Neutrinos seemingly aren’t slowed by ‘spacetime foam’ | Science News


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One particle’s trek suggests that ‘spacetime foam’ doesn’t slow neutrinos

The nearly massless particles appear to travel at virtually the speed of light

7:00am, July 19, 2018
an illustration of a neutron being blasted from a blazar

SPEED TEST  A neutrino blasted from a bright galaxy known as a blazar (illustrated) along with a flare of light reveals that neutrinos travel at roughly the speed of light.  

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An intergalactic race between light and a bizarre subatomic particle called a neutrino has ended in a draw.

The tie suggests that high-energy neutrinos, which are so lightweight they behave as if they’re massless, adhere to a basic rule of physics: Massless particles travel at the speed of light.

Comparing the arrival times of a neutrino and an associated blaze of high-energy light emitted from a bright, flaring galaxy (SN Online: 7/12/18) showed that the neutrino and light differed in speed by less than a billionth of a percent, physicists report in a paper posted July 13 at

Massless particles — including the particles of light known as photons — consistently move about 300,000 kilometers per second, while massive particles move more slowly. Although neutrinos have mass, their heft is so infinitesimal that high-energy neutrinos travel at a rate effectively indistinguishable from that of light.

Some theories propose that a “spacetime foam” might slow particles of very high energies. The idea is that spacetime on extremely small scales is not smooth, but foamy. As a result, high-energy particles could get bogged down, as if moving through molasses. That effect could cause a significant difference between the speeds of the neutrino and the associated light, which would build up into a delay over the 4-billion-light-year trip from the neutrino’s home galaxy to Earth. But since the flare of light was spotted around the same time as the neutrino, there’s no evidence for such a discrepancy.

The result once again refutes a 2011 claim that neutrinos might travel faster than light. That measurement, made by a particle detector known as OPERA, was eventually determined to have been distorted by a loose cable (SN: 4/7/12, p. 9).


J. Ellis et al. Limits on neutrino Lorentz violation from multimessenger observations of TXS 0506+056. arXiv:1807.05155. Posted July 13, 2018.

Further Reading

E. Conover. A high-energy neutrino has been traced to its galactic birthplace. Science News Online, July 12, 2018.

D. Powell. Loose cable blamed for speedy neutrinos. Science News. Vol. 181, April 7, 2012, p. 9.

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