Friday, March 5, 2021

Aaronson joins the many-worlds cult

Scott Aaronson is one of the more sane popularizers of quantum mechanics. Or he used to be. Now he comes out of the closet as a many-worlder:
I have tenure, and anyone who doesn’t like it can close their broswer tab. ...

I’ve dodged the question of which interpretation (if any) I really believe myself. Today, at last, I’ll emerge from the shadows and tell you precisely where I stand.

I hold that all interpretations of QM are just crutches that are better or worse at helping you along to the Zen realization that QM is what it is and doesn’t need an interpretation.  ...

If you had to, you could call even me a “Many-Worlder,” but only in the following limited sense: that in fifteen years of teaching quantum information, my experience has consistently been that for most students, Everett’s crutch is the best currently on the market. At any rate, it’s the one that’s most like a straightforward picture of the equations, and least like a wobbly tower of words that might collapse if you utter the wrong ones.  Unlike Bohr, Everett will never make you feel stupid for asking the questions an inquisitive child would; he’ll simply tell you answers that are as clear, logical, and internally consistent as they are metaphysically extravagant. That’s a start.

This is pathetic. Many-worlds does not answer any questions. It cannot explain why some outcomes are more probable than others, or how the worlds split, or anything else you might ask.
Why are there probabilities in QM? Because QM is a (the?) generalization of probability theory to involve complex numbers, whose squared absolute values are probabilities. It includes probability as a special case.
No, QM is not probability with complex numbers. Probabilities only range from 0 to 1, as real numbers. Furthermore, many-worlds loses the probabilities altogether.
If you start with a quantum state for the early universe and then time-evolve it forward, then yes, you’ll get not only “our” branch but also a proliferation of other branches, in the overwhelming majority of which Donald Trump was never president and civilization didn’t grind to a halt because of a bat near Wuhan.  But how could we possibly know whether anything “breathes fire” into the other branches and makes them real, when we have no idea what breathes fire into this branch and makes it real?
This is just nonsense. No one has ever been able to demonstrate a statement about the majority of branches in many-worlds theory. Nor is there any concept of breathing fire into a branch and making it real.

Aaronson used to talk about writing a new book. His view of QM has not become a hopeless muddle.

You might think that I am being harsh on Aaronson, for merely choosing an interpretation. I don't think so. First, he doesn't describe his view that way. Second, the probabilities make no sense. Let me quote Wikipedia:

To address the quantitative [probability] problem, Everett proposed a derivation of the Born rule based on the properties that a measure on the branches of the wavefunction should have.[4]:70–72 His derivation has been criticized as relying on unmotivated assumptions.[35] Since then several other derivations of the Born rule in the many-worlds framework have been proposed. There is no consensus on whether this has been successful.[36][37][38]
The three references for saying "no consensus" actually argue that probabilities are meaningless in many-worlds. The last says "no plausible set of axioms exists for an MWI that describes known physics."

Even if you think that it might be possible to reconcile many-worlds with probability theory, it is clear that no one has done. There is no published paper that uses many-worlds to derive a probability for anything.

You can find advocates who speak in probabilistic terms. For example, that Wikipedia article says:

DeWitt has stated that "[Everett, Wheeler and Graham] do not in the end exclude any element of the superposition. All the worlds are there, even those in which everything goes wrong and all the statistical laws break down."[87]

Max Tegmark has affirmed that absurd or highly unlikely events are inevitable but rare under the MWI. To quote Tegmark, "Things inconsistent with the laws of physics will never happen — everything else will... it's important to keep track of the statistics, since even if everything conceivable happens somewhere, really freak events happen only exponentially rarely."[88]

But there is no published paper with computations to back up any of those claims. Nobody can say that freak events happen only rarely, because no one can say that any branch is any more probable than any other branch.

The whole field is a big con, and Aaronson just joined it.

He writes:

The many-worlders love to use the example of Copernicus and Galileo, who introduced a bizarre and extravagant hypothesis — that the earth, far from being stationary, circles the sun at unimaginable speed — but then argued that, starting from that hypothesis, you could derive that our experience on earth would be just like it actually is, and this time with no need to postulate epicycles.

There are sophisticated arguments against many-worlds, but I think that a good first step along the Zen path, for someone who already knows QM, would be to understand the strength of the case in many-worlds’ favor.

The history is a little strange, because Copernicus used epicycles, and Galileo did not have a mathematical model of the solar system.

But the argument makes no sense anyway, because many-worlds cannot derive our experience on Earth.

The elephant in the room here is quantum computing. That is Aaronson's chief academic field of interest. His essay on many-worlds says nothing about quantum computing. For some in the field, such as David Deutsch, many-worlds is the main reason for believing in quantum computing. Or maybe quantum computing is the main reason for believing in many-worlds, I am not sure. At any rate, they are related. But Aaronson says nothing. What goes?

And what is all this Zen stuff? Is he conceding that this is all a set of religious views? Is this knowledge that is only available to enlightened geniuses like himself, and not accessible from logic, empiricism, and reasoned argument? Apparently yes.

Update: Commenter Andrei gives arguments for superdeterminism, both below and on Aaronson's blog, and Aaronson responds:

The original papers by Gerard ‘t Hooft on “superdeterminism” were shockingly blase about the absurd implications I mentioned — implications that would mean you could explain basically anything (telepathy, superluminal signaling, etc.) via similar devices, and that physics would be over — and (to their credit) were also clear enough that there was no possible other way to interpret them. None of the other papers I saw about “superdeterminism” showed any inkling of appreciating the enormity of the problem. And none of them contained what I saw as the slightest hint of a promising idea to balance the absurdity.

By the usual standards I apply to anything else, this would be more than enough reason for me to ignore the topic thereafter.

I agree with that. Superdeterminism is essentially the same as rejecting all of modern physics, and adopting solipsism. No one has explained how it is any better. It does not help with any theoretical or experimental problem in physics.

1 comment:

  1. It doesn't matter where you went to college.
    It doesn't matter what grades you got in class.
    It doesn't matter how many sheepskins you have on the wall.
    It doesn't matter who you know that is important.
    It doesn't even matter when you were born...

    If you can't wrap your head around the simple fact that hypostatization is not 1. a force, 2. a causation, 3. physically possible, 4. logically allowed, then you have absolutely no business calling yourself a scientist.

    Wishes aren't horses (even if you are Scott Aaronson).

    A dog's tail is not a fifth leg (no matter what you call it).

    A second hand calculation (which is what a probability is) can not and never could cause anything to physically manifest, disappear, duplicate, multiply, divide, merge, deform, tap dance, Merengue, or Cha-Cha. Just ask any illusionist, making things even look like they are reappearing (the prestige) is a bitch.

    Experiment: Take an actual one dollar bill. Place it on the table in front of you. Stare really really really hard at the bill and try to look like a constipated physicist while pressing your fingers to the sides of your temples for extra concentration and added effect...and then say "By the power of MATH, I multiply you by two, Make it so!" You are also more than welcome to employ any abacus, adding machine, electronic calculator, or super computer with lots of impressive blinking lights to the process if it makes you feel better.

    This is just one simple mathematical operation ...on a physical object.

    So...How did it go?
    Did your dollar duplicate?
    Did it even get a tad larger?
    Perhaps did the number on the bill change to a larger denomination?
    Is the picture of George Washington on the bill even rolling his eyes now?

    If you answered yes to any of the above, congratulations, you have performed a miracle, and are qualified to practice many worlds PR.

    “Those who can make you believe absurdities, can make you commit atrocities.”

    ― Voltaire

    "Probable-Possible, my black hen,
    She lays eggs in the Relative When.
    She doesn't lay eggs in the Positive Now
    Because she's unable to Postulate how."

    - A Space Child's Mother Goose