Causal Universes
Followup to: Stuff that Makes Stuff Happen
Previous meditation: Does the idea that everything is made of causes and effects meaningfully constrain experience? Can you coherently say how reality might look, if our universe did not have the kind of structure that appears in a causal model?
I can describe to you at least one famous universe that didn't look like it had causal structure, namely the universe of J. K. Rowling's Harry Potter.
You might think that J. K. Rowling's universe doesn't have causal structure because it contains magic - that wizards wave their wands and cast spells, which doesn't make any sense and goes against all science, so J. K. Rowling's universe isn't 'causal'.
In this you would be completely mistaken. The domain of "causality" is just "stuff that makes stuff happen and happens because of other stuff". If Dumbledore waves his wand and therefore a rock floats into the air, that's causality. You don't even have to use words like 'therefore', let alone big fancy phrases like 'causal process', to put something into the lofty-sounding domain of causality. There's causality anywhere there's a noun, a verb, and a subject: 'Dumbledore's wand lifted the rock.' So far as I could tell, there wasn't anything in Lord of the Rings that violated causality.
You might worry that J. K. Rowling had made a continuity error, describing a spell working one way in one book, and a different way in a different book. But we could just suppose that the spell had changed over time. If we actually found ourselves in that apparent universe, and saw a spell have two different effects on two different occasions, we would not conclude that our universe was uncomputable, or that it couldn't be made of causes and effects.
No, the only part of J. K. Rowling's universe that violates 'cause and effect' is...
The Contrarian Status Catch-22
It used to puzzle me that Scott Aaronson still hasn't come to terms with the obvious absurdity of attempts to make quantum mechanics yield a single world.
I should have realized what was going on when I read Scott's blog post "The bullet-swallowers" in which Scott compares many-worlds to libertarianism. But light didn't dawn until my recent diavlog with Scott, where, at 50 minutes and 20 seconds, Scott says:
"What you've forced me to realize, Eliezer, and I thank you for this: What I'm uncomfortable with is not the many-worlds interpretation itself, it's the air of satisfaction that often comes with it."
-- Scott Aaronson, 50:20 in our Bloggingheads dialogue.
It doesn't show on my face (I need to learn to reveal my expressions more, people complain that I'm eerily motionless during these diavlogs) but at this point I'm thinking, Didn't Scott just outright concede the argument? (He didn't; I checked.) I mean, to me this sounds an awful lot like:
Sure, many-worlds is the simplest explanation that fits the facts, but I don't like the people who believe it.
And I strongly suspect that a lot of people out there who would refuse to identify themselves as "atheists" would say almost exactly the same thing:
What I'm uncomfortable with isn't the idea of a god-free physical universe, it's the air of satisfaction that atheists give off.
Quantum Mechanics and Personal Identity
This is one of several shortened indices into the Quantum Physics Sequence.
Suppose that someone built an exact duplicate of you on Mars, quark by quark - to the maximum level of resolution that quantum physics permits, which is considerably higher resolution than ordinary thermal uncertainty. Would the duplicate be really you, or just a copy?
It may seem unlikely a priori that physics, or any experimental science, could have something to say about this issue.
But it's amazing, the things that science can tell you.
In this case, it turns out, science can rule out a notion of personal identity that depends on your being composed of the same atoms - because modern physics has taken the concept of "same atom" and thrown it out the window. There are no tiny billiard balls with individual identities. It's experimentally ruled out.
"Huh? What do you mean, physics has gotten rid of the concept of 'same atom'?"
No one can be told this, alas, because it involves replacing the concept of little billiard balls with a different kind of math. If you read through the introduction that follows to basic quantum mechanics, you will be able to see that the naive concept of personal identity - the notion that you are made up of tiny pieces with individual identities that persist through time, and that your identity follows the "same" tiny pieces - is physical nonsense. The universe just doesn't work in a way which would let that idea be meaningful.
There are more abstract and philosophical arguments that you could use to rule out atom-following theories of personal identity. But in our case, it so happens that we live in a universe where the issue is flatly settled by standard physics. It's like proposing that personal identity follows phlogiston. You could argue against it on philosophical grounds - but we happen to live in a universe where "phlogiston" itself is just a mistaken theory to be discarded, which settles the issue much more abruptly.
And no, this does not rely on a woo-woo mysterian interpretation of quantum mechanics. The other purpose of this series of posts, was to demystify quantum mechanics and reveal it as non-mysterious. It just happens to be a fact that once you get to the non-mysterious version of quantum mechanics, you find that the reason why physics once looked mysterious, has to do with reality being made up of different stuff than little billiard balls. Complex amplitudes in configuration spaces, to be exact, though here I jump ahead of myself.
Living in Many Worlds
Followup to: Many Worlds, One Best Guess
Some commenters have recently expressed disturbance at the thought of constantly splitting into zillions of other people, as is the straightforward and unavoidable prediction of quantum mechanics.
Others have confessed themselves unclear as to the implications of many-worlds for planning: If you decide to buckle your seat belt in this world, does that increase the chance of another self unbuckling their seat belt? Are you being selfish at their expense?
Just remember Egan's Law: It all adds up to normality.
(After Greg Egan, in Quarantine.)
The Failures of Eld 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.
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