On 1/8/2025 9:42 PM, Quentin Anciaux wrote:
Brent,
The issue I see with a single-world framework is the reliance on
possibilities that have no existence or causal link to the realized
world. In this view, possibilities are entirely notional, they don’t
exist ontologically, and they have no impact on the single realized
history. This makes their invocation seem unnecessary, even absurd,
because they don’t contribute to the reality we observe in any
meaningful way.
But they do. They reduce its probability of occurence.
If the only thing that exists is the realized world, why appeal to a
theoretical ensemble of possibilities?
Because that's what the equations of quantum mechanics produces. We're
not "appealing to them" where taking them into account as things that
might occur. That's why the Born rule assigns probabilities less than
one to them.
It’s as if the single-world view borrows the language and tools of
probability to describe outcomes but discards the explanatory depth
provided by an actual ensemble.
I'd say that's looking at it exactly backwards, as though the "tools of
probability" on applied to cases that were really deterministic (had
explanatory depth) and what work is done by the word "actual" in "actual
ensemble". Usually it is an ensemble of possibilities. When you're
dealt a bridge hand no one supposes that all other possible hands are
dealt somewhere else; it is enough that they merely possible. During
the Viet Nam was I calculated the probability of dropping a bridge with
a Walleye, I calculated the probability of a missile failure causing it
to hit the launching aircraft, I calculated the probability of a wayward
missile going out of the range safety boundaries, and dozens of other
probabilities. I was always considering a range of instances and their
contrary; but I never needed to suppose the instances were actually
anything more than possibilities. They didn't have to happen anywhere
in any world.
Without the existence of unrealized possibilities, the concept of
"randomness" seems like a placeholder for "it just happened this way,"
offering no real insight into why this one history unfolded.
No, it's a "placeholder" for it could have happened these other ways but
didn't.
In contrast, in a multiverse framework, the ensemble is not merely
theoretical, it has ontological status.
Yes, it's like a bridge tournament in which all possible hands are dealt
at different tables and then you pick one to sit */at random/*. But
wait, that's absurd, we must sit down at every table. And then we must
play every possible card in every possible order. Otherwise we cannot
speak of the probability of making our bid.
The possibilities exist and have causal relationships within the
broader structure. This provides coherence to the use of probability,
as it describes the distribution of outcomes across the ensemble, not
just within a single, isolated history.
The single-world framework effectively asks us to accept a universe
where unrealized possibilities are invoked to explain outcomes, yet
they have no actual role in shaping reality.
Sure they do. If they are things that might possibily happen then they
reduce the probability of something else happening.
Brent
This reliance on something that neither exists nor affects the
realized world strikes me as deeply incoherent.
Quentin
Le jeu. 9 janv. 2025, 03:14, Brent Meeker <meekerbr...@gmail.com> a
écrit :
On 1/8/2025 4:11 AM, Quentin Anciaux wrote:
Brent,
The core of my argument is that in a single-world framework, the
ensemble of possibilities described by Schrödinger’s equation is
only conceptual. If only one history is realized, then those
"possibilities" don’t exist in any meaningful way—they’re
theoretical abstractions. In the absence of an actual ensemble
from which a selection occurs, the notion of randomness is a
metaphor, not a mechanism.
In the many-worlds framework, every possibility is realized, so
the "selection" is an emergent phenomenon from within the
structure of the totality. In the single-world view, however,
there’s no actual ensemble. Probabilities merely describe the
likelihood of the one realized outcome, but there’s no underlying
framework where those possibilities are instantiated. Randomness
then becomes a label for the lack of explanation rather than a
true process.
To say "the single history simply is" and call that random
doesn’t resolve the issue—it just restates it. Without an
ensemble that exists ontologically (even probabilistically), the
idea of selection collapses because there’s nothing to select
from. The photon emission you mentioned is described by
probabilities in QM, but those probabilities don’t correspond to
real, alternate outcomes in a single-world framework. The
realized outcome is the only one that exists, and all other
"possibilities" are simply unrealized ideas.
In contrast, in the many-worlds interpretation, the photon’s
emission in one state is one thread of the total structure, and
alternate emissions exist along other threads. This gives
explanatory power to the probabilities, as they correspond to
real structures within the ensemble.
But small probabilities explain why things */don't/* exist.
Regarding your point that probabilities lose meaning in MWI
because all possibilities are realized—that’s not the case.
Probabilities in MWI are understood as the measure of the
branching structure relative to the observer's perspective. They
still hold meaning because they reflect the structure of the
multiverse, not a singular outcome.
What about the one's for which P=0, you could as well say that
reflect the structure of the multiverse. Will you make an
ensemble of them?
The single-world view still strikes me as incoherent because it
leans on the language of probability and possibility but denies
their actual realization. Without an ensemble, it’s hard to see
what randomness truly means.
In every other application of probability theory (and for years I
headed the Reliability Division at Pt. Mugu) the ensemble is only
notional. It is a the set of possibilities without assuming that
they exist, in which case they would be actualities. With an
ensemble of which every member exists, randomness becomes incoherent.
Brent
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