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Periodic Table Table [Greg Laden's Blog]

Science Blogs Physcial Sciences - 1 March, 2012 - 14:41

With elements inside.

This is important if you need to get your dog's ears to lie flat.

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Categories: Education

Remember How Tiny We All Are [Starts With A Bang]

Science Blogs Physcial Sciences - 1 March, 2012 - 08:05

"The Earth reminded us of a Christmas tree ornament hanging in the blackness of space. As we got farther and farther away it diminished in size. Finally it shrank to the size of a marble, the most beautiful marble you can imagine." -James Irwin With everything that goes on in this world, from our daily lives to concerns around the globe, it's easy to forget just how vast the Universe is, and how small we all really are. You had so much fun playing with the Interactive Scale of the Universe tool a couple of weeks ago that I had to just give you a few things to ponder. We think of the Earth, our entire world, as a pretty large place. But let's put this in perspective.


(Image credit: Windows to the Universe, Randy Russell, SOHO/ESA/NASA/JPL/U. of Arizona.)

The entirety of our planet, immense in both size and mass, is tiny compared to the Sun. The Sun is 109 times larger in diameter, over 300,000 times more massive, and has sunspots bigger than our planet.

But in the context of the Milky Way, our Sun -- and even the entire Solar System -- pales in comparison.


(Image credit: Brown, Trujillo, and Rabinowitz.)

Our Sun, 1.4 million kilometers in diameter, has a Solar System that extends out beyond Pluto, to a distance of about 140 billion kilometers. That's the distance to Sedna at its farthest point from the Sun, the most distant Solar System object ever discovered. But even that great distance is nothing when placed into the context of our galaxy.


(Image credit: NASA / CXC / M. Weiss, Harvard-Smithsonian CfA.)

Because the distance to Sedna is just 1.5% of one light year, meaning it takes light around five days to go from the Sun to Sedna. But our galaxy is 100,000 light years across, or about ten million times the diameter of our Solar System. And it ought to be. Our galaxy alone contains hundreds of billions of stars, most of which have solar systems not unlike our own.

But compared to the rest of what's out there, our galaxy is terribly insignificant.


(Image credit: Mark Subbarao, Dinoj Surendran, and Randy Landsberg for the SDSS team.)

Although "only" about 250,000 galaxies are shown in the above image, the entire Universe is estimated to have at least hundreds of billions of galaxies, spread out over a spherical region about a million times larger in diameter than our galaxy is. In other words, you and everything you know resides on a tiny, wet rock nearly a million times less massive than the star that powers it, in a solar system one ten-millionth the diameter of our galaxy, which contains at least hundreds of billions of stars not so different from ours, in a Universe filled with hundreds of billions of galaxies, and maybe perhaps more.

You. Are. Tiny.

It also inspired me to dig up this old (2008) video, that helps put into perspective just how big the Universe is. Sometimes, pictures can't do the same justice that a well-put-together video visualization can. And the Universe? It's really, really, really big!

[Some of the numbers you just heard are known to be larger now; we now believe that practically all stars have planets (and there are even planets that have no stars), the number of stars in the Milky Way may be closer to 400 billion, and there may be -- when dwarf galaxies are included -- upwards of one trillion galaxies in the Universe.]

Remember how big this Universe is, and how tiny we all are. But despite all of this, we all get to be a part of it, here, on the most beautiful marble you can imagine.

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Categories: Education

How to Teach Relativity to Your Dog in Nature Physics [Uncertain Principles]

Science Blogs Physcial Sciences - 29 February, 2012 - 19:53

The Subject: header pretty much says it all: How to Teach Relativity to Your Dog is reviewed in Nature Physics. I am inordinately pleased with the existence of this-- not because I expect it to sell a significant number of books, but because a serious technical publication recognized it as worth writing up, despite the silly title.

Of course, Nature being Nature, it's paywalled, so you can only read the full thing via the above link if you have institutional access, or know a nice person who will email you a copy when you ask for it on Twitter. The review itself is about what I would expect-- the reviewer, Roger Jones, is a little uncertain about the talking-dog conceit, and dings me for incomplete labeling of some diagrams-- but generally pretty good.

Amusingly, Jones also says that I'm the victim of poor timing, since the publishing schedule didn't allow a more substantial discussion of the OPERA result, which broke while we were in the proof stages of the process. This is funny, because his review is also a victim of timing-- when he wrote it a few weeks ago (presumably), that would've looked like a better criticism of the book than it does after last week's news about problems with the OPERA measurement. (See Matt Strassler's latest update for more detail on the current state of affairs...)

There was a point when I could've made a more substantive change to include additional stuff about the OPERA results, but I elected not to, because the whole thing was too provisional to say much about. I'm fairly happy with that decision at the moment, though if OPERA fixes their problems and still finds the same result, I might tip back the other way. Oh, well. Something for the Second Edition, should I ever be so lucky...

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Categories: Education

How Good Is BookScan Anyway? [Uncertain Principles]

Science Blogs Physcial Sciences - 29 February, 2012 - 18:56

One of the big stories in genre Internet news was Seanan McGuire's post last week, about reactions to the early release of some copies of her book, and the hateful garbage thrown her way by people outraged that the ebook didn't slip out early as well. And let me state right up front that the people who wrote her those things are lower than the slime that pond scum scrapes off its shoes. That's absolutely unconscionable behavior, and has no place in civilized society.

That said, Andrew Wheeler picked up on something that also struck me as odd, namely the way McGuire was so upset about paper copies of the book being sold before the release date. Wheeler does a nice job, using numbers from Nielsen BookScan, of showing exactly why this might matter: McGuire's past sales suggest that, if everything broke just right, rapid sales in the first week could put her book on the extended New York Times bestseller list, which is a Big Deal. That would require, however, that her book sell a lot of copies in the first week, which is hurt by having some copies slip out a week early. So there's some reason why she and her publisher should be concerned about the early release.

Of course, this relies on BookScan, which is an imperfect measurement-- Wheeler includes the usual explanation: "BookScan captures, by general consensus, somewhere from 2/3 to 3/4 of the book outlets in the USA." But exactly how good a measure is it? which leads to this graph:


This shows the sales for the trade paperback of How to Teach Physics to Your Dog, normalized so as to obscure the proprietary values, for a period of several weeks. Black circles are numbers from BookScan (which I've used before in modeling sales), green triangles are point-of-sale values provided by Scribner, which capture all the books sold.

This shows more or less what you'd expect: the two track each other pretty well, with the BookScan numbers generally a bit lower (there's one point that's actually higher, which I think happened because I miscopied the number and included some hardcover sales). The big spike in the data is the week before Christmas, with sales almost five times the average of the other weeks.

This is, however, subject to some rather stringent limitations.

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Categories: Education

The Physics of Leap Day [Starts With A Bang]

Science Blogs Physcial Sciences - 29 February, 2012 - 18:30

"When in doubt, make a fool of yourself. There is a microscopically thin line between being brilliantly creative and acting like the most gigantic idiot on earth. So what the hell, leap." -Cynthia Heimel Once every four years, the elusive entity that is today -- February 29th -- comes along. The historical origins and urban legends associated with it are incredibly interesting, but the reason there's any such thing as Leap Day at all is because of the physics of planet Earth.


(Image credit: Mrs. Snyder at the Seven Hills School.)

The Earth, of course, is rotating on its axis while simultaneously revolving around the Sun. Rotation, as we all learn, is responsible for sunrise, sunset, moonrise, moonset, the Coriolis effect, and the rotation of all the stars in the night sky about the poles. Revolution, on the other hand, is responsible for the seasons; when your hemisphere tilted away from the Sun, that's when you have your winter (and minimum daylight), and when your hemisphere is tilted towards the Sun, that's when you have your luminous summer.

And you probably learned that a day is 24 hours, due to the rotation, while a year is 365 days (with an occasional 366 for leap years), taking care of the revolution. It turns out it's a little more complicated than that, so let's dive in!


(Image credit: Larry McNish at RASC Calgary Centre.)

The Earth completes a full rotation in less than 24 hours: 23 hours, 56 minutes and 4.09 seconds, to be more precise. But even though we've spun around a full 360 degrees, we've progressed just a little bit in our orbit around the Sun. If we insisted on using the 23:56:04.09 figure as our day, the Sun would be out at midnight for half the year! To fix the motion of the Earth around the Sun, we need those extra 3 minutes and 56 seconds to orient ourselves correctly. That takes care of what a day is, but what about a year? A revolution -- for the Earth to return to the same position with respect to the Sun -- might be an interesting astronomical thing to mark, it isn't a useful definition for a year on Earth.

In order for the Earth to achieve the same seasonal position in its orbit around the Sun -- and trust me, if you live on Earth, you'll want to mark your calendars by the seasons -- you'll need for the Earth to be oriented the exact same way with respect to the Sun as it was exactly one revolution ago. We could do this from winter solstice to winter solstice, when the Earth's north pole (for me) points maximally away from the Sun, or any other arbitrary point in its orbit. This way of measuring the year, known as the tropical year, is actually a little shorter than the astronomical measurement of a year we might be tempted to make.


(Image credit: Greg Benson at Wikimedia Commons.)

Because the Earth only needs to revolve slightly less than 360 degrees around the Sun to make one tropical year. The difference is tiny -- 359.986 degrees instead of 360 -- but enough to make the tropical year about 20 minutes shorter than the sidereal (or astronomical) year. This difference is known as precession, and it explains why the pole star in the night sky appears to change very slowly over a period of about 26,000 years. (25,771 years, for the sticklers.)


(Image credit: retrieved from Tom's Astro Blog / Marian Ware.)

Combine all three of those effects together -- rotation, revolution, and precession -- and you can answer the question of how many days will it take the Earth to make a tropical year?

The answer, as precisely as we can figure for 2012, is 365.242188931 days. If we just had 365 days in the year every year, we'd be off by nearly a month every century, which is pretty lousy. Putting in a leap year (with an extra day) every 4th year gets us closer, giving us 365.25 days in a year. (This was how we kept time with the Julian Calendar, which we followed for 1,600 years!) Still, this difference was significant enough that, by 1582, we had put in 10 too many days. For this reason, October 5th through October 14th of 1582 never existed in Italy, Poland, Spain and Portugal, with other countries skipping 10 days at a later date. The Gregorian calendar, which we now follow, is exactly the same as the Julian calendar, except instead of having a leap year if your year is divisible by 4 (as 2012 is), you don't get a leap year on the turn-of-the-century unless your year is also divisible by 400! So even though 2,000 was a leap year, 1,900 wasn't and 2,100 won't be, but 2,400 will be again. When did your country make the switch?


The adoption of the Gregorian calendar gives us a calendar of with -- over time -- 365.2425 days in the year. In comparison with the present, actual figure of 365.242188931 days, it will take over 3,200 years for us to be off by a single day, which is certainly good enough for a little while.

But if we want to be planning for the long term, we shouldn't simply be thinking about this difference. We should be thinking about the fact that the Earth's rotation rate is changing, and over long enough amounts of time, so should our definition of what a "day" is!

What am I talking about? Two things happen that change the Earth's rotation rate, and they push the day in opposite directions.


(Image credit: USGS.)

Every time we have an earthquake, that's mass inside the Earth rearranging itself so that -- by the conservation of angular momentum -- its rotation speeds up a little bit. For instance, last year's Japanese earthquake shortened the day by 1.8 microseconds, and the 9.1 Sumatra earthquake in 2004 shortened the day by 6.8 microseconds. On the other hand, there are two bodies out there with large gravitational effects on the Earth!


(Image credit: Rick Taylor.)

The Sun and the Moon both exert gravitational pulls on the Earth, all while the Earth itself rotates. If the Earth were just a point in space, this wouldn't matter; the Earth would make its elliptical orbit around the Sun, the Earth-Moon system would orbit their center of mass, and nothing would change. But because the Earth is a sphere, both the Sun and the Moon exert greater gravitational pulls on the side of Earth that's closer to them than on the side that's farther away.


(Image credit: the COMET program. Registration required.)

Throw in the Earth's rotation, and you not only get tides, you also get tidal braking, which causes the Earth's rotation to slow down!


(Image credit: Purdue University.)

The slow-down is small but pretty consistent, at an average of 14 microseconds per year, a much larger effect than the speedup due to earthquakes. And over geological times, this really adds up! If we go back to the daily patterns left in the soil from the tides -- known as tidal rhythmites -- we can calculate what the period of Earth's rotation was from it.


(Image credit: Touchet formation by Williamborg.)

If we look at the most ancient one we know of on Earth, from 620 million years ago, we find that a day back then was a little under 22 hours long!

If you extrapolate this tidal braking back to when the Earth was first formed, 4.5 billion years ago, you'll find that a day was originally only around 23,000 seconds, or six-and-a-half hours!


(Image credit: Primeval Earth by Don Dixon.)

And the best part about this is that the Earth continues to slow down! Every 18 months or so, because of the difference between 86,400 seconds and an actual day, we add an extra leap second to our clocks (for now). Wait around for around four million years or so, and the day will lengthen by about 56 seconds, enough that we won't even want leap year anymore; a year will have exactly 365 Earth days!

So appreciate this leap day and our attention to detail to getting the Earth's seasons to remain constant from year-to-year, but also be aware that our Earth, however imperceptibly, means that these leap days, too, shall pass.

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Categories: Education

The Most Distant, Dark Galaxy Ever Found! [Starts With A Bang]

Science Blogs Physcial Sciences - 29 February, 2012 - 01:36

"One mustn't look at the abyss, because there is at the bottom an inexpressible charm which attracts us." -Gustave Flaubert The deepest depths of space, out beyond our atmosphere, our Solar System, and even our galaxy, hold the richness of the great Universe beyond. Stretching for billions of light years in every direction, there are structures large and small, dense and sparse, everywhere we've ever dared to look.


(Image credit: R. Jay GaBany, Cosmotography.com.)

In addition to the visible, luminous matter we see in the image above, there's both non-luminous normal matter and dark matter. The non-luminous matter is made out of protons, neutrons, and electrons, but doesn't emit light. This includes things such as gas, dust, planets, and astrophysicists: in other words, most normal matter in the Universe. But when we take everything we know about normal matter, including how much there is of it, how its pulls together under the force of gravity throughout the Universe, we find that there needs to be about five times as much dark matter as all the normal matter combined.

One of the easiest ways to figure this out and measure it is by looking at some chance locations in the Universe where there are two massive structures directly lined up, one-behind-the-other, relative to our line-of-sight.


(Image credit: ESA, NASA, K. Sharon and E. Ofek.)

Above is what happens when you have a galaxy cluster with both a quasar and a background galaxy directly behind it. This result -- of multiple images and/or distorted, arcing appearances of the background source(s) -- comes about because of gravitational lensing. This intervening mass bends and magnifies the light from the background source, allowing us to see incredibly distant objects that would be otherwise invisible.

It works the other way, too. From the light that we observe from these background objects, we can infer all sorts of things -- like the mass and how it's distributed -- of the intervening, foreground object, as well as how perfectly/imperfectly it's aligned with the background ones.

The results are often breathtaking and, at least to me, always spectacular.


(Image credit: ESA/Hubble & NASA, retrieved from APOD.)

The "horseshoe" above represents a nearly perfect alignment of two sources. Almost perfect, but not quite. If the background and foreground sources were perfectly aligned, the background source would be bend into a uniform-brightness circle -- a great cosmic rarity -- known as an Einstein ring.

If you could zoom into a nearly-but-not-quite-perfect Einstein ring that was lensed by a black hole, the sight would surely, for as long as you remained an intact being, blow your mind. For what you'd find would be an infinite sequence of these rings, progressively decreasing in brightness, as you approached the event horizon.


(Image credit: Public Domain image, retrieved from Wikipedia.)

But I digress. These Einstein rings are lensed by galaxies, not black holes. The circles they make are never exactly perfect, but some come close. In particular, here's a (falsely-colored) image of one that was recently discovered. This one is particularly interesting for the sheer distances involved: the foreground galaxy -- the one doing the lensing -- is a luminous red galaxy located 9.8 billion light years away. But the background galaxy, the one bent into the ring, is an even more spectacular 17.3 billion light years away. And as you'll notice, it forms a nearly, but not quite, perfect ring.


(Image credit: S. Vegetti et al., retrieved from space.com.)

This system, known as JVAS B1938+666, is much more than just a pretty ring of nearly-perfectly aligned galaxies. You remember, when you form a ring like this, one of the things you'll learn is how the foreground mass is distributed. In addition to the central, luminous red galaxy, there's also a dark concentration of mass, a bit off from the center, of about two hundred million Suns.

Incorrectly reported by many as a purely dark matter galaxy, this is simply a standard dwarf galaxy, but it's so far away that the light from its stars are insufficiently bright to be seen, even with a ten-meter telescope!


(Image credit: David Lagattuta / W. M. Keck Observatory.)

So what's really going on here? You can take a look at the full paper (S. Vegetti et al., 2012) for yourself, but let's break it down in simple terms, and (hopefully) clear up the confusion surrounding this. Almost everywhere in the Universe, the structure you form is about 80-85% dark matter and 15-20% normal matter.

Everywhere. In our galaxy, in galaxy clusters, even in superclusters on the largest visible scales. In these large objects, the gravitational forces are huge, and the gas, dust, and all the forms of normal matter stay bound to their parent object, no matter what you do to it.


(Image credit: NASA, ESA, and A. Aloisi (ESA & STScI).)

But in dwarf galaxies, the little guys, large bursts of star formation can be so powerful that they can eject normal matter out of the galaxy itself! This allows them to, over time, become galaxies that are even more dark-matter-dominated than other, more massive objects in the Universe. In the image above, I Zwicky 18 is full of young stars, indicating an intense burst of star formation that's no more than 500 million years old. There are older stars in there, too, which are more like 10 billion years old, but this latest burst, as perhaps the image below shows even more clearly, will turn this galaxy into an even more strongly dark-matter-dominated object in the future.


(Image credit: Centro de Astrofísica da Universidade do Porto, retrieved from here.)

As this intense burst of star formation happens, bright, hot, young stars form, burn brightly, and die in spectacular supernova explosions. The radiation and outward flux from these objects can heat up and energize the normal, non-luminous matter so thoroughly that it can achieve escape velocity, kicking it out of the dwarf galaxy! What gets left behind are the relic, long-lived stars, the old stellar corpses, and the dark matter.

But what's really important here is that this is exactly what we know should happen! Despite what you may have read elsewhere, there's no reason to believe these objects are 100% dark matter, and there's definitely no reason to believe these observations pose a problem for structure formation. Some people argue that dark matter simulations predict a different density of dwarf galaxies than our Local Group has, and therefore dark matter is wrong. But we have to look at the entire Universe! This one fact does not mean that our Local Group is a good representation of the rest of the Universe; in fact we already know many ways in which it is definitely not! So we go to the paper itself, wherein they've found the most distant dwarf galaxy ever, which says: Our results are consistent with the predictions from cold dark matter simulations at the 95 per cent confidence level, and therefore agree with the view that galaxies formed hierarchically in a Universe composed of cold dark matter. And this is as close to a definite (12-σ significance!) detection as one could get: see for yourself!


(Image credit: S. Vegetti et al., Figure 3 in the pdf.)

You're always going to make waves by claiming that you've done something sensational, like disproven dark matter or found an object made out of 100% dark matter and 0% normal matter, but that's not what we have here.

We've just discovered, at nearly 10 billion light years away, the most distant low-mass, dwarf galaxy in the Universe. And that should be impressive enough; do you know how hard these things are to find?


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

The closest galaxy to us, the Sagittarius Dwarf Galaxy, is about the same size: 1-200 million solar masses, and it took the freakin' Hubble Space Telescope to take this picture of it! Considering it's only seventy thousand light years away, maybe we can cut ourselves some slack for not being able to see the starlight from its twin ten billion light years away!

And despite the great cosmic distance, we are still able to find it, all thanks to gravitational lensing. Are you not impressed?

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Categories: Education

The MAA Reviews the BSB [EvolutionBlog]

Science Blogs Physcial Sciences - 28 February, 2012 - 23:01

The Mathematical Association of America has now posted a thorough review of the Big Sudoku Book. The review is by Mark Hunacek, of Iowa State University. His verdict:

This is a delightful book which I thoroughly enjoyed reading. In some sense it is hardly surprising that I would enjoy it, since I enjoy Sudoku, mathematics and good writing, and this book combines all three of these. However, I doubt anyone needs to enjoy all three to enjoy this book; a person with very limited background in mathematics, or a person without much experience solving Sudoku puzzles, could still find something of interest here. While it is not intended as a text for any kind of traditional course in mathematics, I did keep thinking, as I read it, that it would be fun to offer an honor's seminar based on it. Finally, I should also mention that it is quite reasonably priced: it is (as of this writing, at least) available for sale for just over twenty dollars, with a Kindle edition available for ten. I would, however, enthusiastically recommend this book even if it cost more.


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Categories: Education

How to Teach Relativity to Your Dog: The Big Idea [Uncertain Principles]

Science Blogs Physcial Sciences - 28 February, 2012 - 17:23

I'm home with The Pip today, so no extended typing for me, but I pre[ared for this by typing something up ahead of time, and getting John Scalzi to post it for me, as part of his Big Idea series:

In a way, a book about Einstein's theory of relativity is uniquely suited to a series about Big Ideas. Relativity, at its heart, is a theory built on a single Big Idea:

The laws of physics do not depend on how you're moving.

For all its fearsome reputation, everything stems from that single,simple idea. Whether you're moving or standing still, floating in space or on the surface of a planet, you will see the laws of physics work in exactly the same way.

There's a bunch more, but you can read it over at John's blog. And if you're sold on that, well, How to Teach Relativity to Your Dog is released today, so you can get it immediately.

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Categories: Education

How to Teach Relativity to Your Dog is Officially Out Today [Uncertain Principles]

Science Blogs Physcial Sciences - 28 February, 2012 - 16:11

The Pip says, "Hi, folks. My daddy's book is released today, and he's shameless enough to use me to promote it:"


"I can't read it yet, because I'm just a baby, but I can report that it was very satisfying to drool on. So you should definitely buy a copy, maybe two."

"Also, dig the awesome stuffed alligator toy I got from my Aunt Erin and Aunt 'Stasia. It crackles, and it has a mirror! It's so cool!"

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Categories: Education

My First Podcast! [EvolutionBlog]

Science Blogs Physcial Sciences - 28 February, 2012 - 05:38

If you have a few minutes to kill, go check out this podcast over at Sol Lederman's website “Wild About Math.” Laura Taalman and I discuss the BSB (by which I mean the Big Sudoku Book). We talk Sudoku, math, education and plenty of other stuff. We originally planned on talking for thirty minutes. but everything went so well that we ended up hanging around for fifty. So go enjoy and let me know what you think!

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Categories: Education

How to Teach Relativity to Your Dog in the Washington Post [Uncertain Principles]

Science Blogs Physcial Sciences - 28 February, 2012 - 01:43

If you're allergic to hype, you might want to tune this blog out for the next couple of days, because How to Teach Relativity to Your Dog is officially released tomorrow, so it's all I'm going to talk about for a little while. Because, well, I'm pretty excited.

And tonight's exciting finding is that it's mentioned in the Washington Post:

If "Physics for Dummies" left you baffled, maybe it's time to go a step further: Why not physics for pets? In "How to Teach Relativity to Your Dog," physics professor Chad Orzel attempts to explain Einstein's theory of relativity via a dialogue with his dog, Emmy. Orzel breaks down complex concepts -- time dilation, relative motion, black holes, the big bang -- by applying their physics to canine-friendly situations, like chasing rabbits and determining whether a dog can eat enough kibble to run at the speed of light. Rather than barking or growling, Emmy leavens the mood with requests for walks; and when the academics get heavy, she interjects to beg for clarification. Obviously, real-life dogs will not walk away from the book with a grasp of the universe's mechanics, but the human sort of non-scientist can get some benefit.

OK, that one paragraph is the sum total of the mention, and I'm not sure if that's in the print edition or just the web site (then again, who reads print newspapers any more?), but, dude! The Washington Post acknowledged my book! Woo-hoo!

"All right!," says Emmy. "The Post represents the conventional wisdom of political elites, so if they say nice things about our book, it's only a matter of time before Congress dishes me some of that sweet, sweet pork I keep hearing about. Mmmmm.... pork...."

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Categories: Education

Ground Resonance Shakes Apart Chopper? [Greg Laden's Blog]

Science Blogs Physcial Sciences - 28 February, 2012 - 00:30

I know many of you enjoy discussing resonance. Check this out:

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Categories: Education

Final Notes on a Toy Model of the Arrow of Time [Uncertain Principles]

Science Blogs Physcial Sciences - 27 February, 2012 - 19:20

We're in the home stretch of this term, and it has become clear that I won't actually be using the toy model of the arrow of time I've talked about in the past in my timekeeping class this term. These things happen. Having spent a not-insignificant amount of time playing with the thing, though, I might as well get a final blog post about it, with something that sort-of worked and something that shows why I'm not a computational physicist:

First, the thing that sort-of worked: in thinking about trying to use the code I wrote, I was struggling to come up with a way to quantify the apparent irreversibility of the evolution of my toy system for larger numbers of "particles" in a relatively non-technical way that might be comprehensible for non-physicists. After a bit of thinking, I realized that there's an easy-ish way to do this, because the system has an easily calculated maximum entropy, which it ought to converge to. And empirically, when I start it going, it shoots up toward the maximum, and then noodles around up there, with occasional downward fluctuations as more "atoms" randomly end up on one side or the other.

To quantify the number and amount of those downward fluctuations, I realized I could just use the number of points dropping below various fractions of the maximum entropy, once the system got close to the maximum value. Which led to this graph:


To get these, I ran for 100,000 time steps, throwing out the first 1000 (as the entropy climbed upward from the initial low-entropy state with all the "atoms" in the left half of the array), and set up some simple counters that recorded the number of time steps where the entropy was below 90%, 75%, and 50% of the maximum possible for that number of lattice sites and atoms.

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Categories: Education

Not Your Daddy's Science Classroom! [USA Science and Engineering Festival: The Blog]

Science Blogs Physcial Sciences - 27 February, 2012 - 16:00

By Stacy Jannis

Thumbnail image for classroom1950.jpgExciting things are happening in 21st century classrooms all over our country. Teachers and students are using cutting-edge technology, working in teams, and connecting and sharing projects with classrooms all over the world. Innovative groups like the Concord Consortium , Promethean World , Project Lead the Way and Epals are at the forefront of creating the curriculum, software, tools and environment of tomorrow's classroom, today. A rich and exciting mix is brewing, one that combines multimedia, digital simulations, games, computer programming, inquiry and project-based learning, to accelerate our children's skills to think creatively, work collaboratively, and train to tackle 21st century problems.

Can we save the world through science and engineering? We think so! We are inspired by the excellence and passion for science and science education that takes place in innovative classrooms all over the country, every day.

A 6th grade classroom at Friends School Haverford took up this challenge as part of the Kavli Science Video Contest. As a class, they researched, brainstormed ideas, and focused on topics including energy, health, and the environment. Then they let their creativity go wild, including writing and recording original music, animations, and video. Here's what some of the kids said on the last day of the project:

"This project has changed how I think about science. I knew science could cure sickness and diseases, but I never realized science could save the world."

"I really got a better understanding of what science can do."

"I already thought [science] was fun and important but doing this project made me think about science as a way to change the world."

"Science isn't always just researching, working in the lab, or finding solutions to problems every day. Science can be fun and exciting."

The Kavli Science Video Contest challenges students to investigate how science and engineering saves our world, and answer the central theme creatively.
Grades 6-12 students compete for the chance to win $2000 (first prize) and a travel stipend to Washington DC to attend the festival. The winners are also honored in an awards ceremony, hosted by Bill Nye, as part of the festival.

Our central theme, or driving question, is how to "Save the World through Science and Engineering". Students make a short video( :30-:90) that shows how scientific discoveries and inventions can improve our lives and change our world, either right now or in the future. Enter by Mar. 21, 2012.

Click here to read more about the Festival and the Kavli Video Contest.

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Categories: Education

Space Chronicles: Neil deGrasse Tyson's New Book [Greg Laden's Blog]

Science Blogs Physcial Sciences - 27 February, 2012 - 13:52

9780393082104_custom.jpgNeil deGrasse Tyson has a new book out: Space Chronicles: Facing the Ultimate Frontier. It is (as one might guess) about space exploration, and assembles earlier speeches and writings with some new stuff. This is an interesting time to be talking about the space program, as NASA seems to be producing new results ever week, there are large and small space robots on their way to distant orbs, or soon to be launched, we are on the verge of understanding the potential of life on Mars on a basic level, we are finding more earth-ish Exoplanets and at the same time the sky is falling, or at least, trashed with litter from one of the most significant, direct and obvious side effects of the space program: We humans get to ruin not just the air and the sea and the land, but also, near space!

From a recent NPR interview:

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Categories: Education

How to Teach Relativity to Your Dog in the Wild [Uncertain Principles]

Science Blogs Physcial Sciences - 27 February, 2012 - 01:49

Hey, you might not know this, but I wrote a book...

The official release date for How to Teach Relativity to Your Dog isn't until Tuesday, but a friend reported buying a copy in Missouri, so when I was headed out to do some work this afternoon, I went to the cafe at the local Barnes&Noble so I could check for myself, and there it was:


That's How to Teach Relativity to Your Dog spotted in the wild. I'm not going to say "in its natural habitat," because it's really a domestic animal, which belongs in a loving home, with people to care for it. Copies in the bookstore are feral editions, which need to be tracked down, taken in, and adopted.

So, please, head down to your local store, and take one home, won't you? You could even arrange to have one sent directly to you, from one of the nice retailers linked at DogPhysics.com...

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Categories: Education

Con or Bust Auction Nearing Its End [Uncertain Principles]

Science Blogs Physcial Sciences - 25 February, 2012 - 14:13

Once again, Kate is running an auction to benefit the Con or Bust project providing financial support for fans of color(*) to attend science fiction/ fantasy conventions. The auction is run via LiveJournal, with a variety of cool items on offer in individual posts to that community, with an overall index here.

Among the items on offer are signed copies of How to Teach Relativity to Your Dog and How to Teach Physics to Your Dog (in your choice of several languages). You can also bid on some of our excess books.

Bidding ends at midnight Sunday, so you've got a little time left. Check out the lists of stuff, and get your bids in soon.

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Categories: Education

On Cox vs. Swans [Uncertain Principles]

Science Blogs Physcial Sciences - 24 February, 2012 - 19:57

The other controversial thing this week that I shouldn't get involved in is the debate over whether Brian Cox is talking nonsense in a recent discussion of the Pauli Exclusion Principle. Tom at Swans on Tea kicked this off with an inflammatory title, and Cox turned up in the comments to take umbrage at that. Sean Carroll provides a calmer and very thorough discussion, the comments to which include a number of well-known science popularizers duking it out.

My take on it is basically the same as Tom and Jim Kakalios in Sean's comments: unless the two particles you're talking about are within about a de Broglie wavelength of each other, Pauli exclusion doesn't really matter. This was actually a question at my Ph.D. defense, because a big part of my thesis was about quantum statistical effects in ultracold collisions, where Pauli exclusion forbids certain types of collisions from taking place. When we think about that sort of thing, we require that the two colliding atoms be in an overall antisymmetric wavefunction, but we don't worry about the state of other atoms of the same element elsewhere in the apparatus, because they're so far away that they don't change the energy states available to the colliding atoms in any significant way.

In Tom's comments, Cox insists that hes right, and says that the whole thing is worked out in detail in his new book. I haven't read the new book, though I've been offered a copy by a publicist, so we'll see. I think Sean and Matt Leifer at comment #6 have covered pretty much all of the bases, though, so I'm inclined to think that Cox is just wrong. There may be a narrow philosophical sense in which he's correct, but I don't think it's useful, and given that there are large numbers of people working scams based on woo-woo notions of quantum phenomena enabling paranormal abilities, I think this is a bad direction to take popular quantum mechanics.

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Categories: Education

The Hubble Rate [Dynamics of Cats]

Science Blogs Physcial Sciences - 24 February, 2012 - 19:12

Is approaching 1 per minute and accelerating.

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Categories: Education

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