Mid-morning. You are at the Joseph Collision
Center on Joseph Street at Colerain Avenue waiting for them to pick up the car
for the Xzilon application. – Amorella
Mid-afternoon.
You were home by eleven and you had a breakfast lunch at First Watch in West
Chester, filled up the car at a UDF for one dollar and seventy-five and
nine-tenths cents, the lowest regular fuel price in years. Once home Carol worked
on laundry while you and Jadah took a nap in the bedroom black leather lounger.
Doug sent you an interesting science article that strikes your fancy as
important stuff.
1556
hours. The Nature article Doug sent I cannot put on the blog because of
copyright; however I found a recent similar article (Science News) on the same
subject that is sharable on Facebook (which I shared).
** **
Entanglement:
Gravity's long-distance connection
Wormhole
links between black holes could broker quantum-general relativity merger
BY
ANDREW GRANT 10:42AM, OCTOBER 7, 2015
Magazine issue: Vol. 188, No. 8, October 17, 2015, p.
28
When
Albert Einstein scoffed at a “spooky” long-distance connection between
particles, he wasn’t thinking about his general theory of relativity.
Einstein’s
century-old theory describes how gravity emerges when massive objects warp the
fabric of space and time. Quantum entanglement, the spooky source of Einstein’s
dismay, typically concerns tiny particles that contribute insignificantly to
gravity. A speck of dust depresses a mattress more than a subatomic particle
distorts space.
Yet
theoretical physicist Mark Van Raamsdonk suspects that entanglement and
spacetime are actually linked. In 2009, he calculated that space without
entanglement couldn’t hold itself together. He wrote a paper
asserting that quantum entanglement is the needle that stitches together the
cosmic spacetime tapestry.
Multiple
journals rejected his paper. But in the years since that initial skepticism,
investigating the idea that entanglement shapes spacetime has become one of the
hottest trends in physics. “Everything points in a really compelling way to
space being emergent from deep underlying physics that has to do with
entanglement,” says John Preskill, a theoretical physicist at Caltech.
In
2012, another provocative paper presented a paradox about entangled particles
inside and outside a black hole. Less than a year later, two experts in the
field proposed a radical resolution: Those entangled particles are connected by
wormholes — spacetime tunnels imagined by Einstein that nowadays appear as
often in sci-fi novels as in physics journals. If that proposal is correct,
then entanglement isn’t the spooky long-distance link that Einstein thought it
was — it’s an actual bridge linking distant points in space.
Many
researchers find these ideas irresistible. Within the last few years,
physicists in seemingly unrelated specialties have converged on this confluence
of entanglement, space and wormholes. Scientists who once focused on building
error-resistant quantum computers are now pondering whether the universe itself
is a vast quantum computer that safely encodes spacetime in an elaborate web of
entanglement. “It’s amazing how things have been progressing,” says Van
Raamsdonk, of the University of British Columbia in Vancouver.
Physicists
have high hopes for where this entanglement-spacetime connection will lead
them. General relativity brilliantly describes how spacetime works; this new
research may reveal where spacetime comes from and what it looks like at the small
scales governed by quantum mechanics. Entanglement could be the secret
ingredient that unifies these supposedly incompatible views into a theory of
quantum gravity, enabling physicists to understand conditions inside black
holes and in the very first moments after the Big Bang.
Holograms
and soup cans
Van
Raamsdonk’s 2009 insight didn’t materialize out of thin air. It’s rooted in the
math of the holographic principle, the idea that the boundary enclosing a
volume of space can contain all the information about what’s inside. If the
holographic principle applied to everyday life, then a nosy employee could
perfectly reconstruct the inside of a coworker’s office cubicle — piles of
papers, family photos, dust bunnies in the corner, even files on the computer’s
hard drive — just by looking at the cubicle’s outer walls. It’s a
counterintuitive idea, considering walls have two dimensions and a cubicle’s
interior has three. But in 1997, Juan Maldacena, a string theorist then at
Harvard, perceived an intriguing example
of what the holographic principle could reveal about the universe (SN: 11/17/07, p. 315).
He
started with anti-de Sitter space, which resembles the universe’s
gravity-dominated spacetime but also has some quirky attributes. It is curved
in such a way that a flash of light emitted at any location eventually returns
to where it started. And while the universe is expanding, anti-de Sitter space
neither stretches nor contracts. Because of these features, a chunk of anti-de
Sitter spacetime with four dimensions (three spatial, one time) can be
surrounded by a three-dimensional boundary.
Maldacena
considered a cylinder of anti-de Sitter spacetime. Each horizontal slice of the
cylinder represented the state of its space at a given moment, while the
cylinder’s vertical dimension represented time. Maldacena surrounded his
cylinder with a boundary for the hologram; if the anti-de Sitter space were a
can of soup and its contents, then the boundary was the label.
Just
as nobody would mistake a Campbell’s label for the actual soup, the boundary
seemingly shared nothing in common with the cylinder’s interior. The boundary “label,”
for instance, observed the rules of quantum mechanics, with no gravity. Yet
gravity described the space inside containing the “soup.” Maldacena showed,
though, that the label and the soup were one and the same; the quantum
interactions on the boundary perfectly described the anti-de Sitter space it
enclosed. “They are two theories that seem completely different but describe
exactly the same thing,” Preskill says.
Maldacena
added entanglement to the
holographic equation in 2001. He considered the space within two soup cans,
each containing a black hole. Then he created the equivalent of a tin can
telephone by connecting the black holes with a wormhole — a tunnel through
spacetime first
proposed by Einstein and Nathan Rosen in 1935. Maldacena looked for
a way to create the equivalent of that spacetime connection on the cans’
labels. The trick, he realized, was entanglement.
Like
a wormhole, quantum entanglement links entities that share no obvious
relationship. The quantum world is a fuzzy place: An electron can seemingly be
spinning up and down simultaneously, a state called superposition, until a
measurement provides a definitive answer. But if two electrons are entangled,
then measuring the spin of one enables an experimenter to know what the spin of
the other will be — even though the partner electron is still in a
superposition state. This quantum link remains if the electrons are separated
by meters, kilometers or light-years.
Maldacena
demonstrated that by entangling particles on one can’s label with particles on
the other, he could perfectly describe the wormhole connection between the cans
in the language of quantum mechanics. In the context of the holographic
principle, entanglement is equivalent to physically tying chunks of spacetime
together.
Inspired
by this entanglement-spacetime link, Van Raamsdonk wondered just how large a
role entanglement might play in shaping spacetime. He considered the blandest quantum
soup-can label he could think of: a blank one, which corresponded to an empty
disk of anti-de Sitter space. But he knew that because of quantum mechanics,
empty space is never truly empty. It is filled with pairs of particles that
blink in and out of existence. And those fleeting particles are entangled.
So
Van Raamsdonk drew an imaginary line bisecting his holographic label and then
mathematically severed the quantum entanglement between particles on one half
of the label and those on the other. He discovered that the corresponding disk
of anti-de Sitter space started to split in half. It was as if the entangled
particles were hooks that kept the canvas of space and time in place; without
them, spacetime pulled itself apart. As Van Raamsdonk decreased the degree of
entanglement, the portion connecting the diverging regions of space got
thinner, like the rubbery thread that narrows as a chewed wad of gum is pulled
apart. “It led me to suggest that the origin of having space at all is having
this entanglement,” he says.
That
was a bold claim, and it took a while for Van Raamsdonk’s paper, published
in General Relativity and
Gravitation in 2010, to garner
serious attention. The spark came in 2012, when four physicists at the
University of California, Santa Barbara wrote a paper challenging conventional wisdom about the event
horizon, a black hole’s point of no return.
Insight
behind a firewall
In
the 1970s, theoretical physicist Stephen Hawking showed
that pairs of entangled particles — the same kinds Van Raamsdonk later analyzed
on his quantum boundary — can get split up at the event horizon. One falls into
the black hole, and the other escapes as what’s known as Hawking radiation. The
process gradually saps the mass of a black hole, ultimately leading to its demise.
But if black holes disappear, then so would the record of everything that ever
fell inside. Quantum theory maintains that information cannot be destroyed.
By
the 1990s several theoretical physicists, including Stanford’s Leonard
Susskind, had proposed
resolutions of the issue. Sure, they said, matter and energy fall into a black
hole. But from the perspective of an outside observer, that stuff never quite
makes it past the event horizon; it seemingly teeters on the edge. As a result,
the event horizon becomes a holographic boundary containing all the information
about the space inside the black hole. Eventually, as the black hole shrivels
away, that information will leak out as Hawking radiation. In principle, the
observer could collect the radiation and piece together information about the
black hole’s interior.
In
their 2012 paper, Santa Barbara physicists Ahmed Almheiri, Donald Marolf, James
Sully and Joseph Polchinski claimed
something was wrong with that picture. For an observer to assemble the puzzle
of what’s inside a black hole, they noted, all the individual puzzle pieces —
the particles of Hawking
radiation — would have to be entangled with each other. But each
Hawking particle also has to be entangled with its original partner that fell
into the black hole.
Unfortunately,
there is not enough entanglement to go around. Quantum theory dictates that the
entanglement required to link all the particles outside the black hole precludes
those particles from also linking up with particles inside the black hole.
Compounding the problem, the physicists found that severing one of those
entanglements would create an impenetrable wall of energy, called a firewall,
at the event horizon (SN: 5/31/14, p. 16).
Many
physicists doubted that black holes actually vaporize everything trying to
enter. But the mere possibility that firewalls exist had disturbing
implications. Previously, physicists had wondered what the space inside a black
hole looked like. Now they weren’t sure whether black holes even had an inside.
“It was kind of humbling,” Preskill says.
Susskind
was not so much humbled as restless. He had spent years trying to show that
information wasn’t lost inside a black hole; now he was just as convinced that
the firewall idea was wrong, but he couldn’t prove it. Then one day he received
a cryptic email from Maldacena: “It had very little in it,” Susskind says, “except
for ER = EPR.” Maldacena, now at the Institute for Advanced Study in Princeton,
N.J., had thought back to his 2001 paper on interconnected soup cans and
wondered whether wormholes could resolve the entanglement mess raised by the
firewall problem. Susskind quickly jumped on the idea.
In
a paper in the German journal Fortschritte
der Physik in 2013, Maldacena and
Susskind argued
that a wormhole — technically, an Einstein-Rosen bridge, or ER — is the
spacetime equivalent of quantum entanglement. (EPR stands for Einstein, Boris
Podolsky and Rosen, authors of the 1935 paper that
belittled entanglement.) That means that every particle of Hawking
radiation, no matter how far away it is from where it started, is directly
connected to a black hole’s interior via a shortcut through spacetime. “Through
the wormhole, the distant stuff is not so distant,” Susskind says.
Susskind
and Maldacena envisioned gathering up all the Hawking particles and smushing
them together until they collapse into a black hole. That black hole would be
entangled, and thus connected via wormhole, with the original black hole. That
trick transformed a confusing mess of Hawking particles — paradoxically
entangled with both a black hole and each other — into two black holes
connected by a wormhole. Entanglement overload is averted, and the firewall
problem goes away.
Not
everyone has jumped aboard the ER = EPR bandwagon. Susskind and Maldacena admit
they have more work to do to prove the equivalence of wormholes and
entanglement. But after pondering the implications of the firewall paradox,
many physicists agree that the spacetime inside a black hole owes its existence
to entanglement with radiation outside. That’s a major insight, Preskill says,
because it also implies that the entire universe’s spacetime fabric, including
the patch on which we reside, is a product of quantum spookiness.
Cosmic
computer
It’s
one thing to say the universe constructs spacetime through entanglement; it’s
another to show how the universe does it. The trickier of those assignments has
fallen on Preskill and colleagues, who have come to view the cosmos as a
colossal quantum computer. For two decades scientists have worked on building
quantum computers that use information encoded in entangled entities, such as
photons or tiny circuits, to solve problems intractable on traditional
computers, such as factoring large numbers. Preskill’s team is using knowledge
gained in that effort to predict how particular features inside a soup-can
would be depicted on the entanglement-filled label.
Quantum
computers work by exploiting components that are in superposition states as
data carriers — they can essentially be 0s and 1s at the same time. But
superposition states are very fragile. Too much heat, for example, can destroy
the state and all the quantum information it carries. These information losses,
which Preskill compares to having pages torn out of a book, seem inevitable.
But
physicists responded by creating a protocol called quantum error correction.
Instead of relying on one particle to store a quantum bit, scientists spread
the data among multiple entangled particles. A book written in the language of
quantum error correction would be full of gibberish, Preskill says, but its
entire contents could be reconstructed even if half the pages were missing.
Spooky
entanglement
Quantum
error correction has attracted a lot of attention in recent years, but now
Preskill and his colleagues suspect
that nature came up with it first. In the June Journal of High Energy Physics,
Preskill’s team showed how the entanglement of multiple particles on a
holographic boundary perfectly describes a single particle being pulled by
gravity within a chunk of anti-de Sitter space. Maldacena says this insight
could lead to a better understanding of how a hologram encodes all the details
about the spacetime it surrounds.
Physicists
admit that their approximations have a long way to go to match reality. While
anti-de Sitter space offers physicists the advantage of working with a
well-defined boundary, the universe doesn’t have a straightforward soup-can
label. The spacetime fabric of the cosmos has been expanding since the Big Bang
and continues to do so at an increasing clip. If you shoot a pulse of light
into space, it won’t turn around and come back; it will just keep going. “It is
not clear how to define a holographic theory for our universe,” Maldacena
wrote in 2005. “There is no convenient place to put the hologram.”
Yet
as crazy as holograms, soup cans and wormholes sound, they seem to be promising
lenses in the search for a way to meld quantum spookiness with spacetime
geometry. In their paper on wormholes, Einstein and Rosen discussed possible
quantum implications but didn’t make a connection to their earlier entanglement
paper. Today that link may help reconcile quantum mechanics and general
relativity in a theory of quantum gravity. Armed with such a theory, physicists
could dig into mysteries such as the state of the infant universe, when matter
and energy were packed into an infinitesimally small space. “We don’t really
know the answers yet by any means,” Preskill says. “But we’re excited to find a
new way of looking at things.”
This article appeared in
the October 17, 2015, Science News under the headline, "Gravity's long distance
connection."
Selected
and edited from - https://www.sciencenewsDOTorg/article/entanglement-gravitys-long-distance-connection
** **
1628
hours. I need to read both articles (Nature and Science News) again to gain a
better plausibility depth. I am highly attracted to the concept even if it is
still conjecture and not theory. I really would like to know (or have an
inkling) of how the universe exists because I think it is essential to better
knowing how we exist and why we are as we are. Environment across the board is
the issue here.
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