- There is an article in Nature by Philip Ball about decoherence and many

good references about MWI/decoherence related experiments:

http://www.nature.com/news/2008/080430//full/453022a.html

A commentor also raises an interesting alternative explanation to MWI -

non-linearity at mesoscopic scale:

"Decoherence by itself cannot explain the quantum-classical transition;

it must be supplemented by the many-worlds interpretation. This is

because while decoherence destroys interference amongst alternatives, it

preserves superpositions, since it works within the framework of linear

quantum mechanics.

An alternate explanation for emergent classicality, not ruled out by

experiments, is that quantum mechanics is modified, say to a non-linear

theory, on mesoscopic scales.

As a result of the non-linearity, the life-time of a quantum

superposition becomes dependent on the number of degrees of freedom of

the system, and goes to zero for large systems. Experiments should be

attempted, to test for the presence/absence of non-linearity in quantum

mechanics on the mesoscopic scale."

(T. P. Singh, Tata Institute of Fundamental Research, Mumbai)

Does anybody know of experiments/theories shedding light on this

alternative possibility?

Cheers,

Günther

--

Günther Greindl

Department of Philosophy of Science

University of Vienna

guenther.greindl@...

http://www.univie.ac.at/Wissenschaftstheorie/

Blog: http://dao.complexitystudies.org/

Site: http://www.complexitystudies.org - On Mon, May 05, 2008 at 10:08:26AM -0400, Gary Oberbrunner wrote:
> Günther Greindl wrote:

The probabilities all depend on what is measured. If I choose to

> > A middle ground would be something like this:

> >

> > http://hanson.gmu.edu/mangledworlds.html

> > <http://hanson.gmu.edu/mangledworlds.html>

> >

> > (QM stays linear, but some worlds are destroyed via interference - to

> > recover Born's rule)

>

> Very interesting. But why does he say this:

>

> "The big problem with the many worlds view is that no one has really

> shown how the usual linear rule in disguise can reproduce Born

> probability rule evolution. Many worlders who try to derive the Born

> rule from symmetry assumptions often forget that there is no room for

> "choosing" a probability rule to go with the many worlds view; if all

> evolution is the usual linear deterministic rule in disguise, then aside

> from unknown initial or boundary conditions, all experimentally

> verifiable probabilities must be calculable from within the theory. So

> what do theory calculations say? After a world splits a finite number of

> times into a large but finite number of branch worlds, the vast majority

> of those worlds will not have seen frequencies of outcomes near that

> given by the Born rule, but will instead have seen frequencies near an

> equal probability rule. If the probability of an outcome is the fraction

> of worlds that see an outcome, then the many worlds view seems to

> predict equal probabilities, not Born probabilities."

>

>

> I don't understand exactly what he's getting at, but it seems like he's

> assuming a binary split at each measurement, i.e. exactly two worlds

> rather than a continuum of worlds at each point with measures according

> to the Born rule. As I understand MWI, it seems to predict the Born

> rule fine, but IANAP. Anyone care to comment?

>

> --

> Gary Oberbrunner

measure the angle of a particle after having collided with a massive

target, I would expect that forward angles to be much more probable

than reverse angles for instance.

The connection with equiprobability must be via the uniform measure on

bitstrings in something like my all strings ensemble, but the MWI is

at a much higher level of abstraction than that.

My understanding based on van Esch's paper in 2005 is that the MWI per se is

insuffucient to generate the Born rule. But then Youness mentioned

Gleason's theorem as possibly indicating the opposite. More reading of

the literature is require, methinks (as if I don't have enough already!).

--

----------------------------------------------------------------------------

A/Prof Russell Standish Phone 0425 253119 (mobile)

Mathematics

UNSW SYDNEY 2052 hpcoder@...

Australia http://www.hpcoders.com.au

----------------------------------------------------------------------------