Archive for January, 2009

Magic Mirror

Making magnetic monopoles, and other exotica, in the lab

Physicist Shou-Cheng Zhang has proposed a way to physically realize the magnetic monopole. In a paper published online in the January 29 issue of Science Express, Zhang and post-doctoral collaborator Xiao-Liang Qi predict the existence of a real-world material that acts as a magic mirror, in which the never-before-observed monopole appears as the image of an ordinary electron. If his prediction is confirmed by experiments, this could mean the opening of condensed matter as a new venue for observing the exotica of high-energy physics.

This is Who Watches the Watchers

When You Watch These Ads, The Ads Check You Out

Watch an advertisement on a video screen in a mall, health club or grocery store and there’s a slim – but growing – chance the ad is watching you too.

Small cameras can now be embedded in the screen or hidden around it, tracking who looks at the screen and for how long. The makers of the tracking systems say the software can determine the viewer’s gender, approximate age range and, in some cases, ethnicity – and can change the ads accordingly.

When the Night has Come, and the Land is Dark

Movie Trivia: Stand By Me

Jerry O’Connell (Vern) had never really acted before – he had just one commercial under his belt. When he auditioned, he recognized Rob Reiner and said, “Aren’t you the guy on channel 5?” At the time, the local channel 5 had been airing reruns of All in the Family at the time and Jerry recognized Rob as Meathead.

(BTW, John Lennon’s cover of this song is pretty good)

On a Wing and a Prayer

I’ll link to this before the day of the big game this time.

Buffalo Hot Wing Dip

Spiting Your Face

Terrorists may use Google Earth, but fear is no reason to ban it

Criminals have used telephones and mobile phones since they were invented. Drug smugglers use airplanes and boats, radios and satellite phones. Bank robbers have long used cars and motorcycles as getaway vehicles, and horses before then. I haven’t seen it talked about yet, but the Mumbai terrorists used boats as well. They also wore boots. They ate lunch at restaurants, drank bottled water, and breathed the air. Society survives all of this because the good uses of infrastructure far outweigh the bad uses, even though the good uses are – by and large – small and pedestrian and the bad uses are rare and spectacular. And while terrorism turns society’s very infrastructure against itself, we only harm ourselves by dismantling that infrastructure in response – just as we would if we banned cars because bank robbers used them too.

Hot Dog Etiquette

The Slaw of the Land: West Virginia Hot Dog Map

Cole slaw on hot dogs? Ugh.

[I]t has this to say about ketchup on hot dogs: “There are many reasons why one shouldn’t eat ketchup on a hot dog any hot dog.First, the National Hot Dog and Sausage Council’s Hot Dog Etiquette rules dictate that no one over 18 should ever eat ketchup on a hot dog. Ketchup is destructive of all that is right and just about a properly assembled hot dog since its sweetness and acidic taste overpowers food and disguises its true flavor.”

Yes, there is a National Hot Dog and Sausage Council, and they do have etiquette rules. I guess I’m an outlaw or a rebel, because I like ketchup. (Cole slaw is OK, but ketchup is taboo?) But the actual admonishment is “Don’t use ketchup on your hot dog after the age of 18.” I never eat 18-year-old hot dogs, though. That would just be weird.

The House that Wasn't There

As I was going up the stair
I saw a man who wasn’t there
He wasn’t there again today
Oh, how I wish he’d go away…

Hughes Mearns

Laser-cut art book by Olafur Eliasson

[A] laser-cut negative space rendering of his house in 85:1 scale


This Never Happens to the Other Particles

The Secret Lives of Photons

Measuring Bilbo

How do you measure the properties of something that’s really hard to detect? It turns out that because of the wonderful usefulness of conservation laws, you can infer what you can’t easily see by finding as much as you can from what you can detect, and then figuring out what’s left over. Somewhat like detecting the invisible Bilbo Baggins by spotting his shadow. The original discovery of the neutrino, in fact, was due to the beta energy spectrum being continuous, which only makes sense if there is a third particle being emitted, and conservation of charge dictated that the neutrino be neutral.

Ultra-Cold Atoms and Neutrino Masses

The proposed experiment is to trap a large amount of tritium at very low temperatures (meaning that the atoms are very nearly stationary), and look at the recoil of the helium that’s produced. When the tritium decays into helium, one of two things happens: either the helium captures the electron on the way out, becoming neutral helium, in which case the atom recoils in a direction opposite the direction of the neutrino; or the electron and neutrino both escape, in which case the helium ion recoils in a direction that depends on the exit direction of both the electron and the neutrino. In either case, the helium is moving, and if everything is done right, it’s moving considerably faster than the trapped tritium atoms.

To measure the neutrino mass, then, all you need to do is detect the helium and measure both the magnitude and direction of its velocity. If the electron was captured, that alone is enough to let you find the momentum (and thus mass) of the neutrino; if the electron escaped, you need to determine its velocity as well, but again, you can calculate the momentum of the neutrino.

Unfortunately the link to the Physics World article doesn’t work work for me, since it’s subscription-only. Fortunately Chad also provides a link to the ArXiv proposal

This sounds very familiar to me, since measuring the recoil from beta decay is the experiment I worked on as postdoc at TRIUMF. The idea in that experiment (for a metastable K-38 atom decaying to Ar-38, both with zero-spin nuclei) is that the parent decays and the daughter is no longer held in the trap, so the escaping beta and daughter can be detected. If the beta and Ar have traveled in opposite directions, it means the neutrino must be either counter-propagating or co-propagating with the beta, since there has been no change in the spin of the nucleus; this has implications for the type of weak interaction that has taken place (scalar or vector, i.e. does the W-boson have any spin) but each case has a different implication for the amount of recoil the Ar atom will have, and this shows up in the time-of-flight. The standard model predicts that, in this case, the beta and the neutrino will be emitted in the same direction. Here’s a PRL and ArXiv for that experiment.

In one approach of the Tritium experiment they’re banking on the electron being captured, so you remove the three-body complication, and having a metastable helium recoil to detect (rather than neutral Helium, which is a lot harder), but adding the complication of photons to detect as the He decays into that metastable state. The other approach involves the three-body momentum, in which the emitted beta is not captured. This allows them to detect a Helium ion, which is much easier to do.

Risky Business

The benefits of teaching the statistics of risk analysis.

Probability lessons may teach children how to weigh life’s odds and be winners

“You can tick off story after story that’s probably interesting to the people it happened to, but not statistically unusual at all. There was a recent story about a family in Gloucestershire with three children all born on January 29. We were contacted by a journalist and asked what are the chances of this happening.

“The chances are about one in 135,000, or seven in a million. But there are a million families with three children in the UK. So it’s almost certain that this family is not unique and when the story went online, someone wrote in and said, ‘I was born on the same day as my two brothers’.”


The unfounded scare over the MMR vaccine, and outlandish claims of success for alternative medicines, were prime examples.“One must think all the time of what is not being reported – the dog that didn’t bark. When we see a hole-in-one video on YouTube we are sensible enough to know that this has been selected out of millions of shots that missed. We need to think the same way every time we hear of someone claiming that some new treatment has cured them.”


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