blike Posted July 16, 2004 Share Posted July 16, 2004 Let's say there are two people floating towards each other in space at the same speed. Neither astronaut is experiencing any acceleration. They are both moving at 0.5c. I have two questions about what happens when they pass each other:' 1) Won't both astronauts measure the other ones speed at 1.0c? 2) Won't both astronauts see the other astronaut's watch ticking slower? Link to comment Share on other sites More sharing options...
TheProphet Posted July 16, 2004 Share Posted July 16, 2004 1) No, but i can't math it out too u right now.. or maybe.. If they traveled in speeds over 0,5c this would imply speeds over 1c. which is impossible! and they are also traveling against each other so my speed is 0,5c his is -0,5c out of my view. Hope u follow me here, im not shure i do myselve 2) Yes they would Link to comment Share on other sites More sharing options...
JaKiri Posted July 16, 2004 Share Posted July 16, 2004 1) Won't both astronauts measure the other ones speed at 1.0c? No. (0.5c+0.5c)/(1+(0.5c)^2/c^2)' date=' or 1c/1.25, or 4/5 c. 2) Won't both astronauts see the other [/i']astronaut's watch ticking slower? Why yes. Link to comment Share on other sites More sharing options...
blike Posted July 16, 2004 Author Share Posted July 16, 2004 No. (0.5c+0.5c)/(1+(0.5c)^2/c^2)' date=' or 1c/1.25, or 4/5 c. Why yes.[/quote'] Oh ok, whats the name of that equation you used JaKiri? Also, with regards to question #2, if they both decide to meet up, who is older? By one's standard, the other one should be younger.. Link to comment Share on other sites More sharing options...
JaKiri Posted July 16, 2004 Share Posted July 16, 2004 Oh ok, whats the name of that equation you used JaKiri? God knows the name. It's just recession speed ( a+b/1+ab/c^2 ). Also, with regards to question #2, if they both decide to meet up, who is older? By one's standard, the other one should be younger.. Which ever one accelerates. To copy and paste a bit of a post I made earlier this month (which is why it doesn't make sense): Acceleration breaks the symmetry. Notice in the twin example, the one that, in the end, suffered the effects had accelerated in the middle; let us examine the Twin Paradox again. In this case, the twins are in two spaceships, travelling at constant velocity away from eachother. One thinks (rightly) that the other is suffering time dilation relative to him, and the other thinks (rightly) the opposite. (The key word there is relative. No pun intended.) However, if Twin 1 accelerates, and travels back to Twin 2, Twin 1 has aged slowly and Twin 2 has aged quickly. Why this result? As I said before, it's because of the acceleration. Remember, all our observations are made relative to rest frames. As Twin 1 has accelerated, he's now moving relative to his (former) rest frame, and so suffers time dilation relative to it. If you look at his new rest frame, then he was travelling relative to it before he accelerated, and so is time dilated in that one too. To summarise: if you accelerate, there is no longer any rest frame in which, relative to it, you have not been moving, and therefore will always suffer time dilation. Link to comment Share on other sites More sharing options...
blike Posted July 16, 2004 Author Share Posted July 16, 2004 Wonderful. Thanks! Link to comment Share on other sites More sharing options...
MacM Posted July 20, 2004 Share Posted July 20, 2004 God knows the name. It's just recession speed ( a+b/1+ab/c^2 ). It is called "Velocity Addition Formula" Link to comment Share on other sites More sharing options...
JaKiri Posted July 20, 2004 Share Posted July 20, 2004 It is called "Velocity Addition Formula" That's the worst name ever. Link to comment Share on other sites More sharing options...
MacM Posted July 20, 2004 Share Posted July 20, 2004 That's the worst name ever. Don't blame me. Blame the Relavitists. Link to comment Share on other sites More sharing options...
Primarygun Posted July 22, 2004 Share Posted July 22, 2004 Oh ok' date=' whats the name of that equation you used JaKiri? Also, with regards to question #2, if they both decide to meet up, who is older? By one's standard, the other one should be younger..[/quote'] The equation is " V1 + V2 _________ 1+ V1 X V2 ______ c2 " Not sure about whether this can be used in all velocity. Both are the same age No one is older by appearance or other what you can think of Link to comment Share on other sites More sharing options...
JaKiri Posted July 22, 2004 Share Posted July 22, 2004 The equation is " V1 + V2 _________ 1+ V1 X V2 ______ c2 " You need to use if you want spaces to seperate stuff. Normal vb just cuts them out. Not sure about whether this can be used in all velocity. What do you mean' date=' 'can be used'? It's THE way of adding velocities together. Both are the same ageNo one is older by appearance or other what you can think of Fraid not. Link to comment Share on other sites More sharing options...
Primarygun Posted July 22, 2004 Share Posted July 22, 2004 but they are not in the same "world" Sorry I don't know the word ,I haven't watched the relativity so deeply Maybe I am wrong ,just want to ask about it Link to comment Share on other sites More sharing options...
JaKiri Posted July 22, 2004 Share Posted July 22, 2004 but they are not in the same "world"Sorry I don't know the word ' date='I haven't watched the relativity so deeply Maybe I am wrong ,just want to ask about it[/quote'] Read my longer explanation. Link to comment Share on other sites More sharing options...
Primarygun Posted July 22, 2004 Share Posted July 22, 2004 ok thanks I print to read Link to comment Share on other sites More sharing options...
Dave Posted July 22, 2004 Share Posted July 22, 2004 The equation is " V1 + V2 _________ 1+ V1 X V2 ______ c2 " [math]v_x = \frac{v_1 + v_2}{1+\frac{v_1 v_2}{c^2}}[/math] Link to comment Share on other sites More sharing options...
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