Sheldon, Leonard, Raj and Howard have finally returned from their National Science Foundation expedition above the Arctic Circle, having been away from the apartment (and us) for the past three months. Even the whiteboards in their apartment have not changed–they are as they were left in the season finale. Sheldon is ecstatic about their trip, convinced the data he’s collected will win him a Nobel Prize. Sheldon has finally observed a signal of magnetic monopoles.
Or has he? Sheldon is a theorist, not an experimentalist. We saw Sheldon’s experimental skills on display back in the fighting robots episode–he could not even open the toolbox. An experimentalist is always on the lookout for stray signals, or “noise”. Every discovery is not initially met with shouting and champagne as one might expect, but close consideration of every recorded signal as a mundane process that could possibly be noise fooling the apparatus. The process can take years.
A few years ago, I was taking data with some electronics we set up with scientists from the Jet Propulsion Lab in the pedestal of their large (230-foot diameter) radio telescope. We designed the electronics to look for neutrinos, but by design the apparatus would record a signal, most likely an uninteresting background, about once every six minutes. But there was something else going on. Sometimes we would see a burst of signals recorded at once. Could it be that neutrinos were arriving in bursts? Ultimately it turned out to occur whenever someone sat in a particular chair. When its wheels passed over a speck of dirt on the floor, the weight would compress it slightly and cause a tiny spark, much like how a piezoelectric cigarette lighter works. That was a source of electrical noise. With a quick tweak to the electronics, we were on our way with no more chair-trigger events.
Coming back to Sheldon’s experiment, some time ago an experiment at Stanford saw a beautiful magnetic monopole candidate. The induced current in a loop of superconducting wire took a sudden jump, as measured by the magnetic flux through the loop. The event became famous:
Other experiments sometimes noticed that such jumps could be produced by ordinary electrical noise: interference, perhaps from spark plugs, or, as Sheldon eventually finds out, from a nearby small motor. An electric motor constantly makes and breaks electrical contact with small brushes that carry the current from a spinning wheel. These interruptions in the circuit can make a very tiny spark, and thus produce a spurious electrical signal, noise. You can sometimes hear these on your AM radio as static. Still, the Stanford event was special because the change in current was exactly the value expected from a magnetic monopole. The experimenters were absolutely first-rate and took pains to show they were not subject to stray electrical noise. A monopole was never seen again. But the world’s one candidate has never been disproved either.