The transactional interpretation of quantum mechanics

An entry in Ars Mathematica has alerted me to John Cramer’s Transactional Interpretation of Quantum Mechanics [see also Wikipedia]. It feels exactly right.

The trouble with quantum mechanics has always been that it makes accurate predictions but doesn’t make sense. People make a virtue of this. It shows how far above our heads the whole theory is. “My thoughts are not your thoughts, my ways are not your ways, says the Lord”.

This is self-indulgent obscurantism and it leads to such New Age loopiness as The Dancing Wu Li Masters (in which, among other delights, every chapter is called Chapter One).

The transactional interpretation is solidly and sensibly based on mathematics – specifically, on a bit of mathematics that has mostly been ignored because it’s embarrassing.

When anthropic reasoning won’t work

If you want to use anthropic arguments to get rid of “why” questions in physics, then these work quite well when you’re dealing with integer-valued questions – “why does space have three dimensions and not two or four?”. They work less well in other cases.

Take the Fine Structure Constant, for example. This is usually written as 1/α²=137.0359 (or thereabouts) and there is a respectable body of work showing that a change of even a few percentage points in this value would make intelligent-life-as-we-know-it impossible.

Let’s leave to one side all the begged questions about intelligent-life-as-we-don’t-know-it and consider: can anthropic considerations explain the value of 1/α²?

The Anthropic Principle: high minds and High Table

The Anthropic Principle is a way for physics to deal with awkward "why?" questions. It answers "Why is the world like this?" with "Because if it weren't, you wouldn't be here to ask the question". We are here, in other words, because we're here because we're here.

J.R. Lucas gives an excellent example of the Anthropic Principle in his classic "high-don" and "low-don" arguments for the world having at least three dimensions. Why are there not just two dimensions? The high don answers that in two dimensions we wouldn't be able to think intelligently; the low don answers that in two dimensions we wouldn't be able to eat without stopping. (More respectably: in two dimensions there is little scope for non-intersecting neural connections; and a creature with a gut would be split by the gut into two creatures).