Artist concept of matter swirling around a black hole. (NASA/Dana Berry/SkyWorks Digital)
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Imagine a spinning black hole so colossal and so powerful that it kicks photons, the basic units of light, and sends them careening thousands of light years through space. Some of the photons make it to Earth. Scientists are announcing in the journal NaturePhysics today that those well-traveled photons still carry the signature of that colossal jolt, as a distortion in the way they move. The disruption is like a long-distance missive from the black hole itself, containing information about its size and the speed of its spin.
The researchers say the jostled photons are key to unraveling the theory that predicts black holes in the first place.
“It is rare in general-relativity research that a new phenomenon is discovered that allows us to test the theory further,” says Martin Bojowald, a Penn State physics professor and author of a News & Views article that accompanies the study.
Black holes are so gravitationally powerful that they distort nearby matter and even space and time. Called framedragging, the phenomenon can be detected by sensitive gyroscopes on satellites, Bojowald notes.
Lead study author Fabrizio Tamburini, an astronomer at the University of Padova (Padua) in Italy, and his colleagues have calculated that rotating spacetime can impart to light an intrinsic form of orbital angular momentum distinct from its spin. The authors suggest visualizing this as non-planar wavefronts of this twisted light like a cylindrical spiral staircase, centered around the light beam.
“The intensity pattern of twisted light transverse to the beam shows a dark spot in the middle — where no one would walk on the staircase — surrounded by concentric circles,” they write. “The twisting of a pure [orbital angular momentum] mode can be seen in interference patterns.” They say researchers need between 10,000 and 100,000 photons to piece a black hole’s story together.
And telescopes need some kind of 3D (or holographic) vision in order to see the corkscrews in the light waves they receive, Bojowald said: “If a telescope can zoom in sufficiently closely, one can be sure that all 10,000-100,000 photons come from the accretion disk rather than from other stars farther away. So the magnification of the telescope will be a crucial factor.”
He believes, based on a rough calculation, that “a star like the sun as far away as the center of the Milky Way would have to be observed for less than a year. So it is not going to be a direct image, but one would not have to wait very long.”
Study co-author Bo Thidé, a professor and program director at the Swedish Institute of Space Physics, said a year may be conservative, even in the case of a small rotation and a need for up to 100,000 photons.
“But who knows,” he said. “We will know more after we have made further detailed modelling – and observations, of course. At this time we emphasize the discovery of a
new general relativity phenomenon that allows us to make observations, leaving precise quantitative predictions aside.”
This NASA Hubble Space Telescope image shows the distribution of dark matter in the center of the giant galaxy cluster Abell 1689, containing about 1,000 galaxies and trillions of stars. Credit: NASA, ESA, D. Coe (NASA Jet Propulsion Laboratory/California Institute of Technology, and Space Telescope Science Institute), N. Benitez (Institute of Astrophysics of Andalusia, Spain), T. Broadhurst (University of the Basque Country, Spain), and H. Ford (Johns Hopkins University)
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Our Universe is an enormous place; that’s no secret. What is up for discussion, however, is just how enormous it is. And new research suggests it’s a whopper – over 250 times the size of our observable universe.
Currently, cosmologists believe the Universe takes one of three possible shapes:
1) It is flat, like a Euclidean plane, and spatially infinite.
2) It is open, or curved like a saddle, and spatially infinite.
3) It is closed, or curved like a sphere, and spatially finite.
While most current data favors a flat universe, cosmologists have yet to come to a consensus. In a paper recently submitted to Arxiv, UK scientists Mihran Vardanyan, Roberto Trotta and Joseph Silk present their fix: a mathematical version of Occam’s Razor called Bayesian model averaging. The principle of Occam’s Razor states that the simplest explanation is usually the correct one. In this case, a flat universe represents a simpler geometry than a curved universe. Bayesian averaging takes this consideration into account and averages the data accordingly. Unsurprisingly, the team’s results show that the data best fits a flat, infinite universe.
But what if the Universe turns out to be closed, and thus has a finite size after all? Cosmologists often refer to the Hubble volume – a volume of space that is similar to our visible Universe. Light from any object outside of the Hubble volume will never reach us because the space between us and it is expanding too quickly. According to the team’s analysis, a closed universe would encompass at least 251 Hubble volumes.
That’s quite a bit larger than you might think. Primordial light from just after the birth of the Universe started traveling across the cosmos about 13.75 billion years ago. Since special relativity states that nothing can move faster than a photon, many people misinterpret this to mean that the observable Universe must be 13.75 billion light years across. In fact, it is much larger. Not only has space been expanding since the big bang, but the rate of expansion has been steadily increasing due to the influence of dark energy. Since special relativity doesn’t factor in the expansion of space itself, cosmologists estimate that the oldest photons have travelled a distance of 45 billion light years since the big bang. That means that our observable Universe is on the order of 90 billion light years wide.
To top it all off, it turns out that the team’s size limit of 251 Hubble volumes is a conservative estimate, based on a geometric model that includes inflation. If astronomers were to instead base the size of the Universe solely on the age and distribution of the objects they observe today, they would find that a closed universe encompasses at least 398 Hubble volumes. That’s nearly 400 times the size of everything we can ever hope to see in the Universe!
Given the reality of our current capabilities for observation, to us even a finite universe appears to go on forever.
Six areas of the sky in which distant galaxies can be seen by Planck, overlaid on the Planck’s first all-sky image. The emission from our own Galaxy, seen in blue and white, has to be removed before the distant population of galaxies can be seen. Each square inset image is around the same size as the Full Moon. Image credit: ESA / Planck Collaboration.
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The mission began on 13th August 2009 with a goal to image the echo’s of the birth of the Universe, the cosmic background radiation. But scientists working on the European Space Agency’s (ESA) Planck mission got more than they bargained for making ground breaking discoveries and shedding light on old mysteries. By studying light from the far reaches of the Universe, Planck has to look through the rest of the Universe first and it was during this, that the incredible discoveries were made.
The crazy thing about looking at the far reaches of the Universe is that we actually look back in time as it takes billions of years for the light to reach us here on Earth. This enables astronomers to look back in time and study the evolution of the Universe almost back to the Big Bang itself. Amongst the discoveries was evidence for an otherwise invisible population of galaxies that seem to be shrouded in dust billions of years in the past. Star formation rates in these galaxies seem to be happening at an incredible pace, some 10-1000 times higher than we see in our own Milky Way galaxy today. Joanna Dunkley, of Oxford University, said “Planck’s measurements of these distant galaxies are shedding new light on when and where ancient stars formed in the early universe”.
One of the challenges of getting a clear view of these galaxies though has been removing the so called ‘anomalous microwave emission’ (AME) foreground haze. This annoying and poorly understood interference, which is thought to originate in our own Galaxy, has only just been pierced through with Planck’s instruments. But in doing so, clues to its nature have been unveiled. It seems that the AME is coming from dust grains in our Galaxy spinning several tens of billions of times per second, perhaps from collisions with incoming faster-moving atoms or from ultra-violet radiation. Planck was able to ‘remove’ the foreground microwave haze, leaving the distant galaxies in perfect view and the cosmic background radiation untouched.
Its also the ideal instrument to detect very cold matter in the form of dust in our Galaxy and beyond, thanks to its broad wavelength coverage. During its study, it detected over 900 clumps of cold dark dust clouds which are thought to represent the first stages of star birth. By studying a number of nearby galaxies within a few billion light years, the study shows that some of them contain much more cold dust than previously thought. Dr David Clements from Imperial College London says “Planck will help us to build a ladder connecting our Milky Way to the faint, distant galaxies and uncovering the evolution of dusty, star forming galaxies throughout cosmic history.”
These results make Planck a roaring success but it doesn’t stop there. Other results just published include data on galaxy clusters revealing them silhouetted against the cosmic microwave background. These clusters contain thousands of individual galaxies gravitational bound together into gigantic strings and loops.
The Planck mission, which was in development for 15 years is already providing some ground breaking science in its first few years of operation and its exciting to wonder what we will see from it in the years that lie ahead.
Representation of the timeline of the universe over 13.7 billion years, and the expansion in the universe that followed. Credit: NASA/WMAP Science Team.
Remnants of the first stars have helped astronomers get closer to unlocking the “dark ages” of the cosmos. A team of researchers from the University of Cambridge and California Institute of Technology are using light emitted from massive black holes called quasars to “light up” gases released by the early stars, which exploded billions of years ago. As a result, they have found what they refer to as the missing link in the evolution of the chemical universe.
The first stars are believed to hold the key to one of the mysteries of the early cosmos: how it evolved from being predominantly filled with hydrogen and helium to a universe rich in heavier elements, such as oxygen, carbon and iron.
However, although telescopes can detect light reaching Earth from billions of light-years away, enabling astronomers to look back in time over almost all of the 13.7-billion-year history of the universe, one observational frontier remains: the so-called “dark ages.” This period, lasting half a billion years after the Big Bang, ended when the first stars were born and is inaccessible to telescopes because the clouds of gas that filled the universe were not transparent to visible and infrared light.
“We have effectively been able to peer into the dark ages using the light emitted from a quasar in a distant galaxy billions of years ago. The light provides a backdrop against which any gas cloud in its path can be measured,” said Professor Max Pettini at Cambridge’s Institute of Astronomy (IoA), who led the research with PhD student Ryan Cooke.
Taking precision measurements using the world’s largest telescopes in Hawaii and Chile, the researchers have used Quasar Absorption Line Spectroscopy to identify gas clouds called ‘damped Lyman alpha systems’ (DLAs). Among the thousands of DLAs known, the team have succeeded in finding a rare cloud released from a star very early in the history of the universe.
“As judged by its composition, the gas is a remnant of a star that exploded as much as 13 billion years ago,” Pettini explained. “It provides the first analysis of the interior of one of the universe’s earliest stars.”
The results provide experimental observations of a time that has so far been possible to model only with computers simulations, and will help astronomers to fill gaps in understanding how the chemical universe evolved.
“We discovered tiny amounts of elements present in the cloud in proportions that are very different from their relative proportions in normal stars today. Most significantly, the ratio of carbon to iron is 35 times greater than measured in the Sun,” Pettini said. “The composition enables us to infer that the gas was released by a star 25 times more massive than the Sun and originally consisting of only hydrogen and helium. In effect this is a fossil record that provides us with a missing link back to the early universe.”
The study was published in Monthly Notices of the Royal Astronomical Society by Ryan Cooke, Max Pettini and Regina Jorgenson at the IoA, together with Charles Steidel and Gwen Rudie at the California Institute of Technology in Pasadena.
Anyhow, this prompted me to look up different ways in which apparent superluminal motion might be generated, partly to reassure myself that the bottom hadn’t fallen out of relativity physics and partly to see if these things could be adequately explained in plain English. Here goes…
1) Cause and effect illusions
The faster than light pulsar story is essentially about hypothetical light booms – which are a bit like a sonic booms, where it’s not the sonic boom, but the sound source, that exceeds the speed of sound – so that individual sound pulses merge to form a single shock wave moving at the speed of sound.
Now, whether anything like this really happens with light from pulsars remains a point of debate, but one of the model’s proponents has demonstrated the effect in a laboratory – see this Scientific American blog post.
What you do is to arrange a line of light bulbs which are independently triggered. It’s easy enough to make them fire off in sequence – first 1, then 2, then 3 etc – and you can keep reducing the time delay between each one firing until you have a situation where bulb 2 fires off after bulb 1 in less time than light would need to travel the distance between bulbs 1 and 2. It’s just a trick really – there is no causal connection between the bulbs firing – but it looks as though a sequence of actions (first 1, then 2, then 3 etc) moved faster than light across the row of bulbs. This illusion is an example of apparent superluminal motion.
There are a range of possible scenarios as to why a superluminal Mexican wave of synchrotron radiation might emanate from different point sources around a rapidly rotating neutron star within an intense magnetic field. As long as the emanations from these point sources are not causally connected, this outcome does not violate relativity physics.
2) Making light faster than light
You can produce an apparent superluminal motion of light itself by manipulating its wavelength. If we consider a photon as a wave packet, that wave packet can be stretched linearly so that the leading edge of the wave arrives at its destination faster, since it is pushed ahead of the remainder of the wave – meaning that it travels faster than light.
However, the physical nature of ‘the leading edge of a wave packet’ is not clear. The whole wave packet is equivalent to one photon – and the leading edge of the stretched out wave packet cannot carry any significant information. Indeed, by being stretched out and attenuated, it may become indistinguishable from background noise.
Also this trick requires the light to be moving through a refractive medium, not a vacuum. If you are keen on the technical details, you can make phase velocity or group velocity faster than c (the speed of light in a vacuum) – but not signal velocity. In any case, since information (or the photon as a complete unit) is not moving faster than light, relativity physics is not violated.
3) Getting a kick out of gain media
You can mimic more dramatic superluminal motion through a gain medium where the leading edge of a light pulse stimulates the emission of a new pulse at the far end of the gain medium – as though a light pulse hits one end of a Newton’s Cradle and new pulse is projected out from the other end. If you want to see a laboratory set-up, try here. Although light appears to jump the gap superluminally, in fact it’s a new light pulse emerging at the other end – and still just moving at standard light speed.
Light faster than light. Left: Stretching the waveform of light can make the leading edge of the wave seem to move faster than light. Right: Gain media can act like a Newton's Cradle, making light seem to jump the gap superluminally.
4) The relativistic jet illusion
If an active galaxy, like M87, is pushing out a jet of superheated plasma moving at close to the speed of light – and the jet is roughly aligned with your line of sight from Earth – you can be fooled into thinking its contents are moving faster than light.
If that jet is 5,000 light years long, it should take at least 5,000 years for anything in it to cross that distance of 5,000 light years. A photon emitted by a particle of jet material at point A near the start of the jet really will take 5,000 years to reach you. But meanwhile, the particle of jet material continues moving towards you nearly as fast as that photon. So when the particle emits another photon at point B, a point near the tip of the jet – that second photon will reach your eye in much less than 5,000 years after the first photon, from point A. This will give you the impression that the particle crossed 5,000 light years from points A to B in much less than 5,000 years. But it is just an optical illusion – relativity physics remains unsullied.
5) Unknowable superluminal motion
It is entirely possible that objects beyond the horizon of the observable universe are moving away from our position faster than the speed of light – as a consequence of the universe’s cumulative expansion, which makes distant galaxies appear to move away faster than close galaxies. But since light from hypothetical objects beyond the observable horizon will never reach Earth, their existence is unknowable by direct observation from Earth – and does not represent a violation of relativity physics.
And lastly, not so much unknowable as theoretical is the notion of early cosmic inflation, which also involves an expansion of space-time rather than movement within space-time – so no violation there either.
Other stuff…
I’m not sure that the above is an exhaustive list and I have deliberately left out other theoretical proposals such as quantum entanglement and the Alcubierre warp drive. Either of these, if real, would arguably violate relativity physics – so perhaps need to be considered with a higher level of skepticism.
The signatures of a bubble collision at various stages in our analysis pipeline. A collision (top left) induces a temperature modulation in the CMB temperature map (top right). The "blob" associated with the collision is identi ed by a large needlet response (bottom left), and the presence of an edge is determined by a large response from the edge detection algorithm (bottom right). (Feeny, et al.)
In the realm of far out ideas in science, the notion of a multiverse is one of the stranger ones. Astronomers and physicists have considered the possibility that our universe may be one of many. The implications of this are somewhat more fuzzy. Nothing in physics prevents the possibilities of outside universes, but neither has it helped to constrain them, leaving scientists free to talk of branes and bubbles. Many of these ideas have been considered untestable, but a paper uploaded to arXiv last month considers the effects of two universes colliding and searches for fingerprints of such a collision of our own universe. Surprisingly, the team reports that they may have detected not one, but four collisional imprints.
The foamy cosmic web – at this scale we run out of superlatives to describe the large scale structure of the universe.
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The so-called End of Greatness is where you give up trying to find more superlatives to describe large scale objects in the universe. Currently the Sloan Great Wall – a roughly organised collection of galactic superclusters partitioning one great void from another great void – is about where most cosmologists draw the line.
Beyond the End of Greatness, it’s best just to consider the universe as a holistic entity – and at this scale we consider it isotropic and homogenous, which we need to do to make our current cosmology math work. But at the very edge of greatness, we find the cosmic web.
The cosmic web is not a thing we can directly observe since its 3d structure is derived from red shift data to indicate the relative distance of galaxies, as well as their apparent position in the sky. When you pull all this together, the resulting 3d structure seems like a complex web of galactic cluster filaments interconnecting at supercluster nodes and interspersed by huge voids. These voids are bubble-like – so that we talk about structures like the Sloan Great Wall, as being the outer surface of such a bubble. And we also talk about the whole cosmic web being ‘foamy’.
It is speculated that the great voids or bubbles, around which the cosmic web seems to be organised, formed out of tiny dips in the primordial energy density (which can be seen in the cosmic microwave background), although a convincing correlation remains to be demonstrated.
The two degree field (2df) galaxy redshift survey – which used an instrument with a field of view of two degrees, although the survey covered 1500 square degrees of sky in two directions. The wedge shape results from the 3d nature of the data - where there are more galaxies the farther out you look, within one region of the sky. The foamy bubbles of the cosmic web are visible. Credit: The Australian Astronomical Observatory.
As is well recorded, the Andromeda Galaxy is probably on a collision course with the Milky Way and they may collide in about 4.5 billion years. So, not every galaxy in the universe is rushing away from every other galaxy in the universe – it’s just a general tendency. Each galaxy has its own proper motion in space-time, which it is likely to continue to follow despite the underlying expansion of the universe.
It may be that much of the growing separation between galaxies is a result of expansion of the void bubbles, rather than equal expansion everywhere. It’s as though once gravity loses its grip between distant structures – expansion (or dark energy, if you like) takes over and that gap begins to expand unchecked – while elsewhere, clusters and superclusters of galaxies still manage to hold together. This scenario remains consistent with Edwin Hubble’s finding that the large majority of galaxies are rushing away from us, even if they are not all equally rushing away from each other.
van de Weygaert et al are investigating the cosmic web from the perspective of topology – a branch of geometry which looks at spatial properties which are preserved in objects undergoing deformation. This approach seems ideal to model the evolving large scale structure of an expanding universe.
The paper below represents an early step in this work, but shows that a cosmic web structure can be loosely modelled by assuming that all data points (i.e. galaxies) move outwards from the central point of the void they lie most proximal to. This rule creates alpha shapes, which are generalised surfaces that can be built over data points – and the outcome is a mathematically modelled foamy-looking cosmic web.
WMAP data of the Cosmic Microwave Background. Credit: NASA
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Have scientists seen evidence of time before the Big Bang, and perhaps a verification of the idea of the cyclical universe? One of the great physicists of our time, Roger Penrose from the University of Oxford, has published a new paper saying that the circular patterns seen in the WMAP mission data on the Cosmic Microwave Background suggest that space and time perhaps did not originate at the Big Bang but that our universe continually cycles through a series of “aeons,” and we have an eternal, cyclical cosmos. His paper also refutes the idea of inflation, a widely accepted theory of a period of very rapid expansion immediately following the Big Bang.
Penrose says that inflation cannot account for the very low entropy state in which the universe was thought to have been created. He and his co-author do not believe that space and time came into existence at the moment of the Big Bang, but instead, that event was just one in a series of many. Each “Big Bang” marked the start of a new aeon, and our universe is just one of many in a cyclical Universe, starting a new universe in place of the one before.
Penrose’s co-author, Vahe Gurzadyan of the Yerevan Physics Institute in Armenia, analyzed seven years’ worth of microwave data from WMAP, as well as data from the BOOMERanG balloon experiment in Antarctica. Penrose and Gurzadyan say they have identified regions in the microwave sky where there are concentric circles showing the radiation’s temperature is markedly smaller than elsewhere.
These circles allow us to “see through” the Big Bang into the aeon that would have existed beforehand. The circles were created when black holes “encountered” or collided with a previous aeon.
“Black-hole encounters, within bound galactic clusters in that previous aeon, would have the observable effect, in our CMB sky,” the duo write in their paper, “of families of concentric circles over which the temperature variance is anomalously low.”
And these circles don’t jive with the idea of inflation, because inflation proposes that the distribution of temperature variations across the sky should be Gaussian, or random, rather than having discernable structures within it.
Penrose’s new theory even projects how the distant future might emerge, where things will again be similar to the beginnings of the Universe at the Big Bang where the Universe was smooth, as opposed to the current jagged form. This continuity of shape, he maintains, will allow a transition from the end of the current aeon, when the universe will have expanded to become infinitely large, to the start of the next, when it once again becomes infinitesimally small and explodes outwards from the next big bang.
Penrose and Gurzadyan say that the entropy at the transition stage will be very low, because black holes, which destroy all information that they suck in, evaporate as the universe expands and in so doing remove entropy from the universe.
“These observational predictions of (Conformal cyclic cosmology) CCC would not be easily explained within standard inflationary cosmology,” they write in their paper.
Ancient woodcarving of where heaven and earth meet. Credit: Heikenwaelder Hugo at Wikimedia Commons.
Cosmology is a fairly young science, one which attempts to reconstruct the history of our Universe from billions of years ago. Looking back so far in time is extremely difficult, and adding to the complexity is that many of the pillars upon which the theories of cosmology rest have only been conceived within the last 20 years or so. That hasn’t given scientists and theorists much time to fully flesh out and comprehend the situation, and cosmologist Michael Turner says either some important new physics will have to be discovered or we’re going to find a fatal flaw in our prevailing view of the Universe.
So, what will it take to push cosmology over the edge, where it goes fully from theory to science, and we have at least a grasp of cosmological understanding? I had the chance to ask that question to Turner at last week’s National Association of Science Writers conference. Turner, who coined the term “dark energy,” is the Director of the Kavli Institute for Cosmological Physics at the University of Chicago. Here are his top four wishes for discoveries in cosmology:
Wish # 1: Figure out the nature of dark matter.
“I think we’re very close to solving this dark matter problem and I think its going to be stunning when it sinks in to everyone that most of the stuff in the Universe is made of something other than what we are,” Turner said.
Dark matter holds universe together, according to cosmologists. But since it does not emit electromagnetic radiation and we can’t see it, how do we know it is there? “It is needed to hold galaxies together, it is needed to hold clusters together, it is that simple,” Turner said. “There is not enough gravity in all the stars put together to hold clusters together.”
Turner has likened dark matter to an outdoor tree decorated with Christmas lights. From far away, all that can be seen are the lights, but it is the unseen tree that holds the lights where they are and gives them their shape. More poetically Turner said, “The universe is a web of dark matter that is decorated by stars.”
Turner made a bold prediction: “The 2010 is the decade of dark matter – we are going to finish this thing off.”
Dark matter in the Bullet Cluster. Otherwise invisible to telescopic views, the dark matter was mapped by observations of gravitational lensing of background galaxies. Credit: X-ray: NASA/CXC/CfA/ M.Markevitch et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/ D.Clowe et al. Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.;
Wish # 2. Figure out the nature of dark energy.
“Dark energy may be most profound problem in cosmology today, and I’ve been wandering around for 10 years saying this,” Turner said. “If dark matter holds the Universe together, dark energy controls its destiny.”
Dark energy likely makes up 66% of the cosmos, and it’s existence has only been theorized since 1998 when astronomers realized that contrary to the prevailing notion that the expansion of the universe should be slowing down, it is actually moving faster as time goes on.
What is the current theoretical understanding of dark energy? “We don’t have a clue,” said Turner. “But let me go out here on a limb with dark energy, and say we may find it is not vacuum energy. Vacuum energy is mathematical equivalent to Einstein’s cosmological constant, and I hope we’ll figure out it is something weirder than the energy of nothing. That doesn’t solve the problem, but it would be a gift to my younger colleagues, because science is all about big questions and they need clues and something big they can sink their teeth into.”
Yes, dark energy is a big problem, but for theorists it’s a big opportunity. However, Turner has some doubts. “Dark energy is one of the big questions that will occupy the next decade, and I don’t know if we’ll be able to solve it,” he said.
Michael Turner at the 2010 National Association of Science Writers conference at Yale University. Image: Nancy Atkinson
Wish # 3: Confirming inflation with the discovery of B-Mode polarization.
Our current best theory about the earliest moments of the universe is called inflation, where during a tiny fraction of a second after the Big Bang, the Universe appears to have expanded exponentially. In particular, high precision measurements of the so-called B-modes (evidence of gravity waves) of the polarization of the cosmic microwave background radiation would be evidence of the gravitational radiation produced by inflation, and they will also show whether the energy scale of inflation predicted by the simplest models is correct.
“That is the smoking gun for inflation.” said Turner. “It explains where all the structure came from – that quantum mechanical fluctuations at the subatomic scale were blown up by this enormous expansion. That is an amazing idea, and in one equation we could figure out exactly when inflation took place. You’ll notice in all our talk of inflation no one ever tells you when it took place, because we don’t know. But those B-modes would tell us.”
Wish #4. Make the mulitiverse go away.
If there was inflation, that means there is also very likely a multitude of Universes out there.
Turner called the concept of the multiverse the 800 lb gorilla in the room.
“The dilemma is, we have evidence that inflation took place and the equations of inflation say that if it took place once, it took place twice and it’s sort of like the mouse and the cookie – if it took place twice it could have taken place an infinite number of times,” he said.
The multiverse hypothesizes multiple universes or parallel universes comprise everthing that is, not just our one “local” universe. “If there is a mulitverse structure, and if you marry this with string theory you end up with a picture of a Universe where there might be different local laws of physics and the different sub-universes might be incredibly different from each other – differences in space and time, some don’t have stable particles, many don’t have life, and so on. This is an incredibly bold idea and may even be the most important idea since Copernicus.”
But, Turner asked, how do you test it? “And if you can’t test it, therefore you can’t call it science,” he said. “So I call it the mulitiverse headache – you have this incredibly important idea, but is it science?”
“That’s where we are in cosmology,” he said. “We are the blind cosmologists feeling the Universe and each piece of data describes something. There are still big questions to be answered, and what we’re doing in cosmology is trying to put it all together, and we might actually, in the next 10-15 years put it all together. That is absolutely amazing; the universe is very big and our abilities are very primitive. But look what we’ve done so far.”
Slide from Turner's presentation showing the Universe as an elephant. Image: Nancy Atkinson
Allan Sandage. Credit: Carnegie Institution for Science.
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Cosmologist Allan R. Sandage, who helped define the fields of observational cosmology and extragalactic astronomy, died November 13, 2010, at his home in San Gabriel, California, of pancreatic cancer. He was Edwin Hubble’s former observing assistant and one of the most prominent astronomers of the last century. Sandage was 84. Below is his biography from the Carnegie Institution for Science:
Allan Sandage became a Carnegie staff member in 1952 after serving as the observing assistant in observational cosmology to Edwin Hubble on both Mount Wilson and Palomar from 1950 to 1953, and Walter Baade’s PhD student in stellar evolution starting in 1949. Upon the death of Hubble in 1953, Sandage became responsible for developing the cosmology program using the 60- and 100-inch telescopes on Mount Wilson and with the newly commissioned Palomar 200-inch reflector. The programs centered on the recalibration of Hubble’s extragalactic distance scale and combining discoveries in stellar evolution with observational cosmology. Much of his research in the past 50 years has been directed toward these goals.
Early discoveries at Palomar showed that Hubble’s distances to galaxies were progressively incorrect, starting with Baade’s finding in 1950 that Hubble’s measured distance to the Andromeda Nebula, M31, was too small by a factor of about two. Sandage, first alone and later with G.A. Tammann professor of astronomy at the University of Basel, have carried the corrections progressively outward. This work indicates that by the time we reach the nearest cluster of galaxies in Virgo, the correction to Hubble’s scale is close to a factor of 10. Since 1988, Sandage and Tammann have led a consortium using the Hubble Space Telescope to determine distances to parent galaxies that have produced type Ia supernovae, shown earlier to be one of the best standard candles in luminosity known. From the results of the calibrations, Sandage, Tammann, and Abijit Saha of the Kitt Peak National Optical Observatory have determined at this writing (2005) the value of the Hubble constant to be 60 km s -1 Mpc -1.
Sandage’s other early research in observational stellar evolution led to a method developed in 1952 with Martin Schwarzschild of age-dating the stars from the luminosity turn-off from the main sequence of evolving stars in the Hertzsprung-Russell diagram. This method, improved over the years from theoretical calculations of stellar structure by many astronomers, remains the principal method of age dating. Sandage recently returned to problems related to the absolute magnitudes of RR Lyrae variable stars in globular clusters, important to the age dating of these most ancient of objects in the Galaxy.
