
Thermodynamical cost of some interpretations of quantum theory - n4r9
http://arxiv.org/abs/1509.03641
======
rubidium
To save others some time.

Input 1: authors check out (PRL, Nature pubs). Not a one-off crazy posting to
arXiv.

Input 2: Unless this your field, I'd be surprised if you get much from the
paper other than interpretation of quantum mechanics is still an active field
and information theory / thermodynamics has an important role in that field.

Input 3: After a few reads, I don't like the phrasing the authors put on Type-
II interpretations. They say "Another class sees quantum probabilities as not
directly dealing with intrinsic properties of the world but with relational
experiences between an observer and the world." Another way to say it may be
that it's impossible to separate observation from the intrinsic properties of
the world. That is, reality is tightly bound up with observation and trying to
separate the two is artificial. But I'd be happy to hear what others think
about it.

~~~
danharaj
> Another way to say it may be that it's impossible to separate observation
> from the intrinsic properties of the world.

I think it is more parsimonious to say that there are no intrinsic properties
of the world that are not relational, not that they are impossible to separate
from observation. It defeats the purpose of interpretations like relational
quantum mechanics to hold on to the concept of an intrinsic reality when the
interpretation makes such a concept superfluous.

I would say that it is impossible to disentangle the intrinsic properties of
the world from observations in the same way that going north of the North Pole
is impossible.

~~~
rubidium
"no intrinsic properties of the world that are not relational." I like that
better. Thanks!

------
Strilanc
Why are the quantum measurements the focus of this paper? The real source of
entropy is the random bits being generated to decide which measurement to
perform; the measurement actually being performed is just an after-show.

Regardless, I think it's clear that assumption `(i)` is the one that breaks:
the system affects the decision of what to measure. The stream of random bits
will consume all the neg-entropy in the system, cause heat death, and thereby
break whatever mechanism was doing the measuring (e.g. if it was you, then you
would die).

------
senekerim
I haven't read the paper, nor am I an expert, but the assumption (i) sounds
fishy "the decision of which measurement is performed on a quantum system can
be made independently of the system". By fishy, I mean obviously false. Which
means being incompatible with this assumption is OK. I'm probably missing
something...

~~~
catpolice
"Independently" is also a loaded word - one could mean that there's no direct
causal connection between the state of the system and the state of the
measurement apparatus, or one could mean that those two states are (in
ensemble experiments) independent in the statistical sense.

In order for Bell's theorem (and a lot of subsequent quantum theory) to work,
we have to interpret causal and statistical independence as being one and the
same. But the more one learns about the theoretical justification for this
conflation, the shakier it seems. Bell, in particular, justified it by
claiming that it was unscientific to assume that experimenters didn't have
free will. Okay, sure.

Any universe where the assumption that experimental measurement settings are
always already statistically correlated with the state of the system being
measured (even if that correlation would have to have been established
millennia ago) is fundamentally weird in certain ways - these kinds of
theories are sometimes called 'conspiracy theories' as it sort of seems like
all the information is there and nature is conspiring to hide it from us. But
there's a whole branch of super-determinist interpretations of quantum
mechanics motivated by the sense that this kind of weirdness is not as bad as
the kind of weirdness we'd have to otherwise accept. This kind of work has
been out of fashion for a while, but it seems to be gaining a certain amount
of momentum in the last decade or so.

~~~
effie
_" Bell, in particular, justified it by claiming that it was unscientific to
assume that experimenters didn't have free will. Okay, sure."_ You make some
good points. I am not sure how Bell meant this, but read out of context, this
is obviously false. Deterministic modelling (and therefore lack of absolute
free will of the components of the system) is a long tradition of science.

~~~
catpolice
For various reasons, in quantum mechanics, one typically excludes the observer
from the system being modeled. This is obviously problematic, especially if
you're doing large scale cosmology. But that's the measurement problem for
you.

Regarding the context, the quote I'm thinking of comes from one of the essays
in Speakable and Unspeakable in Quantum Mechanics, which is an enlightening
read, both in terms of content and for its historical value. The issue, I
think, is that the kind of 'conspiracy' implied by superdeterminist theories,
wherein nature sort of guides our hand in picking certain experimental
settings so as to hide information seems troubling to many scientists. See
Zeilinger's quote at
[https://en.wikipedia.org/wiki/Superdeterminism](https://en.wikipedia.org/wiki/Superdeterminism)

------
lukeqsee
Science aside, I found the authorship fascinating and encouraging; it is
composed of individuals from five different countries and cultures (Sweden,
Germany, UK, Spain, and China).

Is this typical for science?

~~~
n4r9
Not that uncommon in quantum foundations, where researchers are often few and
far between (partly due to the competitive academic job market).

