Tag Archives: big bang

The Accelerated Acceleration

Dark_Energy

Until the mid-1990s accepted scientific understanding of the universe held that the cosmos was expanding. Scientists have accepted this since 1929 when Edwin Hubble‘s celestial observations showed that distant galaxies were all apparently moving away from us.

But, in 1998 two independent groups of cosmologists made a startling finding. The universe was not only expanding, its expansion was accelerating. Recent studies show that this acceleration in the fabric of spacetime is actually faster than first theorized and observed.

And, nobody knows why. This expansion, indeed the accelerating expansion, remains one of our current great scientific mysteries.

Cosmologists, astronomers and theoreticians of all stripes have proposed no shortage of possible explanations. But, there is still scant observational evidence to support any of the leading theories. The most popular revolves around the peculiar idea of dark energy.

From Scientific American:

Our universe is flying apart, with galaxies moving away from each other faster each moment than they were the moment before. Scientists have known about this acceleration since the late 1990s, but whatever is causing it—dubbed dark energy—remains a mystery. Now the latest measurement of how fast the cosmos is growing thickens the plot further: The universe appears to be ballooning more quickly than it should be, even after accounting for the accelerating expansion caused by dark energy.

Scientists came to this conclusion after comparing their new measurement of the cosmic expansion rate, called the Hubble constant, to predictions of what the Hubble constant should be based on evidence from the early universe. The puzzling conflict—which was hinted at in earlier data and confirmed in the new calculation—means that either one or both of the measurements are flawed, or that dark energy or some other aspect of nature acts differently than we think.

“The bottom line is that the universe looks like it’s expanding about eight percent faster than you would have expected based on how it looked in its youth and how we expect it to evolve,” says study leader Adam Riess of the Space Telescope Science Institute in Baltimore, Md. “We have to take this pretty darn seriously.” He and his colleagues described their findings, based on observations from the Hubble Space Telescope, in a paper submitted last week to the Astrophysical Journal and posted on the preprint server arXiv.

One of the most exciting possibilities is that dark energy is even stranger than the leading theory suggests. Most observations support the idea that dark energy behaves like a “cosmological constant,” a term Albert Einstein inserted into his equations of general relativity and later removed. This kind of dark energy would arise from empty space, which, according to quantum mechanics, is not empty at all, but rather filled with pairs of “virtual” particles and antiparticles that constantly pop in and out of existence. These virtual particles would carry energy, which in turn might exert a kind of negative gravity that pushes everything in the universe outward.

Read the entire story here.

Image: The universe’s accelerated expansion. Courtesy: NASA and ESA.

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It’s Official — Big Rip Coming!

San_Sebastian-Cementerio_de_PolloeThe UK’s Daily Telegraph newspaper just published this article, so it must be true. After all, the broadsheet has been a stalwart of conservative British journalism since, well, the dawn of time, some 6,000 year ago.

Apparently our universe will end in a so-called Big Rip, and not in a Big Freeze. Nor will it end in a Big Crunch, which is like the Big Bang in reverse. The Big Rip seems to be a rather calm and quiet version of the impending cosmological apocalypse. So, I’m all for it. I can’t wait… 22 billion years and counting.

From the Daily Telegraph:

A group of scientists claim to have evidence supporting the Big Rip theory, explaining how the universe will end – in 22 billion years.

Researchers at Vanderbilt University in Nashville, Tennessee, have discovered a new mathematical formulation that supports the Big Rip theory – that as the universe expands, it will eventually be ripped apart.

“The idea of the Big Rip is that eventually even the constituents of matter would start separating from each other. You’d be seeing all the atoms being ripped apart … it’s fair to say that it’s a dramatic scenario,” Dr Marcelo Disconzi told the Guardian.

Scientists observed distant supernovae to examine whether the Big Rip theory, which was first suggested in 2003, was possible.

The theory relies on the assumption that the universe continues to expand faster and faster, eventually causing the Big Rip.

“Mathematically we know what this means. But what it actually means in physical terms is hard to fathom,” said Dr Disconzi.

Conflicting theories for how the universe will end include the Big Crunch, whereby the Big Bang reverses and everything contracts, and the Big Freeze, where as the universe slowly expands it eventually becomes too cold to sustain life.

Previous questions raised over the Big Rip theory include explaining how sticky fluids – that have high levels of viscosity – can travel faster than the speed of light, defying the laws of physics.

However, the Vanderbilt team combined a series of equations, including some dating back to 1955, to show that viscosity may not be a barrier to a rapidly expanding universe.

“My result by no means settles the question of what the correct formulation of relativistic viscous fluids is. What it shows is that, under some assumptions, the equations put forward by Lichnerowicz have solutions and the solutions do not predict faster-than-light signals. But we still don’t know if these results remain valid under the most general situations relevant to physics,” Dr Disconzi told the New Statesman.

Read the story here.

Image: Cementerio de Polloe, en Donostia-San Sebastián, 2014. Courtesy of Zarateman. Public domain.

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The Inflaton and the Multiverse

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Last week’s announcement that cosmologists had found signals of gravitational waves from the primordial cosmic microwave background of the Big Bang made many headlines, even on cable news. If verified by separate experiments this will be ground-breaking news indeed — much like the discovery of the Higgs Boson in 2012. Should the result stand, this may well pave the way for new physics and greater support for the multiverse theory of the universe. So, in addition to the notion that we may not be alone in the vast cosmos, we’ll now have to consider not being alone in a cosmos made up of multiple universes — our universe may not be alone either!

From the New Scientist:

Wave hello to the multiverse? Ripples in the very fabric of the cosmos, unveiled this week, are allowing us to peer further back in time than anyone thought possible, showing us what was happening in the first slivers of a second after the big bang.

The discovery of these primordial waves could solidify the idea that our young universe went through a rapid growth spurt called inflation. And that theory is linked to the idea that the universe is constantly giving birth to smaller “pocket” universes within an ever-expanding multiverse.

The waves in question are called gravitational waves, and they appear in Einstein’s highly successful theory of general relativity (see “A surfer’s guide to gravitational waves”). On 17 March, scientists working with the BICEP2 telescope in Antarctica announced the first indirect detection of primordial gravitational waves. This version of the ripples was predicted to be visible in maps of the cosmic microwave background (CMB), the earliest light emitted in the universe, roughly 380,000 years after the big bang.

Repulsive gravity

The BICEP2 team had spent three years analysing CMB data, looking for a distinctive curling pattern called B-mode polarisation. These swirls indicate that the light of the CMB has been twisted, or polarised, into specific curling alignments. In two papers published online on the BICEP project website, the team said they have high confidence the B-mode pattern is there, and that they can rule out alternative explanations such as dust in our own galaxy, distortions caused by the gravity of other galaxies and errors introduced by the telescope itself. That suggests the swirls could have been left only by the very first gravitational waves being stretched out by inflation.

“If confirmed, this result would constitute the most important breakthrough in cosmology over the past 15 years. It will open a new window into the beginning of our universe and have fundamental implications for extensions of the standard model of physics,” says Avi Loeb at Harvard University. “If it is real, the signal will likely lead to a Nobel prize.”

And for some theorists, simply proving that inflation happened at all would be a sign of the multiverse.

“If inflation is there, the multiverse is there,” said Andrei Linde of Stanford University in California, who is not on the BICEP2 team and is one of the originators of inflationary theory. “Each observation that brings better credence to inflation brings us closer to establishing that the multiverse is real.” (Watch video of Linde being surprised with the news that primordial gravitational waves have been detected.)

The simplest models of inflation, which the BICEP2 results seem to support, require a particle called an inflaton to push space-time apart at high speed.

“Inflation depends on a kind of material that turns gravity on its head and causes it to be repulsive,” says Alan Guth at the Massachusetts Institute of Technology, another author of inflationary theory. Theory says the inflaton particle decays over time like a radioactive element, so for inflation to work, these hypothetical particles would need to last longer than the period of inflation itself. Afterwards, inflatons would continue to drive inflation in whatever pockets of the universe they inhabit, repeatedly blowing new universes into existence that then rapidly inflate before settling down. This “eternal inflation” produces infinite pocket universes to create a multiverse.

Quantum harmony

For now, physicists don’t know how they might observe the multiverse and confirm that it exists. “But when the idea of inflation was proposed 30 years ago, it was a figment of theoretical imagination,” says Marc Kamionkowski at Johns Hopkins University in Baltimore, Maryland. “What I’m hoping is that with these results, other theorists out there will start to think deeply about the multiverse, so that 20 years from now we can have a press conference saying we’ve found evidence of it.”

In the meantime, studying the properties of the swirls in the CMB might reveal details of what the cosmos was like just after its birth. The power and frequency of the waves seen by BICEP2 show that they were rippling through a particle soup with an energy of about 1016 gigaelectronvolts, or 10 trillion times the peak energy expected at the Large Hadron Collider. At such high energies, physicists expect that three of the four fundamental forces in physics – the strong, weak and electromagnetic forces – would be merged into one.

The detection is also the first whiff of quantum gravity, one of the thorniest puzzles in modern physics. Right now, theories of quantum mechanics can explain the behaviour of elementary particles and those three fundamental forces, but the equations fall apart when the fourth force, gravity, is added to the mix. Seeing gravitational waves in the CMB means that gravity is probably linked to a particle called the graviton, which in turn is governed by quantum mechanics. Finding these primordial waves won’t tell us how quantum mechanics and gravity are unified, says Kamionkowski. “But it does tell us that gravity obeys quantum laws.”

“For the first time, we’re directly testing an aspect of quantum gravity,” says Frank Wilczek at MIT. “We’re seeing gravitons imprinted on the sky.”

Waiting for Planck

Given the huge potential of these results, scientists will be eagerly anticipating polarisation maps from projects such as the POLARBEAR experiment in Chile or the South Pole Telescope. The next full-sky CMB maps from the Planck space telescope are also expected to include polarisation data. Seeing a similar signal from one or more of these experiments would shore up the BICEP2 findings and make a firm case for inflation and boost hints of the multiverse and quantum gravity.

One possible wrinkle is that previous temperature maps of the CMB suggested that the signal from primordial gravitational waves should be much weaker that what BICEP2 is seeing. Those results set theorists bickering about whether inflation really happened and whether it could create a multiverse. Several physicists suggested that we scrap the idea entirely for a new model of cosmic birth.

Taken alone, the BICEP2 results give a strong-enough signal to clinch inflation and put the multiverse back in the game. But the tension with previous maps is worrying, says Paul Steinhardt at Princeton University, who helped to develop the original theory of inflation but has since grown sceptical of it.

“If you look at the best-fit models with the new data added, they’re bizarre,” Steinhardt says. “If it remains like that, it requires adding extra fields, extra parameters, and you get really rather ugly-looking models.”

Forthcoming data from Planck should help resolve the issue, and we may not have long to wait. Olivier Doré at the California Institute of Technology is a member of the Planck collaboration. He says that the BICEP2 results are strong and that his group should soon be adding their data to the inflation debate: “Planck in particular will have something to say about it as soon as we publish our polarisation result in October 2014.”

Read the entire article here.

Image: Multiverse illustration. Courtesy of National Geographic.

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Gravity Makes Some Waves

Gravity, the movie, made some “waves” at the recent Academy Awards ceremony in Hollywood. But the real star in this case, is the real gravity that seems to hold all macroscopic things in the cosmos together. And the waves in the this case are real gravitational waves. A long-running experiment based at the South Pole has discerned a signal from the Cosmic Microwave Background that points to the existence of gravitational waves. This is a discovery of great significance, if upheld, and confirms the Inflationary Theory of our universe’s exponential expansion just after the Big Bang. Theorists who first proposed this remarkable hypothesis — Alan Guth (1979) and Andrei Linde (1981) — are probably popping some champagne right now.

From the New Statesman:

The announcement yesterday that scientists working on the BICEP2 experiment in Antarctica had detected evidence of “inflation” may not appear incredible, but it is. It appears to confirm longstanding hypotheses about the Big Bang and the earliest moments of our universe, and could open a new path to resolving some of physics’ most difficult mysteries.

Here’s the explainer. BICEP2, near the South Pole (where the sky is clearest of pollution), was scanning the visible universe for cosmic background radiation – that is, the fuzzy warmth left over from the Big Bang. It’s the oldest light in the universe, and as such our maps of it are our oldest glimpses of the young universe. Here’s a map created with data collected by the ESA’s Planck Surveyor probe last year:

ESA-Planck-Surveyor-image

What should be clear from this is that the universe is remarkably flat and regular – that is, there aren’t massive clumps of radiation in some areas and gaps in others. This doesn’t quite make intuitive sense.

If the Big Bang really was a chaotic event, with energy and matter being created and destroyed within tiny fractions of nanoseconds, then we would expect the net result to be a universe that’s similarly chaotic in its structure. Something happened to smooth everything out, and that something is inflation.

Inflation assumes that something must have happened to the rate of expansion of the universe, somewhere between 10-35 and 10-32 seconds after the Big Bang, to make it massively increase. It would mean that the size of the “lumps” would outpace the rate at which they appear in the cosmos, smoothing them out.

For an analogy, imagine if the Moon was suddenly stretched out to the size of the Sun. You’d see – just before it collapsed in on itself – that its rifts and craters had become, relative to its new size, made barely perceptible. Just like a sheet being pulled tightly on a bed, a chaotic structure becomes more uniform.

Inflation, first theorised by Alan Guth in 1979 and refined by Andrei Linde in 1981, became the best hypothesis to explain what we were observing in the universe. It also seemed to offer a way to better understand how dark energy drove the expansion of the Big Bang, and even possibly lead a way towards unifying quantum mechanics with general relativity. That is, if it was correct. And there have been plenty of theories which tied-up some loose ends only to come apart with further observation.

The key evidence needed to verify inflation would be in the form of gravitational waves – that is, ripples in spacetime. Such waves were a part of Einstein’s theory of general relativity, and in the 90s scientists observed some for the first time, but until now there’s never been any evidence of them from inside the cosmic background radiation.

BICEP2, though, has found that evidence, and with it scientists now have a crucial piece of fact that can falsify other theories about the early universe and potentially open up entirely new areas of investigation. This is why it’s being compared with the discovery of the Higgs Boson last year, as just as that particle was fundamental to our understanding of molecular physics, so to is inflation to our understanding of the wider universe.

Read the entire article here.

Video: Professor physicist Chao-Lin Kuo delivers news of results from his gravitational wave experiment. Professor Andrei Linde reacts to the discovery, March 17, 2014. Courtesy of Stanford University.

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MondayMap: Quiet News Day = Map of the Universe

It was surely a quiet news day on March 21 2013 — most major online news outlets showed a fresh map of the Cosmic Microwave Background (CMB) on the front page. It was taken by the Planck Telescope, operated by the European Space Agency, over a period of 15 months. The image shows a landscape of primordial cosmic microwaves from when the universe was only around 380,000 years old, and is often referred to as “first light”.

From ESA:

Acquired by ESA’s Planck space telescope, the most detailed map ever created of the cosmic microwave background – the relic radiation from the Big Bang – was released today revealing the existence of features that challenge the foundations of our current understanding of the Universe.

The image is based on the initial 15.5 months of data from Planck and is the mission’s first all-sky picture of the oldest light in our Universe, imprinted on the sky when it was just 380 000 years old.

At that time, the young Universe was filled with a hot dense soup of interacting protons, electrons and photons at about 2700ºC. When the protons and electrons joined to form hydrogen atoms, the light was set free. As the Universe has expanded, this light today has been stretched out to microwave wavelengths, equivalent to a temperature of just 2.7 degrees above absolute zero.

This ‘cosmic microwave background’ – CMB – shows tiny temperature fluctuations that correspond to regions of slightly different densities at very early times, representing the seeds of all future structure: the stars and galaxies of today.

According to the standard model of cosmology, the fluctuations arose immediately after the Big Bang and were stretched to cosmologically large scales during a brief period of accelerated expansion known as inflation.

Planck was designed to map these fluctuations across the whole sky with greater resolution and sensitivity than ever before. By analysing the nature and distribution of the seeds in Planck’s CMB image, we can determine the composition and evolution of the Universe from its birth to the present day.

Overall, the information extracted from Planck’s new map provides an excellent confirmation of the standard model of cosmology at an unprecedented accuracy, setting a new benchmark in our manifest of the contents of the Universe.

But because precision of Planck’s map is so high, it also made it possible to reveal some peculiar unexplained features that may well require new physics to be understood.

“The extraordinary quality of Planck’s portrait of the infant Universe allows us to peel back its layers to the very foundations, revealing that our blueprint of the cosmos is far from complete. Such discoveries were made possible by the unique technologies developed for that purpose by European industry,” says Jean-Jacques Dordain, ESA’s Director General.

“Since the release of Planck’s first all-sky image in 2010, we have been carefully extracting and analysing all of the foreground emissions that lie between us and the Universe’s first light, revealing the cosmic microwave background in the greatest detail yet,” adds George Efstathiou of the University of Cambridge, UK.

One of the most surprising findings is that the fluctuations in the CMB temperatures at large angular scales do not match those predicted by the standard model – their signals are not as strong as expected from the smaller scale structure revealed by Planck.

Read the entire article after the jump.

Image: Cosmic microwave background (CMB) seen by Planck. Courtesy of ESA (European Space Agency).

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Mutant Gravity and Dark Magnetism

Scientific consensus states that our universe is not only expanding, but expanding at an ever-increasing rate. So, sometime in the very distant future (tens of billions of years) our Milky Way galaxy will be mostly alone, accompanied only by its close galactic neighbors, such as Andromeda. All else in the universe will have receded beyond the horizon of visible light. And, yet for all the experimental evidence, no one knows the precise cause(s) of this acceleration or even of the expansion itself. But, there is no shortage of bold new theories.

From New Scientist:

WE WILL be lonely in the late days of the cosmos. Its glittering vastness will slowly fade as countless galaxies retreat beyond the horizon of our vision. Tens of billions of years from now, only a dense huddle of nearby galaxies will be left, gazing out into otherwise blank space.

That gloomy future comes about because space is expanding ever faster, allowing far-off regions to slip across the boundary from which light has time to reach us. We call the author of these woes dark energy, but we are no nearer to discovering its identity. Might the culprit be a repulsive force that emerges from the energy of empty spaceMovie Camera, or perhaps a modification of gravity at the largest scales? Each option has its charms, but also profound problems.

But what if that mysterious force making off with the light of the cosmos is an alien echo of light itself? Light is just an expression of the force of electromagnetism, and vast electromagnetic waves of a kind forbidden by conventional physics, with wavelengths trillions of times larger than the observable universe, might explain dark energy’s baleful presence. That is the bold notion of two cosmologists who think that such waves could also account for the mysterious magnetic fields that we see threading through even the emptiest parts of our universe. Smaller versions could be emanating from black holes within our galaxy.

It is almost two decades since we realised that the universe is running away with itself. The discovery came from observations of supernovae that were dimmer, and so further away, than was expected, and earned its discoverers the Nobel prize in physics in 2011.

Prime suspect in the dark-energy mystery is the cosmological constant, an unchanging energy which might emerge from the froth of short-lived, virtual particles that according to quantum theory are fizzing about constantly in otherwise empty space.

Mutant gravity

To cause the cosmic acceleration we see, dark energy would need to have an energy density of about half a joule per cubic kilometre of space. When physicists try to tot up the energy of all those virtual particles, however, the answer comes to either exactly zero (which is bad), or something so enormous that empty space would rip all matter to shreds (which is very bad). In this latter case the answer is a staggering 120 orders of magnitude out, making it a shoo-in for the least accurate prediction in all of physics.

This stumbling block has sent some researchers down another path. They argue that in dark energy we are seeing an entirely new side to gravity. At distances of many billions of light years, it might turn from an attractive to a repulsive force.

But it is dangerous to be so cavalier with gravity. Einstein’s general theory of relativity describes gravity as the bending of space and time, and predicts the motions of planets and spacecraft in our own solar system with cast-iron accuracy. Try bending the theory to make it fit acceleration on a cosmic scale, and it usually comes unstuck closer to home.

That hasn’t stopped many physicists persevering along this route. Until recently, Jose Beltrán and Antonio Maroto were among them. In 2008 at the Complutense University of Madrid, Spain, they were playing with a particular version of a mutant gravity model called a vector-tensor theory, which they had found could mimic dark energy. Then came a sudden realisation. The new theory was supposed to be describing a strange version of gravity, but its equations bore an uncanny resemblance to some of the mathematics underlying another force. “They looked like electromagnetism,” says Beltrán, now based at the University of Geneva in Switzerland. “We started to think there could be a connection.”

So they decided to see what would happen if their mathematics described not masses and space-time, but magnets and voltages. That meant taking a fresh look at electromagnetism. Like most of nature’s fundamental forces, electromagnetism is best understood as a phenomenon in which things come chopped into little pieces, or quanta. In this case the quanta are photons: massless, chargeless particles carrying fluctuating electric and magnetic fields that point at right angles to their direction of motion.

Alien photons

This description, called quantum electrodynamics or QED, can explain a vast range of phenomena, from the behaviour of light to the forces that bind molecules together. QED has arguably been tested more precisely than any other physical theory, but it has a dark secret. It wants to spit out not only photons, but also two other, alien entities.

The first kind is a wave in which the electric field points along the direction of motion, rather than at right angles as it does with ordinary photons. This longitudinal mode moves rather like a sound wave in air. The second kind, called a temporal mode, has no magnetic field. Instead, it is a wave of pure electric potential, or voltage. Like all quantum entities, these waves come in particle packets, forming two new kinds of photon.

As we have never actually seen either of these alien photons in reality, physicists found a way to hide them. They are spirited away using a mathematical fix called the Lorenz condition, which means that all their attributes are always equal and opposite, cancelling each other out exactly. “They are there, but you cannot see them,” says Beltrán.

Beltrán and Maroto’s theory looked like electromagnetism, but without the Lorenz condition. So they worked through their equations to see what cosmological implications that might have.

The strange waves normally banished by the Lorenz condition may come into being as brief quantum fluctuations – virtual waves in the vacuum – and then disappear again. In the early moments of the universe, however, there is thought to have been an episode of violent expansion called inflation, which was driven by very powerful repulsive gravity. The force of this expansion grabbed all kinds of quantum fluctuations and amplified them hugely. It created ripples in the density of matter, for example, which eventually seeded galaxies and other structures in the universe.

Crucially, inflation could also have boosted the new electromagnetic waves. Beltrán and Maroto found that this process would leave behind vast temporal modes: waves of electric potential with wavelengths many orders of magnitude larger than the observable universe. These waves contain some energy but because they are so vast we do not perceive them as waves at all. So their energy would be invisible, dark… perhaps, dark energy?

Beltrán and Maroto called their idea dark magnetism (arxiv.org/abs/1112.1106). Unlike the cosmological constant, it may be able to explain the actual quantity of dark energy in the universe. The energy in those temporal modes depends on the exact time inflation started. One plausible moment is about 10 trillionths of a second after the big bang, when the universe cooled below a critical temperature and electromagnetism split from the weak nuclear force to become a force in its own right. Physics would have suffered a sudden wrench, enough perhaps to provide the impetus for inflation.

If inflation did happen at this “electroweak transition”, Beltrán and Maroto calculate that it would have produced temporal modes with an energy density close to that of dark energy. The correspondence is only within an order of magnitude, which may not seem all that precise. In comparison with the cosmological constant, however, it is mildly miraculous.

The theory might also explain the mysterious existence of large-scale cosmic magnetic fields. Within galaxies we see the unmistakable mark of magnetic fields as they twist the polarisation of light. Although the turbulent formation and growth of galaxies could boost a pre-existing field, is it not clear where that seed field would have come from.

Even more strangely, magnetic fields seem to have infiltrated the emptiest deserts of the cosmos. Their influence was noticed in 2010 by Andrii Neronov and Ievgen Vovk at the Geneva Observatory. Some distant galaxies emit blistering gamma rays with energies in the teraelectronvolt range. These hugely energetic photons should smack into background starlight on their way to us, creating electrons and positrons that in turn will boost other photons up to gamma energies of around 100 gigaelectronvolts. The trouble is that astronomers see relatively little of this secondary radiation. Neronov and Vovk suggest that is because a diffuse magnetic field is randomly bending the path of electrons and positrons, making their emission more diffuse (Science, vol 32, p 73).

“It is difficult to explain cosmic magnetic fields on the largest scales by conventional mechanisms,” says astrophysicist Larry Widrow of Queen’s University in Kingston, Ontario, Canada. “Their existence in the voids might signal an exotic mechanism.” One suggestion is that giant flaws in space-time called cosmic strings are whipping them up.

With dark magnetism, such a stringy solution would be superfluous. As well as the gigantic temporal modes, dark magnetism should also lead to smaller longitudinal waves bouncing around the cosmos. These waves could generate magnetism on the largest scales and in the emptiest voids.

To begin with, Beltrán and Maroto had some qualms. “It is always dangerous to modify a well-established theory,” says Beltrán. Cosmologist Sean Carroll at the California Institute of Technology in Pasadena, echoes this concern. “They are doing extreme violence to electromagnetism. There are all sorts of dangers that things might go wrong,” he says. Such meddling could easily throw up absurdities, predicting that electromagnetic forces are different from what we actually see.

The duo soon reassured themselves, however. Although the theory means that temporal and longitudinal modes can make themselves felt, the only thing that can generate them is an ultra-strong gravitational field such as the repulsive field that sprang up in the era of inflation. So within the atom, in all our lab experiments, and out there among the planets, electromagnetism carries on in just the same way as QED predicts.

Carroll is not convinced. “It seems like a long shot,” he says. But others are being won over. Gonzalo Olmo, a cosmologist at the University of Valencia, Spain, was initially sceptical but is now keen. “The idea is fantastic. If we quantise electromagnetic fields in an expanding universe, the effect follows naturally.”

So how might we tell whether the idea is correct? Dark magnetism is not that easy to test. It is almost unchanging, and would stretch space in almost exactly the same way as a cosmological constant, so we can’t tell the two ideas apart simply by watching how cosmic acceleration has changed over time.

Ancient mark

Instead, the theory might be challenged by peering deep into the cosmic microwave background, a sea of radiation emitted when the universe was less than 400,000 years old. Imprinted on this radiation are the original ripples of matter density caused by inflation, and it may bear another ancient mark. The turmoil of inflation should have energised gravitational waves, travelling warps in space-time that stretch and squeeze everything they pass through. These waves should affect the polarisation of cosmic microwaves in a distinctive way, which could tell us about the timing and the violence of inflation. The European Space Agency’s Planck spacecraft might just spot this signature. If Planck or a future mission finds that inflation happened before the electroweak transition, at a higher energy scale, then that would rule out dark magnetism in its current form.

Olmo thinks that the theory might anyhow need some numerical tweaking, so that might not be fatal, although it would be a blow to lose the link between the electroweak transition and the correct amount of dark energy.

One day, we might even be able to see the twisted light of dark magnetism. In its present incarnation with inflation at the electroweak scale, the longitudinal waves would all have wavelengths greater than a few hundred million kilometres, longer than the distance from Earth to the sun. Detecting a light wave efficiently requires an instrument not much smaller than the wavelength, but in the distant future it might just be possible to pick up such waves using space-based radio telescopes linked up across the solar system. If inflation kicked in earlier at an even higher energy, as suggested by Olmo, some of the longitudinal waves could be much shorter. That would bring them within reach of Earth-based technology. Beltrán suggests that they might be detected with the Square Kilometre Array – a massive radio instrument due to come on stream within the next decade.

If these dark electromagnetic waves can be created by strong gravitational fields, then they could also be produced by the strongest fields in the cosmos today, those generated around black holes. Beltrán suggests that waves may be emitted by the black hole at the centre of the Milky Way. They might be short enough for us to see – but they could easily be invisibly faint. Beltrán and Maroto are planning to do the calculations to find out.

One thing they have calculated from their theory is the voltage of the universe. The voltage of the vast temporal waves of electric potential started at zero when they were first created at the time of inflation, and ramped up steadily. Today, it has reached a pretty lively 1027 volts, or a billion billion gigavolts.

Just as well for us that it has nowhere to discharge. Unless, that is, some other strange quirk of cosmology brings a parallel universe nearby. The encounter would probably destroy the universe as we know it, but at least then our otherwise dark and lonely future would end with the mother of all lightning bolts.

Read the entire article after the jump.

Graphic courtesy of NASA / WMAP.

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A Great Mind Behind the Big Bang

Davide Castelvecchi over at Degrees of Freedom visits with one of the founding fathers of modern cosmology, Alan Guth.

Now professor of physics at MIT, Guth originated the now widely accepted theory of the inflationary universe. Guth’s idea, with subsequent supporting mathematics, was that the nascent universe passed through a phase of exponential expansion. In 2009, he was awarded the 2009 Isaac Newton Medal by the British Institute of Physics.

From Scientific American:

On the night of December 6, 1979–32 years ago today–Alan Guth had the “spectacular realization” that would soon turn cosmology on its head. He imagined a mind-bogglingly brief event, at the very beginning of the big bang, during which the entire universe expanded exponentially, going from microscopic to cosmic size. That night was the birth of the concept of cosmic inflation.

Such an explosive growth, supposedly fueled by a mysterious repulsive force, could solve in one stroke several of the problems that had plagued the young theory of the big bang. It would explain why space is so close to being spatially flat (the “flatness problem”) and why the energy distribution in the early universe was so uniform even though it would not have had the time to level out uniformly (the “horizon problem”), as well as solve a riddle in particle physics: why there seems to be no magnetic monopoles, or in other words why no one has ever isolated “N” and “S” poles the way we can isolate “+” and “-” electrostatic charges; theory suggested that magnetic monopoles should be pretty common.

In fact, as he himself narrates in his highly recommendable book, The Inflationary Universe, at the time Guth was a particle physicist (on a stint at the Stanford Linear Accelerator Center, and struggling to find a permanent job) and his idea came to him while he was trying to solve the monopole problem.

Twenty-five years later, in the summer of 2004, I asked Guth–by then a full professor at MIT and a leading figure of cosmology– for his thoughts on his legacy and how it fit with the discovery of dark energy and the most recent ideas coming out of string theory.

The interview was part of my reporting for a feature on inflation that appeared in the December 2004 issue of Symmetry magazine. (It was my first feature article, other than the ones I had written as a student, and it’s still one of my favorites.)

To celebrate “inflation day,” I am reposting, in a sligthly edited form, the transcript of that interview.

DC: When you first had the idea of inflation, did you anticipate that it would turn out to be so influential?

AG: I guess the answer is no. But by the time I realized that it was a plausible solution to the monopole problem and to the flatness problem, I became very excited about the fact that, if it was correct, it would be a very important change in cosmology. But at that point, it was still a big if in my mind. Then there was a gradual process of coming to actually believe that it was right.

DC: What’s the situation 25 years later?

AG: I would say that inflation is the conventional working model of cosmology. There’s still more data to be obtained, and it’s very hard to really confirm inflation in detail. For one thing, it’s not really a detailed theory, it’s a class of theories. Certainly the details of inflation we don’t know yet. I think that it’s very convincing that the basic mechanism of inflation is correct. But I don’t think people necessarily regard it as proven.

Read the entire article here.

Image: Alan Guth. Courtesy of Scientific American.

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The Infant Universe

Long before the first galaxy clusters and the first galaxies appeared in our universe, and before the first stars, came the first basic elements — hydrogen, helium and lithium.

Results from a just published study identify these raw materials from what is theorized to be the universe’s first few minutes of existence.

From Scientific American:

By peering into the distance with the biggest and best telescopes in the world, astronomers have managed to glimpse exploding stars, galaxies and other glowing cosmic beacons as they appeared just hundreds of millions of years after the big bang. They are so far away that their light is only now reaching Earth, even though it was emitted more than 13 billion years ago.

Astronomers have been able to identify those objects in the early universe because their bright glow has remained visible even after a long, universe-spanning journey. But spotting the raw materials from which the first cosmic structures formed—the gas produced as the infant universe expanded and cooled in the first few minutes after the big bang—has not been possible. That material is not itself luminous, and everywhere astronomers have looked they have found not the primordial light-element gases hydrogen, helium and lithium from the big bang but rather material polluted by heavier elements, which form only in stellar interiors and in cataclysms such as supernovae.

Now a group of researchers reports identifying the first known pockets of pristine gas, two relics of those first minutes of the universe’s existence. The team found a pair of gas clouds that contain no detectable heavy elements whatsoever by looking at distant quasars and the intervening material they illuminate. Quasars are bright objects powered by a ravenous black hole, and the spectral quality of their light reveals what it passed through on its way to Earth, in much the same way that the lamp of a projector casts the colors of film onto a screen. The findings appeared online November 10 in Science.

“We found two gas clouds that show a significant abundance of hydrogen, so we know that they are there,” says lead study author Michele Fumagalli, a graduate student at the University of California, Santa Cruz. One of the clouds also shows traces of deuterium, also known as heavy hydrogen, the nucleus of which contains not only a proton, as ordinary hydrogen does, but also a neutron. Deuterium should have been produced in big bang nucleosynthesis but is easily destroyed, so its presence is indicative of a pristine environment. The amount of deuterium present agrees with theoretical predictions about the mixture of elements that should have emerged from the big bang. “But we don’t see any trace of heavier elements like carbon, oxygen and iron,” Fumagalli says. “That’s what tells us that this is primordial gas.”

The newfound gas clouds, as Fumagalli and his colleagues see them, existed about two billion years after the big bang, at an epoch of cosmic evolution known as redshift 3. (Redshift is a sort of cosmological distance measure, corresponding to the degree that light waves have been stretched on their trip across an expanding universe.) By that time the first generation of stars, initially comprising only the primordial light elements, had formed and were distributing the heavier elements they forged via nuclear fusion reactions into interstellar space.

But the new study shows that some nooks of the universe remained pristine long after stars had begun to spew heavy elements. “They have looked for these special corners of the universe, where things just haven’t been polluted yet,” says Massachusetts Institute of Technology astronomer Rob Simcoe, who did not contribute to the new study. “Everyplace else that we’ve looked in these environments, we do find these heavy elements.”

Read the entire article here.

Image: Simulation by Ceverino, Dekel and Primack. Courtesy of Scientific American.

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Dark energy spotted in the cosmic microwave background

From Institute of Physics:

Astronomers studying the cosmic microwave background (CMB) have uncovered new direct evidence for dark energy – the mysterious substance that appears to be accelerating the expansion of the universe. Their findings could also help map the structure of dark matter on the universe’s largest length scales.

The CMB is the faint afterglow of the universe’s birth in the Big Bang. Around 400,000 years after its creation, the universe had cooled sufficiently to allow electrons to bind to atomic nuclei. This “recombination” set the CMB radiation free from the dense fog of plasma that was containing it. Space telescopes such as WMAP and Planck have charted the CMB and found its presence in all parts of the sky, with a temperature of 2.7 K. However, measurements also show tiny fluctuations in this temperature on the scale of one part in a million. These fluctuations follow a Gaussian distribution.

In the first of two papers, a team of astronomers including Sudeep Das at the University of California, Berkeley, has uncovered fluctuations in the CMB that deviate from this Gaussian distribution. The deviations, observed with the Atacama Cosmology Telescope in Chile, are caused by interactions with large-scale structures in the universe, such as galaxy clusters. “On average, a CMB photon will have encountered around 50 large-scale structures before it reaches our telescope,” Das told physicsworld.com. “The gravitational influence of these structures, which are dominated by massive clumps of dark matter, will each deflect the path of the photon,” he adds. This process, called “lensing”, eventually adds up to a total deflection of around 3 arc minutes – one-20th of a degree.

Dark energy versus structure

In the second paper Das, along with Blake Sherwin of Princeton University and Joanna Dunkley of Oxford University, looks at how lensing could reveal dark energy. Dark energy acts to counter the emergence of structures within the universe. A universe with no dark energy would have a lot of structure. As a result, the CMB photons would undergo greater lensing and the fluctuations would deviate more from the original Gaussian distribution.

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Brilliant, but Distant: Most Far-Flung Known Quasar Offers Glimpse into Early Universe

From Scientific American:

Peering far across space and time, astronomers have located a luminous beacon aglow when the universe was still in its infancy. That beacon, a bright astrophysical object known as a quasar, shines with the luminosity of 63 trillion suns as gas falling into a supermassive black holes compresses, heats up and radiates brightly. It is farther from Earth than any other known quasar—so distant that its light, emitted 13 billion years ago, is only now reaching Earth. Because of its extreme luminosity and record-setting distance, the quasar offers a unique opportunity to study the conditions of the universe as it underwent an important transition early in cosmic history.

By the time the universe was one billion years old, the once-neutral hydrogen gas atoms in between galaxies had been almost completely stripped of their electrons (ionized) by the glow of the first massive stars. But the full timeline of that process, known as re-ionization because it separated protons and electrons, as they had been in the first 380,000 years post–big bang, is somewhat uncertain. Quasars, with their tremendous intrinsic brightness, should make for excellent markers of the re-ionization process, acting as flashlights to illuminate the intergalactic medium. But quasar hunters working with optical telescopes had only been able to see back as far as 870 million years after the big bang, when the intergalactic medium’s transition from neutral to ionized was almost complete. (The universe is now 13.75 billion years old.) Beyond that point, a quasar’s light has been so stretched, or redshifted, by cosmic expansion that it no longer falls in the visible portion of the electromagnetic spectrum but rather in the longer-wavelength infrared.

Daniel Mortlock, an astrophysicist at Imperial College London, and his colleagues used that fact to their advantage. The researchers looked for objects that showed up in a large-area infrared sky survey but not in a visible-light survey covering the same area of sky, essentially isolating the high-redshift objects. They could thus discover a quasar, known as ULAS J1120+0641, at redshift 7.085, corresponding to a time just 770 million years after the big bang. That places the newfound quasar about 100 million years earlier in cosmic history than the previous record holder, which was at redshift 6.44. Mortlock and his colleagues report their finding in the June 30 issue of Nature. (Scientific American is part of Nature Publishing Group.)

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More subatomic spot changing

From the Economist:

IN THIS week’s print edition we report a recent result from the T2K collaboration in Japan which has found strong hints that neutrinos, the elusive particles theorists believe to be as abundant in the universe as photons, but which almost never interact with anything, are as fickle as they are coy.

It has been known for some time that neutrinos switch between three types, or flavours, as they zip through space at a smidgen below the speed of light. The flavours are distinguished by the particles which emerge on the rare occasion a neutrino does bump into something. And so, an electron-neutrino conjures up an electron, a muon-neutrino, a muon, and a tau-neutrino, a tau particle (muons and tau are a lot like electrons, but heavier and less stable). Researchers at T2K observed, for the first time, muon-neutrinos transmuting into the electron variety—the one sort of spot-changing that had not been seen before. But their results, with a 0.7% chance of being a fluke, was, by the elevated standards of particle physics, tenuous.

Now, T2K’s rival across the Pacific has made it less so. MINOS beams muon-neutrinos from Fermilab, America’s biggest particle-physics lab located near Chicago, to a 5,000-tonne detector sitting in the Soudan mine in Minnesota, 735km (450 miles) to the north-west. On June 24th its researchers annouced that they, too, had witnessed some of muon-neutrinos change to the electron variety along the way. To be precise, the experiment recorded 62 events which could have been caused by electron-neutrinos. If the proposed transmutation does not occur in nature, it ought to have seen no more than 49 (the result of electron-neutrinos streaming in from space or radioactive rocks on Earth). Were the T2K figures spot on, as it were, it should have seen 71.

As such, the result from MINOS, which uses different methods to study the same phenomenon, puts the transmutation hypothesis on a firmer footing. This advances the search for a number known as delta (?). This is one of the parameters of the formula which physicists think describes neutrinos spot-changing antics. Physicists are keen to pin it down, since it also governs the description of the putative asymmetry between matter and antimatter that left matter as the dominant feature of the universe after the Big Bang.

In light of the latest result, it remains unclear whether either the American or the Japanese experiment is precise enough to measure delta. In 2013, however, MINOS will be supplanted by NOvA, a fancier device located in another Minnesota mine 810km from Fermilab’s muon-neutrino cannon. That ought to do the trick. Then again, nature has the habit of springing surprises.

And in more ways than one. Days after T2K’s run was cut short by the earthquake that shook Japan in March, devastating the muon-neutrino source at J-PARC, the country’s main particle-accelerator complex, MINOS had its own share of woe when the Soudan mine sustained significant flooding. Fortunately, the experiment itself escaped relatively unscathed. But the eerie coincidence spurred some boffins, not a particularly superstitious bunch, to speak of a neutrino curse. Fingers crossed that isn’t the case.

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Image courtesy of Fermilab.

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Cosmic Smoothness

Simulations based on the standard cosmological model, as shown here, indicate that on very large distance scales, galaxies should be uniformly distributed. But observations show a clumpier distribution than expected. (The length bar represents about $2.3$ billion light years.)

From American Physical Society, Michael J. Hudson:

The universe is expected to be very nearly homogeneous in density on large scales. In Physical Review Letters, Shaun Thomas and colleagues from University College London analyze measurements of the density of galaxies on the largest spatial scales so far—billions of light years—and find that the universe is less smooth than expected. If it holds up, this result will have important implications for our understanding of dark matter, dark energy, and perhaps gravity itself.

In the current standard cosmological model, the average mass-energy density of the observable universe consists of 5% normal matter (most of which is hydrogen and helium), 23% dark matter, and 72% dark energy. The dark energy is assumed to be uniform, but the normal and dark matter are not. The balance between matter and dark energy determines both how the universe expands and how regions of unusually high or low matter density evolve with time.

The same cosmological model predicts the statistics of the nonuniform structure and their dependence on spatial scale. On scales that are small by cosmological standards, fluctuations in the matter density are comparable to its mean, in agreement with what is seen: matter is clumped into galaxies, clusters of galaxies, and filaments of the “cosmic web.” On larger scales, however, the contrast of the structures compared to the mean density decreases. On the largest cosmological scales, these density fluctuations are small in amplitude compared to the average density of the universe and so are well described by linear perturbation theory (see simulation results in Fig. 1). Moreover, these perturbations can be calibrated at early times directly from the cosmic microwave background (CMB), a snapshot of the universe from when it was only 380,000 years old. Despite the fact that only 5% of the Universe is well understood, this model is an excellent fit to data spanning a wide range of spatial scales as the fluctuations evolved from the time of the CMB to the present age of the universe, some 13.8 billion years. On the largest scales, dark energy drives accelerated expansion of the universe. Because this aspect of the standard model is least understood, it is important to test it on these scales.

Thomas et al. use publicly-released catalogs from the Sloan Digital Sky Survey to select more than 700,000 galaxies whose observed colors indicate a significant redshift and are therefore presumed to be at large cosmological distances. They use the redshift of the galaxies, combined with their observed positions on the sky, to create a rough three-dimensional map of the galaxies in space and to assess the homogeneity on scales of a couple of billion light years. One complication is that Thomas et al. measure the density of galaxies, not the density of all matter, but we expect that fluctuations of these two densities about their means to be proportional; the constant of proportionality can be calibrated by observations on smaller scales. Indeed, on small scales the galaxy data are in good agreement with the standard model. On the largest scales, the fluctuations in galaxy density are expected to be of order a percent of the mean density, but Thomas et al. find fluctuations double this prediction. This result then suggests that the universe is less homogeneous than expected.

This result is not entirely new: previous studies based on subsets of the data studied by Thomas et al. showed the same effect, albeit with a lower statistical significance. In addition, there are other ways of probing the large-scale mass distribution. For example, inhomogeneities in the mass distribution lead to inhomogeneities in the local rate of expansion. Some studies have suggested that, on very large scales, this expansion too is less homogeneous than the model predictions.

Future large-scale surveys will produce an avalanche of data. These surveys will allow the methods employed by Thomas et al. and others to be extended to still larger scales. Of course, the challenge for these future surveys will be to correct for the systematic effects to even greater accuracy.

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Are Black Holes the Architects of the Universe?

From Discover:

Black holes are finally winning some respect. After long regarding them as agents of destruction or dismissing them as mere by-products of galaxies and stars, scientists are recalibrating their thinking. Now it seems that black holes debuted in a constructive role and appeared unexpectedly soon after the Big Bang. “Several years ago, nobody imagined that there were such monsters in the early universe,” says Penn State astrophysicist Yuexing Li. “Now we see that black holes were essential in creating the universe’s modern structure.”

Black holes, tortured regions of space where the pull of gravity is so intense that not even light can escape, did not always have such a high profile. They were once thought to be very rare; in fact, Albert Einstein did not believe they existed at all. Over the past several decades, though, astronomers have realized that black holes are not so unusual after all: Supermassive ones, millions or billions of times as hefty as the sun, seem to reside at the center of most, if not all, galaxies. Still, many people were shocked in 2003 when a detailed sky survey found that giant black holes were already common nearly 13 billion years ago, when the universe was less than a billion years old. Since then, researchers have been trying to figure out where these primordial holes came from and how they influenced the cosmic events that followed.

In August, researchers at the Kavli Institute for Particle Astrophysics and Cosmology at Stanford University ran a supercomputer simulation of the early universe and provided a tantalizing glimpse into the lives of the first black holes. The story began 200 million years after the Big Bang, when the universe’s first stars formed. These beasts, about 100 times the mass of the sun, were so large and energetic that they burned all their hydrogen fuel in just a few million years. With no more energy from hydrogen fusion to counteract the enormous inward pull of their gravity, the stars collapsed until all of their mass was compressed into a point of infinite density.

The first-generation black holes were puny compared with the monsters we see at the centers of galaxies today. They grew only slowly at first—adding just 1 percent to their bulk in the next 200 million years—because the hyperactive stars that spawned them had blasted away most of the nearby gas that they could have devoured. Nevertheless, those modest-size black holes left a big mark by performing a form of stellar birth control: Radiation from the trickle of material falling into the holes heated surrounding clouds of gas to about 5,000 degrees Fahrenheit, so hot that the gas could no longer easily coalesce. “You couldn’t really form stars in that stuff,” says Marcelo Alvarez, lead author of the Kavli study.

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Image courtesy of KIPAC/SLAC/M.Alvarez, T. Able, and J. Wise.

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Stephen Hawking Is Making His Comeback

From Discover:

As an undergraduate at Oxford University, Stephen William Hawking was a wise guy, a provocateur. He was popular, a lively coxswain for the crew team. Physics came easy. He slept through lectures, seldom studied, and criticized his professors. That all changed when he started graduate school at Cambridge in 1962 and subsequently learned that he had only a few years to live.

The symptoms first appeared while Hawking was still at Oxford. He could not row a scull as easily as he once had; he took a few bad, clumsy falls. A college doctor told him not to drink so much beer. By 1963 his condition had gotten bad enough that his mother brought him to a hospital in London, where he received the devastating diagnosis: motor neuron disease, as ALS is called in the United Kingdom. The prognosis was grim and final: rapid wasting of nerves and muscles, near-total paralysis, and death from respiratory failure in three to five years.

Not surprisingly, Hawking grew depressed, seeking solace in the music of Wagner (contrary to some media reports, however, he says he did not go on a drinking binge). And yet he did not disengage from life. Later in 1963 he met Jane Wilde, a student of medieval poetry at the University of London. They fell in love and resolved to make the most of what they both assumed would be a tragically short relationship. In 1965 they married, and Hawking returned to physics with newfound energy.

Also that year, Hawking had an encounter that led to his first major contribution to his field. The occasion was a talk at Kings College in London given by Roger Penrose, an eminent mathematician then at Birkbeck College. Penrose had just proved something remarkable and, for physicists, disturbing: Black holes, the light-trapping chasms in space-time that form in the aftermath of the collapse of massive stars, must all contain singularities—points where space, time, and the very laws of physics fall apart.

Before Penrose’s work, many physicists had regarded singularities as mere curiosities, permitted by Einstein’s theory of general relativity but unlikely to exist. The standard assumption was that a singularity could form only if a perfectly spherical star collapsed with perfect symmetry, the kind of ideal conditions that never occur in the real world. Penrose proved otherwise. He found that any star massive enough to form a black hole upon its death must create a singularity. This realization meant that the laws of physics could not be used to describe everything in the universe; the singularity was a cosmic abyss.

At a subsequent lecture, Hawking grilled Penrose on his ideas. “He asked some awkward questions,” Penrose says. “He was very much on the ball. I had probably been a bit vague in one of my statements, and he was sharpening it up a bit. I was a little alarmed that he noticed something that I had glossed over, and that he was able to spot it so quickly.”

Hawking had just renewed his search for a subject for his Ph.D. thesis, a project he had abandoned after receiving the ALS diagnosis. His condition had stabilized somewhat, and his future no longer looked completely bleak. Now he had his subject: He wanted to apply Penrose’s approach to the cosmos at large.

Physicists have known since 1929 that the universe is expanding. Hawking reasoned that if the history of the universe could be run backward, so that the universe was shrinking instead of expanding, it would behave (mathematically at least) like a collapsing star, the same sort of phenomenon Penrose had analyzed. Hawking’s work was timely. In 1965, physicists working at Bell Labs in New Jersey discovered the cosmic microwave background radiation, the first direct evidence that the universe began with the Big Bang. But was the Big Bang a singularity, or was it a concentrated, hot ball of energy—awesome and mind-bending, but still describable by the laws of physics?

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The Great Cosmic Roller-Coaster Ride

From Scientific American:

Could cosmic inflation be a sign that our universe is embedded in a far vaster realm

You might not think that cosmologists could feel claustrophobic in a universe that is 46 billion light-years in radius and filled with sextillions of stars. But one of the emerging themes of 21st-century cosmology is that the known universe, the sum of all we can see, may just be a tiny region in the full extent of space. Various types of parallel universes that make up a grand “multiverse” often arise as side effects of cosmological theories. We have little hope of ever directly observing those other universes, though, because they are either too far away or somehow detached from our own universe.

Some parallel universes, however, could be separate from but still able to interact with ours, in which case we could detect their direct effects. The possibility of these worlds came to cosmologists’ attention by way of string theory, the leading candidate for the foundational laws of nature. Although the eponymous strings of string theory are extremely small, the principles governing their properties also predict new kinds of larger membranelike objects—“branes,” for short. In particular, our universe may be a three-dimensional brane in its own right, living inside a nine-dimensional space. The reshaping of higher-dimensional space and collisions between different universes may have led to some of the features that astronomers observe today.

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The Dark Ages of the Universe

From Scientific American:

Astronomers are trying to fill in the blank pages in our photo album of the infant universe.

When I look up into the sky at night, I often wonder whether we humans are too preoccupied with ourselves. There is much more to the universe than meets the eye on earth. As an astrophysicist I have the privilege of being paid to think about it, and it puts things in perspective for me. There are things that I would otherwise be bothered by–my own death, for example. Everyone will die sometime, but when I see the universe as a whole, it gives me a sense of longevity. I do not care so much about myself as I would otherwise, because of the big picture.

Cosmologists are addressing some of the fundamental questions that people attempted to resolve over the centuries through philosophical thinking, but we are doing so based on systematic observation and a quantitative methodology. Perhaps the greatest triumph of the past century has been a model of the universe that is supported by a large body of data. The value of such a model to our society is sometimes underappreciated. When I open the daily newspaper as part of my morning routine, I often see lengthy descriptions of conflicts between people about borders, possessions or liberties. Today’s news is often forgotten a few days later. But when one opens ancient texts that have appealed to a broad audience over a longer period of time, such as the Bible, what does one often find in the opening chapter? A discussion of how the constituents of the universe–light, stars, life–were created. Although -humans are often caught up with mundane problems, they are curious about the big -picture. As citizens of the universe we -cannot help but wonder how the first sources of light formed, how life came into existence and whether we are alone as in-telligent beings in this vast space. Astronomers in the 21st century are uniquely positioned to answer these big questions.

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The First Few Microseconds

From Scientific American:

In recent experiments, physicists have replicated conditions of the infant universe–with startling results.

For the past five years, hundreds of scientists have been using a powerful new atom smasher at Brookhaven National Laboratory on Long Island to mimic conditions that existed at the birth of the universe. Called the Relativistic Heavy Ion Collider (RHIC, pronounced “rick”), it clashes two opposing beams of gold nuclei traveling at nearly the speed of light. The resulting collisions between pairs of these atomic nuclei generate exceedingly hot, dense bursts of matter and energy to simulate what happened during the first few microseconds of the big bang. These brief “mini bangs” give physicists a ringside seat on some of the earliest moments of creation.

During those early moments, matter was an ultrahot, superdense brew of particles called quarks and gluons rushing hither and thither and crashing willy-nilly into one another. A sprinkling of electrons, photons and other light elementary particles seasoned the soup. This mixture had a temperature in the trillions of degrees, more than 100,000 times hotter than the sun’s core.

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