Re: [asa] Spooky Action At A Distance: Still Spooky

On 4/19/07, David Campbell <pleuronaia@gmail.com> wrote:
>
> > Most working scientists hold fast to the concept of 'realism'—a
> viewpoint
> > according to which an external reality exists independent of
> observation.
> > But quantum physics has shattered some of our cornerstone beliefs...Our
> result suggests that giving up the concept of locality is not sufficient to
> be consistent with quantum experiments, unless certain intuitive features of
> realism are abandoned.
>
> This seems (the full article won't open for me) to address some
> specific aspects of particular versions of realism. However, the new
> study is still firmly grounded on the assumption that an external
> reality exists independent of observation. It asserts that making the
> observation has an effect on the external reality; however, making the
> same observation has the same effect on the external reality. In
> other words, the existence but not the behavior of the external
> reality is independent of observation. They are claiming that anyone
> with the equipment could make the same experiment and reach the same
> conclusions. Thus, these results do not provide legitimate support
> for relativism of the sort that claims, e.g., that science is merely a
> cultural product or that there cannot be moral absolutes.

Not only that, but on further looking into it, I noted the review article in
Nature which implied that results are not as earth shattering as I had
originally assumed:

> But after Bell's discovery that local realism entailed a limit on the
> correlations — a limit he expressed in his celebrated inequalities4<http://www.nature.com/nature/journal/v446/n7138/full/446866a.html#B4>— a series of ever more ideal experiments (ref.
> 5 <http://www.nature.com/nature/journal/v446/n7138/full/446866a.html#B5>and references therein) has led us to abandon the concept. It is then
> natural to raise the question of whether one should drop locality — which
> equates to the impossibility of any influence travelling faster than light —
> or rather drop the notion of physical reality.
>
> There is no logical answer to that question: one can choose to abandon
> either concept, or even both. Tony Leggett has explored6<http://www.nature.com/nature/journal/v446/n7138/full/446866a.html#B6>one of these possibilities by considering a particular class of physically
> plausible theories that abandon locality, but maintain realism. He found
> these theories to be incompatible with quantum mechanics, and expressed the
> disagreement by new inequalities6<http://www.nature.com/nature/journal/v446/n7138/full/446866a.html#B6>.
> As there was no experimental result available to test Leggett's
> inequalities, a new type of measurement was necessary.
>
> In experiments detailed on page 871<http://www.nature.com/nature/journal/v446/n7138/full/nature05677.html>of this issue
> 7 <http://www.nature.com/nature/journal/v446/n7138/full/446866a.html#B7>,
> Gröblacher *et al*. have carried out such measurements. They modified an
> experiment previously used to test Bell's inequalities through measurements
> on two photons (Box 1<http://www.nature.com/nature/journal/v446/n7138/box/446866a_BX1.html>)
> by changing the original linear polarization measurement into an elliptical
> polarization measurement. This is readily done by inserting a quarter-wave
> plate in front of a standard (linear) polarizer. From an experimental point
> of view, however, the new test is more demanding, and requires almost ideal
> optical elements and a high signal-to-noise ratio. Thanks to their
> high-efficiency source of entangled photons, the authors meet these
> requirements, and find a significant violation of the generalized Leggett's
> inequalities that they have established. Following Leggett, they conclude by
> questioning realism rather than locality — at variance with the often-heard
> statement that "quantum mechanics is non-local".
>
> Interesting as this conclusion is, it remains a matter of personal
> preference, not of logical deduction. The violation of Bell's inequalities
> implied that realism and locality are not simultaneously tenable. Violation
> of Leggett's inequalities implies only that realism and a certain type of
> non-locality are incompatible: there are *other types of non-local models
> that are not addressed by either Leggett's inequalities or the experiment*.
> [emphasis mine]
>
>
>
>

To unsubscribe, send a message to majordomo@calvin.edu with
"unsubscribe asa" (no quotes) as the body of the message.
Received on Thu Apr 19 15:56:06 2007