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Philip Gibbs: "The contest has succeeded in generating open discussions on the nature o..."
in The End of Time (The E...
Kate: "I recently came accross your blog and have been reading along. I thought..."
in Cosmology for Kids, FQ...
Myke: "Greetings Anthony, the essay contest is a great innovation at FQXi and a..."
in The End of Time (The E...
Lost in Space: "I guess in part it depends how "real" the universe is and what sort of r..."
in Shutdown of the LHC, b...
Count Iblis: "William, thanks for the links to these interesting articles!"
in Impact
Count Iblis: "The experimentalists can experiment and interpret as much as they like. ..."
in Has Superluminal Tunne...
intereesting: "hmm maybe they were right"
in Shutdown of the LHC, b...
amrit: "see also Eleven steps to right understanding of time 1. Motion of obj..."
in Has Superluminal Tunne...
click titles to download PDF files
Back to Mach
Want a theory of quantum gravity? Then look to the man who inspired Einstein.
The End of the Quantum Road?
Have we already found the ultimate theory of nature, without realizing it?
The Universe's Odyssey?
How our youthful universe may have wandered the string landscape in search of home—with help from its anti-universe counterpart.
Hunting for Theories of (Not) Everything
The architect of "doubly special relativity" wants to probe the quantum nature of spacetime—one step at a time.
Quantum Darwinism
How does objective reality emerge from quantum fuzziness? It's a case of the survival of the fittest.
Don't miss the inaugural FQXi Essay Contest! read | submit
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FQXi BLOGS
New Blog Entries
The End of Time (The Essay Contest)
By ANTHONY AGUIRRE • Jan. 2, 2009 @ 15:44 GMT
Happy New Year! With the end of 2008 comes also the end of the FQXi essay contest on The Nature of Time. Judging will be taking place over the next month or so, after which winners can be announced. In the meantime, I thought it would be worth opening up a forum to discuss how this very experimental project has unfolded so far. I have some thoughts, to kick off the discussion.
First, it's been really fun, and very satisfying, to see so much real interest and high-quality thought put by people into the contest. In the essays I've read, there was an amazing range of content and also style, ranging from poetry to literary discussions of Jung, Heidigger, Hegel and others, all the way to abstruse mathematical tracts. Quality-wise, some of the essays were, shall we say, content-challenged, but even these showed for the most part a real enthusiasm, interest, and humility before the problem. And many of the essays I read were really very good, including some by complete not-academics.
In addition, I was somewhat surprised at the positive and supportive tone of much of the discussion. I expected a brawl, but instead saw a lot of friendliness, genuine interest, and discovery of common ground. (With of course, a significant dash of grandstanding and self-advertisement thrown in.)
To the extent that the essay contest was designed to get a lot of smart people thinking about, and collectively discussing, a compelling question, I think things have worked out really well.
I was less thrilled about how the voting system worked out; next time we will definitely change to a 'rating' system, so that people do not feel compelled to read lots of essays before providing some judgement on them. (It will be interesting to see how the public votes versus the restricted votes versus the judges' evaluations will compare. I suspect there will be significant differences.) Also, I was disturbed to hear (from various sources) of people who would have liked to enter but found out about the contest too late. This sort of community is one that it is very difficult to get the word out to, but we will keep working to improve this; suggestions are welcome.
So: as we wait for results, what are your thoughts: what worked, and what didn't? what should we do differently next time? and what should the next contest be about?
Has Superluminal Tunneling Been Observed?
By DIETER ZEH • Dec. 27, 2008 @ 17:21 GMT
Earlier this month, in Science (Vol. 322, p. 1525), P. Eckle et al. reported an experiment from which they conclude that an electron can tunnel through the potential barrier of an He atom in practically no time. This would indeed be a fundamental discovery, but I think the analysis of their technically brilliant experiment is faulty. It may instead represent further evidence that the interpretation of an electron as a particle is simply wrong. There had already been earlier claims of superluminal tunneling, but some were based on doubtful definitions of clocks, while most of them used questionable concepts or classical pictures (particles) for their interpretation.
 | | Huge apparutus is needed to attempt to time a tiny quantum effect (Credit: Keller, ETH, Zurich) |
Before discussing this new experiment, let me remind you of a mathematical paper by G. Hegerfeldt (Phys. Rev. Lett. 72, 596, 1994), who claimed that an atom in a state that is formed at some definite time by means of a quantum jump can _immediately_ cause an effect in another atom at an arbitrary distance with very small but finite probability.
Understandably, this claim caused a considerable stir in the media when it was published, although it is partly trivial and partly wrong. Since the eigenstate of a bound electron has an infinitely long, exponentially decreasing tail in the forbidden external region, there is some probability that it (or its electromagnetic force) does not have to travel the distance to the other atom in order to interact with it. What is physically wrong in the considered scenario is the assumption that the bound state can form instantaneously and exactly in a quantum jump. Physicists should know that a time-dependent process has to be described by the time-dependent Schrödinger equation (or its relativistic equivalent). Therefore, the tails of the wave function require sufficient time to _form_, and the suggested experiment would fail.
In the new experiment, a similar mistake seems to be responsible for its proposed interpretation. In this case the authors assume (directly or indirectly) that the electron is initially inside the potential barrier of the He atom. They then lower the barrier at a precisely defined time, and they observe the emitted electron immediately thereafter (at a time earlier than it would be required to travel through the barrier region at light speed). Here they neglect again the exponential tail of the wave function that existed even before the potential barrier was lowered (regarded as the “onset of efficient tunneling”).
The details of the experiment are complex, so I cannot exclude that other aspects may be important, too, for explaining the result in a realistic manner. However, every physics student with a computer can numerically calculate the time-dependence of the exact wave function (with an initially present tail) in a one-dimensional model after the barrier has been lowered. Even more than that: because of the linearity of the Schrödinger equation, one can do this calculation separately for all _parts_ of the wave function (internal part, tail in the forbidden region, or any other chosen position interval), and thereafter superpose their final states.
This might be the most informative part of the story! For a relativistic wave equation it must confirm the light speed limit for all corresponding wave fronts (“signal speed”) in accordance with the Sommerfeld theorem. (Relativistically, sharp wave fronts may require negative frequencies, which would have to be interpreted as contributions from particle-antiparticle pairs in the particle picture—but this exact case is here not necessarily relevant.) If the wave function describes reality, its propagation represents the only physical motion in the experiment. The peak velocity of the wave packet does not represent any causal motion under a potential barrier, while the rest of the rich debate about tunneling times in the literature is concerned with particle metaphysics.
So why all the fuss about tunneling times if the results can be readily predicted? The reason is presumably that most physicists once learned, and still believe, that “the wave function only describes probabilities for positions (or other properties) of particles.” If the electron, as a particle, does not possess a trajectory (“because of the uncertainty relations”) it must acausally hop from here to there—possibly at superluminal speed. However, this hopping of postulated particles depends on artificial definitions. Even the usual pragmatic probability interpretation in terms of particles would not allow superluminal effects in this way. So the true scandal is that such misleading interpretations are readily accepted (or uncritically commented) by reputed journals, such as PRL, Science or Nature. As a related example, consider the hype about so-called “quantum teleportation”, which is but another quantum misnomer.
There is in fact no evidence for the existence of particles in any form. The occurrence of spots on a screen or clicks of a detector can be dynamically described in quantum mechanical terms by means of wave functions, taking into account environmental decoherence (see here for a recent account). Although physicists should know that the wave function is defined in configuration space, it is often exclusively understood as a spatial wave (thereby giving rise to the pseudo-concept of a “wave-particle dualism”). However, these two kinds of spaces are isomorphic only in the case of single mass points, such as the centers of mass of more or less complex objects. This very special case applies to most practicable experiments (scattering experiments or single particle problems)--so one often finds the conclusion that “the wave function loses its meaning at the final detector”.
This pragmatism is really astonishing in view of the fact that there are solid state and other quantum physicists who have studied the physics of complex systems, which must include measurement devices, in much detail in terms of many-particle wave functions. As I understand the new experiment, the measurement selects (“projects out”, branches into) that partial wave in which the electron was already deep in the barrier region when the barrier was lowered.
Cosmology for Kids, FQXi-style
By GRAEME STEMP-MORLOCK • Dec. 23, 2008 @ 21:30 GMT
It’s that gift-giving time of year and, as a father of two, I’m always on the lookout for books that will amuse my kids. So I jumped at the chance to chat to FQXi’s Brian Greene, who recently published a kids’ book covering modern physics and cosmology.
Now, I’m a firm believer in teaching children good science and not just pacifying them with simplistic answers such as “because that’s the way it is.” But I have to admit, I did wonder if this was going a bit too far. After all, general relativity, quantum entanglement and dark matter are tough concepts for adults concentrating really hard to get.
But Greene, along with other leaders in theoretical physics, are taking these headache-inducing topics and making them accessible for children and youth.
It turns out, I needn’t have worried. Greene, a professor of mathematics and physics at Columbia University is already a renowned science promoter, and author of the best-selling “The Elegant Universe.” Now he has written a gripping 30-page board book aimed at showing eight year olds that science can reveal a reality far stranger than anything from Hollywood.
In "Icarus at the Edge of Time," Greene takes readers on an interstellar journey aboard a spaceship sent from Earth to visit aliens living on a planet orbiting Proxima Centauri. Icarus, the angst-ridden great-grandson of the spaceship’s leading scientist, decides to leave the ship to explore a nearby black hole. Although Icarus survives his brush with the black hole, he forgets about the time-bending properties of gravity returning from his adventure many thousands of years later.
So why did Greene decide to target a young audience?
“I strongly feel that we begin life as scientists,” Greene told me. “When a kid is pulling things apart and smashing it back together they are doing a childlike version of what we do at the Large Hadron Collider, and what we have to do is nurture that starting point as opposed to setting up a framework that zaps the passion and joy.”
When NOVA released the television version of “The Elegant Universe,” Greene was surprised to receive letters from kids asking him questions about string theory. Using those letters and his experience organizing the World Science Festival in New York that had an entire program for youth and families, Greene wrote the book emphasizing exciting narrative proven to kept young audiences’ attention.
“This book is a small step in the direction of bringing the wonders of modern science to kids or adults that haven’t grappled yet with some of the major insights of the last century, such as Einstein’s general relativity,” said Greene. “The story can be taken in by kids or adults, and by merely following the narrative one of the strangest features of relativity becomes clear by what happens in the story.”
Well that sounds impressive, so I put it to the test—trying it out on my daughter. She’s only two, so I doubted that she’d get much of the book, but I was surprised to be asked later “Who made the Big Bang?” I gracefully said I had no idea, but suggested she call Neil Turok.
Greene likewise has read his book to his oldest son, 4 years old, who was the inspiration for the book and who apparently enjoys reading the story. In addition to just showing kids how cool science can be, it’s hoped that the book will interest students in modern physics.
“Our current education of physics for many students ends in the late 1600s,” said Greene. “A lot of students never experience anything more than Newton.”
The Perimeter Institute for Theoretical Physics (PI) in Waterloo, Ontario, Canada has recognized that void, and is working hard to fill the minds of high school students with the last few centuries of modern physics.
Since February, PI has offered a 25-minute video and courseware on dark matter to high school teachers teaching 16 and 17 year old science students. Already, it’s become a hit in the educational curriculum world, receiving over 2500 requests from teachers for the free course material.
I chatted to Damian Pope, the senior manager of scientific outreach for PI. “There are so many cool stories in modern physics that students don’t know about,” Pope told me. “Dark matter is just an incredible mystery and hole in the knowledge, but when I explain it to students often they didn’t know about it before. And, they get very excited when I point out that there are some unsolved problems in physics, that it’s not a done deal, and there’s so much more for future generations of scientists to discover.”
In addition to a succinct explanation of the history of dark matter, there is a hands-on experiment. (I couldn’t help but wonder how on Earth you design a dark matter experiment for kids, when adults aren’t having that much luck finding the stuff.) The experiment harks back to early observations that led to the discovery of dark matter, which Niayesh Afshordi discusses in an earlier post. In the experiment, students spin a weighted string. As the weight changes so does the speed of the spinning string, showing students the relationship between mass and orbit just like in stars orbiting a galaxy.
As well, teachers and students really get to hear from leading physicists musing on what they think new experiments are most likely to show about dark matter. Looking behind the curtain of theoretical physics might go a long way to inspiring not just the next generation of physicists but all future scientists.
Impact, Part Two
By WILLIAM OREM • Dec. 22, 2008 @ 21:18 GMT
In keeping with the subject of Earth-shaking historical impacts -- the last resting place of Copernicus has now been positively identified.
From Science News:
"Polish archaeologist Jerzy Gassowski told a news conference that forensic facial reconstruction of the skull, missing the lower jaw, his team found in 2005 buried in a Roman Catholic Cathedral in Frombork, Poland, bears striking resemblance to existing portraits of Copernicus."
. . . including the scar on his temple, a suggestive detail. The skull in itself wouldn’t settle the issue, of course, but the next step in analysis is a fascinating one:
". . . in the next stage, Swedish genetics expert Marie Allen analyzed DNA from a vertebrae, a tooth and femur bone and matched and compared it to that taken from two hairs retrieved from a book that the 16th-century Polish astronomer owned, which is kept at a library of Sweden's Uppsala University where Allen works. 'We collected four hairs and two of them are from the same individual as the bones,' Allen said."
That all but clinches it; this is indeed the Great Man’s mortal coil. Unless, of course, the person whose skull was buried in Frombork happened to lean over the book Copernicus was reading and two of his hairs fell onto the page. (Stranger things have happened. Those who believe Shakespeare’s plays were written by the glover’s son from Stratford with the semi-legible scrawl still have to explain why Edward de Vere’s bible has critical words from the plays underlined in it. Unless – my radical idea for this month -- Shakespeare borrowed de Vere’s book. But that’s a discussion for another blog.)
Copernicus, as we all know, quietly circulated his burgeoning heliocentric cosmology among the cognoscenti but delayed a general publication until just before his death – partly out of concern that said death not be hastened along a bit by the church to which he belonged. If it was a charge of heresy the astronomer cleric feared, he was right to do so: the book, De Revolutionibus Orbium Caelestium, was eventually placed on the Index of Prohibited Books, there to remain until the middle of the 19th century. Even before it was banned, a deflating forward was added by Osiander to De Revolutionibus, saying it was, after all, only a mathematical nicety (today Osiander would call it “just a theory”) and certainly not the truth. During the counter-reformation, the Church looked ever more thinly on dissenting cosmological ideas, though it was the Protestant countries that first took up the banner against Copernicus. Both Luther and Calvin decried him in low terms, and it fell to men like Galileo, himself threatened with torture by Rome, to turn the Copernican insight into the shape of modernity.
But it started with the polymath from Poland. Without Copernicus, none of what we do at FQXi would exist, and along with it would fade the great majority of our contemporary world. His willingness to speculate freely (even, in the context of his day, “absurdly”) on a fringe idea; to ground his speculations on cautious data; to work them out in mathematical detail; these powerful strokes created the Scientific Revolution out of which our era of interplanetary probes and quantum chips was born. Titans such as Copernicus and Galileo did more foundational work – and took greater personal risk for it – than any of us are likely to again.
And yet the possibility is always there. Nature is, quite probably, infinite in its complexity, and another Copernican revolution is always waiting. What would it mean for humanity, for example, if we were to discover that the entire observable universe is in fact inside a black hole? That history can be reversed, or that time does not, in a deep sense, exist? That the cosmos is both eternal and self-creating? That there is another version of me writing these words, just now undergoing quantum decoherence and headed off to live his own, separate life?
Would such discoveries run afoul of the religious establishments of our day? The social and societal norms, the political norms? What would we be willing to risk in terms of being thought crazy, or blasphemous, or “not a real scientist,” in order to discover that we are all Boltzmann brains, emerged randomly from a sea of chaotic data points? Or that the mathematics we choose to employ determines the objective structure of the phenomena it describes? What I admire most about Copernicus is not his daring in finally printing De Revolutionibus, but his daring in *thinking* it. How difficult it must have been to set aside virtually the whole cosmology with which his world was familiar and try something truly new.
We have technology now of which the Renaissance could not have conceived. Have we the courage of Copernicus to shake the very Earth?
Impact
By WILLIAM OREM • Dec. 11, 2008 @ 22:38 GMT
 | | image:goldenrectangle |
Remember my radical idea from last August? This was the suggestion that microbial life might be lying dormant in the centers of some craters on the moon, having been transferred there, panspermia-style, via impactors originating elsewhere in the Solar System (or beyond). Perhaps Copernicus crater is right now home to a colony of alien bacteria, and the first samples of extraterrestrial life not light years but only a couple hundred thousand miles away.
To this I added a long shot of which I am particularly fond: the suggestion that preserved cellular life up there might have come from down here, having evolved on Earth before the super-impactor that formed the moon. Indeed, if the ejecta that coalesced into the moon was not 100% molten, there is some non-zero possibility that moon rocks now contain fossilized strains of Earth-based biota that evolved before, and independently of, the current biosphere *altogether*. If so, who knows what they might look like? Or how might they have operated at a cellular or genetic level? I was musing again on this somehow sparkling idea just last weekend as I visited the National Cathedral in Washington, D.C., where one stained glass window is devoted to space exploration and holds, in its center, an authentic moon rock.
Turns out FQXi was once again ahead of the curve on this one. COSMOS magazine, which I recommend for all popular science readers, reported last month on this very idea. (Do they read this blog?) I just want to say you heard it here first.
 | | image:diongillard |
Earth, of course, isn’t alone in bearing the slings and arrows of what planetary geologists call the Bombardment Period. In a recent interpretation, the odd magnetic field of Mars is hypothesized to be the result of a collision almost as Dantean as the moon-forming cataclysm on primeval Earth. In a nice, though merely coincidental, symmetry, a Mars-size impactor is thought to have hit us, while Mars itself was evidently struck by an impactor the size of our moon. From New Scientist:
"The relatively smooth, flat surface of Mars' northern hemisphere lies around 6 kilometres lower than the more mountainous surface of the southern hemisphere. Earlier this year, researchers proposed that this 'Mars dichotomy' can be explained if a huge object, almost as big as Earth's moon, hit the northern hemisphere of Mars at a shallow angle."
Rather wonderfully, asteroid collisions, famous for K-T-style mass extinctions and even sterilizing planetary surfaces altogether, may well be responsible for having started the biosphere in the first place. From USA Today:
"Perhaps 'the bulk of the organic molecules necessary for life's origins were (created) by oceanic impacts of extraterrestrial objects,' Furukawa and colleagues say in the current edition of the journal Nature Geoscience. Most asteroids contain some carbon, the basic element in organic molecules. So the researchers investigated whether an asteroid impact could serve as a chemistry lab for cooking up the ingredients for living tissues, the 'pre-biotic soup' that some biologists suggest led to life . . ."
In our end, to paraphrase Eliot, is our beginning.
 | | image:logan.fulcher |
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