than you’ve ever achieved, a higher energy than humanity’s ever reached, a higher-resolution image of the Universe, or the ability to detect a predicted effect that’s never quite been measured before. Pushing the frontiers of fundamental science in a novel way is high-risk, high-reward stuff. You can spend your entire career on a single idea, and never find anything new. But if you make the key breakthrough and find what you’ve been seeking, you can win the ultimate prize in all of science: the Nobel Prize. In his new book, Losing the Nobel Prize, observational cosmologist Brian Keating takes us through his story of ambition, heartbreak, and the questionable lessons learned from the endeavor.
Brian Keating’s new book, ‘Losing the Nobel Prize,’ tells a tale of ambition, loss, and what the perils are of pursuing the vainglorious goal of winning a Nobel Prize. (Brian Keating / Twitter)
Right around 20 years ago, cosmologists were measuring the fluctuations in the Big Bang’s leftover glow to unprecedented precision. Balloon-borne experiements like BOOMERanG and MAXIMA, along with ground-based ones like CBI and DASI, were looking at smaller and smaller scales to very high precision, measuring sub-millikelvin fluctuations on small scales. These fluctuations could, for the first time, tell us the shape of the Universe, and would lead the way to more advanced, space-based observatories like WMAP and Planck, which could cover the whole sky and tell us what the Universe was made of.
The leftover glow from the Big Bang, the CMB, isn’t uniform, but has tiny imperfections and temperature fluctuations on the scale of a few hundred microkelvin. The patterns of these fluctuations teach us about the composition and origin of the Universe. (ESA and the Planck collaboration)
ESA/Planck
Along the way, however, a very clever, complementary technique was discovered that could do what none of these experiments could: look for evidence of not just density and temperature fluctuations, but of ripples in spacetime from the moment of the Big Bang itself. The theory of our Universe’s origin, cosmic inflation, predicts the creation of both scalar fluctuations, which create temperature/density imperfections, and tensor (gravitational wave) fluctuations, which should polarize the light left over from the Big Bang in a very specific way. Brian Keating, the author, came up with the first experimental design that could measure the “curling” of this light: Background Imaging of Cosmic Extragalactic Polarization (BICEP).
The contribution of gravitational waves left over from inflation to the B-mode polarization of the Cosmic Microwave background has a known shape, but its amplitude is dependent on the specific model of inflation. These B-modes from gravitational waves from inflation have not yet been observed. (Planck science team)
If you could measure this polarization and saw the evidence of these tensor fluctuations, you would have the first evidence for the gravitational waves left over from inflation: a smoking gun that not only would verify inflation, but would tightly constrain which model was correct. It would have been a huge deal. In a remarkable story, Brian lays out in painstaking detail — from a first-person perspective — what it was like to:
design BICEP,
work on multiple competing experiments designed to measure this effect,
watch the power players come in and shut him and other researchers out of the inner-circle,
be amazed at the positive-detection that BICEP2 made,
and to watch in horror as his Nobel Prize dreams evaporated as the “signal” turned out to be nothing but dust.
He still, from what I read and like most scientists, doesn’t know how to cope with being wrong. At no point does he say, “I was wrong and should have done X instead of Y.” There is no responsibility taken on either his part or the part of BICEP2.
Polarized dust emission from the Milky Way is a major factor in what can confound a B-mode signal. Without the appropriate measurements, BICEP2 announced the discovery of B-modes from inflation prematurely, a ‘discovery’ that has been robustly overturned.(ESA and the Planck collaboration)
Brian’s major point in writing this book is to warn of the dangers of pursuing the Nobel Prize at all costs, and to point out the inherent ways the awarding of the prize is unfair. It’s certainly problematic that there are no posthumous awards; that awards are limited to being shared between 3 people; that collaborations cannot be awarded; and that the prize rewards luck/serendipity, which are factors no scientist, no matter how solid, can control. In this, he succeeds admirably. No rational, open-minded reader will come away from this book thinking that the great glory of winning the Nobel Prize is all it’s cracked up to be. Instead, as in many walks of life, who receives the award is determined not solely by merits, but by egos, PR, and a lot of biases. One doesn’t need to look far to find a slew of people who should have won, were the prizes awarded on merit alone.
This book, however, isn’t merely about BICEP2 and the Nobel Prize; it tells a multitude of different stories. It’s part-autobiography, as Brian shares his stories of his upbringing, his religiosity, his estrangement from and reconciliation with his dad, and his perspective on it all. It’s part tell-all about what it’s like to work in science, from the pressure to have your career be all-consuming, to how you can get forced out of your own collaboration/experiment, to watching your close friends and colleagues die of suicide (an extremely common experience that I sadly share with Brian), to the insane competition and fear of being scooped, to the pursuit of prestige and glory, and how all of that leads to sloppy work. In all of this, it’s a well-told story that will either bore you where you can’t relate or make you nod along in agreement where you can.
Illustration of the density (scalar) and gravitational wave (tensor) fluctuations arising from the end of inflation. Note where the BICEP2 collaboration places the Big Bang: before inflation, even though this hasn’t been the leading thought in the field in nearly 40 years.(National Science Foundation (NASA, JPL, Keck Foundation, Moore Foundation, related) — Funded BICEP2 Program)
There are also some big misses in this book. Brian attempts to weave into the narrative both historical stories of the development of physics and astronomy and the scientific story of where we are today and how we got to be here. These portions of the book are, unfortunately, grossly oversimplified and outright wrong in detail in a great many aspects. As the tale is told, you would think that:
there were no scientists or scientific developments before Galileo (in fact there were a great deal);
that every controversy in astronomy, including the value of the Hubble constant, is due to dust (ignoring the actual evidence and the work of Walter Baade);
that sunlight is made of different colors because of the elements present in the Sun (that is only true of the absorption lines; the Sun’s color comes from being a blackbody radiator);
and that the Steady-State model was a viable alternative to the Big Bang as late as the late-1990s (it was ruled out far earlier, with the reflected starlight explanation demonstrably disproven previously).
He includes many graphics that demonstrate the super-outdated fallacy that the Big Bang means “extrapolating back to t=0” and takes place before inflation, despite knowing this cannot be so. Given the number of cosmologists who’ve read/reviewed this book, I expected these outright errors would have been caught, but weren’t. If you walk away from the book confused about whether the Big Bang takes place before or after inflation, or confused about when and where inflation occurs, it’s because the book itself is inconsistent on this account.
Long before the data from BOOMERanG came back, the measurement of the spectrum of the CMB, from COBE, demonstrated that the leftover glow from the Big Bang was a perfect blackbody in a way that reflected starlight, as the quasi-steady-state model predicted, could not explain what we saw. (E. Siegel / Beyond The Galaxy)
Cosmic Infrared Background, Credit: Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASANASA/COBE
Those mistakes and oversights aside, there are two major missed opportunities I felt this book could have taken advantage of: one about the science and one about the societal aspect. Scientifically, Brian falls for perhaps the most common fallacy among scientists: the belief that sure, there was work done on this field/problem in the past, but it’s my contribution that will really, truly, definitively be the important one. Inflation isn’t waiting to be verified (it’s been verified by many different lines of evidence), as Brian contends, nor will the presence-or-absence of B-mode CMB polarization settle the issue.
You must not overstate the importance of your own work, and you must not diminish the importance of the results that others in your field have found. This kind of self-unaware navel-gazing is symptomatic of the culture of self-importance and the lack of recognition of others that’s so frustrating. Brian recognizes that these are problems and speaks out when others do it, but doesn’t look inward to see where he’s falling for the same trap.
While many signals in the CMB and in the large-scale structure of the Universe have verified and validated inflation, the B-mode polarization predicted by inflation’s tensor modes have failed to appear. This doesn’t mean inflation is wrong, but rather that the models that produce the largest tensor fluctuations are disfavored.(Kamionkowski and Kovetz, ARAA (2016), via http://lanl.arxiv.org/abs/1510.06042)
The societal problem is much bigger than merely how we glorify the Nobel Prize. It’s that we treat science like a competition, we reward, in general, being first, being right (even if it’s for the wrong reasons), while simultaneously devaluing the contributions of other fields to our own lines of inquiry. We attempt to glorify individuals, rather than scientific principles. We have a myth of a brilliant idea coming out of the blue to a single, unique mind, rather than rewarding hard work, care, collaboration, and taking the time to get things right. There’s a tacit pressure to join a big group, rise through the ranks to a position of leadership, and then direct these massive “big science” campaigns, rather than to focus on and explore whatever clever, niche ideas might be of interest. This lack of scientific playing-around means that most people in the field are doomed to mediocre careers working on mundane aspects of problems, rather than attempting new, bold paths forward.
U Washington Majorana Demonstrator Experiment at SURF
Brian recognizes the problem with the Nobel Prize, but never addresses this larger, more widespread problem. He’s guilty of exactly what he criticizes in his hero-worship of various scientific and historical figures throughout the book, where people close to him or his heart (like Andrew Lange, John Kovac, and Galileo) are seemingly placed on a pedestal, but contributors of equal-or-greater importance to the field (like Paolo de Bernardis, Tycho Brahe, or Johannes Kepler) are omitted. But with all that said, his book is good enough to reveal the cracks in how we do science today. It clearly illustrates why chasing Nobel Prizes — or glory, or to be worshiped as a hero in general — is an unfulfilling goal that dooms even those who succeed to an ultimately dissatisfying existence.
Lise Meitner, one of the scientists whose fundamental work led to the development of nuclear fission, was never awarded a Nobel Prize for her work, and was forced from Germany due to her Jewish heritage. Her contribution to science, and the benefit to humanity’s body of knowledge, is no less great as a result. (Archives of the Max Planck Society)
This is science. Our goal is to fully understand the Universe, one incremental step at a time. Our human failings are many, and we must not let them get the best of us. In Losing the Nobel Prize, Brian Keating exposes not only the failings of the Nobel Prize system, but also his own personal frailties. What emerges is a flawed but sympathetic read, where you’ll find yourself rooting not only for quality science to win out in the end, but for every contributor to work together in an open fashion for the benefit of human knowledge in general. We may be a long way from achieving that goal, but it’s arguable that by losing the Nobel Prize, Keating and BICEP2 has led us to an even greater victory: the recognition that there are more important things in this Universe, like scientific truths, than the fleeting glory of an earthly award.
“Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan
The Big Bang. The discovery that the Universe has been expanding for billions of years is one of the biggest revelations in the history of science. In a single moment, the entire Universe popped into existence, and has been expanding ever since.
We know this because of multiple lines of evidence: the cosmic microwave background radiation, the ratio of elements in the Universe, etc. But the most compelling one is just the simple fact that everything is expanding away from everything else. Which means, that if you run the clock backwards, the Universe was once an extremely hot dense region.
A billion years after the big bang, hydrogen atoms were mysteriously torn apart into a soup of ions. Credit: NASA/ESA/A. Felid (STScI)).
Let’s go backwards in time, billions of years. The closer you get to the Big Bang, the closer everything was, and the hotter it was. When you reach about 380,000 years after the Big Bang, the entire Universe was so hot that all matter was ionized, with atomic nuclei and electrons buzzing around each other.
Keep going backwards, and the entire Universe was the temperature and density of a star, which fused together the primordial helium and other elements that we see to this day.
Continue to the beginning of time, and there was a point where everything was so hot that atoms themselves couldn’t hold together, breaking into their constituent protons and neutrons. Further back still and even atoms break apart into quarks. And before that, it’s just a big question mark. An infinitely dense Universe cosmologists called the singularity.
When you look out into the Universe in all directions, you see the cosmic microwave background radiation. That’s that point when the Universe cooled down so that light could travel freely through space.
And the temperature of this radiation is almost exactly the same in all directions that you look. There are tiny tiny variations, detectable only by the most sensitive instruments.
Cosmic microwave background seen by Planck. Credit: ESA
ESA/Planck
When two things are the same temperature, like a spoon in your coffee, it means that those two things have had an opportunity to interact. The coffee transferred heat to the spoon, and now their temperatures have equalized.
When we see this in opposite sides of the Universe, that means that at some point, in the ancient past, those two regions were touching. That spot where the light left 13.8 billion years ago on your left, was once directly touching that spot on your right that also emitted its light 13.8 billion years ago.
This is a great theory, but there’s a problem: The Universe never had time for those opposite regions to touch. For the Universe to have the uniform temperature we see today, it would have needed to spend enough time mixing together. But it didn’t have enough time, in fact, the Universe didn’t have any time to exchange temperature.
Imagine you dipped that spoon into the coffee and then pulled it out moments later before the heat could transfer, and yet the coffee and spoon are exactly the same temperature. What’s going on?
To address this problem, the cosmologist Alan Guth proposed the idea of cosmic inflation in 1980. That moments after the Big Bang, the entire Universe expanded dramatically.
Alan Guth, Highland Park High School and M.I.T., who first proposed cosmic inflation HPHS Owls
Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex MittelmannColdcreation
And by “moments”, I mean that the inflationary period started when the Universe was only 10^-36 seconds old, and ended when the Universe was 10^-32 seconds old.
And by “expanded dramatically”, I mean that it got 10^26 times larger. That’s a 1 followed by 26 zeroes.
Before inflation, the observable Universe was smaller than an atom. After inflation, it was about 0.88 millimeters. Today, those regions have been stretched 93 billion light-years apart.
This concept of inflation was further developed by cosmologists Andrei Linde, Paul Steinhardt, Andy Albrecht and others.
Inflation resolved some of the shortcomings of the Big Bang Theory.
The first is known as the flatness problem. The most sensitive satellites we have today measure the Universe as flat. Not like a piece-of-paper-flat, but flat in the sense that parallel lines will remain parallel forever as they travel through the Universe. Under the original Big Bang cosmology, you would expect the curvature of the Universe to grow with time.
The horizon problem in Big Bang cosmology. How is it that distant parts of the universe possess such similar physical properties? Credit: Addison Wesley.
The second is the horizon problem. And this is the problem I mentioned above, that two regions of the Universe shouldn’t have been able to see each other and interact long enough to be the same temperature.
The third is the monopole problem. According to the original Big Bang theory, there should be a vast number of heavy, stable “monopoles”, or a magnetic particle with only a single pole. Inflation diluted the number of monopoles in the Universe so don’t detect them today.
Although the cosmic microwave background radiation appears mostly even across the sky, there could still be evidence of that inflationary period baked into it.
The Big Bang and primordial gravitational waves. Credit: bicepkeck.org
In order to do this, astronomers have been focusing on searching for primordial gravitational waves. These are different from the gravitational waves generated through the collision of massive objects. Primordial gravitational waves are the echoes from that inflationary period which should be theoretically detectable through the polarization, or orientation, of light in the cosmic microwave background radiation.
A collaboration of scientists used an instrument known as the Background Imaging of Cosmic Extragalactic Polarization (or BICEP2) to search for this polarization, and in 2014, they announced that maybe, just maybe, they had detected it, proving the theory of cosmic inflation was correct.
Gravitational Wave Background from BICEP 2 which ultimately failed to be correct. The Planck team determined that the culprit was cosmic dust.
Unfortunately, another team working with the space-based Planck telescope posted evidence that the fluctuations they saw could be fully explained by intervening dust in the Milky Way.
Bicep 2 Collaboration Steffen Richter Harvard
Planck’s view of its nine frequencies. Credit: ESA and the Planck Collaboration
The problem is that BICEP2 and Planck are designed to search for different frequencies. In order to really get to the bottom of this question, more searches need to be done, scanning a series of overlapping frequencies. And that’s in the works now.
BICEP2 and Planck and the newly developed South Pole Telescope as well as some observatories in Chile are all scanning the skies at different frequencies at the same time.
South Pole Telescope SPTPOL
Distortion from various types of foreground objects, like dust or radiation should be brighter or dimmer in the different frequencies, while the light from the cosmic microwave background radiation should remain constant throughout.
There are more telescopes, searching more wavelengths of light, searching more of the sky. We could know the answer to this question with more certainty shortly.
One of the most interesting implications of cosmic inflation, if proven, is that our Universe is actually just one in a vast multiverse. While the Universe was undergoing that dramatic expansion, it could have created bubbles of spacetime that spawned other universes, with different laws of physics.
In fact, the father of inflation, Alan Guth, said, “It’s hard to build models of inflation that don’t lead to a multiverse.”
And so, if inflation does eventually get confirmed, then we’ll have a whole multiverse to search for in the cosmic microwave background radiation.
The Big Bang was one of the greatest theories in the history of science. Although it did have a few problems, cosmic inflation was developed to address them. Although there have been a few false starts, astronomers are now performing a sensitive enough search that they might find evidence of this amazing inflationary period. And then it’ll be Nobel Prizes all around.
30 January 2015
Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31-71-565-6799
Mob: +31-61-594-3-954
Email: Markus.Bauer@esa.int
Jan Tauber
ESA Planck Project Scientist
Tel: +31-71-565-5342
Email: Jan.Tauber@esa.int
Planck view of BICEP2 field
Despite earlier reports of a possible detection, a joint analysis of data from ESA’s Planck satellite and the ground-based BICEP2 and Keck Array experiments has found no conclusive evidence of primordial gravitational waves.
ESA/Planck
BICEP2
Keck Array
The Universe began about 13.8 billion years ago and evolved from an extremely hot, dense and uniform state to the rich and complex cosmos of galaxies, stars and planets we see today.
An extraordinary source of information about the Universe’s history is the Cosmic Microwave Background, or CMB, the legacy of light emitted only 380 000 years after the Big Bang.
CMB per Planck
ESA’s Planck satellite observed this background across the whole sky with unprecedented accuracy, and a broad variety of new findings about the early Universe has already been revealed over the past two years.
But astronomers are still digging ever deeper in the hope of exploring even further back in time: they are searching for a particular signature of cosmic ‘inflation’ – a very brief accelerated expansion that, according to current theory, the Universe experienced when it was only the tiniest fraction of a second old.
This signature would be seeded by gravitational waves, tiny perturbations in the fabric of space-time, that astronomers believe would have been generated during the inflationary phase.
Theorized gravitational wave pattern
Interestingly, these perturbations should leave an imprint on another feature of the cosmic background: its polarisation.
When light waves vibrate preferentially in a certain direction, we say the light is polarised.
The CMB is polarised, exhibiting a complex arrangement across the sky. This arises from the combination of two basic patterns: circular and radial (known as E-modes), and curly (B-modes).
Different phenomena in the Universe produce either E- or B-modes on different angular scales and identifying the various contributions requires extremely precise measurements. It is the B-modes that could hold the prize of probing the Universe’s early inflation.
“Searching for this unique record of the very early Universe is as difficult as it is exciting, since this subtle signal is hidden in the polarisation of the CMB, which itself only represents only a feeble few percent of the total light,” says Jan Tauber, ESA’s project scientist for Planck.
Planck is not alone in this search. In early 2014, another team of astronomers presented results based on observations of the polarised CMB on a small patch of the sky performed 2010–12 with BICEP2, an experiment located at the South Pole. The team also used preliminary data from another South Pole experiment, the Keck Array.
They found something new: curly B-modes in the polarisation observed over stretches of the sky a few times larger than the size of the full Moon.
The BICEP2 team presented evidence favouring the interpretation that this signal originated in primordial gravitational waves, sparking an enormous response in the academic community and general public.
However, there is another contender in this game that can produce a similar effect: interstellar dust in our Galaxy, the Milky Way.
Planck view of Galactic dust
The Milky Way is pervaded by a mixture of gas and dust shining at similar frequencies to those of the CMB, and this foreground emission affects the observation of the most ancient cosmic light. Very careful analysis is needed to separate the foreground emission from the cosmic background.
Critically, interstellar dust also emits polarised light, thus affecting the CMB polarisation as well.
“When we first detected this signal in our data, we relied on models for Galactic dust emission that were available at the time,” says John Kovac, a principal investigator of BICEP2 at Harvard University, in the USA.
“These seemed to indicate that the region of the sky chosen for our observations had dust polarisation much lower than the detected signal.”
The two ground-based experiments collected data at a single microwave frequency, making it difficult to separate the emissions coming from the Milky Way and the background.
On the other hand, Planck observed the sky in nine microwave and sub-millimetre frequency channels, seven of which were also equipped with polarisation-sensitive detectors. By careful analysis, these multi-frequency data can be used to separate the various contributions.
The BICEP2 team had chosen a field where they believed dust emission would be low, and thus interpreted the signal as likely to be cosmological.
However, as soon as Planck’s maps of the polarised emission from Galactic dust were released, it was clear that this foreground contribution could be much higher than previously expected.
In fact, in September 2014, Planck revealed for the first time that the polarised emission from dust is significant over the entire sky, and comparable to the signal detected by BICEP2 even in the cleanest regions.
So, the Planck and BICEP2 teams joined forces, combining the satellite’s ability to deal with foregrounds using observations at several frequencies – including those where dust emission is strongest – with the greater sensitivity of the ground-based experiments over limited areas of the sky, thanks to their more recent, improved technology. By then, the full Keck Array data from 2012 and 2013 had also become available.
“This joint work has shown that the detection of primordial B-modes is no longer robust once the emission from Galactic dust is removed,” says Jean-Loup Puget, principal investigator of the HFI instrument on Planck at the Institut d’Astrophysique Spatiale in Orsay, France.
“So, unfortunately, we have not been able to confirm that the signal is an imprint of cosmic inflation.”
Deflecting light from the Big Bang
Another source of B-mode polarisation, dating back to the early Universe, was detected in this study, but on much smaller scales on the sky.
This signal, first discovered in 2013, is not a direct probe of the inflationary phase but is induced by the cosmic web of massive structures that populate the Universe and change the path of the CMB photons on their way to us.
This effect is called ‘gravitational lensing’, since it is caused by massive objects bending the surrounding space and thus deflecting the trajectory of light much like a magnifying glass does. The detection of this signal using Planck, BICEP2 and the Keck Array together is the strongest yet.
As for signs of the inflationary period, the question remains open.
“While we haven’t found strong evidence of a signal from primordial gravitational waves in the best observations of CMB polarisation that are currently available, this by no means rules out inflation,” says Reno Mandolesi, principal investigator of the LFI instrument on Planck at University of Ferrara, Italy.
In fact, the joint study sets an upper limit on the amount of gravitational waves from inflation, which might have been generated at the time but at a level too low to be confirmed by the present analysis.
“This analysis shows that the amount of gravitational waves can probably be no more than about half the observed signal,” says Clem Pryke, a principal investigator of BICEP2 at University of Minnesota, in the USA.
“The new upper limit on the signal due to gravitational waves agrees well with the upper limit that we obtained earlier with Planck using the temperature fluctuations of the CMB,” says Brendan Crill, a leading member of both the Planck and BICEP2 teams from NASA’s Jet Propulsion Laboratory in the USA.
“The gravitational wave signal could still be there, and the search is definitely on.”
“A Joint Analysis of BICEP2/Keck Array and Planck Data” by the BICEP2/Keck and Planck collaboration has been submitted to the journal Physical Review Letters.
The study combines data from ESA’s Planck satellite and from the US National Science Foundation ground-based experiments BICEP2 and the Keck Array, at the South Pole.
The analysis is based on observations of the CMB polarisation on a 400 square degree patch of the sky. The Planck data cover frequencies between 30 GHz and 353 GHz, while the BICEP2 and Keck Array data were taken at a frequency of 150 GHz.
A public release of Planck data products will follow next week.
The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.
That you could start with nothing, apply some basic laws of physics, and get a universe out of it—a universe that was uniform on the largest scales but replete with the lumps and bumps we call stars and galaxies, a universe, that is, that looks like ours—well, it didn’t matter that the theory didn’t quite work at first. It was just too beautiful to be wrong.
In Alan Guth’s original version of the theory in 1980, the nothingness at the beginning of time wasn’t really nothing at all. It was a field, the inflaton, and it teetered at the edge of a cliff, momentarily stable but not in its most stable, or lowest energy, state. This gave spacetime a negative pressure, creating a kind of anti-gravitational force that would push outward, sending the inflaton—that nascent field that would give birth to inflation—plummeting toward stability, causing the universe to expand exponentially, growing a million trillion trillion times bigger in the blink of an eye.
Barred spiral galaxy NGC 1672
Inflation explains how everything from galaxies to dust may have come about.
It was creation nearly ex nihilo—all you needed was the tiniest speck of a universe and inflation would transform it into something truly cosmic. There was just one problem: the plunge to the lowest energy state was a kind of phase transition, like water vapor condensing to liquid, and the transition would dissolve the inflaton into a sea of bubbles—pockets of lowest-energy regions—which would eventually collide and merge, collisions that would leave astronomical upheavals more disfiguring than anything we see on the sky today.
Then, in 1981, Andrei Linde saved inflation from itself. He suggested that we didn’t have to worry about those bubbles because inflation could make them so big that our entire universe could fit inside just one of them. It didn’t matter what happened out at the edges or beyond—we’d never see it anyway.
There was just one problem. The smooth, scarless space inside the bubble was too smooth, the density of matter so perfectly uniform that nothing so lumpy as stars or galaxies could ever form. It was Linde’s friend and fellow physicist Slava Mukhanov who had the solution: quantum fluctuations.
Quantum fluctuations are born of [Werner] Heisenberg’s uncertainty principle, which says that certain pairs of physical characteristics—position and momentum, time and energy—are bound together by a fundamental elusiveness, wherein the more accurately we can specify one, the more wildly the value of the other fluctuates. The universe cannot be perfectly uniform—uncertainty will not allow it. At a precise moment in time, energy varies recklessly; at a well-defined position, momentum soars and swerves. Precise moments and well-defined positions normally mean tiny scales of time and space, but inflation blows all that up. Inflation, Mukhanov told Linde, could take these tiny quantum fluctuations on the order of 10-33 cm and stretch them to astronomical proportions, creating slight peaks and valleys throughout space and laying a gravitational blueprint for what would eventually become a network of stars and galaxies.
Still, Linde wasn’t satisfied. Getting inflation to start and end in just the right way required the whole thing to be improbably fine-turned. It was beautiful, but unnatural. There would be two more years of work before he found the solution: chaos. Inflation didn’t require fine-tuning, he realized; it didn’t need to teeter on a cliff’s edge. If the inflaton started off in a highly-probable and totally random state, then somewhere amongst the mess, there was bound to be a region with the right properties to spark inflation. From a sea of chaos, a vast island of order would emerge.
That’s where the universe stood in the cold Moscow winter of 1986. Gorbachev had recently taken office as the General Secretary of the Communist Party and had just set into motion the perestroika—the restructuring of the Russian political, economic, and educational systems. For physicists like Linde, this engendered a strange silence. The old system for getting academic papers published abroad had been scrapped, but it hadn’t yet been replaced by a new one. So while inflation was being developed in the U.S., Russian physicists were forced to wait.
Linde waited in bed. The doctors told him he was perfectly healthy, but he felt awful nonetheless. He was passing the time reading detective stories when the phone rang. It was the administration from the Lebedev Physical Institute, where he worked. They told him he was to travel to Italy to give a public lecture. He didn’t want to go. Under Gorbachev, Linde was allowed only one trip abroad each year, and he wasn’t about to waste it on a public lecture where he wouldn’t be working with other physicists or learning anything new. He told them he was too ill to travel. You are ill today, they said, but you’ll likely be healthy again soon, no? Or are you saying you are unable to go abroad at all?
Linde grew scared. He knew if he said that he was unable to go abroad, they might never let him leave again—ever. He needed to prove that he could make the trip, and quickly. It was a Friday. He needed to get to the Hospital of the Academy of Sciences in order to obtain a certificate of health, but he was just learning how to drive and couldn’t risk a battle with the Moscow ice. He decided to pay for a taxi, a financial decision that didn’t come easy. Over the weekend he prepared the necessary travel documentation, and on Monday invested in another taxi ride to the Institute. He paid secretaries to immediately type up his paperwork, which he then ran to every corner of the Institute to get every last signature required. That bureaucratic nightmare ought to have taken a month and a half, and he accomplished it in four days. He dropped off the papers, went home, and collapsed into bed. He didn’t get up for two days.
Soon the phone was ringing again. The trip was set, they told him, but the Italians wanted to see his lecture ahead of time—the day after tomorrow. Suddenly, Linde realized he had a golden opportunity. He could get around the systemless system and publish abroad! Instead of handing over his public lecture, he could write a new paper, give it to the powers that be and they would send it abroad for him—by diplomatic mail, no less. There was just one catch: he had half an hour to do it. It was the only way to get it typed up in time.
Linde sat with his head in his hands, rolling it from side to side. Think, think. He felt like a compressed spring—he would either bounce to new heights or break under the stress. He knew that theorists can’t simply order up good ideas at will—physics doesn’t work that way. But today, he thought, it was going to have to.
Thirty minutes later, he had come up with the theory of the chaotic self-reproducing inflationary multiverse. It was his greatest piece of work.
Linde’s new theory reached beyond the bounds of the bubble. In his earlier version, our little patch of inflationary universe would arise from some small stretch of chaos. But while our universe was growing, what was happening behind the scenes? Surely there would be other regions where inflation could crop up. They’d be rare, but it didn’t matter—they would grow so big so rapidly that they would soon dominate the landscape. Each inflationary region creates more of itself—it’s self-reproducing. The process ends locally within each island universe, but on the largest scales it carries on, producing universe after universe after universe. In a half hour, Linde had taken our single universe, once the whole of everything there ever was or would be, and duplicated it, multiplied it, mutated it, sent it through a sequence of funhouse mirrors until it emerged on the other side a mere speck again, a humble, lone bubble in an infinite and growing multiverse.
Seeing gravity waves…it would be like a fish seeing water.
When he first developed the idea of inflation, Linde never for a second thought that it would be technologically feasible to test it. In principle, there were ways—you could look for the tiniest temperature fluctuations in the remnant heat from the Big Bang, those tiny quantum fluctuations that seeded the stars and galaxies, but that was a precision measurement he could barely fathom at the time. And if you wanted to dream even bigger, well, there ought to be something even more fundamental—quantum fluctuations of spacetime itself, primordial gravity waves. Seeing gravity waves…it would be like a fish seeing water. And seeing primordial gravity waves…well, it’s not just any water, it’s the first water, the origin of water, the origin of everything. But the technological skill that it would take to make that kind of measurement—it was downright unthinkable.
On good days, he didn’t care. He knew the theory was right, he knew it in his bones. He knew it with the same kind of certainty that Einstein had about general relativity: When observations of the 1919 eclipse came in, proving that gravity bends light just as general relativity predicted, a reporter asked [Albert] Einstein how he would’ve felt had the experiment turned out differently. “I would have felt sorry for the dear Lord,” Einstein replied, “because the theory is correct.”
The Device
There was a problem with the antennas.
When Chao-Lin Kuo arrived at NASA’s Jet Propulsion Laboratory in Cañada Flintridge, California in 2003, the BICEP. team was trying to implement Jamie Bock’s vision for a new polarization detector in their search for primordial gravity waves. Not that the old detectors didn’t work, but the things were unwieldy. Three copper feed horns, a handmade filter, and two detectors per pixel, all hand assembled. It’s not that they weren’t sensitive—they were nearly as sensitive as you can get. Rather, if they wanted better measurements, they didn’t need more sensitive detectors, they needed more detectors—quickly and cheaply. Bock’s vision was to digitize the whole assemblage and print them on circuit boards with microlithography, creating a kind of mass-producible polarimeter-on-a-chip. If it worked, it would change everything. It would be like upgrading from vacuum tubes to integrated circuits. But the team was stuck. They had designed a beautiful antenna array, but its readings kept coming out wrong.
The plan was to mount the detector to a radio telescope at the South Pole, where it would catch light that’s been traveling through an expanding cosmos for the last 13.8 billion years and measure its polarization, or the direction in which the photons are waving relative to the direction of their motion. If they could pin down each photon’s polarization with enough precision and map them across the sky, they’d have some hope of discerning a pattern known as a B-mode, the signature of primordial gravity waves. Kuo, a 30-year-old postdoc, set to work, putting the array through a host of tests until he figured out the problem: it was because the feed lines were crossed. The array looked like a series of X’s, but at the center of each X, the antennas were picking up each other’s signals and screwing up the reading. He set to work on a new design.
Kuo knew he had to keep the antennas at right angles from one another so they could subtract the horizontal polarization from the vertical and take the difference. And he had to keep them as symmetric as possible, because the difference they were looking for was one part in 30 million. One part in 30 million. All to find a B-mode. How exactly do you make something like that?
When he really thought about it, this thing they were trying to do, this thing they were trying to measure, it pushed the bounds of sanity. But Kuo already had a taste for pulling something like this off. As a grad student back at Berkeley, he had worked on the ACBAR experiment, which took measurements of the cosmic microwave background temperature fluctuations.
The idea that you could build something with your own two hands, point it at the sky, and see the faintest details of the nascent universe some 14 billion years in the past…well, you had to see it to believe it. You see the pattern. It’s not an image in a textbook or an idea in your mind—it’s on the sky. You look at it and suddenly you realize that you are one of a handful of human beings who has ever cast his eyes on the Big Bang. Well, it’s not exactly the Big Bang; it’s 380,000 years later–a mere eyeblink in the cosmic course of things, but still. To see back to the very beginning, the very first fraction of the very first second, you need something better than light. You need gravity.
…suddenly you realize that you are one of a handful of human beings who has ever cast his eyes on the Big Bang.
Kuo tried design after design. On some level, the antennae weren’t all that different from the kind you’d find in a cell phone, except this cell phone needed to answer calls from the beginning of time. The antenna array would shuffle the incoming photons down to the focal plane, where electromagnetism would be converted to heat and measured by an ultrasensitive thermometer. If you want to capture a signal that’s been steadily weakened over 14 billion years, you better make sure there’s virtually no heat and zero polarization coming from the instrument itself or it will totally swamp the measurement. That means keeping the detectors cooled to 0.25 Kelvin, just the slightest shiver above absolute zero. In the old way of thinking, the signal had to be transported off the focal plane and out of the cooling element to be read out by some room temperature electronics, but the transmission itself through heat conducting wires could warm the focal plane enough to drown out the signal. So Bock’s idea was to have the signals read by superconducting electronics on the focal plane itself using quantum-scale magnetic sensors developed at the National Institute of Standards and Technology in Colorado.
In the meantime, they deployed the old detector to the South Pole in an experiment they named BICEP1. For three years, from 2006 to 2008, it would collect that nascent light and look for the slightest patterns of polarization.
The BICEP2 focal plane
Back at JPL, it was Kuo’s fifth design that stuck. He built an antenna array that looked like a series of H’s, with spaces between the vertical and horizontal lines to avoid having the feed lines intersect. Once the array had been fabricated at JPL, it was time to put them to the test. Kuo placed them carefully in the cryostat. Then he waited.
It would take several days to get things cold enough. First, liquid nitrogen would cool it down to 77 Kelvin. Then the liquid helium would kick in, lowering the temperature to 4 Kelvin. Finally, a few cubic centimeters of helium-3, a rare isotope. With helium-3, you have to tread carefully. The stuff is expensive; as a byproduct of plutonium production, it’s a controlled substance.
While Kuo waited, he thought about inflation. If that exponential expansion really gave birth to the universe, it ought to have taken quantum fluctuations in spacetime and blown them up across the sky. Some 380,000 years later, the photons that make up the cosmic microwave background radiation would have navigated that same warped spacetime, a journey that would imprint itself uniquely in their polarization. Find the B-mode polarization and you’ve found inflation’s smoking gun. Looking around the lab, he wondered if he was the only one worrying about inflation. These guys were hardware wizards—they want to build cool things. Most of them didn’t have a lot of faith in theory. Kuo respected that. But for him, he needed to understand why he was doing this. Yes, he wanted to build a kickass detector. But he also wanted to know how the universe began.
Once the helium-3 had everything cooled to 0.25 Kelvin, Kuo had to test the things, to see if they worked and to diagnose any problems. Start by sticking something room temperature in front of it and see what temperature reads out. Then something cooled with liquid nitrogen. Shine a source of microwaves at it, rotate their polarization, watch what happens. He ran every calibration test he could think of. The antenna array worked.
Kuo had transformed Bock’s vision into a groundbreaking—and more important, functioning—detector. Because they used lithography, they could pack 512 of them on the focal plane, which meant BICEP2 would achieve the same sensitivity as BICEP1 in one-tenth the detection time, much like a bigger camera sensor can capture more stars at night. Kuo’s timing couldn’t have been better. BICEP1 was going off-line and the new technology had to ship out on the first flights of the year to Antarctica in September.
Despite the pioneering technology, the truth was, no one on the team seemed to believe that a detection was in the cards. Even if inflation were correct, there was a good chance that primordial gravity waves would be way too small to measure. They just thought they’d use the telescope as a proving ground for the technology so that later it could be confidently incorporated into a next-generation space satellite. Satellites are expensive, and if something breaks once it’s up in orbit, you’re out of luck. So the BICEP2 team figured they’d take the technology out for a terrestrial test drive; in the meantime, they could place more upper limits on the amplitude of gravity waves and constrain some inflationary models in the process.
No one on the team seemed to believe that a detection was in the cards.
The physicist Andrew Lange had said that this was a wild goose chase. Still, Kuo couldn’t help hoping. Every once in awhile, he figured, you catch a goose. When [Arno] Penzias and [Robert] Wilson first discovered the cosmic microwave background in 1964, they thought it was literally pigeon shit. At least the BICEP2 team knew what they were looking for.
In the middle of all that, Kuo had moved up the coast, from Pasadena to Palo Alto. He took a position at Stanford University, where he recruited an eager young grad student named Jamie Tolan to work with him on the measurement. One day, Tolan approached his advisor—he was writing a proposal for a NASA graduate student fellowship, and he asked Kuo to read the draft. In the proposal, Tolan laid out the goal of BICEP2: to see just how elusive primordial gravity waves are. Kuo smiled at Tolan. That’s not it, he told him. The goal is to detect them.
The Questions
Linde had wanted to be a geologist. His father was a radio physicist, his mother an experimental physicist who studied cosmic rays. The younger Linde wanted to do something different, something tangible. Something like rocks. But during the summer vacation between 7th and 8th grade, the Linde family drove from Moscow to the Black Sea. For a week, Linde sat in the back seat reading. He had brought two books: one on stars and the universe, the other on Einstein’s theory of special relativity. When they arrived at the Black Sea, three physicists stepped out of that car.
At Moscow State University, Linde sought his colleagues’ advice: should he be a theorist or an experimentalist? The truth was, he didn’t think he was that great at calculation. He did, however, possess a certain intuition coupled with an obsessive mind. Once he became interested in a question, he couldn’t stop thinking about it. Linde soon realized he wasn’t nearly as impressed by measurements as he was by explanatory power. He didn’t want data—he wanted answers. Answers to big questions, the biggest: What happened when he was born? What will happen when he dies? What is it to feel, to think, to live, to exist? But he figured he’d start with simpler questions, the kind with more straightforward answers, like, how does an airplane fly? He promised himself he’d get to the hard ones eventually. There was no denying it. He was a theorist through and through.
Eventually the hard questions snuck back in. When Linde came up with chaotic eternal inflation in that fateful half hour, he immediately realized the implications. In an infinite multiverse where physical constants can vary from one universe to the next, everything that can happen will happen—an infinite number of times. Every possible world, every incarnation of reality, every possible version of you living every possible version of your life. What then does it mean to want something, to do something, to be something? It was a vertiginous thought, but Linde didn’t let it get to him. So what if there were infinite Andrei Lindes? If I killed myself, he figured, it’s not like I’d survive as a copy—my death would simply become the moment that I was no longer identical to my copy, because I, unlike him, would be dead.
In any case, it wasn’t clear that the copies existed in any meaningful way. That was the thing about quantum mechanics—the very nature of things seem to be determined by what an observer can measure. In the world of classical physics, you could have two baseballs that were identical in every way, and yet it’s fair to say that there are two of them. In the quantum realm, if you have two indistinguishable particles, you only have one particle. Wheeler and Feynman had emphasized that—in a sense, they said, there’s only one electron in the universe. Linde could never quite shake that.
Even those quantum fluctuations—the very fluctuations that gave rise to the stars, polarized the microwave light, and created universe after universe—they are determined directly by what an observer can measure. Position and momentum, time and energy—these partners bound by uncertainty are so bound because the accurate measurement of one precludes the accurate measurement of the other. A particle doesn’t have a simultaneous position and momentum because an observer can’t measure a simultaneous position and momentum. Gravity waves are waves of uncertainty—uncertainty not only of existence but of observation. It was a fact that seemed to suggest that observers play some deep role in the nature of reality, a fact that Linde kept tucked away in the back of his mind. What is it to feel, to think, to live, to exist? If there was no observer who could simultaneously observe more than one Andrei Linde, then on some level you might say there’s still only one.
Despite this, Linde was convinced that the existence of all those parallel universes held great explanatory power. While the multiverse was ultimately governed by the same laws of physics—by quantum mechanics and relativity, by inflation itself—each universe would be born with its own local sub-laws, a set of accidents that would determine its geometry, its physical constants, its particles, its forces, its own unique history. Inflation meant diversity. And diversity, Linde realized, was its own kind of explanation.
So many features of our universe appear inexplicably fine-tuned for the existence of biological life. Change the strength of a force here or the mass of a particle there and poof!—no stars, no carbon, no life. Such coincidences demand explanation, and inflation had one: the strengths and masses vary from universe to universe, and we just happen to find ourselves in the one in which we can live. The inflationary multiverse may not have been predictive or observable, but it was explanatory. It could explain the illusion of design, the comprehensibility of the cosmos, the unreasonable effectiveness of mathematics. It could explain why the cosmological constant is so small and why the universe is so big. It could explain why we are here, why anything is here, because at the end of the day, Linde knew, physics isn’t really about the universe. It’s about us.
Linde didn’t like being told what to think.
The mass of the electron is 2,000 times lighter than that of the proton. Why? Well, if it were ten-times heavier or ten times lighter we wouldn’t be here to ask. Spacetime has four large dimensions. Why? Well, any more dimensions and the gravitational force between two objects would fall off faster than r-2; any fewer and general relativity couldn’t support any such forces all. Either way, you’ve got no stable planetary systems and no life.
Such explanations are called “anthropic,” and they made people nervous, the theoretical physics equivalent of “just because.” Colleagues told Linde he shouldn’t think about such things, but he didn’t like being told what to think. When he decided to include a section on the anthropic principle in the cosmology book he wrote, his editor in Moscow told him to take it out. If you leave it in, she said, you’ll lose the respect of your colleagues. Yes, Linde replied, but if I take it out, I’ll lose my respect for myself.
As far as he was concerned, the metaphysical is always brought into the fold of physics in the end, and inflation meant that the burden of proof was on those who wished to believe in a single universe. Einstein had once said, “What really interests me is whether God had any choice in the creation of the world.” He wanted the universe to be a singular specimen of logical perfection and uniqueness. Not Linde. Linde wanted diversity, choice. In Russia, they only had one choice of cheese.
At the Bottom of the World
It was Kuo’s fourth visit here, at the bottom of the world, but he still wasn’t used to the whiteness of it all. Everything, everywhere—just white. A blank spot on the world, like someone forgot to fill it in. An endless white that makes you think about infinity. He must’ve been ten years old the first time he thought about it, whether the universe was infinite or finite. That was back in Taiwan—some 8,000 miles from here—where the sun still sets on a summer’s night. It hadn’t made sense to him, as a boy, that reality would just come to an end, that there was a place beyond which there is no more place. What if you sat there at the edge and threw a ball? Where would it go? Someone else had made the same argument, he remembered. A philosopher? Now, as a physicist, he knew it wasn’t so simple— that the universe could be curved and closed, like the surface of a sphere, finite but without an edge. He supposed he had always been a physicist. Funny how all this white makes you think of that. Of all the colors, he missed green the most. Green and the smell of humidity. He had never realized what humidity smelled like until it was gone.
An LC-130 takes off from the Amundsen-Scott South Pole Station.
It was hard to say how many days he had been here—hard to differentiate time when the scenery never changes, the weather never shifts, and the sun never goes down. Getting here had been an adventure, as usual. He had flown some 15 hours from California to Christchurch, New Zealand, for a stopover at the International Antarctic Center, where he traded his belongings for extreme cold weather gear before boarding an Air Force aircraft and flying another 14 hours to McMurdo Station here in Antarctica. From McMurdo it was another three-hour flight to the Amundsen-Scott South Pole Station on a plane that landed on skis. Stepping out onto the ice sheet, he had marveled again at the sky, so perfectly blue—the clearest sky on the planet.
That’s why they were here. Antarctica is the largest desert on Earth. The altitude gets you up above most of the problematic parts of the atmosphere and the biting cold takes care of the rest—any stray water vapor in the air is frozen out of the sky, leaving microwave light from the early universe to stream through unimpeded. It also helps that the sun only rises and sets once a year.
It was December now; he would be here until Valentine’s Day. The sun would set in March. He didn’t know how the “winter overs”—the people who stayed here past March—did it, not when -20°F was a warm summer day. Of course, the science station had grown more comfortable lately. It had a sauna now and a greenhouse for growing hydroponic fruits and vegetables. Earlier, they used to give you this weird yellow powder, and you’d mix it with water, fry it up, and call it a meal. Now, you could enjoy fresh produce in the cafeteria then go play on the basketball court or relax in the library or game room.
Between the porthole windows in the doors and the firemen’s lockers lining the corridors, the place looked like the perfect combination of a research ship and a high school. Ship was more accurate—the Amundsen-Scott station, perched on Antarctica’s high plateau, stands on stilts to avoid the snow that never thaws atop a glacier some 9,000 feet thick that ever so slowly drifts.
The Dark Sector Lab
To get to work, Kuo would walk along the ice sheet, across the airplane runway, upwind to the Dark Sector lab, so-named because all white light and radio transmission is forbidden there. The lab was hardly a mile away, but cold, wind, and altitude have a funny way of stretching distance. By the time he reached the telescope, he was queasy and out of breath.
BICEP2 was a refracting telescope with a small aperture—just 26 centimeters. It could afford to be small because the features it was looking for were the size of the full moon on the sky. All of its moving parts were kept inside where it’s warm. Only its head poked out through a hole they had cut in the roof. The telescope was focused on a 20° patch of the so-called Southern Hole, the cleanest stretch of sky available with a clear view straight out of our Milky Way. At the South Pole, the same patch of sky just keeps spinning in circles above you; it never slips behind the horizon or disappears from sight. The telescope can stare it down for years and never blink.
BICEP2 observed only photons with a frequency of 150 GHz, filtering everything else out. They had opted for a single frequency because it was the only way to optimize every part of the instrument. When you’re trying to avoid dust, which can polarize your light and mimic the signal of gravity waves, 150 GHz is the sweet spot. It’s where you’re most likely to see the clearest signal of gravity waves. The two possible impostors, magnetized radiation from extreme astronomical phenomenon and interstellar dust, rise at low and high frequencies respectively. But 150 GHz is right in the Goldilocks middle. It also happens to be the peak frequency of the cosmic microwave background, the photons that flew out of the dense early universe 380,000 years ago.
The telescope had two lenses that focused the light, a design similar to Galileo’s, except that this one fed the light into the most sensitive superconducting detectors ever built. Kuo and his team were here to assemble the thing and then take some calibrations, but even turning a screw was proving to be difficult in the cold.
Once the telescope was up and running it would start collecting data, which it would store temporarily on the computers at the South Pole. But soon a low Earth orbit communications satellite would appear above the horizon and relay the data from the South Pole station to NASA’s White Sands complex in New Mexico. From there it would bounce around the U.S. until it landed in a cluster of computers at Harvard University, which the BICEP2 team could later access from California.
California. Kuo wondered what his wife and children were doing back home in Stanford. They were probably enjoying the green, green grass and the warmth of a more fleeting sun.
The Observer and the Observed
California. Linde moved here in 1990 with his wife, Renata Kallosh, and their two sons. A year earlier they had left Moscow for Switzerland, intending to spend a year at CERN before heading back to the Soviet Union. But offers came in while they were there, including a double offer from Stanford University for both Linde and Kallosh, who is a string theorist, and so they changed course and immigrated to the U.S.
In the two decades that followed, evidence for inflation mounted, and, in 2003, cosmologists hit the jackpot. NASA’s Wilkinson Microwave Anisotropy Probe (WMAP)—an 1,800-pound spacecraft that orbited the sun nearly a million miles out— had produced an unprecedented map of the microwave sky, measuring temperature differences in the near-uniform radiation down to one part in 100,000.
WMAP
CMB per WMAP
Those slight hot and cold spots traced quantum fluctuations in the density of matter 380,000 years after the Big Bang, when the microwave light was first emitted. The pattern in the map bore out several key predictions of inflation with astounding precision. Even the inflation doubters were coming around. Now there was just one piece of evidence missing: B-mode polarization, the mark of primordial gravity waves.
Linde wasn’t worried about B-modes. Most versions of inflation predicted them at amplitudes way too small to measure, which meant that even a non-detection could be a strange kind of confirmation, at least for those who already believed. As far as he was concerned, the experimental evidence was already overwhelming. Still, he supposed, on the off-chance they did discover B-modes—well, it would just drive home the fact that quantum mechanics needs to be taken seriously, even at cosmic scales. The beauty of inflation was that it provided the missing link between the tiny quantum world and the largest scales of the universe. We are the great-great-great-grandchildren of quantum fluctuations, he liked to say.
When you try to apply the laws of quantum mechanics to the universe as a whole, you hit a paradox: all things quantum are defined in terms of what an observer can measure, but no one can measure the universe as a whole because, by definition, you can’t be outside the universe. The issue was captured most perfectly in the famous Wheeler-DeWitt equation, which showed that the quantum state of the universe could not evolve in time, stuck, as it were, in a frozen, eternal moment. As Linde often put it, without observers, the universe is dead.
Linde knew that the only way to get time flowing was to observe the universe from here, on the inside. When we look out at the cosmos through a telescope, he thought, we don’t see ourselves in the picture. And so we split the world in two: observer and observed. We make a measurement, and the universe comes to life. It sounded awfully solipsistic, but there it was.
As Linde often put it, without observers, the universe is dead.
Everyone assumed you can talk about “observers” without talking about consciousness—things like Geiger counters or space telescopes—but Linde wasn’t so sure. If you remove subjective experience from the picture, he thought, there’s no more picture. He couldn’t help wondering whether consciousness was the missing ingredient that would make the ultimate theory of physics consistent. The idea was inspired by gravity waves.
Back in the day, physicists thought of space and time as tools that we use to describe the motion of matter—not as things in their own right. It was Einstein who realized that even if you emptied the universe of matter, spacetime itself would remain and could exhibit a behavior all of its own: it could wave. Gravity waves meant that spacetime was equally as real and fundamental as matter itself. Later theoretical developments—namely supergravity—extended the symmetries of this space-time so that matter turned out to be nothing deeper than excitations of the geometry of superspace. In other words, it was spacetime that was fundamental and matter was derived, a tool for describing the excitations of spacetime.
Linde wondered if consciousness awaited the same vindication. Today we think of it as a tool we use to describe the external world, and not as an entity on its own. But what if the external world were empty? What if consciousness was fundamental and the universe derived? Could space, time, and matter together be nothing more than excitations, the gravity waves of consciousness?
What is it to feel, to think, to live, to exist? It was still the only question he really cared to answer. The rest was just details.
The Signal
They must have made a mistake.
They had screwed up the analysis or there was some design flaw they hadn’t accounted for yet. A signal this bright—it had to be coming from the instrument itself. There was no way this thing was coming from the sky.
BICEP2 had collected data for three years and now the team had set out to scour it for B-modes. But they barely had to scour. The B-modes were glaring.
They couldn’t figure out what they’d done wrong. They could have sworn they’d accounted for any spurious polarization, any stray morsel of heat. The detectors had passed every last performance test with flying colors. Where was this thing coming from?
They split the data in half, made a map from the first year and a half of observation and a map from the second year and a half. Then they subtracted them. They figured if the signal went away, they’d know it had been in both halves equally, that it hadn’t changed over time. But if it had changed over time—well then it wasn’t cosmological, it was an engineering blip. They ran the test. The signal canceled out. It wasn’t a blip.
They split and recombined the data in every which way, pushed themselves to imagine even the most unlikely scenarios that would have the signal originating in the instrument. Again and again they came up empty handed. Eventually there was no alternative left standing: the signal was coming from the sky.
Of course, there was always the issue of the dust. Everyone knew that interstellar dust in the Milky Way could polarize the photons and mimic the effect of gravity waves. Obviously the dust contributed to the signal, but the question was, how much? The Southern Hole at 150 GHz ought to be pretty clean. That’s why they chose it. But you never know.
Obviously dust contributed to the signal, but the question was, how much?
The team didn’t have access to any full sky maps with a decent signal-to-noise of polarized emissions from dust—but they knew exactly who did. The ESA’s Planck satellite had been mapping the dust from space and ought to be able to tell them exactly how much of it was contributing to their signal. The BICEP2 team submitted a request to share data. Request denied. They waited, then tried again. Request denied. Was the Planck team being competitive or did they simply feel the data wasn’t ready? Who could say. Either way, Kuo and his team were simply going to have to make do with whatever data they could get their hands on.
As the Milky Way passes overhead, charged particles of the aurora australis billow over the Dark Sector.
They combed the literature for the leading dust models and fed the results of five of them into their own model. Unfortunately, the models were all built from observations of unpolarized dust at various points on the sky, which were then extrapolated. But without Planck’s actual data, it was their best shot.
They used the models to create fake maps of dust, and they put in 3 million CPU hours on the Harvard supercomputer simulating the results 500 times. The signal wasn’t going away. Even after they subtracted the signal for the dust, the B-modes appeared to be still sitting there in plain sight.
That’s when they noticed that a member of the Planck team, J.P. Bernard, had given a public lecture on the dust data. His presentation contained a slide with an image of the dust map. The BICEP team figured it was time to get creative. They digitized the image, reverse engineering it to extract their best guess at the raw data. They knew it was an uncertain procedure, but that was ok—they weren’t staking their claim on it. They were just going to use it as model #6.
Again they subtracted the dust, and again the B-modes remained visible, bright as day.
They had to strike the right balance between being careful and being quick. A signal this bright—someone else was bound to see it. They could feel the competition nipping at their heels. They all agreed to not say a word about it to anyone. Not until they were sure. They were at three-sigma certainty—that meant there was a 1 in 740 chance that the signal was a statistical fluke. In physics, three sigma is considered evidence. Five sigma, a 1 in 3.5 million chance…well that’s a discovery.
The B-mode pattern from BICEP2
For a year they sat on the result. Kuo was hoping to hell it was real, though if you asked him to bet on it, he wouldn’t risk the money. He had a nagging fear that the B-modes were nothing more than mathematical contamination, just mundane E-mode polarization leaking out. The problem was that BICEP2 had only studied a small patch of sky. Each fragment of data is just a little line segment—it’s only when you look at the way those lines are drawn across the entire sky that a pattern emerges. If the line segments form a series of symmetric shapes, like circular ripples, that’s an E-mode: the standard pattern produced by the same old density fluctuations that create the hot and cold spots in the CMB. But if the pattern looks asymmetric, like pinwheels turning in a given direction, that’s the jackpot. Only primordial gravity waves can turn those pinwheels.
They had data from a 20° patch of sky, which is to say, not a lot. What do you do with the line segments out toward the edges? You see hints of pattern there, perhaps a slight arc, a suggestion of a pinwheel. But what if it’s a circle? Your statistics start to break down. So you throw away some signal, a sacrifice to the gods of error bars. But how to strike just the right balance between signal and certainty was far from clear.
One evening in Stanford, after he’d had dinner and helped put the kids to bed, Kuo noticed an e-mail from his grad student, Tolan.
Two years earlier, Kuo had urged Tolan to find a better way to distinguish the E-modes from the B-modes out at the edges. Tolan began working on the problem on the side, “off pipeline.” They were told again and again, stick to the pipeline, it’s the only way to keep things running smoothly, and it was. Everyone treated Tolan’s work as a kind of side hobby, so he just kept at it, posting updates now and then to the team’s internal website.
Kuo opened the e-mail. I’ve got a preliminary posting of the matrix estimator. Tolan had done it. He had found a way to cleanly separate the B-modes from the E-modes, and he had run their data. Kuo prepared himself for disappointment. He was sure the signal had disappeared. He clicked on the link to the internal website and scanned Tolan’s results.
The signal hadn’t disappeared.
The signal had gotten stronger.
The error bars had shrunk, and the certainty had risen—from three sigma to five sigma. A discovery.
That night, the sun went down, but Kuo couldn’t sleep.
In the morning he e-mailed Tolan: If this signal is real, this is the home run of all home runs…
If it were real, it would be the closest anyone had ever come to seeing the beginning of time. It would be the smoking gun proof of inflation. It would be a direct look at the quantum mechanical underpinnings of the universe, probing physics at energies a trillion times greater than what particle physicists could achieve in the hallowed tunnels of the LHC. If it were real, Kuo could finally tell his ten-year-old self the answer: if the universe isn’t infinite, it is really damn big.
Funny, the difference between experiment and theory. Theory is the stuff of great drama, littered with “aha” moments. It’s Archimedes shouting, “eureka!” in the bathtub, it’s Guth writing, “spectacular realization” in his notebook, it’s Linde waking his wife to tell her, “I think I know how the universe was created.” But experiment—experiment is more like life. It’s messy and it happens gradually after a good amount of soldering and shivering and the turning of screws. Sometimes the results are null—and sometimes the results are dust—but little by little it adds up to something tangible and true.
Never Again?
Linde and his wife were packing their things for a Caribbean vacation.
They needed it. They’d been working together again, writing paper after paper, producing a whirlwind of work. Linde couldn’t believe how much they’d done. Every time he had a good idea, he was convinced it would be his last.
As people, and as physicists, they were a perfect match. Where Linde had physical intuition, Kallosh had mathematical intuition. What was difficult for one came easy for the other. They saw the universe differently, and while the process was painful, they each raised the other up in their thinking. Not that it seemed so grand in the moment. Every time they were finishing yet another paper, they’d end up shouting, “Never again!” But they’d take a break, perhaps a vacation, and then they’d start all over again. That’s just how it was in their household. Ideas were nourishment. Physics was air.
Linde thought back to his younger days. It was funny now to think he’d ever wondered exactly what he ought to be. Now he understood that he was a theorist for the same reason an artist is an artist or a poet is a poet—because it’s too painful not to be.
At The Door
Kuo walked up the long driveway, the cameraman keeping pace behind him. For Kuo, the B-mode measurement was a technological achievement, the end of a marathon, the feeling of knowing that he had played an indelible part in the grand unfolding of science. But he knew that for Linde it would be something different: a moral victory, the triumph of reason and intuition, a validation 30 years coming. He was itching to tell him, he was rehearsing it in his mind. Five sigma. Clear as day. R equals 0.2. He raised his hand to knock on Linde’s door.
Epilogue
As of October 2014, maps made by Planck suggest that there is far more polarized dust in the Milky Way than theoretical models had predicted and that the entire B-mode signal measured by BICEP2 may be due to dust. Physicists and astronomers still need more data to determine the source of the signal and to figure out whether gravity waves are lurking behind the dust. Kuo is gearing up to head back down to the South Pole in December to set up BICEP3. The new instrument’s field of view will be three times larger than BICEP2’s and will measure light at a frequency of 95GHz. By comparing its results with BICEP2, Kuo and his team say they will be able to differentiate gravity waves from dust. As for Linde, he is hard at work incorporating inflationary theory into theories of fundamental physics, satisfied that the experimental evidence for inflation is overwhelming even in the absence of gravity waves and motivated, as ever, by the theory’s explanatory power and beauty. Science carries on.
NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.
Results of four years of observations made by the Planck space telescope provide the most precise confirmation so far of the Standard Model of cosmology, and also place new constraints on the properties of potential dark-matter candidates. That is the conclusion of astronomers working on the €700m mission of the European Space Agency (ESA). Planck studies the intensity and the polarization of the cosmic microwave background (CMB), which is the thermal remnant of the Big Bang. These latest results will no doubt frustrate cosmologists, because Planck has so far failed to shed much light on some of the biggest mysteries of physics, including what constitutes the dark matter and dark energy that appears to dominate the universe.
Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe)
ESA/Planck
Cosmic Background Radiation per Planck
NASA/WMAP spacecraft
Cosmic Background Radiation per WMAP
Planck ran from 2009–2013, and the first data were released in March last year, comprising temperature data taken during the first 15 months of observations. A more complete data set from Planck will be published later this month, and is being previewed this week at a conference in Ferrara, Italy (Planck 2014 – The microwave sky in temperature and polarization). So far, Planck scientists have revealed that a previous disagreement of 1–1.5% between Planck and its predecessor – NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) – regarding the mission’s “absolute-temperature” measurements has been reduced to 0.3%.
Winnowing dark matter
Planck’s latest measurement of the CMB polarization rules out a class of dark-matter models involving particle annihilation in the early universe. These models were developed to explain excesses of cosmic-ray positrons that have been measured by three independent experiments – the PAMELA mission, the Alpha Magnetic Spectrometer and the Fermi Gamma-Ray Space Telescope.
PAMELA
AMS-02
NASA/Fermi
The Planck collaboration also revealed that it has, for the first time, “detected unambiguously” traces left behind by primordial neutrinos on the CMB. Such neutrinos are thought to have been released one second after the Big Bang, when the universe was still opaque to light but already transparent to these elusive particles. Planck has set an upper limit (0.23 eV/c2) on the sum of the masses of the three types of neutrinos known to exist. Furthermore, the new data exclude the existence of a fourth type of neutrino that is favoured by some models.
Planck versus BICEP2
Despite the new data, the collaboration did not give any insights into the recent controversy surrounding the possible detection of primordial “B-mode” polarization of the CMB by astronomers working on the BICEP2 telescope.
BICEP 2 with South Pole Telescope
If verified, the BICEP2 observation would be “smoking-gun” evidence for the rapid “inflation” of the early universe – the extremely rapid expansion that cosmologists believe the universe underwent a mere 10–35 s after the Big Bang. A new analysis of polarized dust emission in our galaxy, carried out by Planck earlier in September, showed that the part of the sky observed by BICEP2 has much more dust than originally anticipated, and while this did not completely rule out BICEP2’s original claim, it established that the dust emission is nearly as big as the entire BICEP2 signal. Both Planck and BICEP2 have since been working together on joint analysis of their data, but a result is still forthcoming.
[THIS IS THE BEST WE CAN DO UNTIL ESA RELEASES THEIR LATEST FINDINGS FROM PLANCK]
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“The paradigm of physics — with its interplay of data, theory and prediction — is the most powerful in science.” -Geoffrey West
Earlier this year, the BICEP2 experiment shook up the world of cosmology, announcing that they had detected gravitational waves originating from before the Big Bang! Not only did they announce this, but they announced that they had done so with a signal in excess of 5σ, which is regarded as the gold standard for a detection in physics.
BICEP2 (With South Pole Telescope
Image credit: BICEP2 Collaboration — P. A. R. Ade et al, 2014 (R).
But this may all turn out — despite the hoopla — to be absolutely nothing. Or, as it were, nothing more than a phantasm, as the observed signal may have originated from a source as mundane as our own galaxy, and have nothing to do with anything from billions of years ago!
How did we get into this mess, and how do we get out of it? The answer to both questions is “science,” and it’s a great illustration of how the process and the body of knowledge actually evolves. Put your preconceptions of how it ought to work aside, and let’s dive in!
This is a snapshot of the cosmic microwave background (CMB), the leftover glow from the Big Bang, as viewed by the Planck satellite. Planck has the best resolution of any all-sky map of the CMB, getting down to resolutions smaller than one tenth of a degree. The temperature fluctuations are minuscule: on the order of just a few tens of microKelvin, less than 0.01% of the actual CMB temperature.
Image credit: Wikimedia Commons user SuperManu.
But buried in this signal is another, even more subtle one: the signal of photon polarization.
Basically, when photons pass through electrically charged particles in certain configurations, their polarizations — or how their electric and magnetic fields are oriented — are affected. If we look at how the two types of polarization, the E-modes and B-modes, are affected on a variety of angular scales, we ought to be able to reconstruct what caused these signals.
Images credit: Amanda Yoho [Upper]; http://b-pol.org/ [Lower], of an E-mode polarization pattern at left and a B-mode pattern at right.
A portion of this signal, in addition to charged particles, could also originate from gravitational waves created in the early Universe. There are two main classes of models of inflation that give us a Universe consistent with what we observe in all ways: new inflation, which was actually the second model (and first viable model) ever proposed, and chaotic inflation, which was the third model (and second viable one).
Images credit: two inflation potentials, with chaotic inflation [Upper] and new inflation [Lower] shown. Chaotic inflation generates very large gravitational waves, while new inflation generates tiny ones. Generated by me, using google graph.
These two models of inflation make vastly different predictions for gravitational radiation: new inflation predicts gravitational waves (and primordial B-modes) that are extraordinarily tiny, and well beyond the reach of any current or even planned experiment or observatory, while chaotic inflation predicts huge B-modes, some of the largest ones allowable. These signatures have a characteristic frequency spectrum and affect all wavelengths of light identically, so it should be an easy signal to find if our equipment is sensitive to it.
Rather than measuring the whole sky, BICEP2 measured just a tiny fraction of the sky — about three fingers held together at arm’s length worth — but were able to tease out both the E-mode and B-mode polarization signals. And based on their analysis of the B-modes, which was very careful and very good, mind you, they claimed the greater-than-5σ detection.
What this means is that they had enough data so that the odds that what they were seeing was a “fluke” of having observed just a serendipitous patch of sky was tiny, or a one in 1.7 million chance. Flukes happen all the time at the one-in-100 level or the one-in-1,000, but one-in-1.7 million flukes… well, let’s just say you don’t win the lotto jackpot very often.
But there’s another type of error that they didn’t report. Not a statistical error, which is the kind you can improve on by taking more data, but a systematic error, which could be an effect that causes what you think is your signal, but is actually due to some other source! This type of error normally goes undetected because if you knew about it you’d account for it!
This is exactly what happened a couple of years ago, if you remember the “faster-than-light-neutrino” business. An experiment at CERN had reported the early arrival by just a few nanoseconds of thousands upon thousands of neutrinos, meaning that they would have exceeded the speed of light by something like 0.003%, a small but meaningful amount. As it turned out, the neutrinos weren’t arriving early; there was a loose cable that accounted for the error!
Well, one of the things the BICEP2 team didn’t measure was the galactic foreground emission. Polarized light — including light that contains these B-modes — gets emitted by the Milky Way galaxy, and that can contaminate your signal. The BICEP2 team used a very clever trick to try and eliminate this, by interpolating unreleased Planck data about galactic foregrounds, but when the Planck team actually released their data, the foregrounds were significantly different from what BICEP2 had anticipated. And with the new Planck data, the announcement of a “discovery” needed to be walked back; the evidence was now something like a one-in-200 chance of being a fluke.
Image credit: John Kovac, viahttp://cosmo2014.uchicago.edu/depot/invited-talk-kovac-john.pdf.
In other words, although gravitational waves could have caused this signal, so could other, far more mundane sources, including just our boring old galaxy!
Sometime later this month, the Planck team will release their all-sky polarization results, and either at that moment or shortly thereafter, we’ll find out whether there really are gravitational waves from inflation that can be detected with our current generation of telescopes, satellites and observatories. We’ll find out whether chaotic inflation is right, or whether we need to keep searching for the gravitational wave signal from before the Big Bang. We already have the density fluctuation signal, so we can be confident that inflation happened. It’s just a question of which type.
Image credit: Bock et al. (2006, astro-ph/0604101); modifications by me.
Stay curious, stay hungry for more knowledge, but always demand that your scientific claims be independently verified, that your possible systematic errors be checked, and that you have overwhelming evidence before believing the extraordinary claims. It’s easy to make a bold statement; it’s hard to start a bona fide scientific revolution!
Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible.
October 21, 2014
The Daily Galaxy via University of California – Berkeley
An international team of physicists has measured a subtle characteristic in the polarization of the cosmic microwave background radiation that will allow them to map the large-scale structure of the universe, determine the masses of neutrinos and perhaps uncover some of the mysteries of dark matter and dark energy. The POLARBEAR team is measuring the polarization of light that dates from an era 380,000 years after the Big Bang, when the early universe was a high-energy laboratory, a lot hotter and denser than now, with an energy density a trillion times higher than what they are producing at the CERN collider.
CMB per Planck
The Large Hadron Collider near Geneva is trying to simulate that early era by slamming together beams of protons to create a hot dense soup from which researchers hope new particles will emerge, such as the newly discovered Higgs boson. But observing the early universe, as the POLARBEAR group does may also yield evidence that new physics and new particles exist at ultra-high energies.
The team uses these primordial photon’s light to probe large-scale gravitational structures in the universe, such as clusters or walls of galaxies that have grown from what initially were tiny fluctuations in the density of the universe. These structures bend the trajectories of microwave background photons through gravitational lensing, distorting its polarization and converting E-modes into B-modes. POLARBEAR images the lensing-generated B-modes to shed light on the intervening universe.
In a paper published this week in the Astrophysical Journal, the POLARBEAR consortium, led by University of California, Berkeley, physicist Adrian Lee, describes the first successful isolation of a “B-mode” produced by gravitational lensing in the polarization of the cosmic microwave background radiation.
Polarization is the orientation of the microwave’s electric field, which can be twisted into a “B-mode” pattern as the light passes through the gravitational fields of massive objects, such as clusters of galaxies.
“We made the first demonstration that you can isolate a pure gravitational lensing B-mode on the sky,” said Lee, POLARBEAR principal investigator, UC Berkeley professor of physics and faculty scientist at Lawrence Berkeley National Laboratory (LBNL). “Also, we have shown you can measure the basic signal that will enable very sensitive searches for neutrino mass and the evolution of dark energy.”
The POLARBEAR team, which uses microwave detectors mounted on the Huan Tran Telescope in Chile’s Atacama Desert, consists of more than 70 researchers from around the world. They submitted their new paper to the journal one week before the surprising March 17 announcement by a rival group, the BICEP2 (Background Imaging of Cosmic Extragalactic Polarization) experiment, that they had found the holy grail of microwave background research. That team reported finding the signature of cosmic inflation – a rapid ballooning of the universe when it was a fraction of a fraction of a second old – in the polarization pattern of the microwave background radiation.
Subsequent observations, such as those announced last month by the Planck satellite, have since thrown cold water on the BICEP2 results, suggesting that they did not detect what they claimed to detect.
While POLARBEAR may eventually confirm or refute the BICEP2 results, so far it has focused on interpreting the polarization pattern of the microwave background to map the distribution of matter back in time to the universe’s inflationary period, 380,000 years after the Big Bang.
POLARBEAR’s approach, which is different from that used by BICEP2, may allow the group to determine when dark energy, the mysterious force accelerating the expansion of the universe, began to dominate and overwhelm gravity, which throughout most of cosmic history slowed the expansion.
BICEP2 and POLARBEAR both were designed to measure the pattern of B-mode polarization, that is, the angle of polarization at each point in an area of sky. BICEP2, based at the South Pole, can only measure variation over large angular scales, which is where theorists predicted they would find the signature of gravitational waves created during the universe’s infancy. Gravitational waves could only have been created by a brief and very rapid expansion, or inflation, of the universe 10-34 seconds after the Big Bang.
In contrast, POLARBEAR was designed to measure the polarization at both large and small angular scales. Since first taking data in 2012, the team focused on small angular scales, and their new paper shows that they can measure B-mode polarization and use it to reconstruct the total mass lying along the line of sight of each photon.
The polarization of the microwave background records minute density differences from that early era. After the Big Bang, 13.8 billion years ago, the universe was so hot and dense that light bounced endlessly from one particle to another, scattering from and ionizing any atoms that formed. Only when the universe was 380,000 years old was it sufficiently cool to allow an electron and a proton to form a stable hydrogen atom without being immediately broken apart. Suddenly, all the light particles – called photons – were set free.
“The photons go from bouncing around like balls in a pinball machine to flying straight and basically allowing us to take a picture of the universe from only 380,000 years after the Big Bang,” Lee said. “The universe was a lot simpler then: mainly hydrogen plasma and dark matter.”
These photons, which, today, have cooled to a mere 3 degrees Kelvin above absolute zero, still retain information about their last interaction with matter. Specifically, the flow of matter due to density fluctuations where the photon last scattered gave that photon a certain polarization (called E-mode polarization).
“Think of it like this: the photons are bouncing off the electrons, and there is basically a last kiss, they touch the last electron and then they go for 14 billion years until they get to telescopes on the ground,” Lee said. “That last kiss is polarizing.”
While E-mode polarization contains some information, B-mode polarization contains more, because photons carry this only if matter around the last point of scattering was unevenly or asymmetrically distributed. Specifically, the gravitational waves created during inflation squeezed space and imparted a B-mode polarization that BICEP2 may have detected. POLARBEAR, on the other hand, has detected B-modes that are produced by distortion of the E-modes by gravitational lensing.
While many scientists suspected that the gravitational-wave B-mode polarization might be too faint to detect easily, the BICEP2 team, led by astronomers at Harvard University’s Center for Astrophysics, reported a large signal that fit predictions of gravitational waves. Current doubt about this result centers on whether or not they took into account the emission of dust from the galaxy that would alter the polarization pattern.
In addition, BICEP2’s ability to measure inflation at smaller angular scales is contaminated by the gravitational lensing B-mode signal.
“POLARBEAR’s strong suit is that it also has high angular resolution where we can image this lensing and subtract it out of the inflationary signal to clean it up,” Lee said.
Two other papers describing related results from POLARBEAR were accepted in the spring by Physical Review Letters.
One of those papers is about correlating E-mode polarization with B-mode polarization, which “is the most sensitive channel to cosmology; that’s how you can measure neutrino masses, how you might look for early behavior of dark energy,” Lee said.
The [basically blue] image [above] shows the scale of a large quasar group” (LQG), the largest structure ever seen in the entire universe that runs counter to our current understanding of the scale of the universe. Even traveling at the speed of light, it would take 4 billion years to cross. This is significant not just because of its size but also because it challenges the Cosmological Principle, which has been widely accepted since [Albert] Einstein, the assumption that the universe, when viewed at a sufficiently large scale, looks the same no matter where you are observing it from.
Space dust accounts for at least some of the possible signal of cosmic inflation the BICEP2 experiment announced in March. How much remains to be seen.
That includes the area of space studied by the BICEP2 experiment, which in March announced seeing a faint pattern left over from the big bang that could tell us about the first moments after the birth of the universe.
Gravitational Wave Background from BICEP2
The Planck analysis, which started before March, was not meant as a direct check of the BICEP2 result. It does, however, reveal that the level of dust in the area BICEP2 scientists studied is both significant and higher than they thought.
“There is still a wide range of possibilities left open,” writes astronomer Jan Tauber, ESA project scientist for Planck, in an email. “It could be that all of the signal is due to dust; but part of the signal could certainly be due to primordial gravitational waves.”
BICEP2 scientists study the cosmic microwave background, a uniform bath of radiation permeating the universe that formed when the universe first cooled enough after the big bang to be transparent to light. BICEP2 scientists found a pattern within the cosmic microwave background, one that would indicate that not long after the big bang, the universe went through a period of exponential expansion called cosmic inflation. The BICEP2 result was announced as the first direct evidence of this process.
The problem is that the same pattern, called B-mode polarization, also appears in space dust. The BICEP2 team subtracted the then known influence of the dust from their result. But based on today’s Planck result, they didn’t manage to scrub all of it.
How much the dust influenced the BICEP2 result remains to be seen.
In November, Planck scientists will release their own analysis of B-mode polarization in the cosmic microwave background, in addition to a joint analysis with BICEP2 specifically intended to check the BICEP2 result. These results could answer the question of whether BICEP2 really saw evidence of cosmic inflation.
“While we can say the dust level is significant,” writes BICEP2 co-leader Jamie Bock of Caltech and NASA’s Jet Propulsion Laboratory, “we really need to wait for the joint BICEP2-Planck paper that is coming out in the fall to get the full answer.”
[Me? I am rooting for my homey, Alan Guth, from Highland Park, NJ, USA]
But to be sure, it needs the best data on factors that confound its research – data that Planck has been compiling.
If the two teams come to an arrangement, it is more likely they will hammer down the uncertainties.
“We’re still discussing the details but the idea is to exchange data between the two teams and eventually come out with a joint paper,” Dr Jan Tauber, the project scientist on the European Space Agency’s Planck satellite, told BBC News.
This paper, hopefully, would be published towards the end of the year, he added.
Foreground dust per Planck
The question of whether the BICEP2 team did, or did not, identify a signal on the sky for inflation has gripped the science world for weeks.
The group used an extremely sensitive detector in its Antarctic telescope to study light coming to Earth from the very edge of the observable Universe – the famous Cosmic Microwave Background (CMB) radiation.
Planck artist impression The Planck satellite was launched in 2009 to map the Cosmic Microwave Background
BICEP2 looked for swirls in the polarisation of the light.
This pattern in the CMB’s directional quality is a fundamental prediction of inflation – the idea that there was an ultra-rapid expansion of space just fractions of a second after the Big Bang.
The twists, known as B-modes, are an imprint of the waves of gravitational energy that would have accompanied the violent growth spurt.
But this primordial signal – if it exists – is expected to be extremely delicate, and a number of independent scientists have expressed doubts about the American team’s finding. And the BICEP2 researchers themselves lowered their confidence in the detection when they formally published their work in a Physical Review Letters paper last month.
At issue is the role played by foreground dust in our galaxy.
Nearby spinning grains can produce an identical polarisation pattern, and this effect must be removed to get an unambiguous view of the primordial, background signal.
The BICEP2 team used every piece of dust information it could source on the part of the sky it was observing above Antarctica.
What it lacked, however, was access to the dust data being compiled by the Planck space telescope, which has mapped the microwave sky at many more frequencies than BICEP2.
This allows it to more easily characterise the dust and discern its confounding effects.
Dust Planck released dust information close to the galactic plane in May
In May, the Planck Collaboration published dust polarisation information gathered close to the galaxy’s centre – where the grains are most abundant.
In a few weeks’ time, the Planck team plans to release further information detailing galactic dust in high latitude regions, including the narrow patch of the southern sky examined by BICEP2.
And then, in late October, the Planck Collaboration is expected to say something about whether it can detect primordial B-modes.
As Dr Tauber explained, Planck’s approach to the problem is a different one to BICEP2’s.
“Planck’s constraints on primordial B-modes will come from looking at the whole sky with relatively low sensitivity as compared to BICEP2,” he said.
“But because we can look at the whole sky, it makes up for some of that [lower sensitivity] at least. On the other hand, we have to deal with the foregrounds – we can’t ignore them at all.
“At the same time, we will work together with BICEP2 so that we can contribute our data to improve the overall assessment of foregrounds and the Cosmic Microwave Background.
“We hope to start working with them very soon, and if all goes well then we can maybe publish in the same timeframe as our main result [at the end of October].”
Chao-Lin Kuo and Kent Irwin Helped Develop Technology for Imaging Gravitational Waves
Two scientists at Stanford University and SLAC National Accelerator Laboratory made key contributions to the discovery of the first direct evidence for cosmic inflation – the rapid expansion of the infant universe in the first trillionth of a trillionth of a trillionth of a second after the Big Bang.
Chao-Lin Kuo is one of four co-leaders of the BICEP2 collaboration that announced the discovery on Monday. An assistant professor at SLAC and Stanford, he led the development of the BICEP2 detector and is building the BICEP3 follow-on experiment in his Stanford lab for deployment at the South Pole later this year.
Chao-Lin Kuo at the South Pole research station where the BICEP2 experiment operated from 2010 to 2012. (Photo courtesy of Chao-Lin Kuo)
BICEP With South Pole Telescope
Kent Irwin invented the type of sensor used in BICEP2 as a graduate student at Stanford, adapted it for X-ray experiments and studies of the cosmos during a 20-year career at the National Institute for Standards and Technology, and returned to SLAC and Stanford as a professor in September to lead a major initiative in sensor development.
“It’s exciting that the same technology I developed as a grad student to search for tiny particles of dark matter is also being used to do research on the scale of the universe and to study the practical world of batteries, materials and biology in between,” Irwin said. His group is working toward installing a version of the BICEP2 sensors at SLAC’s X-ray light sources – Stanford Synchrotron Radiation Lightsource (SSRL) and Linac Coherent Light Source (LCLS) – as well as at a planned LCLS upgrade.
Searching for Ripples in Space-time
BICEP is a series of experiments that began operating at the South Pole in January 2006, taking advantage of the cold, clear, dry conditions to look for a faint, swirling polarization of light in the Cosmic Microwave Background (CMB) radiation. The light in the CMB dates back to 380,000 years after the Big Bang; before that, the early universe was opaque and no light could get through.
CMB Planck
But some theories predicted that gravitational waves – ripples in space-time – would have been released in the first tiny fraction of a second after the Big Bang, as the universe expanded exponentially in what is known as “cosmic inflation.” If that were the case, scientists might be able to detect the imprint of those waves in the form of a slight swirling pattern known as “B-mode polarization” in the CMB.
On Monday, researchers from the BICEP2 experiment, which ran from January 2010 through December 2012, announced that they had found that smoking-gun signature, confirming the rapid inflation that had been theorized more than 30 years ago by Alan Guth and later modified by Andrei Linde, a Russian theorist who is now at Stanford.
Building a Better Detector
Kuo started working on BICEP1 as a postdoctoral researcher at Caltech in 2003. The circuitry in the experiment’s detectors was all made by hand. For the next-generation detector, BICEP2, the collaborating scientists wanted something that could be mass-produced in larger quantities, allowing them to pack more sensors into the array and collect data 10 times faster. So Kuo also started designing that technology, which used photolithography – a standard tool for making computer chips – to print sensors onto high-resolution circuit boards.
The sun sets behind BICEP2 (in the foreground) and the South Pole Telescope (in the background). (Steffen Richter, Harvard University)
The BICEP2 detector shown in this electron-beam micrograph works by converting the light from the cosmic microwave background into heat. A titanium film tuned on its transition to a superconducting state makes a sensitive thermometer to measure this heat. The sensors are cooled to just 0.25 degrees above absolute zero to minimize thermal noise. (Anthony Turner, JPL)
In 2008 Kuo arrived at SLAC and Stanford and began working on the next-generation experiment, BICEP3, for which he is principal investigator. Scheduled for deployment at the South Pole later this year, BICEP3 will look at a larger patch of the sky and collect data 10 times faster than its predecessor; it’s also more sensitive and more compact.
SLAC took on a bigger role in this research in October 2013 by awarding up to $2 million in Laboratory Directed Research and Development funding over three years for the “KIPAC Initiative for Cosmic Inflation,” with Kuo as principal investigator. The grant establishes a large-scale Cosmic Microwave Background program at the lab, with part of the funding going toward BICEP3, and has a goal of establishing KIPAC as a premier institute for the study of cosmic inflation. There are also plans to establish a comprehensive development, integration, and testing center at SLAC for technologies to further explore the CMB, which holds clues not only to gravitational waves and cosmic inflation but also to dark matter, dark energy and the nature of the neutrino.
A Fancy Thermometer for Tiny Signals
Kent Irwin entered the picture in the early 1990s, while a graduate student in the laboratory of Stanford/SLAC Professor Blas Cabrera. There he invented the superconducting Transition Edge Sensor, or TES, for the Cryogenic Dark Matter Search, which is trying to detect incoming particles of dark matter in a former iron mine in Minnesota. When he moved to NIST, he and his team adapted the technology for other uses and also developed a very sensitive way to read out the signal from the sensors with devices known as SQUID multiplexers.
Printing TES devices on circuit boards and using the SQUID multiplexers to read them out made it possible to create large TES arrays and greatly expanded their applications in astronomy, nuclear non-proliferation, materials analysis and homeland defense. It was also the key factor in allowing the BICEP team to expand the number of detectors in its experiments from 98 in BICEP1 to 500 in BICEP2, and opens the path to even larger arrays that will greatly increase the sensitivity of future experiments.
A TES is “basically a very fancy thermometer,” Irwin says. “We’re measuring the power coming from the CMB.” The TES receives a microwave signal from an antenna and translates it into heat; the heat then warms a piece of metal that’s chilled to the point where it hovers on the edge of being superconducting – conducting electricity with 100 percent efficiency and no resistance. When a material is at this edge, a tiny bit of incoming heat causes a disproportionately large change in resistance, giving scientists a very sensitive way to measure small temperature changes. The TES devices for BICEP2 were built at NASA’s Jet Propulsion Laboratory, and Irwin’s team at NIST made the SQUID multiplexers.
The Road Ahead
Looking ahead, CMB researchers in the United States developed a roadmap leading to a fourth-generation experiment as part of last year’s Snowmass Summer Study, which lays out a long-term direction for the national high energy physics research program. That experiment would deploy hundreds of thousands of detector sensors and stare at a much broader swath of the cosmos at an estimated cost of roughly $100 million.
“These are incredibly exciting times, with theory, technology and experiment working hand in hand to give us an increasingly clear picture of the very first moments of the universe,” said SLAC Lab Director Chi-Chang Kao. “I want to congratulate everyone in the many collaborating institutions who made this spectacular result possible. We at SLAC are looking forward to continuing to invest and work in this area as part of our robust cosmology program.”
SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
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