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Does spacetime imply fatalism?

  1. May 1, 2015 #1
    I'm currently reading Relativity: A Very Short Introduction. One part caught my attention:

    spacetime2.PNG

    Does this mean that the future is already embedded in spacetime?
     
    Last edited: May 1, 2015
  2. jcsd
  3. May 1, 2015 #2

    PeterDonis

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    Only to the extent that the future is determined by the past. Spacetime is a model, not reality. In the model, when we are analyzing scenarios, we simply declare by fiat what the future is; that is, we idealize the situation as one which is perfectly deterministic, and in which we know all of the relevant initial conditions to be able to determine the entire spacetime. In any real situation, we do not have that kind of knowledge; we don't know all the initial conditions, and we don't even know that the universe as a whole is deterministic, because of quantum uncertainty. So we can't use the spacetime model to make metaphysical claims about our actual universe. (Not that that stops a lot of people from trying.)
     
  4. May 1, 2015 #3

    bcrowell

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    The word "spacetime" isn't a label for a theory or a true/false statement. It doesn't make predictions or imply anything. The word "fatalism" doesn't have any well-defined meaning that I know of in physics, although you may mean determinism or causality. Causality is a complicated issue in the philosophy of science, but as far as I know special relativity doesn't say anything about causality that is at all different from what Galilean relativity says. A typical physicist's definition of causality is that Cauchy surfaces exist. Cauchy surfaces exist in Galilean relativity, and they also exist in special relativity.
     
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