Reply To: General "Block Universe" Discussion

Robert Griffiths

I confess I don’t know what a block universe is supposed to be. I looked briefly at the attachments at #2659 (Ken) and #2664 (Mark), and did not find them very enlightening. So maybe I’m just a blockhead. Anyway, here is my vague idea of what is involved, which then motivates a couple of questions which may be equally vague. Comments would be appreciated.

My assumption is that a block universe (blockworld) is an attempt to model events in spacetime by assigning to every point in spacetime a something, a state of affairs, assuming that one has introduced a suitable 4-dimensional coordinate system to label those points. These events at different points are then related to each other via some physical law or laws, probably deterministic, at least for classical physics. Since there are various ways to choose coordinate systems one also wants to have some idea of the rules for transforming from one coordinate system to another, but the transformation rules are then assumed to be ‘local’. I.e., given what is going on at or near some point in spacetime I can carry out the transformation, which will tell me what is going on at the same (but relabeled) point in the new coordinate system according to some well-defined rules, such as how to transform energy and momentum when one goes to a different Lorentz frame.

This is reasonably easy to visualize in the deterministic world of classical physics. However, if we allow some sort of stochastic time development where there is a probabilistic association between events at different times, the picture is not so clear to me: do we have a single block world filled with what actually occurs, or do we just say that there are a large number of different possibilities (different block worlds) to which we will assign probabilities? And, which is probably harder, how am I supposed to think about entangled quantum states in a block universe? Or is this last difficulty a good reason for abandoning the idea of a quantum block universe?

Bob Griffiths

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