From Symmetry: “Exploring the dark universe with supercomputers”

Symmetry

01/14/16
Katie Elyce Jones

Next-generation telescopic surveys will work hand-in-hand with supercomputers to study the nature of dark energy.

The 2020s could see a rapid expansion in dark energy research.

For starters, two powerful new instruments will scan the night sky for distant galaxies. The Dark Energy Spectroscopic Instrument, or DESI, will measure the distances to about 35 million cosmic objects, and the Large Synoptic Survey Telescope, or LSST, will capture high-resolution videos of nearly 40 billion galaxies.

LBL DESI

LSST, the building that will house it in Chile, and the camera, being built at SLAC

Both projects will probe how dark energy—the phenomenon that scientists think is causing the universe to expand at an accelerating rate—has shaped the structure of the universe over time.

But scientists use more than telescopes to search for clues about the nature of dark energy. Increasingly, dark energy research is taking place not only at mountaintop observatories with panoramic views but also in the chilly, humming rooms that house state-of-the-art supercomputers.

The central question in dark energy research is whether it exists as a cosmological constant—a repulsive force that counteracts gravity, as Albert Einstein suggested a century ago—or if there are factors influencing the acceleration rate that scientists can’t see. Alternatively, Einstein’s theory of gravity [General Relativity] could be wrong.

“When we analyze observations of the universe, we don’t know what the underlying model is because we don’t know the fundamental nature of dark energy,” says Katrin Heitmann, a senior physicist at Argonne National Laboratory. “But with computer simulations, we know what model we’re putting in, so we can investigate the effects it would have on the observational data.”

A simulation shows how matter is distributed in the universe over time. Katrin Heitmann, et al., Argonne National Laboratory

Growing a universe

Heitmann and her Argonne colleagues use their cosmology code, called HACC, on supercomputers to simulate the structure and evolution of the universe. The supercomputers needed for these simulations are built from hundreds of thousands of connected processors and typically crunch well over a quadrillion calculations per second.

The Argonne team recently finished a high-resolution simulation of the universe expanding and changing over 13 billion years, most of its lifetime. Now the data from their simulations is being used to develop processing and analysis tools for the LSST, and packets of data are being released to the research community so cosmologists without access to a supercomputer can make use of the results for a wide range of studies.

Risa Wechsler, a scientist at SLAC National Accelerator Laboratory and Stanford University professor, is the co-spokesperson of the DESI experiment. Wechsler is producing simulations that are being used to interpret measurements from the ongoing Dark Energy Survey, as well as to develop analysis tools for future experiments like DESI and LSST.

DES, The DECam camera, built at FNAL, and the Victor M Blanco 4 meter telescope in Chile that houses the camera.

“By testing our current predictions against existing data from the Dark Energy Survey, we are learning where the models need to be improved for the future,” Wechsler says. “Simulations are our key predictive tool. In cosmological simulations, we start out with an early universe that has tiny fluctuations, or changes in density, and gravity allows those fluctuations to grow over time. The growth of structure becomes more and more complicated and is impossible to calculate with pen and paper. You need supercomputers.”

Supercomputers have become extremely valuable for studying dark energy because—unlike dark matter, which scientists might be able to create in particle accelerators—dark energy can only be observed at the galactic scale.

“With dark energy, we can only see its effect between galaxies,” says Peter Nugent, division deputy for scientific engagement at the Computational Cosmology Center at Lawrence Berkeley National Laboratory.

Trial and error bars

“There are two kinds of errors in cosmology,” Heitmann says. “Statistical errors, meaning we cannot collect enough data, and systematic errors, meaning that there is something in the data that we don’t understand.”

Computer modeling can help reduce both.

DESI will collect about 10 times more data than its predecessor, the Baryon Oscillation Spectroscopic Survey, and LSST will generate 30 laptops’ worth of data each night. But even these enormous data sets do not fully eliminate statistical error.

LBL BOSS telescope

Simulation can support observational evidence by modeling similar conditions to see if the same results appear consistently.

“We’re basically creating the same size data set as the entire observational set, then we’re creating it again and again—producing up to 10 to 100 times more data than the observational sets,” Nugent says.

Processing such large amounts of data requires sophisticated analyses. Simulations make this possible.

To program the tools that will compare observational and simulated data, researchers first have to model what the sky will look like through the lens of the telescope. In the case of LSST, this is done before the telescope is even built.

After populating a simulated universe with galaxies that are similar in distribution and brightness to real galaxies, scientists modify the results to account for the telescope’s optics, Earth’s atmosphere, and other limiting factors. By simulating the end product, they can efficiently process and analyze the observational data.

Simulations are also an ideal way to tackle many sources of systematic error in dark energy research. By all appearances, dark energy acts as a repulsive force. But if other, inconsistent properties of dark energy emerge in new data or observations, different theories and a way of validating them will be needed.

“If you want to look at theories beyond the cosmological constant, you can make predictions through simulation,” Heitmann says.

A conventional way to test new scientific theories is to introduce change into a system and compare it to a control. But in the case of cosmology, we are stuck in our universe, and the only way scientists may be able to uncover the nature of dark energy—at least in the foreseeable future—is by unleashing alternative theories in a virtual universe.

See the full article here .

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Symmetry is a joint Fermilab/SLAC publication.

From IBT: “‘Green Pea’ Galaxies May Hold The Key To Understanding The Early Universe”

International Business Times

01/13/16
Charles Poladian

The galaxy J0925 is known as a “green pea” galaxy. Researchers used the Hubble Space Telescope to observe UV radiation being emitted by this galaxy. Photo: Ivana Orlitová, Astronomical Institute, Czech Academy of Sciences (Prague)

The universe began with a big bang followed by a great expansion [inflation]. The subsequent creation of hydrogen and helium led to the dark ages of the universe, but something happened that caused hydrogen to heat up — the process known as [re]ionization where superheated gases obtain a positive or negative charge — and usher the visible universe era.

All of this took place within a billion years after the big bang. A study released Wednesday shows that the first galaxies in the early universe may have been the catalyst behind cosmic reionization.

The dark ages of the universe comprised neutral helium, hydrogen, dark matter and normal matter. Gravity would soon pull all of this together to create the first stars. The creation of the first stars would pave the way for the first galaxies. The young stars and early galaxies were hot enough to strip electrons from the neutral gases. Cosmic reionization started out as a flashlight revealing what was out in the darkness. As more stars and galaxies formed, more gas was ionized. Soon, the lights were turned on and the early universe became visible.

“Though the Epoch of Reionization took place deep in the universe’s past, it lies at the very frontier of our current cosmological observations. The more researchers learn about this period, in fact, the more it reveals about the end of the cosmic dark ages, the first stars and galaxies and the structure of our universe,” Stanford University’s Kavli Institute for Particle Astrophysics and Cosmology explained.

Infographic detailing the history of the universe. Photo: S. G. Djorgovski et al., Caltech

Stars emit UV radiation and ionizing photons necessary to heat and strip surrounding gas. Galaxies were believed to have triggered cosmic reionization, but researchers had yet to find a galaxy emitting enough radiation necessary to reionize hydrogen. Galaxies need to eject the ionizing photons instead of absorbing the photons, according to the researchers from the University of Geneva.

The researchers focused on tiny galaxies known as “green pea” galaxies due to their compact size.

Pea Scientific Montage. Galaxy Zoo

These active star-forming galaxies located 1.5 billion and 5 billion light-years from Earth are similar to galaxies in the early universe. If these galaxies were emitting radiation that could heat and strip hydrogen, it’s likely similar galaxies were doing the same thing 13 billion years ago.

The researchers found 5,000 green pea galaxies using the Sloan [Digital Sky] Survey’s [SDSS] collection of more than 1 million galaxies.

SDSS telescope at Apache Point, NM, USA

After finding potential candidates, the Hubble Space Telescope’s ability to detect UV radiation was used to determine if any green peas were emitting radiation.

NASA/ESA Hubble

One such galaxy, J0925 — located 3 billion light-years from Earth — was emitting UV radiation and ejecting photons. This is just the first step in understanding what caused cosmic reionization in the early universe. The researchers hope to use Hubble for further observations of J0925 and other galaxies that could be emitting radiation.

See the full post here .

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From ESO: “XXL Hunt for Galaxy Clusters”

European Southern Observatory

15 December 2015
Marguerite Pierre
CEA
Saclay, France
Email: marguerite.pierre@cea.fr

Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org.

Observations from ESO telescopes provide crucial third dimension in probe of Universe’s dark side

ESO telescopes have provided an international team of astronomers with the gift of the third dimension in a plus-sized hunt for the largest gravitationally bound structures in the Universe — galaxy clusters. Observations by the VLT and the NTT complement those from other observatories across the globe and in space as part of the XXL survey — one of the largest ever such quests for clusters.

Galaxy clusters are massive congregations of galaxies that host huge reservoirs of hot gas — the temperatures are so high that X-rays are produced. These structures are useful to astronomers because their construction is believed to be influenced by the Universe’s notoriously strange components — dark matter and dark energy. By studying their properties at different stages in the history of the Universe, galaxy clusters can shed light on the Universe’s poorly understood dark side.

The team, consisting of over 100 astronomers from around the world, started a hunt for the cosmic monsters in 2011. Although the high-energy X-ray radiation that reveals their location is absorbed by the Earth’s atmosphere, it can be detected by X-ray observatories in space. Thus, they combined an ESA XMM-Newton survey — the largest time allocation ever granted for this orbiting telescope — with observations from ESO and other observatories.

ESA/XMM-Newton

The result is a huge and growing collection of data across the electromagnetic spectrum [1], collectively called the XXL survey.

“The main goal of the XXL survey is to provide a well-defined sample of some 500 galaxy clusters out to a distance when the Universe was half its current age,” explains XXL principal investigator Marguerite Pierre of CEA, Saclay, France.

The XMM-Newton telescope imaged two patches of sky — each one hundred times the area of the full Moon — in an attempt to discover a huge number of previously unknown galaxy clusters. The XXL survey team have now released their findings in a series of papers using the 100 brightest clusters discovered [2].

Observations from the EFOSC2 instrument installed on the New Technology Telescope (NTT), along with the FORS instrument attached to ESO’s Very Large Telescope (VLT), also were used to carefully analyse the light coming from galaxies within these galaxy clusters.

EFOSC2 instrument

FORS1

Crucially, this allowed the team to measure the precise distances to the galaxy clusters, providing the three-dimensional view of the cosmos required to perform precise measurements of dark matter and dark energy [3].

The XXL survey is expected to produce many exciting and unexpected results, but even with one fifth of the final expected data, some surprising and important findings have already appeared.

One paper reports the discovery of five new superclusters — clusters of galaxy clusters — adding to those already known, such as our own, the Laniakea Supercluster.

The Laniakea Supercluster

Another reports followup observations of one particular galaxy cluster (informally known as XLSSC-116), located over six billion light-years away [4]. In this cluster unusually bright diffuse light was observed using MUSE on the VLT.

MUSE

“This is the first time that we are able to study in detail the diffuse light in a distant galaxy cluster, illustrating the power of MUSE for such valuable studies,” explained co-author Christoph Adami of the Laboratoire d’Astrophysique, Marseille, France.

The team have also used the data to confirm the idea that galaxy clusters in the past are scaled down versions of those we observe today — an important finding for the theoretical understanding of the evolution of clusters over the life of the Universe.

The simple act of counting galaxy clusters in the XXL data has also confirmed a strange earlier result — there are fewer distant clusters than expected based on predictions from the cosmological parameters measured by ESA’s Planck telescope.

ESA/Planck

The reason for this discrepancy is unknown, however the team hope to get to the bottom of this cosmological curiosity with the full sample of clusters in 2017.

These four important results are just a foretaste of what is to come in this massive survey of some of the most massive objects in the Universe.

Notes

[1] The XXL survey has combined archival data as well as new observations of galaxy clusters covering the wavelength range from 1 × 10—4 μm (X-ray, observed with XMM) to 492 μm (submillimetre range, observed with the Giant Metrewave Radio Telescope [GMRT]).

GMRT

[2] The galaxy clusters reported in the thirteen papers are found at redshifts between z = 0.05 and z = 1.05, which correspond to when the Universe was approximately 13 and 5.7 billion years old, respectively.

[3] Probing the galaxy clusters required their precise distances to be known. While approximate distances — photometric redshifts — can be measured by analysing their colours at different wavelengths, more accurate spectroscopic redshifts are needed. Spectroscopic redshifts were also sourced from archival data, as part of the VIMOS Public Extragalactic Redshift Survey (VIPERS), the VIMOS-VLT Deep Survey (VVDS) and the GAMA survey.

From VIPERS

From GAMA

[4] This galaxy cluster was found to be at a redshift of z = 0.543.

More information

A description of the survey, and some of the early science results, will be presented in a series of papers to appear in the journal Astronomy & Astrophysics on 15 December 2015.

XXL is an international project based around an XMM Very Large Programme surveying two 25 square degrees extragalactic fields at a depth of ~5 × 10–15 erg cm—2 s—1 in the [0.5—2] keV band for point-like sources. The XXL website is found here. Multi-band information and spectroscopic follow-up of the X-ray sources are obtained through a number of survey programmes is summarised here.

Links:

XXL Survey
Scientific Papers in Astronomy & Astrophysics

The full XXL CONSORTIUM:
C. Adami (Laboratoire d’Astrophysique, Marseille, FR)
S. Alis (Observatoire de la Cote d’Azur, Nice, FR)
A. Alshino (University of Bahrain, BH)
B. Altieri (European Space Astronomy Center, Madrid, SP)
N. Baran (University of Zagreb, HR)
S. Basilakos (Research Center for Astronomy, Academy of Athens, GR)
C. Benoist (Observatoire de la Cote d’Azur, Nice, FR)
M. Birkishaw (University of Bristol, UK)
A. Bongiorno (Rome Observatory, Italy)
V. Bouillot (Observatoire de Paris, FR)
M. Bremer (University of Bristol, UK)
T. Broadhurst (Basque University, Bilbao, SP)
M. Brusa (INAF-OABO, Bologna, IT)
A. Butler (University of Western Austalia, AU)
N. Cappelluti (INAF-OABO, Bologna, IT)
A. Cappi (INAF-OABO, Bologna, IT)
T. Chantavat (Naresuan University, TH)
L. Chiappetti (INAF-IASF, Milano, IT)
P. Ciliegi (INAF-OABO, Bologna, IT)
F. Civano (H. S. Center for Astrophysics, Cambridge, US)
A. Comastri (INAF-OABO, Bologna, IT)
P. S. Corasaniti (Observatoire de Paris, FR)
J. Coupon (ASIAA, Taipei, TW)
N. Clerc (Service d’Astrophysique CEA, Saclay, FR)
C. De Breuck (ESO Garching, DE)
J. Delhaize (University of Zagreb, HR)
J. Democles (University of Birmingham, UK)
Sh. Desai (University of Illinois, US)
J. Devriendt (University of Oxford, UK)
O. Dore (JPL Caltech, Pasadena, US)
Y. Dubois (University of Oxford, UK)
D. Eckert (ISCD, Geneva Observatory, CH)
L. Edwards (Mount Allison Observatory, CA)
D. Elbaz (Service d’Astrophysique CEA, Saclay, FR)
A. Elyiv (University of Liege, BE)
S. Ettori (INAF-OABO, Bologna, IT)
A. E. Evrard (University of Michigan, Ann Arbor, US)
L. Faccioli (Service d’Astrophysique CEA, Saclay, FR)
A. Farahi (University of Michigan, Ann Arbor, US)
C. Ferrari (Observatoire de la Cote d’Azur, FR)
F. Finet (Aryabhatta Research institute for Observational Science, IN)
F. Fiore (Observatory of Roma, IT)
S. Fotopoulou (ISCD, Geneva Observatory, CH)
W. Forman (H. S. Center for Astrophysics, Cambridge, US)
E. Freeland (Stockholm University)
P. Gandhi (ISAS, JAXA, Sagamihara, JP)
F. Gastadello (INAF-IASF, Milan, IT)
I. Georgantopoulos (Observatory of Athens, GR)
P. Gilles (University of Bristol, UK)
R. Gilli (INAF-OABO, Bologna, IT)
A. Goulding (H. S. Center for Astrophysics, Cambridge, US)
Ch. Gordon (University of Oxford, UK)
L. Guennou (University of Kwazulu-Natal, ZA)
V. Guglielmo (Observatory of Padova, IT)
R. C. Hickox (Durham University, UK)
C. Horellou (Chalmers University of Technology, Onsala, SE)
K. Husband (University of Bristol, UK)
M. Huynh (University of Western Austalia, AU)
A. Iovino (INAF-OAB, Brera, IT)
Ch. Jones (H. S. Center for Astrophysics, Cambridge, US)
S. Lavoie (University of Victoria, CA)
A. Le Brun (Service d’Astrophysique CEA, Saclay, FR)
J.-P. Le Fevre (Service d’Informatique CEA, Saclay, FR)
M. Lieu (University of Birmingham, UK)
C.A Lin (Service d’Astrophysique CEA, Saclay, FR)
M. Kilbinger (Service d’Astrophysique CEA, Saclay, FR)
E. Koulouridis (Service d’Astrophysique CEA, Saclay, FR)
Ch. Lidman (Australian Astronomical Observatory, Epping, AU)
M. Matturi (ITA/ZAH Heildelberg, DE)
B. Maughan (University of Bristol, UK)
A. Mantz (University of Chicago, US)
S. Maurogordato (Observatoire de la Cote d’Azur, Nice, FR)
I. McCarthy (University of Liverpool, UK)
S. McGee (Leiden Univeristy, NL)
F. Menanteau (University of Illinois, US)
J.-B. Melin (Service de Physique des Particules CEA, Saclay, FR)
O. Melnyk (University of Liege, BE)
J. Mohr (University of Munich, DE)
S. Molnar (ASIAA, Taipei, TW)
E. Mörtsell (Stockholm University, SE)
L. Moscardini (University of Bologna, IT)
S. S. Murray (Jon Hopkins, Baltimore, US)
M. Novak (University of Zagreb, HR)
F. Pacaud (Argelander-Institut fur Astronomie, Bonn, DE)
S. Paltani (ISCD, Geneva Observatory, CH)
S. Paulin-Henriksson (Service d’Astrophysique CEA, Saclay, FR)
E. Piconcelli (INAF, Roma Observatory, IT)
M. Pierre (Service d’Astrophysique CEA, Saclay, FR)
T. Plagge (University of Chicago, US)
M. Plionis (Aristotle University of Thessaloniki, Department of Physics, GR)
B. Poggianti (Observatory of Padova, IT)
D. Pomarede (Service d’Informatique CEA, Saclay, FR)
E. Pompei (European Souhern Observatory, Garching, DE)
T. Ponman (University of Birmingham, UK)
M. E. Ramos Ceja (Argelander-Institut fur Astronomie, Bonn, DE)
P. Ranalli (Observatory of Athens, GR)
D. Rapetti (Copenhagen University, DK)
S. Raychaudhury (University of Birmingham, UK)
T. Reiprich (Argelander-Institut fur Astronomie, Bonn, DE)
H. Rottgering (Leiden Observatory, NL)
E. Rozo (SLAC National Accelerator Laboratory, US)
E. Rykoff (SLAC National Accelerator Laboratory, US)
T. Sadibekova (Service d’Astrophysique CEA, Saclay, FR)
M. Sahlén (University of Oxford, UK)
J. Santos (INAF – Osservatorio Astronomico di Arcetri, IT)
J.-L. Sauvageot (Service d’Astrophysique CEA, Saclay, FR)
C. Schimd (Laboratoire d’Astrophysique, Marseille, FR)
M. Sereno (University of Bologna, IT)
J. Silk (University of Oxford, UK)
G.P. Smith (University of Birmingham, UK)
V. Smolcic (University of Zagreb, HR)
S. Snowden (NASA, GSFC, US)
D. Spergel (Princeton University, US)
A. Stanford (University of California, Davis, US)
J. Surdej (University of Liege, BE)
K. Umetsu (ASIAA, Taipei, TW)
P. Valageas (Institut de Physique Theorique du CEA, Saclay, FR)
A. Valotti (Service d’Astrophysique CEA, Saclay, FR)
I. Valtchanov (European Space Astronomy Center, Madrid, SP)
C. Vignali (University of Bologna, IT)
J. Willis (University of Victoria, CA)
F. Ziparo (University of Birmingham, UK)

See the full article here .

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ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

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From FQXI: “Detecting Parallel Universes Hidden Inside Back Holes — The First Proof of the Multiverse?”

FQXI

Dec. 10, 2015
FQXi Administrator Zeeya Meral

Garriga et al, arXiv:1512.01819v2

It’s hard to say what’s the most exciting element of this new paper on parallel universes, the inflationary multiverse, and black holes, by Tufts cosmologist (and FQXi member) Alex Vilenkin and colleagues. Is it the idea that black holes hide baby universes inside them — inflating their own spacetimes — connected to our universe by wormholes? Could it be that, according to the authors, astronomers may soon be able to find evidence to confirm this crazy notion? Perhaps it’s the fact that this paper could be presenting the first way to find definitive evidence that an inflationary multiverse of parallel worlds exists. Oh yes, and the authors also say that such black holes could have seeded supermassive black holes — the origin of which remains a mystery — *and*, in some of the scenarios they’ve looked at, they could comprise dark matter, the invisible stuff that makes up most of the matter in the universe.

Phew! No wonder the paper by Vilenkin along with Jaume Garriga, at the University of Barcelona, and Jun Zhang also at Tufts, is almost 50 pages long! (Black Holes and the Multiverse arXiv:1512.01819v2.)

Let’s take this piece by piece. Vilenkin sent me the paper, which he has just posted to the physics preprint server, arXiv, because, for him, what’s exciting is that it provides a “new way to test multiverse models observationally.” Their analysis is based on inflation theory — the idea that our universe underwent a phase of rapid expansion, or inflation, in its early history. This is now a pretty mainstream notion, which serves to solve a number of mysteries about the state of our universe today. It has also had good observational backing since various satellites have now measured the slight temperature differences in the afterglow of the big bang — the cosmic microwave background [CMB] radiation — and found patterns that match those predicted by inflationary models.

CMB per ESA/Planck

ESA/Planck

(There are still alternative proposals out there to explain these features, however. See Sophie Hebden’s Faster than Light for an example.)

Slightly more controversial is the idea that inflation forces us to accept that we live in a multiverse of neighbouring universes with potentially very different physical parameters than our cosmos. This stems from the realisation, by Vilenkin and others, that inflation is unlikely to have been a one-off event. Just as the patch of space that we now call home once inflated to create an entire cosmos for us to wonder at, other neighbouring patches are probably inflating all around us, creating parallel bubble universes nearby.

The multiverse idea has been criticised because it’s tough to test. Almost by definition, parallel bubbles are spacetimes that are divorced from ours, and so we can’t interact with them directly. That hasn’t stopped cosmologists like Vilenkin, and our own Anthony Aguirre, from coming up with inventive ways we might be able to detect them. For instance, two neighbouring bubbles might collide and leave a scar on our universe, which we could pick out of the cosmic microwave background data. (See “When Worlds Collide” by Kate Becker.)

In their new paper, Garriga, Vilenkin, and Zhang have investigated another possible consequence of inflationary cosmology — providing a new mechanism for the formation of black holes in our universe. We often talk about stellar mass black holes that were formed from the collapse of stars. There are also supermassive black holes that can be found at the centre of galaxies, which can have masses up to a billion times that of the Sun. Astrophysicists aren’t quite sure how those latter behemoths are formed.

According to Garriga, Vilenkin and Zhang, black holes could also have been formed by little bubbles of vacuum in our early universe. These would have expanded during our universe’s inflationary phase (as the cosmos they were embedded in was also growing around them). When inflation ended in our cosmos, these bubbles would — depending on their mass — have either collapsed down to a singularity (an infinitely dense point that we think lies at the core of a black hole) — or, if they were heavier than some critical mass, the bubble interior would continue to inflate into an entirely new baby universe. This universe would look to us, from the outside, like a black hole, and would be connected to our universe by a wormhole. (See the image, taken from the paper, at the top of this post.)

The team has also examined another mechanism in which black holes are formed inside spherical “domain walls” that are thought to be created during inflation. A domain wall is like a fracture or defect in space, created as the universe cools. You can think of it like a defect created in a cube of ice, where the crystal structure in the solid has misaligned as the water froze.

The paper takes a detailed look at some of the possible properties of such black holes formed by these novel processes, including the masses they might have, and the sort of observable signs they might give out that astronomers could pick up. They caution that they would need to carry out comprehensive computer simulations to work out all possible signatures and the possible effects of, for instance, energy being siphoned off from our universe through the wormhole. But a preliminary analysis suggests that these novel black holes could provide noticeable signatures, in the form of gamma rays given out by the black holes, or distortions induced on the cosmic microwave background spectrum created by radiation that was emitted as gas accreted onto large black holes in the early universe.

By looking at observational evidence that is already out there, the team can rule out inflationary black holes with certain parameters, but others are still allowed. Those that remain viable could have seeded today’s supermassive black holes, the team says. And for certain model parameters they have investigated, the number and mass of black holes they expect to see suggests that these black holes could make up the missing dark matter in the universe.

The authors also calculated that the baby universe could contain very different physical parameters from each other. Thus the network of baby universes within black holes, linked by wormholes, would create an inflationary multiverse.

“We note that the mass distributions of black holes resulting from domain walls and from vacuum bubbles are expected to be different and can in principle be distinguished observationally,” the teams writes in their paper. “If a black hole population produced by vacuum bubbles or domain walls is discovered, it could be regarded as evidence for the existence of a multiverse.”

It’s worth noting here that this isn’t the first time that physicists have suggested that black holes lead to parallel universes. For example, FQXi members Lee Smolin and Jorge Pullin have independently had similar ideas in the past. On the podcast, on the June 2013 edition, you can hear Pullin talking about how loop quantum gravity predicts that black holes are tunnels to parallel worlds. (Smolin is also on that edition, talking about his book.) But this is the first analysis carried out using inflationary theory.

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To catalyze, support, and disseminate research on questions at the foundations of physics and cosmology, particularly new frontiers and innovative ideas integral to a deep understanding of reality but unlikely to be supported by conventional funding sources.

Goals

FQXi has five goals:

To expand the purview of scientific inquiry to include scientific disciplines fundamental to a deep understanding of reality, but which are currently largely unsupported by conventional grant sources

To redress incrementalism in research programming by establishing or expanding new “islands” of understanding via flexible funding of high-risk, high-reward research in these areas

To forge and maintain useful collaborations between researchers working on foundational questions in physics, cosmology, and related fields

To provide the public with a deeper understanding of known and future discoveries in these areas, and their potential implications for our worldview

To create a logistically, intellectually, and financially self-sustaining independent Institute to accomplish these goals during and beyond the initial four year program beginning in 2006, thereby pioneering a new model of philanthropically-funded scientific research

FQXi therefore aims to support research that is both foundational (with potentially significant and broad implications for our understanding of the deep or “ultimate” nature of reality) and unconventional (enabling research that, because of its speculative, non-mainstream, or high-risk nature, would otherwise go unperformed due to lack of funding).

From AAS NOVA: “The Q Continuum Simulation”

Amercan Astronomical Society

28 September 2015
Susanna Kohler

Each frame in this image ([in the full article]click for the full view!) represents a different stage in the simulated evolution of our universe, ending at present day in the rightmost panel. In a recently-published paper, Katrin Heitmann (Argonne National Laboratory) and collaborators reveal the results from — and challenges inherent in — the largest cosmological simulation currently available: the Q Continuum simulation. Evolving a volume of 1300 Mpc3, this massive N-body simulation tracks over half a trillion particles as they clump together as a result of their mutual gravity, imitating the evolution of our universe over the last 13.8 billion years. Cosmological simulations such as this one are important for understanding observations, testing analysis pipelines, investigating the capabilities of future observing missions, and much more. For more information and the original image (as well as several other awesome images!), see the paper below.
Citation:

Katrin Heitmann et al 2015 ApJS 219 34. doi:10.1088/0067-0049/219/2/34

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From NOVA: “Could the Universe Be Lopsided?”

NOVA

28 Sep 2015
Paul Halpern

One hundred years ago, [Albert] Einstein re-envisioned space and time as a rippling, twisting, flexible fabric called spacetime. His theory of general relativity showed how matter and energy change the shape of this fabric. One might expect, therefore, that the fabric of the universe, strewn with stars, galaxies, and clouds of particles, would be like a college student’s dorm room: a mess of rumpled, crumpled garments.

Indeed, if you look at the universe on the scale of stars, galaxies, and even galaxy clusters, you’ll find it puckered and furrowed by the gravity of massive objects. But take the wider view—the cosmologists’ view, which encompasses the entire visible universe—and the fabric of the universe is remarkably smooth and even, no matter which direction you turn. Look up, down, left, or right and count up the galaxies you see: you’ll find it’s roughly the same from every angle. The cosmic microwave background [CMB], the cooled-down relic of radiation from the early universe, demonstrates the same remarkable evenness on the very largest scale.

CMB per ESA/Planck

ESA/Planck satellite

A computer simulation of the ‘cosmic web’ reveals the great filaments, made largely of dark matter, located in the space between galaxies. By NASA, ESA, and E. Hallman (University of Colorado, Boulder), via Wikimedia Commons

Physicists call a universe that appears roughly similar in all directions isotropic. Because the geometry of spacetime is shaped by the distribution of matter and energy, an isotropic universe must posses a geometric structure that looks the same in all directions as well. The only three such possibilities for three-dimensional spaces are positively curved (the surface of a hypersphere, like a beach ball but in a higher dimension), negatively curved (the surface of a hyperboloid, shaped like a saddle or potato chip), or flat. Russian physicist [Alexei] Fridmann, Belgian cleric and mathematician Georges Lemaître and others incorporated these three geometries into some of the first cosmological solutions of Einstein’s equations. (By solutions, we mean mathematical descriptions of how the three spatial dimensions of the universe behave over time, given the type of geometry and the distribution of matter and energy.) Supplemented by the work of American physicist Howard Robertson and British mathematician Arthur Walker, this class of isotropic solutions has become the standard for descriptions of the universe in the Big Bang theory.

However, in 1921 Edward Kasner—best known for his coining of the term “Googol” for the number 1 followed by 100 zeroes—demonstrated that there was another class of solutions to Einstein’s equations: anisotropic, or “lopsided,” solutions.

Known as the Kasner solutions, these cosmic models describe a universe that expands in two directions while contracting in the third. That is clearly not the case with the actual universe, which has grown over time in all three directions. But the Kasner solutions become more intriguing when you apply them to a kind of theory called a Kaluza-Klein model, in which there are unseen extra dimensions beyond space and time. Thus space could theoretically have three expanding dimensions and a fourth, hidden, contracting dimension. Physicists Alan Chodos and Steven Detweiler explored this concept in their paper Where has the fifth dimension gone?

Kasner’s is far from the only anisotropic model of the universe. In 1951, physicist Abraham Taub applied the shape-shifting mathematics of Italian mathematician Luigi Bianchi to general relativity and revealed even more baroque classes of anisotropic solutions that expand, contract or pulsate differently in various directions. The most complex of these, categorized as Bianchi type-IX, turned out to have chaotic properties and was dubbed by physicist Charles Misner the “Mixmaster Universe” for its resemblance to the whirling, twirling kitchen appliance.

Like a cake rising in a tray, while bubbling and quivering on the sides, the Mixmaster Universe expands and contracts, first in one dimension and then in another, while a third dimension just keeps expanding. Each oscillation is called a Kasner epoch. But then, after a certain number of pulses, the direction of pure expansion abruptly switches. The formerly uniformly expanding dimension starts pulsating, and one of those formerly pulsating starts uniformly expanding. It is as if the rising cake were suddenly turned on its side and another direction started rising instead, while the other directions, including the one that was previously rising, just bubbled.

One of the weird things about the Mixmaster Universe is that if you tabulate the number of Kasner epochs in each era, before the behavior switches, it appears as random as a dice roll. For example, the universe might oscillate in two directions five times, switch, oscillate in two other directions 17 times, switch again, pulsate another way twice, and so forth—without a clear pattern. While the solution stems from deterministic general relativity, it seems unpredictable. This is called deterministic chaos.

Could the early moments of the universe have been chaotic, and then somehow regularized over time, like a smoothed-out pudding? Misner initially thought so, until he realized that the Mixmaster Universe couldn’t smooth out on its own. However, it could have started out “lopsided,” then been stretched out during an era of ultra-rapid expansion called inflation until its irregularities were lost from sight.

As cosmologists have collected data from instruments such as the Hubble Space Telescope, Planck Satellite, and WMAP satellite (now retired), the bulk of the evidence supports the idea that our universe is indeed isotropic.

NASA/ESA Hubble

NASA/WMAP

But a minority of researchers have used measurements of the velocities of galaxies and other observations, such as an odd line up of temperature fluctuations in the cosmic microwave background dubbed the “Axil of Evil” to assert that the universe could be slightly irregular after all.

For example, starting in 2008, Alexander Kashlinsky, a researcher at NASA’s Goddard Space Flight Center, and his colleagues have statistically analyzed cosmic microwave background data gathered by first the WMAP satellite and the Planck satellite to show that, in addition to their motion due to cosmic expansion, many galaxy clusters seem to be heading toward a particular direction on the sky. He dubbed this phenomenon “dark flow,” and suggested that it is evidence of a previously-unseen cosmic anisotropy known as a “tilt.” Although the mainstream astronomical community has disputed Kashlinsky’s conclusion, he has continued to gather statistical evidence for dark flow and the idea of tilted universes.

Whether or not the universe really is “lopsided,” it is intriguing to study the rich range of solutions of Einstein’s general theory of relativity. Even if the preponderance of evidence today points to cosmic regularity, who knows when a new discovery might call that into question, and compel cosmologists to dust off alternative ideas. Such is the extraordinary flexibility of Einstein’s masterful theory: a century after its publication, physicists are still exploring its possibilities.

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NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.

From RT: “Time-traveling photons connect general relativity to quantum mechanics”

RT

23 Jun, 2014
No Writer Credit

Space-time structure exhibiting closed paths in space (horizontal) and time (vertical). A quantum particle travels through a wormhole back in time and returns to the same location in space and time. (Photo credit: Martin Ringbauer)

Scientists have simulated time travel by using particles of light acting as quantum particles sent away and then brought back to their original space-time location. This is a huge step toward marrying two of the most irreconcilable theories in physics.

Since traveling all the way to a black hole to see if an object you’re holding would bend, break or put itself back together in inexplicable ways is a bit of a trek, scientists have decided to find a point of convergence between general relativity and quantum mechanics in lab conditions, and they achieved success.

Australian researchers from the UQ’s School of Mathematics and Physics wanted to plug the holes in the discrepancies that exist between two of our most commonly accepted physics theories, which is no easy task: on the one hand, you have Einstein’s theory of general relativity, which predicts the behavior of massive objects like planets and galaxies; but on the other, you have something whose laws completely clash with Einstein’s – and that is the theory of quantum mechanics, which describes our world at the molecular level. And this is where things get interesting: we still have no concrete idea of all the principles of movement and interaction that underpin this theory.

Natural laws of space and time simply break down there.

The light particles used in the study are known as photons, and in this University of Queensland study, they stood in for actual quantum particles for the purpose of finding out how they behaved while moving through space and time.

The team simulated the behavior of a single photon that travels back in time through a wormhole and meets its older self – an identical photon. “We used single photons to do this but the time-travel was simulated by using a second photon to play the part of the past incarnation of the time traveling photon,” said UQ Physics Professor Tim Ralph asquotedby The Speaker.

The findings were published in the journal Nature Communications and gained support from the country’s key institutions on quantum physics.

Some of the biggest examples of why the two approaches can’t be reconciled concern the so-called space-time loop. Einstein suggested that you can travel back in time and return to the starting point in space and time. This presented a problem, known commonly as the ‘grandparents paradox,’ theorized by Kurt Godel in 1949: if you were to travel back in time and prevent your grandparents from meeting, and in so doing prevent your own birth, the classical laws of physics would prevent you from being born.

But Tim Ralph has reminded that in 1991, such situations could be avoided by harnessing quantum mechanics’ flexible laws: “The properties of quantum particles are ‘fuzzy’ or uncertain to start with, so this gives them enough wiggle room to avoid inconsistent time travel situations,” he said.

There are still ways in which science hasn’t tested the meeting points between general relativity and quantum mechanics – such as when relativity is tested under extreme conditions, where its laws visibly seem to bend, just like near the event horizon of a black hole.

But since it’s not really easy to approach one, the UQ scientists were content with testing out these points of convergence on photons.

“Our study provides insights into where and how nature might behave differently from what our theories predict,” Professor Ralph said.

See the full article here.

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From NOVA: “Black Holes Could Turn You Into a Hologram, and You Wouldn’t Even Notice”

NOVA

01 Jul 2015
Tim De Chant

Black holes may not have event horizons, but fuzzy surfaces.

Few things are as mysterious as black holes. Except, of course, what would happen to you if you fell into one.

Physicists have been debating what might happen to anyone unfortunate enough to slip toward the singularity, and so far, they’ve come up with approximately 2.5 ways you might die, from being stretched like spaghetti to burnt to a crisp.

The fiery hypothesis is a product of Stephen Hawking’s firewall theory, which also says that black holes eventually evaporate, destroying everything inside. But this violates a fundamental principle of physics—that information cannot be destroyed—so other physicists, including Samir Mathur, have been searching for ways to address that error.

Here’s Marika Taylor, writing for The Conversation:

The general relativity description of black holes suggests that once you go past the event horizon, the surface of a black hole, you can go deeper and deeper. As you do, space and time become warped until they reach a point called the “singularity” at which point the laws of physics cease to exist. (Although in reality, you would die pretty early on on this journey as you are pulled apart by intense tidal forces).

In Mathur’s universe, however, there is nothing beyond the fuzzy event horizon.

Mathur’s take on black holes suggests that they aren’t surrounded by a point-of-no-return event horizon or a firewall that would incinerate you, but a fuzzball with small variations that maintain a record of the information that fell into it. What does touch the fuzzball is converted into a hologram. It’s not a perfect copy, but a doppelgänger of sorts.

Perhaps more bizarrely, you even wouldn’t be aware that of the transformation. Say you were to be sucked toward a black hole. At the point where you’d normally hit the event horizon, Mathur says, you’d instead touch the fuzzy surface. But instead of noticing anything, the fuzzy surface would appear like any other part of space immediately around you. Everything would seem the same as it was, except that you’d be a hologram.

See the full article here.

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NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.

From NOVA: “How Time Got Its Arrow”

NOVA

15 Jul 2015

Lee Smolin, Perimeter Institute for Theoretical Physics

I believe in time.

I haven’t always believed in it. Like many physicists and philosophers, I had once concluded from general relativity and quantum gravity that time is not a fundamental aspect of nature, but instead emerges from another, deeper description. Then, starting in the 1990s and accelerated by an eight year collaboration with the Brazilian philosopher Roberto Mangabeira Unger, I came to believe instead that time is fundamental. (How I came to this is another story.) Now, I believe that by taking time to be fundamental, we might be able to understand how general relativity and the standard model emerge from a deeper theory, why time only goes one way, and how the universe was born.

The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

Flickr user Robert Couse-Baker, adapted under a Creative Commons license.

The story starts with change. Science, most broadly defined, is the systematic study of change. The world we observe and experience is constantly changing. And most of the changes we observe are irreversible. We are born, we grow, we age, we die, as do all living things. We remember the past and our actions influence the future. Spilled milk is hard to clean up; a cool drink or a hot bath tend towards room temperature. The whole world, living and non-living, is dominated by irreversible processes, as captured mathematically by the second law of thermodynamics, which holds that the entropy of a closed system usually increases and seldom decreases.

It may come as a surprise, then, that physics regards this irreversibility as a cosmic accident. The laws of nature as we know them are all reversible when you change the direction of time. Film a process described by those laws, and then run the movie backwards: the rewound version is also allowed by the laws of physics. To be more precise, you may have to change left for right and particles for antiparticles, along with reversing the direction of time, but the standard model of particle physics predicts that the original process and its reverse are equally likely.

The same is true of Einstein’s theory of general relativity, which describes gravity and cosmology. If the whole universe were observed to run backwards in time, so that it heated up while it collapsed, rather than cooled as it expanded, that would be equally consistent with these fundamental laws, as we currently understand them.

This leads to a fundamental question: Why, if the laws are reversible, is the universe so dominated by irreversible processes? Why does the second law of thermodynamics hold so universally?

Gravity is one part of the answer. The second law tells us that the entropy of a closed system, which is a measure of disorder or randomness in the motions of the atoms making up that system, will most likely increase until a state of maximum disorder is reached. This state is called equilibrium. Once it is reached, the system is as mixed as possible, so all parts have the same temperature and all the elements are equally distributed.

But on large scales, the universe is far from equilibrium. Galaxies like ours are continually forming stars, turning nuclear potential energy into heat and light, as they drive the irreversible flows of energy and materials that characterize the galactic disks. On these large scales, gravity fights the decay to equilibrium by causing matter to clump,,creating subsystems like stars and planets. This is beautifully illustrated in some recent papers by Barbour, Koslowski and Mercati.

But this is only part of the answer to why the universe is out of equilibrium. There remains the mystery of why the universe at the big bang was not created in equilibrium to start with, for the picture of the universe given us by observations requires that the universe be created in an extremely improbable state—very far from equilibrium. Why?

So when we say that our universe started off in a state far from equilibrium, we are saying that it started off in a state that would be very improbable, were the initial state chosen randomly from the set of all possible states. Yet we must accept this vast improbability to explain the ubiquity of irreversible processes in our world in terms of the reversible laws we know.

In particular, the conditions present in the early universe, being far from equilibrium, are highly irreversible. Run the early universe backwards to a big crunch and they look nothing like the late universe that might be in our future.

In 1979 Roger Penrose proposed a radical answer to the mystery of irreversibility. His proposal concerned quantum gravity, the long-searched-for unification of all the known laws, which is believed to govern the processes that created the universe in the big bang—or transformed it from whatever state it was in before the big bang.

Penrose hypothesized that quantum gravity, as the most fundamental law, will be unlike the laws we know in that it will be irreversible. The known laws, along with their time-reversibility, emerge as approximations to quantum gravity when the universe grows large and cool and dilute, Penrose argued. But those approximate laws will act within a universe whose early conditions were set up by the more fundamental, irreversible laws. In this way the improbability of the early conditions can be explained.

In the intervening years our knowledge of the early universe has been dramatically improved by a host of cosmological observations, but these have only deepened the mysteries we have been discussing. So a few years ago, Marina Cortes, a cosmologist from the Institute for Astronomy in Edinburgh, and I decided to revive Penrose’s suggestion in the light of all the knowledge gained since, both observationally and theoretically.

Dr. Cortes argued that time is not only fundamental but fundamentally irreversible. She proposed that the universe is made of processes that continuously generate new events from present events. Events happen, but cannot unhappen. The reversal of an event does not erase that event, Cortes says: It is a new event, which happens after it.

In December of 2011, Dr. Cortes began a three-month visit to Perimeter Institute, where I work, and challenged me to collaborate with her on realizing these ideas. The first result was a model we developed of a universe created by events, which we called an energetic causal set model.

This is a version of a kind of model called a causal set model, in which the history of the universe is considered to be a discrete set of events related only by cause-and-effect. Our model was different from earlier models, though. In it, events are created by a process which maximizes their uniqueness. More precisely, the process produces a universe created by events, each of which is different from all the others. Space is not fundamental, only the events and the causal process that creates them are fundamental. But if space is not fundamental, energy is. The events each have a quantity of energy, which they gain from their predecessors and pass on to their successors. Everything else in the world emerges from these events and the energy they convey.

We studied the model universes created by these processes and found that they generally pass through two stages of evolution. In the first stage, they are dominated by the irreversible processes that create the events, each unique. The direction of time is clear. But this gives rise to a second stage in which trails of events appear to propagate, creating emergent notions of particles. Particles emerge only when the second, approximately reversible stage is reached. These emergent particles propagate and appear to interact through emergent laws which seem reversible. In fact, we found, there are many possible models in which particles and approximately reversible laws emerge after a time from a more fundamental irreversible, particle-free system.

This might explain how general relativity and the standard model emerged from a more fundamental theory, as Penrose hypothesized. Could we, we wondered, start with general relativity and, staying within the language of that theory, modify it to describe an irreversible theory? This would give us a framework to bridge the transition between the early, irreversible stage and the later, reversible stage.

In a recent paper, Marina Cortes, PI postdoc Henrique Gomes and I showed one way to modify general relativity in a way that introduces a preferred direction of time, and we explored the possible consequences for the cosmology of the early universe. In particular, we showed that there were analogies of dark matter and dark energy, but which introduce a preferred direction of time, so a contracting universe is no longer the time-reverse of an expanding universe.

To do this we had to first modify general relativity to include a physically preferred notion of time. Without that there is no notion of reversing time. Fortunately, such a modification already existed. Called shape dynamics, it had been proposed in 2011 by three young people, including Gomes. Their work was inspired by Julian Barbour, who had proposed that general relativity could be reformulated so that a relativity of size substituted for a relativity of time.

Using the language of shape dynamics, Cortes, Gomes and I found a way to gently modify general relativity so that little is changed on the scale of stars, galaxies and planets. Nor are the predictions of general relativity regarding gravitational waves affected. But on the scale of the whole universe, and for the early universe, there are deviations where one cannot escape the consequences of a fundamental direction of time.

Very recently I found still another way to modify the laws of general relativity to make them irreversible. General relativity incorporates effects of two fixed constants of nature, Newton’s constant, which measures the strength of the gravitational force, and the cosmological constant [usually denoted by the Greek capital letter lambda: Λ], which measures the density of energy in empty space. Usually these both are fixed constants, but I found a way they could evolve in time without destroying the beautiful harmony and consistency of the Einstein equations of general relativity.

These developments are very recent and are far from demonstrating that the irreversibility we see around us is a reflection of a fundamental arrow of time. But they open a way to an understanding of how time got its direction that does not rely on our universe being a consequence of a cosmic accident.

See the full article here.

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NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.

From Daily Galaxy: “Our Observed Universe is a Tiny Corner of an Enormous Cosmos –‘Ruled by Dark Energy'”

The Daily Galaxy

March 01, 2015
No Writer Credit

“This new concept is, potentially, as drastic an enlargement of our cosmic perspective as the shift from pre-Copernican ideas to the realization that the Earth is orbiting a typical star on the edge of the Milky Way.” Sir Martin Rees, physicist, Cambridge University, Astronomer Royal of Great Britain.

Is our universe merely a part of an enormous universe containing diverse regions each with the right amount of the dark energy and each larger than the observed universe, according to Raphael Bousso, Professor of Theoretical Physics, U of California/Berkeley and Leonard Susskind, Felix Bloch Professor of Physics, Stanford University. The two theorize that information can leak from our causal patch into others, allowing our part of the universe to “decohere” into one state or another, resulting in the universe that we observe.

The many worlds interpretation of quantum mechanics is the idea that all possible alternate histories of the universe actually exist. At every point in time, the universe splits into a multitude of existences in which every possible outcome of each quantum process actually happens.The reason many physicists love the many worlds idea is that it explains away all the strange paradoxes of quantum mechanics.

Putting the many world interpretation aside for a moment, another strange idea in modern physics is the idea that our universe was born along with a large, possibly infinite, number of other universes. So our cosmos is just one tiny corner of a much larger multiverse.

Susskind and Bousso have put forward the idea that the multiverse and the many worlds interpretation of quantum mechanics are formally equivalent, but if both quantum mechanics and the multiverse take special forms.

Let’s take quantum mechanics first. Susskind and Bousso propose that it is possible to verify the predictions of quantum mechanics. In theory, it could be done if an observer could perform an infinite number of experiments and observe the outcome of them all, which is known as the supersymmetric multiverse with vanishing cosmological constant.

If the universe takes this form, then it is possible to carry out an infinite number of experiments within the causal horizon of each other. At each instant in time, an infinite (or very large) number of experiments take place within the causal horizon of each other. As observers, we are capable of seeing the outcome of any of these experiments but we actually follow only one.

Bousso and Susskind argue that since the many worlds interpretation is possible only in their supersymmetric multiverse, they must be equivalent. “We argue that the global multiverse is a representation of the many-worlds in a single geometry,” they say, calling this new idea the multiverse interpretation of quantum mechanics.

But we have now entered the realm of what mathematical physicist Peter Woit of Columbia calls “Not Even Wrong, because the theory lacks is a testable prediction that would help physicists distinguish it experimentally from other theories of the universe. And without this crucial element, the multiverse interpretation of quantum mechanics is little more than philosophy, according to Woit.

What this new supersymmetric multiverse interpretation does have is a simplicity– it’s neat and elegant that the many worlds and the multiverse are equivalent. Ockham’s Razor is fulfilled and no doubt, many quantum physicists delight in what appears to be an exciting. plausible interpretation of ultimate if currently untestable, reality.

Ref: arxiv.org/abs/1105.3796: The Multiverse Interpretation of Quantum Mechanics

The Daily Galaxy via technologyreview.com

Image credit: hellstormde.deviantart.com

See the full article here.

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