AtD: The history of the world is the story of light

[Joseph Tracy]

Great and wonderfully preposterous stuff.So parts of the universe are  
less like star wars and more like Laurel and Hardy, Masion &Dixon,  
Boris and Natasha.
On Mar 10, 2009, at 9:42 PM, Mark Kohut wrote:

>
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> I'M NOT LOOKING, HONEST!
> Mar 5th 2009
>
>
> The good news is reality exists. The bad is it's even stranger than
> people thought
>
> "HOW wonderful that we have met with a paradox. Now we have some hope
> of making progress." So said Niels Bohr, one of the founders of  
> quantum
> mechanics. Since its birth in the 1920s, physicists and philosophers
> have grappled with the bizarre consequences that his theory has for
> reality, including the fundamental truth that it is impossible to know
> everything about the world and, in fact, whether it really exists at
> all when it is not being observed. Now two groups of physicists,
> working independently, have demonstrated that nature is indeed real
> when unobserved. When no one is peeking, however, it acts in a really
> odd way.
>
> In the 1990s a physicist called Lucien Hardy proposed a thought
> experiment that makes nonsense of the famous interaction between  
> matter
> and antimatter--that when a particle meets its antiparticle, the pair
> always annihilate one another in a burst of energy. Dr Hardy's scheme
> left open the possibility that in some cases when their interaction is
> not observed a particle and an antiparticle could interact with one
> another and survive. Of course, since the interaction has to remain
> unseen, no one should ever notice this happening, which is why the
> result is known as Hardy's paradox.
>
> This week Kazuhiro Yokota of Osaka University in Japan and his
> colleagues demonstrated that Hardy's paradox is, in fact, correct.  
> They
> report their work in the NEW JOURNAL OF PHYSICS. The experiment
> represents independent confirmation of a similar demonstration by Jeff
> Lundeen and Aephraim Steinberg of the University of Toronto, which was
> published seven weeks ago in PHYSICAL REVIEW LETTERS.
>
> The two teams used the same technique in their experiments. They
> managed to do what had previously been thought impossible: they probed
> reality without disturbing it. Not disturbing it is the
> quantum-mechanical equivalent of not really looking. So they were able
> to show that the universe does indeed exist when it is not being
> observed.
>
> The reality in question--admittedly rather a small part of the
> universe--was the polarisation of pairs of photons, the particles of
> which light is made. The state of one of these photons was  
> inextricably
> linked with that of the other through a process known as quantum
> entanglement.
>
> The polarised photons were able to take the place of the particle and
> the antiparticle in Dr Hardy's thought experiment because they obey  
> the
> same quantum-mechanical rules. Dr Yokota (and also Drs Lundeen and
> Steinberg) managed to observe them without looking, as it were, by not
> gathering enough information from any one interaction to draw a
> conclusion, and then pooling these partial results so that the total
> became meaningful.
>
> What the several researchers found was that there were more photons in
> some places than there should have been and fewer in others. The
> stunning result, though, was that in some places the number of photons
> was actually less than zero. Fewer than zero particles being present
> usually means that you have antiparticles instead. But there is no  
> such
> thing as an antiphoton (photons are their own antiparticles, and are
> pure energy in any case), so that cannot apply here.
>
> The only mathematically consistent explanation known for this  
> result is
> therefore Hardy's. The weird things he predicted are real and they  
> can,
> indeed, only be seen by people who are not looking. Dr Yokota and his
> colleagues went so far as to call their results "preposterous". Niels
> Bohr, no doubt, would have been delighted.
>
>
>
> See this article with graphics and related items at http:// 
> www.economist.com/science/displaystory.cfm?story_id=13226725
>
> Go to http://www.economist.com for more global news, views and  
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