> Quantum untanglement: Is spookiness under threat?
>
>
> * 02 November 2007
> * NewScientist.com news service
>
> Recent experiments have gone further and tried to establish which
> of
> the two ideas has to go: locality or realism. They concluded that
> we
> have to abandon the idea of an objective reality (New Scientist, 23
>
> June, p 30). All of this rests on the fundamental assumption that
> Bell's original argument was sound, and most physicists have
> accepted
> his conclusions for 40 years. But if Christian is right, they've
> been
> overlooking an alternative all this time.
>
> Bell assumed the hidden variables in his argument would be familiar
>
> numbers, akin to the value of a velocity or a mass. Such numbers
> obey
> the ordinary rules of algebra, including a law that says that the
> order of multiplication doesn't matter - so that, for example, 2 ×
> 5
> equals 5 × 2. This property of multiplication is called
> commutation.
> The idea that hidden variables are commuting numbers might seem so
> basic as to be beyond question, but Christian argues it is
> important
> to question this point because mathematicians know that different
> kinds of variables needn't obey commutative algebra. Take rotations
>
> in space, for example. They differ fundamentally from ordinary
> numbers in one important respect: the order of rotations matters
> (see
> Diagram). Rotations do not commute.
>
> In 1843, the Irish mathematician William Rowan Hamilton found a way
>
> to capture this non-commuting property in a set of number-like
> quantities called quaternions. Later, the English mathematician
> William Clifford generalised Hamilton's quaternions into what
> modern
> mathematicians call Clifford algebra, widely considered the best
> mathematics for representing rotations. So convenient are
> quaternions
> that they are commonly used in computer graphics and aviation.
>
> So why is all this important? Christian argues that the existence
> of
> this other algebra reveals a weakness at the core of Bell's proof:
> the only hidden variables Bell considered were ordinary numbers.
> But
> ordinary numbers are not the be all and end all. "Why should
> theorists be obliged to remain unimaginative and consider only
> commuting numbers in their theories?" Christian says.
>
> Was Bell wrong?
>
> He claims that Bell's argument no longer leads to its impressive
> conclusion if you allow that hidden variables can have other
> algebraic properties. Following the logic through, Christian shows
> that a local, realistic model can actually reproduce everything
> that
> quantum theory can. Christian concludes that Bell's theorem is
> simply
> not equipped to say whether or not hidden variables are a possible
> explanation for non-local quantum effects. "When I started out
> looking at this, it never occurred to me that Bell's theorem might
> turn out to be wrong," says Christian. "But that's what I found."
>
> Einstein might have been relieved, and it's a shot in the arm for
> those seeking a deeper reality beyond quantum theory that might be
> more "reasonable" and akin to classical physics. At this early
> stage,
> however, many physicists consider it too good to be true.
>
> Philippe Grangier at the Institute of Optics in Orsay, France, is
> one
> of those who believe Christian's claim is unwarranted. "The
> argument
> is just too remote from Bell's hypothesis to have anything relevant
>
> to say about his theorem," he says. "It might be worth considering
> as
> an alternate formulation of quantum mechanics, maybe with a more
> 'realistic' flavour, but the 'disproof' argument simply makes no
> sense."
>
