Archivi tag: universe

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Latest News from the Universe: LambdaWDM, CMB,Warm Dark Matter, Dark Energy, Neutrinos and Sterile Neutrinos

The new concordance model in agreement with observations: ΛWDM (Lambda-dark energy- Warm Dark Matter). Recently, Warm (keV scale) Dark Matter emerged impressively over CDM (Cold Dark Matter) as the leading Dark Matter candidate. Astronomical evidence that Cold Dark Matter (LambdaCDM) and its proposed tailored baryonic cures do not work at galactic and small scales is staggering. LambdaWDM solves naturally the problems of LambdaCDM and agrees remarkably well with the observations at galactic and small scales as well as large and cosmological scales. In contrast, LambdaCDM simulations only agree with observations at large scales. In the context of this new Dark Matter situation, which implies novelties in the astrophysical, cosmological, particle and nuclear physics context, the 18th Paris Colloquium 2014 is devoted to the Latest News from the Universe. Continua a leggere Latest News from the Universe: LambdaWDM, CMB,Warm Dark Matter, Dark Energy, Neutrinos and Sterile Neutrinos →

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Max Tegmark ‘welcomes’ the multiverse idea

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What is the Universe made of? The ancient Greeks conceived of the “atom”, the indivisible unit of matter. Today’s physicists talk of smaller particles, quarks and electrons, neutrinos, Higgs Bosons and photons. Understand them, and the forces that hold everything together, and we may finally get a handle on what makes it all tick. The trouble is, the more we drill down into the subatomic world, the more complexity we find. The bedrock of reality seems as elusive as ever. Perhaps, says a leading theoretical physicist Max Tegmark, we do not live in a world of particles and forces at all, but of pure mathematics.

The Telegraph: It’s goodbye to the universe – hello to the multiverse

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Secrets of the Universe’s First Light

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The  first definite proof that the Universe underwent an almost unimaginably fast expansion when it was only a trillionth of a trillionth of a trillionth of a second old has taken the world by storm. This sudden growth spurt was first theorized more than three decades ago. Yet only last month did astrophysicists reveal what may be “smoking gun” evidence that the Universe swelled from microscopic to cosmic size in an instant, an announcement that’s being compared to the discovery of the Higgs boson.

More at The Kavli Foundation: Secrets of the Universe’s First Light

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Observing the Universe with the Cosmic Microwave Background

The Planck satellite mission has provided a multifrequency detailed view of the Universe at millimeter waves, exploring the cosmic microwave background (CMB) and the relevant foregrounds with an unprecedented combination of sensitivity, angular resolution and frequency coverage. Meanwhile, a number of ground based and balloon-borne experiments are exploring the tiniest details of the CMB (anisotropy, polarization, spectral anisotropy, etc.) providing a wealth of new knowledge on our universe. New space mission concepts have also been proposed, involving significant technology improvements, and are actively investigated.

This school will provide an up to date review of the latest results and of their impact on cosmology and on fundamental physics. Experimental, interpretation and theoretical activities will be weighted to provide a well balanced understanding of the current status and of the forthcoming efforts in this field.

Astrofisica,Astronomia,Cosmologia,Spazio

Making ‘your own’ Universe at home

An image of a simulated cluster of galaxies captured when the Universe was half its present age, as seen through the TAO virtual telescope module. Credit: TAO
La Swinburne University of Technology ha ideato un programma virtuale di astronomia che permetterà agli scienziati di ricostruire una serie di visualizzazioni complesse, e a piacere, dell’Universo. Tutto ciò si potrà fare da casa con il proprio computer.

The Theoretical Astrophysical Observatory (TAO), funded by the Australian Government’s $48 million NeCTAR project, draws on the power of Swinburne’s gSTAR GPU supercomputer to allow astronomers to simulate the Universe and see how it would look through a wide range of telescopes. “TAO lets researchers take the data from massive cosmological simulations and map it onto an observer’s viewpoint, to test theories of how galaxies and stars form and evolve”, TAO project scientist, Swinburne Associate Professor Darren Croton, said. “TAO makes it easy and efficient for any astronomer to create these virtual universes. It’s the culmination of years of effort that is now at the fingertips of scientists around the world. Using TAO it might take a few minutes to create a mock catalogue of galaxies, versus months or even years of development previously“. Swinburne worked with eResearch company Intersect Australia Ltd, who designed the web interface with simplicity and user-friendliness in mind. Associate Professor Croton said that “it was important to create a service that could be used by any astronomer regardless of their area of expertise, because that accelerates the pace of science and boosts the chance of breakthroughs”. As new survey telescopes and instruments become available, they can be modelled within TAO to maintain an up-to-date set of observatories. “TAO could be especially useful for comparing theoretical predictions against observations coming from next-generation survey telescopes, like the Australian Square Kilometre Array Pathfinder (ASKAP) in Western Australia, and the SkyMapper Telescope run by the Australian National University (ANU). These will cover large chunks of the sky and peer back into the early stages of the Universe and are tasked with answering some of the most fundamental questions know to humankind”.

Swinburne University: Creating virtual universes with Swinburne's Theoretical Astrophysical Observatory
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The Cosmic Distance Scale

Understanding the distance scale has always been central to astronomy, and its determination has been a multi-pronged pursuit. More than two decades ago the distance scale was uncertain by a factor of two, and the resolution of this conundrum had been a major driver for HST. Today a wealth of new cosmological measurements from both the local and the high redshift Universe are reaching a precision of a few percent, with further improvements on the horizon. Better knowledge of the distance scale has profound impacts in areas ranging from stellar astrophysics to the cosmological model. We believe that now is an excellent time to discuss what has been learned and what we can expect to learn in the near future.

More info: The Cosmic Distance Scale

Astrofisica,Astronomia,Cosmologia,Fisica,Fisica delle particelle

Will the Universe collapse in a Big Crunch?

Nel 1922, il cosmologo russo Alexander Friedmann propose delle soluzioni alle equazioni di campo di Einstein nel caso di un Universo omogeneo, isotropo e non statico. Sotto queste ipotesi, è possibile definire una densità media dell’Universo, ossia una densità di massa-energia e, come lo stesso Friedmann dimostrò a suo tempo, descrivere lo spazio in ogni istante con un solo numero, la curvatura scalare. Da qui si ricavano tre modelli di Universo, detti modelli di Friedmann, in funzione del parametro di curvatura k per cui l’Universo può assumere o una geometria iperbolica (k=-1, aperto), o una geometria euclidea (k=0, piatto), oppure una geometria ipersferica (k=1, chiuso). Dunque, una previsione di questi modelli implica che l’Universo potrebbe un giorno collassare a causa della mutua interazione gravitazionale dovuta alla materia presente nell’Universo, una ipotesi che sembra essere confermata oggi da alcuni calcoli eseguiti da un gruppo di fisici dell’University of Southern Denmark. Il risultato è che il rischio di una possibile contrazione gravitazionale sembra essere molto maggiore di quanto sia stato finora ipotizzato.

Sooner or later a radical shift in the forces of the Universe will cause every little particle in it to become extremely heavy. Everything, every grain of sand on Earth, every planet in the Solar System and every galaxy, will become millions of billions times heavier than it is now, and this will have disastrous consequences: the new weight will squeeze all material into a small, super hot and super heavy ball, and the Universe as we know it will cease to exist. This violent process is called a phase transition and is very similar to what happens when, for example water turns to steam or a magnet heats up and loses its magnetization. The phase transition in the Universe will happen if a bubble is created where the Higgs-field associated with the Higgs-particle reaches a different value than the rest of the Universe. If this new value results in lower energy and if the bubble is large enough, the bubble will expand at the speed of light in all directions. All elementary particles inside the bubble will reach a mass, that is much heavier than if they were outside the bubble, and thus they will be pulled together and form supermassive centers. “Many theories and calculations predict such a phase transition, but there have been some uncertainties in the previous calculations. Now we have performed more precise calculations, and we see two things: 1) yes, the Universe will probably collapse, and 2) a collapse is even more likely than the old calculations predicted“, says Jens Frederik Colding Krog of the Center for Cosmology and Particle Physics Phenomenology (CP ³ – Origins) at University of Southern Denmark and co-author of an article on the subject in the Journal of High Energy Physics. “The phase transition will start somewhere in the Universe and spread from there. Maybe the collapse has already started somewhere in the Universe and right now it is eating its way into the rest of the Universe. Maybe a collapsed is starting right now right here here. Or maybe it will start far away from here in a billion years. We do not know”, says Jens Frederik Colding Krog. More specifically he and his colleagues looked at three of the main equations that underlie the prediction of a phase change. These are about the so-called beta functions, which determine the strength of interactions between for example light particles and electrons as well as Higgs bosons and quarks. So far physicists have worked with one equation at a time, but now the physicists from CP3 show that the three equations actually can be worked with together and that they interact with each other. When applying all three equations together the physicists predict that the probability of a collapse as a result of a phase change is even greater than when applying only one of the equations.

The theory of phase transition is not the only theory predicting a collapse of the Universe. Also the so-called Big Crunch theory is in play.

This theory is based on the Big Bang, the formation of the Universe. After the Big Bang all material was ejected into the Universe from one small area, and this expansion is still happening. At some point, however, the expansion will stop and all the material will again begin to attract each other and eventually merge into a small area again. This is called the Big Crunch. “The latest research shows that the Universe’s expansion is accelerating,  so there is no reason to expect a collapse from cosmological observations. Thus it will probably not be Big Crunch that causes the Universe to collapse“,  says Jens Frederik Colding Krog.

Although the new calculations predict that a collapse is now more likely than ever before, it is actually also possible, that it will not happen at all.

It is a prerequisite for the phase change that the Universe consists of the elementary particles that we know today, including the Higgs particle. If the Universe contains undiscovered particles, the whole basis for the prediction of phase change disappears. “Then the collapse will be canceled”, says Jens Frederik Colding Krog. In these years the hunt for new particles is intense. Only a few years ago the Higgs-particle was discovered, and a whole field of research known as high-energy physics  is engaged in looking for more new particles. At CP3 several physicists are convinced that the Higgs particle is not an elementary particle, but that it is made up of even smaller particles called techni-quarks. Also the theory of supersymmetry predicts the existence of yet undiscovered particles, existing somewhere in the Universe as partners for all existing particles (superparticles). According to this theory there will be a selectron for the electron, a fotino for the photon, etc. While the physical results discussed in the article were partially established earlier in the literature, the work of the Danish based researchers deals with the mathematical foundations of the technique used among other things also to determine the stability of the Universe. In their work the researchers assumed valid the current knowledge of the Standard Model interactions augmented by the discovery of the Higgs and the latest mathematical constraints.

University of Southern Denmark: Collapse of the universe is closer than ever before

arXiv: Standard Model Vacuum Stability and Weyl Consistency Conditions

Astronomia,Cosmologia,Fisica,Fisica delle particelle,Matematica,Scienza

Is our Universe a hologram?

E’ circolata di recente nei media la notizia pubblicata da Nature secondo la quale un gruppo di fisici giapponesi avrebbero formulato una teoria che “potrebbe essere considerata l’evidenza più chiara sul fatto che il nostro Universo sarebbe una gigantesca proiezione“. Nei loro articoli, Yoshifumi Hyakutake e colleghi della Ibaraki University in Giappone spiegano  come la loro idea suggerisca che la realtà fisica, così come noi la concepiamo, potrebbe essere in definitiva un ologramma appartenente ad un altro spazio bidimensionale.

In 1997, theoretical physicist Juan Maldacena proposed that an audacious model of the Universe in which gravity arises from infinitesimally thin, vibrating strings could be reinterpreted in terms of well-established physics. The mathematically intricate world of strings, which exist in nine dimensions of space plus one of time, would be merely a hologram: the real action would play out in a simpler, flatter cosmos where there is no gravity. Maldacena’s idea thrilled physicists because it offered a way to put the popular but still unproven theory of strings on solid footing, and because it solved apparent inconsistencies between quantum physics and Einstein’s theory of gravity. It provided physicists with a mathematical “Rosetta stone”, a ‘duality’, that allowed them to translate back and forth between the two languages, and solve problems in one model that seemed intractable in the other and vice versa (see ‘Collaborative physics: String theory finds a bench mate‘). But although the validity of Maldacena’s ideas has pretty much been taken for granted ever since, a rigorous proof has been elusive.

In two papers posted on the arXiv repository, Yoshifumi Hyakutake of Ibaraki University in Japan and his colleagues now provide, if not an actual proof, at least compelling evidence that Maldacena’s conjecture is true.

In one paper, Hyakutake computes the internal energy of a black hole, the position of its event horizon (the boundary between the black hole and the rest of the Universe), its entropy and other properties based on the predictions of string theory as well as the effects of so-called virtual particles that continuously pop into and out of existence (see ‘Astrophysics: Fire in the Hole!‘). In the other, he and his collaborators calculate the internal energy of the corresponding lower-dimensional cosmos with no gravity. The two computer calculations match. “It seems to be a correct computation”, says Maldacena, who is now at the Institute for Advanced Study in Princeton, New Jersey and who did not contribute to the team’s work.

The findings “are an interesting way to test many ideas in quantum gravity and string theory”, Maldacena adds.

The two papers, he notes, are the culmination of a series of articles contributed by the Japanese team over the past few years. “The whole sequence of papers is very nice because it tests the dual [nature of the universes] in regimes where there are no analytic tests. They have numerically confirmed, perhaps for the first time, something we were fairly sure had to be true, but was still a conjecture, namely that the thermodynamics of certain black holes can be reproduced from a lower-dimensional Universe”, says Leonard Susskind, a theoretical physicist at Stanford University in California who was among the first theoreticians to explore the idea of holographic universes. Neither of the model universes explored by the Japanese team resembles our own, Maldacena notes. The cosmos with a black hole has ten dimensions, with eight of them forming an eight-dimensional sphere. The lower-dimensional, gravity-free one has but a single dimension, and its menagerie of quantum particles resembles a group of idealized springs, or harmonic oscillators, attached to one another. Nevertheless, says Maldacena, the numerical proof that these two seemingly disparate worlds are actually identical gives hope that the gravitational properties of our Universe can one day be explained by a simpler cosmos purely in terms of quantum theory.

Nature: Simulations back up theory that Universe is a hologram

arXiv: Quantum Near Horizon Geometry of Black 0-Brane

arXiv: Holographic description of quantum black hole on a computer
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Could life have existed soon after the Big Bang?

L’astrofisico teorico Abraham Loeb dell’Università di Harvard ha pubblicato un articolo in cui spiega come la vita possa essere esistita, subito dopo il Big Bang, da qualche parte nell’Universo,  per un brevissimo lasso di tempo.

Loeb notes that according to theory, 14 million years after the Big Bang, the entire Universe would have been warm enough to support life due to the cooling of superheated gases that eventually led to what scientists believe is  (CMB). Today, it’s very cold of course, (2.7 Kelvin), but not long, relatively speaking, after the Big Bang, the temperature would have been closer to 300 Kelvin, more than warm enough to support life if there were a place for it to appear.

And that Loeb suggests, might have been possible as well. He notes that it would have been possible for  to have existed at that time too, in places where matter was exceptionally dense.

Because of that, he believes it’s possible that all of the pieces necessary for the appearance of life might have been in place in some parts of the Universe, for approximately two or three million years, enough time for the initial brewing that could have led to the development of microbes of some sort. Of course, if it did happen, that life would not have lived long enough (2 to 3 million years) to evolve into anything complex, it would have been snuffed out as the CMB cooled, happening as it would have before stars would have had enough time to form and emit heat of their own.

Thus, no evidence would have been left behind, which means Loeb’s theory can never be proven.

If it could, that might upset another principle regarding the Universe, the anthropic principle, which suggests that all of the things that needed to happen in the Universe for us to be here today to observe them, exist because we are here to observe them. If  existed and died out before we arrived, it would not have been sophisticated enough to know that it existed, much less observe conditions in the Universe that led to its existence. And that would mean the anthropic principle might just be an idea that exists because we have nothing better to explain how and why we are here.

Phys.org: Astrophysicist suggests life may have existed shortly after Big Bang


arXiv: The Habitable Epoch of the Early Universe
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New hints on the primordial gravitational waves in the CMB

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Grazie ad una serie di osservazioni realizzate mediante il telescopio del Polo Sud in Antartide e l’osservatorio spaziale Herschel, gli astronomi sono stati in grado di rivelare per la prima volta un segnale molto debole nella radiazione cosmica di fondo che potrebbe fornire informazioni di vitale importanza sui primi momenti della creazione dell’Universo. Le misure di questo segnale elusivo sono state realizzate studiando il modo con cui la luce viene deflessa nel suo viaggio cosmico prima di arrivare sulla Terra, passando attraverso gli ammassi di galassie e la distribuzione della materia scura. La scoperta permette di fornire nuovi indizi su come rivelare le onde gravitazionali che si sono originate durante l’epoca dell’inflazione cosmica, un risultato cruciale anticipato dalla missione Planck (post).

The relic radiation from the Big Bang, the Cosmic Microwave Background, or CMB, was imprinted on the sky when the Universe was just 380 000 years old. Today, some 13.8 billion years later, we see it as a sky filled with radio waves at a temperature of just 2.7 degrees above absolute zero. Tiny variations in this temperature, around a few tens of millionths of a degree, reveal density fluctuations in the early Universe corresponding to the seeds of galaxies and stars we see today. The most detailed all-sky map of temperature variations in the background was revealed by Planck in March (post). But the CMB also contains a wealth of other information. A small fraction of the light is polarised, like the light we can see using polarised glasses. This polarised light has two distinct patterns: E-modes and B-modes. E-modes were first found in 2002 with a ground-based telescope. B-modes, however, are potentially much more exciting to cosmologists, although much harder to detect. They can arise in two ways. The first involves adding a twist to the light as it crosses the Universe and is deflected by galaxies and dark matter, a phenomenon known as gravitational lensing. The second has its roots buried deep in the mechanics of a very rapid phase of enormous expansion of the Universe, which cosmologists believe happened just a tiny fraction of a second after the Big Bang, namely the ‘inflation’.

The new study has combined data from the South Pole Telescope and Herschel to make the first detection of B-mode polarisation in the CMB due to gravitational lensing.

“This measurement was made possible by a clever and unique combination of ground-based observations from the South Pole Telescope, which measured the light from the Big Bang, with space-based observations from Herschel, which is sensitive to the galaxies that trace the dark matter which caused the gravitational lensing,” says Joaquin Vieira, of the California Institute of Technology and the University of Illinois at Urbana-Champaign, who led the Herschel survey used in the study. By using Herschel’s observations, the scientists mapped the gravitational lensing material along the line of sight, and then searched for correlations between that pattern and the polarised light coming from the CMB, as measured by the South Pole Telescope. “It’s an important checkpoint that we’re able to detect this small lensing B-mode signal and it bodes well for our ability to ultimately measure an even more elusive type of B-mode created during the inflationary Big Bang”, adds Duncan Hanson of McGill University, Montreal, Canada. Scientists believe that during inflation, violent collisions between clumps of matter and between matter and radiation, should have created a sea of gravitational waves. Today, those waves would be imprinted in a primordial B-mode component of the CMB.

Finding such a signal would yield crucial information about the very early Universe, well before the time when the CMB itself was generated, and would provide confirmation of the inflation scenario.

In 2014, new results will be released from ESA’s Planck, and the most eagerly anticipated is whether primordial B-modes have been detected. In the meantime, Herschel has helped to point the way.

ESA: HERSCHEL THROWS NEW LIGHT ON OLDEST COSMIC LIGHT

arXiv: Detection of B-mode Polarization in the Cosmic Microwave Background with Data from the South Pole Telescope

arXiv: A CMB lensing mass map and its correlation with the cosmic infrared background