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"Everything should be as simple as it is, but not simpler", Albert Einstein
Browsing All Posts filed under »RELATIVITY«
Interfering atoms could help detect gravitational waves
Scientists in California have proposed a new type of gravitational-wave detector that is immune to laser noise – a problem that adds to the expense of current detector designs. The researchers believe that their proposal – a modified form of an atom interferometer – would be cheaper and easier to implement in space than current […]
Einstein’s gravity theory passes toughest test yet
April 25, 2013
Record-breaking pulsar takes tests of general relativity into new territory Astronomers have used ESO’s Very Large Telescope, along with radio telescopes around the world, to find and study a bizarre stellar pair consisting of the most massive neutron star confirmed so far, orbited by a white dwarf star. This strange new binary allows tests of […]
Gravity-less toy black hole solves cosmic puzzles
March 26, 2013
With a pull so strong not even light escapes, a black hole is defined by its gravity. But now a model that ignores gravity is proving surprisingly useful for pinning down how these cosmic giants work. Black holes are where big ideas in cosmology, such as gravity and quantum mechanics, collide. That makes them great […]
Ultrarelativistic Black Hole Formation
March 13, 2013
William E. East, Frans Pretorius We study the ultrarelativistic head-on collision of equal mass particles, modeled as self-gravitating fluid spheres, by numerically solving the coupled Einstein-hydrodynamic equations. We focus on cases well within the kinetic energy dominated regime, where between 88-92% (γ=8 to 12) of the initial net energy of the spacetime resides in the […]
Black Hole Complementarity and the Harlow-Hayden Conjecture
January 22, 2013
Leonard Susskind Black hole complementarity, as originally formulated in the 1990′s by Preskill, ‘t Hooft, and myself is now being challenged by the Almheiri-Marolf-Polchinski-Sully firewall argument. The AMPS argument relies on an implicit assumption—the “proximity postulate—which says that the interior of a black hole must be constructed from degrees of freedom that are physically near […]
Common physics among black holes
December 13, 2012
A Universal Scaling for the Energetics of Relativistic Jets from Black Hole Systems R. S. Nemmen, M. Georganopoulos, S. Guiriec, E. T. Meyer, N. Gehrels, R. M. Sambruna Black holes generate collimated, relativistic jets, which have been observed in gamma-ray bursts (GRBs), microquasars, and at the center of some galaxies [active galactic nuclei (AGN)]. How […]
Space-time waves may be hiding in dead star pulses
December 8, 2012
by Lisa Grossman TAKE the pulse of the universe, and its invisible wrinkles become visible. The first direct evidence of Einstein’s gravitational waves, may already exist in records of light pulses from rapidly spinning dead stars. Crucially, we may uncover those waves as early as 2013. New research suggests that we’ve underestimated the rate at […]
How Einstein Discovered Dark Energy
December 1, 2012
Alex Harvey In 1917 Einstein published his Cosmological Considerations Concerning the General Theory of Relativity. In it was the first use of the cosmological constant. Shortly thereafter Schröodinger presented a note providing a solution to these same equations with the cosmological constant term transposed to the right hand side thus making it part of the […]
First Observation of Gravitational Waves is ‘Imminent’
November 26, 2012
Gravitational waves are ripples in the fabric of spacetime caused by cataclysmic events such as neutron stars colliding and black holes merging. The biggest of these events, and the easiest to see, are the collisions between supermassive black holes at the centre of galaxies. So an important question is how often these events occur. Today, […]
Thermodynamics of a Black Hole with Moon
November 13, 2012
Samuel E. Gralla, Alexandre Le Tiec For a rotating black hole perturbed by a particle on the “corotating” circular orbit (angular velocity equal to that of the event horizon), the black hole remains in equilibrium in the sense that the perturbed event horizon is a Killing horizon of the helical Killing field. The associated surface […]
Why Einstein never received a Nobel prize for relativity
October 8, 2012
Nobel prizes often attract controversy, but usually after they have been awarded. Albert Einstein’s physics prize was the subject of argument for years before it was even a reality Stuart Clark - guardian.co.uk There was a lot riding on Einstein winning a Nobel prize. Beyond his academic reputation, and that of the Nobel Institute for recognising greatness, […]
Ripping a hole in space and time
October 6, 2012
By Kenneth Macdonald In an unassuming laboratory at Heriot-Watt University in Edinburgh, they are ripping a hole in the fabric of space and time. Not too far away, they are working with information that can mean two things at once. They are two separate studies, but what they have in common is the interaction of […]
Gravitational Field Equations and Theory of Dark Energy and Dark Matter
September 7, 2012
Mathematicians offer unified theory of dark matter, dark energy, altering Einstein field equations A pair of mathematicians—one from Indiana University and the other from Sichuan University in China—have proposed a unified theory of dark matter and dark energy that alters Einstein’s equations describing the fundamentals of gravity. Shouhong Wang, a professor in the IU College […]
Space-time ripples record black hole crashes
August 19, 2012
Did monster black holes pull the first galaxies together, or were they born inside those galaxies? It’s a long-standing mystery. Now a new analysis of the gravitational ripples from colliding black holes could reveal the answer by helping astronomers reconstruct a crash rather than just surveying its aftermath. Most large galaxies we see have supermassive black holes […]
An Underlying Theory for Gravity
August 18, 2012
Yuan K. Ha A new direction to understand gravity has recently been explored by considering classical gravity to be a derived interaction from an underlying theory. This underlying theory would involve new degrees of freedom at a deeper level and it would be structurally different from classical gravitation. It may conceivably be a quantum […]
Einstein’s Equations, Cosmology and Astrophysics
August 18, 2012
Paul S. Wesson I give a compact, pedagogical review of our present understanding of the universe as based on general relativity. This includes the uniform models, with special reference to the cosmological ‘constant’; and the equations for spherically-symmetric systems, in a particularly convenient form that aids their application to astrophysics. New ideas in research are […]
Most distant black hole ‘heard’ munching star
August 3, 2012
by Kelly Oakes The wobbles in energy produced as a black hole consumes a star have been detected from further away than ever before. Because they are so regular, their discoverer likes to think of the wobbles as a kind of sound. “We are able to metaphorically hear a star being devoured by a supermassive […]
Measuring g with a beam of antihydrogen
August 1, 2012
AEgIS is a physics experiment that takes place at the european laboratory CERN, using the antiprotons delivered by the AD accelerator. AEgIS is a collaboration of physicists from all around the world. The primary scientific goal of the AEgIS experiment is the direct measurement of the Earth’s gravitational acceleration g on antihydrogen. In the first […]
Probing gravity
July 30, 2012
Einstein’s theory of relativity is remarkable not only because it is so successful in explaining seemingly bizarre observations (like the bending of starlight) or because it has assembled a coherent picture of nature. One would expect these results from any good theory. Relativity is also amazing because its has shown that the universe behaves in […]
Machian gravity and the giant galactic forces
June 30, 2012
Santanu Das One of the main motivations behind formulating the general theory of relativity was to provide a mathematical description to the Machian gravity’s principle. However, soon after its formulation, it was realized that the theory does not follow Mach’s principle. As the theoretical predictions were matching with the observations, Einstein believed that the theory […]
Is science without spacetime possible?
June 28, 2012
Nick Huggett, Christian Wuthrich Numerous approaches to a quantum theory of gravity posit fundamental ontologies that exclude spacetime, either partially or wholly. This situation raises deep questions about how such theories could relate to the empirical realm, since arguably only entities localized in spacetime can ever be observed. Are such entities even possible in a […]
Super Physics Smackdown: Relativity v Quantum Mechanics…In Space
June 25, 2012
The only way to study the conflict between relativity and quantum mechanics is to test them over enormous distances in space. And physicists are already making plans One of the great puzzles of modern science is that the laws that govern the universe on the largest scale are entirely different from the ones that govern […]
Torques without Rotation: the Right-Angle Lever
June 21, 2012
Joel A. Shapiro An extended body subject to external forces which exert zero net force and zero total torque in the rest frame, may experience a nonzero torque in another inertial frame, and nonetheless does not rotate. Long known as the Trouton-Noble or right-angle lever paradox, there has been extensive discussion and indeed controversy, but […]
Teaching General Relativity To Undergraduates
June 5, 2012
Here’s an article in this month’s Physics Today on what is needed to teach General Relativity in an undergraduate physics curriculum. Not sure how effective it is, but it is certainly worth an attempt, I suppose. This is in line with Hartle’s earlier paper in AJP on teaching this same subject to the same group of […]
From black holes to strange metals
June 2, 2012
Hong Liu Ever since the end of the Stone Age, metals have fascinated humankind and have been vital in the development of civilization. More recently, physicists have been fascinated by a new class of “strange” metals, discovered two decades ago, whose exotic properties challenge fundamental notions of condensed-matter physics. In this Quick Study I describe […]
Still waiting to catch the gravitational wave
May 5, 2012
European Space Agency (Esa) member states have decided to select a mission to Jupiter and its icy moons as their next great venture. Juice, as the spacecraft is currently known, will leave Earth in 2022 on a long journey that should see it returning science from the outer Solar System in the 2030s. The champagne […]
Trouble with the Lorentz law of force
May 3, 2012
Incompatibility with special relativity and momentum conservation Masud Mansuripur The Lorentz law of force is the fifth pillar of classical electrodynamics, the other four being Maxwell’s macroscopic equations. The Lorentz law is the universal expression of the force exerted by electromagnetic fields on a volume containing a distribution of electrical charges and currents. If electric […]
The twin paradox in relativity revisited
April 26, 2012
Vasant Natarajan The accepted resolution of the twin paradox in relativity states that the age of the inertial twin `jumps’ when the traveling twin undergoes his turn-around acceleration. This resolution is based on the use of the equivalent gravitational shift in the frame of the accelerating twin. We use the same analysis to propose a […]
The analogue cosmological constant in Bose-Einstein condensates….
April 16, 2012
… a lesson for quantum gravity Stefano Finazzi, Stefano Liberati, Lorenzo Sindoni For almost a century, the cosmological constant has been a mysterious object, in relation to both its origin and its very small value. By using a Bose-Einstein condensate analogue model for gravitational dynamics, we address here the cosmological constant issue from an analogue […]
Footprints of Higher-Dimensional Decaying Black Holes
April 12, 2012
Panagiota Kanti We review the current results for the emission of Hawking radiation by a higher-dimensional black hole during the Schwarzschild and the spin-down phases. We discuss particularly the role of the angular variation of the emitted radiation on the brane during the latter phase, the radiation spectra for gravitons in the bulk, and the […]
Can GPS find variations in Planck’s constant?
March 28, 2012
Read more: physicsworld.com/cws/article/news/49135 Global Positioning System Test of the Local Position Invariance of Planck’s Constant J. Kentosh and M. Mohageg Phys. Rev. Lett. 108, 110801 (2012) Published March 15, 2012 Pinpointing Planck’s Constant with GPS GPS is helping drivers find their way and parents track their kids and pets. But now a pair of researchers—reporting in Physical Review Letters—has used […]
Looking at quantum gravity in a mirror
March 18, 2012
Einstein’s theory of gravity and quantum physics are expected to merge at the Planck-scale of extremely high energies and on very short distances. At this scale, new phenomena could arise. However, the Planck-scale is so remote from current experimental capabilities that tests of quantum gravity are widely believed to be nearly impossible. Now an international […]
Network Cosmology
March 17, 2012
Dmitri Krioukov, Maksim Kitsak, Robert S. Sinkovits, David Rideout, David Meyer, Marian Boguna Causal sets are an approach to quantum gravity in which the causal structure of spacetime plays a fundamental role. The causal set is a quantum network which underlies the fabric of spacetime. The nodes in this network are tiny quanta of spacetime, […]
Intergalactic subway: All aboard the wormhole express
March 12, 2012
Video: What it would look like to travel through a wormhole IT IS not every day that a piece of science fiction takes a step closer to nuts-and-bolts reality. But that is what seems to be happening to wormholes. Enter one of these tunnels through space-time, and a few short steps later you may emerge near […]
Artificial Braneworlds Made to Collide In Lab
January 30, 2012
Physicists have simulated two universes colliding inside a metamaterial One interesting way in which our cosmos may have formed is in a collision between two other universes with extra spatial dimensions called braneworlds. In this scenario, known as the ekpyrotic model of the universe, our cosmos is just a small four-dimensional corner of a much […]
Are OPERA neutrinos faster than light because of non-inertial reference frames?
January 22, 2012
Claudio Germana ABSTRACT Recent results from the OPERA experiment reported a neutrino beam traveling faster than light. The experiment measured the neutrino time of flight (TOF) over a baseline from the CERN to the Gran Sasso site. The neutrino beam arrives 60 ns earlier than a light ray would do. Because the result has an […]
The Computing Spacetime
January 18, 2012
Fotini Markopoulou The idea that the Universe is a program in a giant quantum computer is both fascinating and suffers from various problems. Nonetheless, it can provide a unified picture of physics and this can be very useful for the problem of Quantum Gravity where such a unification is necessary. In previous work we proposed […]
New telescope array will capture the first-ever photograph of a black hole
January 16, 2012
A new telescope array could allow scientists to photograph a black hole for the first time – teaming up 50 radio telescopes around the world into a global telescope that will capture the ‘shadow’ of a black hole for the first time. Scientists will meet on Wednesday 18th to discuss the project, which will also […]
Black holes without spacelike singularities
January 14, 2012
Mihalis Dafermos It is shown that for small, spherically symmetric perturbations of asymptotically flat two-ended Reissner-Nordstrom data for the Einstein-Maxwell-real scalar field system, the boundary of the dynamic spacetime which evolves is globally represented by a bifurcate null hypersurface across which the metric extends continuously. Under additional assumptions, it is shown that the Hawking mass […]
The fastest way to circle a black hole
January 4, 2012
Shahar Hod Black-hole spacetimes with a “photonsphere”, a hypersurface on which massless particles can orbit the black hole on circular null geodesics, are studied. We prove that among all possible trajectories (both geodesic and non-geodesic) which circle the central black hole, the null circular geodesic is characterized by the shortest possible orbital period as measured […]
Martin Rees: Stephen Hawking at 70
January 2, 2012
Astronomer royal and master of Trinity College, Cambridge. Like Hawking, he studied under Dennis Sciama in the 1960s I first met Stephen in 1964. I was in my first week as a Cambridge graduate student. He was two years ahead of me in his studies – but already unsteady on his feet and speaking with […]
Did Poincaré discover Special Relativity?
December 18, 2011
Poincaré and Special Relativity Emily Adlam Henri Poincare’s work on mathematical features of the Lorentz transformations was an important precursor to the development of special relativity. In this paper I compare the approaches taken by Poincare and Einstein, aiming to come to an understanding of the philosophical ideas underlying their methods. In section (1) I […]
Toward a fully relativistic theory of quantum information
December 9, 2011
Christoph Adami Information theory is a statistical theory dealing with the relative state of detectors and physical systems. Because of this physicality of information, the classical framework of Shannon needs to be extended to deal with quantum detectors, perhaps moving at relativistic speeds, or even within curved space-time. Considerable progress toward such a theory has […]
Relativity on Rotated Graph Paper
December 3, 2011
Roberto B. Salgado We present visual calculations in special relativity using spacetime diagrams drawn on graph paper that has been rotated by 45 degrees. The rotated lines represent lightlike directions in Minkowski spacetime, and the boxes in the grid (called “light-clock diamonds”) represent units of measurement modeled on the ticks of an inertial observer’s lightclock. […]
On the invariance of the speed of light
November 30, 2011
Harihar Behera, Gautam Mukhopadhyay The invariance of the speed of light in all inertial frames – the second postulate of special theory of relativity (STR) – is shown to be an inevitable consequence of the relativity principle of special theory of relativity taken in conjunction with the homogeneity of space and time in all inertial […]
How Superconductors Can Detect Gravitational Waves
November 15, 2011
Superconducting metal bars could revolutionise the detection of gravitational waves, says physicists Gravitational waves are vibrations in the fabric of spacetime. They are among the most exciting phenomena in the universe because they are generated by exotic processes such as collisions between black holes and even in the moment of creation itself, the Big Bang. […]
Relativistic quantum information and time machines
November 14, 2011
Timothy C. Ralph, Tony G. Downes Relativistic quantum information combines the informational approach to understanding and using quantum mechanics systems – quantum information – with the relativistic view of the universe. In this introductory review we examine key results to emerge from this new field of research in physics and discuss future directions. A particularly […]
Reactionaries and Einstein’s Fame…
November 12, 2011
…. “German Scientists for the Preservation of Pure Science,” Relativity, and the Bad Nauheim Meeting Jeroen van Dongen Two important and unpleasant events occurred in Albert Einstein’s life in 1920: That August an antirelativity rally was held in the large auditorium of the Berlin Philharmonic, and a few weeks later Einstein was drawn into a […]
The equation of “Nothing”
November 5, 2011
On ‘Nothing’ Adam R. Brown and Alex Dahlen Abstract Nothing-the absence of spacetime-can be either an endpoint of tunneling, as in the bubble of nothing, or a starting point for tunneling, as in the quantum creation of a universe. We argue that these two tunnelings can be treated within a unified framework, and that, in […]
May 3, 2013
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