THE SOUTHWORTH PLANETARIUM
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Altitude: 10 feet below sea level
Founded January 1970
Julian Date: 2458877.16
2019-2020: XCIV
“Experience is a hard teacher. She gives the test first and the
lessons afterwards."
Anonymous
My apologies!
I inadvertently sent the first part of the article without having finished
it earlier. You see, when a DA is in progress, I'll e-mail it to myself
because I generally don't find e-mails from me to be that annoying,
generally.
THE DAILY ASTRONOMER
Wednesday, January 29, 2020
Traveling Light
It is not uncommon for the material in one DA to elicit questions that
spawn into another DA: akin to a black hole in one Universe given rise to
another Universe: to use the most appallingly self-important analogy
possible. The DA written to the subscriber who wanted to escape to a
nearby nebula prompted yesterday's DA and today's, as well, as another
subscriber was curious about the notion of light speed.
"Why would somebody on a vessel not experience any time when traveling at
light speed? How can we possibly know that? Why don't science fiction
movies take this into account."
-Helen (no, not THAT Helen.)
Greetings, not that Helen,
Time dilation.
The tendency of time to dilate when a given vessel moves. Such an effect
is negligible unless the craft travels at an appreciable fraction of light
speed. This strange phenomenon is part of Albert Einstein's Theory of
Special Relativity, published in 1905. It derives from one
deceptively simple statement:
*The speed of light is constant in all inertial reference frames.*
To explain how this simple statement could affect time, let's put ourselves
in a spaceship. As we needn't worry about such pesky matters as
acceleration times and other real world nonsense, we can set the speed to
any value we desire. Moreover, we're going to play tag with a light
beam.
First, we simply hover in space and let the light beam move across our
viewfield. We instruct the on-board science geek to measure the beam's
velocity. Unsurprisingly, she measured the speed of light to be, well,
speed of light, or 'c'. You'll see why we have denoted light speed as
"c" soon."
Next, we accelerate from a dead stop to half the speed of light as we try
-in vain, of course- to catch up to the beam. This time, the science geek
measures the speed of light again and discovers that it still measures c,
the speed of light. Flummoxed, we accelerate to 85% light speed (the
geek calls it 0.85c) and she measures the light beam again. Again, the beam
is going at light speed and not at 15% light speed as we would expect.
Now that we're really all mad (well, the geek seems content), we accelerate
to 99% light speed and measure the beam again. Of course, the beam's speed
remains stubbornly the same: c, or the speed of light.
In ordinary circumstances, our speed affects the measurement of any other
moving object. A person in a car moving at 100 mph toward another car
also moving at 100 mph measures the oncoming car's speed as being 200 mph!
Light is different. No matter how one travels relative to the light beam,
the beam's speed remains constant. That is the startling consequence
of the speed of light being constant in all inertial reference frames.
For this reason scientists use the letter "c" to specify light speed. The
ramification is startling: time dilates on a moving vessel. The faster
the vessel travels, the greater the time dilation becomes. IF a vessel
could move at light speed, time aboard the vessel stops.
The problem is that mass increases, as well. As the vessel's mass
increases, it becomes exceedingly more difficult to accelerate it to higher
velocities.
Why don't sci-fi movies take that into account.
Because most sci-fi movie producers consider science to be a real
inconvenience that is best ignored. After all, starship battles would be
truly boring if you couldn't see the beams.
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