- #1
boswell
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Hi everyone! This is my first post so I hope I’m following all the correct rules and such. I am a second year Physics major and I’m having a bit of trouble with special relativity. I don’t have much trouble with doing homework problems, but I always stump myself when trying to understand SR for what it really is. Whenever I think about SR I find another logical problem with my understanding, and my textbook can’t answer me whenever I get stumped. So here is just one of many problems I’ve encountered when thinking about SR. This is not a HW problem; this is just a simple scenario I’ve envisioned. I’ve tried to make it as simple as possible:
A man is running with a speed of (0.5c) towards a photon of light that is heading towards him initially (4.5*10^8 m) away, all of this is with respect to a stationary observer. I assume that (c=3.0*10^8 m/s), so with respect to this stationary observer after one second has passed the light will have moved (3.0*10^8 m) towards the man, while the man will have run (1.5*10^8 m) towards the photon. Since the two were initially (4.5*10^8 m) apart, they should meet after one second with respect to the stationary observer.
But in the runner’s reference frame the runner views himself as stationary, while the photon heads towards him. I know that the distance between the runner and the photon should have contracted, and the time will also tick slower for the runner when compared to the stationary observer. So assuming I have done the Lorentz contraction and time dilation formulas correctly, t(runner)=0.866 t(stationary) and L(runner)=0.866 L(stationary). Since the stationary observer originally recorded one second for the two to meet, it should now take (0.866) sec, and since the stationary observer also recorded that initially they were (4.5*10^8 m) apart, they should now be (3.9*10^8 m) apart. However this would mean that the photon traveled (3.9*10^8 m) in (0.866 sec), which is a speed of (4.5*10^8 m/s), meaning c=1.5c. That can’t be right! Where is the flaw in my logic? What am I missing?
A man is running with a speed of (0.5c) towards a photon of light that is heading towards him initially (4.5*10^8 m) away, all of this is with respect to a stationary observer. I assume that (c=3.0*10^8 m/s), so with respect to this stationary observer after one second has passed the light will have moved (3.0*10^8 m) towards the man, while the man will have run (1.5*10^8 m) towards the photon. Since the two were initially (4.5*10^8 m) apart, they should meet after one second with respect to the stationary observer.
But in the runner’s reference frame the runner views himself as stationary, while the photon heads towards him. I know that the distance between the runner and the photon should have contracted, and the time will also tick slower for the runner when compared to the stationary observer. So assuming I have done the Lorentz contraction and time dilation formulas correctly, t(runner)=0.866 t(stationary) and L(runner)=0.866 L(stationary). Since the stationary observer originally recorded one second for the two to meet, it should now take (0.866) sec, and since the stationary observer also recorded that initially they were (4.5*10^8 m) apart, they should now be (3.9*10^8 m) apart. However this would mean that the photon traveled (3.9*10^8 m) in (0.866 sec), which is a speed of (4.5*10^8 m/s), meaning c=1.5c. That can’t be right! Where is the flaw in my logic? What am I missing?