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kottke.org posts about physics
New Scientist recently compiled a list of
New Scientist recently compiled a list of strange substances (with accompanying video): ferrofluids, non-Newtonian liquids, superfluids, and materials that get thicker when stretched. (via bb)
Does free will exist? “The conscious brain
Does free will exist? “The conscious brain was only playing catch-up to what the unconscious brain was already doing. The decision to act was an illusion, the monkey making up a story about what the tiger had already done.”
“The Mpemba effect is the observation that,
“The Mpemba effect is the observation that, in some specific circumstances, hotter water freezes faster than colder water.” I remember hearing about this on an old episode of Newton’s Apple, but I think they never really got to the bottom of it on that show, which was highly disappointing to me at the time.
David Pogue and Boing Boing have been
David Pogue and Boing Boing have been ensnared by the airplane-on-a-treadmill problem we debated here last February. The airplane still takes off. :)
Physicists at the University of Washington are
Physicists at the University of Washington are hoping to use entangled photons to send information back in time. “Here’s where it gets weird.”
Man tries to jump the mile-wide St.
Man tries to jump the mile-wide St. Lawrence River in a rocket-powered Lincoln Continental. I don’t want to spoil the result for you, but the concepts of gravity, force, and aerodynamics are fairly well established and understood, so why did anyone involved ever think that this jump was even close to possible?
Stephen Hawking is making an Imax 3D
Stephen Hawking is making an Imax 3D film about “cosmology and the meaning of existence”. The film “will be like Groundhog Day meets Star Trek”.
Jim Holt reports on a pair of
Jim Holt reports on a pair of books that argue that string theory is hurting theoretical physics. The article contains a good overview of the history and current status of the theory. For those looking to discover which book is better, Holt recommends Smolin’s The Trouble with Physics.
Nobel Prize winning physicist Gerard ‘t Hooft
Nobel Prize winning physicist Gerard ‘t Hooft on how to become a good theoretical physicist. He lists the subjects you need to learn (from languages to quantum field theory) and resources (both online and off) for learning them. A note on the ‘t in his name.
Satellites measuring the earth’s gravity from orbit
Satellites measuring the earth’s gravity from orbit detected a change in gravity from the massive earthquake that caused the tsunami in the Indian Ocean. “The gravity at the earth’s surface decreased by as much as about 0.0000015 percent, meaning that a 150-pound person would experience a weight loss of about one-25,000th of an ounce.”
This image of the participants of a 1927
This image of the participants of a 1927 conference on quantum mechanics sets the record for the most brainpower in one photograph. Schrodinger, Pauli, Heisenberg, Dirac, Compton, Bohr, Einstein, Planck, Curie, de Broglie, and Lorenz, all in one place.
Update: A Great Day in Harlem depicts several of the world’s top jazz musicians. More here. (thx, jim & greg)
On the heels of two books critical
On the heels of two books critical of string theory, a look at the string theory backlash.
Interesting tour/visualization imagining 10 dimensions. (thx, james)
Interesting tour/visualization imagining 10 dimensions. (thx, james)
Physicist Lawrence Krauss sums up his thoughts
Physicist Lawrence Krauss sums up his thoughts from a small conference he organized on the topic of gravity. “There appears to be energy of empty space that isn’t zero! This flies in the face of all conventional wisdom in theoretical particle physics. It is the most profound shift in thinking, perhaps the most profound puzzle, in the latter half of the 20th century.”
Vincent van Gogh painted turbulence quite accurately.
Vincent van Gogh painted turbulence quite accurately. Mexican scientists “have found that the Dutch artist’s works have a pattern of light and dark that closely follows the deep mathematical structure of turbulent flow”.
Spielberg’s new film…a wormhole movie based
Spielberg’s new film…a wormhole movie based on the work of Kip Thorne?
Italian scientists have created glass made out
Italian scientists have created glass made out of carbon dioxide. At high pressure, instead of forming a crystal (dry ice), the CO2 forms a clear, hard, vitreous material. More info. (Little known fact: I did research on glass in college, rubidium and cesium borosilicates mostly. Here’s a few citations on Google Scholar.)
Bill and Ted’s Excellent Adventure
I know I’m going to get mail about my five-star rating for this movie, but it cannot be helped. One summer when I was a kid, a friend and I watched Bill and Ted’s Excellent Adventure — no joke — every single day for a span of 2 months. I still know every line by heart, the timing, inflection, everything. If there were a Broadway production of this movie, I could slide effortlessly into the role of either Bill S. Preston, Esq. or Ted Theodore Logan, no rehearsal needed.
In my high school physics class my senior year, we had to do a report on something we hadn’t learned about in class — which, I discovered when I got to college, was a lot — and I did mine on time travel. I went to our small school library and read articles in Discover and Scientific American magazines about Stephen Hawking, Kip Thorne, quantum mechanics, causality, and wormholes. To illustrate the bit about wormholes, I brought in my well-worn VHS tape of Bill and Ted’s (a dub of a long-ago video rental) and showed a short clip of the phone booth travelling through space and time via wormhole. I got a B+ on my presentation. The teacher told me it was excellent but marked me down because it was “over the heads” of everyone in the class…which I thought was completely unfair. How on earth is Bill and Ted’s Excellent Adventure over anyone’s head?
Get yer Richard Feynman on at Google
Get yer Richard Feynman on at Google Video, particularly this 50-minute video of The Pleasure of Finding Things Out. A bit more Feynman at YouTube.
This is the most wonderfully nerdy thing
This is the most wonderfully nerdy thing I’ve ever read about politics and blogging. “So in fact, Reynolds has managed to fit five units of wrongness into only four declarative statements! This is the hackular equivalent of crossing the Chandrasekhar Limit, at which point your blog cannot help but collapse in on itself.” (via cyn-c)
Maybe the universe is a trillion years
Maybe the universe is a trillion years old and has experienced several big bangs and big collapses over the years. “People have inferred that time began then, but there really wasn’t any reason for that inference. What we are proposing is very radical. It’s saying there was time before the big bang.”
Science blog Cocktail Party Physics has a
Science blog Cocktail Party Physics has a list of “physics cocktails” in the sidebar (scroll down a bit). The Black Hole is “so called because after one of these, you have already passed the event horizon of inebriation.” Boy, am I a huge sucker for physics puns.
A moving mass has been shown to
A moving mass has been shown to generate a gravitomagnetic field (just like a moving electrical charge creates a magnetic field) and “the measured field is a surprising one hundred million trillion times larger than Einstein’s General Relativity predicts”. (via rw)
An Antarctic project has detected the first
An Antarctic project has detected the first neutrinos observed outside of a laboratory setting.
Still with the planes and conveyor belts
Now that I’ve closed the comments on the question of the airplane and the conveyor belt, I’m still getting emails calling me an idiot for thinking that the plane will take off. Having believed that after first hearing the question and formulating several reasons reinforcing my belief, I can sympathize with that POV, but that doesn’t change the fact that I was initially wrong and that if you believe the plane won’t take off, you’re wrong too[1].
The only thing is, I’m not sure how to prove it to you if you don’t understand the problem and the physics involved. I guess I could urge you to read the question and answer again carefully. I could tell you that not only does the conveyor belt not keep the plane stationary with respect to the ground but it *can’t* keep that plane stationary with respect to the ground[2] and once you know that, of course it’ll take off. My pal Mouser has a Ph.d in Physics from MIT and he says the plane will take off:
The airplane would take off normally, with the wheels spinning twice as fast as normal and a *slight* reduction in acceleration due to added friction.
Is that enough to convince you?
[1] This situation reminds me of Richard Dawkins’ and Jerry Coyne’s assertion that “one side can be wrong”.
[2] The motion of the conveyor belt does nothing[3] to affect the movement of the plane when the plane is in motion…it doesn’t matter if it’s moving forward, backward, at 2 MPH, or at 400 MPH. If the plane were on castors that could spin freely from side to side as well as front to back, that treadmill could be spinning 100 MPH to the left and the plane would take off.
[3] Well, almost nothing. The friction of the turning wheels will slow things down a bit, but not enough to not make the plane take off. After all, the main function of the wheels of a plane is to provide a near-frictionless interface with the ground (or whatever the plane happens to be taking off from).
Robert Birnbaum interviews physicist Lisa Randall about
Robert Birnbaum interviews physicist Lisa Randall about string theory and science popularizers.
How do you find extra-solar planets? “I
How do you find extra-solar planets? “I think the techniques employed by planet-hunters are pretty cool so the following is a brief primer on how the techniques work and the pros and cons of each.”
The case of the plane and conveyor belt
This question posed to Cecil at The Straight Dope has occupied most of my day today:
Here’s the original problem essentially as it was posed to us: “A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?”
I’ll give you a few moments to think about that before discussing the answer…
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Cecil says that the obvious answer — that the plane does not take off because it remains stationary relative to the ground and the air — is wrong. The plane, he says, can take off:
But of course cars and planes don’t work the same way. A car’s wheels are its means of propulsion—they push the road backwards (relatively speaking), and the car moves forward. In contrast, a plane’s wheels aren’t motorized; their purpose is to reduce friction during takeoff (and add it, by braking, when landing). What gets a plane moving are its propellers or jet turbines, which shove the air backward and thereby impel the plane forward. What the wheels, conveyor belt, etc, are up to is largely irrelevant. Let me repeat: Once the pilot fires up the engines, the plane moves forward at pretty much the usual speed relative to the ground—and more importantly the air—regardless of how fast the conveyor belt is moving backward. This generates lift on the wings, and the plane takes off. All the conveyor belt does is, as you correctly conclude, make the plane’s wheels spin madly.
After reading the question this morning and discussing it with Meg for, oh, about 3 hours on and off, I was convinced that Cecil was wrong. There’s no way that plane could take off. The conveyor belt keeps pace with the speed of the plane, which means the plane remains stationary from the POV of an observer on the ground, and therefore cannot lift off.
Then I read Cecil’s answer again this evening and I’ve changed my mind; I’m fairly certain he’s right. For a sufficiently long conveyor belt, that plane is taking off. It doesn’t matter what the conveyor belt is doing because the airplane’s energy is acting on the air, not the belt. I had better luck simplifying the problem like so: imagine instead of a plane, you’ve got a rocket with wheels sitting on that belt. When that rocket fires, it’s eventually going to rocket off the end of that belt…which means that it doesn’t remain stationary to the ground and if it had wings, it would fly.
What do you think? Can that plane take off?
See also Feynman’s submerged sprinkler problem and an old argument of Newton and Huygens: can you swim faster through water or syrup?
Update: Well, that got out of control in a hurry…almost 300 comments in about 16 hours. I had to delete a bunch of trolling comments and it’s not productive to keep going, so I closed it. Thanks for the, er, discussion and remember, the plane takes off. :)
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