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The Fat Lady Sings for OPERA [Starts With A Bang]

17 March, 2012 - 02:10

"The saying 'It's not over 'til the fat lady sings' is erroneous, because women who are fat are never listened to." -Margaret Cho Last year, the OPERA collaboration made worldwide headlines when they announced the results of a remarkable experiment.

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(Image credit: OPERA / CERN.)

From over 730 kilometers away, in another country, neutrinos were created by one of the most powerful particle accelerators in the world. Protons at over 99.999% the speed of light were smashed into matter, creating a highly collimated beam of neutrinos, which was launched through the Earth at, presumably, speeds indistinguishable from the speed of light.

Underground, beneath the Italian mountain of Gran Sasso, laid the huge OPERA detector, capable of detecting these high-energy neutrinos.

operadetector.jpeg

(Image credit: OPERA / INFN / CERN.)

But what it was also able to do, so they claimed, was to measure the timing of these neutrinos so accurately as to be able to test Einstein's theory of special relativity!

As you well-know, nothing is supposed to be able to move faster than the speed of light in a vacuum. Nothing. Which is why it was absolutely shocking when they released their first results.

opera.jpeg

(Image credit: OPERA Collaboration; T. Adam et al.)

60 nanoseconds early, they said, their neutrinos arrived. This wasn't an error, either, they said, as their uncertainties were only around 10 nanoseconds. And if that was true, over the distances they were talking about, that means these neutrinos would be moving something like 7,500 m/s faster than light, which is huge!

speed_of_light_4.jpeg

(Image credit: United Visual Artists / Tom Oldham.)

As we've said many times, claims like these, that are extraordinary, require evidence that is also extraordinary. So I was very excited to report that, in short order, we were going to either confirm or refute OPERA's claims!

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Because two experiments -- T2K in Japan, above, and MINOS in the USA, below -- were all set up to measure the same exact thing to even better precision.

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But another experiment, one that had come out earlier and challenged OPERA's results, had other plans. You see, OPERA had recently announced that they had uncovered two potential problems with their experiment -- the loose cable and a possible timing miscalibration -- which threw their results into doubt.

What it really meant, if you look up at the image of their claimed results, is that their claimed errors, which were tiny, should have actually been much larger due to those issues.

operasynopclarified1.png

(Image credit: Matt Strassler.)

This is a problem that plagues a great many experimental and observational sciences: fully accounting for your systematic errors. After all, it is difficult to account for uncertainties and / or errors due to something you were simply expecting would work properly! You account for systematics based on all the errors you can reasonably anticipate, but once those are over and done with, you stop counting. But when an unexpected error does happen, and you weren't expecting it, it can lead you to have an undue amount of false confidence in what are actually insignificant results.

And it was the ICARUS team -- another neutrino detector underneath Gran Sasso -- that set out to show that OPERA had done exactly that. Intending to refute the OPERA team's results, ICARUS has gone out to set the record straight about Einstein's relativity.

icarus.png

(Image credit: the ICARUS-T600 detector installed in LNGS - HallB, retrieved here.)

Evoking shades of Ethel Merman, ICARUS basically said to OPERA, "Anything you can do, I can do better." And, over practically the same baseline, using the same energy neutrinos created from the same proton beam, ICARUS set out to re-test the OPERA experiment.

Icarus_fig_1.jpg

(Image credit: the latest ICARUS paper; M. Antonello et al.)

Except, you know, without the errors. And what they found should put the whole issue to rest. The OPERA neutrinos, you'll remember, arrived around 60 nanoseconds early, with an originally claimed uncertainty of 10 ns. The ICARUS results, making the same measurements with different equipment?

Icarus_fig_3.jpg

(Image credit: the latest ICARUS paper; M. Antonello et al.)

As others have noted, this time, there can be no doubt that ICARUS has directly refuted OPERA.

It means that, combined with ICARUS' earlier results, we can constrain that not only are neutrinos of this energy not moving at the speed OPERA concluded, but they must be moving much closer to the speed of light than OPERA's original results would have indicated.

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(Image credit: Matt Strassler, edited by me.)

And that's pretty much the end of the line for these faster-than-light neutrino claims. It will be interesting to see what OPERA's next results are, as well as what MINOS and T2K have to say, but with the ICARUS results in and the OPERA uncertainties known to be much larger than originally claimed, there's suddenly no reason to believe that neutrinos move faster-than-light at all.

And if you were skeptical the whole time, good for you. The extraordinary evidence you were waiting for just came in, and it's the sound of the fat lady singing!

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Categories: Education

Neutrinos in the News [Uncertain Principles]

16 March, 2012 - 22:10

A little more tab clearance, here, this time a few recent stories dealing with those elusive little buggers, neutrinos. In roughly chronological order:< /p>

  • The Daya Bay experiment in China has measured a key parameter for neutrino oscillation (arxiv paper), the phenomenon where neutrinos of one of the three observed types slowly evolve into one of the others. Mathematically, this is described as each of the three types we observe being an admixture of three more fundamental types. This mixing is described in terms of the sine of some "mixing angle," because physicists love geometry, and two of the three mixing angles had already been measured. The Daya Bay experiment measured the third-- or, more precisely, they found that the square of the sine of the third mixing angle is 0.092 +/- 0.016 +/- 0.005, where the two uncertainty values are for statistical and systematic uncertainties. This is somewhat larger than expected, which is probably a good thing, because it may imply more of a difference between matter and antimatter than you get from the simplest models, which in turn would help explain why everything we see in the universe is matter and not antimatter.
  • A group at Fermilab has sent a message via neutrinos (press release), encoding a simple signal in on-off pulses of neutrinos generated at Fermilab and detected by a giant underground detector a kilometer away. This is not particularly useful for anything, because they need a big particle accelerator to make the pulses and a detector with a mass on the order of tons to detect them, but it's kind of cute.
  • Finally, a second group at the Gran Sasso laboratory in Italy has used the same neutrino beam used by the OPERA collaboration to check the time of flight of the neutrinos passing from CERN to Italy, and find that it agrees perfectly with what you expect for neutrinos moving at light speed, not the tiny bit faster that OPERA saw. As usual with particle physics stuff, Matt Strassler has a good and balanced round-up. These results from the ICARUS experiment (I'm not even going to try to figure out what linguistic crimes they committed to get that acronym) are fairly conclusive evidence that OPERA's result was in error, though given the complexity of both measurements, it's still worth repeating the experiment as planned in May.

And that's the news regarding the elusive neutrino.

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Categories: Education

One Year After Fukushima, a Startup Named Kurion Continues to Shed Light on What it Means to Live in the Nuclear Age [USA Science and Engineering Festival: The Blog]

15 March, 2012 - 16:00

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By Larry Bock
Founder and organizer, USA Science & Engineering Festival
When searching for a prime, real-life example of how science and technology are making a difference in the world right now, my thoughts lately turn to a small but feisty greentech startup that you may never have heard of: Kurion, Inc.

Based in Irvine, CA with 15 employees, this profitable three-year-old company which specializes in nuclear waste cleanup has quietly and effectively been using its technology at the front lines of Fukushima, the site of what is being called one of the largest nuclear disasters in history. Weeks after the unforgettable earthquake and ensuing tsunami struck Japan last year which caused emissions of nuclear contaminants to be released into the air from reactors at the Fukushima Daiichi Nuclear Power Station, Kurion was selected to join a group of multi-billion dollar companies to help clean seawater that was being pumped into the reactors to cool them down.

Within three weeks of first contact, TEPCO authorized Kurion's proposed solution to the challenge. Eight weeks later, Kurion's system had been designed, built, air freighted by three Russian Antonov transports, installed and was fully operational removing more than 99.9% of the seawater radioactivity of greatest concern. Other companies which were awarded contracts by the Japan utility TEPCO to aid in this challenging duty were France's AREVA, Japan's Hitachi-GE Nuclear Energy and Toshiba. Of these, only Kurion and AREVA were able to deliver systems in time to prevent the highly contaminated seawater from overflowing the limited available tankage into the ocean and of these only Kurion continues to operate today.

Kurion stands out as the only startup selected -- and for good reason: the firm for a while has been developing a material called "ion specific media" that greatly improves the way cleanup technology is deployed to soak up nuclear particles and as a result shrink the radioactive material down to a small manageable size. The resulting waste stream, an inorganic powder, can further be turned into glass (a standard industry process known as vitrification). Kurion's innovation brings a more modular approach to the vitrification process, so the clean-up technology can be quickly adapted and installed in the contaminated spill site. Add to that Kurion's team composed of nuclear waste industry veterans, and you'll understand why the company was able to enter a direct contractual arrangement with TEPCO.

Since last June, says Kurion's CEO John Raymont, the company's technology has been used as part of what he calls "an unprecedented external reactor water cooling system," designed to replace Fukushima's in-plant reactor water cooling mechanism until the reactor's original nuclear cores can be removed. Bottom line: Kurion's presence at Fukushima is helping to mitigate radiation contamination to humans and the environment, dramatically turning a disastrous situation around.

As the first anniversary of the Fukushima disaster past on March 11th, Kurion and the cleanup are perfect examples of how science and technology are making a difference where it matters around the world. In my opinion, it illustrates in realistic terms what it means to be human in the nuclear age -- with all the benefits and risks nuclear power brings.

To help get this message across, we are proud to include Kurion and its representatives as key participants in the upcoming USA Science & Engineering Festival hosted by Lockheed Martin, the nation's largest celebration of science and engineering. The Festival is on a mission to inspire the next generation of innovators by reinvigorating the interest of our nation's youth in science, technology, engineering and math via hands-on presentations with experts that motivate, compel, excite, entertain as well as educate.

Kurion's participation is especially exciting for me for a couple of reasons. As a startup entrepreneur myself before establishing the Festival several years ago, I co-founded or financed the early stage growth of 40 companies in the life and physical sciences from inception, so I know well of the rigors and challenges that Kurion has and continues to experience to further establish itself in the competitive field of technology. Second, at Lux Capital (one of two venture capital firms backing Kurion), I serve as Chairman of Lux's Advisory Board of industry experts where we are all extremely proud of Kurion's success.

Join visitors at the Festival Expo on April 28-29, 2012, in Washington, DC when we take you inside the power of nuclear energy (along with other exciting areas of science and engineering) with such experts as Kurion, the U.S. Department of Energy, the University of Massachusetts Lowell Physics Department, and the ATLAS Experiment at the Large Hadron Collider who are all helping to make our co-habitation with nuclear power safer and more beneficial. Here is just a sampling of what you'll discover:

How Kurion is Cleaning Up Fukushima -- From Kurion, learn how they perform remediation on contaminated water and stop the spread of radioactive isotopes at Fukushima and other sites. Kurion experts will also demonstrate how an ion-exchange column works and how they trap dangerous particles using their 3-D vitrification simulator.

Future Implications of the Fukushima Disaster -- Meet and hear Fred Bortz, Ph.D., who is among our Featured Authors at the Expo's Book Fair. A physicist-turned-writer, Bortz (whose science training includes three years in nuclear core design), is the author --among other works -- of the recent book, Meltdown: The Nuclear Disaster in Japan and Our Energy Future, which sheds light on the future of nuclear and what the next generation will face in dealing with its development.

Real-Life Applications: From National Defense to Biomedical Photonics -- Learn from these experts: how the U.S. Department of Defense is developing solutions that protect first responders from potential nuclear, radiological, chemical and biological threats; how renowned physicists from the University of Massachusetts Lowell are making life-saving advances in areas ranging from nuclear physics and radiation science to biomedical photonics, and from the American Nuclear Society how to compute your own annual radiation dose.

The Wonders of the Large Hadron Collider (LHC) -- Scientists from the ATLAS Experiment at the LHC take you inside the wonders of the world's largest and highest-energy particle accelerator which was developed over a 10-year period to probe new frontiers in high energy physics including the origins of the universe.

How the DoE is Impacting Climate and Energy Solutions -- Department of Energy scientists from its Atmospheric Radiation Measurement (ARM) facility will demonstrate how its measurements are bringing science solutions to the world, including improving climate models, and researchers from the Department's Berkeley National Laboratory will shed light on how they are developing new approaches to energy by studying infinitesimal particles at the sub-atomic level.

Radiation Physics in 3-D -- Enter a 3D virtual treatment room with experts from the American Association of Physicists in Medicine and learn how a radiation treatment accelerator works. See how medical physics and science are used in the radiation treatment of cancer. Participants will get a 3D view of the technological advances used in this cancer treatment.

Nuclear power, the byproduct of our existence in the modern age, is here to stay. Join us at the Festival as we explore how to coexist with it responsibly and safely for the benefit of all. For more on the Festival, visit: http://www.usasciencefestival.org/

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Categories: Education

Pi Day Fun Facts! [Starts With A Bang]

15 March, 2012 - 02:28

"Now go on, boy, and pay attention. Because if you do, someday, you may achieve something that we Simpsons have dreamed about for generations: you may outsmart someone!" -Homer Simpson Today, March 14th, is known tongue-in-cheek as Pi Day here in the United States, as 3.14 (we write the month first) are the first three well-known digits to the famed number, π. As you know, it's the ratio of a perfect circle's circumference to its diameter.

pie.jpeg

(Image credit: LeJyBy at Flickr Creative Commons, retrieved here.)

It's also very, very, very hard to calculate exactly, because it's impossible to represent π as a fraction. (You may remember that's part of the definition of an irrational number.) But that doesn't mean we haven't tried!

The easiest way to try is to either inscribe or circumscribe a regular polygon around a circle of radius 1, and calculate the polygon's area. The more sides you make, the closer you'll get.

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(Image credit: Archimedes' Pi approximation, by Leszek Krupinski.)

Archimedes, who discovered the fraction 22/7 (which is why Pi Day is July 22 in Europe), took the equivalent of a 96-sided polygon to do this, and found that π was between 220/70 and 224/71, which is not bad for two thousand years ago!

But it's hardly the most impressive approximation for π from back then. That honor goes to the Chinese mathematician, Zu Chongzhi.

%E6%98%86%E5%B1%B1%E4%BA%AD%E6%9E%97%E5%85%AC%E5%9B%AD%E7%A5%96%E5%86%B2%E4%B9%8B%E5%83%8F.jpeg

(Image credit: Statue of Zu Chongzi in Tinglin Park in Kunshan, by Gisling.)

He discovered -- in the 5th Century -- the approximation Milü, which is 355/113. Which is equal to, for those of you at home, 3.1415929... meaning you have to go to the eighth digit to see the difference between this number and π. In fact, if we look at the best fractional approximations of π...

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(Image credit: Gisling.)

we wouldn't find a better one until 52163/16604! (Exclamation point, not factorial!) That was the world's best approximation for π for something like 900 years, until this guy came along. Pretty impressive!

But what if you wanted to calculate π, but wanted to do as little math as possible? No geometry, just basic counting and four-function mathematics? Well, if you can play darts, you can do it!

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It will only get you to π very slowly, but throwing darts (randomly) at a circle with a square of area equal to the circle's radius will allow you to calculate π! How so? Count the darts that land in the circle, divide by the number of darts that land in the square, and that's how you calculate π. (For those of you who write a computer program that can do this, congratulations, you've just written your first monte carlo simulation!)

But let's say you wanted to be more efficient, but you wanted to get to π with arbitrary accuracy, given enough time. Have I got a fun method for you: you can represent it as a continued fraction, and the farther you continue it, the more accurate you'll get!

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For example, here's the results from the first few terms; not bad!

Pi Day is also a special day for anyone interested in astronomy and space! Four famous astronomy and space heroes have their birthday on Pi Day; can you name them all from their pictures?

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(Okay, okay, one of them is easy!)

As far as the pies go, I'm still no good at making pie crust, but I do have a special treat that I can make, with a circumference and a diameter and everything.

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(Image credit: Jemma.)

Yes, it's a Leche Flan! Hope your day is as sweet as they come, hope that you enjoyed all the fun facts about pi, and if you're up late over the next couple of nights, enjoy the Pi Day miracle of the Jupiter-Venus conjunction in the night sky!

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(Image credit: Laurent Lavedar, TWAN, retrieved from National Geographic.)

Happy Pi Day!

(And your birthday boys are, from L-R, Albert Einstein, Apollo 8 Commander Frank Borman, Astronomer Giovanni Schiaparelli, and last-man-on-the-Moon Gene Cernan.) Read the comments on this post...


Categories: Education

Entanglement Is Not That Magic [Uncertain Principles]

14 March, 2012 - 16:37

One of the things that made me very leery of the whole Brian Cox electron business was the way that he seemed to be justifying dramatic claims through dramatic handwaving: "Moving an electron here changes the state of a very distant electron instantaneously because LOOK! THE WINGED VICTORY OF SAMOTHRACE EINSTEIN-PODOLSKY-ROSEN PAPER!" On closer inspection, it's not quite that bad, though it takes very close inspection to work out just what they are claiming.

That said, though, it's fairly common to hear claims of the form "when two particles are entangled, anything you do to one of them changes the state of the other." This is not strictly true, though, and it's worth going through in detail, if only so I have something to point to the next time somebody starts using that line. This will necessarily involve some math, but I'll try to keep it as simple as I can.

So: the problematic claim is that doing things to one particle of an entangled pair of particles affects the state of the other particle in the pair. This is true only for a very small subset of "doing things" and "affects the state"-- that is, it is absolutely and unequivocally true that measuring the state of one entangled particle in some basis determines the possible outcomes of measurements on the other particle in the pair. However, the vast majority of things you might do to one of the two particles do not produce corresponding changes in the state of the other. In fact, most of the things you might do will appear to destroy the entanglement altogether.

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Categories: Education

The Most Difficult Course... For A Teacher [Starts With A Bang]

14 March, 2012 - 02:30

"It is the supreme art of the teacher to awaken joy in creative expression and knowledge." -Albert Einstein Last month, an interesting conversation happened on the topic of the most difficult course that a student takes in their studies.

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(Image credit: Steve Perrin / University of Michigan MSIS.)

The question, of course, was asking about most difficult in terms of the course content that the student must learn. In any field, there are plenty of options to choose from, and while an individual student's mileage may vary, teachers and professors tend to learn very quickly just which courses (and what course material) students have the most difficulty gaining a working understanding of. On that topic, I have to agree with Chad that, for an undergraduate physics major, the advanced electromagnetism course is the toughest.

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(Image credit: Mike Willis.)

But I thought it'd be much more interesting -- on behalf of all teachers at all levels -- to take on the following question: What is the most difficult course to teach? Having taught a huge variety of courses over my life, ranging from public secondary school to high school to public and private Colleges and Universities, I have to say that the courses with the most difficult content are by no means the most difficult courses to teach.

In my experience, the most difficult course to teach is the one where you, the teacher, cannot control what or how you are teaching.

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(Image credit: Mr. Lawrence / Eagles4Kids.com.)

There are a handful of qualities that are basically required of an individual to be a good teacher; qualities for which there are no substitute. A good teacher -- in my experience -- must be:

  • Competent: with the curriculum/subject matter that they're teaching,
  • Attentive: to the skill level, needs, and abilities of the students,
  • Prepared: to explain, demonstrate, and challenge students in a variety of ways,
  • Empowered: to teach the material in whatever way, however unorthodox or creative, they see fit, and
  • Self-aware: of their own strengths, weaknesses, abilities and limitation.
As you're probably all aware, there have been recent pushes in education to micromanage teaching methods and implement standards-based learning, like this is going to accomplish something meaningful.

Let me share two important secrets with you.

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(Image credit: Eric Joselyn, retrieved from thenotebook.org.)

1.) There is no amount of control you can take away from a bad teacher that will turn them into a good teacher.

2.) There is nothing worse you can do to a good teacher than take away their autonomy as to how and what they teach to their students in their classrooms.

That's it. We've all had experiences of good and bad teachers that have been seared into our memories, but all of my best experiences would never have happened if my education was as micromanaged as many classrooms are today.

And that's truly a shame. Because the best courses I've ever taught are -- at least from my perspective -- college-level introductory astronomy and the advanced electromagnetism course mentioned above.

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(Image credit: Chris Proctor, retrieved from here.)

For both of those courses, I had complete creative control over everything: the material covered, the assignments, the exams, etc. I could take the journey that I not only chose with my students, I could tailor that journey to their needs and abilities, my strengths, and all the other obligations and necessities that came up.

And we had a ball. They got to learn skills and take on challenges that they wouldn't have been confronted with anywhere else; they got an experience that was unique to having me as their teacher. And it was a joy, for me, too. On the other hand...

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(Image credit: MemeCenter.com / Austin Powers.)

what was the most difficult course I've had to teach? That would have to be the introductory physics course geared towards non-majors. The curriculum is simply too rigid and comprehensive to do a high-quality job in the time allotted to do it. It is a curriculum that has been unreasonably standardized for the skill level of most students. As a result, a teacher is either forced to skip many important topics that students will be held responsible for, or to expose the students to a great deal of material without the time necessary to teach for mastery. Either way, it's a losing proposition, and one that a great many teachers (and students) resent.

If you want your children to get the highest quality education possible, don't forget this lesson. Demand competent, attentive, prepared and self-aware teachers, and make sure you empower them to do the best job that they can do!

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Categories: Education

Commuting Dust Mites [Dean's Corner]

13 March, 2012 - 20:19
Racecar.jpg This is a 285 micrometer racecar, printed at the Vienna University of Technology. Credit: Vienna University of Technology

Imagine a car small enough for a dust mite. Crazy, right?

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Categories: Education

On the Interconnectedness of Things [Uncertain Principles]

13 March, 2012 - 17:07

I finally got a copy of Cox and Forshaw's The Quantum Universe, and a little time to read it, in hopes that it would shed some light on the great electron state controversy. I haven't finished the book, but I got through the relevant chapter and, well, it doesn't, really. That is, the discussion in the book doesn't go into all that much more detail than the discussion on-line, and still requires a fair bit of work to extract a coherent scientific claim.

The argument basically boils down to the idea that the proper mathematical description of a universe containing more than one fermion is a many-particle wavefunction that is overall antisymmetric under the exchange of any two electrons. That is, if you numbered every electron in the universe, you would write the wavefunction down one way, and if you swapped the numbers on two of the electrons, then re-wrote the wavefunction, you would get the same thing you had the first time, but with an overall negative sign. Thus in seeking to make a quantum model of a hydrogen atom in your living room, you would need to write down some sort of 1090x1090 Slater determinant (or whatever the actual total number of electrons in the universe is) to get the proper state of the many-(many-many-many...)-body system. The total energy of this state will depend on the energy of all of the individual electrons, and some complicated overlap integrals between every single electron state and every single other electron state, so I hope you have a lot of paper or a really fast (quantum?) computer to help you work it out.

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Categories: Education

Another Week of GW News, March 11, 2012 [A Few Things Ill Considered]

13 March, 2012 - 02:18

Logging the Onset of The Bottleneck Years
This weekly posting is brought to you courtesy of H. E. Taylor. Happy reading, I hope you enjoy this week's Global Warming news roundup

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Categories: Education

Oslo gets hit again [Dynamics of Cats]

12 March, 2012 - 20:15


Seems like all the action is in Norway these last few years...

Meteorite crashes through roof in Oslo
from Verdens Gang

Fist size meteorite smashes through roof in Oslo suburb

Nice looking chunk - be worth a pretty penny, as one of the few meteorites with confirmed provenance of hitting a structure.

see also Fireball over Norway - at VG


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Categories: Education

Geyser Gets a Little Help From Chemistry [USA Science and Engineering Festival: The Blog]

12 March, 2012 - 16:00

By Joe Schwarcz PhD, Author, USASEF Expo Performer, AT&T Sponsored Nifty Fifty Program Speaker
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Yellowstone National Park's iconic "Old Faithful" geyser is pretty faithful. It can be counted on to erupt every 50-90 minutes. Iceland's "Great Geysir," from which all other geysers get their name is less reliable. It was mostly dormant for sixty five years before it began semi-regular eruptions again in 2000 thanks to an earthquake. But in New Zealand, you can set your watch by the eruption of the Lady Knox Geyser, named after a former Governor of the country. At exactly 10:15 AM every day a spectacular plume of water and steam bursts into the air to a height of up to twenty meters. How can a natural phenomenon be so predictable? Well, in this case nature gets a little help from chemistry.

At the appointed time, a detergent solution is poured down the channel from which the water erupts. This has the effect of reducing the surface tension of the water that deep within the shaft has been heating up to boiling temperatures due to underground volcanic activity. Surface tension refers to the attractive force between water molecules, and is in fact responsible for water being a liquid at ordinary temperatures. Liquids are characterized by the close proximity of their component molecules, while in gases the distance between molecules is much greater. If the surface tension of a liquid is decreased, the H2O molecules can separate from each other with greater ease, with the result that the liquid turns into a gas. Molecules of "surfactants," a class of substances that encompasses soaps and detergents, wiggle their way in-between water molecules, allowing the boiling liquid to instantly turn into steam. The steam then forces the water that has collected in the channel to burst upwards, and we have an eruption.

The possibility of making a geyser erupt artificially was discovered by accident in New Zealand in 1901 when an "open prison" was established at Waiotapu for criminals who were deemed not to be a danger to society. It so happens that this is one of the most volcanically active areas of the world and the prisoners took advantage of the hot water seeping up from the natural thermal springs to wash their clothes. One day one of them must have used just the right amount of soap and triggered an eruption when the soap solution found its way down the fissures in the rock into the chambers in which underground water had pooled. This is the concept used today to stimulate eruption of the Lady Knox Geyser although detergents have replaced soap because they have been found to be less damaging to the geyser's internal natural plumbing. On occasion Iceland's Great Geysir has also been "soaped" but this is now prohibited for environmental concerns.

Long before the prisoners made their accidental discovery, the science of geyser eruptions had been worked out by none other than Robert Bunsen, of burner fame. Actually Bunsen did not invent the famous burner but did improve upon existing equipment by showing that mixing the combustible gas with just the right amount of air led to a high temperature non-luminous flame. Such a flame was very useful in the development of Bunsen's most famous discovery, the spectroscope. In collaboration with physicist Gustav Kirchoff, Bunsen designed an instrument that would pass the light emitted from a sample heated by his burner through a prism. The "spectrum" of light produced was found to be characteristic of the element found in the sample. Before long Kirchoff and Bunsen had identified cesium and rubidium as new elements and paved the way to the identification of thallium, indium, gallium, scandium by others through spectroscopy.

In 1845, during his tenure as Professor of chemistry at Marsburg University, Bunsen was invited by the Danish government on a geological trip to Iceland following the eruption of Mount Hekla. Bunsen had a lifelong interest in geology and used the occasion to study the gases released from volcanoes and performed analyses on volcanic rocks. He also became interested in Iceland's abundant geysers, especially "The Great Geysir" that propelled water to a height of some fifty meters. Bunsen hypothesized that eruption occurred when a column of underground water was heated around its middle by volcanic activity. In the true spirit of science, Bunsen constructed an artificial geyser in the laboratory consisting of a basin of water from which a long tube filled with water extended upwards. He heated the tube at various points and showed that it was when the water in the middle reached its boiling point that an eruption occurred just like in a natural geyser.

Geysers can do more than excite tourists. In Iceland hot water from geysers is used to heat homes and warm greenhouses, allowing food to be grown in an otherwise inhospitable climate. The accumulation of steam deep within the ground that makes geysers possible can also be tapped by geothermal power plants to produce electricity. Geothermal energy is a great source of electricity but drawing off the steam can lead to the destruction of geyser activity.

Not all geysers gush steam and hot water. In the case of cold-water geysers the eruptions are driven by carbon dioxide gas that forms as limestone, calcium carbonate, decomposes. The gas becomes trapped in underground aquifers until it builds up enough pressure to explode towards the surface through cracks in the strata propelling water into the air. Some of the gas remains in the water in the form of small bubbles so that the geyser actually dispenses soda water.

If you want to experience a mini-cold-water geyser, just drop a couple of Mentos into a bottle of Diet Coke. But do it outside. It makes a mess. If you use a special tube (available from Steve Spangler Science) that can simultaneously drop 7-10 Mentos into the bottle, you'll be treated to a true spectacle as the liquid bursts to the stunning height of about ten meters. That's still some 490 meters short of the super eruptions once produced by the Waimangu Geyser in New Zealand between 1900 and 1904 before the natural plumbing was destroyed by a landslide. The world's tallest geyser now is Yellowstone's Steamboat Geyser that propels water some ninety meters into the air. Unfortunately its eruptions are not predictable. Except on YouTube.

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Categories: Education

Incremental Progress in Quantum [Uncertain Principles]

12 March, 2012 - 15:08

The Links Dump item about software patents this morning includes a lament that there are so many silly little software patents, organized so badly, that finding one you might be infringing would take forever. This may or may not be a convincing argument against them, but for a physics geek like me, my first reaction was "You just need a quantum computer running Grover's algorithm for searching an unsorted database." And I suppose there's a background element for a satirical SF novel in that-- quantum computers ultimately being developed not by banks or the NSA, but by lawyers looking to speed the process of document discovery.

Of course, this in turn reminded me that I have a bunch of quantum-related tabs open in Chrome, and I really ought to do something with those. So, here's a special quantum-themed links dump sort of post:

-- Scott Aaronson, a noted critic of the quantum computing claims by D-Wave, who famously (well, nerd-famously) declared their supposed quantum processor about as useful as a roast beef sandwich, made a visit to their facility, and moderates his stance somewhat.

-- Every few weeks, there's a story about some new promising quantum computing technology. The most recent is the demonstration of topological error correction, which might be essential for making quantum processors that can withstand the noise that inevitably creeps into any real system. This would be good fodder for a ResearchBlogging post, if I had the time to understand it in detail, but I don't. So you get this passing mention.

-- Matt Leifer has written another article about the theorem ruling out some kinds of interpretations that made a bunch of news a little while back. It's for the "Quantum Times," the newsletter of an APS group on quantum information, so it's not exactly at the level your dog might want to read, but if you know a little about it, and want to know more, it's a good piece.

And that's three browser tabs closed. Only 20-odd left...

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Categories: Education

Why is the Far Side of the Moon Always Far? [The Weizmann Wave]

12 March, 2012 - 10:35

The patterns of the dark craters on the near side of the Moon have spurred the imagination of observers from all cultures: Some visualize a woman, others a rabbit, or, like most of us, they see the "Man in the Moon."

Moon_near side (2).jpg
Near side

The explanation as to why we always see the Man in the Moon - that is, why we only see one side - is that tidal forces caused the Moon to slow its spin until it reached the present point. It now takes the same amount of time to rotate around its own axis as it does to revolve around Earth. It is this synchronous rotation that causes the moon to "lock" with Earth, with one hemisphere constantly facing us.

But Prof. Oded Aharonson of the Weizmann Institute's Center for Planetary Science, together with Prof. Peter Goldreich of the California Institute of Technology and Prof. Re'em Sari of the Hebrew University of Jerusalem wanted to know whether there is a reason why this particular half of the Moon locked with Earth or if it is pure luck that it didn't turn its "back" on us?

Moon_far side (2).jpg
Far side

Unlike the near side, which is covered in dense craters, the far side is made up of more mountainous regions, and these differences affect the Moon's gravitational energy. Taking this into consideration, the scientists, through careful analysis and simulations, have shown that it is not coincidence but rather, the Moon's geophysical properties that determine its orientation. Their findings have recently been published in Icarus. A more detailed description can also be found on our website: http://wis-wander.weizmann.ac.il/why-do-we-see-the-man-in-the-moon-oded-aharonson

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Categories: Education

Weekend Diversion: Preparing for May 20th's Annular Eclipse! [Starts With A Bang]

12 March, 2012 - 03:15

"They call it a great wonder
That the Sun would not
though the sky was cloudless
Shine warm upon the men." -Sighvald, Icelandic poet A couple of times a year, during the New Moon, the Sun, Moon, and Earth all line up in the same plane. As seen from Earth, the Sun's disc appears blocked, either in whole or in part, by the Moon. As The Beta Band would have told you, this creates an

Eclipse.

Depending on how close the Moon and Sun are to the Earth, either the Moon's shadow will fall on the Earth, creating a total solar eclipse, or the shadow will end before it ever reaches Earth, in which case we get to see an annular solar eclipse.

Eclipses.gif

(Image credit: Total Solar Eclipse in Russia.)

Back in 1994, I was living in New York; this was the last time an annular eclipse happened anyplace close to where I was living. From where I was, about 87% of the Sun's disk was blocked by the Moon, and there were two very interesting (and obvious) things that happened:

  • The Sun remained incredibly, blindingly bright to look at, but gave off virtually no warmth, and
  • shadows looked, well, really weird.

eclipseshirt_haake.jpeg

(Image credit: Philippe Haake, retrieved from APOD.)

I didn't have the fun kitchen skimmer that Philippe Haake had, above, but I discovered that, with my back towards the Sun, if I held my fingers, crossed together, over my head, the shadows produced by the tiny spaces in between my fingers would produce miniature eclipses Suns.

But if I had been in a more fortuitous location, where there actually was a full annular eclipse, those tiny little apertures would have produced images of the ringed annulus, such as the rings Steve G.S. saw shining through the tree leaves in 2005.

ann_suns.jpeg

(Image credit: Steve G.S., from the 2005 annular eclipse in Spain.)

Well, I live on the West Coast of the United States now, and I'm finally getting another chance to see an annular eclipse! This May 21st/May 20th, depending on which side of the international date line you're on, is our planet's next eclipse. Those of you in Hong Kong, Taipei, Tokyo and other areas will get to see the annular eclipse shortly after sunrise on the 21st, but those of you in the west/southwest United States are in for an extra special treat.

US_Annular_Eclipse.jpg

(Image credit: Google Maps / NASA.)

In the waning hours of the day on May 20th, as Sun descends in the west, the Moon will pass in front of it, creating the first annular eclipse in the United States since 1994!

This time, I'm going to be prepared.

1.jpeg

(Image credit: Frisius Gemma's Camera Obscura, 1544, retrieved here.)

First off, I'm going to make sure I have a pinhole camera with me. A pinhole camera is as simple as having a piece of cardboard with a pinhole poked in it and a white screen behind it. As the sunlight passes through the pinhole, the (inverted) image of the Sun's disk gets displayed on the screen in the back.

If the Sun's disk is partially blocked, then what shows up on the display screen is the eclipsed Sun, completely safe for viewing. There are a number of quality, ultra-low-tech options readily available for your display screen.

solar_eclipse.jpeg

(Image credit: Shree Nayar of BigShotCamera.org.)

Because the eclipse is happening late in the day -- in the Pacific Time Zone, it starts at about 5:10 PM and ends at around 7:30 PM -- I'll want to make sure I have a clear view to the west, where the Sun will be descending. I am taking no chances, and will be staking out a spot along the coast. With over 200 miles of prime viewing coastline available, I'm even hoping for a little solitude while it happens.

WY5T0628-crop-715800.jpeg

(Image credit: Craig Wolf Photography.)

The ocean is sure to provide me with very little in the way of obstacles that will obscure the Sun's view. The only possible interference will come from the astronomer's nemesis: clouds.

I also plan on photographing the Sun, directly, during the eclipse! Although I'm not a skilled photographer by any stretch, anything from a pair of welder's goggles to the interior of a 3.5" floppy disk, placed over the lens of your camera, will allow you to successfully photograph the Sun during an eclipse!

6414_111501452095_671522095_2717667_8101171_n.jpeg

(Image credit: Chin-Yu Hsu, who was in high school with me during the 1994 eclipse, of the 2009 solar eclipse, from Taiwan, using a 3.5" floppy filter.)

I won't, however, be looking at the Sun through the 3.5" floppy disk; welder's goggles are okay (as are some other types of protective eyewear), but be careful! You won't feel the damage the Sun can do to your eyes until it's too late; make sure if you're going to look at the Sun directly that you get the proper equipment to protect your eyes.

I'm hoping to get some images as good as the ones taken by Steve G.S. with his solar filter in 2005. (Yeah, right!)

eclipseq.jpeg

(Image credit: Steve G.S.)

The United States will get a shot at a total solar eclipse -- perhaps the only sight more spectacular than an annular eclipse -- on August 21, 2017. But for those of you with a chance to go out and view this one, including those of you just crazy enough to be eclipse chasers (which may include me, now), start planning for it now.

You won't get another chance at an annular eclipse in the USA until 2023, so don't miss it!

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Categories: Education

The Most Astounding Fact About The Universe [Starts With A Bang]

10 March, 2012 - 02:29

"Is no one inspired by our present picture of the Universe? This value of science remains unsung by singers, you are reduced to hearing not a song or poem, but an evening lecture about it. This is not yet a scientific age." -Richard Feynman Back in 2008, Time Magazine interviewed Neil de Grasse Tyson, and asked him, " What is the most astounding fact you can share with us about the Universe?" His answer was indeed a very good, true, and astounding fact about the Universe: that all the complex atoms that make up everything we know owe their origins to ancient, exploded stars, dating back billions of years.

heic0507a.jpeg

(Image credit: NASA, ESA, HEIC, Hubble Heritage Team (STScI/AURA).)

It's a great fact, and it's definitely on the short list of the most remarkable things we've learned about the Universe. But if I were to choose the most astounding fact about the Universe, I'd want you to consider something else.

It didn't have to be this way.

cliffs-ocean-slieve-league.jpeg

Not just the trees, the mountains, the skies and the oceans. Not merely everything on this Earth, mind you. Not even everything in the entire Universe.

PerseusCluster_gabany_abell426.jpeg

(Image credit: R. Jay Gabany.)

The way it all turned out, no doubt, is absolutely wondrous. Just here, in our own little corner of the Universe, we find ourselves in a forgotten, non-descript little group of galaxies no more or less special than any of the billions out there.

5_Local_Galactic_Group_%28ELitU%29.png

(Image credit: Wikimedia user Azcolvin429.)

But when we look out at the Universe, whether we look at the internal structure of matter, probing things down to the tiniest subatomic scales...

Lucas-Higgs-CE0047H-nice_0.jpeg

(Image credit: CERN / Lucas Taylor, via simulation.)

...or out into the expansive abyss of deep space, billions of light years away, at the largest scales visible to an observer within our Universe, there is one fact that stands out as the most astounding.

Gravitationell-lins-4.jpeg

(Image credit: NASA, ESA, the ACS Science Team and N. Benitez et al.)

The entire Universe,

on all scales,

in all places,

and at all times,

obeys the same fundamental laws of nature.

freq_doubler.jpeg

(Image credit: M. Csele/Niagara College, retrieved from here.)

From the weakest photon of light to the largest galaxy ever assembled, from the unstable atoms of Uranium decaying in the Earth's core to the neutral hydrogen atoms forming for the first time 46 billion light years away, the laws that everything in this Universe obey are the same.

feat24-3.jpeg

(Image credit: Nancy Ellen Abrams and Joel R. Primack.)

This is the most remarkable thing of all.

Imagine an existence where nature behaves randomly and unpredictably, where gravity turns on-and-off on a whimsy, where the Sun could simply stop burning its fuel for no apparent reason, where the atoms that form you could spontaneously cease to hold together.

46-effects.jpeg

(Image credit: Karim Fakoury.)

A Universe like this would truly be frightening, because it could never be understood. The things you learn here and now might not be true later, or even five feet away.

But the Universe isn't like this at all.

chart_2006_4.jpeg

(Image credit: U.S. DOE, NSF, CPEP and LBNL, retrieved from here.)

The Universe is a place where the matter and energy in it can change, the spacetime itself that we all occupy can change, but the fundamental laws -- that everything is subject to -- are constant.

Because what that means is that we can observe the Universe, experiment with the Universe, assemble and disassemble the things we find in it, and learn.

197545main_image_feature_740_946x710.jpeg

(Image credit: NASA, ESA and the Hubble Heritage Team (STScI / AURA).)

Only if the fundamental laws of the Universe are the same everywhere and at all times can we learn what they are today, and use that knowledge to figure out what the Universe -- and everything in it -- was doing in the past, and what it will be doing in the future.

In other words, it is this one fact, this most astounding fact, that allows us to do science, and to learn something meaningful, at all.

1305874500-science-xkcd-geek-wallpaper.jpg

(Image credit: xkcd.)

In short, the most astounding fact about the Universe is that it can be understood at all.

But Neil's answer was pretty good, too.


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Categories: Education

The most astounding fact is said to be ... [Greg Laden's Blog]

9 March, 2012 - 17:15


Yes, folks, it's YouTube Weekend! (Our daycare is closed and it's convention/caucus season in Minnesota and I've got a candidate!)

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Categories: Education

A Musical Interlude [Uncertain Principles]

8 March, 2012 - 14:24

Yesterday was a really grueling day, and I'm home with The Pip today, so no substantive blogging. But here's a song about the universe, written and performed by one of my colleagues:

If this becomes the next LHC Rap, remember you heard it here first.

By a weird coincidence, we've been watching our Animaniacs DVD's with SteelyKid, and just a couple of days ago got to this one:

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Categories: Education

Are You Being Honest With Yourself? [Starts With A Bang]

8 March, 2012 - 02:11

"Be careful. People like to be told what they already know. Remember that. They get uncomfortable when you tell them new things. New things...well, new things aren't what they expect. They like to know that, say, a dog will bite a man. That is what dogs do. They don't want to know that man bites a dog, because the world is not supposed to happen like that. In short, what people think they want is news, but what they really crave is olds...Not news but olds, telling people that what they think they already know is true." -Terry Pratchett We all like to think that our opinions are the result of years of hard-earned accumulation of knowledge. That we've gone and aggregated all of the relevant facts on a particular issue, put them together in the most sensible way, and that's how we've arrived at our picture of the world.

But, of course, that isn't the way we work at all.

dilbert-confirmation-bias.gif

(Image credit: Scott Adams, 2011.)

Known as confirmation bias, it's the very human tendency to, once we've formed an opinion, place our faith in the new evidence that appears to support that position, but to look for holes in the evidence that undermines or disagrees with that opinion.

In other words, changing our minds -- especially once we've made our minds up -- is extraordinarily difficult. The way we often deal with this, in the case of a divisive issue, is to think that the other side on an issue is (any combination of) misinformed, ignorant, foolish, or conspiring against the truth. And we often miss no opportunity to present them (and their position) as inferior to our own.

brainiac.jpeg

(Wish I knew the true origin of this, retrieved from here.)

When was the last time you saw someone who held a passionate position on one side or another of a divisive issue actually change their mind and switch to the other side in the face of overwhelming evidence? It doesn't happen very frequently, does it?

You may not see it very frequently in your own life, in politics, or most places that you look, but it happens all the time in science. Not for everyone, of course, but science is one of the only places where you'll see a vast majority of scientific experts in their field change their mind on an issue based on the evidence that comes in.

Blog_Bild3_KuT1.jpeg

(Image credit: retrieved from the CCCB LabZine.)

When a uniform-temperature, all-sky microwave radiation background was discovered in the 1960s by Penzias and Wilson (above), it provided overwhelming scientific evidence supporting the Big Bang picture of the Universe, and disfavoring alternative explanations such as the Steady State theory. A few notable exceptions held out, but modern cosmology simply does not make sense without the Big Bang, and this was the observation that sealed it.

clad.jpeg

(Image credit: University of Bristol, Sharon Mooney et al.)

Same deal with evolution. Without it, modern biology -- including genetics, DNA, and modern medicine -- makes no sense. Evolution was an amazing idea that came in multiple variants for a time, but when the archaeological evidence of transitional fossils started pouring in, it became clear that all living things on the planet were descended from previous generations of living things dating back at least hundreds of millions of years. (We know that's longer, now.) Even transitional forms for organisms like whales and dolphins exist, and when this type of evidence started rolling in, even the most skeptical of competent scientists started changing their minds.

027369-richard-muller.jpeg

(Image credit: Associated Press, retrieved from here.)

And in a very notable recent example, climate science skeptics such as Richard Muller, above, are overwhelmingly concluding that there is a link between the observed rising temperatures of the Earth and the effects of human activity, once again in the face of overwhelming scientific evidence. As always, there are holdouts, but that does not change the scientific facts or conclusions.

My favorite example, though, of a scientist who held strong convictions on an issue, but changed their mind, dates back more than 400 years!

Johannes_Kepler_1610.jpeg

(Image credit: Johannes Kepler, 1610, Public Domain image.)

Towards the end of the 16th Century, after the death of Tycho Brahe, Johannes Kepler, pictured above, was -- perhaps along with Galileo -- the foremost astronomer in all of Europe. Much like Galileo, Kepler was intimately familiar with the work of Copernicus, and recognized how beautiful the possibility of a heliocentric Universe was.

After all, it could explain the retrograde motion of the planets -- how some planets appeared to reverse direction with respect to the fixed stars -- in their motion from night-to-night!

retrogrademars03_tezel_big.jpg

(Image credit: Tunc Tezel, of Mars in retrograde.)

Instead of a stationary Earth, where the planets orbit the Earth in a superposition of circular orbits, occasionally reversing course and appearing to move backwards, the heliocentric model had the outer planets (Mars, Jupiter, Saturn, etc.) move backwards because the Earth, in its faster orbit around the Sun, overtook the outer planets in their position! (Mars, for those of you astutely watching it, is finishing up its retrograde motion as I write this!)

This is nearly a hundred years before Newton's gravity, so there was the great question of how these orbits came to be. And Kepler's idea was nothing short of genius. Sheer, unbridled, and beautiful genius.

Kepler%20Mysterium%20plate%203.jpeg

(Image credit: Mysterium Cosmographicum, J. Kepler's notebook, retrieved here.)

Envisioning the six planets as being supported by the five Platonic solids with spheres inscribed/circumscribed upon them, the orbits would be defined by the circumferences of these spheres. It was a beautiful idea, with very explicit predictions for the ratios of the scales of the planetary orbits. Because there are only five Platonic solids and were only (at the time) six planets, this scheme was beautiful, compelling, and created an incredible buzz amongst scholars.

But unlike Galileo, Kepler had access to the finest data in the world: the observations of his predecessor, Tycho Brahe. And the data simply did not agree with Kepler's theory. The orbits were all wrong.

Not by that much, mind you, but by enough that it clearly didn't fit. At the time, there was tremendous prejudice in favor of the circle being the only acceptable shape for an orbit, but -- ever the scientist -- Kepler followed the data to its logical conclusion. He even rejected his beautiful Mysterium Cosmographicum, creating, instead, the model we use today.

OuterOrbits.jpeg

(Image credit: Phillip Brown and James Braselton.)

They're not circles, or a superposition of a number of circles at all; the orbits are ellipses! Planets move around the Sun with the Sun at one focus of an ellipse; the first of Kepler's three laws of planetary motion!

And so Kepler was able to throw away the most beautiful idea he ever had, and in place of it, discover the way the Universe actually worked. And that's my favorite example of defeating your own confirmation bias; from more than 400 years ago! That's the reward of being honest with yourself, one of the most difficult things, apparently, for us, as humans, to do.

So let me ask you; what's your favorite example, from your own life, of when you changed your mind on an issue, based on the new evidence that you learned and couldn't ignore?

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Categories: Education

Experimental Particle Physics: Still Really Difficult [Uncertain Principles]

7 March, 2012 - 19:54

So, the news of the moment in high-energy physics is the latest results being reported from a conference in Europe. The major experimental collaborations are presenting their newest analyses, sifting through terabyte-size haystacks of data looking for the metaphorical needle that is the Higgs boson.

And what are those results? It sort of depends on who you ask. Tommaso Dorigo points at the final data from the Tevatron and claims victory; Matt Strassler thinks the lack of evidence at the LHC is almost as important, though there is progress there in excluding some new regions. The net result is a step of size dx in the general direction of progress, but still a long way from anything conclusive. I think.

My primary reaction to this is relief. I'm partly relieved that I'm not an experimental particle physicist, but mostly relieved that they didn't discover the Higgs in a way that would make me look foolish for not talking more about it in How to Teach Relativity to Your Dog. The current results make me feel better about being vague and equivocal about the Higgs in the book. And since this is my blog, the really important thing is how I feel about the whole thing...

Also, here's me and Emmy talking about the canine version of particle physics, just because:

No sign of the Bacon Boson, either, but Emmy's still hopeful.

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Categories: Education

Fukushima Fallout [USA Science and Engineering Festival: The Blog]

7 March, 2012 - 16:00

meltdown.jpgby Fred Bortz, author of Meltdown! The Nuclear Disaster in Japan and Our Energy Future (Twenty-First Century Books, 2012)

A year ago this week, on March 11, 2011, the biggest earthquake in Japan's history devastated the Tohoku region, 320 kilometers northeast of Tokyo. In the huge tsunami that followed, more than 13,000 people drowned, and thousands of buildings and homes were reduced to rubble.

Within hours, horrifying photos and videos spread around the world. But the most frightening news was yet to come. The Fukushima Dai'ichi nuclear power plant was seriously damaged and three of its reactors were heading for meltdowns.

Over the next few days, explosions and fires released radioactivity into the air, and the Japanese government declared a 20-kilometer evacuation zone. It was the world's worst nuclear disaster since the Chernobyl explosion in 1986.

I knew something about meltdowns. I had previously written about Chernobyl and the accident at Three Mile Island in a chapter of my 1995 book Catastrophe! Great Engineering Failure--and Success. I knew the arguments for and against nuclear power.

After Fukushima, those arguments resounded with added urgency. If engineers know how to build safe reactors, why did the Fukushima reactors fail? But if we stop building nuclear reactors, how can we replace enough fossil fuel plants to limit global warming?

I knew I had to share those questions for middle grade readers. The result was Meltdown! The Nuclear Disaster in Japan and Our Energy Future, just published by Twenty-First Century Books. I'm delighted to have the opportunity to discuss that book as a Featured Author at the 2012 USASEF Book Fair.

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Categories: Education

WebElements: the periodic table on the WWW [http://www.webelements.com/]

Copyright 1993-2011 Mark Winter [The University of Sheffield and WebElements Ltd, UK]. All rights reserved.