The Fastest Object in the Universe

Q: What is the fastest moving thing in the universe, other than light or other types of electromagnetic radiation? I've always supposed that it would be the surface of some fast spinning Quasar, but I'm not sure.
Richard, Dayton, Ohio

A: Pulsars are certainly the fastest spinning star. Some spin so fast that a spot on their equator goes about 50 000 km/s, which is about 20% of light speed.

Probably the fastest moving thing known in the Universe is a neutrino (a fundamental particle akin to an electron, but much, much lighter).

At first, we weren't even sure neutrinos have mass, but now "the experimental evidence is definitive that they do," emails physicist Erik Ramberg of Fermilab. Ramberg tells the story:

The first evidence came from Ray Davis' underground experiment in South Dakota in the Homestake mine, looking at neutrinos coming from the Sun. Now that was a classic iconoclastic experiment! In the early 1970's, Davis struggled making incredibly delicate measurements that could measure a single radioactive atom in a vat of 100,000 gallons of cleaning fluid. He succeeded in extracting a few atoms of argon from the tank. The argon was produced by solar neutrinos, which demonstrated the Sun does indeed produce neutrinos, but only a third the number expected. Why only a third?

But do they have mass?
There were other supporting experiments, but most people regard the 1996 Super-Kamiokande's observation of cosmic ray neutrino oscillations to be the final proof that neutrinos have non-zero mass. Fermilab has recently confirmed their experiments: Fermilab sees the same oscillations in the laboratory.

Then the Sudbury Neutrino Observatory confirmed that the total number of neutrinos coming from the Sun was actually right on the prediction. They oscillate into different species on their way to Earth — thus explaining Ray Davis' old puzzling result. Only a third of the number reaching Earth stayed the same species on the way to Earth, but all actually made it to Earth.

Even more important, neutrinos can only change species if they have non-zero mass. And there you have it.

Ramberg continues the tale: These oscillation observations indicate that neutrinos have mass, but they only tell us the mass difference between the species. If that mass difference also indicates the absolute scale of neutrino masses, which is likely, then they weigh about 100,000 times less than an electron, which is already a pretty light particle.

Cosmic ray neutrinos are almost certainly the fastest piece of matter in the Universe.

Further Reading:

Ray Davis' solar neutrino experiments

The history of neutrinos, IceCube Neutrino Observatory

Neutrino physics, Science @ Berkeley Labs

(Answered July 14, 2008)