Launching the FQXi Podcast!
By ZEEYA MERALI • Apr. 30, 2012 @ 19:03 GMT

www.fqxi.org/community/podcast

Eagle-eyed visitors to the community homepage may have noticed that we have added a link to the shiny new FQXi podcast, available here:

www.fqxi.org/community/podcast

Two editions are up and available for your perusal (one from March and one from April).

Some items are related to FQXi grant winners: Markus Aspelmeyer talks about his proposed table-top test of quantum gravity, which could allow physicists to probe the Planck scale using current quantum optics technology; and Jeff Tollaksen describes time-symmetric quantum mechanics and the idea that laser experiments have shown the future influencing the past.

Other items you may be familiar with from the blog: If you liked Matt Roberts’ review of the physics opera, The Astronaut’s Tale, last month, then you’ll enjoy the interview with Nancy Rhodes, the director of Encompass New Opera Theatre, who describes how chats with FQXi’s Brian Greene, as well as with Ed Witten and Michio Kaku, helped her develop an opera about string theory. The podcast includes audio snippets from one of her operas too. Neuroscientist David Eagleman also talks about “neural relativity,” the nature of time as constructed by the brain, and how schizophrenia may be related to a disorder in time perception.

We also have a bit of physics news: Jeroen van den Brink and Krzysztof Wohlfeld talk about how they have split the electron into two quasiparticles -- the spinon and the orbiton.

And, talking to us back in March, Nobel Laureate Frank Wilczek had a bit of a moan about the way the faster-than-light neutrino saga was handled by the media.

So please go ahead and have a listen, and tell us what you think. (There are also forum threads set up where you can discuss individual editions -- have a look at the podcast page for the link.)


Exploding the Supernova Paradigm
By ZEEYA MERALI • Apr. 24, 2012 @ 15:14 GMT

What makes a supernova go boom? I’ve just been at a meeting on ways to observe such stellar explosions at the Royal Society in London, where there was a session discussing this question.

Type Ia supernovae result from the explosion of white dwarf stars and are now celebrated for their role in revealing that the expansion of the universe is accelerating. Textbooks say that they can form in one of two ways: The first (known as the single-degenerate model) is when a white dwarf -- itself an extremely dense star and thus gravitationally hungry -- rips matter from a binary companion until its own mass exceeds a critical limit (the Chandrasekhar mass, about 1.38 times the mass of the sun), triggering nuclear fusion and an explosion. Since they all explode when they hit the same mass, they explode with the same energy and peak luminosity, which means they can be used as "standard candles" for measuring distance -- that is, just by looking at how bright (or faded) they are, you can calculate how far away they must be. The second theorized way that fusion could be triggered is through the merger of two white dwarfs that have a combined mass that is greater than the Chandrasekhar limit (the double-degenerate model).

But that standard story contains a few gaping plot holes, as Marten van Kerkwjik of the University of Toronto pointed out at the meeting. First, there don’t seem to be enough white dwarfs in close binaries to explain the number of Type Ia supernovae seen. Also, even in theory, explosions triggered in these ways do not naturally produce the mix of elements seen in observations -- unless you tweak the theory to make it fit. Oh, and the standard candle thing? They aren’t so much "standard" as "standardizable" as van Kerkwjik also noted (that is technically, they aren’t identical -- a consideration that was well understood and accounted for the in the dark energy discovery). All of these factors, van Kerwjik says, "cast doubt on the standard picture."

In 2010, van Kerkwjik and colleagues suggested an alternative theory: The merger of two carbon-oxygen white dwarfs can lead to Type Ia supernovae, even if their combined mass is less that the Chandrasekhar mass limit (arXiv:1006.4391v3). Simulations show that a merger of two white dwarfs, each with a mass of around 60 per cent of the sun could lead to an explosion that provides a better match with observations. (Follow up simulations by van Kerkwjik and others here.)

It’s going to be hard to prove that van Kerkwjik’s idea is correct with actual observations, however, since his predictions tend be "negative." For instance, if you look at a supernova remnant and *fail* to find evidence of a companion from which matter was accreted, then that’s consistent with his alternative model -- but doesn’t stand as proof for it. Astronomers have been searching for such evidence -- see for example, "An absence of ex-companion stars in the type Ia supernova remnant SNR 0509-67.5", Schaefer &Pagnotta, Nature 481, 164-166 (12 January 2012), which seems to at least rule out the single-degenerate models for that particular supernova.

The take-home message seemed to be that Type Ia supernovae are even more of a mixed bag than previously thought. Now variety may be the spice of life, but these supernovae have been lauded as standard candles because they all seem to be doing the same thing. The suggestions that things aren’t quite that simple don’t seem to affect the conclusion that the expansion of the universe is accelerating -- at least Brian Schmidt, who won a share of the Nobel for the discovery and who was sitting alongside van Kerkwjik on the discussion panel didn’t seem to be sweating. But since so much of our understanding of the past and future of the universe is tied to these entities, it might be a good idea to work out what’s going on with them.


The Astronaut's Tale: Physics Meets Opera
By MATTHEW ROBERTS • Mar. 31, 2012 @ 18:45 GMT

When I was asked to review The Astronaut's Tale (music by Charles Fussell, libretto by Jack Larson), I will admit that I had no idea what to expect. The blurb describes the opera as being about the “confrontation of science and religion” (which certainly raised a red flag!), but the temptation of seeing of an opera written by Larson, the original Jimmy Olsen from the Adventures of Superman, was undeniable. I should preface this review by pointing out that I have not seen the entirety of The Astronaut's Tale. I attended a preview performance which only contained about half of the opera. What I did see was a pleasant surprise; despite a rather (perhaps intentionally) overly melodramatic opening scene, the piece manages to tell a compelling tale about a young man, Abel, aspiring to be an astronaut, and what science is and is not able to provide him.

But first, the opening––a scene that is supposed to display Abel's loss of innocence, as he witnesses his dog being hit by a car and killed. This scene, and the rest of the opera, is presented with a spoken narration that (probably intentionally) is reminiscent of the stereotypical mid-century announcer, somewhere between Rod Sterling and Cary Grant. While this threw me for a loop when it first began (in my notes I underlined "Intentionally camp??" twice), it actually does a surprising job of setting the tone of the piece as the story progresses.

Abel, a hopeful cosmonaut, realizes that he has to become adept at math and science before accomplishing his goals. He meets a wandering peddler of goods (in the program he is described as an “Einstein-like” figure, which I think is a bit of a stretch) who sells him a programmable calculator, which apparently is the key to academic success. Abel, initially skeptical of modern science, and the Peddler have a great duet in which they contrast the biblical and modern cosmological genesis stories, with Abel recounting the biblical version and the Peddler correcting him with science. This begins with low-hanging fruit, equating “Let there be light” with the big bang, but also contains more subtle comparisons such as God dividing day from night compared to the scientific fact that matter and energy are one and the same, and the belief that God created man in his image against the statement that the cosmos is the actual “image of God.” The music for this duet is a delight, with Abel supported by more traditional church music while the Peddler sings with a sound that sounds large, vast, and dark, but just as beautiful.

What I appreciated most about this piece, which captures a lot of the tone of the opera as a whole, is that while it compares these two ideas, it does not simply do so in the traditional "I'm right/you're wrong, I'm smart/you're stupid" structure that a lot of "science versus religion" debate quickly devolves to in modern discourse (side note: there is a monkey joke, but it is not mean-spirited). It's not that the Book of Genesis is a laughable joke--it was an attempt to explain the world we see around us, written when the scientific tools at our disposal were obviously not what we have now. I'm sure there are people out there who will find a way to take offense at this, but I thought the subject was treated with appropriate dignity. And I am happy to report that, to the best of my ability, all of the facts laid out were right (the age of the universe is approximated as twenty-thousand million years, which is pretty spot-on!).

Abel eventually works his way up in the American rocket program, and meets a tragic fate as his first flight is on a Challenger-like disaster; his last living line was the now famous, “Uh-oh.” It is at this point that I felt the opera (or at least the parts of it I was able to see in preview) lost some of its focus--it dissolves into a piece of the afterlife being "in space," which from my perhaps cynical physicist point of view is not as interesting, though it was still lovely to listen to. I understand the point being made: that there are some things, such as the afterlife, which are beyond the realm of what science is tasked to explain, but to me it just came off a bit too vague and sounded of empty philosophy. I won't say this spoiled the whole show, but I will say it bothered me more than the melodrama of pet death.

On the whole, though, the opera was great-- the music was highly enjoyable, and I'm always happy to see a heroic lead portrayed as someone whose trials and tribulations involve learning mathematics and physics. I will admit, though, that the whole thing made me sad mostly for the current state of the American space program (an opera review is not the right place for a political diatribe so I will stop here). The Astronaut's Tale should remind people both of the majesty of space exploration and the amazing story of how our universe was born, and perhaps even inspire them to call up their Congressman and demand more funding for basic sciences! Sorry, couldn't help myself.

--

Matthew Roberts is a string theorist at NYU.

Excerpts from "The Astronaut's Tale" were recorded on Sunday, March 18, 2012, during Encompass New Opera Theatre's performance at the Manhattan School of Music. The performers were Brittany Palmer (Ann), Eapen Leubner (The Astronaut), Frank Basile (Peccavit, the old Peddler), and Christopher Vettel (The Narrator). The Encompass performance was the first-time the opera had been staged. Prior to that, "The Astronaut's Tale" was performed in concert by Collage New Music in 1998.


If God were to simulate reality, would he prefer it quantum?
By MILE GU • Mar. 27, 2012 @ 16:49 GMT

--or How Quantum Theory May Sharpen the Blade of Occam’s Razor

.

The 1999 movie ‘The Matrix’ explored a world where humans are plugged into a virtual reality. They go about their daily lives, unaware that the sensory inputs that they receive do not originate from their perceived reality. When a person, Alice, within the matrix observes a watermelon falling from a skyscraper, there is no skyscraper, nor watermelon, nor even gravity responsible for the watermelon's fall. Instead a complex computer program works silently in the background. The initial state of the watermelon, and the location of the observer, is all encoded by bits. The computer takes these bits, processes them according to a predetermined algorithm, and outputs the electrical signals that dictate what the observer should see.

To we who live in the twenty first century, whose lives are enmeshed in various information processors, the eventual plausibility of the Matrix does not appear as radical as it once did. One by one, the photos we view and the mail we send, have been converted to digital form. Common questions, such as, “How many megabytes does that song take up?" reflect a society that is becoming increasingly accepting of the idea that the observable qualities of every object can be represented by bits, and physical processes by how they manipulate these bits. Some scientists have even gone as far as to speculate we could live within a giant information processor, a giant ‘Matrix’, programmed to simulate the laws of physics we know.

If our observed reality were indeed a simulation constructed by some ultimate architect, what is the underlying code of our universe? What sort of information processing would they use? Would it be merely classical logic on classical bits, or would they harness the unique properties of quantum logic? On first impressions, such questions seem difficult to answer. After all, all observations we make lie within ‘The Matrix’, how could we say anything about what lies beyond?

One way to approach this problem is to walk in the shoes of the architect. Suppose you were an young architect, tasked to simulate a simple reality. A universe, consisting of a single observable bit evolving in discrete time steps, such that at each time, the bit flipped with probability 0.2 (see note (*) below, for why I have chosen 0.2). Being a beginner, you are presented with two potential solutions:

(i) A system consisting of two binary coins. At each time-step, the system sets the observable bit to 0 or 1 depending on whether the state of the two coins coincide, and one of the two coins is chosen at random and flipped with probability 0.2.

(ii) A system consisting of a single coin. At each time-step, the system sets the observable bit to 0 or 1 depending on the state of the coin, and the coin is flipped with probability 0.2.

Either solution works: The output of either system behaves exactly according to desired specifications. Yet, if tasked to select one of the two, most of us are likely to prefer the second option. A solution with a single coin simply appears more appealing than a solution that requires two.

This natural sense of aesthetics was first formalized by William of Ockham, a 13th century friar. Occam’s Razor posited that ‘plurality is not to be posited without necessity.' When given two different ways of doing the same thing, there’s no sense in choosing the more complex one without good reason. Since its inception, the principle has become an important heuristic that guides the development of theoretical models in quantitative science. In the words of Isaac Newton, “We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances."

When applied to the two potential simulators above, the natural appeal of the second solution can be given more rigorous footing. The first simulator kept track of two coins to simulate our toy universe. Since all configurations occur with equal probability, it would have an entropy of 2. In contrast, the second simulator keeps track of only a single coin, and thus requires only half this entropy. If we are tasked with simulating a plethora of such realities with a hard drive of limited space, we could manage twice as many realities with the second approach.

Therefore, should we assume that whoever designed The Matrix would have similar aesthetic tastes, and so we may use similar reasoning to deduce the underlying code to our own reality––or, at the very least, deduce how our reality should be designed if our computer overlords cared about how much storage space they used. These considerations thus motivate the question:

If we are to construct a simulator of observed reality, would we need to store less data if we chose to exploit quantum dynamics?

Let us return to the simple universes that consist of a single bit evolving in discrete time steps. The behavior of such realities can be characterized as a stochastic process, a probability distribution over a sequence of bits. A simulator for a stochastic process can be thought of as a physical system that stores select information about past outputs, and uses them to generate the require statistics for the future (see image, top right). Ideally, we want to construct a simulator that as simple as possible, such that its information storage requirements are minimized.

A priori, it is not obvious quantum dynamics would be of direct benefit; after all, the required behavior is merely a string of classical bits that obey a particular classical probability distribution. Quantum dynamics does seem to be of immediate relevance.

Yet, classical simulators have turned out to be less than ideal. Take for example, the simple case of our toy reality that is simulated by a single coin. The amount of information stored within the simulator is a single bit, namely the state of the coin. However, even if we could observe the entire future of this reality, we would still be unable to ascertain whether our simulator started with a coin in state 0, or state 1. Thus, not all information stored by the simulator was ever visible in its simulated reality, and thus should never be stored in the first place.

This is in fact, a generic property of classical simulators. For most stochastic processes, even the provable optimal classical simulator stores more information than it needs. If a binary property ‘X’ (such as the state of coin), had an effect on the future evolution of observed reality, then the value X must be stored. This is unavoidable; even all future observations made within the reality does not guarantee one can deduce the value of X. Therefore, classical simulators erase information; they contain a source of irreversibly that cannot be removed.

Quantum simulators, however, have greater potential freedom. Instead of allocating a full bit to store the value of X, we may store the conditions ‘X= 0’ and ‘X=1’ in non-orthogonal states. Consequently, the simulator saves memory, as it was never sure what state the property was in the first place. Nevertheless, we show in Nature Communications, this week, that it is often possible to engineer dynamics such that the simulator can still replicate the dynamics of our desired reality (full paper available at arXiv:1102.1994v4 ). The use of quantum processing has essentially sharpened Occam’s razor, allowing us to shave off the parts of X that we never needed to remember.

The applications of this result go beyond programming The Matrix for memory conscious computer overlords. The minimum amount of information required to simulate a given stochastic process is a significant topic of study in the field of complexity theory, where it is known in scientific literature as statistical complexity. The rationale is that if we are supplied any complex system, we can still make a meaningful statement about how complicated it must be by looking only at the statistical complexity of its output. If the system displays a statistical complexity of C, then whatever the underlying mechanics of the system, we need at least a memory of C to simulate its statistics.

The fact that this memory can be reduced quantum mechanically implies the counterintuitive conclusion that quantizing such simulators can reduce their complexity beyond this classical bound, even if the process they're simulating is purely classical. Many organisms and devices operate based on the ability to predict and thus react to the environment around them, the fact that it is possible to make identical predictions with less memory by exploiting quantum dynamics implies that such systems need not be as complex as one originally thought.

Nevertheless a puzzle remains: Quantum simulators are still not wholly reversible. For many stochastic processes, even the best quantum simulators we know still erase information--they still store unnecessary information. Could an even more general probability theory, with even more bizarre correlations, side-step this restriction? If our reality indeed lay with a grand Matrix run by some memory-conscious architect, he could certainly prefer a ‘quantum Matrix’ over a classical one; but could he have some even more exotic Matrix in mind?

Note (*): Many of you might wonder why in this toy universe, I chose to have each bit flip with probability 0.2 rather than the more natural 0.5. The answer is actually rather illuminating. 0.5 is a bit of a special case. If you, as the young architect, were given the task to design a universe where each bit was to be flipped with probability 0.5, then you should consider yourself very lucky. To anyone living inside the universe, the universe would look like a string of completely random bits. To simulate this, you won't need anything sophisticated. Just design a system that blindly tosses a coin into the air! Such a system is remarkably simple, it would need to keep track of absolutely nothing!

--

Mile Gu is a research fellow at the Centre for Quantum Technologies in Singapore.


Disproofs of disproofs of disproofs of disproofs...
By ZEEYA MERALI • Mar. 19, 2012 @ 16:27 GMT

It has been brought to my attention that the discussion threads for Parts 1, 2 and 3 of "To Be or Not to Be (a Local Realist)" and "On the Origins of Quantum Correlations" are getting increasingly unwieldy and slow, due to the huge numbers of comments.

Since there have also been recent further contributions to this discussion on the arXiv, from Richard Gill and from Joy Christian, I am opening up this thread for new discussions about these recent papers.

Please be polite and reasonable in your responses. No personal comments are necessary.

Recent Blog Entries

Two predictions for the Post-Quantum World
By VLATKO VEDRAL
Every time physicists face experiments that cannot be explained with the existing theories they have to decide which aspects of these theories to keep and which to throw away. Planck, when faced with the inability of classical physics to explain...

Elegance and Enigma: The Quantum Interviews
By MAXIMILIAN SCHLOSSHAUER
[picture]To say that quantum theory is about describing how atoms behave would be like saying that all Hemingway ever did was show us how to write terse prose. Quantum theory, more than any other physical theory, seems to rub against what we have...

Hanny's Voorwerp, and Other Year-End Goodies
By WILLIAM OREM
[picture]

The new year is upon us: first step—according to the Gregorian calendar, anyway—of our next long loop around the sun. Time to look back over some of the most interesting Foundational stories from the previous trip.

Here, in no...

Proving You Are Where You Say You Are:...
By GEORGE MUSSER
This is the second part of a post on garden hoses, quantum cryptography, and schemes to verify position. The first part, which details the first proposed scheme to verify your position--and exactly how you can cheat it with the help of two...

Proving You Are Where You Say You Are:...
By GEORGE MUSSER
When a speaker brings a tangle of garden hoses, a bottle of water, and a towel to the podium, you know it’s going to be a fun talk. Computer scientist Harry Buhrman of the Centrum Wiksunde & Informatica in Amsterdam recently visited Singapore to help...

Greetings from Goa
By BRENDAN FOSTER
Greetings from Goa, India, on the shores of the Arabian Sea. [picture] I am here at the International Conference on Gravitation and Cosmology, hosted by the Indian Association for General Relativity and Gravitation and the International Centre for...

The Secret History of that Infamous Boson
By GERALD GURALNIK
- Comments on the much anticipated December 13 CERN seminar on the status of the ATLAS and CMS searches for THE BOSON.

[picture]Headlines have been buzzing for the past week or so about a possible glimpse of a certain long-sought particle at...

Are we getting closer to nailing down what the...
By OSCAR DAHLSTEN
-Comment on recent preprint by Pusey, Barrett and Rudolph.

A quantum system is said to have a state, also known as a wavefunction. The minimal interpretation of the state is that it encodes our knowledge about measurement outcomes. But many of...

The Whole and Nothing But
By ZEEYA MERALI
More videos from the Setting Time Aright meeting, this time from the session on Truth. The talks covered both the philosophical question of what scientific “truth” is -- Is science as objective as we might hope? -- and the practical question of how...

On the Origins of Quantum Correlations
By JOY CHRISTIAN
John Stewart Bell is undoubtedly one of the icons of contemporary physics. His name has become inseparable from the notion of quantum non-locality, however, Bell himself always stressed that it was Einstein--together with Podolsky and Rosen--who...