What if LIGO Actually Proved Einstein Wrong – and Found Signs of Quantum Gravity?

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What if LIGO Actually Proved Einstein Wrong – and Found Signs of Quantum Gravity?

By Vasudevan Mukunth on 14/12/2016 •

Three physicists have predicted that finding ‘echoes’ of gravitational waves coming from blackhole mergers might be signs of a theory that finally unifies quantum mechanics and general relativity.

A computer simulation shows two neutron stars, the extremely dense cores of now-dead stars, smashing into each other to form a blackhole. Credit: NASA Goddard Space Flight Centre/Flickr, CC BY 2.0

Your high-school physics teacher would’ve likely taught you to think about the smallest constituents of nature by asking you to start with a large object – like a chair – and then keep breaking it down into smaller bits. For the purposes of making sense of your syllabus, you probably stopped at protons, electrons and neutrons. That’s a pity because, if you’d kept going, you’d have stumbled upon some of the biggest mysteries of the universe. At some point, you’d have hit the Planck scale: the smallest region of space, the shortest span of time. This is the smallest scale that quantum mechanics can make sense of, and this is where many physicists expect to find the fundamental particles that make up space itself.
If this region – or some phenomena that are thought to belong exclusively to this region – are found, then physicists will have made a stunning discovery. Apart from finding the ‘atoms’ of space itself, they’d have opened the doors to marrying the two biggest theories of physics: quantum mechanics and the theory of general relativity (GR). The former’s demesne is the small and smaller particles you passed along the way to the Planck scale. The latter’s is the largest distances and spans of time in the universe. And the discovery would be stunning because GR, created by Albert Einstein 101 years ago, doesn’t allow space to have any constituent ‘atoms’. For GR, space is smooth. And it is this fundamental conflict that has prevented the theories from being reconciled into a single ‘quantum gravity’ theory.
But the first signs of change might be here.
In 2015, the twin Laser Interferometer Gravitational-wave Observatories (LIGO) in the US had made the first direct detection of gravitational waves. These are ripples of energy sent strumming through space at the speed of light when a massive object accelerates. LIGO had in fact detected gravitational waves created by two blackholes that were spinning rapidly around each other before colliding and merging to form a larger blackhole. The discovery was unequivocal proof that Einstein’s GR was valid and realistic. But curiously enough, three physicists recently announced that the discovery may have in fact achieved the opposite: invalidate GR and instead signal proof that the first signs of quantum gravity may have been found.
A blackhole is a particularly interesting thing. One is formed when the core of a dying star of a certain kind becomes so massive that, after the initial supernova explosion, it collapses inwards, tightly curving space around itself such that even light can’t escape its prodigious gravity. A blackhole is a consequence of GR – though Einstein didn’t himself predict its existence first. At the same time, because of its freaky nature, a blackhole also often exhibits quantum mechanical properties that physicists have been interested in for their potential to reveal something about quantum gravity. And many of these properties have to do with the blackhole’s outer shell: the event horizon, behind which nothing can escape the blackhole’s heart no matter how fast it is moving away.
GR can’t perfectly predict what the insides of a blackhole are like – and the theory simply breaks down when it comes to the blackhole’s heart itself. But using LIGO’s data when it tuned in to the mergers of two blackhole-pairs in 2015, three physicists are now saying there’s some reason to believe GR may be breaking down at the event horizon itself. They say they are motivated by having spotted signs (in the data) of a quantum-gravity effect known simply as an echo.
According to GR, the event horizon is a smooth and infinitely thin surface: at any given moment, you’re either behind it, falling into the blackhole, or in front of it, looking into the abyss that is the blackhole. But according to quantum mechanics, the event horizon is actually a ‘firewall’ of particles popping in and out of existence. You step into it and you’re immediately incinerated. But apart from making for an interesting gedanken experiment about suicidal astronauts, the existence of such a firewall can have very real consequences.
When two blackholes collide to form a larger blackhole, there is a very large amount of energy released. In LIGO’s first detection of a merger, made on September 14, 2015, two blackholes weighing 29 and 36 solar masses merged to form a blackhole weighing 62 solar masses. The remaining three solar masses – equivalent to 178.7 billion trillion trillion trillion joules of energy – were expelled as gravitational waves. If GR has its way, with an infinitely thin event horizon, then the waves are immediately expelled into space. However, if quantum mechanics has its way, then some of the waves are first trapped inside the firewall of particles, where they bounce around like echoes depending on the angle at which they were ensnared, and escape in instalments. Corresponding to the delay in setting off into space, LIGO would have detected them similarly: not arriving all at once but with delays.

LIGO original template for GW150914, along with Abedi-Dykaar-Afshordi’s best fit template for the echoes. Caption and credit: arXiv:1612.00266

The three physicists – Jahed Abedi, Hannah Dykaar and Niayesh Afshordi – simulated firewall-esque conditions using mirrors placed close to a computer-simulated blackhole to determine the intervals at which gravitational echoes from each of the three events LIGO has detected so far would arrive at. When they had their results, they went looking for similar signals in the LIGO data. In a pre-print paper uploaded to the arXiv server on December 1, the trio writes that it did find them, with a statistical significance of 2.9 sigma. This is a mathematical measure of confidence that’s not good enough to technically be considered evidence (3 sigma), let alone proof of any kind (5 sigma). And when tested for each event, the odds are lower: they max out at 2 sigma in the case of the merger known as GW150914, the first one that LIGO detected. Finally, even if the signal persists, it might not ultimately be due to quantum gravity at all but some other sources.
Nonetheless, the significance isn’t zero – and the LIGO team has confirmed that it is looking for more signs of echoes in its data. Luckily for everyone, the detectors also recently restarted with upgrades to make it more sensitive, to more accurately study the gravitational wave signals arising from blackholes of diverse masses. If future experiments can’t detect stronger echoes (or eliminate existing sources of noise that could be clouding observations), then that’s that for this line of verifying quantum gravity. But until then, it wouldn’t be amiss to speculate on its veracity – or on variations of it that might yield better results, results closer to LIGO’s capabilities – if only because the data LIGO collects for each merger is so complex.
Ultimately, the most heartening takeaway from the Abedi-Dykaar-Afshordi thesis is that there is an experimental way to confirm the predictions of quantum gravity at all. Physicists have long held it to be out of human reach. This is obvious when you realise the Planck length is 100-billion-billion-times smaller than the diameter of a proton and the Planck second is 10-billion-billion-billion-times smaller than the smallest unit of time that some of the most powerful atomic clocks can measure. If quantum gravity is a true theory, then it will be to nature’s unending credit that it spawned blackholes that can magnify the effects of such infinitesimal provenance – and to humankind’s for building machines that can eavesdrop on them.
An Indian LIGO detector is currently under development and is expected to join the twin American ones to study gravitational waves by 2023.
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What would happen if asteroid struck the ocean["not a hell of a lot we can do at the moment"].'

What would REALLY happen if an asteroid struck the ocean: Simulation reveals impact would launch BILLIONS of tons of water into the atmosphere

If it hit far from coastlines, massive waves would die down before hitting cities
But, impact would have devastating effects if within 10-20km from the coast
Bigger threat would come from billions of tons of water vapor injected in the air
This could loft into the stratosphere and linger for months, altering the climate

By Cheyenne Macdonald For Dailymail.com

Published: 22:00 GMT, 14 December 2016 | Updated: 23:03 GMT, 14 December 2016

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If an asteroid were to slam into Earth, there’s a strong chance it would end up at sea, with oceans covering roughly 70 percent of our planet’s surface.

An impact would have devastating effects if it occurred within 10-20 kilometers of a city's coastline, potentially killing thousands of people - but if it hit out in the middle of the ocean, the massive waves generated by the collision would quickly die down.

A new simulation reveals that the destructive waves would be unable to travel long distances, preventing city-swallowing tsunamis from reaching the shorelines.

Water vapour, instead, could pose a larger threat – the impact would launch billions of tons of the greenhouse gas into the air, with potential to linger in the stratosphere for months or even years.

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The visualization from the Los Alamos National Laboratory shows what would happen if an asteroid slammed into the ocean. This revealed that, if it occured far from the coastlines, the threat of a tsunami hitting cities would be low. But, water vapour would pose a greater risk

WHAT WOULD HAPPEN

If an asteroid struck the ocean, the researchers say it would create a transient crater, launching a splash curtain into the air.

As water rushes into the crater, a jet would form - and this could be several kilometers high.

The jet would then collapse to form a rim wave, which would be hundreds of meters high.

A new water jet would form, and create a new rim wave, and the process would go on.

Each rim wave has potential to become a tsunami, the researchers explain.

Far away from the coastlines, however, the risks to populated areas would be low.

A larger threat may come from the large amounts of water vapour sent into the air, which would be lofted into the stratosphere.

The greenhouse gas could linger for months or years, with severe implications for the global climate.

The new visualization from the Los Alamos National Laboratory comes as a result of NASA’s Second International Workshop on Asteroid Threat Assessment.

Given the likelihood of an asteroid making impact with the ocean if it were set to hit Earth, the researchers explored what the risks of a resulting tsunami would be.

Scientists at LANL used high performance computing to investigate how an asteroid’s kinetic energy is transferred to the atmosphere and the ocean.

They created simulations with varying asteroid size, angle of impact, and whether or not it exploded in an airburst.

The simulations focused on three materials: basalt asteroid, static air, and static water.

The investigation revealed that more kinetic energy would be transferred to the water, and in the largest scenario, the visualization shows how a 250-meter-wide asteroid could create a transient crater, giving rise to a massive plume of water and water vapour.

But, the researchers say, colliding shockwaves in the atmosphere and water, along with the wind at the water’s surface would hinder the creation of a propagating wave.

Scientists at LANL used high performance computing to investigate how an asteroid’s kinetic energy is transferred to the atmosphere and the ocean. They created simulations with varying asteroid size, angle of impact, and whether or not it exploded in an airburst

It also revealed that a direct impact with the water would be more likely to create a tsunami than an airburst would, in contrast to what’s previously been thought.

An airburst would break the asteroid apart, the researchers explain, causing much of it to skim the surface rather than slamming into it.

Even if it wouldn’t travel hundreds of miles to threaten cities, an asteroid that hit the ocean would still create waves of staggering enormity.

‘Immediately upon impact, a transient crater is created and a splash curtain is thrown high into the air,’ the researchers explain.

An impact would have devastating effects if it occurred within 10-20 kilometers of a city's coastline, but if it hit out in the middle of the ocean, the massive waves generated by the collision would quickly die down. Stock image

'NOTHING WE CAN DO' ABOUT AN ASTEROID IMPACT, EXPERTS WARN

Experts have warned that humans are not prepared for an asteroid impact, and should one head for Earth, there's not much we can do about it.

A Nasa scientist has said that our best hope is building an interceptor rocket to keep in storage that could be used in deflection missions.

Dr Joseph Nuth, a researcher at Nasa's Goddard Space Flight Centre in Maryland was speaking at the annual meeting of the American Geophysical Union earlier this week.

He said: 'The biggest problem, basically, is there's not a hell of a lot we can do about it at the moment.'

While dangerous asteroids and comets rarely hit Earth, Dr Nuth warned that the threat was always there.

He said: 'They are the extinction-level events, things like dinosaur killers, they're 50 to 60 million years apart, essentially.

'You could say, of course, we're due, but it's a random course at that point.'

‘Water rushes into the crater forming a water jet which can be several kilometers high. This jet collapses to form a rim wave, which is hundreds of meters high.

‘A new water jet begins to form and to, in turn, create a new rim wave, a process that continues for some time.

‘Each of these rim waves has the potential to become a tsunami.’

The researchers also noted another threat of ‘equal importance.’

An asteroid impact out at sea would send large amounts of water vapour into the air, which would be lofted into the stratosphere.

According to the team, this could linger for months or even years, and as it is a greenhouse gas, there would be severe implications for the global climate.

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Universe will die soon as it has started agieng, reveal astronomers

The TeCake

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The latest study showed that it is happening around all the wavelengths from the ultraviolet to the infrared, representing the most comprehensive assessment of the energy output of the nearby Universe.

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