- #1
stovepipe
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Hi everyone,
I recently decided that I wanted to the understand the concepts and applications of SR better. I've been reading a lot about it, but it gets confusing at points. For now I'm only concerned with SR and not GR. Here are some examples that I'm sure many of you would find trivial, and I want to know if I'm understanding them correctly.
-The twin paradox.
Two clocks are synchronized in frame A. Clock 1 stays put in frame A. Clock 2 is accelerated to a relativistic velocity, say v=.8c. Due to time dilation Clock 2 should be running at .6 the speed of Clock 1 for the observer in frame A. Here's my confusion. I read that this dilation is independent of acceleration. Yet I consistently read answers to this problem saying that it is the Clock that was accelerated that runs slower. And when I choose to ignore acceleration I see that from the point of view of an observer that is in frame B, in which Clock 2 is at rest after acceleration, Clock 1 is running slower, and I can no longer make a judgment on which clock is truly slower, because now the slower clock depends on which frame you are in. But examples I read always say that Clock 2 is slower.
-Multiple frames/bodies.
Frame B is traveling at .8c to the right with respect to frame A. Frame C is traveling at .8c to the left with respect to frame A. An obsever in frame B measures and object stationary in frame C to be moving away at 0.9756c. After traveling 1ly according to frame A, an observer in frame B makes a measurement of how far he has traveled. Due to length contraction, he measures that he has only traveled .6 ly. The same happens for frames A and C. According to A, an object in B and an object in C have grown appart by 2 ly. I can't seem to figure out how far the objects have grown appart according to frames B or C. Would it be 2 ly times the contraction factor for .9756c or 1.2 ly or something completely different. I'm leaning towards 1.2 ly assuming the measurement was made based on references in A. Now my confusing twist, again involving acceleration. Suppose both the observers in frames B and C rapidly deccelerate to come to rest in frame A. They make the messurements again and find that they are 2 ly appart not 1.2. If they had been trying to measure the distance during the decceleration would they conclude that the other body was accelerating away from them and exceeding the speed of light since it apparently traveled .8 ly in a very short time.
-Doppler effect.
A human would have a hard time navigating a relativistic rocket. If I'm moving towards a violet (400nm reflected wavelength) object at .8c. The reflected wavelength would be red-shifted to appear 1200nm (invisible infrared light). If I'm moving away from a red (750nm reflected wavelength) object at .8c. The reflected wavelength would be blue shifted to appear 250nm (invisible ultraviolet light). So any objects that you are moving towards or away from that reflects only visible light, would now appear invisible. I guess if you were navigating by stars it wouldn't be such a big problem since the infrared or ultraviolet light that they emit would now be visible. One more question. Silicon is opaque to visible light but transparent to infrared light due to its crystal structure. If a crystal of silicon was moving towards the source of a blue light at .8c, would an observer in the lights source's frame see the silicon as transparent to blue light?
Thanks everyone,
-Steve
I recently decided that I wanted to the understand the concepts and applications of SR better. I've been reading a lot about it, but it gets confusing at points. For now I'm only concerned with SR and not GR. Here are some examples that I'm sure many of you would find trivial, and I want to know if I'm understanding them correctly.
-The twin paradox.
Two clocks are synchronized in frame A. Clock 1 stays put in frame A. Clock 2 is accelerated to a relativistic velocity, say v=.8c. Due to time dilation Clock 2 should be running at .6 the speed of Clock 1 for the observer in frame A. Here's my confusion. I read that this dilation is independent of acceleration. Yet I consistently read answers to this problem saying that it is the Clock that was accelerated that runs slower. And when I choose to ignore acceleration I see that from the point of view of an observer that is in frame B, in which Clock 2 is at rest after acceleration, Clock 1 is running slower, and I can no longer make a judgment on which clock is truly slower, because now the slower clock depends on which frame you are in. But examples I read always say that Clock 2 is slower.
-Multiple frames/bodies.
Frame B is traveling at .8c to the right with respect to frame A. Frame C is traveling at .8c to the left with respect to frame A. An obsever in frame B measures and object stationary in frame C to be moving away at 0.9756c. After traveling 1ly according to frame A, an observer in frame B makes a measurement of how far he has traveled. Due to length contraction, he measures that he has only traveled .6 ly. The same happens for frames A and C. According to A, an object in B and an object in C have grown appart by 2 ly. I can't seem to figure out how far the objects have grown appart according to frames B or C. Would it be 2 ly times the contraction factor for .9756c or 1.2 ly or something completely different. I'm leaning towards 1.2 ly assuming the measurement was made based on references in A. Now my confusing twist, again involving acceleration. Suppose both the observers in frames B and C rapidly deccelerate to come to rest in frame A. They make the messurements again and find that they are 2 ly appart not 1.2. If they had been trying to measure the distance during the decceleration would they conclude that the other body was accelerating away from them and exceeding the speed of light since it apparently traveled .8 ly in a very short time.
-Doppler effect.
A human would have a hard time navigating a relativistic rocket. If I'm moving towards a violet (400nm reflected wavelength) object at .8c. The reflected wavelength would be red-shifted to appear 1200nm (invisible infrared light). If I'm moving away from a red (750nm reflected wavelength) object at .8c. The reflected wavelength would be blue shifted to appear 250nm (invisible ultraviolet light). So any objects that you are moving towards or away from that reflects only visible light, would now appear invisible. I guess if you were navigating by stars it wouldn't be such a big problem since the infrared or ultraviolet light that they emit would now be visible. One more question. Silicon is opaque to visible light but transparent to infrared light due to its crystal structure. If a crystal of silicon was moving towards the source of a blue light at .8c, would an observer in the lights source's frame see the silicon as transparent to blue light?
Thanks everyone,
-Steve