Tiny Enigmas Around Us

Neutrinos are electrically neutral subatomic particles that can pass through matter without being altered, and without being noticed. In fact, millions of them are passing through your body right now. Despite their somewhat elusive nature, theories suggest that they play a big role in shaping the universe, and are in fact, are the primary candidate in one explanation for dark matter—the Hot Dark Matter theory (although it is not believed to be dark matter on its own; the Cold Dark Matter theory is still needed).

In any case, neutrinos are one of the least understood fundamental particles in physics, and theories on them have been swinging from one side to the complete opposite throughout history.

For a long time, they were believed to have no mass. That was debunked. It was also first believed that neutrino types (electron, muon, and tau) were dictated by the origin of each specific neutrino. However, after several experiments showing results that conflict with this idea, more investigations ensued. And last year, a study conclusively disproved this original assumption, establishing that neutrinos oscillate, and are therefore in a state of superposition—one of the many models of quantum mechanics that completely conflict with the laws of classical physics.

This neutrino oscillation means they have no definite identities, or “flavors,” and change from one type of neutrino to another throughout its life. Last year, this study won authors Takaaki Kajita (University of Tokyo, Kashiwa, Japan) and Arthur B. McDonald (Queen's University, Kingston, Canada) a Nobel Prize in physics, just like the original study it disproved (and so did two other neutrino studies).

Quantum Effects on Macroscale

Now, physicists from MIT have conducted an experiment proving neutrino oscillation over hundreds of miles—the longest distance the effects of quantum mechanics were ever tested…and proven. The superposition took effect through hundreds of miles between Illinois and Minnesota.

The researchers used data from Fermilab's Main Injector Neutrino Oscillation Search (MINOS), an experiment that produces neutrinos by scattering other high-energy particles from a Chicago facility and emitted towards the Minnesota detector, 456 miles away. They have found that while the neutrinos left Illinois as one flavor, they may arrive in Minnesota as a completely different one.

"What's fascinating is, many of us tend to think of quantum mechanics applying on small scales," says David Kaiser, the Germeshausen Professor of the History of Science and professor of physics at MIT. "But it turns out that we can't escape quantum mechanics, even when we describe processes that happen over large distances. We can't stop our quantum mechanical description even when these things leave one state and enter another, traveling hundreds of miles. I think that's breathtaking."

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