seattle sightings

Too_cooljenluc_6

I'm back from Seattle, where I didn't get the chance to take in nearly as many of the fantastic papers at the American Astronomical Society (AAS) as I would have liked. Most of the major results have been covered elsewhere in the blogosphere anyway. But I did find time to squeeze in one last press conference: a sort of catch-all session on unique approaches to education and outreach.

For instance, those controversial new NBA basketballs have been in the news over the last few months, so it was particularly timely to have John Fontanella on hand to talk about the four basic physical forces that affect the flight of a basketball: gravity, buoyancy, the drag force, and the Magnus force. Fontanella is a physics professor at the US Naval Academy and author of a new book, The Physics of Basketball (Johns Hopkins University Press). Fontanella has first-hand knowledge of the sport: he was a college basketball star at Westminster College, even setting a school record when he scored 51 points in a single game in 1966.

His basic "hoopothesis" is that the best shooters try to minimize the speed of the basketball just as it reaches the basket. Fontanella filmed several shooting sessions and analyzed the footage, determining such factors as initial position, velocity and launch angle. From that data, he experimented with several computer models. He found that, given just the effects of gravity and the initial conditions, the ball overshoots. So he added in some air resistance: the ball over-corrects. So then he added in lift via a rotational backspin on the ball when it's launched, and found that came pretty close to predicting the perfect trajectory for the basketball to travel.

Fontanella likes to cite his model as an example of how physics can be used to model real-world phenomena. For instance, Shaquille O'Neal — notorious for not being very good at taking foul shots — would probably find Fontanella's "hoopothesis" interesting, since it states he should shoot his foul shots at a launch angle of 48.7 degrees. ("Obviously he doesn't do that," cracked Fontanella.) And as it happens, physicists at the University of Texas, Arlington, were able to demonstrate that the new NBA ball had some critical flaws, which may have influenced the NBA's decision to return to the old regulation basketball.

I also heard about a fascinating acoustical effect that occurs with mugs of hot chocolate, ably demonstrated by Bradley Carroll of Weber State University with a packet of Swiss Miss instant cocoa. Tapping a spoon against the bottom of a mug of freshly made hot cocoa produces a tone of constantly rising pitch.  If you stir the cocoa some more, the pitch will plunge before it starts rising again. And it's a significant increase: about three octaves, "an eightfold increase in frequency, twice the rise in pitch you encounter while singing the 'Star Spangled Banner,'" says Weber. Yet there is no noticeable change in the actual mug of cocoa.

He demonstrates the effect to pique his students' interest and assigns them the task of "solving" the mystery by performing a series of experiments. They test for the effect by changing the variables, using hot water, cold water, milk, cocoa, tea, instant coffee, instant cider Kool-Aid, sugar, salt and even dishwashing liquid, in an attempt to narrow down a possible hypothesis to explain the effect. The students get to satisfy their curiosity and gain first-hand experience with the scientific method — not the severely distilled version of that method routinely described in textbooks, but how scientists work in real life. "A good mystery is far more compelling than mere 'fact,'" according to Weber, who prefers P.W. Bridgman's description of the scientific method: "The scientific method is doing your damnedest, no holds barred."

Weber likes to hoard the "secret" behind the hot chocolate effect a little, so I hope he doesn't mind that I reveal it here. The best explanation he's been able to find is in a May 1982 paper by Frank Crawford published in the American Journal of Physics. The effect is similar to how a sound is produced when one blows air across the top of a partially filled Coke bottle. It's the vibrating air above the Coke's surface that gives rise to a sound wave, and the tone's pitch depends on how full the bottle is: the more liquid, the less air, and the higher the pitch. But with the hot cocoa, it's the liquid below the surface that vibrates, and produces a sound wave.

Crawford argued that stirring the instant cocoa creates tiny bubbles that lower the speed of sound in the liquid. Since it takes longer for the sound to travel through the cocoa, the pitch falls. Over time, the bubbles rise to the surface and burst, enabling the sound to travel faster. So the pitch rises.  Of course, eventually the effect dies out, so Weber thinks there might be more to the story than just the bubbles that get stirred up when the cocoa is first made. Perhaps one of his students will come up with a more thorough explanation someday. 

The other interesting paper involved a strange acoustical effect on a more cosmic scale. NASA's Chandra X-Ray Observatory has detected a "light echo" from the supermassive black hole located at the center of our Milky Way galaxy. It's evidence of a powerful outburst of X-ray radiation from the black hole, generated by gas falling into it. The primary burst would have reached Earth some 50 years ago, before satellites were in space to detect it, but the "echo" consists of reflected radiation from the gas clouds near the black hole. It took longer to travel through space, and by the time it arrived, Chandra was on hand to record it. (Sometimes it really does come down to having the right equipment in the right place at the right time.) The astronomers who detected the echo think it indicates that the black hole consumed a very large mass roughly the size of the planet Mercury.

Finally, here's a few random tidbits for the gossip pages: I met Rob Knop of Galactic Interactions, who wins major points for coming to my talk at Elliott Bay Bookstore — unfortunately held on the same night as a Seahawks playoff game, so we needed as many extra bodies as we could get — and for buying several copies of my books. Also, he's very funny and an excellent dinner conversationalist. Next time I hope he brings his unicycle. Steinn, however, proved more elusive, perhaps because he was so busy covering the actual meeting, along with Rob, that he was never hanging out in the press room.

I also dragged my 14-year-old niece to a Skeptics Society dinner Sunday night, where we briefly met Phil Plait, who was slated to give a talk on the Moon Hoax. He seemed pale and subdued. Within 14 minutes he was going green, excused himself, and ended up cancelling his talk and heading back to his hotel room. Rumor has it he spent an uncomfortable night having "conversations with the porcelain Buddha." I never saw him again, but he's been blogging, so I assume he survived. Perhaps it was the crushing disappointment at finding that I look nothing like my faux-Frech avatar, Jen-Luc Piquant. Or perhaps this is just the effect I have on fellow bloggers. I mean, I met Michael Berube over the Christmas break, and next thing you know, he's retiring his blog. Let's hope Bad Astronomy weathers the "Jen-Luc Curse" and continues its long, fruitful life in the Blogosphere.

9 thoughts on “seattle sightings”

  1. >The astronomers who detected the echo think it indicates that the black hole consumed >a very large mass roughly the size of the planet Mercury.
    Sounds like an astrophysical burp to me. Queue “I can’t believe I ate the whole thing!”

  2. I don’t know why this never occurred to me till just now, but I seem to recall from the pop GR books I’ve read (Kip Thorne’s Black Holes and Time Warps, for instance) that you never actually see anything fall into a black hole; time dilation stops it just above the event horizon. That being the case, how come we see these X-ray bursts? Is what we’re actually seeing just the mass hitting the accretion disk?

  3. I also heard about a fascinating acoustical effect that occurs with mugs of hot chocolate, ably demonstrated by Bradley Carroll of Weber State University with a packet of Swiss Miss instant cocoa. Tapping a spoon against the bottom of a mug of freshly made hot cocoa produces a tone of constantly rising pitch. If you stir the cocoa some more, the pitch will plunge before it starts rising again. And it’s a significant increase: about three octaves, “an eightfold increase in frequency, twice the rise in pitch you encounter while singing the ‘Star Spangled Banner,'” says Weber. Yet there is no noticeable change in the actual mug of cocoa.
    A post-doc I knew in grad school recalled being given a variant of this question as part of his Ph.D. defense– I think it was just stirring sugar into a cup of coffee, not hot cocoa. His guess was also that it had something to do with changing the speed of sound in the liquid, but he wasn’t sure of the “right” answer. It was one of those questions they ask in order to see how well you think on your feet…

  4. David’s recollection of Thorne’s book is correct: to an outside observer, a space craft at the brink of the event horizon will seem to be frozen in time. As I recall, the explanation is that light can’t escape once it moves past the event horizon, and since we get our “information” from light (electromagnetic radiation), that’s where our information ends. But there’s been a lot of research into black holes since Thorne’s book. They’re bizarre objects, and we’re only just beginning to understand their peculiarities. The question of whether anything can “escape” the gravitational pull is an especially knotty one — it seems as if they DO give off some radiation. Stephen Hawking, for instance, has proposed “Hawking radiation” as a possible explanation.
    Briefly, it goes something like this: empty space isn’t really empty. There are “virtual particle” matter/antimatter pairs that continually pop into existence for fractions of a second before annihilating into radiation. (Google the Casimir Effect for an interesting experiment demonstrating this phenomenon.) If a particle pair pops out near a black hole, and one particle falls in, the black hole must emit the remaining particle’s (tiny) mass as radiation in order for energy to be conserved. That’s why black holes eventually evaporate over very long periods of time — depending on their size. The mini-black holes that might be created in the Large Hadron Collider are so small, they would evaporate in fractions of a second… which is probably a very good thing. 🙂
    I’m sure some of my readers/commenters can shed more light on this phenomenon, particularly the X-ray bursts, which are _not_ (I don’t think) Hawking radiation — they’re too intense for that. The point of the above is that, where black holes are concerned, there’s a great deal we don’t know yet, and the crafty supermassve objects are constantly surprising us with new twists. I do know those x-rays are one of the ways we know there’s a black hole at the center of the Milky Way, and probably most other galaxies, too.
    And Chad, asking a poor post-doc to explain the hot chocolate effect on his toes is just, well, cruel. 🙂

  5. X-ray bursts are indeed, as Jennifer Ouellette suspected, not Hawking radiation. They’re an awful lot brighter than the Hawking radiation from a typical black hole, because the Hawking temperature of the hole depends inversely on the hole’s mass. If you want the exact formula, it’s equation 16.120 in Zwiebach’s **First Course in String Theory**:
    T = (hbar * c^3) / (8 * pi * k * G * M).
    In this formula, “hbar” is Planck’s constant, c is the speed of light, k is Boltzmann’s constant, G is the strength of gravity (Newton’s constant) and M is the black hole’s mass. If you’d rather know the mass necessary to have a given Hawking temperature, just swap M and T in the formula. Doing a quick back-of-the-envelope calculation, I get that to be as warm as the cosmic microwave background (2.7 kelvins), a black hole must have a mass of about 4.6e22 kilograms, or 0.77% the mass of the Earth (2.3e-8 solar masses). A black hole formed by a collapsing star will be **much** bigger and hence much colder than this. If a black hole is sitting in otherwise empty space, with no matter to feed it, the only thing it has to eat is cosmic microwave background photons.
    Just like a mug of hot chocolate on a cold day, a black hole will emit energy (via Hawking radiation) until it comes into thermal equilibrium with its surroundings. Imagine for a moment that no matter is falling into the hole, so we only have to consider the CMB. If the hole is hotter than the CMB, we’ll see a net energy flow outward; in order to be this hot, the hole must be small (and the smaller it gets, the hotter it grows). However, a large hole is colder than its surroundings, so the energy flow will go the other way.
    The X-ray emissions come from the matter falling into the hole. As the hole-food spirals inward, forming an accretion disk, it gets squeezed, and it heats up. Big gulps of matter lead to big flashes of X-rays. Let me see. . . aha, thank you NASA:
    http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html

  6. I forgot to say:
    If you want to figure out how long it takes for a hole of a given starting mass to go “boom”, all you need to do is take the Hawking temperature, use the Stefan-Boltzmann Law to calculate the radiant power (which goes as the fourth power of the temperature), multiply that by the surface area given by the Schwarszchild radius and write a differential equation in terms of the black hole mass. Simple! 🙂

  7. Phil may be using time travel to post. Has he responded to anyone since? Computers haven’t passed the Turing test yet…
    You could use time travel for the Seahawks. Best Buy sells camcorders and VCRs, for example.
    This light echo thing is a way of doing time travel, for instruments like Chandra, and other scopes. And that’s for instruments that always look into the past. A search for SN1987a light echoes turned up two or three other super nova light echoes. Very cool stuff.
    I like this particular experiment. I’ll have to try it. Then drink it. I’ve got a packet in my desk drawer. I can switch from my insulated mugs to one that rings.
    Too bad for the Mercurians, though. I’d rather have a nearby event on the horizon than a nearby event horizon.

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