Nordic Institute for Theoretical Physics


Nordic Institute for Theoretical Physics

Time filter
Source Type

News Article | February 15, 2017

Stuff that falls into a black hole is gone forever, right? Not so, says Stephen Hawking. “If you feel you are in a black hole, don’t give up,” he told an audience at a public lecture in Stockholm, Sweden, yesterday. He was speaking in advance of a scientific talk today at the Hawking Radiation Conference being held at the KTH Royal Institute of Technology in Stockholm. “There’s a way out.” You probably know that black holes are stars that have collapsed under their own gravity, producing gravitational forces so strong that even light can’t escape. Anything that falls inside is thought to be ripped apart by the massive gravity, never to been seen or heard from again. What you may not know is that physicists have been arguing for 40 years about what happens to the information about the physical state of those objects once they fall in. Quantum mechanics says that this information cannot be destroyed, but general relativity says it must be – that’s why this argument is known as the information paradox. Now Hawking says this information never makes it inside the black hole in the first place. “I propose that the information is stored not in the interior of the black hole as one might expect, but on its boundary, the event horizon,” he said today. “Black holes ain’t as black as they are painted” The event horizon is the sphere around a black hole from inside which nothing can escape its clutches. Hawking is suggesting that the information about particles passing through is translated into a kind of hologram – a 2D description of a 3D object – that sits on the surface of the event horizon. “The idea is the super translations are a hologram of the ingoing particles,” he said. “Thus they contain all the information that would otherwise be lost.” So how does that help something escape from the black hole? In the 1970s Hawking introduced the concept of Hawking radiation – photons emitted by black holes due to quantum fluctuations. Originally he said that this radiation carried no information from inside the black hole, but in 2004 changed his mind and said it could be possible for information to get out. Just how that works is still a mystery, but Hawking now thinks he’s cracked it. His new theory is that Hawking radiation can pick up some of the information stored on the event horizon as it is emitted, providing a way for it to get out. But don’t expect to get a message from within, he said. “The information about ingoing particles is returned, but in a chaotic and useless form. This resolves the information paradox. For all practical purposes, the information is lost.” Last year Hawking made headlines for saying “there are no black holes” – although what he actually meant was a little more complicated, as he proposed replacing the event horizon with a related concept, an apparent horizon. This new idea is compatible with his previous one, which wasn’t really news to theoretical physicists, says Sabine Hossenfelder of the Nordic Institute for Theoretical Physics in Stockholm, who attending Hawking’s lecture. “He is saying that the information is there twice already from the very beginning, so it’s never destroyed in the black hole to begin with,” she says. “At least that’s what I understood.” More details are expected later today when one of Hawking’s collaborators Malcom Perry expands on the idea, and Hawking and his colleagues say they will publish a paper on the work next month, but it’s clear he is gunning for the idea that black holes are inescapable. It’s even possible information could get out into parallel universes, he told the audience yesterday. “The message of this lecture is that black holes ain’t as black as they are painted. They are not the eternal prisons they were once thought,” he said. “Things can get out of a black hole both on the outside and possibly come out in another universe.”

News Article | March 23, 2016

Boost for AI South Korea announced on 17 March that it would invest 1 trillion won (US$863 million) in artificial-intelligence (AI) research over 5 years. The announcement came two days after Google DeepMind’s Go program AlphaGo beat grandmaster Lee Sedol 4–1 in an exhibition match, a feat that prompted a spate of newspaper headlines concerned that South Korea was falling behind in a crucial growth industry. It is not immediately clear whether the cash represents new funding or is money that had been previously allocated to AI efforts. The investment includes a high-profile, public–private research centre near Seoul. See for more. Satellite tracks sea-surface levels Jason-3, a joint US–European satellite mission to monitor sea-level rise, has produced its first complete global map of sea-surface height anomalies. The image, released on 16 March, draws on ten days of data collected by the probe after it reached its intended orbit following its 17 January launch. NASA and its European partners — the French space agency CNES and the meteorological agency EUMETSAT — plan a three-year mission for Jason-3. The data that the probe collects could help to improve weather and climate forecasts globally. Particle promise Hints of a mysterious particle at the Large Hadron Collider (LHC) near Geneva, Switzerland, just got a little stronger. In December, physicists announced that they had seen an excess of pairs of γ-ray photons — possibly a sign of a particle not predicted by the standard model of physics. The data came from ATLAS and CMS, the two largest detectors at the LHC. A fresh analysis reported on 17 March at a conference in La Thuile, Italy, slightly increases the statistical significance of the signal seen by the CMS experiment. See for more. Virus control Mosquitoes carrying a gene that kills their offspring should be released in small pilot studies during the current Zika outbreak, the World Health Organization (WHO) Vector Control Advisory Group said on 18 March. The group also endorsed field tests of mosquitoes carrying bacteria that reduce the insects’ ability to transmit Zika, dengue and other viruses. Studies show that these interventions can reduce populations of Aedes aegypti mosquitoes, but they have not established whether such interventions can minimize disease burden in humans — a crucial gap that pilot studies could fill, the group said. Offshore plans The US Department of the Interior announced on 15 March that it will not pursue offshore oil and gas development along the US Atlantic coast. The decision, released as part of the offshore-leasing programme for 2017–22, reverses an earlier proposal to sell leases along the central and southern Atlantic coast, from Virginia to Georgia. The proposed plan would move forward with leasing in the Gulf of Mexico and off the Alaskan coast. Ebola flare-up ends Sierra Leone is clear from Ebola after a recent flare-up, the World Health Organization (WHO) announced on 17 March. The date marked 42 days since the last person confirmed to have Ebola virus disease in Sierra Leone tested negative for a second time. The WHO classes this window — twice the incubation period of the virus — as the time needed to declare an outbreak over. On the same day, the WHO confirmed two new cases of Ebola in a rural village in Guinea, which had been declared free of Ebola in December. Coral concerns Faced with ongoing damage to its corals, the Great Barrier Reef Marine Park Authority raised its response status to level three — the highest possible, meaning ‘severe regional bleaching’ — on 20 March. The decision was made despite heavy rains, which have lowered the high water temperatures that have been killing corals along parts of Australia’s northeast coast. According to the authority, divers have found up to 50% coral mortality near the tip of Cape York, but most surveyed sections of the park are in a better state. This regional damage is part of a global coral-bleaching event linked to warmer-than-average waters (see Nature; 2015). Turkey arrests Three Turkish academics in Istanbul were taken in for questioning on 14 March and have now been formally arrested and held without bail. They are under suspicion of ‘making terrorist propaganda’, after signing a petition in January calling for an end to violence between government forces and Kurdish separatists in Turkey’s southeast. Those held (pictured, from left) are psychologist Esra Mungan from Boğaziçi University, political scientist Muzaffer Kaya from Nişantaşı University and mathematician Kıvanç Ersoy from Mimar Sinan University. Four days earlier, the three had held a press conference affirming their commitment to the ‘academics for peace’ petition. See for more. Cancer moonshot Cancer survivor Gregory Simon was named executive director of the US Cancer Moonshot Task Force on 18 March. Simon was founding president of FasterCures, a non-profit organization in Washington DC dedicated to speeding the development of new medicines, and has worked in government and the pharmaceutical industry. He most recently helmed a health-care investment company. The moonshot project, driven by US vice-president Joe Biden, aims to double the pace of cancer research. President Barack Obama has asked Congress for US$755 million to fund the endeavour in 2017. China hunts waves China’s plans to detect gravitational waves took a step forward on 20 March, as construction began on the TianQin project at Sun Yat-sen University in Zhuhai. A research building, observation station and ultra-quiet cave laboratory will be built ahead of the launch of three Earth-orbiting satellites. Gravitational waves should be revealed as disturbances in laser beams bounced between the spacecraft. China also has another space-based gravitational-wave detector in the works: the Taiji project from the Chinese Academy of Sciences will involve a trio of Sun-orbiting satellites. See for more on China’s plans. Nobel Prize home A Nobel Center will be built on the Blasieholmen peninsula in Stockholm’s central waterfront by 2019. The City Planning Committee approved detailed plans for the site on 16 March. At a cost of 1.2 billion Swedish kronor (US$146 million), the building will house the Nobel Museum and future prize ceremonies. The centre will be open to visitors and scientists, incorporating research projects, educational efforts, conferences and a library. But its large size and location has attracted criticism, drawing concerns that it will ruin Stockholm’s skyline. Boaty McBoatface The British public has flocked to a competition to name a new UK polar research vessel, which is under development and set to be finished in 2019. The Natural Environment Research Council (NERC) allowed people to submit and vote on names for the £200-million (US$289-million) ship, but its website crashed repeatedly after the poll was launched on 17 March. As Nature went to press, the proposed name RRS (Royal Research Ship) Boaty McBoatface was the most popular suggestion, with thousands of votes more than the second choice, RRS Henry Worsley. The final name will be chosen by NERC. Around one-fifth of physicists from sexual and genderminorities (LGBT) surveyed by the American Physical Society (APS) said that they had been ignored, intimidated or harassed at work (see Transgender respondents were the most affected: almost half had experienced exclusionary or harassing treatment in the previous year. And more than three times as many women as men had experienced such behaviour. See for more. 28–29 March The US National Institutes of Health holds a special meeting to discuss the spread of Zika virus in the Americas, and ways to contain it. 29–31 March The University of Central Lancashire in Preston, UK, hosts a meeting of academics and industrialists to discuss applications of nanotechnology. 30 March–22 April NORDITA, the Nordic Institute for Theoretical Physics, hosts a meeting in Stockholm on advances in string theory and gauge theory.

Calmet X.,University of Sussex | Hossenfelder S.,Nordic Institute for Theoretical Physics | Percacci R.,International School for Advanced Studies
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

By studying the notion of a fundamentally minimal length scale in asymptotically safe gravity we find that a specific version of deformed special relativity (DSR) naturally arises in this approach. We then consider two thought experiments to examine the interpretation of the scenario and discuss similarities and differences to other approaches to DSR. © 2010 The American Physical Society.

Bettoni D.,Technion - Israel Institute of Technology | Zumalacarregui M.,University of Heidelberg | Zumalacarregui M.,Nordic Institute for Theoretical Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

Kinetic mixing between the metric and scalar degrees of freedom is an essential ingredient in contemporary scalar-tensor theories. This often makes it hard to understand their physical content, especially when derivative mixing is present, as is the case for Horndeski action. In this work we develop a method that allows us to write a Ricci-curvature-free scalar field equation, and we discuss some of the advantages of such a rephrasing in the study of stability issues in the presence of matter, the existence of an Einstein frame, and the generalization of the disformal screening mechanism. For quartic Horndeski theories, such a procedure leaves, in general, a residual coupling to the curvature, given by the Weyl tensor. This gives rise to a binary classification of scalar-tensor theories into stirred theories, in which the curvature can be substituted, and shaken theories, in which a residual coupling to the curvature remains. Quite remarkably, we have found that generalized Dirac-Born-Infeld Galileons belong to the first class. Finally, we discuss kinetic mixing in quintic theories, in which nonlinear mixing terms appear, and in the recently proposed theories beyond Horndeski that display a novel form of kinetic mixing, in which the field equation is sourced by derivatives of the energy-momentum tensor. © 2015 American Physical Society.

Bellini E.,University of Barcelona | Zumalacarregui M.,University of Heidelberg | Zumalacarregui M.,Nordic Institute for Theoretical Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

The scale of baryon acoustic oscillations (BAO) imprinted in the matter power spectrum provides an almost-perfect standard ruler: it only suffers subpercent deviations from fixed comoving length due to nonlinear effects. We study the BAO shift in the large Horndeski class of gravitational theories and compute its magnitude in momentum space using second-order perturbation theory and a peak-background split. The standard prediction is affected by the modified linear growth, as well as by nonlinear gravitational effects that alter the mode-coupling kernel. For covariant Galileon models, we find a 14%-45% enhancement of the BAO shift with respect to standard gravity and a distinct time evolution depending on the parameters. Despite the larger values, the shift remains well below the forecasted precision of next-generation galaxy surveys. Models that produce significant BAO shift would cause large redshift-space distortions or affect the bispectrum considerably. Our computation therefore validates the use of the BAO scale as a comoving standard ruler for tests of general dark energy models. © 2015 American Physical Society.

Martikainen J.-P.,Nordic Institute for Theoretical Physics
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

We study how the bosonic atoms on the excited p band of an optical lattice are coupled to the lowest s band and the second excited d band. We find that in some parameter regimes, the atom-atom interactions can cause a dynamical instability of the p-band atoms toward decay to the s and d bands. Furthermore, even when dynamical instability is not expected s and d bands can become substantially populated. We also find that the stability properties of the excited bands can be improved in superlattices. © 2011 American Physical Society.

Wettlaufer J.S.,Yale University | Wettlaufer J.S.,Nordic Institute for Theoretical Physics
Astrophysical Journal | Year: 2010

The formation of a solar system such as ours is believed to have followed a multi-stage process around a protostar and its associated accretion disk. Whipple first noted that planetesimal growth by particle agglomeration is strongly influenced by gas drag, and Cuzzi and colleagues have shown that when midplane particle mass densities approach or exceed those of the gas, solid-solid interactions dominate the drag effect. The size dependence of the drag creates a "bottleneck" at the meter scale with such bodies rapidly spiraling into the central star, whereas much smaller or larger particles do not. Independent of whether the origin of the drag is angular momentum exchange with gas or solids in the disk, successful planetary accretion requires rapid planetesimal growth to kilometer scales.Acommonly accepted picture is that for collisional velocities Vc above a certain threshold value, Vth ∼ 0.1-10 cm s-1, particle agglomeration is not possible; elastic rebound overcomes attractive surface and intermolecular forces. However, if perfect sticking is assumed for all ranges of interparticle collision speeds the bottleneck can be overcome by rapid planetesimal growth. While previous work has dealt with the influences of collisional pressures and the possibility of particle fracture or penetration, the basic role of the phase behavior of matter-phase diagrams, amorphs, and polymorphs-has been neglected. Here, it is demonstrated for compact bodies that novel aspects of surface phase transitions provide a physical basis for efficient sticking through collisional melting/amorphization/ polymorphization and subsequent fusion/annealing to extend the collisional velocity range of primary accretion to δVc ∼ 1-100 m s-1 ≥ Vth, which encompasses both typical turbulent rms speeds and the velocity differences between boulder-sized and small grains ∼1-50 m s -1. Therefore, as inspiraling meter-sized bodies collide with smaller particles in this high velocity collisional fusion regime they grow sufficiently rapidly to ∼0.1-1 km scale and settle into stable Keplerian orbits in∼105 years before photoevaporative wind clears the disk of source material. The basic theory applies to low and high melting temperature materials and thus to the inner and outer regions of a nebula. © 2010. The American Astronomical Society. All rights reserved.

Zarembo K.,Nordic Institute for Theoretical Physics | Zieme S.,Nordic Institute for Theoretical Physics
JETP Letters | Year: 2012

The spectrum of an infinite spinning string in AdS 5 does not precisely match the spectrum of dual gauge theory operators, interpolated to the strong coupling regime with the help of Bethe-ansatz equations. We show that the mismatch is due to interactions in the string σ-model which cannot be neglected even at asymptotically large' t Hooft coupling. © 2012 Pleiades Publishing, Ltd.

News Article | November 14, 2015

Sabine Hossenfelder, a high-energy physicist at Sweden's Nordic Institute for Theoretical Physics, is the main voice behind the excellent Backreaction blog, which is highly recommended for those seeking reasonably accessible inside takes on, well, physics. It so happens that she makes videos too, which is good news for us. Hossenfelder put this one up last week, "10 Things You Should Know About Black Holes." Some of them you surely already know, but she does a great job concisely explaining some of the harder-to-grasp features of black hole life, such as the Black Hole Information Paradox.

Professor Stephen Hawking is back with a new theory: the hairy black hole hypothesis. His new theory solves the problem of what happens when information from the universe goes into black holes. His new paper titled, "Soft hair on black holes," could help him win his first Nobel prize. The 74-year-old British theoretical physicist said that black holes may have a head of hairs made of zero-energy particles. In August, Hawking exposed that he has the answers to the "black hole paradox". In the recently release paper, he dropped the first detailed discussion of his theory in an online published version at ArXiv. "Whether or not this is the final answer is totally unclear to us," co-author Malcolm Perry, a theoretical physicist at the University of Cambridge said. "We're saying that it's a step on the way," he added. According to the theory of relativity by Albert Einstein, whatever goes in the black hole, never comes out. Black holes are so massive that anything going inside or even just its edge is pulled in and lost forever. The black hole paradox emerged from his own work about 40 years ago. The previous theory proposed a mechanism in which information is lost forever. The paper, written in the '70s, contained information based on mathematical understanding of the time which says that black holes are featureless and bald spheres. In the current paper, however, Hawking and co-researchers tackled how the soft hair looks like and how it preserves information? He revisited his own calculations and found that massive black holes have additional distinguishing features known as "hairs". "We show that if you throw something at a black hole it in the right way, you can implant hair," Andrew Strominger of Harvard University said. Adding to Prof. Hawking's proposal in August 2015, information was said to not disappear in the black hole but instead stored at the event horizon. With co-researchers, they found that a soft, zero-energy photons retain the quantum state information of whatever comes into the massive cosmic black hole. Though they were able to explain the presence of soft hairs in black holes, the paper itself admits that there is still a lot of work to be done. "A complete description of the holographic plate and resolution of the information paradox remains an open challenge, which we have presented new and concrete tools to address," the researchers concluded. However, not all experts on this field are convinced of the new theory. "I am not at all convinced that the new idea proposed by Hawking, Perry, and Strominger solves the information loss problem. But it seems an interesting avenue that is worth further exploration. And I am sure we will see further exploration," Sabine Hossenfelder of the Nordic Institute for Theoretical Physics, wrote in a blog.

Loading Nordic Institute for Theoretical Physics collaborators
Loading Nordic Institute for Theoretical Physics collaborators