6 ms·

The article is of course oversimplifying, but if I understand correctly the irreversibility in the qubit system comes from the fact that they assume you don't k

The article is of course oversimplifying, but if I understand correctly the irreversibility in the qubit system comes from the fact that they assume you don't know the states of the qubit chain that transforms the first qubit from B_1 to B_2. If you'd know that the state would be pure and it would be easy to reverse the entanglement, it's just that if you look at the state of the first qubit alone that it's mixed. I actually envisioned a similar thought experiment that could be done with a very complex quantum computer (say millions of qubits) to test whether the universe is actually keeping tabs of all these states or if it gives up at some point and produces irreversibility. But I guess if you'd formulate it like that the academic community wouldn't take you very seriously anymore. I'd wager Deutsch's actual motivation might be along this line, as he seemed very interested to find a way to test the many worlds interpretation against other interpretations of quantum mechanics.

boole1854 4y ago
Deutsch's position is actually that the many worlds interpretation has already been tested and has passed the tests so far, whereas rival theories have been refuted. See https://www.sciencedirect.com/science/article/pii/S135521981530023X https://www.sciencedirect.com/science/article/pii/S135521981...
- lisper 4y ago
  Deutsch is wrong. http://blog.rongarret.info/2019/07/the-trouble-with-many-worlds.html http://blog.rongarret.info/2019/07/the-trouble-with-many-wor...
  - boole1854 4y ago
    To summarize the argument that the blog post makes: The multiverse interpretation accounts for cases where the probabilities of each distinct observable outcome are equal according to the Born rule. But it cannot account for cases where the Born rule says there are non-equal probabilities for the possible outcomes. This is a fairly common problem which critics of the multiverse interpretation raise. See [1] for another example where a critic raises that problem in more detail (with examples). Deutsch and others have responded. In short, the reply is that the mathematics of the Schrodinger equation describes a density of universes in the continuum which is the multiverse, not a finite set of distinct, interacting single universes. This undercuts the critics' argument. See [2] for an example of this kind of response. [1] https://arxiv.org/pdf/0810.2657.pdf https://arxiv.org/pdf/0810.2657.pdf [2] https://www.pnas.org/doi/pdf/10.1073/pnas.1324238111 https://www.pnas.org/doi/pdf/10.1073/pnas.1324238111
    - spekcular 4y ago
      Your reference [2] is somewhat suspect. As far as I know, it is not generally accepted in the physics community that the Born rule can be derived directly from the Schrodinger equation. In fact, it seems generally accepted that such a derivation does not currently exist, and MWI has to stick it in as an additional postulate in some form (or otherwise give an auxiliary argument for it, none of which seem generally accepted either). Further, the author of that paper, Frank Tipler, is a notorious nutjob: https://en.wikipedia.org/wiki/Frank_J._Tipler https://en.wikipedia.org/wiki/Frank_J._Tipler. I don't have time at the moment to review the paper in detail to locate any potential flaws, but I wanted to flag this for others. I think there is substantial reason to be skeptical.
      - boole1854 4y ago
        I agree that Tipler is far off the deep end on on some topics. But you should check out that one paper I linked nevertheless. PNAS is not a junk journal. I also agree there is no consensus that the problem of getting Born's rule from the Schrodinger equation has been solved to everyone's satisfaction.
        spekcular 4y ago
        PNAS publishes a lot of junk. If you're connected to the Academy you can get papers through with very light review. In fact, one can even seen this happened in the Tipler paper: "This Direct Submission article had a prearranged editor." [0] Andrew Gelman calls it a "tabloid": https://statmodeling.stat.columbia.edu/2014/06/17/hurricaneshimmicanes-extra-problematic-nature-scientific-publication-process/ https://statmodeling.stat.columbia.edu/2014/06/17/hurricanes.... I will check the paper out though. [0] https://www.science.org/content/blog-post/no-more-prearranged-editors-pnas https://www.science.org/content/blog-post/no-more-prearrange... Edit: I read the paper. It is borderline crank work. There are decent arguments for the Born rule in MWI but this is not one of them. (I like David Wallace's book, for example.)
        boole1854 4y ago

boole1854 4y ago

Deutsch's position is actually that the many worlds interpretation has already been tested and has passed the tests so far, whereas rival theories have been refuted. See https://www.sciencedirect.com/science/article/pii/S135521981530023X https://www.sciencedirect.com/science/article/pii/S135521981...

lisper 4y ago
Deutsch is wrong. http://blog.rongarret.info/2019/07/the-trouble-with-many-worlds.html http://blog.rongarret.info/2019/07/the-trouble-with-many-wor...
- boole1854 4y ago
  To summarize the argument that the blog post makes: The multiverse interpretation accounts for cases where the probabilities of each distinct observable outcome are equal according to the Born rule. But it cannot account for cases where the Born rule says there are non-equal probabilities for the possible outcomes. This is a fairly common problem which critics of the multiverse interpretation raise. See [1] for another example where a critic raises that problem in more detail (with examples). Deutsch and others have responded. In short, the reply is that the mathematics of the Schrodinger equation describes a density of universes in the continuum which is the multiverse, not a finite set of distinct, interacting single universes. This undercuts the critics' argument. See [2] for an example of this kind of response. [1] https://arxiv.org/pdf/0810.2657.pdf https://arxiv.org/pdf/0810.2657.pdf [2] https://www.pnas.org/doi/pdf/10.1073/pnas.1324238111 https://www.pnas.org/doi/pdf/10.1073/pnas.1324238111
  - spekcular 4y ago
    Your reference [2] is somewhat suspect. As far as I know, it is not generally accepted in the physics community that the Born rule can be derived directly from the Schrodinger equation. In fact, it seems generally accepted that such a derivation does not currently exist, and MWI has to stick it in as an additional postulate in some form (or otherwise give an auxiliary argument for it, none of which seem generally accepted either). Further, the author of that paper, Frank Tipler, is a notorious nutjob: https://en.wikipedia.org/wiki/Frank_J._Tipler https://en.wikipedia.org/wiki/Frank_J._Tipler. I don't have time at the moment to review the paper in detail to locate any potential flaws, but I wanted to flag this for others. I think there is substantial reason to be skeptical.
    - boole1854 4y ago
      I agree that Tipler is far off the deep end on on some topics. But you should check out that one paper I linked nevertheless. PNAS is not a junk journal. I also agree there is no consensus that the problem of getting Born's rule from the Schrodinger equation has been solved to everyone's satisfaction.
      - spekcular 4y ago
        PNAS publishes a lot of junk. If you're connected to the Academy you can get papers through with very light review. In fact, one can even seen this happened in the Tipler paper: "This Direct Submission article had a prearranged editor." [0] Andrew Gelman calls it a "tabloid": https://statmodeling.stat.columbia.edu/2014/06/17/hurricaneshimmicanes-extra-problematic-nature-scientific-publication-process/ https://statmodeling.stat.columbia.edu/2014/06/17/hurricanes.... I will check the paper out though. [0] https://www.science.org/content/blog-post/no-more-prearranged-editors-pnas https://www.science.org/content/blog-post/no-more-prearrange... Edit: I read the paper. It is borderline crank work. There are decent arguments for the Born rule in MWI but this is not one of them. (I like David Wallace's book, for example.)
        boole1854 4y ago