Re: tv trasmission from near light speed ship

Hello Tiago.

A television transmission beamed to Earth from a space craft traveling at
near light speed would appear like any other television transmission. We
would not see any Doppler effects. The speed of light is constant.

The television transmissions leaving the space craft would also travel away
from it at the speed of light, with no Doppler effects. Again, the speed of
light is constant.

Obviously, this creates a problem. If I'm on a train going 40 kph, and I
toss a ball off the back of the train at 41 kph, it appears to me that the
ball is going away from me at 41 kph. But to an observer on the ground next
to the tracks, the ball is only moving at 1 kph. Why should the speed of
light be different than the speed of the ball? Why is the speed of the ball
relative to the motion of the observer, but the speed of light a constant
to every observer, regardless of their motion?

We'll get to that in a moment. But let's go back a little over 100 years
ago first.

Back then, just as it does now, the Earth revolved around its poles at
about 1600 kph, measured at the equator. A few scientists decided to
measure the speed of light coming from the sun at sunrise, when their
portion of the Earth was moving toward the sun at 1600 kph, while at the
same time their collegues on the opposite side of the world measured the
speed of light from the sun at sunset, and their portion of the planet was
moving away from the sun at 1600 kph. They expected to find a difference of
about 3200 kph.

But there was no difference. The speeds they measured were identical. They
couldn't explain why.

No one could explain why, until Albert Einstein did in 1905.

Einstein figured that if the speed of light is constant to any observer,
ignoring the observer's own motion through time and space, then time and
space themselves must not be constant. The fabric of time and space must be
warpable. (Hey, I think I just made up a new word!) If the speed of light
doesn't make concessions for movement through space and time, then space
and time must make concessions for photons moving at the speed of light.

Back to our space craft and television signal - as a space craft approaches
the speed of light, space and time around it start to warp. To an observer
on the space craft, the television signal it broadcasts is moving at the
speed of light. To an observer on the Earth, the television signal is
moving at the speed of light.

There are a bunch of good web sites that explain special relativity much
better than I can. Stanford University has a great one at 
 http://www2.slac.stanford.edu/vvc/theory/relativity.html

Layne Johnson