Time: it's
continuously running out and we never have enough of it. Some say it’s just an
illusion, some say it flies like an arrow. This arrow of time is a big headache
for physicists. Why does time have a certain direction? And can such a
direction be inverted?
A research,
published in Scientific Reports, is giving a significant point of discussion on
the subject. An international team of scientists has created a time-reversal process
on a quantum computer, in an experiment that has massive implications for our
understanding of quantum computing. Their approach also discovered something
rather important: the time-reversal process is so complex that it is very
improbable, maybe impossible, for it to take place spontaneously in nature.
As far as
laws of physics go, in many scenarios, there’s nothing to stop us going forward
and backward in time. In certain quantum systems it is possible to build a
time-reversal operation. Here, the scientists created a thought experiment
based on a realistic setup.
The evolution
of a quantum system is administered by Schrödinger’s Equation, which gives us
the possibility of a particle being in a certain region. Another significant
law of quantum mechanics is the Heisenberg Uncertainty Principle, which describes
that we cannot know the precise position and momentum of a particle because
everything acts like both a particle and a wave at the same time.
The scientists
wanted to see if they could get time to naturally reverse itself for one
particle for just the fraction of a second. They use the case of a cue breaking
a billiard ball triangle and the balls scattering in all directions – a decent
analog for the second law of thermodynamics, an isolated system will always move
from order to disorder – and then having the balls reverse back into order.
Scientists
set out to test if this can actually happen, both freely in nature and in the
lab. Their assumed experiment started with a localized electron, which means
they were very sure of its position in a small region of space. The laws of
quantum mechanics make knowing this with precision hard. The notion is to have
the highest possibility that the electron is within a certain region. This possibility
"smears" out as times goes on, making it more expected for the
particle to be in a wider region. The scientists then propose a time-reversal
operation to bring the electron back to its precise space. The assumed
experiment was followed up by some real math.
The scientists
expected the possibility of this taking place to a real-world electron due to
random variabilities. If we were to notice 10 billion “freshly localized”
electrons every second over the entire lifespan of the universe (13.7 billion
years), we would only witness it happen once. And it would simply take the
quantum state back one 10-billionth of a second into the past, approximately
the time it takes between a traffic light turning green and the person behind
you beeping.
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