Posted by: dacalu | 25 November 2012

Two Roads and Vision

This post follows up on the last, in which I introduced the question of whether our universe continues down a fixed path or moves between possible paths.  Does the road fork?

Now that we have an idea of a branching or unbranching universe, I want to tackle the question of vision.  This is particularly important for an a empiricist, like myself.  I value what my senses tell me – but I’m also cautious.  Vision may not always be so straightforward as it appears.

I can look see things in the present, both in a literal sense and in a figurative sense.  If I say that I see my desk, that’s a literal statement.  Photons travel from my desk to my eyes, where they cause electrical impulses to travel to my brain.  If I say that I see what you mean, I’m being figurative.  It may well be that the same result occurs – electrical impulses in my brain –  but we think of it differently.  Medieval scholars called this faculty for having pictures in our head “imagination” and they debated quite hotly over the relationship between the internal image and the external reality.  These days we tend to reserve “imagination” for talking about things we see in our heads that don’t exist anywhere else.  Then, scholars wondered (following Plato) if the images came from some real, but non-physical source – the realm of perfect Ideas.  They thought the intellect “saw” things which the senses could not.  Just like sense vision, intellectual vision was an internal process that reflected an external reality.

Thus, when they imagined future events, they thought they must in some sense exist.  Otherwise, we couldn’t “see” them.  This begs the question of what it means to “see” the future.

Let me introduce two new words – retrospection for seeing the past and prospection for seeing the future.  We recognize that retrospection and prospection must be more like imagination than they are like physical vision.  We also recognize that they operate very differently.  Our retrospection may be clouded – we may not know what happened – but we are confident that there is exactly one past.  Beyond the clouds lies a single path stretching back into history.

On the other hand, prospection presents us with multiple futures.  Whether or not I believe in a branching universe, I must admit that two types of prospective images may inhabit my universe, futures that might come to pass and futures that cannot come to pass.  The former are possibilities, the latter illusions.  Strict determinists think that there is only a single future, one actual/possible and many illusions.  Non-determinists think there are at least two possibles (still only one actual) and many illusions.

Sadly, many of us can be confused by retrospection, prospection, and statistics.  How do you interpret statistics?  Retrospective statistics work beautifully.  I can say that the Sun has risen 100% of all days in history.  I can say that I flipped the coin 500 times and it came up heads (roughly) 50% of the times.  I can say that half of the Cesium has decayed or that half of the planets had rings last time I checked.  But what does it mean to apply statistics to the future?  What does it mean to say that 50% of future coin tosses will be heads or half of all planets we will observe have rings?  It becomes a problem of induction.  How do you argue from the past to the future?

The inequality of retrospection and prospection makes this particularly painful.  We want future probabilities to correspond to the proportion of imagined futures that agree with the actual future.  In either case we have to account for illusions, but in the branching path case, we also have to account for the chances of going down different possible paths.

When I say that physical determinism has been ruled out, I mean that the actual future cannot be predicted from the current state of the universe, but I have not said whether it is obscured by ignorance (as with retropsection), by illusions, or by multiple possibilities.  All three are consistent with quantum mechanics.  Empiricism cannot resolve the issue because, even if there are multiple paths, the whole set of communicating scientists travels down exactly one path.  The other patch can never be directly observed, only prospected.

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