Some things are more entertaining than others. Einstein was a relatively special kind of guy

1. Special Theory of Relativity as Entertainment
Dave Barnett, CISSP, CISM, CSSLP, CSDP
A simplified version of some of the counter-intuitive aspects of the Special Theory of
Relativity1
, presented purely for entertainment value.
There’s a speed limit for objects: Matter cannot go faster than the speed of light, or
670,000,000 miles per hour. It’s the Law.
Before we proceed, there are some clarifications we need to address. First, by “objects”
and “matter” I am referring to atoms and bigger clusters of “stuff.” Below that size, we
start to encounter quantum effects, where it is more accurate to talk about probability
waves, and particles that may or may not exist in several places at the same time.
Quantum effects average out as the clumps of particles get bigger, and things behave
more as we are used to.
The second clarification is that the speed of light assumes “in a vacuum.” This is
important because light slows down when it goes through other molecules, such as glass,
air, water, mist, and fiber optic cable. This effect is what causes rainbows and refraction,
among other things. When light is slowed down, other things can go faster than this
slower speed. The speed limit I refer to is the speed of light in a vacuum, not the speed of
light in a fiber optic cable
The other part to this clarification is that the speed of light in a vacuum is constant for all
observers. No matter where you are, the speed of light in a vacuum is always the same.
To paraphrase Richard Feynman, “we don’t know why this is. When we understand what
the consequences are, we may not want to believe that it could possibly be like that, and
we may not like it. However, this is what actually happens, so it doesn’t matter very
much what our opinions about it are.”
A third clarification has to do, again, with quantum effects. There are some special
conditions, such as the propagation of the probability waves of existence, or quantum
entanglements at a distance, that don’t follow the same rules, and may appear to exceed
the speed of light. However, in these cases, I think it’s fair to say that we are not really
talking about matter or objects in the everyday sense.
At the quantum level, however, is common sense and every day experience breaks down.
As things start to approach the speed of light, some strange things happen: (1) time slows
down, (2) the object’s length contracts in the direction of travel, and (3) mass increases.
It’s not as if these strange effects just pop up at some magical point. They are always
present, but are not noticeable at speeds that are much slower than light, as occurs in our
everyday experience. They happen all the time (literally), but are too small notice until
the speed gets near that of light.
© 2010 Dave Barnett Page 1

2. Another thing to remember is all three effects occur together, and influence each other.
For simplicity’s sake, I’m going to treat them as if they were independent.
Time slows down
Imagine someone in a rocket ship. Inside the ship, there’s a 10 foot ceiling. On the floor
is a pitching machine that throws a baseball straight up at 100 feet a second. The person
in the rocket ship sees the baseball travel 10 feet straight up in 1/10th
of a second.
(velocity = distance divided by time)
Now, imagine that the rocket ship itself is traveling 100 feet a second, and someone is
floating outside watching this pitching machine. When the baseball leaves the machine, it
travels 10 feet up to the ceiling – but for the person floating in space, it is also moving
forward 10 feet in the same 1/10th
of a second. If the baseball moves forward 10 feet and
up 10 feet, the total distance is a diagonal line about 14 feet long. For the person inside
the ship, the baseball is still traveling at 100 feet a second straight up. For the person
floating in space, the baseball travels 14 feet in 1/10th
of a second, or 140 feet per second.
© 2010 Dave Barnett Page 2

3. At speeds much less than light, velocity is not a constant for all observers. It can be
different for, and result from summing various speeds, depending on where the observers
are and their speeds relative to each other.
Now, for the weird part: Let’s replace the baseball with a beam of light from a flashlight.
For the person inside the rocket ship, the beam of light travels at the speed of light. It
goes from the floor to the top of the 10 foot ceiling in a little less than 1/100,000,000th
of
a second. But while the light beam is moving toward the ceiling, the ship is also moving
forward. However, unlike baseballs, the speed of light is constant for all observers. For
both the person floating in space and the person in the ship, the light beam will go 670
million miles per hour, even though the distance is greater (due to the diagonal) for the
person floating in space, and less for the person in the ship. In order to make the speed
constant for all observers, time is adjusted. The faster an object goes, the slower time
moves, relative to a stationary observer. This is verified in particle physics regularly –
when a particle is accelerated near the speed of light, its decay rate noticeably slows
down, and it lasts significantly longer than its normal lifetime.
Contraction
Let’s imagine we’re back in the rocket ship. Instead of pitching the baseball from the
floor to the ceiling, suppose we throw it forward, in the direction that the ship is
traveling. If we throw the ball at 100 feet per second, and the ship is moving at 100 feet
per second, the ball will be traveling at 200 feet per second for our observer floating in
space. Inside the ship, it will only appear to be traveling at 100 feet per second. Common
sense applies – the speed to the outside observer is the sum of the ball’s speed plus the
ship’s speed.
Now, let’s again replace the baseball with a beam of light. If the person inside the ship
turns on the flashlight, and measures how fast the beam goes, it will always be traveling
at 670 million miles per hour--- no matter how fast the ship is going. The speed of light is
a constant for all observers. The same is true for the observer floating in space – no
matter how fast the ship is going, even if it is traveling near or at light speed, the beam of
light will travel at 670 million miles per hour. How can it be the same for both?
Velocity is distance divided by time. If velocity of light is constant, and distance is
halved, the amount of time must also be cut in half to maintain the proportion. This is
what happens to objects moving at near light speed – time slows down, and space is
shortened (relative to an outside observer), so that the speed of light remains constant. In
fact, for the previous example about time, there was both time dilation and length
contraction. This contraction in length was first discovered by Hendrik Lorenz, and
formed the part of the basis for Einstein’s work on Relativity.
Mass
The third strange effect of traveling near the speed of light is that mass increases.
Physicists use “mass” instead of “weight” because weight depends on the strength of the
field of gravity, while mass does not. Objects on the Moon weigh 1/6th
of what they do on
Earth – however, the mass is the same.
© 2010 Dave Barnett Page 3

4. Einstein demonstrated that the mass of a body at rest is dependent on how much energy is
contained in it. That is, if you add energy to an object, for example by lifting it 10 feet off
the ground, the object actually becomes heavier. In everyday experience, the amount is
not noticeable. If a car weighing one ton were accelerated to 65 miles per hour, it would
increase in weight about ½ of 100 millionth of a gram. Einstein stated the relationship as:
mass is equal to energy divided by the speed of light squared. (This is more commonly
written as E=mc2
).
At slower speeds (much below light speed) adding energy to an object increases weight
only a small amount. The most noticeable effect is the object moves faster. However, as
the object gets close to light speed, it starts hitting the speed limit. Instead of going faster,
the energy gets converted to mass. The closer the object is to light speed, the more
directly energy converts to mass. In particle accelerators, protons moving at 99.9997% of
the speed of light swell up to 430 times their normal mass. These experiments are
generally performed at night because the power required to move protons that fast dims
the lights of surrounding cities.
Given that the speed of light is a constant for all observers; space, time, and mass
adjust for each observer to make it so.
© 2010 Dave Barnett Page 4

5. 1
Einstein, Albert (1905-06-30). "Zur Elektrodynamik bewegter Körper". Annalen der Physik 17: 891–921. Retrieved
on 2008-02-18.

6. 1
Einstein, Albert (1905-06-30). "Zur Elektrodynamik bewegter Körper". Annalen der Physik 17: 891–921. Retrieved
on 2008-02-18.