Sunday, February 8, 2015

Killing Schroedinger's Cat

Quantum mechanics is often described as teaching that Schrödinger's cat is alive and dead at the same time. I believe that this is a mistake in the first paragraph of the Wikipedia article.

The Wikipedia article on the Copenhagen interpretation describes:
This thought experiment highlights the implications that accepting uncertainty at the microscopic level has on macroscopic objects. A cat is put in a sealed box, with its life or death made dependent on the state of a subatomic particle. Thus a description of the cat during the course of the experiment — having been entangled with the state of a subatomic particle — becomes a "blur" of "living and dead cat." But this can't be accurate because it implies the cat is actually both dead and alive until the box is opened to check on it. But the cat, if it survives, will only remember being alive. Schrödinger resists "so naively accepting as valid a 'blurred model' for representing reality."
This is a reasonable description of the paradox.

Schroedinger's original account does not say that the cat is really alive and dead. He says that this is a ridiculous case, that the psi-function expresses a mixture of a live and dead cat, that direct observation resolves the indeterminacy, and that we do not accept the blurred model as reality.

The Many Worlds interpretation says that the cat is alive and dead in parallel universes. But of course Schroedinger was not talking about any such nonsense.

The Wikipedia philosophy is to prefer secondary sources to primary sources. So if Schroedinger says one thing about his cat, and The Complete Idiot's Guide to Theories of the Universe says something else, Wikipedia goes with the Idiot's Guide.

If you have an informed opinion on this, please express it on Talk:Schrödinger's cat. Otherwise I will be outvoted.

Update: A comment below says that my position is unclear. I proposed:
The scenario presents a cat that is randomly put in a state where alive and dead are both possibilities, requiring further observation to determine which.
The objection was that his sounds boring and non-paradoxical, while popular accounts say that the cat is alive and dead at the same time.

My answer is that the physical set-up is not mysterious at all, and should be explained in a straightforward way. It only becomes mysterious when you add some interpretation of the quantum wave function. But the current page says:
The scenario presents a cat that may be considered as being simultaneously both alive and dead,[1][2][3][4][5][6][7] as a result of being part of a system that exists in a state known as quantum superposition, where the cat is causally linked to a random subatomic event that may or may not occur.
I find this confusing, adn far removed from Schrodinger's original point.

1 comment:

  1. Roger,

    I browsed through the first page on the Talk, but didn't quite follow what exactly the piece should look like, according to you.

    I mean, I found you raising (IMO proper) exceptions to those other proposed pieces, but I didn't quite find your presenting the correct piece to replace these erroneous/misleading/not-so-well-phrased ones.

    So, here is a request.

    Please write the correctly worded piece at this blog (perhaps via an update to this post). Then, I would make sure to give you some feedback, and then, if further necessary, I may also join the discussion at the Wiki, though I would hate to create an account there and all---my usual expectations from the Wiki aren't all that big anyway (and I don't say it in a complaining sort of a tone---just a factual one). It's OK if Wiki isn't too exact when it comes to descriptions, as far as I am concerned. I only want them to be readable and representative of literature, and exact when it comes to definitions, equations, graphics, and links. But if they aren't exact in the verbal descriptions or interpretations, that's not too unsatisfactory by me.

    In short, please see if you can supply in toto the correct replacement for the description.