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Posts Tagged ‘uncertainty principle

“The true sign of intelligence is not knowledge but imagination”*…

 

Perhaps Arthur C. Clarke was being uncharacteristically unambitious. He once pointed out that any sufficiently advanced technology is going to be indistinguishable from magic. If you dropped in on a bunch of Paleolithic farmers with your iPhone and a pair of sneakers, you’d undoubtedly seem pretty magical. But the contrast is only middling: The farmers would still recognize you as basically like them, and before long they’d be taking selfies. But what if life has moved so far on that it doesn’t just appear magical, but appears like physics?

After all, if the cosmos holds other life, and if some of that life has evolved beyond our own waypoints of complexity and technology, we should be considering some very extreme possibilities. Today’s futurists and believers in a machine “singularity” predict that life and its technological baggage might end up so beyond our ken that we wouldn’t even realize we were staring at it. That’s quite a claim, yet it would neatly explain why we have yet to see advanced intelligence in the cosmos around us, despite the sheer number of planets it could have arisen on—the so-called Fermi Paradox…

Caleb Scharf on the possibility that alien life could be so advanced it is indistinguishable from physics: “Is Physical Law an Alien Intelligence?

For a very different perspective (albeit, one seemingly rooted in a more narrowly-defined understanding of “life”), see “A Key Evolutionary Step May Mean Intelligent Alien Life Doesn’t Exist in the Universe.”

* Albert Einstein

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As we think through the thought experiment, we might send uncertain birthday greetings to Werner Karl Heisenberg; he was born on this date in 1901.  A theoretical physicist, he made made important contributions to the theories of the hydrodynamics of turbulent flows, the atomic nucleus, ferromagnetism, superconductivity, cosmic rays, and subatomic particles.  But he is most widely remembered as a pioneer of quantum mechanics and author of what’s become known as the Heisenberg Uncertainty Principle.  Heisenberg was awarded the Nobel Prize in Physics for 1932 “for the creation of quantum mechanics.”

During World War II, Heisenberg was part of the team attempting to create an atomic bomb for Germany– for which he was arrested and detained by the Allies at the end of the conflict.  He was returned to Germany, where he became director of the Kaiser Wilhelm Institute for Physics, which soon thereafter was renamed the Max Planck Institute for Physics. He later served as president of the German Research Council, chairman of the Commission for Atomic Physics, chairman of the Nuclear Physics Working Group, and president of the Alexander von Humboldt Foundation.

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Cracking the uncrackable code?…

 

Heisenberg’s uncertainty principle, a foundational tenet of quantum mechanics, is essentially the assertion that when one tries to measure one aspect of a particle precisely, say its position, one necessarily “blurs out” one’s ability to know with any precision its speed– or vice versa.  Indeed, Heisenberg’s original word for the phenomenon translates better as “indeterminacy”–raising the prospect of a physical world whose nature is, beyond some incomplete point, unknowable.

Still, as mysterious as the concept is, it has offered a tantalizingly-concrete prospect:  the “uncrackable” codes of quantum cryptography.  If “listening in” distorts the message, then the eavesdropper is out of luck.

But now, as the BBC reports, researchers at the University of Toronto have raised some serious uncertainty about the Uncertainty Principle itself:

The Heisenberg uncertainty principle is in part an embodiment of the idea that in the quantum world, the mere act of measuring can affect the result.

But the idea had never been put to the test, and a team writing in Physical Review Letters says “weak measurements” prove the rule was never quite right…

This problem with the act of measuring is not confined to the quantum world, explained senior author of the new study, Aephraim Steinberg of the University of Toronto.

“You find a similar thing with all sorts of waves,” he told BBC News. “A more familiar example is sound: if you’ve listened to short clips of audio recordings you realise if they get too short you can’t figure out what sound someone is making, say between a ‘p’ and a ‘b’.

“If I really wanted to say as precisely as possible, ‘when did you make that sound?’, I wouldn’t also be able to ask what sound it was, I’d need to listen to the whole recording.”

The problem with Heisenberg’s theory was that it vastly predated any experimental equipment or approaches that could test it at the quantum level: it had never been proven in the lab.

“Heisenberg had this intiuition about the way things ought to be, but he never really proved anything very strict about the value,” said Prof Steinberg.

“Later on, people came up with the mathematical proof of the exact value.”…

In 2011, they carried out a version of a classic experiment on photons – the smallest indivisible packets of light energy – that plotted out the ways in which they are both wave and particle, something the rules strictly preclude.

This time, they aimed to use so-called weak measurements on pairs of photons, putting into practice an idea first put forward in a 2010 paper in the New Journal of Physics.

Photons can be prepared in pairs which are inextricably tied to one another, in a delicate quantum state called entanglement, and the weak measurement idea is to infer information about them as they pass, before and after carrying out a formal measurement.

What the team found was that the act of measuring did not appreciably “blur out” what could be known about the pairs.

It remains true that there is a fundamental limit of knowability, but it appears that, in this case, just trying to look at nature does not add to that unavoidably hidden world.

Or, as the authors put it: “The quantum world is still full of uncertainty, but at least our attempts to look at it don’t have to add as much uncertainty as we used to think!”…

“There’s actually a lot of technology that relies on quantum uncertainty now, and the main one is quantum cryptography – using quantum systems to convey our information securely – and that mostly boils down to the uncertainty principle.”

A pdf of the University of Toronto group’s paper is here.

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As we reconsider the benefits of entanglement, we might spare a thought for Pieter van Musschenbroek; he died on this date in 1761.  A one-time student of Isaac Newton (who helped transmit Newton’s ideas through Europe), van Musschenbroek was a professor of mathematics, philosophy, astronomy, and medicine. (Those were the days…)  Fascinated by electrostatics, he used what he learned from his father, an accomplished designer and manufacturer of scientific instruments, to build the first capacitor (that’s to say, device that can store an electric charge), the Leyden Jar– named for the city that was home to van Musschenbroek’s university.

Leyden jar construction

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