5 ms·

Or the QM is just wrong about information never being lost.

tsimionescu 5y ago
Sure, that's a possibility. But, the problem is that this feature comes from a very fundamental place in QM's mathematics - QM is (almost) a linear theory, and with linear equations, information can't be lost. So, to assert that QM is wrong about this is to invalidate all of QM's equations. Now, it's important to recognize one thing: QM is not really a linear theory, because it also has Born's rule, or the Measurement postulate. That is, while the wavefunction evolves according to purely linear equations, when you ultimately want to measure the state of the system, you get a non-linear update: the wavefunction suddenly "collapses" to a single value, and information is indeed lost (different wave-functions can collapse to the same state after a measurement). However, the measurement postulate is itself poorly understood, so its hard to introduce it into the discussion without derailing things. There are even consistent interpretations of QM where this doesn't actually happen, such as Many Worlds, where the information is actually still preserved across the totality of the worlds.
- kgwgk 5y ago
  > the information is actually still preserved across the totality of the worlds That may be correct if the “totality of the worlds” means one single “world” described by a wave function evolving unitarily - corresponding to what you call information. This “information” cannot be destroyed but it cannot be created either. It will always be the same “information” that was already there at the beginning of time. What is unclear is the “many worlds” part. How are they defined?
  - tsimionescu 5y ago
    > It will always be the same “information” that was already there at the beginning of time. Yes, absolutely. Though it's worth noting that QM does allow for the void to have random fluctuations that are not caused by anything else, but that can interact with the existing system. > What is unclear is the “many worlds” part. How are they defined? There are several ways from what I've read. I personally don't think MWI really solves any problems, or that it is a good description of nature, so I haven't taken too much time to remember exactly how they do it.
    - kgwgk 5y ago
      > Though it's worth noting that QM does allow for the void to have random fluctuations that are not caused by anything else, but that can interact with the existing system. The random fluctuations are random only becase we observe whether they happened or not. If you consider QM to be just the deterministic evolution of a pure quantum state there is nothing random about them. You would say that the "information" about those "random fluctuations" was always there. > I personally don't think MWI really solves any problems I think we agree on that.

Sure, that's a possibility. But, the problem is that this feature comes from a very fundamental place in QM's mathematics - QM is (almost) a linear theory, and with linear equations, information can't be lost. So, to assert that QM is wrong about this is to invalidate all of QM's equations. Now, it's important to recognize one thing: QM is not really a linear theory, because it also has Born's rule, or the Measurement postulate. That is, while the wavefunction evolves according to purely linear equations, when you ultimately want to measure the state of the system, you get a non-linear update: the wavefunction suddenly "collapses" to a single value, and information is indeed lost (different wave-functions can collapse to the same state after a measurement). However, the measurement postulate is itself poorly understood, so its hard to introduce it into the discussion without derailing things. There are even consistent interpretations of QM where this doesn't actually happen, such as Many Worlds, where the information is actually still preserved across the totality of the worlds.

kgwgk 5y ago
> the information is actually still preserved across the totality of the worlds That may be correct if the “totality of the worlds” means one single “world” described by a wave function evolving unitarily - corresponding to what you call information. This “information” cannot be destroyed but it cannot be created either. It will always be the same “information” that was already there at the beginning of time. What is unclear is the “many worlds” part. How are they defined?
- tsimionescu 5y ago
  > It will always be the same “information” that was already there at the beginning of time. Yes, absolutely. Though it's worth noting that QM does allow for the void to have random fluctuations that are not caused by anything else, but that can interact with the existing system. > What is unclear is the “many worlds” part. How are they defined? There are several ways from what I've read. I personally don't think MWI really solves any problems, or that it is a good description of nature, so I haven't taken too much time to remember exactly how they do it.
  - kgwgk 5y ago
    > Though it's worth noting that QM does allow for the void to have random fluctuations that are not caused by anything else, but that can interact with the existing system. The random fluctuations are random only becase we observe whether they happened or not. If you consider QM to be just the deterministic evolution of a pure quantum state there is nothing random about them. You would say that the "information" about those "random fluctuations" was always there. > I personally don't think MWI really solves any problems I think we agree on that.