[time-nuts] distribution of precision time via fiber networks

Daniel Schultz n8fgv at usa.net
Sat Sep 1 18:47:17 EDT 2018

Make sure that your fiber optic connectors are properly mated, or else this
could happen to you:
Loose Cable May Unravel Faster-Than-Light Result
Science  02 Mar 2012:
Vol. 335, Issue 6072, pp. 1027
DOI: 10.1126/science.335.6072.1027 

Anomalous data suggesting that neutrinos can travel faster than light probably
resulted from a faulty connection in a GPS timing system, physicists from the
OPERA collaboration revealed last week. Scientists who wish not to be
identified say a few persistent OPERA researchers spotted the problem during
tests the collaboration's leaders at first opposed.

OPERA, or Oscillation Project with Emulsion tRacking Apparatus, is a particle
detector housed under the Gran Sasso mountain in central Italy. In September
2011, 171 scientists from the international collaboration announced that
thousands of measurements made between 2009 and 2011 seemed to show that
neutrinos from the CERN laboratory near Geneva, Switzerland, were reaching
Gran Sasso some 60 billionths of a second (60 nanoseconds) earlier than light
would—a finding at odds with Einstein's special theory of relativity
(Science, 30 September 2011, p. 1809). In November, measurements with shorter,
easier-to-time pulses confirmed the anomaly, but many physicists remained
skeptical (Science, 2 December 2011, p. 1200).

That skepticism has grown with the latest announcement. From December 2011
until a couple of weeks ago, a small group of OPERA researchers carefully
measured how much time it takes light pulses to travel along an 8-kilometer
optical fiber that connects an external GPS receiver to the Gran Sasso
laboratory. The “time stamps” encoded by these pulses are also sent to
CERN to synchronize timing at the two labs, but the time that the pulses take
to travel along the fiber must be added to the time stamp to ensure that the
neutrinos' arrival times are recorded accurately.

The investigators discovered that the pulses' transit time varied by several
tens of nanoseconds depending on how tightly the coaxial fiber cable was
plugged into a socket attached to a card inside the experiment's master-clock
computer. The card converts the light pulses into electronic signals. Any
loose connection was supposed to stop the pulses from being registered, but
instead it appears that the card allowed the delayed pulses to get through. So
a loose connection during the experiment would have stamped neutrino pulses
with arrival times suggesting faster-than-light travel. Although researchers
can't be sure the cable was loose during the experiment, the size of the
delays involved is highly suggestive.

The travel times of pulses along the fiber had been measured in 2008 by
collaboration member Dario Autiero of the University of Lyon in France. A
source familiar with the experiment says some researchers thought the
measurement should have been rechecked before the neutrino velocity results
were submitted to a journal in November, but OPERA's scientific management
resisted carrying out such a check. 


More information about the time-nuts mailing list