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| An artist's impression of the inside of a wormhole. (Image credit: Shutterstock) |
Quantum experiment conducted on Google's Sycamore 2 computer transferred data
across two simulated black holes, adding weight to the holographic principle
of the universe.
Physicists have used a quantum computer to simulate the first-ever holographic
wormhole and transport information through it.
The "baby" wormhole, created on Google's Sycamore 2 quantum computer was not
created with gravity, but through quantum entanglement — the linking of two
particles such that measuring one instantaneously affects the other. By
entangling qubits, or quantum bits, in minuscule superconducting circuits
physicists were able to create a portal through which information was sent.
The experiment has the potential to further the hypothesis that our universe
is a hologram stitched together by quantum information. The researchers
published their findings Nov. 30 in the journal Nature.
"This is a baby step for interrogating quantum gravity in the lab," lead
author Maria Spiropulu, a physicist at the California Institute of
Technology, said at a Nov. 30 news conference. "When we saw the data, I had
a panic attack. We were jumping up and down. But I'm trying to keep it
grounded."
Wormholes are hypothetical tunnels through space-time connected by black
holes at either end. In nature, the immense gravity of the two black holes
is what helps create the conditions of the wormhole, but the wormhole
simulated in the experiment is a little different: It is a toy model that
relies on a process called quantum teleportation to imitate two black holes
and send the information through the portal. These processes appear to be
pretty distinct, but according to the researchers, they may not be that
different after all. In a hypothesis called the holographic principle, the
theory of gravity that breaks down around black hole singularities
(Einstein's general relativity) could actually emerge from the weird rules
governing very small objects like qubits (quantum mechanics) — and their
experiment might provide the first clues that this is the case.
Thankfully, the black hole analogues in the quantum computer are not the
same as the all-consuming monsters lurking in space. But the researchers are
unsure whether they might have simulated the black holes closely enough for
them to be considered strange variants of the real thing, ultimately dubbing
their quantum computer rifts "emergent" black holes.
"It looks like a duck; it walks like a duck; it quacks like a duck. That's
what we can say at this point," co-author Joseph Lykken, a physicist and the
deputy director of research at Fermilab, said at the news conference. "We
have something that, in terms of the properties we look at, it looks like a
wormhole."
Einstein's predictions
The idea of wormholes first emerged from the work of Albert Einstein and his
colleague Nathan Rosen, who, in 1935, demonstrated in a famous paper that
the theory of general relativity permitted black holes to be linked in
bridges that could connect vast distances. The theory was an attempt to
offer an alternative explanation to points in space called singularities:
The cores of black holes where mass has become infinitely concentrated at a
single point, creating a gravitational field so powerful that space-time is
warped to infinity and Einstein's equations collapse. If wormholes existed
somehow, Einstein and Rosen reasoned, then general relativity held up.
A month before the famous 1935 paper, Einstein, Rosen and their colleague
Boris Podolsky had written another. In that research, they made a prediction
that, unlike their later paper in general relativity, wasn’t intended to
bolster quantum theory, but to discredit it for its ridiculous implications.
If the rules of quantum mechanics were true, the physicists outlined, the
properties of two particles could become inextricably linked such that
measuring one would instantaneously affect the other, even if the two were
separated by an enormous gap. Einstein scoffed at the process, known now as
quantum entanglement, dubbing it "spooky action at a distance," but it has
since been observed and is commonly used by physicists.
Despite having produced these two groundbreaking predictions, Einstein's
dislike for the inherent uncertainty and weirdness of quantum physics could
have blinded him to a vital insight: that the two predictions could be, in
fact, connected. By separating general relativity and quantum theory,
physicists have been left with no understanding of the realms where gravity
and quantum effects collide — such as the interiors of black holes or the
infinitesimal point into which the universe was concentrated at the moment
of the Big Bang.
Holographic principle
Since Einstein reached this impasse, the search for where the big and small
stitch together — a theory of everything — has led physicists to come up
with all kinds of colorful propositions. One is the holographic principle,
which posits that the entire universe is a 3D holographic projection of
processes playing out on a remote 2D surface.
This idea finds its roots in Stephen Hawking’s work in the 1970s, which
posed the apparent paradox that if black holes did indeed radiate Hawking
radiation (radiation from virtual particles randomly popping into existence
near event horizons) they would eventually evaporate, breaking a major rule
of quantum mechanics that information cannot be destroyed. General
relativity and quantum mechanics now no longer just seemed irreconcilable;
despite their many incredibly accurate predictions, they could even be
wrong.
To solve this problem, proponents of string theory, who aimed to reconcile
quantum mechanics and relativity, used observations that the information
contained by a black hole was linked with the 2D surface area of its event
horizon (the point beyond which not even light can escape its gravitational
pull). Even the information about the star that collapsed into the black
hole was woven into fluctuations on this horizon surface, before being
encoded onto Hawking radiation and sent away prior to the black hole’s
evaporation.
In the 1990s, theoretical physicists Leonard Susskind and Gerard ‘t Hooft
realized the idea needn’t stop there. If all the information of a 3D star
could be represented on a 2D event horizon, perhaps the universe — which has
its own expanding horizon — was the same: A 3D projection of 2D information.
From this perspective, the two disjointed theories of general relativity and
quantum mechanics might not be separate at all. Space-time's gravitational
warping, along with everything else we see, could instead emerge like a
holographic projection, shimmering into being from the minute interactions
of tiny particles on the lower-dimensional surface of a remote horizon.
Testing for wormholes
To put these ideas to the test, the researchers turned to Google's Sycamore
2 computer, loading it with a bare-bones model of a simple holographic
universe that contained two quantum entangled black holes on either end.
After encoding an input message into the first qubit, the researchers saw
the message get scrambled into gibberish — a parallel to being swallowed by
the first black hole — before popping out unscrambled and intact at the
other end, as if it were spat out by the second.
"The physics that's going on here, in principle, is if if we had two quantum
computers that were on different sides of the Earth, and [if] we improve
this technology a little bit, you could do a very similar experiment where
the quantum information disappeared in our laboratory at Harvard, and
appeared at the laboratory and Caltech," Lykken said. "That would be more
impressive than what we actually did on a single chip. But really, the
physics we're talking about here is the same in both cases."
The surprising aspect of the wormhole trick isn't that the message made it
through in some form but that it emerged completely intact and in the same
order it went in — key clues that the experiment was behaving like a
physical wormhole and that physical wormholes, in turn, could be powered by
entanglement.
The researchers noted that the information traversed a minuscule gap, just a
few factors bigger than the shortest conceivable distance in nature, the
Planck length. In the future, they want to design experiments of greater
complexity, perform them on more advanced hardware and send codes over
greater distances. While going from sending information through their
wormhole to sending something physical, like a subatomic particle, doesn't
take much of a theoretical leap, they say, it would need a density of qubits
great enough to create a real mini black hole.
"Experimentally, I will tell you that it is very, very far away," Spiropulu
said. "People come to me and they ask me, 'Can you put your dog in the
wormhole?' No, that's a huge leap."
Reference:
Jafferis, D., Zlokapa, A., Lykken, J.D. et al. Traversable wormhole dynamics
on a quantum processor. Nature 612, 51–55 (2022).
DOI: 10.1038/s41586-022-05424-3
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Physics