2011-Sep-21 - Quantum Cheshire Cat: Even Weirder Than Schr?¶dinger’s
Just when you thought you’d heard every quantum mystery that was possible, out pops another one. Jeff Tollaksen mentioned it in passing during his talk at the recent Foundation Questions Institute conference. Probably Tollaksen assumed we’d all heard it before. After all, his graduate advisor, Yakir Aharonov??”who has made an illustrious career of poking the Schr?¶dinger equation to see what wild beasts come scurrying out??”first discovered it in the 1990s and discussed it in chapter 17 of his 2005 book, Quantum Paradoxes. But it was new to me.
The situation is an elaboration of Schr?¶dinger’s thought experiment. You have a cat. It is either purring or meowing. It is curled up in one of two boxes. As in Schr?¶dinger’s scenario, you couple the cat to some quantum system, like a radioactive atom, to make its condition ambiguous??”a superposition of all possibilities??”until you examine one of the boxes. If you reach into box 2, you feel the cat. If you listen to the boxes, you hear purring. But when you listen more closely, you notice that the purring is coming from box 1. The cat is in one box, the purring in the other. Like a Cheshire Cat, the animal has become separated from the properties that constitute a cat. What a cat does and what a cat is no longer coincide.
In practice, you’d pull this stunt on an electron rather than a cat. You’d find the electron in one box, its spin in the other. Even by the standards of quantum mechanics, this is surprising. It requires what quantum physicists call “weak measurement,” whereby you interact with a system so gently that you avoid collapsing it from a quantum state to a classical one. On the face of it, such an interaction scarcely qualifies as a measurement; any results get lost in the noise of Heisenberg’s Uncertainty Principle. What Aharonov realized is that, if you sift through the results, you can find patterns buried within them.
In practice, this means repeating the experiment on a large number of electrons (or cats) and then applying a filter or ???postselection.??? Only a few particles will pass through this filter, and among them, the result of the softly softly measurement will stand out.
Because you avoid collapsing the quantum state, quintessentially quantum phenomena such as wave interference still occur. So, for a Cheshire Cat, you apply the following filter: you change the sign of one term in the superposition, causing the location and spin of the electron to interfere constructively in one box and destructively in the other, zeroing out the probability of finding the electron in box 1 and zeroing out the net spin of the electron in box 2. Voil? , the electron is in box 2 and its spin in box 1.
If this leaves your head spinning, it should. The word ???weak??? describes not only the measurement but also my intuitive grasp for what’s really going on. The best I can do is recommend the article on weak measurement by Aharonov, Tollaksen, and Sandu Popescu in last November’s Physics Today, but be prepared to read it several times before you have the slightest idea of what they’re saying. I’ve commissioned an article about Aharonov’s work for an upcoming issue of Scientific American to collapse some of the uncertainty. In the meantime, try sitting in a different room from where your confusion is.
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2011-Sep-21 - “The Quest” for Energy Security: The Search for More Oil and Its Alternatives
 Mottanai: it’s a Japanese term that translates as “too precious to waste.” It’s the philosophy that guides the island nation’s approach to natural resources like energy, and it has become particularly important as the meltdowns at Fukushima have resulted in roughly 25 percent of Japanese electricity supply disappearing as other nuclear reactors remain shutdown.
It is also the antithesis in many ways of the American approach to energy, whether that is electricity, fossil fuels or renewables. We want, in the words applied to nuclear power once upon a time, energy to be “too cheap to meter.”? And, regardless of whether it actually is, we treat it as such.
That has been true throughout the long involvement in the U.S. with the “devil’s excrement,” which is how former Venezuelan oil minister and founder of the Organization of Petroleum Exporting Countries (OPEC) Juan Pablo Perez Alfonzo described oil. We were the Saudi Arabia of oil before Saudi Arabia even existed as a country. Consultant Daniel Yergin of Cambridge Energy Research Associates wrote the definitive history of this Age of Oil, a book called “The Prize.” He has now followed up, some two decades later, with a sequel “The Quest,” that details the search for more and more and more oil and other forms of energy in recent times.
That’s because we’re always worried about running out, as we should be. Back in 1881, preeminent scientist Lord Kelvin proposed windmills or wind-motors (we know them as wind turbines) as the solution to dwindling coal supplies in the U.K. In 1957, “the greatest engineer of all time” and father of both the nuclear Navy and civilian nuclear power, Hyman Rickover argued that fossil fuels in all their forms would run out between 2000 and 2050??”a perhaps prescient prediction. Nuclear power would prove no substitute, he feared, and this would mean the end of cars, which rely almost exclusively on oil.
But Yergin suggests that only 20 percent of the world’s known oil has been produced to date, another 20 percent is accessible today, and rising demand will call forth technological innovation to unlock some of the other 60 percent as time marches on, much as the tar sands of Canada have begun to be exploited (setting aside environmental concerns??”see image above). That’s despite a world that already produces roughly 30 billion barrels of oil per year??”and one of nine of those barrels gets burned in a U.S. automobile.
Then there’s the shale gas explosion in recent years in the U.S. A combination of employing pressurized water to crack rock that contains natural gas and horizontal drilling to more easily access it has opened up new supplies (albeit with some question of how much exactly). At the same time, coal has made a comeback as an energy source, thanks to the rising demand in countries like China and India (much to the discomfort of those concerned about catastrophic climate change). And, despite Fukushima, countries like China are racing ahead to build nuclear power plants to ensure increasing energy supplies.
Last but not least, there are the so-called “alternatives”: Lord Kelvin’s wind turbines but also photovoltaic devices that turn sunlight into electricity and fuels made from plants. Each source of energy feeds off the others??”oil companies were among the early adopters of solar power, according to Yergin, using it to provide the electricity to keep pipelines from corroding. And a wind turbine is “a pure embodiment of power from fossil fuels,” says environmental scientist Vaclav Smil of the University of Manitoba, because it requires coal for its steel and cement as well as oil for its plastic components.
The book is daunting at 800+ pages but also a masterful survey of the global energy landscape today, albeit with perhaps too little understanding of alternative energy supplies and too dismissive an attitude for concerns about dwindling fossil fuel resources. As economist James Hamilton of the University of California, San Diego observed in his blog, “meeting the growing global demand for crude oil over the last five years has posed significant challenges for the world economy. And those who worry that the next 5-10 years might be like the last [5] should not be dismissed as crackpots.”
But Yergin essentially calls for securing energy by diversifying supply, an echo of Winston Churchill’s words on switching the Royal Navy from British coal to foreign oil: “safety and certainty in oil lie in variety, and variety alone.” Modern life is founded on easy energy for light, warmth, cooling, mobility and, increasingly, culture itself. We will need every source of energy going forward??”and more, if possible.
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2011-Sep-21 - Your Friday Forecast: Sunny, with a 1-in-21-Trillion Chance of Getting Hit by Orbital Debris
 Credit: NASA The orbital realm surrounding Earth is filled with millions of pieces of space junk, some of which occasionally fall back to Earth. Rarely, though, does an entire satellite or spacecraft come back uncontrolled, as NASA expects its Upper Atmosphere Research Satellite (UARS) to do sometime on Friday.
The schoolbus-size UARS [see artist's depiction at left] weighs some 5.7 metric tons, and NASA predicts that 500 kilograms of debris will survive reentry and land somewhere on Earth. Because populated land makes up a small part of Earth’s surface, chances are UARS will land in the ocean or on some vast wildland. Still, orbital debris trackers at the space agency estimate that there is a 1-in-3,200 chance that pieces of UARS will strike someone. That stat has been erroneously reported as the odds that any particular person (say, me) will be hit by UARS debris. In actuality, my odds of being struck down by UARS on Friday are about 1 in 21 trillion, since the risk is spread across almost all of Earth’s 6.7 billion inhabitants.
For a bit of perspective, I am about 14,000 times more likely to be struck dead by lightning on Friday than I am to be struck by UARS. (That estimate is based on rates of fatal U.S. lightning strikes, which show that an average American’s risk of being killed by lightning on any given day is about 1 in 1.6 billion.)
And although the reentry of a UARS-size spacecraft is a relatively rare event, large pieces of debris fall back to Earth without incident on a regular basis. As NASA reports: “Since the beginning of the Space Age in the late-1950s, there have been no confirmed reports of an injury resulting from re-entering space objects. Nor is there a record of significant property damage resulting from a satellite re-entry.”
NASA has set up a Web page to update the public with predictions for the reentry of the satellite. So give it a look, and then go back to planning for an ordinary weekend.
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