Followup to:  Science Doesn't Trust Your Rationality, My Wild and Reckless Youth

Once upon a time, a younger Eliezer had a stupid theory.  Let's say that Eliezer₁₈'s stupid theory was that consciousness was caused by closed timelike curves hiding in quantum gravity.  This isn't the whole story, not even close, but it will do for a start.

And there came a point where I looked back, and realized:

1. I had carefully followed everything I'd been told was Traditionally Rational, in the course of going astray.  For example, I'd been careful to only believe in stupid theories that made novel experimental predictions, e.g., that neuronal microtubules would be found to support coherent quantum states.
2. Science would have been perfectly fine with my spending ten years trying to test my stupid theory, only to get a negative experimental result, so long as I then said, "Oh, well, I guess my theory was wrong."

From Science's perspective, that is how things are supposed to work—happy fun for everyone.  You admitted your error!  Good for you!  Isn't that what Science is all about?

But what if I didn't want to waste ten years?

Well... Science didn't have much to say about that.  How could Science say which theory was right, in advance of the experimental test?  Science doesn't care where your theory comes from—it just says, "Go test it."

This is the great strength of Science, and also its great weakness.

Followup to:  The Dilemma: Science or Bayes?

Scott Aaronson suggests that Many-Worlds and libertarianism are similar in that they are both cases of bullet-swallowing, rather than bullet-dodging:

Libertarianism and MWI are both are grand philosophical theories that start from premises that almost all educated people accept (quantum mechanics in the one case, Econ 101 in the other), and claim to reach conclusions that most educated people reject, or are at least puzzled by (the existence of parallel universes / the desirability of eliminating fire departments).

Now there's an analogy that would never have occurred to me.

I've previously argued that Science rejects Many-Worlds but Bayes accepts it.  (Here, "Science" is capitalized because we are talking about the idealized form of Science, not just the actual social process of science.)

It furthermore seems to me that there is a deep analogy between (small-'l') libertarianism and Science:

1. Both are based on a pragmatic distrust of reasonable-sounding arguments.
2. Both try to build systems that are more trustworthy than the people in them.
3. Both accept that people are flawed, and try to harness their flaws to power the system.

Followup to:  If Many-Worlds Had Come First, The Failures of Eld Science

"Eli: You are writing a lot about physics recently.  Why?"
        —Shane Legg (and several other people)

"In light of your QM explanation, which to me sounds perfectly logical, it seems obvious and normal that many worlds is overwhelmingly likely. It just seems almost too good to be true that I now get what plenty of genius quantum physicists still can't. [...] Sure I can explain all that away, and I still think you're right, I'm just suspicious of myself for believing the first believable explanation I met."
        —Recovering irrationalist

RI, you've got no idea how glad I was to see you post that comment.

Of course I had more than just one reason for spending all that time posting about quantum physics.  I like having lots of hidden motives, it's the closest I can ethically get to being a supervillain.

But to give an example of a purpose I could only accomplish by discussing quantum physics...

In physics, you can get absolutely clear-cut issues.  Not in the sense that the issues are trivial to explain.  But if you try to apply Bayes to healthcare, or economics, you may not be able to formally lay out what is the simplest hypothesis, or what the evidence supports.  But when I say "macroscopic decoherence is simpler than collapse" it is actually strict simplicity; you could write the two hypotheses out as computer programs and count the lines of code. Nor is the evidence itself in dispute.

I wanted a very clear example—Bayes says "zig", this is a zag—when it came time to break your allegiance to Science.

Followup to:  Initiation Ceremony, If Many-Worlds Had Come First

This time there were no robes, no hoods, no masks.  Students were expected to become friends, and allies.  And everyone knew why you were in the classroom.  It would have been pointless to pretend you weren't in the Conspiracy.

Their sensei was Jeffreyssai, who might have been the best of his era, in his era.  His students were either the most promising learners, or those whom the beisutsukai saw political advantage in molding.

Brennan fell into the latter category, and knew it.  Nor had he hesitated to use his Mistress's name to open doors.  You used every avenue available to you, in seeking knowledge; that was respected here.

"—for over thirty years," Jeffreyssai said.  "Not one of them saw it; not Einstein, not Schrödinger, not even von Neumann."  He turned away from his sketcher, and toward the classroom.  "I pose to you to the question:  How did they fail?"

The students exchanged quick glances, a calculus of mutual risk between the wary and the merely baffled.  Jeffreyssai was known to play games.

Previously in series: Collapse Postulates
Followup to:  Bell's Theorem, Spooky Action at a Distance, Quantum Non-Realism, Decoherence is Simple, Falsifiable and Testable

If you look at many microscopic physical phenomena—a photon, an electron, a hydrogen atom, a laser—and a million other known experimental setups—it is possible to come up with simple laws that seem to govern all small things (so long as you don't ask about gravity).  These laws govern the evolution of a highly abstract and mathematical object that I've been calling the "amplitude distribution", but which is more widely referred to as the "wavefunction".

Now there are gruesome questions about the proper generalization that covers all these tiny cases.  Call an object 'grue' if it appears green before January 1, 2020 and appears blue thereafter.  If all emeralds examined so far have appeared green, is the proper generalization, "Emeralds are green" or "Emeralds are grue"?

The answer is that the proper generalization is "Emeralds are green".  I'm not going to go into the arguments at the moment.  It is not the subject of this post, and the obvious answer in this case happens to be correct.  The true Way is not stupid: however clever you may be with your logic, it should finally arrive at the right answer rather than a wrong one.

In a similar sense, the simplest generalizations that would cover observed microscopic phenomena alone, take the form of "All electrons have spin 1/2" and not "All electrons have spin 1/2 before January 1, 2020" or "All electrons have spin 1/2 unless they are part of an entangled system that weighs more than 1 gram."

Followup to: Collapse Postulates, Decoherence is Simple, Falsifiable and Testable

Not that I'm claiming I could have done better, if I'd been born into that time, instead of this one...

Macroscopic decoherence—the idea that the known quantum laws that govern microscopic events, might simply govern at all levels without alteration—also known as "many-worlds"—was first proposed in a 1957 paper by Hugh Everett III.  The paper was ignored.  John Wheeler told Everett to see Niels Bohr.  Bohr didn't take him seriously.

Crushed, Everett left academic physics, invented the general use of Lagrange multipliers in optimization problems, and became a multimillionaire.

It wasn't until 1970, when Bryce DeWitt (who coined the term "many-worlds") wrote an article for Physics Today, that the general field was first informed of Everett's ideas.  Macroscopic decoherence has been gaining advocates ever since, and may now be the majority viewpoint (or not).

But suppose that decoherence and macroscopic decoherence had been realized immediately following the discovery of entanglement, in the 1920s.  And suppose that no one had proposed collapse theories until 1957.  Would decoherence now be steadily declining in popularity, while collapse theories were slowly gaining steam?

Imagine an alternate Earth, where the very first physicist to discover entanglement and superposition, said, "Holy flaming monkeys, there's a zillion other Earths out there!"

In the years since, many hypotheses have been proposed to explain the mysterious Born probabilities.  But no one has yet suggested a collapse postulate.  That possibility simply has not occurred to anyone.

One day, Huve Erett walks into the office of Biels Nohr...

Previously in series:  Spooky Action at a Distance
Followup to:  Decoherence is Simple, Falsifiable and Testable

Back when people didn't know about macroscopic decoherence aka many-worlds—before it occurred to anyone that the laws deduced with such precision for microscopic physics, might apply universally at all levels—what did people think was going on?

The initial reasoning seems to have gone something like:

"When my calculations showed an amplitude of -1/3i for this photon to get absorbed, my experimental statistics showed that the photon was absorbed around 107 times out of 1000, which is a good fit to 1/9, the square of the modulus."

to

"The amplitude is the probability (by way of the squared modulus)."

to

"Once you measure something and know it didn't happen, its probability goes to zero."

Read literally, this implies that knowledge itself—or even conscious awareness—causes the collapse.  Which was in fact the form of the theory put forth by Werner Heisenberg!

Followup to:  Bell's Theorem

"Does the moon exist when no one is looking at it?"
        —Albert Einstein, asked of Niels Bohr

Suppose you were just starting to work out a theory of quantum mechanics.

You begin to encounter experiments that deliver different results depending on how closely you observe them.  You dig underneath the reality you know, and find an extremely precise mathematical description that only gives you the relative frequency of outcomes; worse, it's made of complex numbers.  Things behave like particles on Monday and waves on Tuesday.

The correct answer is not available to you as a hypothesis, because it will not be invented for another thirty years.

In a mess like that, what's the best you could do?

Continuation of:  Decoherence is Simple

The words "falsifiable" and "testable" are sometimes used interchangeably, which imprecision is the price of speaking in English.  There are two different probability-theoretic qualities I wish to discuss here, and I will refer to one as "falsifiable" and the other as "testable" because it seems like the best fit.

As for the math, it begins, as so many things do, with:

This is Bayes's Theorem.  I own at least two distinct items of clothing printed with this theorem, so it must be important.

An epistle to the physicists:

When I was but a little lad, my father, a Ph.D. physicist, warned me sternly against meddling in the affairs of physicists; he said that it was hopeless to try to comprehend physics without the formal math. Period.  No escape clauses.  But I had read in Feynman's popular books that if you really understood physics, you ought to be able to explain it to a nonphysicist.  I believed Feynman instead of my father, because Feynman had won the Nobel Prize and my father had not.

It was not until later—when I was reading the Feynman Lectures, in fact—that I realized that my father had given me the simple and honest truth.  No math = no physics.

By vocation I am a Bayesian, not a physicist.  Yet although I was raised not to meddle in the affairs of physicists, my hand has been forced by the occasional gross misuse of three terms:  Simple, falsifiable, and testable.

The foregoing introduction is so that you don't laugh, and say, "Of course I know what those words mean!"  There is math here.