Wednesday, June 1, 2011

Lateral Doppler-Like shift

So it's well known that if you are moving away or towards an emitter of electromagnetic radiation you will perceive what is called a red shift or a blue shift depending on whether you are moving away or towards respectively. The red shift means the frequency of the wave seems to decrease as you move quickly away and the blue shift means the frequency seems to increase as you move quickly towards. Think if you were in a boat at the ocean and moving into the waves each wave would reach the boat more quickly than if you were riding away from the source of the waves.
  So anyway today I was reading about relativity and I had this thought experiment:
A spaceship launched from the planet and accelerated to a significant fraction of the speed of light. Here a wave is being sent from the line A to B. Let's say it's a radio signal and he has a radio on his ship so he can hear some music playing. At a certain velocity it would seem to him because of relativity that he could hear the signal on his radio for 2 seconds but to us it looked like it took him four seconds to pass through the area where the waves were... this is known as the Twin's Paradox or Time dilation if you want to read on Wikipedia.
  But if we saw him pass through for 4 seconds and he only experienced 2 seconds of radio, it seems to me that he must have heard on his radio music at twice the frequency than was being sent out. I mean he heard what to us was 4 seconds of music but in 2 seconds so the singers must have sounded like chipmunks.
  So anyway that's why I call it a lateral Doppler-like ship because he's moving perpendicular to the waves and experiences a blue shift as if he were moving rapidly towards the waves.

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