The latest developments in cosmology point toward the possibility that our universe is merely one of billions. “What really interests me is whether God had any choice in creating the world.” That’s how Albert Einstein, in his characteristically poetic way, asked whether our universe is the only possible universe. The reference to God is easily… [Read more…]
April 27, 2012
Leonard Susskind In this note I respond to Vilenkin’s claim that there must have been a beginning. Mithani and Vilenkin have argued that the universe must have had a beginning [1]. I will argue the opposite point of view; namely, for all practical purposes, the universe was past-eternal. To make the point simply, imagine Hilbertville,… [Read more…]
April 25, 2012
Audrey Mithani, Alexander Vilenkin We discuss three candidate scenarios which seem to allow the possibility that the universe could have existed forever with no initial singularity: eternal infation, cyclic evolution, and the emergent universe. The first two of these scenarios are geodesically incomplete to the past, and thus cannot describe a universe without a beginning.… [Read more…]
April 24, 2012
“I think at some point you need to provoke people. Science is meant to make people uncomfortable.” It is hard to know how our future descendants will regard the little sliver of history that we live in. It is hard to know what events will seem important to them, what the narrative of now will… [Read more…]
April 16, 2012
… a lesson for quantum gravity Stefano Finazzi, Stefano Liberati, Lorenzo Sindoni For almost a century, the cosmological constant has been a mysterious object, in relation to both its origin and its very small value. By using a Bose-Einstein condensate analogue model for gravitational dynamics, we address here the cosmological constant issue from an analogue… [Read more…]
April 12, 2012
An international team of researchers led by Masamune Oguri at Kavli IPMU and Naohisa Inada at Nara National College of Technology conduced an unprecedented survey of gravitationally lensed quasars, and used it to measure the expansion history of the universe. The result provides strong evidence that the expansion of the universe is accelerating. There were… [Read more…]
April 10, 2012
Helge Kragh Ideological considerations have always influenced science, but rarely as directly and massively as in the Soviet Union during the early Cold War period. Cosmology was among the sciences that became heavily politicized and forced to conform to the doctrines of Marxism-Leninism. This field of science developed entirely differently in the Communist countries than… [Read more…]
April 9, 2012
Katherine Freese, Christopher Savage We investigate the interactions of Weakly Interacting Massive Particles (WIMPs) with nuclei in the human body. We are motivated by the fact that WIMPs are excellent candidates for the dark matter in the Universe. Our estimates use a 70 kg human and a variety of WIMP masses and cross-sections. The contributions… [Read more…]
April 7, 2012
Jodi Christiansen, Andy Siver As the universe expands astronomical observables such as brightness and angular size on the sky change in ways that differ from our simple Cartesian expectation. We show how observed quantities depend on the expansion of space and demonstrate how to calculate such quantities using the Friedmann equations. The general solution to… [Read more…]
April 2, 2012
Qiang Xu, Bin Chen We propose a new exponential f(R) gravity model with and n>3, 1≤λ, c>0 to explain late-time acceleration of the universe. At the high curvature region, the model behaves like the ΛCDM model. In the asymptotic future, it reaches a stable de-Sitter spacetime. It is a cosmologically viable model and can evade the… [Read more…]
March 30, 2012
Detectable seismic consequences of the interaction of a primordial black hole with Earth Yang Luo, Shravan Hanasoge, Jeroen Tromp, Frans Pretorius Galaxies observed today are likely to have evolved from density perturbations in the early universe. Perturbations that exceeded some critical threshold are conjectured to have undergone gravitational collapse to form primordial black holes (PBHs) at… [Read more…]
March 26, 2012
Inflation, the brief period that occurred less than a second after the Big Bang, is nearly as difficult to fathom as the Big Bang itself. Physicists calculate that inflation lasted for just a tiny fraction of a second, yet during this time the Universe grew in size by a factor of 1078. Also during this… [Read more…]
March 22, 2012
Wessel Valkenburg, Ole Eggers Bjaelde If we live in the vicinity of the hypothesized Great Attractor, the age of the universe as inferred from the local expansion rate can be off by three per cent. We study the effect that living inside or near a massive overdensity has on cosmological parameters induced from observations of… [Read more…]
March 17, 2012
Dmitri Krioukov, Maksim Kitsak, Robert S. Sinkovits, David Rideout, David Meyer, Marian Boguna Causal sets are an approach to quantum gravity in which the causal structure of spacetime plays a fundamental role. The causal set is a quantum network which underlies the fabric of spacetime. The nodes in this network are tiny quanta of spacetime,… [Read more…]
March 6, 2012
Astrophysicist Dr. Neil DeGrasse Tyson was asked by a reader of TIME magazine, “What is the most astounding fact you can share with us about the Universe?” This is his answer. (subtitles: click CC) http://youtu.be/9D05ej8u-gU
March 5, 2012
Varun Sahni, Aleksey Toporensky A Universe filled with a homogeneous scalar field exhibits `Cosmological hysteresis’. Cosmological hysteresis is caused by the asymmetry in the equation of state during expansion and contraction. This asymmetry results in the formation of a hysteresis loop: $\oint pdV$ (*), whose value can be non-vanishing during each oscillatory cycle. For flat… [Read more…]
March 5, 2012
Raphael Bousso In this colloquium-level account, I describe the cosmological constant problem: why is the energy of empty space at least 60 orders of magnitude smaller than several known contributions to it from the Standard Model of particle physics? I explain why the “dark energy” responsible for the accelerated expansion of the universe is almost… [Read more…]
March 3, 2012
A. D. Ernest A quantum expansion parameter, analogous to the Hubble parameter in cosmology, is defined for a free particle quantum wavefunction. By considering the universe as an initial single Gaussian quantum wavepacket whose mass is that of present-day observable universe and whose size is that of the Planck Length at the Planck Time, it… [Read more…]
March 1, 2012
Alison L. Coil Galaxies are not uniformly distributed in space. On large scales the Universe displays coherent structure, with galaxies residing in groups and clusters on scales of ~1-3 Mpc/h, which lie at the intersections of long filaments of galaxies that are >10 Mpc/h in length. Vast regions of relatively empty space, known as voids,… [Read more…]
February 25, 2012
Masahiro Kawasaki, Alexander Kusenko, Tsutomu T. Yanagida Supermassive black holes exist in the centers of galaxies, including Milky Way, but there is no compelling theory of their formation. Furthermore, observations of quasars imply that supermassive black holes have already existed at some very high redshifts, suggesting the possibility of their primordial origin. In a class… [Read more…]
February 23, 2012
Blame dark matter underdog for mystery missing lithium by David Shiga AN UNDERDOG dark-matter particle could explain why the universe seems strangely low on lithium. If the idea holds up, it will be a boon in the hunt for dark matter, the stuff needed to account for 80 per cent of the universe’s matter. In the… [Read more…]
February 6, 2012
Ram Brustein, Judy Kupferman How was the world created? People have asked this ever since they could ask anything, and answers have come from all sides: from religion, tradition, philosophy, mysticism… and science. While this does not seem like a problem amenable to scientific measurement, it has led scientists to come up with fascinating ideas… [Read more…]
January 31, 2012
discrete integrable systems Abstract Chinese ancient sage Laozi said ‘Dao sheng yi, yi sheng er, er sheng san, san sheng wanwu, • • •’ that means something even everything comes from ‘nothing’ via ‘Dao’. In this paper, various discrete integrable models, including the known discrete Schwarzian KdV, KP, BKP, CKP, special Viallet equations and many… [Read more…]
January 30, 2012
Physicists have simulated two universes colliding inside a metamaterial One interesting way in which our cosmos may have formed is in a collision between two other universes with extra spatial dimensions called braneworlds. In this scenario, known as the ekpyrotic model of the universe, our cosmos is just a small four-dimensional corner of a much… [Read more…]
January 30, 2012
Michael Pagano, Robert Brandenberger Cosmic string loops lead to nonlinear baryon overdensities at early times, even before the time which in the standard LCDM model corresponds to the time of reionization. These overdense structures lead to signals in 21cm redshift surveys at large redshifts. In this paper, we calculate the amplitude and shape of the… [Read more…]
January 29, 2012
Opening Plenary talk given at the Israel Physical Society’s Meeting held at Technion on , Dec. 25, 2011. Prof. Robert Kirshner of Harvard University talks about: Exploding Stars and the Accelerating Universe: Einstein’s Blunder Undone. Prof. Kirshner is a professor os science at the Harvard-Smithsonian Center for Astrophysics at Harvard University. He is the author… [Read more…]
January 27, 2012
The question of whether normal matter’s shadowy counterpart anti-matter exerts a kind of “anti-gravity” is set to be answered, according to a new report. Normal matter attracts all other matter in the Universe, but it remains unclear if anti-matter attracts or repels it. A team reporting in Physics Review Letters says it has prepared stable pairs of… [Read more…]
January 18, 2012
A Historical Review Helge Kragh Abstract. Since the emergence in the late 1960s of the standard hot big-bang theory, cosmology has been dominated by finite-age models. However, the rival view that the universe has existed for an indefinite time has continued to be defended by a minority of researchers. This view has roots far back in… [Read more…]
January 18, 2012
Fotini Markopoulou The idea that the Universe is a program in a giant quantum computer is both fascinating and suffers from various problems. Nonetheless, it can provide a unified picture of physics and this can be very useful for the problem of Quantum Gravity where such a unification is necessary. In previous work we proposed… [Read more…]
January 14, 2012
Mihalis Dafermos It is shown that for small, spherically symmetric perturbations of asymptotically flat two-ended Reissner-Nordstrom data for the Einstein-Maxwell-real scalar field system, the boundary of the dynamic spacetime which evolves is globally represented by a bifurcate null hypersurface across which the metric extends continuously. Under additional assumptions, it is shown that the Hawking mass… [Read more…]
January 10, 2012
Lawrence Krauss gives a talk on our current picture of the universe, how it will end, and how it could have come from nothing. http://youtu.be/7ImvlS8PLIo …. and now the new book: “A universe frοm nothing“, Lawrence Krauss Read also: Trying to make the cosmos out of nothing
January 10, 2012
An exceptional galaxy cluster, the largest seen in the distant universe, has been found using NASA’s Chandra X-ray Observatory and the National Science Foundation-funded Atacama Cosmology Telescope (ACT) in Chile. Officially known as ACT-CL J0102-4915, the galaxy cluster has been nicknamed “El Gordo” (“the big one” or “the fat one” in Spanish) by the researchers… [Read more…]
January 9, 2012
Eli Visbal, Rennan Barkana, Anastasia Fialkov, Dmitriy Tseliakhovich, Christopher Hirata Understanding the formation and evolution of the very first stars and galaxies represents one of the most exciting and challenging questions facing the scientific community today. Since the universe was filled with neutral hydrogen at early times, the most promising method for observing the epoch… [Read more…]
January 8, 2012
(Reuters) – The world’s best known living scientist, Stephen Hawking, was too ill to attend his 70th birthday celebrations Sunday but in a recorded speech urged people to “look up at the stars” and be curious about the universe. Hawking, the author of the international bestseller “A Brief History of Time,” was diagnosed with motor… [Read more…]
January 8, 2012
Scientist who was diagnosed with motor neurone disease at 21 to deliver rare public lecture in Cambridge by Alok Jha The world’s most famous living scientist turns 70 today. ProfessorStephen Hawking has defied medical expectations, since being diagnosed with a form of motor neurone disease at the age of 21 and given only a few years… [Read more…]
January 7, 2012
Intel Studios will kindly be streaming the symposium live on the day. Click here to bring up the webcast in a new window, but please note that the stream won’t start until shortly before the 1st talk on Sunday 8 January 2012. Meanwhile, you can watch the webcasts from the currently going Scientific Conference - day 3 Read… [Read more…]
January 5, 2012
A scientist in the US is arguing that the vacuum should behave as a metamaterial at high magnetic fields. Such magnetic fields were probably present in the early universe, and therefore he suggests that it may be possible to test the prediction by observing the cosmic microwave background (CMB) radiation – a relic of the… [Read more…]
January 5, 2012
by Jean Hannah Edelstein - guardian The scientist who explained the mysteries of the universe confesses to being mystified by women. Here are a few pointers Newscientist: What do you think most about during the day? Stephen Hawking: Women. They are a complete mystery. When I was young, I really struggled to learn to tie my shoelaces.… [Read more…]
January 4, 2012
Shahar Hod Black-hole spacetimes with a “photonsphere”, a hypersurface on which massless particles can orbit the black hole on circular null geodesics, are studied. We prove that among all possible trajectories (both geodesic and non-geodesic) which circle the central black hole, the null circular geodesic is characterized by the shortest possible orbital period as measured… [Read more…]
January 2, 2012
Astronomer royal and master of Trinity College, Cambridge. Like Hawking, he studied under Dennis Sciama in the 1960s I first met Stephen in 1964. I was in my first week as a Cambridge graduate student. He was two years ahead of me in his studies – but already unsteady on his feet and speaking with… [Read more…]
December 19, 2011
Are there parallel universes? And how will we know? Researchers from the universities of Calgary and Waterloo in Canada and the University of Geneva in Switzerland have published a paper this week in Physical Review Letters explaining why we don’t usually see the physical effects of quantum mechanics and why it may be impossible to… [Read more…]
December 16, 2011
…. and Falsify Dark Energy Carl H. Gibson (University of California at San Diego), N. Chandra Wickramasinghe (Cardiff University and Buckingham University, UK), Rudolph E. Schild (Harvard University) Hydrogravitional-dynamics (HGD) cosmology of Gibson/Schild 1996 predicts proto-globular-star-cluster PGC clumps of Earth-mass planets fragmented from plasma at ~0.3 Myr. Protogalaxies retained the ~0.03 Myr baryonic density existing… [Read more…]
December 14, 2011
Carl H. Gibson (University of California at San Diego), Rudolph E. Schild (Harvard University) Is the accelerating expansion of the Universe true, inferred through observations of distant supernovae, and is the implied existence of an enormous amount of anti-gravitational dark energy material driving the accelerating expansion of the universe also true? To be physically useful… [Read more…]
December 12, 2011
The latest computer model of the cosmos involves 400 billion particles in a box about two thirds of the volume of the universe Back in 1970, Jim Peebles at Princeton University carried out a ground-breaking experiment. He used the new-fangled technology of computing to simulate the behaviour of a cluster of galaxies under the force… [Read more…]
December 7, 2011
… and its Implications Branislav Vlahovic The cosmological redshifts z in the frequencies of spectral lines from distant galaxies as compared with their values observed in terrestrial laboratories, which are due to the scale factor a(t), frequently are interpret as a special-relativistic Doppler shift alone. We will demonstrate that this interpretation is not correct and… [Read more…]
December 7, 2011
http://vimeo.com/19568852 The Known Universe takes viewers from the Himalayas through our atmosphere and the inky black of space to the afterglow of the Big Bang. Every star, planet, and quasar seen in the film is possible because of the world’s most complete four-dimensional map of the universe, the Digital Universe Atlas that is maintained and… [Read more…]
December 7, 2011
Dmitry Lyapustin The Axion is a particle arising from the Peccei-Quinn solution to the strong CP problem. Peccei-Quinn symmetry breaking in the early universe could produce a large number of axions which would still be present today, making the axion a compelling dark matter candidate. The goal of the Axion Dark Matter eXperiment (ADMX) is… [Read more…]
December 6, 2011
Researchers in Japan have developed what may be the first string-theory model with a natural mechanism for explaining why our universe would seem to exist in three spatial dimensions if it actually has six more. According to their model, only three of the nine dimensions started to grow at the beginning of the universe, accounting… [Read more…]
November 28, 2011
You wait decades for discoveries that could revolutionise physics, then three come along at once “THE universe is not only queerer than we suppose, but queerer than we can suppose,” as geneticist J. B. S. Haldane once remarked. In recent decades, physicists have done their best to prove Haldane wrong, by supposing some very queer… [Read more…]
November 14, 2011
Time. We waste it, save it, kill it, make it. The world runs on it. Yet ask physicists what time actually is, and the answer might shock you: They have no idea. Even more surprising, the deep sense we have of time passing from present to past may be nothing more than an illusion. How… [Read more…]
November 5, 2011
Dong-Biao Kang We have observed the acceleration of the expansion of the universe. To explain this phenomenon, we usually introduce the dark energy (DE) which has a negative pressure or we need to modify the Einstein’s equation to produce a term which is equivalent to the dark energy. Are there other possibilities? Combining our previous… [Read more…]
November 5, 2011
On ‘Nothing’ Adam R. Brown and Alex Dahlen Abstract Nothing-the absence of spacetime-can be either an endpoint of tunneling, as in the bubble of nothing, or a starting point for tunneling, as in the quantum creation of a universe. We argue that these two tunnelings can be treated within a unified framework, and that, in… [Read more…]
November 2, 2011
Laws we know may be ‘like local by-laws’ say scientists Hints universe is bigger than we think – possibly infinite Other parts of the universe may be hostile to life By ROB WAUGH The laws of physics may not be as set in stone as previously imagined. One of the laws of nature seems to… [Read more…]
October 29, 2011
Nikodem J. Poplawski If spacetime torsion couples to the intrinsic spin of matter according to the Einstein-Cartan-Sciama-Kibble theory of gravity, then the resulting gravitational repulsion at supranuclear densities prevents the formation of singularities in black holes. Consequently, the interior of every black hole becomes a new universe that expands from a nonsingular bounce. We consider gravitational… [Read more…]
October 27, 2011
F. J. Amaral Vieira In this essay a critical review of present conceptual problems in current cosmology is provided from a more philosophical point of view. In essence, a digression on how could philosophy help cosmologists in what is strictly their fundamental endeavor is presented. We start by recalling some examples of enduring confrontations among… [Read more…]
October 25, 2011
Rainer Collier The classical Friedmann-Lemaitre equations are solved using a corrected version of Planck’s radiation law. The function curves of the scale parameter a(t) and the variations with temperature a(T) and t(T) are given. It is shown that a reasonable cosmological evolution is only possible in case of flat spatial slices (k=0). The initial singularity… [Read more…]
October 24, 2011
Least-time paths of light by Arto Annila ABSTRACT The variational principle in its original form á la Maupertuis is used to delineate paths of light through varying energy densities and to associate shifts in frequency and changes in momentum. The gravitational bending and Doppler shift are in this way found as mere manifestations of least-time… [Read more…]
October 20, 2011
by Sean Carroll Lecture One: Introduction to Cosmology http://youtu.be/vUNtO2r_-eo Lecture Two: Dark Matter http://youtu.be/Gq-lGX2PRrc Lecture Three: Dark Energy http://youtu.be/cYVj2RhXxeU Lecture Four: Thermodynamics and the Early Universe http://youtu.be/178mMnGvWs0 Lecture Five: Inflation and Beyond http://youtu.be/M1PeXaMqKto
October 17, 2011
…. and the Primordial Density Perturbation Amplitude Sungwook E. Hong, Ewan D. Stewart, Heeseung Zoe Weinberg et al. calculated the anthropic likelihood of the cosmological constant using a model assuming that the number of observers is proportional to the total mass of gravitationally collapsed objects, with mass greater than a certain threshold, at t \rightarrow \infty.… [Read more…]
October 16, 2011
Ti-Pei Li The discovery of an accelerating cosmic expansion rate implies that, in addition to the attractive gravity of matter, there exist in our universe some other form of energy (dark energy or cosmological constant) producing a repulsive force. The natural interpretation of dark energy is the vacuum energy. However, the density of vacuum energy… [Read more…]
October 15, 2011
Timothy Clemson, Kazuya Koyama, Gong-Bo Zhao, Roy Maartens, Jussi Väliviita In standard cosmologies, dark energy interacts only gravitationally with dark matter. There could be a non-gravitational interaction in the dark sector, leading to changes in the effective DE equation of state, in the redshift dependence of the DM density and in structure formation. We use… [Read more…]
October 14, 2011
There really is a mysterious antigravity force. Einstein’s only mistake was in rejecting it. By Michael D. Lemonick If you want to get your mind around the research that won three astronomers the Nobel Prize in physics last week, it helps to think of the universe as a lump of dough — raisin-bread dough, to… [Read more…]
October 11, 2011
Aniello Mennella, for the Planck Collaboration The ESA Planck satellite, launched on May 14th, 2009, is the third generation space mission dedicated to the measurement of the Cosmic Microwave Background (CMB), the first light in the Universe. Planck observes the full sky in nine frequency bands from 30 to 857 GHz and is designed to… [Read more…]
October 9, 2011
Ruth Durrer In this paper I discuss what we truly know about dark energy. I shall argue that up to date our single indication for the existence of dark energy comes from distance measurements and their relation to redshift. Supernovae, CMB anisotropies and observations of baryon acoustic oscillations, they all simply tell us that the… [Read more…]
October 6, 2011
Hellmut Baumgärtel The note presents a classification of the relevant distinct types of solutions of the general Friedmann equation without assuming a priori restrictions for the parameters occurring in this equation. The emphasis is on the case of a non-vanishing cosmological constant. The classification uses algebraic criteria. The result is: There are four distinct basic… [Read more…]
October 5, 2011
In honor of the Nobel Prize, here are some questions that are frequently asked about dark energy, or should be. What is dark energy? It’s what makes the universe accelerate, if indeed there is a “thing” that does that. (See below.) So I guess I should be asking… what does it mean to say the universe… [Read more…]
October 4, 2011
Observations made by NASA’s Hubble Space Telescope of a special type of supernovae contributed to research on the expansion of the universe that today was honored with the 2011 Nobel Prize in Physics. Adam Riess, an astronomer at the Space Telescope Science Institute and Krieger-Eisenhower professor in physics and astronomy at The Johns Hopkins University… [Read more…]
October 4, 2011
Using very distant supernovae as standard candles, one can trace the history of cosmic expansion and try to find out what’s currently speeding it up. Saul Perlmutter For millennia, cosmology has been a theorist’s domain, where elegant theory was only occasionally endangered by inconvenient facts. Early in the 20th century, Albert Einstein gave us new… [Read more…]
October 4, 2011
Assigning credit for a scientific discovery is never easy, especially when two rival, interacting teams of scientists are involved. That is exactly the problem that the Nobel committee must have grappled with before awarding this year’s physics prize to Saul Perlmutter, Adam Riess and Brian Schmidt. Perlmutter led the Supernova Cosmology Project, while Schmidt and Riess were… [Read more…]
October 4, 2011
(update) The Nobel Prize in Physics 2011 has been awarded to Saul Perlmutter, Brian P Schmidt and Adam G Riess for discovering the accelerating expansion of the universe ………………………………………………………. Three scientists shared the 2011 Nobel Prize for physics for the stunning discovery that the expansion of the universe is speeding up, meaning it may one… [Read more…]
October 4, 2011
How can we tell if another universe has collided with our own? Physicists in Canada and the US believe they have the answer – it would leave “a unique and highly characteristic” imprint in the microwave background that pervades the cosmos. The physicists claim that the prediction can be tested using existing and future space… [Read more…]
October 3, 2011
Suresh Kumar …… Read more: http://arxiv.org
September 28, 2011
Basic scenarios of string theory Gordon has assured me that (almost) no non-expert has understood advanced basics of string phenomenology, despite dozens if not hundreds of blog entries about these topics that have been written on this blog during the years. So I would like to be a little bit (but not too much) more… [Read more…]
September 27, 2011
A review of the development of the concept of dark matter. The dark matter story passed through several stages from a minor observational puzzle to a major challenge for theory of elementary particles. Modern data suggest that dark matter is the dominant matter component in the Universe, and that it consists of some unknown non-baryonic… [Read more…]
September 26, 2011
A way to measure the distance of active galactic nuclei could change the way astronomers think about the Universe and how it is expanding One of the trickiest problems in astronomy is the measure of distance. In theory, distance should be simple to work out. If you know the intrinsic brightness of an object, a… [Read more…]
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May 23, 2012
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