Re: Why even physicists still don’t understand quantum theory 100 years on

[Brent Meeker]

On 2/5/2025 12:10 PM, Quentin Anciaux wrote:
Brent,

You're arguing that probabilities in a single-world framework are as 
real as those of observed events because they are derived from the 
same equations. But if only one history ever happens, then unrealized 
possibilities are just numbers in a calculation, not something that 
ever had a chance of being real.
But that's exactly wrong.  They are in the calculation precisely because 
they did have a chance of being real.  You keep leaning on "only one 
history happens".  But the probabilities are for the individual events.  
The probability of a die landing : is 1/6 .

The theory predicts probabilities, but what actually occurs is just 
one unique sequence of events. The rest—no matter how formally 
predicted—never existed in any form beyond the equations.
It existed as a possibility.  Your theory implies that every event is 
deterministic, which implies a simple close minded rejection of the 
concept of probability.

You claim that this does not imply determinism, but the fact remains 
that only one history ever unfolds.
So what.  Would it help that two histories unfolded?  If so, just divide 
your one history in half.

Whether the process is called "random" or not, in practical terms, 
there is no actual underlying ensemble of events
First, a sequence in time is just as much an ensemble as set in space: 
Whether you throw a die ten times or you throw ten dies at once.  
Second, that's your misunderstanding that probability can only apply to 
ensembles.  I assume you've flown on an airliner.  Did you consider the 
possibilty of it crashing?  If so then you must have considered the 
probability of that occurrence, even though you could not take that 
flight more than once.

—there is just the one sequence that reality plays out. That makes 
probability, in this framework, purely descriptive of an imagined set 
of possibilities that never had any ontological status.
But not just "imagined".  They are imagined as consistent with physical 
theory and their probability can be directly calculated in some cases 
and in others is estimated from statistics.  You have an impoverished 
view of probability, imagining it only applies to frequency within an 
ensemble.  But it also applies to degree of rational belief and quantum 
mechanical events.

You say that unrealized events are "part of reality 
probabilistically," but what does that even mean when they never 
actually happen? If an event is assigned a 60% probability but never 
occurs in the only history that exists, then in what sense was it ever 
a real possibility?
Suppose it does occur, then in what sense was it's non-occurence a 
possibility?    You've adopted an impovoerished view in which there is 
no such thing as probability and you can never flip a coin with 
probability 0.5 it will come up heads.

It was just an abstract calculation with no actual link to reality.
You keep writing that, which is what I point to as just emotive 
argument.  1) all calculation is abstract, that's what makes it 
universally applicable.  2+2=4 no matter what we're counting.  2) That's 
simply false.  Calculated probability are linked to reality in many 
different ways.  Some, like die rolls and coin flips are based on 
physical symmetry.  Others, like quantum events are based on the height 
of energy barriers.  Some are inferred from statistics.  They are all 
linked to reality...unlike multiple-worlds whose only link is an 
inability to conceive of the Born Rule outside of a frequentist 
interpretation.

You keep referring to long strings of experiments as if an infinite 
series of trials is guaranteed to sample all possibilities—but in a 
finite universe with a unique history, that is simply not true.
Well maybe it was before you were born, but philosophers of mathematics 
used to argue that probabilities only referred to infinite sequences of 
events...in much the same way you want to refer to infinite ensembles.


Your attempt to equate probability with other concepts like energy or 
entropy fails because those are directly observable and quantifiable 
properties of physical systems.
The are no more directly observable than probability.  Have you ever 
seen an entropy meter?  How does it work.  How would you measure the 
energy in a glass of water?  Probability theories are tested exactly as 
you would any physical theory.  If the Stern-Gerlach says half the 
silver atoms will go up you run thru enough silver atoms to test it.  
You don't say, "Oh I can't test it because every sequence of UP and DOWN 
is unique.

Probability, in a single-history framework, is not a property of the 
world—it’s a mental construct we impose on it. It’s not like energy or 
momentum; it’s a way of reasoning about things that will never 
actually exist.
I want to play cards with you.  You must be terrible at poker.


MWI, on the other hand, does not set all probabilities to 1 arbitrarily.
Now you're changing you story.  Before whatever happened had probability 
1, nothing else could hav

It gives probability a real foundation by making it about relative 
frequencies across real histories.
What's "real" about the histories.  They are just */imagined/* and their 
number and frequency is just inferred from Born's (abstract) 
/*probability*/ calculation

There, probabilities describe distributions of actualized outcomes,
"Actualized" that are*/never actual/*.  You have a way with words.

not abstract unrealized ones. In contrast, in a single-world view, 
probability is just a way of pretending that things that never existed 
somehow mattered. That is the contradiction you keep glossing over.
Because they could have existed, just like your "actualized" but not 
actual outcomes.  That's what probability means; it means something 
could be but not necessarily be.  You are trying to banish the concept 
of probability by "actualizing" everything; but this fails because then 
there is no meaning to the Born Rule.

Brent

Le mer. 5 févr. 2025, 19:56, Brent Meeker <meekerbr...@gmail.com> a 
écrit :




    On 2/4/2025 11:38 PM, Quentin Anciaux wrote:
    Brent,

    You say that unrealized possibilities are what probabilities
    quantify, but in a single-history framework, those possibilities
    never had any existence beyond the formalism.
    I don't know what "formalism" means in that context.  When you
    calculate probabilities of events in QM the events are not
    "formalisms".  They are implied by the same theories and mechanics
    that attributes possibility to the events that were observed.  And
    on other occasions they the events that happen.  So they are not
    mere formalism, their possibility and probability are as real as
    the possibility and probability of the observed events.

    If only one history is real, then all other possibilities were
    never actually possible in any meaningful way—they were never
    real candidates for realization, just mathematical constructs.
    That’s not an emotive argument; it’s pointing out that the entire
    notion of probability in such a framework is detached from
    anything real.

    If probability is supposed to quantify real possibilities, then
    in a world where only one history exists for all eternity, what
    exactly is being quantified? If an event with a calculated
    probability of 50% never happens in this one history, then its
    true probability was always 0%.
    That's contrary to the meaning of probability.  You are assuming
    underlying determinism.  You seem to conceive of probability as
    always being 1 or 0, which is the same as denying the very concept
    of probability

    Your framework claims to allow for multiple possibilities, but in
    practice, it only ever realizes one, making the rest nothing more
    than empty labels.
    It's not "my framework", it's the theory of probability. I think
    you are confused by the fact that probability theory has many
    applications.  You're stuck on the application to ignorance in a
    deterministic case.  But QM is not deterministic.  The
    probabilities don't refer just to ignorance.  Just because there
    is a single world doesn't make it a deterministic world.  In fact
    MWI has more trouble representing probabilities.

    And you assert that alternatives have a "grounding in
    reality"—but what does that mean in a framework where they never
    actually happen?
    It means that the same theory that predicted the thing that
    happened with probability 0.3, also predicted the thing that
    didn't happen with probability 0.6 and this theory has been
    verified by finding that in long strings of experiments the latter
    happens twice as often as the former.

    If they had a genuine grounding, they would have to be part of
    reality in some form, even if only probabilistically.
    I'm telling you they are part of reality probabilistically.  What
    do you mean by that phrase, if not what I've been saying?

    But in a single-history framework, that never happens. The
    probabilities exist only in the mind of the observer, with no
    external ontological reality. They are tools that describe
    nothing but a retrospective justification of what already happened.
    Energy, moment, entropy, gravity...you could say that they are all
    just tools in the mind of the physicist with no external
    ontological reality.  They are just terms in our mathematics.

    The supposed "problem" in MWI—that all possibilities are
    realized—actually solves this issue. It gives probabilities a
    real basis in the structure of the universe rather than treating
    them as abstract bookkeeping.
    No, according to you they set all probabilities to 1.

    The probabilities describe real distributions across real
    histories rather than referring to things that were never real to
    begin with.
    MWI doesn't distribute across histories.  It asserts that all
    possibilities occur in each event "with probability 1".  That's
    why the assignment of probabilities is a problem for MWI.

    Brent

    The single-world view wants to use probability while
    simultaneously denying the existence of the things probability
    refers to. That’s not just emotive talk—it’s a contradiction at
    the foundation of the framework.

    Quentin

    Le mar. 4 févr. 2025, 23:22, Brent Meeker <meekerbr...@gmail.com>
    a écrit :




        On 2/4/2025 11:38 AM, Quentin Anciaux wrote:
        The fundamental absurdity of single-history frameworks
        becomes clear when we consider the reliance on theoretical
        constructs that, by definition, never exist and never will.
        How can one justify using mathematical tools that invoke
        nonexistent possibilities to explain a reality where only
        one sequence of events is ever realized? If something never
        existed, has no causal influence, and will never exist in
        any possible future, how does it play any role in explaining
        what does exist?

        This contradiction is evident in interpretations like
        Bohmian mechanics, where the pilot wave guides particles but
        remains completely unobservable and uninteractive beyond
        that role. It’s an invisible, untouchable entity that
        affects matter but is never affected in return—something
        that is functionally indistinguishable from the pure
        abstractions of probability waves in a single-world
        interpretation. In both cases, explanations rely on
        constructs that have no true existence beyond their
        mathematical form.

        A single-history universe that leans on unrealized
        possibilities to justify probability
        "Justify"??  Unrealized possibilities are what probabilities
        quantify.  If all possibilities were realized the wouldn't
        have probabilities assigned to them...exactly the problem
        that arises in MWI.

        is making an implicit appeal to something that doesn’t and
        will never exist. It treats the wavefunction as a real tool
        for calculating outcomes while simultaneously denying that
        the alternatives it describes have any grounding in reality.
        This is the absurdity: how can something that never existed
        be part of an explanation for what does?
        That is just a lot of emotive talk.  All the alternatives
        have a "grounding in reality"; that's what makes the
        possibilities with definite probabilities.

        Brent


        In contrast, in a many-worlds framework, all possibilities
        exist and are real branches of the wavefunction, providing
        an actual basis for probability. The probabilities are not
        just mathematical conveniences; they describe distributions
        of real outcomes across real histories. This removes the
        need for metaphysical hand-waving about non-existent
        possibilities influencing reality.

        If physics is about describing reality, then relying on
        things that are, by construction, eternally non-existent to
        justify observed phenomena is conceptually incoherent. It is
        an attempt to have it both ways—to use abstract
        possibilities when convenient while denying their reality
        when inconvenient. That contradiction is why single-history
        frameworks ultimately fail to provide a satisfying
        foundation for probability and existence itself.

        Quentin

        Le mar. 4 févr. 2025, 19:03, John Clark
        <johnkcl...@gmail.com> a écrit :


            On Tue, Feb 4, 2025 at 12:56 PM 'spudboy...@aol.com' via
            Everything List <everything-list@googlegroups.com> wrote:

                /> Bohmian mechanics v Everett-DeWiit-Wheeler? /
                /For Carroll, it probably means they're the same.
                Indistinguishable. /


            *This is what I said about that about a month ago:*


            *Pilot Wave Theory keeps Schrodinger's Equation but
            needs to add another entirely new very complicated
            equation called the Pilot Wave Equation that contains
            non-local variables. When an electron enters the two
            slit experiment the Pilot Wave in effect produces a
            little arrow pointing to one of the electrons with the
            caption under it saying "/this is the real electron,
            ignore all the other ones/".  The Pilot Wave does
            absolutely nothing except erase unwanted universes, it
            is for this reason that some have called Pilot Wave
            theory theMany Worlds theory in denial. *
            *
            *
            *The Pilot Wave is unique in another way, it can affect
            matter but matter cannot affect it, if it's real it
            would be the first time in the history of physics where
            an exception to Newton's credo that for every action
            there is a reaction;  even after the object it is
            pointing to is destroyed the pilot wave continues on,
            although now it is pointing at nothing and has no
            further effect on anything in the universe. Also, nobody
            has ever been able to make a relativistic version of the
            Pilot Wave Equation.Paul diracfound a version of
            Schrodinger's Equation that was compatible with special
            relativity as early as 1927. *
            *
            *
            *John K Clark    See what's on my new list at Extropolis
            <https://groups.google.com/g/extropolis>*
            8b0
            **
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