21 May 2022 | New Scientist | 15A 155-YEAR-OLD thought
experiment, long believed to
break the laws of thermodynamics,
could be made real on a large scale.
Maxwell’s demon was proposed
by Scottish mathematician
James Clerk Maxwell in 1867.
He imagined a tiny demon
controlling a door between two
gas-filled chambers. By carefully
opening and closing the door, the
demon allows only fast-moving
gas particles into one chamber
and slow ones into the other.
Because the speed of its
particles determines a gas’s
temperature, the first chamber
heats up and the other cools
down. The resulting differential
could drive a perpetual engine,
one that runs forever without
an external power source. The
trouble is, the demon’s actions
decrease the entropy, or level of
disorganisation, in this closed
system without expending any
energy – which violates the second
law of thermodynamics.
Practical versions of
Maxwell’s demon that harness
thermal fluctuations have been
demonstrated at microscopic
scales, but they require an external
energy source, leaving the laws of
thermodynamics intact. Studying
such fluctuations in more detail
will require a demon that can be
implemented at different scales.
Nahuel Freitas and
Massimiliano Esposito at the
University of Luxembourg have
come up with a type of demon
that works at any scale, albeit with
lower efficiency the larger it gets.
“The bigger the demon, the more
energy one has to spend to make
it work,” says Esposito.
Their set-up starts with a CMOS
inverter, a small device used in
many electronic circuits thatconsists of two transistors. The
transistors can be thought of as
doors, one of which opens when
a negative voltage is fed into the
inverter, while the other opens
when a positive voltage is fed in.
A second CMOS inverter acts as
the demon, but while the originalMaxwell’s demon sorted particles
by speed, this version sorts
voltages by their direction.
However, rather than storing
each voltage on its own side of
a box, it discards the negative
voltages and sends the positive
ones back into the first inverter
(arxiv.org/abs/2204.09466).
In theory, even when no
external voltage is applied tothe system, the demon should
be able to take advantage of tiny
thermal fluctuations and create a
voltage from nothing. “That would
be super good if you could do it,”
says Freitas. “It would also be a
violation of the second law of
thermodynamics.”
This type of system could
help researchers study thermal
fluctuations, which are governed
by quantum mechanics at small
scales in a way that we don’t
generally see at larger ones.
“This interesting, rich physics
of the micro-scale can be brought
to the macro-scale, so we might
see some of these very fancy
effects that we don’t expect at
the macro-scale,” says Esposito.
The implications might also
extend to biological “machines”
such as enzymes, which amplify
small fluctuations in their
environments to carry out tasks. ❚Physics
Leah Crane
Maxwell’s demon could be made real
without breaking the laws of physics
Health
GETTING vaccinated for the flu may
also reduce your risk of developing
cardiovascular issues.
Bahar Behrouzi at the University
of Toronto and her colleagues
performed a meta-analysis of the
results of six clinical trials involving
flu vaccines conducted between
2000 and 2021. These included
a total of over 9000 people.
The researchers wanted to find
out whether having a flu vaccine
reduced the chance of developing
cardiovascular conditions, such as
stroke and heart attack, in the year
following inoculation – a benefit
suggested by previous studies.
As part of all six of the trials,
participants were followed for
12 months. Their average age was
65.5 years and just over a third of
them had had heart issues in the
12 months leading up to their
enrolment in one of the studies.
Only 4510 of these people had
a flu vaccine, whereas the others
were given either a placebo or
didn’t receive any treatment at all.The researchers found that the
flu vaccine led to a 34 per cent
lower risk, on average, of a major
cardiovascular issue in the
12 months following inoculation.
When looking only at people
who had a recent history of heart
problems, those who went on to get
vaccinated against influenza had a45 per cent lower risk of a heart
condition in the following year than
those who didn’t have the jab (JAMA
Network Open, doi.org/ht3w).
Deepak Bhatt at Harvard
University, who worked on the
study, says this link is probably
because flu can lead to heart
attacks. “It could be the stress
that an infection places on the
heart, such as that caused by an
elevated heart [rate],” he says.
“Some studies also suggest that
the vaccine may interact with the
body’s immune system and help
stabilise plaques in blood vessels,
therefore preventing them from
dislodging or rupturing and causing
further problems,” says Behrouzi. ❚Flu vaccine cuts risk
of heart attack in
next year by a third
Jason Arunn Murugesu“ The original Maxwell’s
demon sorted particles by
speed. This version sorts
voltages by direction”The influenza vaccine
appears to have some
hidden advantagesET
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