Not faster than light after all!

Shubashree Desikan
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Neutrinos Vs Light:The globe of the European Organization for Nuclear Research, CERN, is illuminated outside Geneva, Switzerland.
Neutrinos Vs Light:The globe of the European Organization for Nuclear Research, CERN, is illuminated outside Geneva, Switzerland.

Our Physics textbooks teach us that nothing travels faster than light. A recent controversy in the scientific community led to some scientists questioning this theory but the issue has now been resolved. Light particles do travel the fastest.

Ten days ago, Antonio Ereditato – a professor of high energy physics leading the OPERA experiment – resigned from his post as spokesperson, after the claim that neutrinos travel faster than light was disproved.

Neutrinos have been in the news on and off and have also enjoyed the attention of science fiction writers. Isaaac Asimov in his story, ‘The Dead Past', spoke of neutrinos travelling backwards in time being used to make a machine that could look into the past. Recently, the scientific establishment witnessed happenings no less dramatic.

The drama began in September 2011. In a news report that sent waves across the world of physics Ereditato's team at the OPERA experiment claimed that they had measured the speed of a beam of neutrinos and they had found it to be higher than the speed of light. This claim shocked the world, because the fact that nothing can travel faster than light is at the root of Einstein's famous special theory of relativity. Many important scientific theories formulated in the last hundred years are based on the special theory of relativity. The fact that nothing can travel faster than light has also been observed in all high-energy particle physics experiments. The particle in question, the neutrino, is a very small and unassuming sort of particle. It has no mass and no charge and interacts very, very weakly with matter, unlike, for example, protons or neutrons. Neutrinos are produced in the sun in high-energy nuclear reactions and they travel down to earth without interacting with the matter in between. They may also be produced in the lab, by making a beam of high-energy protons collide with a carbon target.

What are neutrinos?

In the OPERA experiment, the physicists sent a beam of neutrinos from Switzerland's CERN laboratory to the Italian lab Gran Sasso, which was 730 km away, to study its properties. During the course of this experiment they measured the velocity of the neutrino beam and found it to be higher than the velocity of light, though by an extremely small value. Months of excitement and uncertainty followed.

The excitement came to a halt on 28 March this year when another team repeated the measurements and found that the results were disappointingly normal, and that the massless neutrinos did indeed travel exactly at the speed of light and not higher. The results of the earlier experiment had been caused by a faulty cable and flawed timing in the experiment's clock. Following months of tension, this negative result caused the members of the OPERA collaboration to vote for no confidence in Ereditato. After all the attention the team had gained in the last few months, Ereditato and Dan Autiero, OPERA's coordinator, had to step down from their posts.

  • OPERA stands for Oscillation Project with Emulsion tRacking Apparatus. It is a research experiment on neutrinos.

  • CERN is the European Organisation for Nuclear Research located near Geneva

  • The Gran Sasso lab in Italy is called the National Institute of Nuclear Physics

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