From Quanta Magazine (US) : “Cosmologists Parry Attacks on the Vaunted Cosmological Principle”

From Quanta Magazine (US)

December 13, 2021
Charlie Wood

Giant arc of galaxies puts basic cosmology under scrutiny.

A central pillar of Cosmology — the universe is the same everywhere and in all directions — is surviving a storm of possible evidence against it.

Most observations suggest that the cosmos is uniform on scales larger than hundreds of millions of light-years. Recent discoveries of unexpectedly large structures and motions have called that into question. Credit: Olena Shmahalo for Quanta Magazine.

Laniakea supercluster. From Nature: The Laniakea supercluster of galaxies. Milky Way is the red dot. Credit: R. Brent Tully, Hélène Courtois, Yehuda Hoffman & Daniel Pomarède at http://www.nature.com/nature/journal/v513/n7516/full/nature13674.html.

The latest attempt to rattle the foundations of cosmology appeared as a smattering of dots pulled upward into a cosmic sneer. The arc of distant galaxies, which Alexia Lopez presented at The American Astronomical Society’s meeting in June, sprawls so far across the sky that it would take 20 full moons to hide it. Spanning an estimated 3.3 billion light-years of space, the smile-shaped structure joined a controversial club: unexpectedly big things.

“It’s so big that it’s hard to explain with our current beliefs,” Lopez, one of the astrophysicists at The University of Central Lancashire (UK) who identified the galaxy chain, said during the presentation.

Lopez’s “Giant Arc” seemed to clash with an idea that has guided astronomy for centuries: that the universe has no conspicuous features. From a zoomed-out perspective, no matter where you are or which way you look you should see roughly the same number of galaxies pinwheeling around.

This assumption is enshrined as the “cosmological principle,” has let researchers draw sweeping conclusions about the whole universe based only on what we see from our corner of it.

“If that turns out to be wrong then we have to redo many of our measurements or reinterpret many of our measurements,” said Ruth Durrer, a cosmologist at The University of Geneva (CH).

As a load-bearing strut of modern cosmology, the cosmological principle has increasingly become a target. Some challengers, like Lopez and her colleagues, are astrophysicists puzzled by striking celestial conglomerations. Others are maverick cosmologists unsettled by the consensus view that most of the stuff in the cosmos hides from our instruments in the form of “dark matter” and “dark energy”; they wonder whether theorists may have conjured phantasms to patch up an overly simplistic theory of cosmology.

Most everyone agrees that the cosmological principle is worth scrutinizing. So far, though, each new claim of a too-big structure or other anomaly has failed to make a dent. We are “trying to poke as many holes as we can,” said Seshadri Nadathur, a cosmologist at The University College London (UK), “while being very skeptical of someone else saying they’ve poked a hole.”

From Copernicus to Einstein

The cosmological principle grew out of the Copernican principle, Nicolaus Copernicus’ 1543 realization that Earth is not the fixed center of creation. His insight that Earth orbits the sun rather than the other way around set off a series of humbling shifts in perspective. Astronomers proved in the 1800s that the sun is just a normal star. The following century, they spotted countless galaxies beyond our own.

“We’re not special,” said Andrew Howell, a cosmologist at The Las Cumbres Observatory and The University of California-Santa Barbara (US). “The universe keeps telling us that.”

Samuel Velasco / Quanta Magazine; source: A. Lopez/The University of Central Lancashire (UK).

Not only is Earth not special, but nothing anywhere is special. Over the past century, astronomical surveys solidified what’s become known as the cosmological principle in two ways. As powerful telescopes peered deeper into the darkness they saw more-distant galaxies appearing in similar numbers. This suggests that the cosmos is homogeneous, with matter sprinkled smoothly throughout. (Think of the expanding universe as a rising fruitcake with galaxies evenly spread like fruit pieces, each one flying away from its neighbors as the batter between them expands.)

Moreover, telescopes pointed in different directions have all seen similar scenes. Matter is evenly distributed along every line of sight, indicating that the universe is “isotropic.”

The cosmos’s homogeneity and isotropy make it simple enough to analyze.

Theorists reconstruct the cosmos’s past and predict its future using a standard theoretical model based largely on Albert Einstein’s Theory of General Relativity, or theory of gravity. Einstein’s theory describes the interplay between matter and space-time — the bendy fabric of the universe. But Einstein’s treatment involves 10 interlinked equations and 20 variables, a system of equations that is generally too complicated to solve.

Cosmologists lean on the cosmological principle to restrict their focus to a universe acting as a smooth and symmetric fluid. By ignoring bumps of matter like galaxies and requiring the universe to expand in the same way along all three axes, the cosmological principle deletes parts of the equations and links some of the variables, dramatically simplifying the system of equations. Theorists can then predict the velocity and acceleration of the cosmos’s expansion with just two equations — the Friedmann equations, derived from Einstein’s by Alexander Friedmann, a Russian cosmologist, in 1922. It’s a bit like computing the volume of the Earth: You could fret over every mountain and ravine, or you could assume the planet is a sphere and call it a day.

As astronomers map the universe more precisely, however, a few researchers have started to wonder whether the field has pushed the cosmological principle too far. Earth isn’t a sphere, after all — it bulges at the equator. In the same way, large structures or lopsided features could undermine conclusions about the universe’s age, behavior and composition.

Thomas Buchert, a cosmologist at Claude Bernard University Lyon 1 [Université Claude Bernard Lyon 1](FR) in France, is among those who have become convinced that it’s time to move beyond Friedmann’s monotone universe. “It’s strange it’s still alive, this standard model,” he said.

Galaxies Everywhere

The Giant Arc and other giant structures strike at the first pillar of the cosmological principle: homogeneity.

The universe is clearly not homogeneous on the human scale. Teleport a person one light-year from here and you’ll ruin their day. But drop the Hubble Space Telescope halfway across the universe, and it will return familiar-looking galaxy-filled images. In this way, the cosmological principle treats the cosmos like the air in an inflating balloon. Up close, molecules mingle in complicated ways. But from far away, a bland gas expands with bulk properties like pressure and temperature changing steadily.

Galaxy surveys [MNRAS] have found that any patch of space larger than hundreds of millions of light-years across includes roughly the same amount of matter. So structures like the Giant Arc, which spans billions of light years, are as unexpected as a thick clot of air in an otherwise ordinary balloon.

One of the first of these structures was identified in 2013: a putative grouping [MNRAS] of brilliant galaxy cores known as quasars distributed across 4 billion light-years that, its discoverers wrote, “challenges the assumption of the cosmological principle.”

Few others were convinced. Nadathur, the UCL cosmologist, set out to see if randomness alone could create the illusion of megastructures. He simulated digital universes that had galaxies scattered completely haphazardly. Nevertheless, when he set a cluster-hunting program loose on the smooth simulations, it picked out patterns [MNRAS] as large as the quasar group purely by chance. Simulated standard-model universes (in which gravity has drawn galaxies together into groups) would contain groupings of galaxies that were grander still. Nadathur’s work suggested that the cosmological principle has plenty of room for the quasar group, the Giant Arc and others of their ilk. Huge structures will be rare, he said, but the standard model “doesn’t say the probability is zero at any scale.”

A more convincing observation of inhomogeneity, according to Nadathur, would be the discovery that matter maintains some lumpiness as you look at larger and larger scales. But studies [Journal of Cosmology and Astroparticle Physics] to date have consistently found [MNRAS] that as you zoom out, the universe gets ever smoother.

Durrer and other cosmologists agree that seemingly impossible structures can probably be explained by humdrum statistics. “If you make many, many observations, you will have some of them which are statistically not very probable,” she said. “I’m not very much worried about those.”

Directionless Universe

Even if the universe is homogeneous, it could still single out one direction for something special — an “anisotropy.” In such a cosmos, great streams of matter might flow in that direction like a breeze. A few cosmologists think this might be happening.

Strong evidence against any sort of cosmic flow comes from the afterglow of the Big Bang. Astronomers have determined that this “cosmic microwave background” [CMB] has an essentially identical average temperature of 2.725 degrees above absolute zero in every direction.

CMB per European Space Agency(EU) Planck.

But to calculate that temperature, researchers correct for a slight imbalance: The CMB looks a fraction of a degree warmer toward the constellation Aquarius, and a fraction of a degree cooler in the opposite direction.

Light that fills the cosmos from the Big Bang looks slightly warmer coming from one side of the sky than the other, this COBE satellite image revealed in the early 1990s.

National Aeronautics Space Agency(US) Cosmic Background Explorer COBE 1989 to 1993.

The distortion is widely thought to result from our solar system’s motion, but a few cosmologists think the whole universe might drift. Credit: The National Aeronautics and Space Administration (US).

Almost all cosmologists interpret this observation as resulting from our solar system’s own motion, known as our “peculiar velocity.” The sun orbits the Milky Way’s center and the Milky Way moves toward nearby galaxies such that our solar system drifts against the background of the CMB at roughly 300 kilometers per second, distorting incoming microwaves. This local drift is not seen as a problem for the cosmological principle.

But our peculiar velocity might not fully explain the perceived lopsidedness of the CMB; the distortion could also include the effect of the whole universe drifting. If this is the case, gauging our motion against distant galaxies will give a different result than if we measure our speed against the CMB, since those galaxies will be moving too. Imagine going for a train ride and measuring your speed against a mountain range and against clouds on the horizon. If the speeds don’t match, the clouds must be scudding over the mountains.

Several teams have attempted such measurements against distant galaxies and found apparent oddities. In one recent effort [The Astrophysical Journal Letters], researchers calculated our motion against more than 1 million faraway quasars. They observed an optical distortion aligned with the imbalance in the CMB, but twice as large. One interpretation is that the Earth drifts at around 600 kilometers per second relative to the quasars, implying that the quasars may be moving against the CMB.

Subir Sarkar, a cosmologist at The University of Oxford (UK) and a member of the group that made the calculation, called the discrepancy a “body blow” to the standard model and its assumption of an isotropic universe. He pointed to speculation that some giant cloud of matter sits outside the observable universe and drags everything toward it. (We can only observe the spherical volume of the universe whose light has had time to reach us since the Big Bang.) “We don’t know what’s outside, and there is a lot outside,” Sarkar said. “Maybe there is a monster lurking there.” That would upend the leading theory of the cosmos’s first moments, which holds that space exponentially inflated, becoming smooth and flat far beyond our observable patch.

Most cosmologists remain skeptical that the quasars prove an off-kilter universe, however. Several researchers interviewed for this article said that various technical challenges, such as the uneven distribution of the quasars, make it tough to compare the quasars with the CMB. “Those studies are pretty hard to do,” said Tamara Davis, an astrophysicist at The University of Queensland (AU).

Durrer calls the quasar evidence inconclusive and says she is keeping an open mind. She recently devised an alternative test that combines various ways our motion would tweak the appearance of distant galaxies. She and her colleagues calculated that, using their technique, next-generation observatories will be able to pick up peculiar velocities differing by just a few percentage points, allowing precision tests of isotropy and the cosmological principle this decade. They published their new approach [Journal of Cosmology and Astroparticle Physics] in early November.

“This we will be able to resolve,” Durrer said.

Escaping the Background

To keep pace with sharpening observations of the universe, many theorists, in their standard-model calculations, incorporate modest ripples of matter in an otherwise smooth fluid, akin to improving on an estimation of the Earth’s volume by including an assortment of mountain ranges. “You make life more complicated again, but you add the complications in a controlled kind of way,” Nadathur said.

But some, like Buchert, the French cosmologist, want a fuller departure from the assumption that the universe is the same everywhere. To that end, Buchert has spent decades developing a “background-free” model of cosmology.

Einstein’s general relativity theory demolished the classical notion of a background — a fixed stage against which one might measure distances and movements. Instead, it says space-time curves around matter like theater curtains swishing after actors pass by, sometimes making the play’s action hard to follow. The standard model lets space-time bend a bit but uses the cosmological principle to keep the curves small and the expansion rate uniform. In this way, it restores a notion of a backdrop to make calculations feasible.

Buchert’s work [General Relativity and Gravitation] does away with the universal background. Instead, he splits the cosmos into large chunks and averages the amount of matter (and the resulting bending of space-time) in each region. He then treats the average as a local backdrop against which to interpret any events taking place inside that chunk — an approach that has turned up an unexpected result.

In 1998, astrophysicists looking at distant supernovas determined that the universe appears to be expanding faster as time goes on. Their Nobel Prize-winning observation implied that some repulsive energy, dubbed dark energy — probably the energy of space itself — is pushing galaxies apart from each other more forcefully than gravity can draw them together.

Saul Perlmutter (center) [The Supernova Cosmology Project] shared the 2006 Shaw Prize in Astronomy, the 2011 Nobel Prize in Physics, and the 2015 Breakthrough Prize in Fundamental Physics with Brian P. Schmidt (right) and Adam Riess (left) [The High-z Supernova Search Team] for providing evidence that the expansion of the universe is accelerating.

Buchert’s background-free approach has raised another possibility. Compared to small, dense patches of galaxies, emptier “voids” in space expand faster, since they have fewer galaxies gravitationally attracting and slowing each other down. Since the empty parts grow faster than the dense parts, the universe becomes emptier. And so its overall expansion rate grows. Buchert argues that this effect, called backreaction, could explain the cosmic acceleration without the need for dark energy.

Other cosmologists agree that the background-free treatment is mathematically sound, and that backreaction is real. But is it a big enough effect to kill dark energy? This question motivated Durrer and her colleagues to do a large-scale simulation [Physical Review D] in 2019. They prepared a digital universe populated with hundreds of billions of galaxies and calculated how differing expansion rates in voids and galaxy clusters would affect light beams headed for a randomly placed astronomer. They found that backreaction would throw off the astronomer’s measurement of the universe’s expansion rate by about 2%. In other words, the standard model predicts an accelerating expansion of space that appears to be 98% accurate, and backreaction struggles to explain away dark energy.

“The consensus now is that it is a small effect that does not, in the end, cause too much trouble,” Nadathur said.

But that 2% could yet prove consequential. Durrer is investigating whether backreaction might help resolve a growing cosmological crisis. The crisis, known as the Hubble tension, is that the nearby universe appears to expand about 9% faster than what the standard model predicts for the universe’s overall expansion rate. Many explanations have been floated, including radical new ingredients in the cosmos. But Buchert argued last year that the broad-brush cosmological principle might be to blame for the apparent discrepancy. In a lumpy universe, one would expect emptier patches to expand faster than the average.

Durrer is simulating the effects of backreaction to calculate the odds that we could have landed in the middle of such an empty, expansive section of space. “Even if backreaction is not sufficient to explain the accelerated expansion, it might be marginally sufficient to solve the Hubble tension,” she said, although she doesn’t expect it to provide the whole answer.

A Privileged Location

If the Hubble tension does turn out to be a partially backreaction-induced mirage, that will be the first major instance of the cosmological principle hampering rather than aiding our understanding of the cosmos. But for now, researchers say, the predictive power of the principle seems to be holding up quite well.

“Is the universe really homogeneous and isotropic everywhere? To the best of our knowledge at the moment, yes it is,” Nadathur said.

Making grand inferences about the entire cosmos is hard because we are, after all, in a unique location: the here and now. Telescopes can only see so far, making it look as if galaxies peter out toward the limits of their vision. And as astronomers peer farther away and deeper into the past, they see galaxies in the early universe acting differently than they do today. Artifacts of our singular perspective are all too easily mistaken for failures of the cosmological principle itself.

“Almost every effect that can screw you up works in that way,” Howell said. “It’s all because we only have one vantage point to look from in the universe.”

See the full article here .

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Formerly known as Simons Science News, Quanta Magazine (US) is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

From Ethan Siegel: “Ask Ethan: Was The Critical Evidence For The Big Bang Discovered By Accident?”

From Ethan Siegel
Dec 7, 2019

In science, breakthroughs don’t always begin with a ‘eureka’ moment. Sometimes, the true story is absolutely unbelievable.

Penzias and Wilson and the ATT Bell labs Holmdel Horn

A visual history of the expanding Universe includes the hot, dense state known as the Big Bang and the growth and formation of structure subsequently. The full suite of data, including the observations of the light elements and the cosmic microwave background, leaves only the Big Bang as a valid explanation for all we see. As the Universe expands, it also cools, enabling ions, neutral atoms, and eventually molecules, gas clouds, stars, and finally galaxies to form. (NASA / CXC / M. WEISS)

When it comes to our Universe’s origin story, many competing ideas once thrived. Scientists considered a myriad of different possibilities, all of which were compatible with the full suite of data and the laws of nature, at least as they were known at the time. Yet as our measurements and observations of the cosmos improved, these possibilities were put to the test, with most of them falling away. By the 1960s, only a few possibilities remained, when something truly spectacular occurred: the “smoking gun” of the Big Bang was discovered. But was it a complete accident? That’s what Patrick Pallagi wants to know, asking:

The cosmic microwave background [CMB] is a landmark evidence of the Big Bang origin of the universe. How come this discovery is labelled as an accidental one?

CMB per ESA/Planck

ESA/Planck 2009 to 2013

Sometimes, the best discoveries are the ones you don’t expect. Sometimes, you even scoop the scientists searching for what you’ve accidentally found.

If you look farther and farther away, you also look farther and farther into the past. The farthest we can see back in time is 13.8 billion years: our estimate for the age of the Universe. It’s the extrapolation back to the earliest times that led to the idea of the Big Bang. While everything we observe is consistent with the Big Bang framework, it’s not something that can ever be proven. (NASA / STSCI / A. FELID)

The idea of the Big Bang sprouted back in the 1920s, when scientists were first working out the consequences of a Universe governed by General Relativity. In a Universe that had roughly the same amount of matter-and/or-energy in all locations and with no preferred direction, a number of theoretical solutions arose. The Universe could not be stationary and unchanging, but needed to either be expanding or contracting, and could be spatially flat, closed, or open.

Just as, mathematically, the square root of 4 could either be +2 or -2, the field equations of General Relativity alone couldn’t determine what the Universe was made of, what its curvature was, or how the fabric of space itself was evolving with time. An enormous observational breakthrough, spearheaded by Edwin Hubble’s measurements of individual stars in what we now know are distant galaxies, paved the way to the expanding Universe.

First noted by Vesto Slipher back in 1917, some of the objects we observe show the spectral signatures of absorption or emission of particular atoms, ions, or molecules, but with a systematic shift towards either the red or blue end of the light spectrum. When combined with the distance measurements of Hubble, this data gave rise to the initial idea of the expanding Universe: the farther away a galaxy is, the greater its light is redshifted. (VESTO SLIPHER, (1917): PROC. AMER. PHIL. SOC., 56, 403)

But over on the theoretical side, Georges Lemaître had already worked out one remarkable solution for the expanding Universe: one that began with what he called a “primeval atom,” which became the germ of an idea that would grow into the Big Bang.

If the fabric of the Universe is expanding today and driving distant, unbound galaxies apart from one another — the same way a ball of bread dough with raisins throughout it leavens and causes the raisins to apparently spread away from each other — then that should mean the Universe is getting sparser and lower in energy as time goes on. Densities drop and photon wavelengths stretch in an expanding Universe. But what was most remarkable about this scenario is that it meant the reverse is also true: if we look backwards in time, the Universe should have been denser and higher in energy.

The ‘raisin bread’ model of the expanding Universe, where relative distances increase as the space (dough) expands. The farther away any two raisin are from one another, the greater the observed redshift will be by time the light is received. The redshift-distance relation predicted by the expanding Universe is borne out in observations, and has been consistent with what’s been known all the way back since the 1920s. (NASA / WMAP SCIENCE TEAM)

By the time the 1940s rolled around, Lemaître’s ideas — although nothing had demonstrated them to be incorrect — had failed to gain traction. However, George Gamow was extremely curious about them, and began a research program dedicated to developing these ideas. In particular, he noted that if the Universe was expanding while it was gravitating and cooling, the past would have looked very different from the present.

If you went back early enough, you should come to a time where stars and galaxies hadn’t yet formed, since matter needs time for gravitation to clump and cluster it together. At some point even earlier, the photons must have been hot enough to prevent the formation of neutral atoms, ionizing them faster than electrons and nuclei can form stable atoms. And even before that, the photons were likely hot enough to blast apart even atomic nuclei, creating a sea of protons and neutrons.

As the Universe cools, atomic nuclei form, followed by neutral atoms as it cools further. All of these atoms (practically) are hydrogen or helium, and the process that allows them to stably form neutral atoms takes hundreds of thousands of years to complete. (E. SIEGEL)

Those four theoretical predictions:

an expanding Universe,
where stars and galaxies and structure only formed and grew over time,
where there was a moment of transition between the Universe being an ionized plasma and full of neutral atoms,
and where the early hot, dense stage led to an epoch before stars where nuclear fusion occurred,

became the four cornerstones of the theoretical framework of the Big Bang.

Of course, the Big Bang wasn’t the only game in town; there were alternatives that made different predictions. The Steady-State Universe, for example, contended that the Universe was filled with a matter creation field that constantly created new particles as it expanded, and that the elements we see were made in stars. However, that idea of a transition between a plasma phase and a neutral-atom phase would prove to be the differentiator between the Big Bang and all the remaining alternatives.

In the hot, early Universe, prior to the formation of neutral atoms, photons scatter off of electrons (and to a lesser extent, protons) at a very high rate, transferring momentum when they do. After neutral atoms form, owing to the Universe cooling to below a certain, critical threshold, the photons simply travel in a straight line, affected only in wavelength by the expansion of space. (AMANDA YOHO)

Gamow recognized that if the Universe was filled with both matter and radiation, the expansion of space would stretch that radiation to longer and longer wavelengths — and hence, lower energies and lower temperatures — over time. If we want to extrapolate back to a time where the Universe was hot enough to ionize neutral atoms, we’d have to go back to where the mean temperature was thousands of degrees.

No problem, obviously, thought Gamow. The key would then be to estimate how much the Universe had expanded from that early time until the present day. While Gamow and his students and research collaborators did their best, they only came up with a range of possible values for what this radiation should look like today. Once the Universe becomes neutral, those photons should just stream in a straight line, stretched by the expanding Universe, until they arrive at our eyes at just a few degrees above absolute zero.

After the Universe’s atoms become neutral, not only did the photons cease scattering, all they do is redshift subject to the expanding spacetime they exist in, diluting as the Universe expands while losing energy as their wavelength continues to redshift. While we can concoct a definition of energy that will keep it conserved, this is contrived and not robust. Energy is not conserved in an expanding Universe. (E. SIEGEL / BEYOND THE GALAXY)

With the power of hindsight, it’s astonishing to realize what a missed opportunity there was. In 1949, electrical engineer Joseph Weber was hired as a professor and ordered by the University to go get a Ph.D. in something. He approached Gamow, introducing himself by saying, “I’m a microwave engineer with considerable experience. Can you suggest a PhD problem?”

Gamow simply told him “no.”

Which is really a shame, because after billions of years of cosmic evolution and the Universe expanding, the microwave portion of the spectrum is exactly where this leftover radiation from the Big Bang — today’s CMB (cosmic microwave background) and yesteryear’s primeval fireball — should remain today. The right microwave experiment would have revealed it; instead, Weber went on to build primitive gravitational wave detectors.

Joseph Weber with his early-stage gravitational wave detector, known as a Weber bar. A microwave-specialized electrical engineer, Gamow’s dismissal of Weber was an enormous missed opportunity for discovering the CMB. (SPECIAL COLLECTIONS AND UNIVERSITY ARCHIVES, UNIVERSITY OF MARYLAND LIBRARIES)

More time passed, and by the 1960s, a team of researchers at Princeton — including Bob Dicke, Jim Peebles, David Wilkinson and Peter Roll — starting planning a mission to detect this leftover radiation. Temperature estimates had gotten much better, and the development of a detector (a Dicke radiometer) that could find this radiation via a balloon-borne mission, coupled with Peebles’ theoretical work, made this an imminent possibility.

However, some 30 miles away, two scientists (Arno Penzias and Bob Wilson) working on satellite communications for Bell Labs (a subsidiary of AT&T) were using a brand new piece of equipment: the Holmdel horn antenna. It was giant, ultra-sensitive, and designed for receiving signals from Earth. However, there was a problem: no matter where in the sky they pointed their antenna, there was this annoying background of noise they just couldn’t seem to get rid of.

Arno Penzias and Bob Wilson at the location of the antenna in Holmdel, New Jersey, where the cosmic microwave background was first identified. Although many sources can produce low-energy radiation backgrounds, the properties of the CMB confirm its cosmic origin. (PHYSICS TODAY COLLECTION/AIP/SPL)

Arno Penzias and Robert Wilson, AT&T, Holmdel, NJ USA, with the Holmdel horn antenna, first caught the faint echo of the Big Bang

They tried everything. They tried turning it off and on again. They tried pointing it towards the Sun and then away from it. They used it during the day. They used it at night. They aimed it at the plane of the Milky Way. They even discovered pigeons roosting in the horn, resulting in a scene where they cleaned the nests out and mopped up all the bird droppings. Still, that background signal remained constant and omnipresent across the entire sky.

It was only after calling around and sharing their puzzlement that a visiting scientist — who happened to be the referee of a recent Peebles paper — suggested that this might be the long-sought signal of the CMB. Penzias and Wilson gave the Dicke group a call, and after a brief conversation, realized what they had discovered after all. Dicke’s voice rang out through the halls at Princeton, announcing “boys, we’ve been scooped!” Completely by accident, the smoking gun for the Big Bang had just been discovered.

The unique prediction of the Big Bang model is that there would be a leftover glow of radiation permeating the entire Universe in all directions. The radiation would be just a few degrees above absolute zero, would be the same magnitude everywhere, and would obey a perfect blackbody spectrum. These predictions were borne out spectacularly well, eliminating alternatives like the Steady State theory from viability. (NASA / GODDARD SPACE FLIGHT CENTER / COBE (MAIN); PRINCETON GROUP, 1966 (INSET))

Over the subsequent years and decades, the evidence for the Big Bang has strengthened by extraordinary amounts, with large-scale structure, primordial light element abundances, and the specific properties and temperature fluctuations in the CMB all in agreement.

But in 1964, it was a serendipitous accident that resulted in the discovery of the Big Bang’s leftover glow for the very first time. The scientists who unwittingly found it went on to win the Nobel Prize in Physics for their discovery, with Jim Peebles only getting his due 41 years later. Still, this truly accidental discovery only occurred because of Penzias’s and Wilson’s insistence on tracking down the source of that unexpected, omnidirectional noise. There’s an old saying that one astronomer’s noise is another astronomer’s data. By carefully examining every unexplained signal, even the ones you never anticipated, sometimes you can even make a discovery that revolutionizes the Universe.

See the full article here .

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“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

From European Space Agency: “From an almost perfect Universe to the best of both worlds”

From European Space Agency

Jan Tauber
ESA Planck Project Scientist
European Space Agency
Email: jan.tauber@esa.int

Markus Bauer
ESA Science Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer@esa.int

17 July 2018

The Planck consortium has made their final data release, including new processing of the cosmic microwave background temperature and polarisation data. This legacy dataset confirms the model of an ‘almost perfect Universe’, with some remaining oddities giving researchers some intriguing details to puzzle over.

The Cosmic Microwave Background – as seen by Planck. Credit: ESA and the Planck Collaboration

ESA/Planck 2009 to 2013

It was 21 March 2013. The world’s scientific press had either gathered in ESA’s Paris headquarters or logged in online, along with a multitude of scientists around the globe, to witness the moment when ESA’s Planck mission revealed its ‘image’ of the cosmos. This image was taken not with visible light but with microwaves.

Whereas light that our eyes can see is composed of small wavelengths – less than a thousandth of a millimetre in length – the radiation that Planck was detecting spanned longer wavelengths, from a few tenths of a millimetre to a few millimetres. Most importantly, it had been generated at very beginning of the Universe.

Collectively, this radiation is known as the cosmic microwave background, or CMB. By measuring its tiny differences across the sky, Planck’s image had the ability to tell us about the age, expansion, history, and contents of the Universe. It was nothing less than the cosmic blueprint.

Astronomers knew what they were hoping to see. Two NASA missions, COBE in the early 1990s and WMAP in the following decade, had already performed an analogous set of sky surveys that resulted in similar images. But those images did not have the precision and sharpness of Planck.

The new view would show the imprint of the early Universe in painstaking detail for the first time. And everything was riding on it.

If our model of the Universe were correct, then Planck would confirm it to unprecedented levels of accuracy. If our model were wrong, Planck would send scientists back to the drawing board.

When the image was revealed, the data had confirmed the model. The fit to our expectations was too good to draw any other conclusion: Planck had showed us an ‘almost perfect Universe’. Why almost perfect? Because a few anomalies remained, and these would be the focus of future research.

Now, five years later, the Planck consortium has made their final data release, known as the legacy data release. The message remains the same, and is even stronger.

Planck’s view of the sky in nine channels at microwave and sub-millimetre wavelenghts.
Credit: ESA and the Planck Collaboration, animated

“This is the most important legacy of Planck,” says Jan Tauber, ESA’s Planck Project Scientist. “So far the standard model of cosmology has survived all the tests, and Planck has made the measurements that show it.”

Standard Model of Cosmology Timeline

Standard Model of Cosmology Cornell

All cosmological models are based upon Albert Einstein’s General Theory of Relativity. To reconcile the general relativistic equations with a wide range of observations, including the cosmic microwave background, the standard model of cosmology includes the action of two unknown components.

Firstly, an attractive matter component, known as cold dark matter, which unlike ordinary matter does not interact with light. Secondly, a repulsive form of energy, known as dark energy, which is driving the currently accelerated expansion of the Universe. They have been found to be essential components to explain our cosmos in addition to the ordinary matter we know about. But as yet we do not know what these exotic components actually are.

Planck was launched in 2009 and collected data until 2013. Its first release – which gave rise to the almost perfect Universe – was made in the spring of that year. It was based solely on the temperature of the cosmic microwave background radiation, and used only the first two sky surveys from the mission.

The data also provided further evidence for a very early phase of accelerated expansion, called inflation, in the first tiny fraction of a second in the Universe’s history, during which the seeds of all cosmic structures were sown. Inflation

Alan Guth, from 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

Alan Guth’s notes:

Yielding a quantitative measure of the relative distribution of these primordial fluctuations, Planck provided the best confirmation ever obtained of the inflationary scenario.

Besides mapping the temperature of the cosmic microwave background across the sky with unprecedented accuracy, Planck also measured its polarisation, which indicates if light is vibrating in a preferred direction. The polarisation of the cosmic microwave background carries an imprint of the last interaction between the radiation and matter particles in the early Universe, and as such contains additional, all-important information about the history of the cosmos. But it could also contain information about the very first instants of our Universe, and give us clues to understand its birth.

In 2015, a second data release folded together all data collected by the mission, which amounted to eight sky surveys. It gave temperature and polarisation but came with a caution.

“We felt the quality of some of the polarisation data was not good enough to be used for cosmology,” says Jan. He adds that – of course – it didn’t prevent them from doing cosmology with it but that some conclusions drawn at that time needed further confirmation and should therefore be treated with caution.

And that’s the big change for this 2018 Legacy data release. The Planck consortium has completed a new processing of the data. Most of the early signs that called for caution have disappeared. The scientists are now certain that both temperature and polarisation are accurately determined.

“Now we really are confident that we can retrieve a cosmological model based on solely on temperature, solely on polarisation, and based on both temperature and polarisation. And they all match,” says Reno Mandolesi, principal investigator of the LFI instrument on Planck at the University of Ferrara, Italy.

“Since 2015, more astrophysical data has been gathered by other experiments, and new cosmological analyses have also been performed, combining observations of the CMB at small scales with those of galaxies, clusters of galaxies, and supernovae, which most of the time improved the consistency with Planck data and the cosmological model supported by Planck,” says Jean-Loup Puget, principal investigator of the HFI instrument on Planck at the Institut d’Astrophysique Spatiale in Orsay, France.

This is an impressive feat and means that cosmologists can be assured that their description of the Universe as a place containing ordinary matter, cold dark matter and dark energy, populated by structures that had been seeded during an early phase of inflationary expansion, is largely correct.

But there are some oddities that need explaining – or tensions as cosmologists call them. One in particular is related to the expansion of the Universe. The rate of this expansion is given by the so-called Hubble Constant.

To measure the Hubble constant astronomers have traditionally relied on gauging distances across the cosmos. They can only do this for the relatively local Universe by measuring the apparent brightness of certain types of nearby variable stars and exploding stars, whose actual brightness can be estimated independently. It is a well-honed technique that has been developed over the course of the last century, pioneered by Henrietta Leavitt and later applied, in the late 1920s, by Edwin Hubble and collaborators, who used variable stars in distant galaxies and other observations to reveal that the Universe was expanding.

The figure astronomers derive for the Hubble Constant using a wide variety of cutting-edge observations, including some from Hubble’s namesake observatory, the NASA/ESA Hubble Space Telescope, and most recently from ESA’s Gaia mission, is 73.5 km/s/Mpc, with an uncertainty of only two percent. The slightly esoteric units give the velocity of the expansion in km/s for every million parsecs (Mpc) of separation in space, where a parsec is equivalent to 3.26 light-years.

A second way to estimate the Hubble Constant is to use the cosmological model that fits the cosmic microwave background image, which represents the very young Universe, and calculate a prediction for what the Hubble Constant should be today. When applied to Planck data, this method gives a lower value of 67.4 km/s/Mpc, with a tiny uncertainty of less than a percent.

Measurements of the Hubble constant over the past two decades.
Credit: ESA and the Planck Collaboration

On the one hand, it is extraordinary that two such radically different ways of deriving the Hubble constant – one using the local, mature Universe, and one based on the distant, infant Universe – are so close to each other. On the other hand, in principle these two figures should agree to within their respective uncertainties. This is the tension, and the question is how can they be reconciled?

Both sides are convinced that any remaining errors in their measurement methodologies are now too small to cause the discrepancy. So could it be that there is something slightly peculiar about our local cosmic environment that makes the nearby measurement somewhat anomalous? We know for example that our Galaxy sits in a slightly under-dense region of the Universe, which could affect the local value of the Hubble constant. Unfortunately, most astronomers think that such deviations are not large enough to resolve this problem.

“There is no single, satisfactory astrophysical solution that can explain the discrepancy. So, perhaps there is some new physics to be found,” says Marco Bersanelli, deputy principal investigator of the LFI instrument at the University of Milan, Italy.

‘New physics’ means that exotic particles or forces could be influencing the results. Yet, as exciting as this prospect feels, the Planck results place severe constraints on this train of thought because it fits so well with the majority of observations.

“It is very hard to add new physics alleviating the tension and still keep the standard model’s precise description of everything else that already fits,” says François Bouchet, deputy principal investigator of the HFI instrument at the Institut d’Astrophysique de Paris, France.

As a result, no one has been able to come up with a satisfactory explanation for the differences between the two measurements, and the question remains to be resolved.

“For the moment, we shouldn’t get too excited about finding new physics: it could well be that the relatively small discrepancy can be explained by a combination of small errors and local effects. But we need to keep improving our measurements and thinking about better ways to explain it,” says Jan.

This is the legacy of Planck: with its almost perfect Universe, the mission has given researchers confirmation of their models but with a few details to puzzle over. In other words: the best of both worlds.

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

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.

From LBNL: “Tiny Distortions in Universe’s Oldest Light Reveal Clearer Picture of Strands in Cosmic Web”

Berkeley Lab

April 10, 2018

Glenn Roberts Jr.
geroberts@lbl.gov
(510) 486-5582

In this illustration, the trajectory of cosmic microwave background (CMB) light is bent by structures known as filaments that are invisible to our eyes, creating an effect known as weak lensing captured by the Planck satellite (left), a space observatory. Researchers used computers to study this weak lensing of the CMB and produce a map of filaments, which typically span hundreds of light years in length. (Credit: Siyu He, Shadab Alam, Wei Chen, and Planck/ESA)

Cosmic Background Radiation per ESA/Planck

ESA/Planck

Weak gravitational lensing NASA/ESA Hubble

Scientists have decoded faint distortions in the patterns of the universe’s earliest light to map huge tubelike structures invisible to our eyes – known as filaments – that serve as superhighways for delivering matter to dense hubs such as galaxy clusters.

The international science team, which included researchers from the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley, analyzed data from past sky surveys using sophisticated image-recognition technology to home in on the gravity-based effects that identify the shapes of these filaments. They also used models and theories about the filaments to help guide and interpret their analysis.

Published April 9 in the journal Nature Astronomy, the detailed exploration of filaments will help researchers to better understand the formation and evolution of the cosmic web – the large-scale structure of matter in the universe – including the mysterious, unseen stuff known as dark matter that makes up about 85 percent of the total mass of the universe.

Cosmic web Millenium Simulation Max Planck Institute for Astrophysics

Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al

Caterpillar Project A Milky-Way-size dark-matter halo and its subhalos circled, an enormous suite of simulations . Griffen et al. 2016

Dark matter constitutes the filaments – which researchers learned typically stretch and bend across hundreds of millions of light years – and the so-called halos that host clusters of galaxies are fed by the universal network of filaments. More studies of these filaments could provide new insights about dark energy, another mystery of the universe that drives its accelerating expansion.

Filament properties could also put gravity theories to the test, including Einstein’s theory of general relativity, and lend important clues to help solve an apparent mismatch in the amount of visible matter predicted to exist in the universe – the “missing baryon problem.”

“Usually researchers don’t study these filaments directly – they look at galaxies in observations,” said Shirley Ho, a senior scientist at Berkeley Lab and Cooper-Siegel associate professor of physics at Carnegie Mellon University who led the study. “We used the same methods to find the filaments that Yahoo and Google use for image recognition, like recognizing the names of street signs or finding cats in photographs.”

Filament structures in the cosmic web are shown at different time periods, ranging from when the universe was 12.3 billion years old (left) to when the universe was 7.4 billion years old (right). The area in the animation spans 7,500 square degrees of space. Evidence is strongest for the filament structures represented in blue. Other likely filament structures are shaded purple, magenta, and red. (Credit: Yen-Chi Chen and Shirley Ho)

The study used data from the Baryon Oscillation Spectroscopic Survey, or BOSS, an Earth-based sky survey that captured light from about 1.5 million galaxies to study the universe’s expansion and the patterned distribution of matter in the universe set in motion by the propagation of sound waves, or “baryonic acoustic oscillations,” rippling in the early universe.

BOSS Supercluster Baryon Oscillation Spectroscopic Survey (BOSS)

The BOSS survey team, which featured Berkeley Lab scientists in key roles, produced a catalog of likely filament structures that connected clusters of matter that researchers drew from in the latest study.

Researchers also relied on precise, space-based measurements of the cosmic microwave background, or CMB, which is the nearly uniform remnant signal from the first light of the universe. While this light signature is very similar across the universe, there are regular fluctuations that have been mapped in previous surveys.

In the latest study, researchers focused on patterned fluctuations in the CMB. They used sophisticated computer algorithms to seek out the imprint of filaments from gravity-based distortions in the CMB, known as weak lensing effects, that are caused by the CMB light passing through matter.

Since galaxies live in the densest regions of the universe, the weak lensing signal from the deflection of CMB light is strongest from those parts. Dark matter resides in the halos around those galaxies, and was also known to spread from those denser areas in filaments.

“We knew that these filaments should also cause a deflection of CMB and would also produce a measurable weak gravitational lensing signal,” said Siyu He, the study’s lead author who is a Ph.D. researcher from Carnegie Mellon University – she is now at Berkeley Lab and is also affiliated with UC Berkeley. The research team used statistical techniques to identify and compare the “ridges,” or points of higher density that theories informed them would point to the presence of filaments.

“We were not just trying to ‘connect the dots’ – we were trying to find these ridges in the density, the local maximum points in density,” she said. They checked their findings with other filament and galaxy cluster data, and with “mocks,” or simulated filaments based on observations and theories. The team used large cosmological simulations generated at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC), for example, to check for errors in their measurements.

NERSC Cray XC40 Cori II supercomputer

LBL NERSC Cray XC30 Edison supercomputer

The Genepool system is a cluster dedicated to the DOE Joint Genome Institute’s computing needs. Denovo is a smaller test system for Genepool that is primarily used by NERSC staff to test new system configurations and software.

NERSC PDSF

PDSF is a networked distributed computing cluster designed primarily to meet the detector simulation and data analysis requirements of physics, astrophysics and nuclear science collaborations.

The filaments and their connections can change shape and connections over time scales of hundreds of millions of years. The competing forces of the pull of gravity and the expansion of the universe can shorten or lengthen the filaments.

“Filaments are this integral part of the cosmic web, though it’s unclear what is the relationship between the underlying dark matter and the filaments,” and that was a primary motivation for the study, said Simone Ferraro, one of the study’s authors who is a Miller postdoctoral fellow at UC Berkeley’s Center for Cosmological Physics.

Scientists have decoded faint distortions in the patterns of the universe’s earliest light to map huge tubelike structures invisible to our eyes – known as filaments – that serve as superhighways for delivering matter to dense hubs such as galaxy clusters.

The international science team, which included researchers from the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley, analyzed data from past sky surveys using sophisticated image-recognition technology to home in on the gravity-based effects that identify the shapes of these filaments. They also used models and theories about the filaments to help guide and interpret their analysis.

Published April 9 in the journal Nature Astronomy, the detailed exploration of filaments will help researchers to better understand the formation and evolution of the cosmic web – the large-scale structure of matter in the universe – including the mysterious, unseen stuff known as dark matter that makes up about 85 percent of the total mass of the universe.

Dark matter constitutes the filaments – which researchers learned typically stretch and bend across hundreds of millions of light years – and the so-called halos that host clusters of galaxies are fed by the universal network of filaments. More studies of these filaments could provide new insights about dark energy, another mystery of the universe that drives its accelerating expansion.

Filament properties could also put gravity theories to the test, including Einstein’s theory of general relativity, and lend important clues to help solve an apparent mismatch in the amount of visible matter predicted to exist in the universe – the “missing baryon problem.”

“Usually researchers don’t study these filaments directly – they look at galaxies in observations,” said Shirley Ho, a senior scientist at Berkeley Lab and Cooper-Siegel associate professor of physics at Carnegie Mellon University who led the study. “We used the same methods to find the filaments that Yahoo and Google use for image recognition, like recognizing the names of street signs or finding cats in photographs.”
Image – Filament structures in the cosmic web are shown at different time periods: ranging from when the was 12.3 billion years old (left) to when the universe was 7.4 billion years old. The area in the animation spans 7,500 square degrees of space. Evidence is strongest for the filament structures represented in blue – other likely filament structures are shaded pink and red. (Credit: Yen-Chi Chen and Shirley Ho)

Filament structures in the cosmic web are shown at different time periods, ranging from when the universe was 12.3 billion years old (left) to when the universe was 7.4 billion years old (right). The area in the animation spans 7,500 square degrees of space. Evidence is strongest for the filament structures represented in blue. Other likely filament structures are shaded purple, magenta, and red. (Credit: Yen-Chi Chen and Shirley Ho)

The study used data from the Baryon Oscillation Spectroscopic Survey, or BOSS, an Earth-based sky survey that captured light from about 1.5 million galaxies to study the universe’s expansion and the patterned distribution of matter in the universe set in motion by the propagation of sound waves, or “baryonic acoustic oscillations,” rippling in the early universe.

The BOSS survey team, which featured Berkeley Lab scientists in key roles, produced a catalog of likely filament structures that connected clusters of matter that researchers drew from in the latest study.

Researchers also relied on precise, space-based measurements of the cosmic microwave background, or CMB, which is the nearly uniform remnant signal from the first light of the universe. While this light signature is very similar across the universe, there are regular fluctuations that have been mapped in previous surveys.

In the latest study, researchers focused on patterned fluctuations in the CMB. They used sophisticated computer algorithms to seek out the imprint of filaments from gravity-based distortions in the CMB, known as weak lensing effects, that are caused by the CMB light passing through matter.

Since galaxies live in the densest regions of the universe, the weak lensing signal from the deflection of CMB light is strongest from those parts. Dark matter resides in the halos around those galaxies, and was also known to spread from those denser areas in filaments.

“We knew that these filaments should also cause a deflection of CMB and would also produce a measurable weak gravitational lensing signal,” said Siyu He, the study’s lead author who is a Ph.D. researcher from Carnegie Mellon University – she is now at Berkeley Lab and is also affiliated with UC Berkeley. The research team used statistical techniques to identify and compare the “ridges,” or points of higher density that theories informed them would point to the presence of filaments.

“We were not just trying to ‘connect the dots’ – we were trying to find these ridges in the density, the local maximum points in density,” she said. They checked their findings with other filament and galaxy cluster data, and with “mocks,” or simulated filaments based on observations and theories. The team used large cosmological simulations generated at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC), for example, to check for errors in their measurements.

The filaments and their connections can change shape and connections over time scales of hundreds of millions of years. The competing forces of the pull of gravity and the expansion of the universe can shorten or lengthen the filaments.

“Filaments are this integral part of the cosmic web, though it’s unclear what is the relationship between the underlying dark matter and the filaments,” and that was a primary motivation for the study, said Simone Ferraro, one of the study’s authors who is a Miller postdoctoral fellow at UC Berkeley’s Center for Cosmological Physics.

Visualizing the cosmic web: This computerized simulation by the Virgo Consortium, called the Millennium Simulation, shows a web-like structure in the universe composed of galaxies and the dark matter around them. (Credit: Millennium Simulation Project)

New data from existing experiments, and next-generation sky surveys such as the Berkeley Lab-led Dark Energy Spectroscopic Instrument (DESI) now under construction at Kitt Peak National Observatory in Arizona should provide even more detailed data about these filaments, he added.

Researchers noted that this important step in sleuthing the shapes and locations of filaments should also be useful for focused studies that seek to identify what types of gases inhabit the filaments, the temperatures of these gases, and the mechanisms for how particles enter and move around in the filaments. The study also allowed them to determine the length of filaments.

Siyu He said that resolving the filament structure can also provide clues to the properties and contents of the voids in space around the filaments, and “help with other theories that are modifications of general relativity,” she said.

Ho added, “We can also maybe use these filaments to constrain dark energy – their length and width may tell us something about dark energy’s parameters.”

Shadab Alam, a researcher at the University of Edinburgh and Royal Observatory in Edinburgh, U.K.; and Yen-Chi Chen, an assistant professor at the University of Washington, also participated in the study. The work was supported by the U.S. Department of Energy Office of Science, NASA, the National Science Foundation, the European Research Council, and the Miller Institute for Basic Research in Science at UC Berkeley.

NERSC is a DOE Office of Science User Facility

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A U.S. Department of Energy National Laboratory Operated by the University of California

From ESA: “Magnetic mirror design for finding evidence of primordial gravitational waves”

European Space Agency

20 February 2017
No writer credit

Title Polarisation of the Cosmic Microwave Background: finer detail
Released 05/02/2015 3:00 pm
Copyright ESA and the Planck Collaboration
Description

A visualisation of the polarisation of the Cosmic Microwave Background, or CMB, as detected by ESA’s Planck satellite on a small patch of the sky measuring 20º across.

The CMB is a snapshot of the oldest light in our Universe, imprinted on the sky when the Universe was just 380 000 years old. It shows tiny temperature fluctuations that correspond to regions of slightly different densities, representing the seeds of all future structure: the stars and galaxies of today.

A small fraction of the CMB is polarised – it vibrates in a preferred direction. This is a result of the last encounter of this light with electrons, just before starting its cosmic journey. For this reason, the polarisation of the CMB retains information about the distribution of matter in the early Universe, and its pattern on the sky follows that of the tiny fluctuations observed in the temperature of the CMB.

In this image, the colour scale represents temperature differences in the CMB, while the texture indicates the direction of the polarised light. The curly textures are characteristic of ‘E-mode’ polarisation, which is the dominant type for the CMB.

In this image, both data sets have been filtered to show mostly the signal detected on scales around 20 arcminutes on the sky. This shows the fine structure of the measurement obtained by Planck, revealing fluctuations in both the CMB temperature and polarisation on very small angular scales.

ESA has backed the development of a ‘metamaterial’ device to sift through the faint afterglow of the Big Bang, to search for evidence of primordial gravitational waves triggered by the rapidly expanding newborn Universe.

“This technological breakthrough widens the potential for a future follow-on to ESA’s 2009-launched Planck mission, which would significantly increase our detailed understanding of the Universe as it began,” explains Peter de Maagt, heading ESA’s Antennas and Sub-Millimetre Wave section.

ESA/Planck

Planck mapped the ‘cosmic microwave background’ (CMB) – leftover light from the creation of the cosmos, subsequently redshifted to microwave wavelengths – across the deep sky in more detail than ever before.

CMB per ESA/Planck

The CMB retains properties of ordinary light, including its tendency to polarise in differing directions – employed in everyday life by polarised sunglasses to cut out glare, or 3D glasses used to see alternating differently polarised cinema images through separate eyes.

Title Metamaterial-reflective half-wave plate
Released 10/02/2017 4:16 pm
Copyright Cardiff University
Description

Cardiff University’s magnetic mirror half-wave plate design for b-mode polarisation modulation across wide bandwidths. Less than 1 mm thick, this metamaterial-based design employs a combination of a grid-based ‘artificial magnetic conductor’ and metal ‘perfect electrical conductor’ surfaces. The overall effect is to create a differential phase-shift between orthogonal polarisations equal to 180 degrees. The rotation of the plate causes modulation of the polarisation signal.

Researchers are now searching for one particular corkscrew polarisation of the CMB, known as ‘B-mode polarisation’, predicted to have been caused by gravitational waves rippling through the early Universe as it underwent exponential expansion – surging from a subatomic singularity to its current vastness.

Identifying these theorised ‘stretchmarks’ within the CMB would offer solid proof that expansion did indeed occur, bringing cosmologists a big step closer to unifying the physics of the very large and the very small.

“This would be the holy grail of cosmology,” comments Giampaolo Pisano of Cardiff University, heading the team that built the new prototype B-mode polarisation device for ESA.

The history of the Universe

Into what is the universe expanding NASA Goddard, Dana Berry

“Our contribution is only a small bit of the hugely complex instrument that will be necessary to accomplish such a detection. It won’t be easy, not least because it involves only a tiny fraction of the overall CMB radiation.”

One of the main obstacles in detecting primordial B-modes is additional sources of polarisation located between Earth and the CMB, such as dust within our own galaxy.

Such polarised foreground contributions have different spectral signatures to that of the CMB, however, enabling their removal if measurements are taken over a large frequency range.

The challenge is therefore to devise a polarisation modulator that operates across a wide frequency bandwidth with high efficiency.

“Our new ‘magnetic mirror’-based modulator can do just that, thanks to the quite new approach we adopted,” said Giampaolo Pisano.

Polarisation modulation is often achieved with rotating ‘half-wave plates’. These induce the rotation of the polarised signals which can ‘stick out’ from the unpolarised background. However, the physical thickness of these devices defines their operational bandwidths, which cannot be too large.

“Our new solution is based on a combination of metal grids embedded in a plastic substrate – what we call a ‘metamaterial’ – possessing customised electromagnetic properties not found in nature.

“This flat surface transforms and reflects the signal back like a half-wave plate, facing none of the geometrical constraints of previous designs.”

The team’s prototype multiband magnetic mirror polarisation modulator measures 20 cm across. Any post-Planck space mission would need one larger than a metre in diameter, its design qualified to survive the harsh space environment. The team are now working on enlarging it.

“To come so far, the University of Cardiff team has had to develop all the equipment and engineering processes making it possible,” adds Peter. “Their work has been supported through ESA’s long-running Basic Technology Research Programme, serving to investigate promising new ideas to help enable future missions.”

See the full article here .

Please help promote STEM in your local schools.

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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.

From ESA: “Planck reveals first stars were born late”

European Space Agency

5 February 2015
Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799; +34 91 8131 199
Mob: +31 61 594 3954
Email: Markus.Bauer@esa.int

Jan Tauber
ESA Planck Project Scientist
Tel: +31 71 565 5342
Email: Jan.Tauber@esa.int

François Bouchet
Institut d’Astrophysique de Paris (CNRS/UPMC), France
Tel: +33 1 4432 8095
Email: bouchet@iap.fr

Marco Bersanelli
Università degli Studi di Milano, Italy
Tel: +39 02 50317264
Email: marco.bersanelli@mi.infn.it

George Efstathiou
University of Cambridge, UK
Tel: +44 1223 337530
Email: gpe@ast.cam.ac.uk

Polarisation of the Cosmic Microwave Background

5 February 2015

New maps from ESA’s Planck satellite uncover the ‘polarised’ light from the early Universe across the entire sky, revealing that the first stars formed much later than previously thought.

The history of our Universe is a 13.8 billion-year tale that scientists endeavour to read by studying the planets, asteroids, comets and other objects in our Solar System, and gathering light emitted by distant stars, galaxies and the matter spread between them.

A major source of information used to piece together this story is the Cosmic Microwave Background, or CMB, the fossil light resulting from a time when the Universe was hot and dense, only 380 000 years after the Big Bang.

Thanks to the expansion of the Universe, we see this light today covering the whole sky at microwave wavelengths.

Between 2009 and 2013, Planck surveyed the sky to study this ancient light in unprecedented detail. Tiny differences in the background’s temperature trace regions of slightly different density in the early cosmos, representing the seeds of all future structure, the stars and galaxies of today.

Scientists from the Planck collaboration have published the results from the analysis of these data in a large number of scientific papers over the past two years, confirming the standard cosmological picture of our Universe with ever greater accuracy.

“But there is more: the CMB carries additional clues about our cosmic history that are encoded in its ‘polarisation’,” explains Jan Tauber, ESA’s Planck project scientist.

“Planck has measured this signal for the first time at high resolution over the entire sky, producing the unique maps released today.”

History of the Universe

Light is polarised when it vibrates in a preferred direction, something that may arise as a result of photons – the particles of light – bouncing off other particles. This is exactly what happened when the CMB originated in the early Universe.

Initially, photons were trapped in a hot, dense soup of particles that, by the time the Universe was a few seconds old, consisted mainly of electrons, protons and neutrinos. Owing to the high density, electrons and photons collided with one another so frequently that light could not travel any significant distant before bumping into another electron, making the early Universe extremely ‘foggy’.

Slowly but surely, as the cosmos expanded and cooled, photons and the other particles grew farther apart, and collisions became less frequent.

This had two consequences: electrons and protons could finally combine and form neutral atoms without them being torn apart again by an incoming photon, and photons had enough room to travel, being no longer trapped in the cosmic fog.

CMB polarisation: full sky and details

Once freed from the fog, the light was set on its cosmic journey that would take it all the way to the present day, where telescopes like Planck detect it as the CMB. But the light also retains a memory of its last encounter with the electrons, captured in its polarisation.

“The polarisation of the CMB also shows minuscule fluctuations from one place to another across the sky: like the temperature fluctuations, these reflect the state of the cosmos at the time when light and matter parted company,” says François Bouchet of the Institut d’Astrophysique de Paris, France.

“This provides a powerful tool to estimate in a new and independent way parameters such as the age of the Universe, its rate of expansion and its essential composition of normal matter, dark matter and dark energy.”

Planck’s polarisation data confirm the details of the standard cosmological picture determined from its measurement of the CMB temperature fluctuations, but add an important new answer to a fundamental question: when were the first stars born?

CMB polarisation: zoom

“After the CMB was released, the Universe was still very different from the one we live in today, and it took a long time until the first stars were able to form,” explains Marco Bersanelli of Università degli Studi di Milano, Italy.

“Planck’s observations of the CMB polarisation now tell us that these ‘Dark Ages’ ended some 550 million years after the Big Bang – more than 100 million years later than previously thought.

“While these 100 million years may seem negligible compared to the Universe’s age of almost 14 billion years, they make a significant difference when it comes to the formation of the first stars.”

The Dark Ages ended as the first stars began to shine. And as their light interacted with gas in the Universe, more and more of the atoms were turned back into their constituent particles: electrons and protons.

This key phase in the history of the cosmos is known as the ‘epoch of reionisation’.

CMB polarisation: finer detail

The newly liberated electrons were once again able to collide with the light from the CMB, albeit much less frequently now that the Universe had significantly expanded. Nevertheless, just as they had 380 000 years after the Big Bang, these encounters between electrons and photons left a tell-tale imprint on the polarisation of the CMB.

“From our measurements of the most distant galaxies and quasars, we know that the process of reionisation was complete by the time that the Universe was about 900 million years old,” says George Efstathiou of the University of Cambridge, UK.

“But, at the moment, it is only with the CMB data that we can learn when this process began.”

Planck’s new results are critical, because previous studies of the CMB polarisation seemed to point towards an earlier dawn of the first stars, placing the beginning of reionisation about 450 million years after the Big Bang.

This posed a problem. Very deep images of the sky from the NASA–ESA Hubble Space Telescope have provided a census of the earliest known galaxies in the Universe, which started forming perhaps 300–400 million years after the Big Bang.

However, these would not have been powerful enough to succeed at ending the Dark Ages within 450 million years.

“In that case, we would have needed additional, more exotic sources of energy to explain the history of reionisation,” says Professor Efstathiou.

The new evidence from Planck significantly reduces the problem, indicating that reionisation started later than previously believed, and that the earliest stars and galaxies alone might have been enough to drive it.

This later end of the Dark Ages also implies that it might be easier to detect the very first generation of galaxies with the next generation of observatories, including the James Webb Space Telescope.

NASA/Webb

Galactic dust

But the first stars are definitely not the limit. With the new Planck data released today, scientists are also studying the polarisation of foreground emission from gas and dust in the Milky Way to analyse the structure of the Galactic magnetic field.

The data have also enabled new important insights into the early cosmos and its components, including the intriguing dark matter and the elusive neutrinos, as described in papers also released today.

The Planck data have delved into the even earlier history of the cosmos, all the way to inflation – the brief era of accelerated expansion that the Universe underwent when it was a tiny fraction of a second old. As the ultimate probe of this epoch, astronomers are looking for a signature of gravitational waves triggered by inflation and later imprinted on the polarisation of the CMB.

No direct detection of this signal has yet been achieved, as reported last week. However, when combining the newest all-sky Planck data with those latest results, the limits on the amount of primordial gravitational waves are pushed even further down to achieve the best upper limits yet.

“These are only a few highlights from the scrutiny of Planck’s observations of the CMB polarisation, which is revealing the sky and the Universe in a brand new way,” says Jan Tauber.

“This is an incredibly rich data set and the harvest of discoveries has just begun.”

See the full article here.

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Stem Education Coalition

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.

From ESA: “The magnetic field along the Galactic plane”

European Space Agency

15/12/2014
No Writer Credit

While the pastel tones and fine texture of this image may bring to mind brush strokes on an artist’s canvas, they are in fact a visualisation of data from ESA’s Planck satellite. The image portrays the interaction between interstellar dust in the Milky Way and the structure of our Galaxy’s magnetic field.

Planck

Between 2009 and 2013, Planck scanned the sky to detect the most ancient light in the history of the Universe – the cosmic microwave background. It also detected significant foreground emission from diffuse material in our Galaxy which, although a nuisance for cosmological studies, is extremely important for studying the birth of stars and other phenomena in the Milky Way.

CMB per Planck

Among the foreground sources at the wavelengths probed by Planck is cosmic dust, a minor but crucial component of the interstellar medium that pervades the Galaxy. Mainly gas, it is the raw material for stars to form.

Interstellar clouds of gas and dust are also threaded by the Galaxy’s magnetic field, and dust grains tend to align their longest axis at right angles to the direction of the field. As a result, the light emitted by dust grains is partly ‘polarised’ – it vibrates in a preferred direction – and, as such, could be caught by the polarisation-sensitive detectors on Planck.

Scientists in the Planck collaboration are using the polarised emission of interstellar dust to reconstruct the Galaxy’s magnetic field and study its role in the build-up of structure in the Milky Way, leading to star formation.

In this image, the colour scale represents the total intensity of dust emission, revealing the structure of interstellar clouds in the Milky Way. The texture is based on measurements of the direction of the polarised light emitted by the dust, which in turn indicates the orientation of the magnetic field.

This image shows the intricate link between the magnetic field and the structure of the interstellar medium along the plane of the Milky Way. In particular, the arrangement of the magnetic field is more ordered along the Galactic plane, where it follows the spiral structure of the Milky Way. Small clouds are seen just above and below the plane, where the magnetic field structure becomes less regular.

From these and other similar observations, Planck scientists found that filamentary interstellar clouds are preferentially aligned with the direction of the ambient magnetic field, highlighting the strong role played by magnetism in galaxy evolution.

The emission from dust is computed from a combination of Planck observations at 353, 545 and 857 GHz, whereas the direction of the magnetic field is based on Planck polarisation data at 353 GHz.

See the full article here.

Please help promote STEM in your local schools.

Stem Education Coalition

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.

From ESA: “The magnetic field along the Galactic plane”

European Space Agency

15/12/2014

ESA/Planck Collaboration

While the pastel tones and fine texture of this image may bring to mind brush strokes on an artist’s canvas, they are in fact a visualisation of data from ESA’s Planck satellite.

ESA/Planck

The image portrays the interaction between interstellar dust in the Milky Way and the structure of our Galaxy’s magnetic field.

Between 2009 and 2013, Planck scanned the sky to detect the most ancient light in the history of the Universe – the cosmic microwave background. It also detected significant foreground emission from diffuse material in our Galaxy which, although a nuisance for cosmological studies, is extremely important for studying the birth of stars and other phenomena in the Milky Way.

CMB per ESA/Planck

Among the foreground sources at the wavelengths probed by Planck is cosmic dust, a minor but crucial component of the interstellar medium that pervades the Galaxy. Mainly gas, it is the raw material for stars to form.

Interstellar clouds of gas and dust are also threaded by the Galaxy’s magnetic field, and dust grains tend to align their longest axis at right angles to the direction of the field. As a result, the light emitted by dust grains is partly ‘polarised’ – it vibrates in a preferred direction – and, as such, could be caught by the polarisation-sensitive detectors on Planck.

Scientists in the Planck collaboration are using the polarised emission of interstellar dust to reconstruct the Galaxy’s magnetic field and study its role in the build-up of structure in the Milky Way, leading to star formation.

In this image, the colour scale represents the total intensity of dust emission, revealing the structure of interstellar clouds in the Milky Way. The texture is based on measurements of the direction of the polarised light emitted by the dust, which in turn indicates the orientation of the magnetic field.

This image shows the intricate link between the magnetic field and the structure of the interstellar medium along the plane of the Milky Way. In particular, the arrangement of the magnetic field is more ordered along the Galactic plane, where it follows the spiral structure of the Milky Way. Small clouds are seen just above and below the plane, where the magnetic field structure becomes less regular.

From these and other similar observations, Planck scientists found that filamentary interstellar clouds are preferentially aligned with the direction of the ambient magnetic field, highlighting the strong role played by magnetism in galaxy evolution.

The emission from dust is computed from a combination of Planck observations at 353, 545 and 857 GHz, whereas the direction of the magnetic field is based on Planck polarisation data at 353 GHz.

Acknowledgment: M.-A. Miville-Deschênes, >CNRS – Institut d’Astrophysique Spatiale, Université Paris-XI, Orsay, France

See the full article here.

Please help promote STEM in your local schools.

Stem Education Coalition

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.

From Princeton- ” SPIDER: Searching for the Echoes of Inflation”

Princeton University

December 5, 2014
Zigmund Kermish
Zigmund Kermish is an associate research scholar at Princeton University.

Wait, why am I in Antarctica?

I realized I’ve not yet written a blog post explaining why my experiment is in Antarctica. Things are temporarily quiet on the Ice while we’ve been waiting for the SPIDER cryostat to cool down, so now’s a good time to make the attempt.

To get the best results from SPIDER, we have to go to very high and dry locations. This is because water vapor in the atmosphere limits SPIDER’s sensitivity. There are currently two terrestrial locations that are commonly used: the Atacama Desert POLARBEAR and ACTPol
sit at about 5,200 meters above sea level) and the South Pole (where the South Pole Telescope, the KECK array, and this year BICEP3 operate at 2,800 meters).

POLARBEAR

Princeton Atacama Cosmology Telescope

South Pole Telescope (SPT)

Keck Array

BICEP

Of course, one can always go beyond terrestrial limits. With a big enough budget and enough time to develop the project, you can launch a dedicated satellite mission to eliminate the atmosphere all together, achieving dramatically improved individual detector sensitivities. Historically, satellite-based instruments have provided the definitive measurements of various aspects of the cosmic microwave background (the faint signal left over from the Big Bang), but they usually build upon the groundbreaking discoveries made closer to Earth. These discoveries have been made from the ground and from one other platform: balloons.

Balloon-borne instruments have one big advantage: they allow us to get above nearly all of the atmosphere, approaching the detector sensitivity of satellite-based instruments at a fraction of the cost of a satellite mission.

This increased detector sensitivity has two advantages: you can observe a larger fraction of the sky for a significantly shorter amount of time and still get a higher fidelity map than what you can do from the ground (observing for days rather than years) and you can observe in frequency channels that are difficult (if not impossible) to use from the ground. Both of these features, multiple frequencies and larger sky coverage, are necessary to ultimately demonstrate the ‘cosmological nature’ of the signals we’re looking for – to show that it’s not just a signal from some foreground in our local galaxy and that it has the required statistical properties across the sky we expect from proposed theories.

As shown in the below gif, SPIDER can observe a large fraction of the ‘clean’ sky (the white outline) for 20 days and get nearly the same sensitivity over that region as a ground based experiment like the BICEP2 project had on their smaller region (green outline) after several years of observation.
dust_regions

A map of the dust intensity seen in the sky, the bright center band the emission from our own Milky Way galaxy. The overlay that is fading in shows several things: The colored diamonds show the most recent data about the *polarization* strength of the dust signal, blue being less polarized dust, the outlines on the overlay show the regions observed (or to be observed shortly!) by BICEP2 (green), POLARBEAR (red), and SPIDER (white).

Ok, so that’s why we want to dangle our instrument from a balloon. But why Antarctica? Why don’t we just launch our balloon from New Jersey?

Well, for one, at some point, we need to bring the instrument back down to Earth, and that involves literally letting it fall to the ground so that we can recover it. That’s why scientific payload balloon flights only happen in places with low population density. In the US, payloads are flown out of Fort Sumner, New Mexico. They used to fly out of Palestine, Texas as well. Payloads flown out of these locations are limited to flights anywhere from a few hours to a few days because they eventually start getting too close to population centers.

Antarctica doesn’t have any population centers, so rather than being limited by distance, flights are limited by how long the balloons can stay afloat. Currently, that’s about 40 days. Beyond that, weather patterns setup circumpolar winds during the austral summer here.

So if you launch a balloon at the right time, it’ll come back close to where it started, making recovery of the instrument easier (it takes about a week to ‘boomerang’ back around). This is especially important for an experiment like ours since we need to physically recover our data off the drives that fly with the instrument. The bandwidth of in-flight communications limits us to only getting a small fraction of the data from the instrument during flight. One of the many ballooning challenges is to make the system as autonomous as possible so minimal human intervention based on the limited information we decide to ‘downlink’ to the ground is needed.

The other fundamental challenges of ballooning that make this a very different game from ground-based experiments I’ve worked on: weight and power constraints. Having to fly the batteries you need to power the experiment, the solar panels to keep them charged, the cryogenic system to keep the everything cool and all the readout and control electronics systems while still staying below the maximum mass limits current balloons can float makes a project like this a fun problem to solve. The absence of day-night cycles during the austral summer in Antarctica helps address the power and weight constraints by giving us a continual source of solar power. This means we only need to fly a few heavy batteries to provide a non-variable power source and we can dedicate more of our mass budget to the scientific instruments. More compromises have to be made when designing payloads to fly at mid-latitudes, where enough batteries need to fly to power the payload throughout the night. There are many advantages to these mid-latitude flights though: larger available sky and longer (100 day!) flights with NASA’s new, soon-to-launch-with-science-payloads super pressure balloon platform (SPB).

The CMB Cosmology group at Case is led by Prof. John Ruhl. The current members of our group are (GS = Graduate Student, UGS = Undergraduate Student):

Tom Montroy (Senior Research Assoc.)
Rick Bihary (Technician of Everything)
Sean Bryan (GS, Spider)
J.T. Sayre (GS, SPT)
Ben Saliwanchik (GS, SPT)
Adam Stohs (UGS)
Dane Pittock (UGS)

Phone numbers (all have 216 area code):

Rock 117 lab: 368-1153
Rock 117a lab: 368-3608
Rock 117a fax: 368-0952
Rock 114 lab and GS office: 368-2489
Physics Student Shop: 368-3053
Prof. Ruhl’s office: 368-4049

We are located in Rockefeller Hall, on the main quad campus of Case Western Reserve University. Our shipping address is:

Physics Dept, Rockefeller Hall
Case Western Reserve University
10900 Euclid Ave.
Cleveland, OH 44106-7079

Spider is a balloon-borne instrument designed to search for the signature of primordial gravity waves that is (hopefully) encoded in the polarization of the CMB. The design consists of six independent telescopes operating at three frequencies (100, 150, and 220GHz), with the optics cooled to 4 Kelvin and the bolometric detectors cooled to 0.25K.

Spider’s first test flight will be in the fall of 2009, from Alice Springs, Australia. The test flight will be 2-4 nights duration, limited by the requirement that the balloon be brought down before it leaves the continent. The full “around the world” flight will be a year later, if all goes well.
There are two publications describing Spider:

“Spider Optimization: Probing the Systematics of a Large Scale B-Mode Experiment”, C. J. MacTavish etal, arXiv:0710.0375, submitted to ApJ. (This discusses Spider’s potential systematics and scan strategies).
“SPIDER: a new balloon-borne experiment to measure CMB polarization on large angular scales”, T. E. Montroy etal, Proceedings of the SPIE, ed L. M. Step, v 6267, p62670R, (2006). (This describes the Spider instrument as originally conceived.)

In addition to the effort at Case, the Spider collaboration includes groups at Caltech, JPL, U. Toronto, UBC, NIST, Cardiff, and the Imperial College of London. The main SPT website is maintained at Caltech, at http://www.astro.caltech.edu/~lgg/spider_front.htm.
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About Princeton: Overview

Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

From physicsworld: “Planck offers another glimpse of the early universe”

physicsworld.com

Dec 4, 2014
Tushna Commissariat

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]

See the full article here.

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