Physics
drorzel | February 22, 2006Buried beneath some unseemly but justified squee-ing, Scalzi links to an article about "counterfactal computation", an experiment in which the group of Paul Kwiat group at Illinois managed to find the results of a quantum computation without running the computer at all. Really, there's not much to say to that other than "Whoa."
The article describing the experiment is slated to be published in Nature, so I don't have access to it yet, but I'll try to put together an explanation when I get a copy. The experiment involves a phenomenon know as the "Quantum Zeno Effect," though, which deserves a…
drorzel | February 19, 2006A preliminary report on the standings in the Greatest Physics Experiment voting:Michelson-Morley: 13Faraday: 7 (including one vote in the Farady post)Roemer: 5Aspect: 4.5 (one indecisive person voted for both Cavendish and Aspect)Galileo: 3Rutherford: 3Cavendish: 1.5Hertz: 1 (in the comments to the Hertz post)Newton, Hubble, and Mössbauer are currently getting shut out.
Voting will remain open for another couple of days, so if you're a backer of somebody other than Michelson and Morley, you've still got time for a late charge: round up some friends, and get out the vote.
drorzel | February 16, 2006The Top Eleven is now complete. Here's the full list of experiments, with links to my summaries:Galileo Galilei: ~1610: Discovery of the moons of Jupiter, and measurements of the acceleration of falling objects.Ole Roemer ~1675: Measurement of the speed of light by timing the eclipses of Io.Isaac Newton ~1700: Dispersion of light and measurements of circulating fluids.Henry Cavendish, ~1797: Measurement of the gravitational constant G.Michael Faraday ~1831: Discovery of electromagnetic induction.Michelson and Morley ~1887: Disproving the existence of the luminiferous aether.Heinrich Hertz ~…
drorzel | February 16, 2006The final and most recent of the Top Eleven is an experiment that goes right to the heart of the weirdness inherent in quantum mechanics.
Who: Alain Aspect (1947-present), a French physicist. (Again, Wikipedia is a let-down, but CNRS has useful information.)
When: Around 1982 (there are several experiments involved, but the 1982 one is cited by most people).
What: His group performed the first experimental tests of Bell's Inequality, which shows that the predictions of quantum mechanics cannot be explained by a "local hidden variable" theory. Explaining that will take some space, so I'll…
drorzel | February 15, 2006A continuation of the lecture transcription/ working out of idea for Boskone that I started in the previous post. There's a greater chance that I say something stupid about quantum measurement in this part, but you'll have to look below the fold to find out...
At the end of the previous post, I wrote:We can verify this by doing the experiment with single particles, and what we see is exactly the prediction of quantum theory. If we send one electron at a time toward a set of slits, and detect the electron position on the far side, we see individual electrons arriving one at a time, in an…
drorzel | February 14, 2006I'm teaching our sophomore-level modern physics course this term, which goes by the title "Relativity, Quantum Mechanics, and Their Applications." The first mid-term was a couple of weeks ago, on Relativity (special, not general), and the second mid-term is tomorrow, on Quantum Mechanics, and then we get three weeks of applications (basically, whatever topics out of atomic, molecular, solid state, nuclear, and particle physics I can manage to fit in).
I like to end the quantum section with one lecture on superposition and measurement, which isn't covered particularly well in the book. It's…
drorzel | February 13, 2006The penultimate experiment in the Top Eleven brings us up to the first nominee who's still with us..
Who: Rudolf Moessbauer (1929-present) (that's Mössbauer with a heavy-metal ö), a German physicist. (The Wikipedia link is for consistency with the other posts, but contains very little information. A better bio is available from the Nobel Prize site.)
When: 1957-58.
What: This one requires a bit of background, so there will be more below the fold, but basically, he's nominated for discovering an effect that makes it possible to do precision spectroscopy of nuclear transitions.
Spectroscopy is…
drorzel | February 10, 2006The next experiment in the Top Eleven is a set of observations, not an experiment.
Who: Edwin Hubble (1889-1953), an American astronomer, and the guy the Hubble Space Telescope is named after.
When: He was nominated for two related but different discoveries which were announced in 1924 and 1929.
What: Hubble's most famous work concerns galaxies: first, he proved that they were, well, distant galaxies, and then he showed that they were receding from us with a velocity proportional to their distance, which is the first piece of evidence leading to the Big Bang model of the universe. (More after…
drorzel | February 9, 2006In a comment to the AP post, "hogeb" asks an excellent question about pedagogy:
I'd like to enlist your advise and the advise of any readers who can provide it. I teach physical science to pre-service elementary school teachers. I try to elucidate the somewhat subtle differences between the application of a force and the just getting in the way of, among other things, and I try to point out why this isn't just semantics but truly important conceptual skills. I'm not sure they hear me, or how well they hear me, they rarely do well on these questions on my tests. If you can try to go back to…
drorzel | February 8, 2006Kevin Drum reports receiving an email from a professor of physics denouncing the Advanced Placement test in Physics:It is the very apotheosis of "a mile wide and an inch deep." They cover everything in the mighty Giancoli tome that sits unread on my bookshelf, all 1500 pages of it. They have seen not only Newtonian mechanics but also optics, sound, electromagnetic theory, Maxwell's equations, special relativity, quantum mechanics and even AC circuits. They don't understand any of it, but they've seen it all. They come into my class thinking, by and large, that objects move due to the force of…
drorzel | February 8, 2006The eighth of the Top Eleven is an experiment by the man who set the gold standard for arrogance in physics.
Who: Ernest Rutherford (1871-1937), a New Zealand-born physicist who famously declared "In science, there is only physics. All the rest is stamp collecting." He was awarded the Nobel Prize in Chemistry in 1908.
When: He's nominated for the alpha-particle scattering experiments that showed the existence of the nucleus, an 1909.
What: Rutherford is famous for carrying out early experiments with radioactive substances. Among other achievements, he coined the terms "alpha, beta, and gamma…
drorzel | February 7, 2006There was an article about physics blogs a little while back in Physics World, that didn't mention me by name, but did link to the Steelypips site. It mostly talks up the informal information exchange side of things.
In that spirit, here are some things I found via physics blog (mostly through Mixed States (after the cut):
If you were wondering when to expect your pony, Steinn Sigurdsson at Dynamics of Cats has an exhaustive analysis of the budget requests of various science agencies (start with that link, and work your way up through the more recent posts). Verdict: no pony for you!
Former…
drorzel | February 7, 2006The seventh entry in the Top Eleven is an experiment that leads directly to all forms of wireless communications.
Who: Heinrich Rudolf Hertz (1857-1894), a German physicist.
When: 1886
What: Hertz studied electromagnetism, and in particular, the prediction from Maxwell's Equations that it ought to be possible for electromagnetic waves to travel through free space. Today, this is a simple demonstration-- you grab a couple of loops of wire, a signal generator, and an oscilloscope, but in 1886, it required the invention of a good deal of apparatus.
In order to show that electromagnetic waves…
drorzel | February 3, 2006(Because, as anybody knows, that's the answer to "Pop Quiz, Hotshot"...)
The answer to the pop quiz posted below is "v." That is, the speed is unchanged between the start of the problem and the collision between the ball and the pole. There are several ways to see this-- conservation of energy is my usual approach (the only energy at the start of the problem is the kinetic energy of the ball's motion, and nothing else in the problem takes up any energy, so you've got to have the same kinetic energy at the end)., but I really like Ross Smith's dimensional analysis argument. If I were giving…
drorzel | February 2, 2006I play pick-up basketball at lunchtime a couple of days a week (in a good week, anyway). It's become a running joke that after a particularly long or hard-fought game, I'll announce my intention to give a pop quiz that afternoon in class. "Just work quietly at your desks, folks. I'm going to sit here and drink Gatorade."
I'm going to turn the joke around a little for the purposes of blogging: this week is an exceptionally busy week for me, as on top of the backlog of grading that piled up last week when I was sick, I'm teaching the junior/senior level lab course for the next two weeks, and I…
drorzel | February 1, 2006The next experiment in the Top Eleven is probably the most famous failed experiment of all time.
Who: Albert Michelson (1852-1931) and Edward Morley (1838-1923), American physicists.
When: Their first results were reported in 1887.
What: The famous Michelson-Morley experiment, which tried and failed to detect the motion of the Earth through the "luminiferous aether." At the time, light waves were believed to be disturbances in some medium that permeated all of space, and was fixed in an absolute sense. In this picture, objects moving through space should also be moving relative to the aether…
drorzel | January 30, 2006Next up in the Top Eleven is a man who is largely responsible for the fact that we have electricity to run the computer you're using to read this.
Who: Michael Faraday (1791-1867) a poor and self-educated British scientist who rose to become one of the greatest physicists of the 19th Century.
When: Around 1831.
What: Faraday's main achievement was the discovery of Faraday's Law (obviously), one of "Maxwell's Equations" describing the behavior of electric and magnetic fields (in a certain sense, Maxwell was a master of PR-- he took a bunch of equations that other people had already discovered…
drorzel | January 27, 2006This is true.
A guy I knew in graduate school, he had a buddy who was working late in the lab one night. He was all alone, and he got a little bored, so he took a two-liter soda bottle, and he filled it halfway up with liquid nitrogen. Then he screwed the cap on tight.
Now, liquid nitrogen, when it boils, it takes up something like 700 times the volume of the liquid. So this guy, he's got this bottle, and he's kicking it around in the hall. But the bottle starts to swell up, so he tries to open the cap, and it's stuck. So he runs into the bathroom, and he dumps it in a sink, and runs back out…
drorzel | January 27, 2006Next up in the Top Eleven is an experiment whose basic technique is still in use today.
Who: Henry Cavendish (1731-1810), a British scientist who made a number of discoveries in physics and chemistry, but received credit for very few of them.
When: 1797.
What: Cavendish's modern claim to fame is the torsion pendulum experiment, an idea that originated with John Michell, who died before completing it.
The apparatus for the famous experiment, shown at left, consists of a dumbell-shaped pendulum hung from a very fine wire. Two larger masses (Cavendish used 350 lb lead spheres) are brought near…