Quantum bounce could make black holes explode : Nature News & Comment

Quantum bounce could make black holes explode : Nature News & Comment: The theory suggests that the transition from black hole to white hole would take place right after the initial formation of the black hole, but because gravity dilates time, outside observers would see the black hole lasting billions or trillions of years or more, depending on its size. If the authors are correct, tiny black holes that formed during the very early history of the Universe would now be ready to pop off like firecrackers and might be detected as high-energy cosmic rays or other radiation. In fact, they say, their work could imply that some of the dramatic flares commonly considered to be supernova explosions could in fact be the dying throes of tiny black holes that formed shortly after the Big Bang.

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.

Is Dark Matter a Glimpse of a Deeper Level of Reality?

Is Dark Matter a Glimpse of a Deeper Level of Reality?: Black holes provide the strongest argument for this point of view. The laws of gravity predict that these cosmic vacuum cleaners obey versions of the laws of thermodynamics, which is strange, because thermodynamics is the branch of physics that describes composite systems, such as gases made up of molecules. A black hole sure doesn’t look like a composite system. It just looks like a warped region of space that you would do well to stay away from. For it to be composite, space itself must be.

In that case, black holes represent a new phase of matter. Outside the hole, the universe’s “degrees of freedom”—all that its most fundamental building blocks are capable of—are in a low-energy state, forming what you might think of as a crystal, with a fixed, regular arrangement we perceive as the spacetime continuum. But inside the hole, conditions become so extreme that the continuum breaks apart. “You can make spacetime melt,” Verlinde told me. “This is really where spacetime ends. To understand what goes on, you need to use these underlying degrees of freedom.” Those degrees of freedom cannot be thought of as existing in one place or another. They transcend space. Their true venue is a ginormous abstract realm of possibilities—in the jargon, a “phase space” commensurate with their almost unimaginably rich repertoire of behaviors.

Physicists propose test for loop quantum gravity

Physicists propose test for loop quantum gravity: Now in a new study, scientists have found that, when black holes evaporate, the radiation they emit could potentially reveal “footprints” of loop quantum gravity, distinct from the usual Hawking radiation that black holes are expected to emit....
In their study, the scientists have used algorithms to show that primordial black holes are expected to reveal two distinct loop quantum gravity signatures, while larger black holes are expected to reveal one distinct signature. These signatures refer to features in the black hole’s energy spectrum, such as broad peaks at certain energy levels.
Using Monte Carlo simulations, the scientists estimated the circumstances under which they could discriminate the predicted signatures of loop quantum gravity and those of the Hawking radiation that black holes are expected to emit with or without loop quantum gravity. They found that a discrimination is possible as long as there are enough black holes or a relatively small error on the energy reconstruction.

Could the Big Bang have been a quick conversion of antimatter into matter?

Could the Big Bang have been a quick conversion of antimatter into matter?: ...Hajdukovic imagines the existence of a matter-antimatter repulsion that is significant only at short range; specifically, inside a black hole’s event horizon, or smaller than the Schwarzschild radius. Immediately after the gravitational Schwinger mechanism produces particle-antiparticle pairs, the repulsion force would cause a black hole to violently repel the opposite particle type. The result would be the conversion of nearly all matter into antimatter (or vice versa) in a very short time that depends on the size of the black hole.
Through calculations, Hajdukovic shows that the amount of matter that can be converted into antimatter (or vice versa) in one second could be up to 10128 kg, which is several orders of magnitude greater than the entire mass of the universe, about 1053 kg. If correct, it would mean that all of the matter in the universe could be converted into antimatter in a fraction of the Planck time...
... in his paper titled “Is dark matter an illusion created by the gravitational polarisation of the quantum vacuum,” he obtains a “striking equation” in agreement with observations and without invoking dark matter.

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...

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.

Gravity's bias for left may be writ in the sky - space - 05 March 2011 - New Scientist

Gravity's bias for left may be writ in the sky: The pair calculate that if gravity depended on just left or right-handed gravitons, that would have skewed the polarisation pattern in an obvious way. What's more, inflation would have stretched these effects to astronomical proportions, making them easily visible to astronomers...
Evidence of left-handed gravitons in the CMB would be "a triple discovery", says Lee Smolin of the Perimeter Institute in Waterloo, Ontario, Canada, who has worked with Magueijo and Benincasa on the subject. "It would confirm inflation, that gravity is quantum mechanical and that there is left-right asymmetry in quantum gravity."

Big bounce cosmos makes inflation a sure thing - space - 13 October 2010 - New Scientist

Big bounce cosmos makes inflation a sure thing: Enter loop quantum gravity, devised by Abhay Ashtekar of Pennsylvannia State University (PSU) in University Park and colleagues to reconcile general relativity with quantum mechanics. When Ashtekar's team created cosmological models inspired by LQG in 2006, these suggested the universe emerged from the remnants of an earlier universe that was crunched down to a tiny volume by gravity, not from the big bang (see diagram).

Now, together with David Sloan, also at PSU, Ashtekar has calculated the probability of inflation occurring after this big bounce. "We find that the probability of inflation is incredibly close to 1," he says.

Earlier simulations showed that the big bounce creates a repulsive force and so is always followed by a period of rapid expansion that is even faster than inflation. Dubbed superinflation, this episode doesn't last long enough to replace inflation. But the pair's latest calculations show that it has a profound effect on space-time, such that no matter what the initial properties are in the early universe, superinflation "funnels" all the possible ways in which space-time can evolve towards one in which inflation is a near certainty

Dimensions vanish in quantum gravity - physics-math - 22 September 2010 - New Scientist

Dimensions vanish in quantum gravity: "Carlip suggests that this foam behaves similarly to the space-time close to a singularity, the object at the centre of a black hole. According to general relativity, gravity is so strong near a singularity that space-time becomes distorted. Under these conditions, light is so strongly bent that it can take an infinitely long time to travel between nearby points. This means neighbouring patches of space-time become effectively disconnected from one another, allowing them to expand and contract independently.

Carlip suggests that at the tiny length scales of quantum gravity, the same sort of disconnection happens between different regions of space. This in turn allows space at different points to expand or contract faster in one dimension than in the others.

As a result, over very short distances and timescales, the motion of a particle is dominated by one dimension, though this favoured dimension keeps changing randomly. This means that if you wait long enough or look at larger distance scales, space becomes effectively three-dimensional."

Technology Review: Blogs: arXiv blog: Why Spacetime on the Tiniest Scale May Be Two-Dimensional

Technology Review: Blogs: arXiv blog: Why Spacetime on the Tiniest Scale May Be Two-Dimensional: "Carlip says recent work in loop quantum gravity, high temperature string theory, renormalization group analysis applied to general relativity and other areas of quantum gravity research, all hints at a two dimensional spacetime on the smallest scale. In most of these cases, the number of dimensions simply collapse in a process called spontaneous dimensional reduction as the scale reduces.

One obvious question is that if only two dimensions are present on this scale, which two are they? Carlip calculates that they must be one of time and one of space. 'At each point, the dynamics picks out a 'preferred' spatial direction, leading to approximately (1 1)-dimensional local physics,' he says."...

However, unlike many quantum gravity theorists, Carlip hints at the kind of experiments that might prove him right. "The process I have described breaks Lorentz invariance at the Planck scale, and even small violations at that scale can be magnified and lead to observable effects at large scales," he says.