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Intriguing thought experiment

  1. Nov 24, 2011 #1
    Hello all! I was not sure were to post this, but I was asked a very interesting thought experiment on Facebook today and was wondering if I could get everyone's opinions on it.

    Ok, so suppose we could really annoy Einstein and manage to get a car to go the speed of light. The question is, would the stereo speaker's work?

    Now I have two different theories. One, assuming the system within the cabin is unchanging, then the principals of reference frames would dictate that the speakers would work fine relative to you.

    But all of the particles in the car are going faster than the speed of light, so if a sound wave was emitted, would you not move faster than it could propagate? And if that happens, would you be able to hear anything at all?

    Just thought I'd share this little bit of intrigue with you all.
  2. jcsd
  3. Nov 24, 2011 #2


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    We get this a lot.

    Q: If we could ignore the laws of physics what would happen to the laws of physics?

    A: Fairies and unicorns would jump out of your pants.

    Seriously, it cannot happen which is why asking what "would" happen makes no sense.

    The question you want to ask is properly phrased this way:

    Q: If we had a car that could accelerate at a constant rate without limit, so that it approached arbitrarily close to the speed of light (say, 99.9999999999%), would the car's stereo work?

    A: Yes. Everything within the car would go on exactly as it had before, no matter how long you accelerated. The only way you would have any idea you were moving fast relative to something else in the universe is to look out the window.

    Why? Two phrases to look up: Time dilation. Velocity addition.
    Last edited: Nov 24, 2011
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