Let me try an experiment: using a blog post to develop a taxonomy.  Here I'll try to develop a list/taxonomy of (at least semi-coherent) answers to the question I posed yesterday: why is it harder to formally predict pasts, versus futures (from presents)? Mostly these are explanations of the "past hypothesis", but I'm trying to stay open-minded toward a wide range of explanations.

I'll start with a list of answers, and then add more and group them as I read comments, think, etc.  I'll feel free to edit the post from here on:

• Extremely unlikely:

  • Reality isn't different; we just ask different future vs. past questions.

  • An outside "God" intervened to make our past different.

  • We live after a big local ebb (i.e., fluctuation) in matter.

• Rather unlikely:

  • Quantum measurement has a local time asymmetry that makes big effects.

  • A weak local time asymmetry in matter accumulates to big effects.

  • A past ebb in spacetime shape (e.g., inflation) forced a big matter ebb.

  • All spacetime boundaries satisfy a law-like "low entropy" condition.

• Unlikely:

  • Our expanding cosmos violates one-to-one state mappings across time.

  • Past and future have different spacetime law-like boundary conditions.