Archivi tag: cosmological inflation

Fundamental Issues of the Standard Cosmological Model

The Planck Satellite measurement have increased the accuracy of cosmological observations to a level which allows to constrain cosmological models with unprecedented precision. The aim of this workshop is to discuss the implications of these recent results combined with other (i.e. Planck, but also WMAP, galaxy surveys, SNIa data…) on models that aim at describing the primordial epochs and the origin and formation of large scale structures of the Universe. Continua a leggere Fundamental Issues of the Standard Cosmological Model

A subtle distortion in the oldest light of the Universe

La rivista Physics World ha pubblicato le 10 notizie più importanti del 2013 nel campo della fisica tra le quali viene menzionata la scoperta ottenuta dagli scienziati che hanno rivelato per la prima volta delle piccole distorsioni relative alla luce più antica dell’Universo, un risultato che potrebbe fornire nuovi indizi sulle fasi primordiali della storia dell’Universo (post). Le misure si riferiscono alla polarizzazione della radiazione cosmica di fondo, all’epoca durante la quale cioè la luce interagì per l’ultima volta con la materia, circa 380.000 anni dopo il Big Bang. Queste distorsioni, note come “modi-B“, sono dovute al fenomeno della lente gravitazionale che si ha quando la luce viene deflessa da oggetti di grande massa. Nel 2014, si attendono con grande interesse i nuovi dati dal satellite Planck che ci darà delle informazioni ancora più dettagliate sulla polarizzazione della radiazione cosmica di fondo e quindi sulla presenza dei modi-B (vedasi L’Universo Infante).

A multi-institutional collaboration of researchers led by John Carlstrom, the S. Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics at the University of Chicago, made the discovery. They announced their findings in a paper published in the journal Physical Review Lettersusing the first data from SPTpol, a polarization-sensitive camera installed on the telescope in January 2012. “The detection of B-mode polarization by South Pole Telescope is a major milestone, a technical achievement that indicates exciting physics to come”, said Carlstrom, who also is deputy director of the Kavli Institute for Cosmological Physics. The cosmic microwave background is a sea of photons (light particles) left over from the Big Bang that pervades all of space, at a temperature of minus 270 degrees Celsius, a mere 3 degrees above absolute zero.

Measurements of this ancient light have already given physicists a wealth of knowledge about the properties of the Universe. Tiny variations in temperature of the light have been painstakingly mapped across the sky by multiple experiments, and scientists are gleaning even more information from polarized light.

Light is polarized when its electromagnetic waves are preferentially oriented in a particular direction. Light from the cosmic microwave background is polarized mainly due to the scattering of photons off of electrons in the early Universe, through the same process by which light is polarized as it reflects off the surface of a lake or the hood of a car. The polarization patterns that result are of a swirl-free type, known as “E modes,” which have proven easier to detect than the fainter B modes, and were first measured a decade ago by a collaboration of researchers using the Degree Angular Scale Interferometer, another UChicago-led experiment. Simple scattering can’t generate B modes, which instead emerge through a more complex process, hence scientists’ interest in measuring them.

Gravitational lensing, it has long been predicted, can twist E modes into B modes as photons pass by galaxies and other massive objects on their way toward earth. This expectation has now been confirmed.

To tease out the B modes in their data, the scientists used a previously measured map of the distribution of mass in the Universe to determine where the gravitational lensing should occur. They combined their measurement of E modes with the mass distribution to provide a template of the expected twisting into B modes. The scientists are currently working with another year of data to further refine their measurement of B modes. The careful study of such B modes will help physicists better understand the Universe. The patterns can be used to map out the distribution of mass, thereby more accurately defining cosmologically important properties like the masses of neutrinos, tiny elementary particles prevalent throughout the cosmos. Similar, more elusive B modes would provide dramatic evidence of inflation, the theorized turbulent period in the moments after the Big Bang when the Universe expanded extremely rapidly. Inflation is a well-regarded theory among cosmologists because its predictions agree with observations, but thus far there is not a definitive confirmation of the theory. Measuring B modes generated by inflation is a possible way to alleviate lingering doubt. “The detection of a primordial B-mode polarization signal in the microwave background would amount to finding the first tremors of the Big Bang”, said the study’s lead author, Duncan Hanson, a postdoctoral scientist at McGill University in Canada.

B modes from inflation are caused by gravitational waves. These ripples in space-time are generated by intense gravitational turmoil, conditions that would have existed during inflation. These waves, stretching and squeezing the fabric of the Universe, would give rise to the telltale twisted polarization patterns of B modes.

Measuring the resulting polarization would not only confirm the theory of inflation, a huge scientific achievement in itself, but would also give scientists information about physics at very high energies, much higher than can be achieved with particle accelerators. The measurement of B modes from gravitational lensing is an important first step in the quest to measure inflationary B modes. In inflationary B mode searches, lensing B modes show up as noise. “The new result shows that this noise can be accounted for and subtracted off so that scientists can search for and hopefully measure the inflationary B modes underneath”, Hanson said. “The lensing signal itself can also be used by itself to learn about the distribution of mass in the Universe”.

University of Chicago: Swirls in remnants of Big Bang may hold clues to universe’s infancy Cosmic neutrinos named Physics World 2013 Breakthrough of the Year

A holographic origin for the Big Bang

Un gruppo di fisici teorici hanno pubblicato un articolo in cui propongono una nuova idea che spiegherebbe l’origine dell’Universo. Secondo gli scienziati, è possibile che lo spazio e il tempo vennero creati dal collasso quadridimensionale di una stella che spazzò i detriti nel cosmo per poi trasformarsi in un buco nero.

As it stands, the prevailing theory states the Universe was born from an infinitely dense singularity through some currently unknown mechanism. Actually, the entire big bang event itself is entirely unknown. Our equations have yet to be complete enough to describe the moment of creation, a revelation physicists think will follow the discovery of the theory of everything (which scientists might be one-step closer to doing). Until then, what happened “before the big bang,” the nature of the ‘singularity’ that caused the big bang, and the event itself will remain unknown without some major scientific breakthrough. At the moment, it’s anyone’s guess what happened. (Important side note: we have a lot of knowledge and experimental evidence talking about what happened immediately after the big bang, up to about 10-35 or so seconds after the event, so our timeline for cosmology is still preserved.) The standard big bang theory has some limitations and some serious problems. It’s limitations are mostly summed up by our inability to mathematically or practically study the big bang singularity, as mentioned before. On the flip side, the big bang theory doesn’t really explain why the Universe has a nearly uniform temperature (that’s where inflation theory comes in, which suggests that the Universe went through a period of rapid, faster-than-light expansion in its early history).

This new model is based on the slightly older idea that our Universe is basically a three-dimensional membrane floating in a fourth-dimensional “bulk universe.” That’s the basic idea that’s supporting this new model.

The tenets for the new theory are as follows:

  • The “bulk universe” has fourth-dimensional stars that go through the same life cycle that our three-dimensional stars go through.
  • Just as with our stars, the stars in the bulk universe could go supernova and collapse into a black hole.
  • This is where things start to get really cool. Just as our three-dimensional black holes have event horizons that appear two-dimensional, it’s plausible that the fourth-dimensional black holes have event horizons that appear three-dimensional.
  • This three-dimensional event horizon is knows as a hypersphere. This is the region of space in which our Universe exists.

This new way of looking at the Universe has some strong points in its favor. The model is able to explain the expansion of the Universe and is able to describe the Universe’s nearly uniform temperature, with one (rather large) limitation. The model disagrees with observations made by the Planck telescope, which recently created the most detailed map we have of the cosmic microwave background (post). The hypersphere model has about a four percent discrepancy, which means the hypersphere needs to be refined before it’ll gain any credence.

This new model could go a long way to helping us understand the nature of inflation.

Currently, the only thing we really know about inflation is that “it’s happening.” We don’t know why or how, but the named mechanism for it is known as dark energy. The model proposes that inflation is caused by the Universe’s motion through higher dimensions of space. It’s important to note that the paper where this study was published does not state whether the paper has been submitted to peer review. So, whereas the hypersphere idea is fantastic and fun, it has a long way to go before we can considered a viable hypothesis.

From Quarks to Quasars: Revising the Big Bang? New Theory on Creation.
arXiv: Out of the White Hole: A Holographic Origin for the Big Bang

Simulating the evolution of the early Universe

Alcuni fisici dell’Università di Chicago hanno simulato in laboratorio le fasi evolutive primordiali della storia dell’Universo riproducendo in parte la caratteristica struttura della radiazione cosmica di fondo grazie ad un esperimento che utilizza atomi di cesio a bassissime temperature in una apposita camera in cui è stato prodotto il vuoto.

This is the first time an experiment like this has simulated the evolution of structure in the early Universe“, said Cheng Chin, professor in physics.

Chin and his colleagues planned to harness ultracold atoms for simulations of the Big Bang to better understand how structure evolved in the infant Universe.

The cosmic microwave background is the echo of the Big Bang. Extensive measurements of the CMB have come from the orbiting Cosmic Background Explorer in the 1990s, and later by the Wilkinson Microwave Anisotropy Probe and various ground-based observatories, including the UChicago-led South Pole Telescope collaboration. These tools have provided cosmologists with a snapshot of how the Universe appeared approximately 380.000 years following the Big Bang, which marked the beginning of our Universe. It turns out that under certain conditions, a cloud of atoms chilled to a billionth of a degree above absolute zero (-459.67 degrees Fahrenheit) in a vacuum chamber displays phenomena similar to those that unfolded following the Big Bang. “At this ultracold temperature, atoms get excited collectively. They act as if they are sound waves in air“, Chin said. The dense package of matter and radiation that existed in the very early Universe generated similar sound-wave excitations, as revealed by COBE, WMAP and the other experiments. The synchronized generation of sound waves correlates with cosmologists’ speculations about inflation in the early Universe. “Inflation set out the initial conditions for the early Universe to create similar sound waves in the cosmic fluid formed by matter and radiation“, co-author Chen-Lung Hung said. “The sudden expansion of the Universe during its inflationary period created ripples in space-time in the echo of the Big Bang. One can think of the Big Bang, in oversimplified terms, as an explosion that generated sound“, Chin said. “The sound waves began interfering with each other, creating complicated patterns. That’s the origin of complexity we see in the Universe“, he said. These excitations are called Sakharov acoustic oscillations, named for Russian physicist Andrei Sakharov, who described the phenomenon in the 1960s. To produce Sakharov oscillations, Chin’s team chilled a flat, smooth cloud of 10,000 or so cesium atoms to a billionth of a degree above absolute zero, creating an exotic state of matter known as a two-dimensional atomic superfluid. Then they initiated a quenching process that controlled the strength of the interaction between the atoms of the cloud. They found that by suddenly making the interactions weaker or stronger, they could generate Sakharov oscillations.

The Universe simulated in Chin’s laboratory measured no more than 70 microns in diameter, approximately the diameter as a human hair.

It turns out the same kind of physics can happen on vastly different length scales“, Chin explained. “That’s the power of physics“. The goal is to better understand the cosmic evolution of a baby Universe, the one that existed shortly after the Big Bang. It was much smaller then than it is today, having reached a diameter of only a hundred thousand light years by the time it had left the CMB pattern that cosmologists observe on the sky today. In the end, what matters is not the absolute size of the simulated or the real universes, but their size ratios to the characteristic length scales governing the physics of Sakharov oscillations. “Here, of course, we are pushing this analogy to the extreme“, Chin said. “It took the whole Universe about 380,000 years to evolve into the CMB spectrum we’re looking at now“, Chin said. But the physicists were able to reproduce much the same pattern in approximately 10 milliseconds in their experiment. “That suggests why the simulation based on cold atoms can be a powerful tool“, Chin said. None of the Science co-authors are cosmologists, but they consulted several in the process of developing their experiment and interpreting its results. The co-authors especially drew upon the expertise of UChicago’s Wayne Hu, John Carlstrom and Michael Turner, and of Stanford University’s Chao-Lin Kuo. Hung noted that Sakharov oscillations serve as an excellent tool for probing the properties of cosmic fluid in the early Universe. “We are looking at a two-dimensional superfluid, which itself is a very interesting object. We actually plan to use these Sakharov oscillations to study the property of this two-dimensional superfluid at different initial conditions to get more information“. The research team varied the conditions that prevailed early in the history of the expansion of their simulated universes by quickly changing how strongly their ultracold atoms interacted, generating ripples. “These ripples then propagate and create many fluctuations“, Hung said. He and his co-authors then examined the ringing of those fluctuations. Today’s CMB maps show a snapshot of how the Universe appeared at a moment in time long ago (post). “From CMB, we don’t really see what happened before that moment, nor do we see what happened after that“, Chin said. But, Hung noted, “In our simulation we can actually monitor the entire evolution of the Sakharov oscillations“. Chin and Hung are interested in continuing this experimental direction with ultracold atoms, branching into a variety of other types of physics, including the simulation of galaxy formation or even the dynamics of black holes. “We can potentially use atoms to simulate and better understand many interesting phenomena in nature“, Chin said. “Atoms to us can be anything you want them to be“.

University of Chicago: Ultracold Big Bang experiment successfully simulates evolution of early Universe 

arXiv: From Cosmology to Cold Atoms: Observation of Sakharov Oscillations in Quenched Atomic Superfluids

Understanding complexity in the early Universe with simpler models

Il comportamento statistico di alcuni sistemi complessi, come ad esempio l’Universo primordiale, può essere analizzato se viene ridotto ad un insieme di sistemi più semplici. Oggi due fisici, Petr Jizba della Czech Technical University a Praga e Fabio Scardigli ora alla Kyoto University in Giappone, hanno pubblicato i risultati di un lavoro di ricerca che riguarda le previsioni teoriche del comportamento dinamico di tali sistemi cosmologici.

Their work focuses on complex dynamical systems whose statistical behaviour can be explained in terms of a superposition of simpler underlying dynamics.

They found that the combination of two cornerstones of contemporary physics, namely Einstein’s special relativity and quantum-mechanical dynamics, is mathematically identical to a complex dynamical system described by two interlocked processes operating at different energy scales.

The combined dynamic obeys Einstein’s special relativity even though neither of the two underlying dynamics does. This implies that Einstein’s special relativity might well be an emergent concept and suggests that it would be worthwhile to further develop Einstein’s insights to take into account the quantum structure of space and time (post). To model the double process in question, the authors consider quantum mechanical dynamics in a background space consisting of a number of small crystal-like domains varying in size and composition, known as polycrystalline space. There, particles exhibit an analogous motion to pollen grains in water, referred to as Brownian motion. The observed relativistic dynamics then comes solely from a particular grain distribution in the polycrystalline space. In the cosmological context such distribution might form during the early Universe’s formation. Finally, the authors’ new interpretation focuses on the interaction of a quantum particle with gravity, that, according to Einstein’s general relativity, can be understood as propagation in curved space-time. The non-existence of the relativistic dynamics on the basic level of the description leads to a natural mechanism for the formation of asymmetry between particles and anti-particles. When coupled with an inflationary cosmology, the authors’ approach predicts that a charge asymmetry should have been produced at ultra-minute fractions of seconds after the Big Bang. This prediction is in agreement with constraints born out of recent cosmological observations.

EPJ: Removing complexity layers from the universe’s creation
EPJ C: Special relativity induced by granular space