A new kind of black hole analog could tell us a thing or two about an elusive radiation theoretically emitted by the real thing.
Simulation of a warped and spinning black hole.
(Yukterez/Wikimedia Commons, CC BY-SA 4.0) |
Using a chain of atoms in single-file to simulate the event
horizon of a black hole, a team of physicists has observed the equivalent of what
we call Hawking radiation – particles born from disturbances in the quantum
fluctuations caused by the black hole's break in spacetime.
This, they say, could help resolve the tension between two
currently irreconcilable frameworks for describing the Universe: the general
theory of relativity, which describes the behavior of gravity as a continuous
field known as spacetime; and quantum mechanics, which describes the behavior
of discrete particles using the mathematics of probability.
For a unified theory of quantum gravity that can be applied
universally, these two immiscible theories need to find a way to somehow get
along.
This is where black holes come into the picture – possibly
the weirdest, most extreme objects in the Universe. These massive objects are
so incredibly dense that, within a certain distance of the black hole's center
of mass, no velocity in the Universe is sufficient for escape. Not even light
speed.
That distance, varying depending on the mass of the black
hole, is called the event horizon. Once an object crosses its boundary we can
only imagine what happens, since nothing returns with vital information on its
fate. But in 1974, Stephen Hawking proposed that interruptions to quantum
fluctuations caused by the event horizon result in a type of radiation very
similar to thermal radiation.
If this Hawking radiation exists, it's way too faint for us
to detect yet. It's possible we'll never sift it out of the hissing static of
the Universe. But we can probe its properties by creating black hole analogs in
laboratory settings.
This has been done before, but now a team led by Lotte
Mertens of the University of Amsterdam in the Netherlands has done something
new.
A one-dimensional chain of atoms served as a path for
electrons to 'hop' from one position to another. By tuning the ease with which
this hopping can occur, the physicists could cause certain properties to
vanish, effectively creating a kind of event horizon that interfered with the
wave-like nature of the electrons.
The effect of this fake event horizon produced a rise in
temperature that matched theoretical expectations of an equivalent black hole
system, the team said, but only when part of the chain extended beyond the
event horizon.
This could mean the entanglement of particles that straddle
the event horizon is instrumental in generating Hawking radiation.
The simulated Hawking radiation was only thermal for a
certain range of hop amplitudes, and under simulations that began by mimicking
a kind of spacetime considered to be 'flat'. This suggests that Hawking
radiation may only be thermal within a range of situations, and when there is a
change in the warp of space-time due to gravity.
It's unclear what this means for quantum gravity, but the
model offers a way to study the emergence of Hawking radiation in an
environment that isn't influenced by the wild dynamics of the formation of a
black hole. And, because it's so simple, it can be put to work in a wide range
of experimental set-ups, the researchers said.
"This, can open a venue for exploring fundamental
quantum-mechanical aspects alongside gravity and curved spacetimes in various
condensed matter settings," the researchers write.
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