Time
travel was fiction before Einstein, but his calculations took us into the
quantum world and we were introduced to a more complex picture of time.
Einstein's equations permitted time travel into the past, as Kurt Gödel
discovered. The issue? None of the hypothesized time travel systems were ever
physically feasible.
So,
before sending a particle back through time, Argonne National Laboratory,
Moscow Institute of Physics and Technology, and ETH Zurich scientists wondered,
“Why stick to physical grounds?
Many
physics laws treat the future and the past as continuous. A closed system
progresses from order to disorder according to the second rule of
thermodynamics (or entropy). If you scramble an egg to produce an omelet,
you've added a lot of chaos to the closed system that was the egg.
The
arrow of time is an essential consequence of the second law. A process that
develops entropy, like whisking an egg, is irreversible. An omelet won't turn
back into an egg, and billiard balls won't spontaneously reassemble a triangle.
Entropy, like an arrow, goes in one direction, and we see it as time.
The
second rule of thermodynamics holds us captive, but an international team of
scientists sought to test it in the quantum world. Since nature cannot do such
a test, scientists utilized an IBM quantum computer.
Ordinary
computers, such as the one you're reading this on, work with bits of data. A
bit is either a 1 or a 0. A qubit is a fundamental unit of information used by
quantum computers. A qubit may be both a 1 and a 0, allowing the system to
process data considerably quicker.
The
researchers used qubits to simulate subatomic particles in a four-step
experiment. They entangled the qubits first, such that whatever occurred to one
affected the others. Then they utilized microwave radio pulses to evolve the
quantum computer's initial order into a more sophisticated state.
A
specific algorithm changes the quantum computer to bring order out of chaos.
They're zapped by another microwave pulse, but this time they go back to their
old selves. That is, they are de-aged by a millionth of a second.
Argonne
National Laboratory researcher Valerii M. Vinokur compares it to pushing
against a pond's waves to restore them to their source.
Success
was not guaranteed since quantum mechanics is about probability. In a two-qubit
quantum computer, however, the algorithm accomplished a time leap 85 percent of
the time. With three qubits, the success rate decreased to around 50%, which
the scientists blamed on flaws in current quantum computers.
The
findings were just reported in Scientific Reports.
The
results are exciting but don't go buying flux capacitors just yet. This
experiment also illustrates that manipulating even a simulated particle in time
is difficult. Our ability to produce such an external force to influence even
one quantum wave is limited.
To
time-reverse even ONE quantum particle is impossible for nature alone, says
research author Vinokur. “The system
comprising two particles is even more irreversible, let alone the eggs —
comprising billions of particles — we break to prepare an omelette.”
A press
release from the Department of Energy notes that the “timeline required for [an
external force] to spontaneously appear and properly manipulate the quantum
waves” to appear in nature and unscramble an egg “would extend longer than that
of the universe itself.” In other words, this tech specifically binds to
quantum computation.
But the
study isn't just a high-tech exercise. While the approach won't help us build
real-world time machines, it will improve quantum computation.
Einstein's
equations don't prohibit time travel, but they make it a difficult task, as
Kurt Gödel demonstrated.
Reference(s):
The New
York Times | For a Split Second, a Quantum Computer Made History Go Backward
Nature.com
| Arrow of time and its reversal on the IBM quantum computer
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