Science, Technology, and Current Futurism
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Ultra-cold mirrors could reveal gravity's quantum side

Ultra-cold mirrors could reveal gravity's quantum side | Science, Technology, and Current Futurism | Scoop.it

An experiment not much bigger than a tabletop, using ultra-cold metal plates, could serve up a cosmic feast. It could give us a glimpse of quantum gravity and so lead to a "theory of everything": one that unites the laws of quantum mechanics, governing the very small, and those of general relativity, concerning the monstrously huge.

 

Such theories are difficult to test in the lab because they probe such extreme scales. But quantum effects have a way of showing up unexpectedly. In a strange quantum phenomenon known as the Casimir effect, two sheets of metal held very close together in a vacuum will attract each other.

 

The effect occurs because, even in empty space, there is an electromagnetic field that fluctuates slightly all the time. Placing two metal sheets very close to one another limits the fluctuations between them, because the sheets reflect electromagnetic waves. But elsewhere the fluctuations are unrestricted, and this pushes the plates together.

James Quach at the University of Tokyo suggests that we might be able to observe the equivalent effect for gravity. That would, in turn, be direct evidence of the quantum nature of gravity: the Casimir effect depends on vacuum fluctuations, which are only predicted by quantum physics.

 

But in order to detect it, you would need something that reflects gravitational waves – the ripples in space-time predicted by general relativity. Earlier research suggested that superconductors (for example, metals cooled to close to absolute zero such that they lose all electrical resistance) might act as mirrors in this way.

 

"The quantum properties of superconductors may reflect gravitational waves. If this is correct, then the gravitational Casimir effect for superconductors should be large," says Quach. "The experiment I propose is feasible with current technology."

 

It's still unclear if superconductors actually reflect gravitational waves, however. "The exciting part of this paper has to do with a speculative idea about gravitational waves and superconductors," says Dimitra Karabali at Lehman College in New York. "But if it's right, it's wonderful."


Via Dr. Stefan Gruenwald
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Gravitational Waves Finding Confirms Early Universe's Exponential Growth

Gravitational Waves Finding Confirms Early Universe's Exponential Growth | Science, Technology, and Current Futurism | Scoop.it
Astronomers have for the first time witnessed signs of gravitational waves rippling through the explosive first moments of the universe.
Sharrock's insight:

excerpt: "Surprisingly strong gravitational waves rippled through the fiery aftermath of the Big Bang, a finding which confirms the cosmos grew to a stunningly vast size in it very first moments, a team of astronomers announced Monday."

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Black Hole Cores May Not Be Infinitely Dense | Inside Science

Black Hole Cores May Not Be Infinitely Dense | Inside Science | Science, Technology, and Current Futurism | Scoop.it
They may also serve as bridges to the future.
Sharrock's insight:

from the article: "These new findings are based on loop quantum gravity, one of the leading theories seeking to unite quantum mechanics and general relativity into a single theory that can explain all the forces of the universe. In loop quantum gravity, the four dimensions of spacetime are composed of networks of intersecting loops — ripples of the gravitational field."

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Does the Arrow of Time Self-Emerge in a Gravitational System?

Does the Arrow of Time Self-Emerge in a Gravitational System? | Science, Technology, and Current Futurism | Scoop.it
Study of masses interacting via gravity challenges the idea that special initial conditions are needed to give time a direction.

 

The fundamental laws of physics, we believe, do not depend on the direction of time. Why, then, is the future so different from the past? The origin of this “arrow of time” has puzzled physicists and philosophers for more than a century, and it remains one of the fundamental conceptual problems of modern physics [1]. Although a preferred direction of time can occur in models of physical systems, this typically happens only if one inserts very special initial conditions.

 

Julian Barbour at the University of Oxford and his colleagues [2] have now shown this tinkering isn’t necessary to produce an arrow of time in a system of masses interacting via Newtonian gravity. They demonstrate that the evolution of this surprisingly simple system almost always contains a unique moment of lowest “complexity,” a point they identify as a “past” from which two distinct (and more complex) “futures” emerge.


The work of Barbour and his colleagues is the latest in a long history of attempts to explain the arrow of time. One possibility, of course, is that we don’t know the right laws of physics—perhaps the correct fundamental laws do determine a preferred direction of time [3]. Alternatively, if the laws of nature do not pick out a preferred “future,” perhaps boundary conditions do. For example, most cosmological models assume, explicitly or implicitly, that the big bang was a moment of exceptionally low entropy.


Indeed, most physicists accept the view that the direction of time is the same as the direction of increasing entropy. But this is, at best, an incomplete picture, failing to explain why there should have been a rare condition of low entropy in the past. More than a century ago, Boltzmann suggested that our visible Universe might merely be a temporary, low-entropy statistical fluctuation, affecting a small portion of a much larger equilibrium system [4]. In that case, the direction of time would simply be the one that takes us back towards equilibrium. But most contemporary physicists find this explanation unsatisfying: a random fluctuation containing “us” would have been far more likely to produce a single galaxy, a planet, or just a “brain” rather than a whole universe [5, 6]. Moreover, according to the “Loschmidt irreversibility paradox,” if one posits such a moment of low entropy, entropy should increase both to the future and to the past, giving two separate arrows of time [7].

 
Via Dr. Stefan Gruenwald
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Phys.Org Mobile: An end in sight in the long search for gravity waves

Phys.Org Mobile: An end in sight in the long search for gravity waves | Science, Technology, and Current Futurism | Scoop.it
By 1957 physicists had proved that they must carry energy and cause vibrations. But it was also apparent that waves carrying a million times more energy than sunlight would make vibrations smaller than an atomic nucleus.
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