Last Fall 2011,
a consortium of scientists working at OPERA'S
Gran Sasso lab in central Italy uncovered a phenomenon they could not explain.
For several years flight data had been
collected
on nearly 16,000 neutrinos which are non-interacting and nearly massless
particles that can travel at immense speeds through anything. These neutrinos
originated in the SPS accelerator at CERN, near Geneva, and had traveled all
the way underground to Gran Sasso ~ about 450 miles away. The experiment demonstrated
that these neutrinos had traveled at
faster than light speed.
Researchers had gone to great lengths to remove error sources in the
measurements;
distances were measured
with a very high precision GPS named PolarX, time
was measured to an accuracy of one nanosecond using cesium clocks and an accounting
was made for tidal motion, Earth’s rotation, variations between day and night
and spring and fall, etc, etc. The statistical significance of the result was
six-sigma; in other words the probability that the result was a random error
was a one in a billion chance. In a meeting with a
roomful of physicists on
Nov. 2011,
Dario Autiero of OPERA was grilled on possible potential errors and he seemed to be able to account for all
of them.
Still physicists are skeptical
and
now the plan is to confirm these findings in separate experiments in other
laboratories. If
the findings are indeed
true, would Special Relativity be violated? Not really as the theory does admit
superluminal particles that are known as Tachyons.
Let's look at this a little closer. Protons have immense power requirements
(electrical energy equal to that consumed by a large city for a day) to
accelerate them to close to the speed of light. And they cannot attain the
speed of light in that it would require infinite energy with the proton's mass
becoming infinite.
However, this cosmic speed limit
does
not work for all particles (or objects being the sum of
many particles). For example, turning on a
lamp causes it's
light bulb to emit
photons at
light speed. Since photons are
the mass-less components of light, relativity says they can travel at that
speed. Neutrinos are created with a certain speed and they are nearly mass-less
particles that can pass through anything
so they're not likely to start at a relatively low speed accelerating to reach
a higher one. Because they are so speedy and nearly mass-less it
takes a light-year of lead to effectively block a neutrino. Neutrinos don't
slow down either, they
just interact with matter eventually via
the
weak force, ceasing to exist as
neutrinos. Special Relativity says that a particle with mass cannot attain or exceed
the speed of light barrier. However it does allow for the possibility that the
object or particle can be created with a superluminal speed. For this particle,
it can’t slow down to drop below the speed-of-light barrier. Therefore if
a
particle is created subluminal, it has to stay subluminal. If created superluminal, it must
remain superluminal.
It should be noted that most physicists are still skeptical about OPERA's
results, many of them referencing the results
of data from the 1987 supernova explosion, in which neutrinos were detected here
on Earth. It was brought up that if neutrinos are as fast as OPERA's data
indicate, then neutrinos from the supernova at a distance of 168,000
light-years, should have arrived on Earth
years before
photons from the supernova. Data results were
that the
supernova neutrinos arrived
hours before the light did. The reason given for this lag by astronomers was that
the photons were delayed in the collapsing stages of the star, while the
neutrinos sped right on through. However, the fact that the neutrinos arrived
ahead of the photons does appear to support the superluminal hypothesis. A
subsequent experiment was conducted arriving at results confirming those of the
initial experiment.
In the initial experiment proton pulses that were used to generate neutrinos
via
stationary target collisions were
relatively long; lasting 10.5 microseconds. Scientific criticism
was
made that these long pulses may have induced a level of some uncertainty.
Therefore OPERA scientists requested that
CERN shorten the pulses ( three nanoseconds).
The original result
was that neutrinos
traveling from CERN to Gran Sasso 60 nanoseconds faster than light would have
taken in the same 732 kilometers. The standard statistical error
was one-sixth as large
equating to an extremely significant 'six
sigma' meaning that its probability of being a fluke was less than one in 3.5
million. The subsequent shorter pulses make the pulse length fall within the
standard error, and therefore did not contribute to a possible false finding.
More significantly, the new results based on neutrinos generated from the new ultra
short pulses, replicated the earlier OPERA result:
The neutrinos still appear to travel
faster than light.
OPERA scientists are now more confident of their findings and await verification
or refutation of by other research teams.
Speaking of other teams; MINOS (Fermi Lab's Main Injector Neutrino
Oscillation Research), physicists are going through the huge data set on
neutrino speeds accumulated over years of research. While the GPS used in calculating
these speeds is not as accurate as OPERA's, the amount is still useful in confirming
or presenting a challenge of the superluminal findings.
So is the neutrino really a tachyon?
