Re: Does the state-vector collapse?

From: David Blenkinsop (
Date: Fri Oct 06 2000 - 15:08:02 MDT

As a follow-up to my earlier comments on this quantum collapse
controversy, I just thought I'd mention that some of Amara Graps'
earlier info (on advanced probability treatments of this matter) would
seem to be getting through to me. Certainly, I'm interested enough in
what modern physics has to say about the nature of reality to want to
have a reasonably definitive answer on this, and not just simply be
unsure about the real status of the most basic objects in physics.

Earlier, I wrote:

> So, all the properties of quantum waves could be coming from a
> mathematically neat, expanded definition of what it means for a
> particle's position to be uncertain? Follow Jayne's suggestion, consider
> a higher phase space perhaps, and our own uncertainty about location in
> that space could produce interference effects, qubit computers, and
> everything else predicted by the standard quantum math?
> . . .
> One area where I continue to doubt this "non-local vector" idea is when
> I consider that an entire, difficult-to-foresee chain of consequences
> can sometimes block the "travel" of these quantum waves or vectors. I've
> read this in some of the ideas relating to interaction-free
> measurements, where it is said that quantum measurements could even very
> often tell if a "bomb" is live, as opposed to possibly being a dud!
> [. . . then, a whole lot more about the unusual logic of
> So, I still don't know the right answer to this
> question of quantum alternate worlds, given that "might have beens" can
> apparently have a direct causal effect on real measurements.

OK, without necessarily trying to have *all* the answers, I'd say that
something reasonable is starting to filter through into my thoughts on
this, something saying that, while Many Worlds may have some interesting
points as a model for quantum theory, it probably *isn't* literally
true. For instance, looking at my comment about a "might have been"
explosion blocking a quantum path, it certainly seems possible that a
sufficiently complicated mathematical space could encompass such an
explosion in such a way as to exclude a passing photon from ever getting
through that "might have been" scenario. So we're thinking about a state
space that somehow "contains" a lot of such possibilities in a
consistent way -- but that provides no necessity for thinking that the
whole ensemble of chances are all really happening.

If we were to think of this "ultimate" state space as encompassing all
the possible positions and motions of all particles, then maybe it
wouldn't be going too far to think of the actual universe as just a kind
of single particle, occupying some position in that vast state space? If
this is a reasonable picture, there remains a question as to whether the
resulting world history takes a deterministic path, or, alternatively,
whether our universe-history has some sort of ultimate randomness in its
development. There are some standard ideas about quantum theory that
would seem to indicate a degree of ultimate randomness. At the same
time, however, if the real truth about probability is that observers are
simply uncertain about our positioning in state space, then maybe there
is some way that an "ultimate" knowledge could be said to determine the
real position of every particle, as well as the future history of the
universe as a whole?

Mysteries of determinism aside, I'll concede that the simplest
assumption about alternate histories is that we've just got *one*
history wandering through some vast ensemble of possibilities. In this
scheme of things, quantum effects (such as a little bomb threatening to
decohere a photon path), work just the way they do, because of the
interesting structure of the overall state space, or "backdrop". So, I'm
beginning to understand what some physicists, like Seth Lloyd, have been
talking about, when they admit to a vast backdrop of "Many Worlds like"
possibilities, but with the individual chances to be regarded as only
"potentially" real. All probability analysis is like that in some sense
-- for instance, all positions in ordinary 3D space are potentially real
places for a particle to go. As a matter of making a simplest
assumption, then, maybe we've got a Grand Comprehensive State Space that
is actually real, plus a combined position for all the particles in the
whole material universe. To assume that any *other* universes are
following their own histories through that state space, would just mess
things up, presumably. Meanwhile, state vectors and quantum waves are
just ways of expressing our basic uncertainty about where things really
are at any given time -- the state vector and waves never need to
"collapse" if they were never locally "there" to begin with.

Again, thanks to my fellow email posters for the help on this. For now,
I'm thinking that the background space or backdrop for the universe is
just more complicated than intuition would suggest, and that this is the
key to all the most counterintuitive quantum experiments. As a general
answer to the "wave collapse" question, this seems pretty good, pretty
general in nature, and, I'd certainly guess that future developments
won't mess this up this particular insight! With understanding of
quantum matters increasing, maybe we'll even eventually have household
gadgets based on this stuff -- I mean, quantum encipherment, qubit
desktop computers, who knows what the strange logic of Q-space may

David Blenkinsop <>

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