
Thermodynamic processes cannot be reversed, even in a quantum system - jonbaer
http://www.engadget.com/2015/12/01/researchers-confirm-humpty-dumpty-really-can-t-be-put-together-a/
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chris_va
From the phys.org article linked to:

""" If the laws really are reversible, then what are the physical origins of
the time-asymmetric entropy production that we observe?

The physicists explain that the answer to this question lies in the choice of
the initial conditions. The microscopic laws allow reversible processes only
because they begin with "a genuine equilibrium process for which the entropy
production vanishes at all times," the scientists write in their paper.
Preparing such an ideal initial state in a physical system is extremely
complex, and the initial states of all observed processes aren't at "genuine
equilibrium," which is why they lead to irreversible processes.

Read more at: [http://phys.org/news/2015-12-physicists-thermodynamic-
irreve...](http://phys.org/news/2015-12-physicists-thermodynamic-
irreversibility-quantum.html#jCp) """

... This is a writeup of a writeup of a single paper that itself cautions
about experimental conditions.

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jussij
> using an egg analogy, you can't uncook an egg

An Australian man who uncooked an egg has won an Ig Nobel Prize for achieving
the unintentional feat.

[http://www.northerndailyleader.com.au/story/3359027/aussie-s...](http://www.northerndailyleader.com.au/story/3359027/aussie-
scientist-awarded-for-figuring-out-how-to-uncook-an-egg/)

~~~
anigbrowl
Surprised they gave him an Ig Nobel for something so obviously clever and
useful. Perhaps the judges weren't done with breakfast when they encountered
his invention.

~~~
Veedrac
Ig Nobel prizes aren't criticisms, nor do they imply an achievement isn't
clever or useful.

> The stated aim of the prizes is to "honor achievements that first make
> people laugh, and then make them think".

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chrispeel
Here's a pdf of the article [1]. I'd love to hear a guru on quantum
computation (maybe @michael_nielsen [2]) describe how quantum error correcting
codes might interface with this result. I thought the whole point of quantum
computing was that it needed to be reversible, so if you add quantum ECC, can
you still do it?

I'm curious if the person who suggested or posted this to Hacker News knows if
this is for sure cool, or if they just were dazzled (as I am) by the Q word.

[1] [https://physics.aps.org/featured-article-
pdf/10.1103/PhysRev...](https://physics.aps.org/featured-article-
pdf/10.1103/PhysRevLett.115.190601)

[2] [https://twitter.com/michael_nielsen](https://twitter.com/michael_nielsen)

~~~
brudgers
[IANAQCG]

As long as quantum computations employ an arrow of time there is no way to
escape the before and after semantics of the second law. My gut tells me that
the arrow of time and simultaneity are a gestalt. Throwing out the arrow of
time takes the baby with it, i.e. what would simultaneity get us without an
after and before?

Looking at the letter, once the experiment or equations requires initial
conditions, there's no way to avoid an arrow of time. Change comes _later_.
The arrow of time is a premise of the experimental method.

For me, the headline parses out to a dog-bites-man "The Second Law of
Thermodynamics" with "quantum" canceling itself out. As Chevy Chase would say,
Charles De Gaulle is still dead.

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Beltiras
I'm quite sure the experimentalists hedged heavily in the paper.
Sensasionalistic headline boiled away caution.

