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SPECIAL RELATIVITY EXPERIMENTAL VERIFICATION PARTICLE ACCLERATORS |
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SUMMARY Inertial frames of reference You must always identify the frames of
reference station frame (S) moving frame (M) relativity factor
Time dilation effect proper
time interval dilated
time interval Length contraction proper length
contracted
length Particle accelerators can
accelerate charged particles using electric fields to speeds approaching the
speed of light. However, it does not matter how much energy is imparted to
the particle, its speed never exceeds the speed of light. This result is
further experimental evidence so support the theory of special
relativity. |
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PARTICLE ACCELERATORS Particle
accelerators can accelerate charged particles using electric fields to speeds
approaching the speed of light. Without Einstein's theory of special
relativity, they simply wouldn't work.
Einstein’s special relativity theory can be tested using
the measurements gained from particle accelerator where very high velocities
are commonplace. The Tevatron accelerator (Fermilab, USA), Large Hadron Collider (CERN) and many other
accelerators around the world provide excellent evidence that the
counterintuitive ideas of special relativity are accurate. |
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Example 1 A
pi meson (
The
pi meson has a mass of about 270 times larger than the mass of an electron
mass and has the same charge as an electron. When many of these particles are
observed at rest in the laboratory, it is found that they disintegrate to
form other particles. After a time interval of 2x10-8 s, half the
original number of pions have decayed
(disintegrated). This time interval is called the half-life. When pions are used in particle
accelerators, they can reach speeds of 0.98c. How long will it take according to laboratory clocks, for half
these high-speed pions to decay? Solution Little
is known about the process in which pions decay. However, the decay must be
dependent upon the rate of decay. These processes act as a clock, and the
“clock” moves with the pions. As seen from the laboratory frame
(fixed frame), the pion clock will be running slow as described by the time
dilation effect. In
the laboratory frame (fixed system), when the pions are rest, the proper time
interval is t0 = 2x10-8 s. The observer in the laboratory frame
observing the decay process when the pions are moving will measure the
dilated time interval t
= ? s. Velocity
of moving system (pion frame) v = 0.98 c Time dilation
effect Since the pions decay because of their own internal processes,
their “clock” must read 2x10-8 s when half have
decayed. But, when moving, the time interval measured in the laboratory for
half of the pions to decay is 5 times longer, 10x10-8 s. Measurements such as those indicated in this example have been
carried out at particle accelerators for decades, and the predictions of
special relativity have always been confirmed by actual measurements. |
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The Fermilab accelerator complex had five accelerators. Some of the
accelerators can continually add energy to a proton beam until a maximum
energy of 1012 eV is reached where the protons travels at nearly
the velocity of light, v = 0.9999995 c (a proton traveling at this speed could circle the Earth's
equator almost eight times in a single second). The table below shows the
energy given to the proton beam and the maximum proton velocity for the five
Fermilab accelerators and the Large Hadron Collider.
These measurements demonstrate that the velocity of a particle
cannot exceed the speed of light, no matter how much energy imparted to it.
This provides more experimental evidence to support Einstein’s theory
of special relativity, which states that no particle can move faster than the
speed of light. Reference http://www.fnal.gov/pub/today/archive/archive_2014/today14-04-04_NutshellReadMore.html Special Relativity also says that energy and mass
are essentially equivalent. The phenomenon of gaining higher velocities by
adding energy to a particle is often explained as "mass increases as
things go faster." I admit I have uttered those words myself, but the
statement is actually wrong and so can be misleading. For instance, some people hear the words
"mass increases" and think that particles are getting heavier in
the gravitational sense. In fact, it is more accurate to say that inertia
increases as velocity increases. At low velocities, or nonrelativistic
velocities, it is perfectly reasonable to equate inertia and mass. This is
the reason even scientists sometimes say that mass changes with velocity.
They use the phrase "relativistic mass" to label this fallacious
idea of increasing mass. In fact, there is only one mass, and that is what
is often called "rest mass," which is the mass of an object when it
is not moving. Even though the idea of relativistic mass is, strictly
speaking, not correct, it is a valuable mental picture and helps us get used
to the fact that objects cannot exceed the speed of light. So, if you prefer to think about relativistic
mass, go ahead and do so without feeling guilty. Just realize that if you
push the idea too hard, it will lead you astray. Some relativity sceptics are aware that
laboratories such as Fermilab and CERN have demonstrated that the speed of
light is a limitation in particle accelerators. They have an (incorrect)
explanation, and it goes like this: Particle accelerators use electric fields
to impart a force on (say) a proton. These electric fields, which
accelerators use to propel the protons, are composed of photons, according to
the theory of quantum electrodynamics. Thus, they reason, particle
accelerators shoot photons at protons, and if a proton travelled faster than
a photon, it would no longer feel the photon's force. They claim this is the
reason that protons can travel no faster than light. This reasoning does not explain how the tiny
difference in the proton's speed between the Fermilab Booster and the Tevatron particle accelerators results in the beam's
energy increasing by 125 times. So, the explanation is wrong, but it is a
common one. Be aware of it. |