|Is there any particle faster than light? if so,
what is it? Is neutrino faster than light?|
|Question Date: 2014-08-17|
You might know that if you travel on a train at
60 MPH and walk forward briskly at 5 MPH, your
overall speed would be 65 MPH. However, if
Superman was running at nearly the speed of light
and he turned on a flashlight pointed in front of
him, he would still see the light moving as if it
were moving at the speed of light. In this case,
the two speeds are additive. It’s an interesting
consequence of our understanding of relativity.
Einstein imagined himself chasing a beam of light
(when he was only 16!) and saw the logical
contradictions that would lead him to conclude
that the speed of light was a constant that could
not be surpassed.
There are different situations where it might
seem like the speed of light is exceeded. For
example, if I shine a powerful laser at Betelgeuse
and then, as quick as I can, point it at Rigel
(both of these are stars in the Orion
constellation but are 392 light years apart), it
could seem like the spot of light at the tip of
the laser travelled faster than the speed of light
(392 light years in just a couple of seconds).
However, neither the laser (in your hand) nor the
light from the laser (travelling at the speed of
light) move faster than the speed of light, and so
the movement of the spot is delayed. There are
other examples like this that might seemingly
break light-speed but actually don’t.
There are also tachyons. These are
hypothetical particles that move faster than the
speed of light. Physicists argue whether or not it
is possible for these particles to exist, although
most scientists say that since our current laws of
physics disallow it, it likely is not possible.
Tachyons have not been observed, unless you count
the small sailboat I saw in the Santa Barbara
harbor (one boat was named Tachyon while its
neighbor was named Tachytoo).
You might recall a few years ago when
researchers in Europe observed neutrinos
travelling at faster than the speed of light. The
researchers didn’t report this finding without
double- or even triple-checking but couldn’t find
any reason the data was invalid, even though it
contradicted our modern understanding of physics.
They promised the scientific community that more
experiments would be conducted and eventually,
they noticed a fiber optic cable that had been
incorrectly attached and a clock that was ticking
too fast. Later, after the experimental parameters
were corrected, scientists measured multiple
neutrinos with velocities at or near, but not
exceeding the speed of light.
No particle we have ever seen moves faster than
light - or at least faster than light in a vacuum.
The speed of light in a vacuum is a property of
the universe, and no particle that we have any
experience with (including neutrinos) can exceed
this speed. This constant maximum speed of
anything remains the same when traveling through
matter, but light itself slows down when traveling
through matter. Neutrinos and other things can
move at speeds through matter faster than (some)
frequencies of light move through that same
matter, but they can never exceed the speed that
light moves when in a vacuum.
Physicists have speculated about particles
called tachyons, which would move faster than
light, even in a vacuum. Nobody has ever observed
a tachyon, so what their properties are, or if
they even exist, is unknown.
Good question! As far as we know, no particle
faster than light actually exists in our universe.
Neutrinos are SUPER light particles, so they move
at almost the speed of light, but they're still
slower than light.
However, there are theoretical particles
("theoretical" means you can describe it on paper,
but no one actually thinks it really exists)
called tachyons which travel faster than
light (the name comes from the Greek word
"tachys", which means "fast"). It turns out that
these particles have an imaginary mass - this is
imaginary in the sense of complex numbers (so if
you square the mass of a tachyon, you get
something negative). But the problem with
tachyons is the usual problem that you get when
you have things moving faster than light - you can
get all sorts of weird time travel paradoxes like
things causing themselves to happen, or you being
able to go back in time to kill your parents
before you were born, and so on. So usually when
physicists see tachyons appearing in their
theories, that means that something's wrong and
needs to be fixed!
Nothing travels faster than light.
Light speed is a physical speed limit of the
universe, and not even neutrinos breach it. The
results you may have seen suggesting neutrinos
move faster than light was released by scientists
who were confused with their result and were
asking other scientists around the world to help
figure out what was wrong with their experiment.
The news thought this was interesting so it made
headlines, but the real situation was that the
people doing the experiments were asking more
scientists for troubleshooting advice. It turned
out that a fiber optic cable was connected badly
and it ruined their time measurements. Any kind of
clock or time measurement in particle physics must
be incredibly accurate since the phenomena happen
so quickly. Theirs just wasn't working well. New
measurements showed it was under the speed of
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