8 ms·

Thermodynamical cost of some interpretations of quantum theory

49 points by n4r9 11y ago

rubidium 11y ago
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 11y ago
  > 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 11y ago
    "no intrinsic properties of the world that are not relational." I like that better. Thanks!
- tjradcliffe 11y ago
  I agree on the phrasing issue. Both there "types" seem to require Bohr's classical observer, but as soon as you assume that observers are classical you've swept the big question under the carpet, which is, "Why is there a classical world at all?" Decoherence and similar approaches at least try to address this question, and don't fit at all well with their two-Type scheme. Or to put it another way: observers are intrinsic to reality as well as the systems under observation, and any attempt to treat them separately will fail. But this is uninteresting, because any interpretation is going to have to acknowledge this at some level (as Bohr correctly pointed out quite a long time ago.)
  - n4r9 11y ago
    If you've got Many Worlds at the back of your mind there, rest assured (!) that the lead author considers it to be a Type-I interpretation See http://arxiv.org/pdf/1509.04711v1.pdf http://arxiv.org/pdf/1509.04711v1.pdf
senekerim 11y ago
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...
- danbruc 11y ago
  What don't you like about that? Physicists go to great lengths to make sure that random decisions are not accidentally influenced in unexpected ways, for example by basing the decision on light from quasars at the other end of the universe [1]. [1] http://www.nature.com/news/cosmic-light-could-close-quantum-weirdness-loophole-1.14771 http://www.nature.com/news/cosmic-light-could-close-quantum-...
  - senekerim 11y ago
    The influence may be negligible, but it's theoretically there. The decision-maker is part of the same system (decision is happening within a system of neurons augmented with electronic tools, all of which exist in the same physical reality).
    - danbruc 11y ago
      There are no neurons involved, essentially random number generators are making the decisions and in such experiments usually in the nanosecond range while particles are in flight between source and detector to ensure that the decision can not influence the creation and preparation process. And by using a source of randomness billions of light years away it becomes very unlikely that the particle source and the source of randomness could have interacted in an interesting way because the universe is to young to allow interactions due to the finite speed of light. There is of course still a possibility that an interaction happened when the universe was still young and tiny but you can probably imagine what kind of conspiracy the universe would have to have going on for that to work.
      - deleted 11y ago
Strilanc 11y ago
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).
lukeqsee 11y ago
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 11y ago
  Not that uncommon in quantum foundations, where researchers are often few and far between (partly due to the competitive academic job market).
- chessweb01 11y ago
  ... and yet they are entangled ;-)

49 points by n4r9 11y ago

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 11y ago
> 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 11y ago
  "no intrinsic properties of the world that are not relational." I like that better. Thanks!
tjradcliffe 11y ago
I agree on the phrasing issue. Both there "types" seem to require Bohr's classical observer, but as soon as you assume that observers are classical you've swept the big question under the carpet, which is, "Why is there a classical world at all?" Decoherence and similar approaches at least try to address this question, and don't fit at all well with their two-Type scheme. Or to put it another way: observers are intrinsic to reality as well as the systems under observation, and any attempt to treat them separately will fail. But this is uninteresting, because any interpretation is going to have to acknowledge this at some level (as Bohr correctly pointed out quite a long time ago.)
- n4r9 11y ago
  If you've got Many Worlds at the back of your mind there, rest assured (!) that the lead author considers it to be a Type-I interpretation See http://arxiv.org/pdf/1509.04711v1.pdf http://arxiv.org/pdf/1509.04711v1.pdf

senekerim 11y ago

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...

danbruc 11y ago
What don't you like about that? Physicists go to great lengths to make sure that random decisions are not accidentally influenced in unexpected ways, for example by basing the decision on light from quasars at the other end of the universe [1]. [1] http://www.nature.com/news/cosmic-light-could-close-quantum-weirdness-loophole-1.14771 http://www.nature.com/news/cosmic-light-could-close-quantum-...
- senekerim 11y ago
  The influence may be negligible, but it's theoretically there. The decision-maker is part of the same system (decision is happening within a system of neurons augmented with electronic tools, all of which exist in the same physical reality).
  - danbruc 11y ago
    There are no neurons involved, essentially random number generators are making the decisions and in such experiments usually in the nanosecond range while particles are in flight between source and detector to ensure that the decision can not influence the creation and preparation process. And by using a source of randomness billions of light years away it becomes very unlikely that the particle source and the source of randomness could have interacted in an interesting way because the universe is to young to allow interactions due to the finite speed of light. There is of course still a possibility that an interaction happened when the universe was still young and tiny but you can probably imagine what kind of conspiracy the universe would have to have going on for that to work.
    - deleted 11y ago

Strilanc 11y ago

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).

lukeqsee 11y ago

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 11y ago
Not that uncommon in quantum foundations, where researchers are often few and far between (partly due to the competitive academic job market).
chessweb01 11y ago
... and yet they are entangled ;-)