An
international team of researchers were able to create a nifty quantum
experiment that at first might seem to have broken thermodynamics: They were
able to generate a spontaneous heat flow from a cold system to a hot system. Actually,
they were able to do so without violating any physical law. Their study relates
the complex relationship between quantum mechanics, thermodynamics, and time
itself.
Heat constantly
flows from a hot system to a cold one. If you put ice cubes in your soda, your
drink won’t all of a sudden get hotter. When this heat flow occurs, the entropy
of the system increases. So by looking at the entropy of the system, it is probable
to work out if we are looking at the system going “forward” in time or
“backward”. The entropy increase states a thermodynamic arrow of time, and the
macroscopic world experiences this in the similar direction that we do.
While this
is all well and good, there is a significant hypothesis: for heat to flow from
hot to cold, the systems must be uncorrelated. There shouldn’t be any distinct
connections linking the two before you put them in contact. This is apparent
for macroscopic systems – you don’t assume ice cubes to have a distinctive
relationship with the molecules that make up your particular soda.
Yet, this
is not so evident in the quantum world. It is possible to produce quantum
states that are correlated, where rapidly the direction of the arrow of time
can be reversed. This has been proposed theoretically before, but this research
indicates that it's possible to prove experimentally. To do so, they set up two
correlated thermal systems and observed the heat flow from the cold to the hot
system.
So what
gives? In their paper, available on the arXiv, the researchers says there is a
trade-off between the quantum correlation and the entropy of the system. It is
this trade-off that permits for the reversal of heat flow. The thermodynamic
arrow of time is intensely reliant on the initial condition of a system.
There is
another exciting tidbit from the research. According to the scientists, this
reversal of heat flow is not restricted to particularly microscopic systems,
although they are yet to study bigger setups. It is unlikely to be observed in
a macroscopic phenomenon, but since entropy plays such a vital role in the
scientific definition of time, it might be worth keeping an eye on.
References:
https://www.quantamagazine.org/quantum-correlations-reverse-thermodynamic-arrow-of-time-20180402/
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