In the second quarter of the 20th century, quantum theory faced some serious challenges, including unexplained details of atomic spectra and difficulties calculating basic properties of charged particles. In 1947 Willis Lamb and Robert Retherford of Columbia University discovered an unexpected detail in the hydrogen spectrum, later called the Lamb shift, that became an essential clue in solving both problems. The measurement agreed with new calculations and was the first indication that the theoretical approach called renormalization could resolve the mathematical infinities that had threatened to derail the progress of quantum mechanics.
Archive for July, 2012
Towards the end, Hacker’s reasoning gets just bizarre. He keeps emphasising how important “citizen statistics” is. I’m baffled as to how one could teach statistics in any useful way without the material he wants to throw out! Prerequisites: we needz them. “Is Algebra Necessary?” If you want to do statistics or economics, yes, it is.
One thing Blake doesn’t address (perhaps it’s in one of the links he provides) is part of the larger picture: the idea that because students are not graduating, we should lower the bar. Which makes a diploma quite meaningless; they are not simply participation awards.
edit: PZ Myers does bring it up in his post
So last week I posted a bit about Han-Solo-in-Carbonite ice trays, and ordered one (along with some NERF armament). I didn’t have any chocolate around to try that suggestion, but I was able to make some pats of butter, which would be fun if you had a Star Wars dinner party. Or something. Spread on some Millennium Falcon-shaped English muffins!
Not sure what the best technique is. This was softened and scraped into the mold and then zapped in the microwave for 10 seconds, because I wasn’t sure the butter was quite soft enough to fill the body features.
When trekking through a forest in French Guiana to study termites, a group of biologists noticed unique spots of blue on the backs of the insects in one nest. Curious, one scientist reached down to pick up one of these termites with a pair of forceps. It exploded. The blue spots, the team discovered, contain explosive crystals, and they’re found only on the backs of the oldest termites in the colony. The aged termites carry out suicide missions on behalf of their nest mates.
On the night of July 20, 2012, the laser system of the Berkeley Lab Laser Accelerator (BELLA), which is nearing completion at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), delivered a petawatt of power in a pulse just 40 femtoseconds long at a pulse rate of one hertz – one pulse every second. A petawatt is 10^15 watts, a quadrillion watts, and a femtosecond is 10^-15 second, a quadrillionth of a second. No other laser system has achieved this peak power at this rapid pulse rate.
Impressive. Multiplying the two, we see that this is ~40 Joules of energy per pulse, which isn’t a lot of energy, but getting the pulses short and repeating them is the hard part. Lots of interesting things happen when you get a large energy density — there are nonlinear processes that depend on some exponent of field strength.
Today, we know that persistence of vision does not work like the progenitors of film thought it did (the retina does not retain images like Dr. Paris and others theorized), and many movies are filmed in 3-D and displayed on screens that are sometimes five stories tall. But as the technology of moving images has progressed and the group experience of attending a film has gotten increasingly sophisticated, a parallel trend has emerged, namely, to permit anyone to watch anything, anywhere, on a tiny cell phone. Curiously, this medium that was once limited to the single viewer appears to be circling back to that one-at-a-time format. The irony is not lost on Balzer. “It’s a very interesting loop,” he says, pun intended.
Seeing as this is a bug-a-salt, the most powerful salt gun in the world, you have to ask yourself one question … do I feel lucky.
A little BotE calculation: flies are of order 1 cm, and salt grains around 100 microns. Scale this up to human size and it’s like being hot by a chunk of salt 15-20 mm across, or around 75 caliber. At a pretty decent clip, too. So, ouch! And several chunks, really, so (n * ouch), which is why it can do in the fly. I may have to break down and get one of these and use my slow-motion camera to measure the muzzle speed. All in the name of science, of course.
h/t to Moontanman
A positive cloud-to-ground lightning flash triggers upward positive lightning leaders to form from three television towers in Rapid City, South Dakota. Filmed at 9,000 images per second, the video shows positive leaders descending from the thunderstorm with one connecting to ground. The resulting return stroke creates a fast electric field change which causes three tall television towers to initiate upward positive lightning leaders. Fast, short duration, bidirectional/bipolar recoil leaders form on positive leader branches that become cutoff from their main channel.
Video I linked to last week was “only” 7207 fps.