Neutrinos and the speed of light

by Chris Marker 2011

The neutrino was first theorised to exist in 1930 by Wolfgang Pauli in order to preserve the conservation of energy, momentum and angular momentum in a type of radioactive decay known as beta decay. They were first directly detected in 1956 in the Cowan-Reines experiment where antineutrinos are created in a nuclear reactor. Later experiments showed that there are more than one type of neutrino. Today we know that there are electron neutrinos, muon neutrinos and tau neutrinos.

According to the standard model of particle physics, the model that describes the fundamental particles and their interactions, the neutrino should have no mass. Experiments in 1998 at the Super-Kamiokande neutrino detector showed that one type of neutrino can change into another type as they propagate through space, a process known as neutrino oscillation.  This oscillation requires that the neutrino must have some mass, something which can be incorporated into the basic framework of the standard model.

Experiments into the nature and interactions of neutrinos are a fertile area of physics research. This year the OPERA experiment, a collaboration between CERN in Geneva, Switzerland, and the Laboratori Nazionali del Gran Sasso (LNGS) in Gran Sasso, Italy, found some very surprising results whilst looking for its main goal - the production of tau neutrinos from muon neutrinos.

The OPERA experiment apparently found that the neutrinos, which travel 730 kilometres between the two laboratories, were arriving some 60 ns before they theoretically should do if they travelled at the speed of light. The neutrinos appear to be travelling faster than the speed of light. 

This result if true would have huge consequences for modern physics especially Einstein’s theory of relativity which says that nothing can travel faster than light. According to relativity as an object gets closer and closer to the speed of light its mass increases until it becomes so massive that there would not be enough energy in the universe to move it any faster. The result would break the famous E=mc2 equation.  

Many scientists have expressed their disbelief at these experiments. Indeed some scientists involved in the experiment withdrew their names from the pre print of the experiment as they were worried about the results and methods used. OPERA is currently rerunning its experiment in order to check results and next year other collaborations will also check the findings. 

Even if the results are confirmed it does not necessarily mean the end of relativity. One thing commonly overlooked is the fact that special relativity only says that nothing can cross the light speed barrier – if the neutrinos are originally created with a speed faster than that of light  there is no problem. Some scientists have also suggested that the neutrinos could be passing through wormholes in space time – literally a short cut between two places in space.

Whatever the final outcome of the experiments on neutrinos speed, the results has once again shown how thoroughly scientists check their findings and how when something truly unexpected happens the whole world takes notice.

Inspec covers all aspects of neutrinos and relativity

Control terms include

• neutrinos
• beta-decay
• standard model
• neutrino oscillation
• neutrino production
• general relativity
• special relativity

Classification include

• a1460G Neutrinos
• a1317 Neutrino oscillations
• a0330 Special relativity
• a0420 General relativity
• a1210C Standard model of unification
• a2340 beta decay; electron and muon capture