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FQXi BLOGS
August 20, 2014

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Quantum theory escapes locality by accepting uncertainty
By OSCAR DAHLSTEN • Aug. 17, 2014 @ 15:28 GMT

Figure 1
When a ballerina does a pirouette she must escape the friction of the ground in order to get the freedom to move. (Figure 1: Photo by Michael Garner, courtesy of English National Ballet.) She does this by restricting her contact with the ground to a point. In a recent paper I and my collaborators Andrew Garner and FQXi's Vlatko Vedral show that quantum theory in a very similar way escapes a fundamental constraint on movement by accepting uncertainty.

Quantum systems are associated with states which encode the statistics of future possible measurements. The collection of such states may be represented as a geometric shape. In the smallest possible quantum systems, single qubits (quantum bits), this shape is a sphere, called the Bloch sphere.

For example, think about a property of a qubit, such as its position: the qubit could be associated with two possible positions, A and B, say, or it can be in a fuzzy superposition where it exists in both of these mutually incompatible states simultaneously, before being observed. If it's in a superposition then although experimenters cannot know with certainty what position they will find it in when they make a measurement, they will have some sense of the probability of getting a certain outcome. The Bloch sphere helps to visualise this odd feature and the probabilistic nature of quantum mechanics. In the example, a vector pointing to the north pole of the sphere could represent position A, while the south pole represents position B. (In a classical system, this would represent the only two options available for a binary digit, or bit, to access). However, a qubit can also be represented by a vector pointing elsewhere on the surface of the sphere, corresponding to the fuzzy in-between states.

Figure 2
The maximal state space conceivable would actually be the cube outside of the sphere, as shown in figure 2. The quantum state space is the sphere, but if there were no uncertainty principle all states in the outer cube could be allowed. In this case certain measurements could all have predictable outcomes at the same time, in violation of the quantum uncertainty principle.

One may ask why quantum theory is restricted to the sphere, and accordingly to having the uncertainty principle.

We came across an intriguing answer when thinking about how the cube state space would handle an interferometer. In an interferometer the particle or photon is firstly placed in a superposition of being in two places and then operations are done on each site. Now when you have two different sites fundamental locality restrictions come into play. In particular, we point out that if a system has 0 probability of being found on site B, then an operation on site B must leave the state of the system invariant. Otherwise we could do action at a distance. Contrary to some popular science depictions, quantum theory does not allow action at a distance. The universe would be almost inconceivably odd and complicated if action at a distance were possible. We would not be able to make a statement about an individual system without taking into account what happens everywhere else in the world.

On the Bloch diagram, state transformations move points around, e.g. by rotating the shape. So, if one accepts that this locality restriction holds, it turns out that operations on site B must leave all points (states) on the lower plane of the cube invariant. It is like the points are stuck by total friction between the shape and the lower plane. As a result the cube has a big disadvantage over the sphere because if the entire square face touching the ground is restricted, then the whole cube gets stuck and no states can change.

But now imagine metamorphosing the cube into a sphere, or indeed something else with only one point on the lower plane, like how the ballerina goes up on one toe. Then the shape, with all the quantum states in it, can move. The quantum sphere has the advantage over the cube that it can rotate even if there is full friction with the lower (and/or upper) plane, just as the ballerina accepts the uncertainty of only having a point in contact with the ground in return for the ability to pirouette.

One may say that uncertainty, rather than being just limiting, liberates quantum states to change.

--

Oscar Dahlsten is affiliated with Oxford University

The paper appears in Nature Communications.
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F(ilm)QX
By WILLIAM OREM • Aug. 1, 2014 @ 20:34 GMT



Looking for a low-level break from your usual high-level philosophizing about science? Check out Luc Besson's latest: a sci-fi shoot-em-up titled *Lucy* that will keep you crunching popcorn without straining too many neurons.

Okay, it's not really the thinky movie it thinks it is, but it's fun, and the premise is terrific (spoiler alert, obviously).

Our story begins with Lucy, the Australopithecus, sipping water from a primordial stream: hey, look how far make-up has come since *Space Odyssey*! (Plot ideas, not so much; this movie's most interesting parts are *Space Odyssey* on training wheels). Flash forward three million years to Scarlet Johansson as another Lucy, this one a modern-day dimwit who becomes entangled in an evil Japanese scheme to sell a new designer drug. The drug -- it's not clear how the bad guys missed this before they decided to mass-market it -- inadvertently causes people who take it to start utilizing more and more of their untapped cognitive potential. You may remember a similar premise from the 2011 movie *Limitless,* in which . . . well, exactly that.

This time, the bad guys stash a bag of the stuff in poor Scarlet Johansson's abdomen, turning her into a detection-free drug mule. Even worse, halfway to her destination a sadist starts beating her up, kicking her so hard in the gut that the bag full of crystals begins to leak . . .

That's the most intimidating moment of the movie right there, actually. Lucy's enforced participation in these gruesome proceedings; the savagery of the thugs, coupled by the icy sociopathy of the kingpin; it's scary stuff. At exactly this point, however, our suspended disbelief plummets as we dive into what has become the bane of Hollywood thrillers: the whiz-bang CGI sequence. Racing through Lucy's capillaries *Incredible Spider-Man* style, we see what would have been obvious anyway: the leaked drug is infiltrating her brain, causing amazing physiological changes. (The first of these, oddly, is an anti-gravity seizure.)

How we got from "she's becoming more intelligent" to "she's floating on the ceiling" is anyone's guess -- or, rather, it's up to Morgan Freeman, in his usual wise mentor role, to inform us via a series of wildly unscientific lectures. Among the groaners:

The notion that humans only use 10 percent of our brains. Why do so many people think this is true? There isn't a 90 percent block of gray matter that's just sitting in our skulls, not functioning. This movie claims to be about human evolution -- and interrupts itself frequently to montage about the effects of evolving intelligence in the cosmos -- but isn't all that clear on how brains actually evolve. To quote a Scientific American article on this misperception: "Though an alluring idea, the '10 percent myth' is so wrong it is almost laughable . . ."



If you had access to 20% of your brain, science-Morgan tells us, "you could control your own body." (A bit of a head-scratcher: don't humans control their bodies right now? And why does Lucy start having eyeballs from other species?) At 30% you can control other people's bodies as well; next comes telekinesis, morphing, and on up to time travel. How science-Morgan concluded any of these things is left out of the script, probably wisely; just play along.

Religion also gets smooshed in here too, though in a rather perfunctory way: "You never really die," Lucy informs a mere mortal at one point. "I only hope we are worthy of your sacrifice," science-Morgan sighs, as she heads toward her humanity-saving apotheosis. There isn't much of Lucy-as-Savior, though: mostly she kicks ass and shoots guns.

The real fun, however, isn't any of that -- it's in the premise of a dumb, abused woman who quickly becomes not only smart, but smarter than her abusers, then smarter than the police chasing her, the scientists studying her, and everyone else on earth. In a way, we owe all such stories to Arthur Conan Doyle, whose hyper-perceptive detective set the standard (If you doubt the enduring influence of Sherlock Holmes, I would point you toward the Robert Downey Jr. movies, the PBS re-runs of the magnificent Jeremy Brett, the runaway British success *Sherlock*, the American TV shows *Elementary* or *The Mentalist* or even *House* . . . among still others.)

Now it's Lucy, who can out-think the rest of us with ease as she evolves up the Kurzweil ladder of rapidly accelerating intelligence. If only the movie stayed with that idea, which is something that is actually on the way -- technologically enhanced super-intelligence, when we boot-strap ourselves into another evolutionary phase altogether -- instead of the magical stuff. As Mr. Spock, an earlier Sherlock Holmes knock-off, would have said, that's fascinating.

credit: public library toronto

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“Utopia or Dystopia”
By ZEEYA MERALI • Jul. 8, 2014 @ 14:03 GMT

Rick Searle of the Institute for Ethics and Emerging Technologies has a post up about this year’s essay contest. Check it out here.

The essay contest is now closed for votes, but as you know, it is still open for debate.

Also, don’t forget that there is still time to enter and vote in our video contest, Show Me the Physics!.
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Consciousness = Maths, Simulating Time Travel, BICEP2 Scrutinised and Quantum Entropy
By ZEEYA MERALI • Jul. 7, 2014 @ 17:23 GMT

Just a quick round-up of some more video and audio on offer.

If you've been following Max Tegmark's latest ideas on consciousness as a state of matter (which I blogged about in January), then you'll enjoy his TEDx Cambridge talk:



I've also posted the latest FQXi podcast, which this month includes physicists Andrew White and Martin Ringbauer talking about their quantum experiments to simulate time travel, in particular closed timeline curves (CTCs), in the lab. The team uses two photons -- one representing the older version of the time travel and the other its younger self -- and then monitors what happens when the two interact. When CTCs are involved, they have found that a some standard quantum rules need to be rewritten: Heisenberg's Uncertainty Principle is violated, and the quantum no-cloning theorem no longer applies.

Physicist Malcolm Fairbairn also chats about his analysis which shows that if the BICEP2 results stand, the model of inflation they favour -- combined with data we now know about Higgs boson -- suggests that the universe should have collapsed long ago. The BICEP2 results are, of course, under scrutiny, right now, as cosmologists ponder whether the results, which I blogged about in March, really do provide evidence of primordial gravitational waves, or were instead caused by contamination from dust in our galaxy. In the main podcast, we're hear Alan Guth's thoughts on the controversy (recorded in May). On the podcast page, you can also listen to a longer interview with Guth, where he discusses the implications for reconciling the data with Planck, models of inflations, grand unified theories and the multiverse, if the results do hold.

Plus, Colin Stuart talks to FQXi members Jon Barrett and Matt Leifer about their quest to explain why nature chose quantum theory, based on an investigation of entropy in thermodynamics and information theory. You can read and discuss Colin's profile of their work here too.

The podcast is available here.

And back to Max, on an older podcast special, in January, we shared the audio from his talk at the FQXi conference in Puerto Rico. The video of that talk is now up, if you haven't seen it already:



We've also uploaded this panel discussion on consciousness from that meeting, featuring Max, along with neuroscientists Christof Koch and Giulio Tononi, psychiatrist Larissa Albantakis and electronics developer Federico Faggin:


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Show Me the Physics!
By BRENDAN FOSTER • May. 9, 2014 @ 16:19 GMT

Video idea 1: Debunk your favorite physics myth
Part of our goal at FQXi is to get people talking and wondering about the fascinating and confusing foundational physics research we support. We also want to be a point of connection between the researchers and teachers and everyone else who has an interest in physics.

That's why we are excited to announce our new VIDEO contest Show Me the Physics!

FQXi wants to see your best videos that highlight how fun and stimulating physics can be.This contest aims to get people around the world excited about studying physics, with the hope that some of them go on to make their own physics discoveries. This Contest will show people (and/or pets) exploring and learning about physics phenomena in wild, innovative, and fun ways.

Video topics and content can cover everything from unsolved physics mysteries, interviews with physicists, fictional tales (that use CORRECT physics), and even fuzzy animals doing cute things that Show Us the Physics!

Video idea 2: Explain your favorite equation
We welcome entries from everyone -- no experience required, all experience allowed. You can record using professional equipment, amateur camcorders, smartphones, tablets, or whatever. The main idea is that learning physics, doing physics -- and making videos about the experience -- is fun. We will judge entries based on the quality of physics content and their entertainment value, with less focus on the technical quality of the footage.

Entry is easy -- you make a video, post it on YouTube (with the hashtag #FQXiVideoContest2014), then fill out the application form. (Entrants under the age of 18 must be represented by an adult parent, guardian, or teacher.)

Video idea 3: Demo your favorite experiment
To stimulate the discussion, we will award prizes up to $10,000, including a 'Young Scientists' prize for entrants under 18--which includes a Skype chat with FQXi directors and foundational physicists Max Tegmark and Anthony Aguirre.

You can find our full rules here. Accepting entries until August 8, so you have some time to storyboard and round up your crew, or to charge up your iphone. Check the contest page for early entries now, and check back regularly for new entries.
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Recent Blog Entries

How Should Humanity Steer the Future?
By BRENDAN FOSTER
Greetings all -- Just a quick announcement to say our current essay contest -- How Should Humanity Steer the Future? -- is closed for entries as of now. We are currently reviewing all the great entries that arrived in the past few days, so expect to...
April 19th, 2014 | 368 comments | view blog entry & comments

FQXb (bio)
By WILLIAM OREM
[picture]

Everyone is talking this week about the dramatic confirmation of inflationary theory: those first-instant gravitational waves whose details may even point--being, if you will, quantum phenomena that went suddenly...
March 23rd, 2014 | 9 comments | view blog entry & comments

BICEP2: Primordial Gravitational Waves & Evidence...
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Updated: Congratulations to FQXi's Alan Guth and Andrei Linde following the announcement of the first direct detection of B modes -- evidence of their inflation theory. Well done to those working on BICEP2, and all others who have contributed to the...
March 17th, 2014 | 14 comments | view blog entry & comments

Time and the Nature of Reality
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[picture]We recently ran an article (courtesy of Nautilus Magazine) in which physicist Paul Davies ran through some open questions about the nature of time.

I want to alert you to another discussion currently taking place on the Big...
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Video: Seth Lloyd, "What Happens When You Fall...
By ZEEYA MERALI
Some of you may have noticed that I enjoy writing about the question of what happens when you fall into a black hole. At the recent FQXi meeting in Vieques, Puerto Rico, "quantum mechanic" Seth Lloyd talked through this problem and discussed a way to...
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Is the universe infinite or just really really...
By IAN DURHAM
As promised, this is a follow-up to one of the summary posts from the FQXi conference in Vieques. If you have read those, you may recall that Anthony Aguirre asked the intriguing question: is there any way for us to tell if the universe is infinite...
February 3rd, 2014 | 46 comments | view blog entry & comments

Might the Infinity of the Universe Have a Tangible...
By GEORGE MUSSER
“There is a difference between whether the universe is infinite or just really really really really really really big,” Anthony Aguirre said at the recent FQXi conference in Puerto Rico. I’m pretty sure I counted six reallys. With that remark,...
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Consciousness as a State of Matter--Max Tegmark's...
By ZEEYA MERALI
[picture]More audio from the FQXi meeting in Vieques, this time from cosmologist Max Tegmark. As Ian has already blogged, Max has been pondering what qualities conscious matter would have that differentiates it from non-conscious matter.

In...
January 21st, 2014 | 47 comments | view blog entry & comments

Time From a Timeless World
By GEORGE MUSSER
Theoretical physicists commonly say their biggest challenge is to unite general relativity with quantum theory. But at this month’s FQXi conference in Puerto Rico, Carlo Rovelli said they have an even bigger challenge: to unite general relativity...
January 21st, 2014 | 55 comments | view blog entry & comments

Interesting Ways to Die (and More)
By IAN DURHAM
[picture]The final full day of the conference in Vieques began with a session on quantum gravity. (Some slides and videos from the meeting are now up: here.) Seth Lloyd led off the longer talks by essentially summarizing what we know about in-falling...
January 20th, 2014 | 7 comments | view blog entry & comments

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