What's the Time?

What's The Time?
Well It's Gotta Be Close To Midnight
My Body's Talking To Me
It Says, 'Time For Danger'
.....................Mimi, in Rent

Time is a subject of endless fascination. It seems like most of the songs in Rent feature time as a major character. Proust's great novel is called "The Search for Times Lost" (more or less).

Physics has quite a bit to say about time, but a lot of it does violence to our familiar perceptions. Nothing in physics is more counterintuitive than the notion that the present is a sort of illusion. Classical physics, including special and general relativity tend to give us a picture of time as a sort of four-dimensional block, with a continuum leading from past to future with absolutely nothing special about the present. gr-qc/0605049 by G F R Ellis takes on this notion of "block time" and presents a sort of alternative.
The Block Universe idea, representing spacetime as a fixed whole, suggests the flow of time is an illusion: the entire universe just is, with no special meaning attached to the present time. This view is however based on time-reversible microphysical laws and does not represent macro-physical behaviour and the development of emergent complex systems, including life, which do indeed exist in the real universe. When these are taken into account, the unchanging block universe view of spacetime is best replaced by an evolving block universe which extends as time evolves, with the potential of the future continually becoming the certainty of the past. However this time evolution is not related to any preferred surfaces in spacetime; rather it is associated with the evolution of proper time along families of world lines

The answer to Mimi's question, it seems, comes down to a matter of coarse graining:
...unpredictability is a result of the implicit coarse-grained description of the physical system: changes in space time curvature occur that cannot be predicted from external view of the objects because that description does not include details of the internal mechanisms, including the specific bits making up the stored computer programme (these would be represented at a much finer level of description).

I hope he is right, because I really hate block time.

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