The part of decoherence that is supposed to be testable is not the many worlds per se, but just the general law that governs the wavefunction. The decoherentists note that, applied universally, this law implies the existence of entire superposed worlds. Now there are critiques that can be leveled at this theory, most notably, “But then where do the Born probabilities come from?” But within the internal logic of decoherence, the many worlds are not offered as an explanation for anything, nor are they the substance of the theory that is meant to be tested; they are simply a logical consequence of those general laws that constitute the substance of the theory.
If A ⇒ B then ¬B ⇒¬A. To deny the existence of superposed worlds is necessarily to deny the universality of the quantum laws formulated to govern hydrogen atoms and every other examinable case; it is this denial that seems to the decoherentists like the extra and untestable detail. You can’t see the other parts of the wavefunction—why postulate additionally that they don’t exist?
The events surrounding the decoherence controversy may be unique in scientific history, marking the first time that serious scientists have come forward and said that by historical accident humanity has developed a powerful, successful, mathematical physical theory that includes angels. That there is an entire law, the collapse postulate, that can simply be thrown away, leaving the theory strictly simpler.
To this discussion I wish to contribute the assertion that, in the light of a mathematically solid understanding of probability theory, decoherence is not ruled out by Occam’s Razor, nor is it unfalsifiable, nor is it untestable.
We may consider e.g. decoherence and the collapse postulate, side by side, and evaluate critiques such as “Doesn’t decoherence definitely predict that quantum probabilities should always be 50/50?” and “Doesn’t collapse violate Special Relativity by implying influence at a distance?” We can consider the relative merits of these theories on grounds of their compatibility with experience and the apparent character of physical law.
To assert that decoherence is not even in the game—because the many worlds themselves are “extra entities” that violate Occam’s Razor, or because the many worlds themselves are “untestable,” or because decoherence makes no “new predictions”—all this is, I would argue, an outright error of probability theory. The discussion should simply discard those particular arguments and move on.
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236
Privileging the Hypothesis
Suppose that the police of Largeville, a town with a million inhabitants, are investigating a murder in which there are few or no clues—the victim was stabbed to death in an alley, and there are no fingerprints and no witnesses.
Then, one of the detectives says, “Well . . . we have no idea who did it . . . no particular evidence singling out any of the million people in this city . . . but let’s consider the hypothesis that this murder was committed by Mortimer Q. Snodgrass, who lives at 128 Ordinary Ln. It could have been him, after all.”
I’ll label this the fallacy of privileging the hypothesis. (Do let me know if it already has an official name—I can’t recall seeing it described.)
Now the detective may perhaps have some form of rational evidence that is not legal evidence admissible in court—hearsay from an informant, for example. But if the detective does not have some justification already in hand for promoting Mortimer to the police’s special attention—if the name is pulled entirely out of a hat—then Mortimer’s rights are being violated.
And this is true even if the detective is not claiming that Mortimer “did” do it, but only asking the police to spend time pondering that Mortimer might have done it—unjustifiably promoting that particular hypothesis to attention. It’s human nature to look for confirmation rather than disconfirmation. Suppose that three detectives each suggest their hated enemies, as names to be considered; and Mortimer is brown-haired, Frederick is black-haired, and Helen is blonde. Then a witness is found who says that the person leaving the scene was brown-haired. “Aha!” say the police. “We previously had no evidence to distinguish among the possibilities, but now we know that Mortimer did it!”
This is related to the principle I’ve started calling “locating the hypothesis,” which is that if you have a billion boxes only one of which contains a diamond (the truth), and your detectors only provide 1 bit of evidence apiece, then it takes much more evidence to promote the truth to your particular attention—to narrow it down to ten good possibilities, each deserving of our individual attention—than it does to figure out which of those ten possibilities is true. It takes 27 bits to narrow it down to ten, and just another 4 bits will give us better than even odds of having the right answer.
Thus the detective, in calling Mortimer to the particular attention of the police, for no reason out of a million other people, is skipping over most of the evidence that needs to be supplied against Mortimer.
And the detective ought to have this evidence in their possession, at the first moment when they bring Mortimer to the police’s attention at all. It may be mere rational evidence rather than legal evidence, but if there’s no evidence then the detective is harassing and persecuting poor Mortimer.
During my recent diavlog with Scott Aaronson on quantum mechanics, I did manage to corner Scott to the extent of getting Scott to admit that there was no concrete evidence whatsoever that favors a collapse postulate or single-world quantum mechanics. But, said Scott, we might encounter future evidence in favor of single-world quantum mechanics, and many-worlds still has the open question of the Born probabilities.
This is indeed what I would call the fallacy of privileging the hypothesis. There must be a trillion better ways to answer the Born question without adding a collapse postulate that would be the only non-linear, non-unitary, discontinous, non-differentiable, non-CPT-symmetric, non-local in the configuration space, Liouville’s-Theorem-violating, privileged-space-of-simultaneity-possessing, faster-than-light-influencing, acausal, informally specified law in all of physics. Something that unphysical is not worth saying out loud or even thinking about as a possibility without a rather large weight of evidence—far more than the current grand total of zero.
But because of a historical accident, collapse postulates and single-world quantum mechanics are indeed on everyone’s lips and in everyone’s mind to be thought of, and so the open question of the Born probabilities is offered up (by Scott Aaronson no less!) as evidence that many-worlds can’t yet offer a complete picture of the world. Which is taken to mean that single-world quantum mechanics is still in the running somehow.
In the minds of human beings, if you can get them to think about this particular hypothesis rather than the trillion other possibilities that are no more complicated or unlikely, you really have done a huge chunk of the work of persuasion. Anything thought about is treated as “in the running,” and if other runners seem to fall behind in the race a little, it’s assumed that this runner is edging forward or even entering the lead.
And yes, this is just the same fallacy committed, on a much more blatant scale, by the theist who points out that modern science does not offer an absolutely complete explanation of the entire universe, and takes this as evidence for the existence of Jehovah. Rather than Allah, the Flying Spaghetti Monster, or a trillion other gods no less complicated—never mind the space of naturalistic explanations!
To talk about “intelligent design” whenever you point to a purported flaw or open problem in evolutionary theory is, again, privileging the hypothesis—you must have evidence already in hand that points to intelligent design specifically in order to justify raising that particular idea to our attention, rather than a thousand others.
So that’s the sane rule. And the corresponding anti-epistemology is to talk endlessly of “possibility” and how you “can’t disprove” an idea, to hope that future evidence may confirm it without presenting past evidence already in hand, to dwell and dwell on possibilities without evaluating possibly unfavorable evidence, to dr
aw glowing word-pictures of confirming observations that could happen but haven’t happened yet, or to try and show that piece after piece of negative evidence is “not conclusive.”
Just as Occam’s Razor says that more complicated propositions require more evidence to believe, more complicated propositions also ought to require more work to raise to attention. Just as the principle of burdensome details requires that each part of a belief be separately justified, it requires that each part be separately raised to attention.
As discussed in Perpetual Motion Beliefs, faith and type 2 perpetual motion machines (water → ice cubes + electricity) have in common that they purport to manufacture improbability from nowhere, whether the improbability of water forming ice cubes or the improbability of arriving at correct beliefs without observation. Sometimes most of the anti-work involved in manufacturing this improbability is getting us to pay attention to an unwarranted belief—thinking on it, dwelling on it. In large answer spaces, attention without evidence is more than halfway to belief without evidence.
Someone who spends all day thinking about whether the Trinity does or does not exist, rather than Allah or Thor or the Flying Spaghetti Monster, is more than halfway to Christianity. If leaving, they’re less than half departed; if arriving, they’re more than halfway there.
An oft-encountered mode of privilege is to try to make uncertainty within a space, slop outside of that space onto the privileged hypothesis. For example, a creationist seizes on some (allegedly) debated aspect of contemporary theory, argues that scientists are uncertain about evolution, and then says, “We don’t really know which theory is right, so maybe intelligent design is right.” But the uncertainty is uncertainty within the realm of naturalistic theories of evolution—we have no reason to believe that we’ll need to leave that realm to deal with our uncertainty, still less that we would jump out of the realm of standard science and land on Jehovah in particular. That is privileging the hypothesis—taking doubt within a normal space, and trying to slop doubt out of the normal space, onto a privileged (and usually discredited) extremely abnormal target.
Similarly, our uncertainty about where the Born statistics come from should be uncertainty within the space of quantum theories that are continuous, linear, unitary, slower-than-light, local, causal, naturalistic, et cetera—the usual character of physical law. Some of that uncertainty might slop outside the standard space onto theories that violate one of these standard characteristics. It’s indeed possible that we might have to think outside the box. But single-world theories violate all these characteristics, and there is no reason to privilege that hypothesis.
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237
Living in Many Worlds
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.1)
Frank Sulloway said:2
Ironically, psychoanalysis has it over Darwinism precisely because its predictions are so outlandish and its explanations are so counterintuitive that we think, Is that really true? How radical! Freud’s ideas are so intriguing that people are willing to pay for them, while one of the great disadvantages of Darwinism is that we feel we know it already, because, in a sense, we do.
When Einstein overthrew the Newtonian version of gravity, apples didn’t stop falling, planets didn’t swerve into the Sun. Every new theory of physics must capture the successful predictions of the old theory it displaced; it should predict that the sky will be blue, rather than green.
So don’t think that many-worlds is there to make strange, radical, exciting predictions. It all adds up to normality.
Then why should anyone care?
Because there was once asked the question, fascinating unto a rationalist: What all adds up to normality?
And the answer to this question turns out to be: quantum mechanics. It is quantum mechanics that adds up to normality.
If there were something else there instead of quantum mechanics, then the world would look strange and unusual.
Bear this in mind, when you are wondering how to live in the strange new universe of many worlds: You have always been there.
Religions, anthropologists tell us, usually exhibit a property called minimal counterintuitiveness; they are startling enough to be memorable, but not so bizarre as to be difficult to memorize. Anubis has the head of a dog, which makes him memorable, but the rest of him is the body of a man. Spirits can see through walls; but they still become hungry.
But physics is not a religion, set to surprise you just exactly enough to be memorable. The underlying phenomena are so counterintuitive that it takes long study for humans to come to grips with them. But the surface phenomena are entirely ordinary. You will never catch a glimpse of another world out of the corner of your eye. You will never hear the voice of some other self. That is unambiguously prohibited outright by the laws. Sorry, you’re just schizophrenic.
The act of making decisions has no special interaction with the process that branches worlds. In your mind, in your imagination, a decision seems like a branching point where the world could go two different ways. But you would feel just the same uncertainty, visualize just the same alternatives, if there were only one world. That’s what people thought for centuries before quantum mechanics, and they still visualized alternative outcomes that could result from their decisions.
Decision and decoherence are entirely orthogonal concepts. If your brain never became decoherent, then that single cognitive process would still have to imagine different choices and their different outcomes. And a rock, which makes no decisions, obeys the same laws of quantum mechanics as anything else, and splits frantically as it lies in one place.
You don’t split when you come to a decision in particular, any more than you particularly split when you take a breath. You’re just splitting all the time as the result of decoherence, which has nothing to do with choices.
There is a population of worlds, and in each world, it all adds up to normality: apples don’t stop falling. In each world, people choose the course that seems best to them. Maybe they happen on a different line of thinking, and see new implications or miss others, and come to a different choice. But it’s not that one world chooses each choice. It’s not that one version of you chooses what seems best, and another version chooses what seems worst. In each world, apples go on falling and people go on doing what seems like a good idea.
Yes, you can nitpick exceptions to this rule, but they’re normal exceptions. It all adds up to normality, in all the worlds.
You cannot “choose which world to end up in.” In all the worlds, people’s choices determine outcomes in the same way they would in just one single world.
The choice you make here does not have some strange balancing influence on some world elsewhere. There is no causal communication between decoherent worlds. In each world, people’s choices control the future of that world, not some other world.
If you can imagine decisionmaking in one world, you can imagine decision-making in many worlds: just have the world constantly splitting while otherwise obeying all the same rules.
In no world does two plus two equal five. In no world can spaceships travel faster than light. All the quantum worlds obey our laws of physics; their existence is asserted in the first place by our laws of physics. Since the beginning, not one unusual thing has ever happened, in this or any other world. They are all lawful.
Are there horrible worlds out there, which are utterly beyond your ability to affect? Sure. And horrible things happened during the twelfth century, which a
re also beyond your ability to affect. But the twelfth century is not your responsibility, because it has, as the quaint phrase goes, “already happened.” I would suggest that you consider every world that is not in your future to be part of the “generalized past.”
Live in your own world. Before you knew about quantum physics, you would not have been tempted to try living in a world that did not seem to exist. Your decisions should add up to this same normality: you shouldn’t try to live in a quantum world you can’t communicate with.
Your decision theory should (almost always) be the same, whether you suppose that there is a 90% probability of something happening, or if it will happen in 9 out of 10 worlds. Now, because people have trouble handling probabilities, it may be helpful to visualize something happening in 9 out of 10 worlds. But this just helps you use normal decision theory.
Now is a good time to begin learning how to shut up and multiply. As I note in Lotteries: A Waste of Hope:
The human brain doesn’t do 64-bit floating-point arithmetic, and it can’t devalue the emotional force of a pleasant anticipation by a factor of 0.00000001 without dropping the line of reasoning entirely.
And in New Improved Lottery:
Between zero chance of becoming wealthy, and epsilon chance, there is an order-of-epsilon difference. If you doubt this, let epsilon equal one over googolplex.
Rationality- From AI to Zombies Page 101
