Re: Many Worlds invalidated?

2004-04-26 Thread Hal Finney
Jeff Bone forwards:
   http://www.boingboing.net/2004/04/26/many_worlds_theory_i.html

   Many Worlds theory invalidated

 Kathryn Cramer breaks the story on a to-be-presented Harvard talk on an 
 experiment that appears to invalidate both the Many Worlds and 
 Copenhagen theories of quantum mechanics. Kathryn is the daughter of 
 John Cramer, a physicist whose Transactional Interpretetation 
 hypothesis is the only one left intact by the experiment's findings.

This is nonsense.  It's nothing but sophistry and playing with language.
Neither the Copenhagen nor the Many Worlds interpretations says what
she claims.  The CI has always been vague about what constitutes a
measurement, and it looks to me like this experiment falls through the
cracks.  The MWI merely says that experimentally unrealized quantum worlds
exist just like ours, it makes no absolute claims about distinguishable
worlds lacking interference.  The MWI is just the quantum formalism minus
wave function collapse and is therefore perfectly compatible with this
experiment, since the experiment is itself compatible with the quantum
formalism.

Hal Finney

 It has been widely accepted that the rival interpretations of quantum 
 mechanics, e.g., the Copenhagen Interpretation, the Many-Worlds 
 Interpretation, and my father John Cramer's Transactional 
 Interpretation, cannot be distinguished or falsified by experiment, 
 because the experimental predictions come from the formalism that all 
 such interpretations describe. However, the Afshar Experiment 
 demonstrates in an interaction-free way that there is a loophole in 
 this logic: if the interpretation is inconsistent with the formalism, 
 then it can be falsified. In particular, the Afshar Experiment 
 falsifies the Copenhagen Interpretation, which requires the absence of 
 interference in a particle-type measurement. It also falsifies the 
 Many-Worlds Interpretation which tells us to expect no interference 
 between worlds that are physically distinguishable, e.g., that 
 correspond to the photon's passage through one pinhole or the other. 
 Link (Thanks, Kathryn!)

   http://www.kathryncramer.com/wblog/archives/000530.html



Re: Many Worlds invalidated?

2004-04-26 Thread Jesse Mazer
Hal Finney wrote:

The MWI is just the quantum formalism minus
wave function collapse and is therefore perfectly compatible with this
experiment, since the experiment is itself compatible with the quantum
formalism.
Would this experimental result actually be predicted by the quantum 
formalism, though? It sounds like they had a setup similar to the 
double-slit experiment and found a small amount of interference even when 
they measured which hole the particle traveled through, but I thought the 
quantum formalism predicts that interference would be completely destroyed 
by such a measurement.

Either way, the claim that this supports the transactional interpretation 
but not the MWI interpretation can't be right, since both are supposed to be 
equally compatible with the quantum formalism.

Jesse

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RE: Many Worlds invalidated?

2004-04-26 Thread Ben Goertzel

A powerpoint reviewing these ideas is at John Cramer's website:

http://faculty.washington.edu/jcramer/PowerPoint/43

I suspect that advocates of the Copenhagen and MW Interpretations will
give different applications of their interpretations to the Afshar
experiment than Cramer does.  His applications of these rival
interpretations to the experiment have a straw man flavor to them.

-- Ben


 -Original Message-
 From: Jeff Bone [mailto:[EMAIL PROTECTED] 
 Sent: Monday, April 26, 2004 2:27 PM
 To: [EMAIL PROTECTED]
 Cc: [EMAIL PROTECTED]
 Subject: Many Worlds invalidated?
 
 
 
 Hot off the press, via Boingsters:
 
   http://www.boingboing.net/2004/04/26/many_worlds_theory_i.html
 
   Many Worlds theory invalidated
 
 Kathryn Cramer breaks the story on a to-be-presented Harvard 
 talk on an 
 experiment that appears to invalidate both the Many Worlds and 
 Copenhagen theories of quantum mechanics. Kathryn is the 
 daughter of 
 John Cramer, a physicist whose Transactional Interpretetation 
 hypothesis is the only one left intact by the experiment's findings.
 
 It has been widely accepted that the rival interpretations of quantum 
 mechanics, e.g., the Copenhagen Interpretation, the Many-Worlds 
 Interpretation, and my father John Cramer's Transactional 
 Interpretation, cannot be distinguished or falsified by experiment, 
 because the experimental predictions come from the formalism that all 
 such interpretations describe. However, the Afshar Experiment 
 demonstrates in an interaction-free way that there is a loophole in 
 this logic: if the interpretation is inconsistent with the formalism, 
 then it can be falsified. In particular, the Afshar Experiment 
 falsifies the Copenhagen Interpretation, which requires the 
 absence of 
 interference in a particle-type measurement. It also falsifies the 
 Many-Worlds Interpretation which tells us to expect no interference 
 between worlds that are physically distinguishable, e.g., that 
 correspond to the photon's passage through one pinhole or the other. 
 Link (Thanks, Kathryn!)
 
http://www.kathryncramer.com/wblog/archives/000530.html



Re: Many Worlds invalidated?

2004-04-26 Thread Jeff Bone
BTW, just a caveat --- and I should've caveated the initial forward.   
I'm not endorsing this or any interpretation of this experiment at all,  
rather just offering it up to the list in case others had not seen it.

$0.02,

jb

On Apr 26, 2004, at 2:34 PM, Jesse Mazer wrote:

Hal Finney wrote:

The MWI is just the quantum formalism minus
wave function collapse and is therefore perfectly compatible with this
experiment, since the experiment is itself compatible with the quantum
formalism.
Would this experimental result actually be predicted by the quantum  
formalism, though? It sounds like they had a setup similar to the  
double-slit experiment and found a small amount of interference even  
when they measured which hole the particle traveled through, but I  
thought the quantum formalism predicts that interference would be  
completely destroyed by such a measurement.

Either way, the claim that this supports the transactional  
interpretation but not the MWI interpretation can't be right, since  
both are supposed to be equally compatible with the quantum formalism.

Jesse

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Re: Many Worlds invalidated?

2004-04-26 Thread Jesse Mazer
I wrote:

Would this experimental result actually be predicted by the quantum  
formalism, though? It sounds like they had a setup similar to the  
double-slit experiment and found a small amount of interference even  when 
they measured which hole the particle traveled through, but I  thought the 
quantum formalism predicts that interference would be  completely 
destroyed by such a measurement.
After googling, I found a power point presentation by John Cramer (creator 
of the transactional interpetation) at http://tinyurl.com/29atj which 
towards the bottom discusses Afshar's experiment and what it says about the 
various interpretations...this page claims that while the MWI and CI predict 
no interference, the transactional interpretation Predicts interference, as 
does the QM formalism. So, it sounds like he really is claiming that the 
MWI predicts something different than the quantum formalism, which cannot be 
correct since the MWI is just the pure formalism (ie the deterministic rules 
for the evolution of a system's wavefunction over time) without the idea of 
the wavefunction being collapsed when the system is measured (the 
projection postulate).

Jesse

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Re: Many Worlds invalidated?

2004-04-26 Thread Saibal Mitra
Even if there is only one World, there would still be a sort of Many Worlds
branching after each quantum observation, see here:

http://arxiv.org/abs/gr-qc/0102010


Many worlds in one
Authors: Jaume Garriga, Alexander Vilenkin
Comments: 9 pages, 2 figures, comments and references added
Journal-ref: Phys.Rev. D64 (2001) 043511

A generic prediction of inflation is that the thermalized region we inhabit
is spatially infinite. Thus, it contains an infinite number of regions of
the same size as our observable universe, which we shall denote as
$\O$-regions. We argue that the number of possible histories which may take
place inside of an $\O$-region, from the time of recombination up to the
present time, is finite. Hence, there are an infinite number of $\O$-regions
with identical histories up to the present, but which need not be identical
in the future. Moreover, all histories which are not forbidden by
conservation laws will occur in a finite fraction of all $\O$-regions. The
ensemble of $\O$-regions is reminiscent of the ensemble of universes in the
many-world picture of quantum mechanics. An important difference, however,
is that other $\O$-regions are unquestionably real.


- Oorspronkelijk bericht -
Van: Jeff Bone [EMAIL PROTECTED]
Aan: [EMAIL PROTECTED]
CC: [EMAIL PROTECTED]
Verzonden: Monday, April 26, 2004 08:26 PM
Onderwerp: Many Worlds invalidated?



 Hot off the press, via Boingsters:

 http://www.boingboing.net/2004/04/26/many_worlds_theory_i.html

   Many Worlds theory invalidated

 Kathryn Cramer breaks the story on a to-be-presented Harvard talk on an
 experiment that appears to invalidate both the Many Worlds and
 Copenhagen theories of quantum mechanics. Kathryn is the daughter of
 John Cramer, a physicist whose Transactional Interpretetation
 hypothesis is the only one left intact by the experiment's findings.

 It has been widely accepted that the rival interpretations of quantum
 mechanics, e.g., the Copenhagen Interpretation, the Many-Worlds
 Interpretation, and my father John Cramer's Transactional
 Interpretation, cannot be distinguished or falsified by experiment,
 because the experimental predictions come from the formalism that all
 such interpretations describe. However, the Afshar Experiment
 demonstrates in an interaction-free way that there is a loophole in
 this logic: if the interpretation is inconsistent with the formalism,
 then it can be falsified. In particular, the Afshar Experiment
 falsifies the Copenhagen Interpretation, which requires the absence of
 interference in a particle-type measurement. It also falsifies the
 Many-Worlds Interpretation which tells us to expect no interference
 between worlds that are physically distinguishable, e.g., that
 correspond to the photon's passage through one pinhole or the other.
 Link (Thanks, Kathryn!)

 http://www.kathryncramer.com/wblog/archives/000530.html






RE: Many Worlds invalidated?

2004-04-26 Thread Jesse Mazer
Brent Meeker wrote:
I don't find any reference to Afshar or his experiment on the
Harvard web site or on arXiv.org?
Maybe it hasn't been written up yet, or it just wasn't submitted to 
arXiv.org. But the Kathryn Cramer blog entry on this had a link to a 
schedule of talks at a Texas AM physics seminar, with Afshar's talk near 
the bottom:

http://faculty.physics.tamu.edu/belyanin/amoseminars.html

I didn't find any other references to him being at Harvard, maybe he's just 
working with physicists at Harvard on this experiment...there's a Shahriar 
Afshar listed as being an assistant professor in quantum field theory at 
Urmia University in Iran at 
http://www.urmia.ac.ir/Fac_Sci/phys/staff_list.htm

Jesse

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Re: Many Worlds invalidated?

2004-04-26 Thread scerir
From: Jesse Mazer

 Would this experimental result actually be predicted by the quantum
 formalism, though? It sounds like they had a setup similar to the
 double-slit experiment and found a small amount of interference even when
 they measured which hole the particle traveled through, but I thought the
 quantum formalism predicts that interference would be completely destroyed
 by such a measurement.

There is a lot of confusion about all that.
I hope I do not make more damages here!

There are also many different versions of Bohr's complementarity
principle. Complementarity of what? Waves (there are no waves in
matrix mechanics!) and particles? Interference pattern and which
way? Continuous and discontinuous? Localization and superposition?
Separability and unitarity? Reversibility and irreversibility?

The modern view says that ...

The superposition of amplitudes is only valid if there
is no way to know, even in principle, which path the particle
took. It is important to realize that this does not imply
that an observer actually takes note of what happens.
It is sufficient to destroy the interference pattern,
if the path information is accessible in principle from
the experiment or even if it is dispersed in the environment
and beyond any technical possibility to be recovered, but
in principle 'still out there'.
Anton Zeilinger, Rev. Mod. Phys., 1999, page S-288

In an experiment the state reflects not what is actually
known about the system, but rather what is knowable, in principle,
with the help of auxiliary measurements that do not disturb
the original experiment. By focusing on what is knowable in
principle, and treating what is known as largely irrelevant,
one completely avoids the anthropomorphism and any reference
to consciousness that some physicists have tried to inject
into quantum mechanics
Leonard Mandel, Rev. Mod. Phys., 1999, p. S-274.

So, the key word now is indistinguishability. Must this
indistinguishability be absolute? What does it happen in case of
partial indistinguishability? (Anticipated answer: there is a smooth
transition between particle-like and wave-like behaviour).

In 1979, Wootters and Zurek (Complementarity in the double-slit
experiment: Quantum nonseparability and a quantitative statement of
Bohr's principle, PR, D-19, 1979, p. 473-484) presented a famous
gedanken experiment, showing that photons still have a wave-like
behaviour even if their paths are predicted almost (say: 99%)
certainly. The set-up, in the gedanken, was essentially a single-slit
plus a double-slit; and also a double-slit plus a specific
'textured' screen capable of detect and record both the interference
pattern and the 'which way'. Yes this is possible.

Coupling Wheeler's 'delayed choice' and the above gedanken experiment,
Wim Rietdijk wrote (circa 1982) an interesting paper. Very shortly,
QM explains the two-slit interference via Heisenberg principle.
Hence the slits measure the position of the 'object'; because of this
measurement there is a scattering; |p(y)|psi|^2 gives the probability
function for the 'object' emerging from the slits with momentum
p(y); this probability function causes the interference pattern.
Thus - that is important - after the 'object' has passed through
the two-slit, the probability function |p(y)|psi|^2 is fixed.
And - second important point - there is a principle of conservation
of momentum. Thus, nothing can change that fixed momentum (rectius:
that fixed probability function). Now comes the weirdness. After
the 'object' has passed the two-slit, we have *still* some time to
choose if we wish to detect the 'welcher weg' (wich way, which path)
the 'object' took, or if we wish to record just the 'impact' of the
'object' on the screen or, in general, if we wish to get both,
the 'welcher weg' and the 'interference pattern' at the same time
(this is technically possible, provided we use a screen with a special
'texture'). Here is the weirdness: does QM say that any knowledge
of the 'welcher weg' causes the loss of the interference pattern? Yes?
Does Feynman say this in his Lectures? Ok. Thus QM says that the
the probability function |p(y)|psi|^2, already fixed at the two-slit
level, is a function of our later, delayed, free choice of a specific
detector (of the interference pattern only; of the interference pattern
and the 'wich path' at the same time).

Coming back to the point of that absolute indistinuishability.

Greenberger and Yasin wrote down the relation, P^2 + V^2 = 1,
where P is the probability for the electron (or photon)
taking one of the two possible paths, and V the visibility
of the fringes (interference pattern).
http://arxiv.org/abs/quant-ph/9908072
http://arxiv.org/abs/quant-ph/0311179
http://arxiv.org/abs/quant-ph/0201026
In other words, the Greenberger and Yasin relation states that
the entity (electron, photon, etc.) has a double nature (wave-like,
particle-like) and there is a smooth transition between one and the
other nature.

So, the