Friday, September 12th, 2014

Time	Event
12:00a	Fluid mechanics suggests alternative to quantum orthodoxy The central mystery of quantum mechanics is that small chunks of matter sometimes seem to behave like particles, sometimes like waves. For most of the past century, the prevailing explanation of this conundrum has been what’s called the “Copenhagen interpretation” — which holds that, in some sense, a single particle really is a wave, smeared out across the universe, that collapses into a determinate location only when observed. But some founders of quantum physics — notably Louis de Broglie — championed an alternative interpretation, known as “pilot-wave theory,” which posits that quantum particles are borne along on some type of wave.  According to pilot-wave theory, the particles have definite trajectories, but because of the pilot wave’s influence, they still exhibit wavelike statistics. John Bush, a professor of applied mathematics at MIT, believes that pilot-wave theory deserves a second look. That’s because Yves Couder, Emmanuel Fort, and colleagues at the University of Paris Diderot have recently discovered a macroscopic pilot-wave system whose statistical behavior, in certain circumstances, recalls that of quantum systems. Couder and Fort’s system consists of a bath of fluid vibrating at a rate just below the threshold at which waves would start to form on its surface. A droplet of the same fluid is released above the bath; where it strikes the surface, it causes waves to radiate outward. The droplet then begins moving across the bath, propelled by the very waves it creates. “This system is undoubtedly quantitatively different from quantum mechanics,” Bush says. “It’s also qualitatively different: There are some features of quantum mechanics that we can’t capture, some features of this system that we know aren’t present in quantum mechanics. But are they philosophically distinct?” Tracking trajectories Bush believes that the Copenhagen interpretation sidesteps the technical challenge of calculating particles’ trajectories by denying that they exist. “The key question is whether a real quantum dynamics, of the general form suggested by de Broglie and the walking drops, might underlie quantum statistics,” he says. “While undoubtedly complex, it would replace the philosophical vagaries of quantum mechanics with a concrete dynamical theory.” Last year, Bush and one of his students — Jan Molacek, now at the Max Planck Institute for Dynamics and Self-Organization — did for their system what the quantum pioneers couldn’t do for theirs: They derived an equation relating the dynamics of the pilot waves to the particles’ trajectories. In their work, Bush and Molacek had two advantages over the quantum pioneers, Bush says. First, in the fluidic system, both the bouncing droplet and its guiding wave are plainly visible. If the droplet passes through a slit in a barrier — as it does in the re-creation of a canonical quantum experiment — the researchers can accurately determine its location. The only way to perform a measurement on an atomic-scale particle is to strike it with another particle, which changes its velocity. The second advantage is the relatively recent development of chaos theory. Pioneered by MIT’s Edward Lorenz in the 1960s, chaos theory holds that many macroscopic physical systems are so sensitive to initial conditions that, even though they can be described by a deterministic theory, they evolve in unpredictable ways. A weather-system model, for instance, might yield entirely different results if the wind speed at a particular location at a particular time is 10.01 mph or 10.02 mph. The fluidic pilot-wave system is also chaotic. It’s impossible to measure a bouncing droplet’s position accurately enough to predict its trajectory very far into the future. But in a recent series of papers, Bush, MIT professor of applied mathematics Ruben Rosales, and graduate students Anand Oza and Dan Harris applied their pilot-wave theory to show how chaotic pilot-wave dynamics leads to the quantumlike statistics observed in their experiments. What’s real? In a review article appearing in the Annual Review of Fluid Mechanics, Bush explores the connection between Couder’s fluidic system and the quantum pilot-wave theories proposed by de Broglie and others. The Copenhagen interpretation is essentially the assertion that in the quantum realm, there is no description deeper than the statistical one. When a measurement is made on a quantum particle, and the wave form collapses, the determinate state that the particle assumes is totally random. According to the Copenhagen interpretation, the statistics don’t just describe the reality; they are the reality. But despite the ascendancy of the Copenhagen interpretation, the intuition that physical objects, no matter how small, can be in only one location at a time has been difficult for physicists to shake. Albert Einstein, who famously doubted that God plays dice with the universe, worked for a time on what he called a “ghost wave” theory of quantum mechanics, thought to be an elaboration of de Broglie’s theory. In his 1976 Nobel Prize lecture, Murray Gell-Mann declared that Niels Bohr, the chief exponent of the Copenhagen interpretation, “brainwashed an entire generation of physicists into believing that the problem had been solved.” John Bell, the Irish physicist whose famous theorem is often mistakenly taken to repudiate all “hidden-variable” accounts of quantum mechanics, was, in fact, himself a proponent of pilot-wave theory. “It is a great mystery to me that it was so soundly ignored,” he said. Then there’s David Griffiths, a physicist whose “Introduction to Quantum Mechanics” is standard in the field. In that book’s afterword, Griffiths says that the Copenhagen interpretation “has stood the test of time and emerged unscathed from every experimental challenge.” Nonetheless, he concludes, “It is entirely possible that future generations will look back, from the vantage point of a more sophisticated theory, and wonder how we could have been so gullible.” “The work of Yves Couder and the related work of John Bush … provides the possibility of understanding previously incomprehensible quantum phenomena, involving 'wave-particle duality,' in purely classical terms,” says Keith Moffatt, a professor emeritus of mathematical physics at Cambridge University. “I think the work is brilliant, one of the most exciting developments in fluid mechanics of the current century.” (Comment on this)
12:00a	Wrinkles in time Take a walk along any sandy shoreline, and you’re bound to see a rippled pattern along the seafloor, formed by the ebb and flow of the ocean’s waves. Geologists have long observed similar impressions — in miniature — embedded within ancient rock. These tiny, millimeter-wide wrinkles have puzzled scientists for decades: They don’t appear in any modern environment, but seem to be abundant much earlier in Earth’s history, particularly following mass extinctions. Now MIT researchers have identified a mechanism by which such ancient wrinkles may have formed. Based on this mechanism, they posit that such fossilized features may be a vestige of microbial presence — in other words, where there are wrinkles, there must have been life. “You have about 3 billion years of Earth’s history where everything was microbial. The wrinkle structures were present, but don’t seem to have been all that common,” says Tanja Bosak, the Alfred Henry and Jean Morrison Hayes Career Development Associate Professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “But it seems they become really abundant at the time when early animals were around. Knowing the mechanism of these features gives us a better sense of the environmental pressures these early animals were experiencing.” Bosak and her colleagues have published their study, led by postdoc Giulio Mariotti, in the journal Nature Geoscience. Sedimentary footprints Ancient sedimentary wrinkles can be found in rocks up to 575 million years old — from a time when the earliest animals may have arisen — in places such as Australia, Africa, and Canada. “Some of them look like wave ripples, and others look like raindrop impressions,” Mariotti says. “They’re shapes that remain in the sediment, like the footprint of a dinosaur.” Researchers have put forth multiple theories for how these shapes may have arisen. Some believe that ocean waves may have created such patterns, while others think the answer may lie in ancient sea foam. But the prevailing theory involves the presence of microbes: In a post-extinction world, microbial mats likely took over the seafloor in wide, leathery patches that were tough enough to withstand the overlying flow. As these mats were destroyed, they left small, lightweight microbial aggregates that shifted the underlying sand, creating wavelike patterns that were later preserved in sediment. A fragmentary sweet spot To test this last theory, Mariotti attempted to recreate the wrinkled patterns by growing microbial mats in custom-built wave tanks, partially filled with sand. To track his progress, he set up a camera to take time-lapse images of the tank. His initial results were successful — although, he admits, accidental. “I reproduced something that looked like wrinkle structures, although at first it wasn’t on purpose,” Mariotti says. In his first attempts to seed a tank with microbes, Mariotti obtained fragments of microbial mats from another wave tank in which microbes were growing at a moderate rate. After a few days, he spotted tiny, millimeter-wide ripples in the sand. Looking back at the time-lapse images, he discovered the mechanism: Fragments of microbial mats were rolling along the surface and, within a few hours, rearranging sediments to create wavelike patterns in the sand. Mariotti followed up on the observation with more controlled experiments with various wave conditions and microbial fragments, confirming that fragments, and not whole microbes, were forming the wrinkled features in the sediment. The results led the group to raise another question: What might have created such microbial fragments? Bosak says the likely answer is the early appearance of small animals, which may have grazed on microbial mats, ripping them into fragments in the process. “What we’re suggesting is that there may be some sort of sweet spot: You can’t have too many animals feeding, because then you lose microbial mats completely, but you need enough to produce these fragments,” Bosak says. “And that sweet spot could occur after a large marine extinction event.” Mariotti says the mechanism he’s identified may shed light on the environmental conditions early animals faced as they tried to gain a foothold following an extinction event. For example, early animals may have thrived in protected environments such as shallow lagoons, where microbial fragments might best create wrinkled patterns. “You need an environment where there’s not much energy, but still some wave motion, and close enough to the photic zone where you have light, so that microbial mats can grow,” Mariotti says. “Our finding may change how we see early animals.” David Bottjer, a professor of earth sciences at the University of Southern California, says knowing the mechanism by which these wrinkle structures formed is important not just for understanding life on Earth, but life on other planets as well. “It has been suggested that if a Martian rover was scanning sedimentary rocks that had been deposited underwater, and it saw wrinkle structures, that this could mean that there was microbial life present when the rocks were deposited,” says Bottjer, who was not involved in the work. “This study provides experimental evidence that, indeed, microbial fragments derived from microbial mats would be necessary to produce wrinkle structures. So, as a ‘biomarker’ indicating that microbial life would have existed on Mars, this strengthens the case for wrinkle structures, if they are found.” This research was partially supported by NASA and the National Science Foundation. (Comment on this)
4:21p	MIT releases endowment figures for 2014 The Massachusetts Institute of Technology Investment Management Company (MITIMCo) announced today that MIT’s unitized pool of endowment and other MIT funds generated an investment return of 19.2 percent during the fiscal year ending June 30, 2014. At the end of the fiscal year, MIT’s endowment funds totaled $12.4 billion, excluding pledges. MIT’s endowment is intended to support current and future generations of MIT scholars with the resources needed to advance knowledge, research, and innovation. As such, endowment funds are used for Institute activities including education, research, campus renewal, faculty work, and student financial aid. The Institute’s need-blind undergraduate admissions policy ensures that an MIT education is accessible to all qualified candidates regardless of financial resources. MIT provides financial aid to meet the full cost of an MIT education, based on the calculated need of the family. In 2013-14, the average financial aid award for need-based-aid recipients from all sources was $42,007. Currently, 59 percent of MIT undergraduates receive need-based financial aid, and 32 percent of MIT students receive scholarship funding sufficient to cover the total cost of tuition. MITIMCo is a division of the Massachusetts Institute of Technology, created to manage and oversee the investment of the Institute’s endowment, retirement, and operating funds. MIT’s Report of the Treasurer for fiscal year 2014 was made available publicly today. (Comment on this)

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