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Stumbled upon this the other day and have added the book to my TBR list:


From page:

This is something else that fascinates me. Sophia Leto touches on it a little in ANOMALY but I was tempted to add more in. It’s very strange how breaking scientific news in the past six months correlates exactly with the ideas for the science I had for the book.

No Big Bang? Quantum equation predicts universe has no beginning




5 Dimensional Black Holes May Break General Relativity

Original page via  Science Alert

If you thought regular black holes were about as weird and mysterious as space gets, think again, because for the first time, physicists have successfully simulated what would happen to black holes in a five-dimensional world, and the way they behave could threaten our fundamental understanding of how the Universe works.

The simulation has suggested that if our Universe is made up of five or more dimensions – something that scientists have struggled to confirm or disprove – Einstein’s general theory of relativity, the foundation of modern physics, would be wrong. In other words, five-dimensional black holes would contain gravity so intense, the laws of physics as we know them would fall apart.

There’s a lot to wrap your head around here, so let’s start with the black holes themselves. In a five-dimensional universe, physicists have hypothesised that black holes are more like very thin rings rather than holes, and as they evolve, they can give rise to a series of ‘bulges’ that become thinner and thinner over time, and eventually break off to form mini black holes elsewhere.

These ring-shaped black holes (or ‘black rings’) were first proposed in 2002, but until now, no one’s been able to successfully simulate their evolution. This has been made possible thanks to the COSMOS supercomputer at the University of Cambridge in the UK – the largest shared-memory computer in Europe that can perform 38.6 trillion calculations per second.


The problem with five-dimensional black holes is that they’re thought to consist of ‘ultragravity rings’, where gravity is so intense, it gives rise to a state known as naked singularity. Naked singularity is an event so strange, no one really knows what would occur, except that the laws of general relativity would no longer apply.

Einstein’s general theory of relativity is based on how we think gravity governs the behaviour of the Universe. We know that matter in the Universe warps the surrounding fabric of spacetime, and this warping effect is what we refer to as gravity. Since it was first proposed 100 years ago, general relativity has passed every test – everything we observe in the Universe follows its stipulations, but singularity can pose some problems.

In a four-dimensional universe (where the fourth dimension is time), singularity is thought to be the point of a black hole where gravity is at its most intense – the centre – and this is surrounded by the event horizon at the black hole’s edge.

“As long as singularities stay hidden behind an event horizon, they do not cause trouble and general relativity holds – the ‘cosmic censorship conjecture’ says that this is always the case,” says theoretical physicist Markus Kunesch from the University of Cambridge. “As long as the cosmic censorship conjecture is valid, we can safely predict the future outside of black holes.”

But what if singularity could exist outside a black hole’s event horizon? When Physicists have hypothesied that in five or more dimensions, if an object that has collapsed to an infinite density – singularity – is not bound by an event horizon, it becomes naked singularity, and things would get so crazy in and around that object, we’d need to completely rethink our understanding of how physics works. The whole thing just makes me really nervous.

“If naked singularities exist, general relativity breaks down,” said one of the team, Saran Tunyasuvunakool. “And if general relativity breaks down, it would throw everything upside down, because it would no longer have any predictive power – it could no longer be considered as a standalone theory to explain the Universe.”

If our Universe only has four dimensions, everything is cool, and ring-shaped black holes and naked singularity are not a thing. But physicists have proposed that our Universe could be made up of as many as 11 dimensions. The problem is that because humans can only perceive three, the only way we can possibly confirm the existence of more dimensions is through high-energy experiments such as the Large Hadron Collider.

Kunesch and his team say they’ve just about hit the limits of what their supercomputer can simulate, but would like to figure out what it is about four-dimensional universes that make naked singularity impossible, and general relativity correct. “If cosmic censorship doesn’t hold in higher dimensions, then maybe we need to look at what’s so special about a four-dimensional universe that means it does hold,” says Tunyasuvunakool.

The study has been published in Physical Review Letters, and for more on those 11 dimensions, here’s theoretical physicist, Michio Kaku:

The Big Deal About Gravitational Waves

Original article in ‘Nature’:

Gravitational waves: 6 cosmic questions they can tackle

The discovery of ripples in space-time will vindicate Einstein — but it can also do so much more.

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S. Shapiro, R. Gold, V. Paschalidis, M. Ruiz, Z. Etienne & H. Pfeiffer. Movie: S. Shapiro, S. Connelly, A. Khan and L. Kong

Mergers between black holes (simulation) are expected to be strong sources of gravitational waves.

The first direct detection of gravitational waves is now widely expected to be announced on 11 February by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO). Using LIGO’s twin giant detectors — one in Livingston, Louisiana, and the other in Hanford, Washington — researchers are said to have measured ripples in space-time produced by a collision between two black holes.

Such an announcement would vindicate Albert Einstein’s prediction of gravitational waves, which he made almost exactly 100 years ago1 as part of his general theory of relativity — but it would also have much further significance. As vibrations in the fabric of space-time, gravitational waves are often compared to sound, and have even been converted into sound snippets. In effect, gravitational-wave telescopes allow scientists to ‘hear’ phenomena at the same time as light-based telescopes ‘see’ them. (Already, members of LIGO and its  smaller counterpart Virgo in Pisa, Italy have set up a system for alerting communities working on other types of telescope).

When LIGO fought to get US government funding in the early 1990s, its major opponents at congressional hearings were astronomers3. “The general view was that LIGO didn’t have much to do with astronomy,” says Clifford Will, a general-relativity theorist at the University of Florida in Gainesville and an early LIGO supporter. But things have changed now, he says.

Welcome to the field of gravitational-wave astronomy2: we take a look at the questions and phenomena that it can explore.

Do black holes actually exist?

Black hole merger

A simulation of two black holes spiralling into each other, and the gravitational waves they would produce.

S. Shapiro, R. Gold, V. Paschalidis, M. Ruiz, Z. Etienne & H. Pfeiffer. Movie: S. Shapiro, S. Connelly, A. Khan and L. Kong.

The signal that LIGO is expected to announce on Thursday is rumoured to have been produced by two merging black holes. Such events are the most energetic known; the power of the gravitational waves that they emit can briefly rival that of all the stars in the observable Universe combined. Black-hole mergers are also among the cleanest gravitational-wave signals to interpret.

A black-hole merger occurs when two black holes start to spiral towards each other, radiating energy as gravitational waves. These waves should have a characteristic sound called a chirp, which can be used to measure the masses of the two objects. Next, the black holes actually fuse. “It’s as if you get two soap bubbles so close that they form one bubble. Initially, the bigger bubble is deformed,” says Thibault Damour, a gravity theorist at the Institute of Advanced Scientific Studies near Paris. The resulting single black hole will settle into a perfectly spherical shape, but first it is predicted to radiate gravitational waves in a pattern called a ringdown.

One of the most important scientific consequences of detecting a black-hole merger would be confirmation that black holes really do exist — at least as the perfectly round objects made of pure, empty, warped space-time that are predicted by general relativity. Another would be that mergers proceed as predicted. Astronomers already have plenty of circumstantial evidence for these phenomena, but so far that has come from observations of the stars and super-heated gas that orbit black holes, not of black holes themselves.

“The scientific community, including myself, has become very blasé about black holes. We have taken them for granted,” says Frans Pretorius, a specialist in general-relativity simulations at Princeton University in New Jersey. “But if you think of what an astonishing prediction it is, we really need astonishing evidence.”

Do gravitational waves travel at the speed of light?

When scientists start to compare observations from LIGO with those from other types of telescope, one of the first things that they will check is whether the signals arrive at the same time. Physicists hypothesize that gravity is transmitted by particles called gravitons, the gravitational analogue of photons. If, like photons, these particles have no mass, then gravitational waves would travel at the speed of light, matching the prediction of the speed of gravitational waves in classical general relativity. (Their speed can be affected by the accelerating expansion of the Universe, but that should manifest only over distances much greater than LIGO can probe4).

But it is possible that gravitons have a slight mass, which would mean that gravitational waves would travel at less than the speed of light. So if, say, LIGO and Virgo were to detect gravitational waves from a cosmic event, and find that the waves took slightly longer to arrive at Earth than the associated burst of γ-rays detected by a more conventional telescope, that could have momentous consequences for fundamental physics.

Is space-time made of cosmic strings?

Cosmic strings

A simulation of cosmic strings.

Mark Hindmarsh/University of Sussex.

An even weirder discovery would occur if bursts of gravitational waves were detected coming from ‘cosmic strings’. These hypothetical defects in the curvature of space-time, which may or may not be related to string theory, would be infinitesimally thin but would stretch across cosmic distances. Researchers have predicted that cosmic strings, if they exist, might occasionally develop kinks; if a string snapped, it would suddenly release a burst of gravitational waves, which detectors such as LIGO and Virgo could measure.

Are neutron stars rugged?

Neutron stars are the remnants of bigger stars that collapsed under their own weight, becoming so dense that they pushed their constituent electrons and protons to fuse into neutrons. Their extreme physics is poorly understood, but gravitational waves could provide unique insights. For example, the intense gravity at their surface tends to make neutron stars almost perfectly spherical. But some researchers have theorized that there could still be ‘mountains’ — at most a few millimetres high — that make these dense objects, themselves about 10 kilometres in diameter, slightly asymmetrical. Neutron stars usually spin very rapidly, so the asymmetric distribution of mass would deform space-time and produce a continuous gravitational-wave signal in the shape of a sine wave, which would radiate energy and slow down the star’s spin.

NASA’s Goddard Space Flight Center/S. Wiessinger

A ruptured neutron star (artist’s impression) could produce a burst of gravitational waves.

Pairs of neutron stars that orbit each other would also produce a continuous signal. Just like black holes, the stars would spiral into each other and eventually merge, sometimes producing an audible chirp. But their final instants would differ dramatically from those of black holes. “You have a zoo of possibilities, depending on masses and how much pressure neutron-dense matter can exert,” says Pretorius. For example, the resulting merged star could be a huge neutron star, or it could immediately collapse and turn into a black hole.

What makes stars explode?

Black holes and neutron stars form when massive stars stop shining and collapse in on themselves. Astrophysicists think that this process is what powers a common type of supernova explosion, known as Type II. Simulations of such supernovae have not yet clearly explained what ignites them, but listening to the gravitational-wave bursts that real supernova are expected to produce could help to provide an answer. Depending on what the bursts’ waveforms look like, how loud the bursts are, how frequent they are and how they correlate with the supernovae as seen with electromagnetic telescopes, the data could help to validate or discard various, existing models.

Zolt Levay/ESA/NASA

SN1006, a supernova remnant.

How fast is the Universe expanding?

The expansion of the Universe means that distant objects that are receding from our Galaxy look redder than they really are, because the light that they emit stretches as it travels. Cosmologists estimate the rate of the Universe’s expansion by comparing this redshift of galaxies with how far the galaxies are from us. But that distance is usually gauged from the brightness of ‘Type Ia’ supernovae — a technique that leaves large uncertainties.

If several gravitational-wave detectors across the world detect signals from the same neutron-star merger, together they will be able to provide an estimate of the absolute loudness of the signal, which will reveal how far away the merger occurred. They will also be able to estimate the direction it came from; astronomers could then deduce which galaxy hosted the merger. Comparing that galaxy’s redshift with the distance of the merger as measured by the loudness of the gravitational waves could provide an independent estimate of the rate of cosmic expansion, possibly more accurate than current methods.