Published by the Students of Johns Hopkins since 1896
December 8, 2021

Neutrinos may have broken Einstein's speed limit

By Mali Wiederkehr | September 28, 2011

Einstein's theory of relativity, which states that particles cannot travel faster than the speed of light, has been a bedrock of our understanding of modern physics for the last 100 years. However, recent research suggests that particles known as neutrinos are potentially capable of exceeding this speed.

Scientists at the CERN laboratory in the Franco-Swiss border shot neutrinos a distance of 730 km to Italy's INFN Gran Sasso laboratory and measured their speed to be 20 parts per million faster than the speed of light. The experiment took three years to complete and sent over 15,000 neutrinos to travel underground between the two laboratories.

The surprising findings of this Oscillation Project with Emulsion-tRacking Apparatus (OPERA) experiment cannot be attributed to a faulty experimental design; scientists have noted that the experiment was performed with extreme precision and statistical accuracy. The error reported was also incredibly small — an uncertainty of a mere 20 cm over the 730 km range that the neutrinos travelled.

Nevertheless, the reaction of the world-wide physics community has been highly skeptical of the findings. "Fundamentally, I think the OPERA experiment is wrong. In fact, I haven't yet met any physicist who believes the result," Barry Blumenfeld, an experimental physicist at Hopkins who is currently involved with experiments at CERN, wrote in an email to The News-Letter.

Given that the experiment took three years to complete, it could take a long time before other research laboratories replicate its findings.

Ongoing research on neutrinos includes an experiment called MINOS which shoots neutrinos from Chicago to Northern Minnesota, covering approximately the same distance as the CERN experiment. The results of this experiment were published four years ago, but the uncertainties were too large and thus inconclusive. Blumenfeld believes that MINOS will try to repeat the experiment in the future.

There is also an ongoing neutrino experiment in Japan which covers a shorter distance than that of the CERN experiment.

Neutrinos are subatomic entities that exhibit both particle and wave-like characteristics. They are electrically neutral and therefore untouched by the electromagnetic forces affecting electrons.

"We know that neutrinos come in three varieties as far as interactions are concerned and that neutrinos appear to have a very small mass but we don't know yet what the value of the masses are. They only interact by the weak nuclear force (and presumably gravity). They have spin of ½," Blumenfeld wrote.

Particles with the ability to travel faster than speed of light are termed tachyons. Scientists have searched for these particles, but have not found them experimentally.  

Neutrinos can potentially be the first-ever particles to have surpassed the speed of light. The validity of the experiment cannot be confirmed until it is replicated elsewhere. If the results do hold, neutrinos may suggest the existence of extra dimensions.

"Physicists have been considering the possibility of extra dimensions for many years," wrote Blumenfeld, "If, somehow, the neutrinos take a little short-cut through an extra dimension that's one possibility."


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