Black Holes Aren’t Black After All, Say Theoretical Physicists — The Physics arXiv Blog — Medium

Black Holes Aren’t Black After All, Say Theoretical Physicists — The Physics arXiv Blog — Medium: Stephen Hawking proposed a potential solution earlier this year. His idea is that gravitational collapse can never continue beyond the so-called event horizon of a black hole beyond which information is lost. Gravitational collapse would approach the boundary but never go beyond it...

Micro-macro entangled 'cat states' could one day test quantum gravity

Micro-macro entangled 'cat states' could one day test quantum gravity: The proposed method involves storing one component of an entangled state of light (consisting of just one or a few photons) in a mechanical resonator (consisting of billions of atoms). During this process, the initial microscopic entangled state of photons is amplified with a strong coherent beam, the photons are converted into phonons, and then the entangled states are retrieved.
This approach makes it possible to create optomechanical "cat states," in which the quantum states of the photons and phonons are in superposition.

First glimpse of big bang ripples from universe's birth - physics-math - 17 March 2014 - New Scientist

First glimpse of big bang ripples from universe's birth - physics-math - 17 March 2014 - New Scientist: Inflation should have stretched the very first gravitational waves created during the big bang, taking them from imperceptible wavelengths to a size we can detect in the CMB... Rippling gravitational waves would subtly change the polarisation pattern, twisting the CMB into distinctive swirls called B-modes...

"We see a big excess of power, and it looks exactly like the gravitational wave signal that we had been seeking," says Pryke. "There's a huge zoo of inflationary models, but if we look at the simplest ones, they would predict values in the ballpark that we're seeing..."

"If gravity were not quantised, inflation would not produce gravitational waves," says Guth.

Why space has exactly three dimensions - physics-math - 26 September 2013 - New Scientist

Why space has exactly three dimensions - physics-math - 26 September 2013 - New Scientist: Quantum states are described not by 1D real numbers, which all lie on a single line, but by 2D complex numbers that represent points on a plane. The way these numbers interact to produce a complete description of objects such as photons that can be in more than one state at once naturally sketches out a 3D sphere describing all those possible states. Perhaps this result is just emphasising how the dimensionality of basic quantum objects and the dimensionality of space happen to be the same.

Müller thinks not: he thinks it points to an inextricable link between space's geometry and the degree of probability inherent in quantum theory. If so, the roots of relativity and quantum theory would be embedded in the way information is exchanged in the cosmos, suggesting where to look for any unifying theories. "It offers a clue that the notion of information will be an important part of quantum gravity," says Müller.

Physicists Discover Geometry Underlying Particle Physics | Simons Foundation

Physicists Discover Geometry Underlying Particle Physics | Simons Foundation: The amplituhedron looks like an intricate, multifaceted jewel in higher dimensions. Encoded in its volume are the most basic features of reality that can be calculated, “scattering amplitudes,” which represent the likelihood that a certain set of particles will turn into certain other particles upon colliding.

Wormhole entanglement solves black hole paradox - space - 20 June 2013 - New Scientist

Wormhole entanglement solves black hole paradox - space - 20 June 2013 - New Scientist:  First, the pair showed that these space-time tunnels, usually described by the maths of general relativity, also emerge from quantum theory, if two black holes are entangled. It's as if the wormhole is the physical manifestation of entanglement.

The pair then extended this idea to a single black hole and its Hawking radiation, resulting in a new kind of wormhole (see diagram). Crucially, they suggest that this wormhole, which links a black hole and its Hawking radiation, may not be a problem for quantum monogamy in the way that normal entanglement is. As a result, the firewall needn't appear, preserving relativity

Gravity-less toy black hole solves cosmic puzzles

Gravity-less toy black hole solves cosmic puzzles: His team modelled a minimal black hole, defined only by having an inside and an outside, using quantum theory. To their surprise, they found that this object reproduces a lot of the features of real black holes that are thought to rely on gravity, including Hawking radiation, which could occur via a process called quantum tunneling.

This chimes with suggestions that gravity is not a fundamental component of the universe but an emergent property of quantum mechanics, just as waves are an emergent property of water molecules.

Curves in spacetime violate Heisenberg's uncertainty principle

Curves in spacetime violate Heisenberg's uncertainty principle: "Deutsch's model describes the strange quantum effects that we might see in the presence of CTCs, within a future theory of quantum gravity," Pienaar said. "However, if there are no CTCs in the universe, then we would not expect to see the effects. But since the slowing of time due to gravity looks just like the effect of an OTC from the outside, and since OTCs still lead to strange effects (as we have shown), we suggested that these effects might turn up in strong gravitational fields, even without any closed loops in time. If so, then they would allow us to violate the Heisenberg uncertainty principle and clone coherent states of light without needing a full-blown time machine.

"Of course, the connection between OTCs and gravitational fields is still very speculative and might turn out to be wrong..."

Fairly Simple Math Could Bridge Quantum Mechanics and General Relativity

Fairly Simple Math Could Bridge Quantum Mechanics and General Relativity: The analysis does not model gravity explicitly, and so is not an attempt to formulate a theory of ‘quantum gravity’ that brings general relativity and quantum mechanics under one umbrella. Instead... their work might provide a simplified framework for understanding the effects of gravity on quantum particles, as well as describing other situations in which the spaces that quantum particles move in can radically alter, such as in condensed-matter-physics experiments...
Wilczek and his co-authors set up a hypothetical system with a single quantum particle moving along a wire that abruptly splits into two. The stripped-down scenario is effectively the one-dimensional version of an encounter with ripped space-time, which occurs when the topology of a space changes radically. The theorists concentrate on what happens at the endpoints of the wire — setting the ‘boundary conditions’ for the before and after states of the quantum wave associated with the particle. They then show that the wave can evolve continuously without facing any disruptions as the boundary conditions shift from one geometry to the other, incompatible one.

Quantum Horse Races and Crystals of Light

Quantum Horse Races and Crystals of Light: Bloch’s team and others bring them to heel by cooling them to a temperature of nanokelvins and pouring them into an optical lattice, which, depending on your poetic frame of mind, you might call an optical egg crate or a crystal of light... The atoms are spaced perhaps 400 nanometers apart, so they reach a density of about 100 trillion atoms per cubic centimeter—which is a lot of atoms per cubic centimeter, but still only about a hundred-thousandth the density of hydrogen gas at room temperature and pressure. So these systems let physicists explore a domain they seldom otherwise enter, a frigid, sparse realm where quantum is king...

There are all sorts of other fun experiments you can do. Last year, Bloch’s team tracked the insulator-superfluid transition and showed that the system goes through a “hidden” phase of matter—a subtly patterned arrangement that conventional theory doesn’t capture...

Yet another experiment touches on the fundamental question of what determines the speed of events in the world... They began with an insulator, dialed up the interaction energy, and watched the atoms start to self-organize. A wave of activity spread though the system at twice the speed of sound. What governed the velocity was that atoms did not passively roll on the wave, but actively contributed to it. Some quantum gravity theorists have speculated that the speed of light represents the Lieb-Robinson bound of some underlying quantum system out of which space and time emerge.

Black Holes, Safety, and the LHC Upgrade - Technology Review

Black Holes, Safety, and the LHC Upgrade - Technology Review: These guys assume that after microscopic black holes form, they would go through four phases. First there is the balding phase in which the newly formed back hole evolves from a highly asymmetric object to a more symmetric one, shedding its asymmetry through gravitational radiation.

In the second phase, called the spin-down phase, the black hole loses mass and angular momentum by emitting Hawking radiation. The third, the Schwarzschild phase, the black hole becomes spherical and the rate of mass loss slows down. And in the final Planck phase, the black hole winks out of existence.

One weird theory could make anti-gravity and faster-than-light travel possible

One weird theory could make anti-gravity and faster-than-light travel possible: Heim Theory was originated by Burkhard Heim, a German physicist, in the mid-twentieth century. It was attempted as a way to reconcile the two pillars of physics, quantum theory and general relativity. It takes what's currently the only way out, between the two theories - extra dimensions...
Heim's goal was to find ways to convert between all kinds of energy, and in adding two dimensions to his calculations he was able to equate, at least in theory, gravitational energy and electromagnetism.

One clock with two times: When quantum mechanics meets general relativity

One clock with two times: When quantum mechanics meets general relativity: The team at the University of Vienna considers a single clock (any particle with evolving internal degrees of freedom such as spin) which is brought in a superposition of two locations – one closer and one further away from the surface of the Earth. According to general relativity, the clock ticks at different rates in the two locations, in the same way as the two twins would age differently. But since the time measured by the clock reveals the information on where the clock was located, the interference and the wave-nature of the clock is lost. "It is the twin paradox for a quantum 'only child', and it requires general relativity as well as quantum mechanics. Such an interplay between the two theories has never been probed in experiments yet..."

Hologram revolution: The theory changing all physics - physics-math - 13 July 2011 - New Scientist

Hologram revolution: The theory changing all physics: Leonard Susskind of Stanford University in California, one of the original architects of the holographic principle, describes the duality as the "new orthodoxy". Skenderis is convinced that we are only just beginning to see its potential. "If we look forward to 50 years from now, we will see this period as a precursor to a time when physics is totally reformulated in the language of holography," he says. "Once the theory is properly fleshed out, we will be able to apply it to almost any problem."

Distant light hints at size of space-time grains - space - 07 July 2011 - New Scientist

Distant light hints at size of space-time grains: terrestrial telescopes... have seen low-energy photons from a gamma-ray burst (GRB) arriving before their high-energy counterparts. While this could be due to delays in emission at the source, it could also be caused by the interaction of photons with the structure of space-time...
Now a team has used data from the Integral satellite, run by the European Space Agency (ESA), to study an entirely different effect: the polarisation of light of different energies from a GRB...
this puts an important limit on the size of the grains of space-time. According to an ESA press release, it means they must be smaller than 10-48 metres, many orders of magnitude smaller than the Planck length of 10-35 metres, the universe's smallest length scale...

Graphene may reveal the grain of space-time - physics-math - 13 May 2011 - New Scientist

Graphene may reveal the grain of space-time: So how about the electron's intrinsic spin? It cannot be a rotation in the ordinary sense, as electrons are point particles with no radius and no innards. Instead, like pseudospin, it might come from a lattice pattern in space-time itself, says Regan. This echoes some attempts to unify quantum mechanics with gravity in which space-time is built out of tiny pieces or fundamental networks

Observations: Garrett Lisi Responds to Criticism of his Proposed Unified Theory of Physics

Observations: Garrett Lisi Responds to Criticism of his Proposed Unified Theory of Physics:  Distler's colleagues also wrote a letter to the editor of Scientific American decrying the lack of parity violation. This fact would seem very damning for E8 Theory, but it is simply not true. The structure of gravity and the Standard Model along with one generation of fermions (including their parity-violating interactions) does fit in E8, as I described explicitly in a recent paper. In their misleading argument, Distler and Garibaldi make unnecessary assumptions about how the embedding needs to happen, and then prove it can't happen that way -- a "straw man" argument.

Out Of The Fabric - Science News

Out Of The Fabric - Science News: Further study of spaceless theories may help solve serious problems confronting physicists today, Seiberg believes. String theory implies countless possible vacuum states — that is, spaces of differing physical properties — with no obvious method for determining which one the visible universe should have chosen. Knowing how space emerges from spacelessness might help explain why humans exist in one particular space from among the countless possibilities.

Doing away with time poses more difficult problems, Seiberg acknowledges. Basic notions in physics, such as that of causes preceding effects, or predicting the outcome of experiments before the experiment is done, seem to lose their meaning if there is no time to define before and after. So some physicists, Markopoulou for one, have suggested that even if space is emergent, time may remain fundamental. In fact, she conjectures, time is needed to allow quantum processes to create the illusion of space. Space may not have been around at the beginning, but that beginning would be stillborn without time to get reality going.

Doubly special relativity

Doubly special relativity: It turns out that at the Planck scale e = m, even though at macro scales e=mc2. And at the Planck scale, a Planck mass is 2.17645 × 10-8 kg – supposedly the mass of a flea’s egg – and has a Schwarzschild radius of a Planck length – meaning that if you compressed this mass into such a tiny volume, it would become a very small black hole containing one Planck unit of energy.
To put it another way, at the Planck scale, gravity becomes a significant force in quantum physics. Although really, all we are saying that is that there is one Planck unit of gravitational force between two Planck masses when separated by a Planck length – and by the way, a Planck length is the distance that light moves within one unit of Planck time!
And since one Planck unit of energy (1.22×1019 GeV) is considered the maximal energy of particles – it’s tempting to consider that this represents conditions expected in the Planck epoch, being the very first stage of the Big Bang.

Physicists investigate lower dimensions of the universe

Physicists investigate lower dimensions of the universe: So far, there may already be one piece of experimental evidence for the existence of a lower-dimensional structure at a higher energy scale. When observing families of cosmic ray particles in space, scientists found that, at energies higher than 1 TeV, the main energy fluxes appear to align in a two-dimensional plane. This means that, above a certain energy level, particles propagate in two dimensions rather than three dimensions.

In the current study, Mureika and Stojkovic have proposed a second test for lower dimensions that would provide independent evidence for their existence. The test is based on the assumption that a (2 + 1)-dimensional spacetime, which is a flat plane, has no gravitational degrees of freedom. This means that gravity waves and gravitons cannot have been produced during this epoch. So the physicists suggest that a future gravitational wave detector looking deep into space might find that primordial gravity waves cannot be produced beyond a certain frequency, and this frequency would represent the transition between dimensions. Looking backwards, it would appear that one of our spatial dimensions has “vanished.”
The scientists added that it should be possible, though perhaps more difficult, to test for the existence of (1 + 1)-dimensional spacetime.