Why Can't We Predict The Past?

A curious quirk of reputation means occasionally I am posed parlor questions with a scent of the obtuse, if not a stench. The latest was "Why can't we predict the future?"

Drawing some opposing and passing vectors in my mind and considering recent speculations on the assymmetry of time it seemed appropriate to reply "Why can't we predict the past?"

Leaving that as the koan of the moment, let's add a few snags.

There is some speculation about a quantum of time, but no smoking clock. We tend to see the future as ephemeral and to some extent slightly probable, but view the past as fixed -- as if it were still there somewhere, even if we can't visit directly.

What if it isn't? What if there is no physical manifestation of the past or future, but just their fossils in the present?

Then let's speculate there is no quanta of time, no minimal durance of any particular event, no length to the vector of "now."

What are we left with?

What is the mass of the universe during an infinitely small "now" with no extant manifestion of "then" in either direction?

Or what if there is a quanta of time (either fixed or variable. It's not clear there would be any subjective difference). Let's call this "digital time."

For extra credit, consider Wolfram's idea that this would open the door to a universe where particle interactions could be described by a simple ruleset vis a vis cellular automata. In such a circumstance, what practical differences would there be compared to "analog time"?

Why does time always answer a question with another question?

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