MadSci Network: Physics

Re: tv trasmission from near light speed ship (cont.)

Date: Wed Nov 3 18:25:03 2004
Posted By: Layne Johnson, Undergraduate
Area of science: Physics
ID: 1099019081.Ph

Hello again Tiago.

Thank you for clarifying. It seems I missed the entire point of your
question. Sorry about that.

Back to your question - The frequency of the broadcast would definitely
change. It would get slower as the speed of the space craft sending it got
faster. As the space craft accelerated, the equipment we would need to
capture a television transmission would change. It would fall from the
television frequencies to the shortwave radio frequencies, then down to the
AM radio frequencies, and finally down to the aircraft and maritime
shipping commercial frequencies.

Once the frequency slips below that used by aircraft and commercial
shipping bandwidths, we'd have to start making our own reception devices,
because there aren't any commercial applications of communication using
frequencies below that point.

Television transmissions are not instant in nature. They have a starting
time and an ending time, and are emitting a stream of photons from the
beginning until the end. Since the source of the signal is moving away from
Earth at near light-speed, the signal near the end of the transmission must
travel farther to reach us than the signal at the beginning of the
transmission. So we would see a slow motion image on our television
receiver. As you pointed out, this would be a Doppler effect, not an effect
of time dilation.

Again, I apologize for not reading your first question more carefully, and
hope we're now on the same (here it comes) wavelength.

Layne Johnson

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