What is the Universe?

A student shared the following with me. First, Through the Wormhole asks whether the universe could be alive:


IS THE UNIVERSE ALIVE?(2012) by costello74

Second, Seth Lloyd talking about the universe as a quantum computer:

YouTube Preview Image

And finally, here’s Catherine Keller talking about quantum theology.

  • David_Evans

    I gave up on Through The Wormhole when the professor explained that the larger an organism is, the slower its pulse rate. This even works for cities, he said, their pulse rate is twice a day. Well, guess what, that’s true for all towns and cities whatever their size. It’s to do with the day/night cycle of work and rest, not with any imagined organic relationship depending on size.

    There are processes in the universe that bear some sort of analogy to life. For instance, gas and dust clouds form into stars which ultimately explode, throwing their material out into space to form new gas and dust clouds. You could say the clouds reproduce in that way. But that’s a very limited process. It doesn’t evolve or learn. And it will run out of material, because not all stars explode.

  • arcseconds

    I haven’t listened to any of these yet, but I always find claims that the universe is a computer (quantum or not) frustrating.

    What is it supposed to be computing exactly? Its own state from moment to moment? Why should we view that as a computation, and how does calling it a computation distinguish it from any other process?

    If any process is a computational process, then ‘computational’ has just lost any distinctive meaning. ‘The universe is a quantum computer’ would just reduce to an assertion that ‘the universe is quantum’, and we knew that already.

    • Pseudonym

      If any process is a computational process, then ‘computational’ has just lost any distinctive meaning.

      Maybe.

      People aren’t just throwing out this idea for no reason. It’s actually to do with modern mathematics which finds deep connections everywhere, largely thanks to the language of category theory.

      This is at least a semester-long course, so I can’t really explain why here. It started with the Curry-Howard isomorphism, which states that, in a very deep sense, computer programs are mathematical proofs in disguise (and vice versa, which is why it’s an isomorphism). One good summary is this survey by Baez and Stay which shows the formal connections between physics, topology, computer science, and logic.

      So the statement that the universe is a quantum computer is really saying that they are formally equivalent.

      • arcseconds

        I know what the Curry-Howard isomorphism is, but this doesn’t clarify anything for me. The universe is far less obviously a proof than it is a computer program, so this does nothing to convince me it ought to be considered a computer program.

        The notion of a computer program used in the Curry-Howard isomorphism is the notion normally used in computability theory, where a computer program is fundamentally considered to be implementing a function which terminates and outputs a value. It’s this outputted value which is isomorphic to the conclusion of a proof. This is in a sense quite an old fashioned notion of what a computer is for, and it’s quite different from a computer program being an interactive thing that runs indefinitely, like facebook or whatever.

        What value do you suppose the Universe is computing? Are you expecting it to terminate once it has computed this value?

        (Also, the notion of computability used in the Curry-Howard isomorphism is the typed lambda calculus, or equivalent, which is a more restricted notion than general Turing computability. In particular, a typed lambda calculus program can be guaranteed to terminate. To the extent the universe can be said to be computable at all, it’s almost certainly a richer notion of computability that is required than Turing computability, not a more restricted notion. Plus it seems weird to suggest that the Universe is guaranteed to terminate, not because of the usual sorts of physical considerations, but because of the kind of computer it is.)

        Consider an engine (a steam engine, maybe) that has behaviour computable by an ordinary non-quantum computer. The states of the machine are isomorphic to the states of a computer simulation. But is it correct to say it is a computer? Of course not: it’s an engine, and we use it to move stuff, not produce information.

        As far as I know, a quantum computer (at least as they are normally considered) can only compute what a Turing machine can, except in some cases it can do so more efficiently. A qubit can exist in a superposition of states, but on output it collapses into either a 1 or a 0. Whereas as far as we know, physics is real-valued.

        Also, there are plenty of other things we associate with computers. They are designed with a purpose in mind, so there are such things as malfunctions. They are programmed (programs are separable from hardware) and programs, while informational entities rather than physical ones, also have purposes and therefore can have bugs. Memory is separate from the computing engine. These are not strictly part of an abstract view of computing, no, but they are important considerations nevertheless. None of this appears to be remotely true of the universe, unless someone knows something I don’t.

        So the best I can make sense of this claim that the universe is a quantum computer is to say that the states of the universe are in principle computable by a real-valued quantum computer. This is already a much less sexy claim than ‘the universe is a computer’.

        This putative (hyper)computer is already a very different kind of thing to the computer that sits on your desk, but it still has a purpose (computing the state of the universe) which it can in principle fail at. So there the notion of a computer seems somewhat applicable in a way in which it is not to the universe.

        But maybe I should just listen to the video…

        thanks for the link by the way, I’ll read it later.


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