cHIs- Posted May 17, 2003 Share Posted May 17, 2003 Just wondering, i thought it was in a post somewhere but i cant find it :/ If you travelled at the speed of light for ten minute somewhere or over the speed of light, then came back, what would be the effect on time in earth? Does traveling at that speed do anything with time, like make it go back or forward ? Link to comment Share on other sites More sharing options...
superchump Posted May 17, 2003 Share Posted May 17, 2003 Originally posted by cHIs- Just wondering, i thought it was in a post somewhere but i cant find it :/ If you travelled at the speed of light for ten minute somewhere or over the speed of light, then came back, what would be the effect on time in earth? Does traveling at that speed do anything with time, like make it go back or forward ? As you move toward the speed of light, time in your frame of reference slows down in comparison to earth's time in its frame of reference. So if you were to take a 4 year trip (in your frame of reference) at 90% the speed of light in your spacecraft, about 9 years would have pasted on earth during your trip. At 10 minutes in your spacecraft (again in your frame of reference) at 99.99% the speed of light (approx. the closest speed objects with mass can go), about 50000 minutes passed. I might have screwed up the math folks...please check it. Link to comment Share on other sites More sharing options...
cHIs- Posted May 17, 2003 Author Share Posted May 17, 2003 ok, thanks, hmm so if they did find away to at least travel near c it woudlent be all that great on the trip back, the earth would of ages but not you. If thats right. So wait, you are basicly traveling forward in time , so earth would be waiting years for your return, so it would be a quick way to see the future, and the whole idea of traveling at light speed isnt all that great considering earth would be waiting years for your return... kinda sucks Link to comment Share on other sites More sharing options...
blike Posted May 17, 2003 Share Posted May 17, 2003 Originally posted by cHIs- ok, thanks, hmm so if they did find away to at least travel near c it woudlent be all that great on the trip back, the earth would of ages but not you. If thats right. So wait, you are basicly traveling forward in time , so earth would be waiting years for your return, so it would be a quick way to see the future, and the whole idea of traveling at light speed isnt all that great considering earth would be waiting years for your return... kinda sucks Right. Basically travelling foward in time. Link to comment Share on other sites More sharing options...
Radical Edward Posted May 17, 2003 Share Posted May 17, 2003 Originally posted by cHIs- ok, thanks, hmm so if they did find away to at least travel near c it woudlent be all that great on the trip back, the earth would of ages but not you. If thats right. So wait, you are basicly traveling forward in time , so earth would be waiting years for your return, so it would be a quick way to see the future, and the whole idea of traveling at light speed isnt all that great considering earth would be waiting years for your return... kinda sucks the issue in this matter is more to do with general relativity rather than special. at some point you have to accelerate towards the earth, that is when you age less than it does. the SR stuff is not really important in this case (twins paradox) Link to comment Share on other sites More sharing options...
blike Posted May 17, 2003 Share Posted May 17, 2003 Originally posted by Radical Edward the issue in this matter is more to do with general relativity rather than special. at some point you have to accelerate towards the earth, that is when you age less than it does. the SR stuff is not really important in this case (twins paradox) Why isn't special relativity involved? I thought special relativity dealt with velocity, and general relativity dealt with gravity.. Link to comment Share on other sites More sharing options...
Raider Posted May 17, 2003 Share Posted May 17, 2003 SR only works in "special" cases (hence the name) which is with a rest frame. GR is what you actually apply to the universe since we don't have a rest frame. Link to comment Share on other sites More sharing options...
Radical Edward Posted May 20, 2003 Share Posted May 20, 2003 Originally posted by blike Why isn't special relativity involved? I thought special relativity dealt with velocity, and general relativity dealt with gravity.. well look at it relativistically: ignore the earth and all gravity for the moment. You get in your spaceship and fly away from your twin at very high speed, watching him age more slowly than you. but he also watches you fly away at a very high speed, and he sees you ageing more slowly then him. so he turns round, and comes back, seeing the same thing happen again. oh no you think, what happens when he gets home: I am older than him, but he is also older than me! where has everything gone wrong? well the only difference between the two situations (relativistically) is that he had to accelerate to that speed, and accelerate back towards you, and then decelerate (still acceleration really, just in the opposite direction). during these periods, the twin who doesn't accelerate sees time pass more slowly for the other brother, the other brother sees time flying by for his accelerating twin, and the issue is resolved. Link to comment Share on other sites More sharing options...
cHIs- Posted May 20, 2003 Author Share Posted May 20, 2003 ok, im tryng to make sense of what you said, im sure you said it clear enough, im just slow and getting things Link to comment Share on other sites More sharing options...
Radical Edward Posted May 20, 2003 Share Posted May 20, 2003 put really simply, the only measureable difference between the two twins is that one of them accelerated. Link to comment Share on other sites More sharing options...
Tom Mattson Posted May 20, 2003 Share Posted May 20, 2003 General relativity is not required to understand the twin paradox. While it has been correctly noted that the difference between the two twins is that one of them accelerated, Special Relativity is perfectly capable of dealing with accelerations. This should make sense, because if you have a 4-velocity vu and take the time derivative of it, you get the 4-acceleration. Simply taking this derivative does not change the metric from flat to curved, so we are still working with SR. Here is a document that shows how to deal with accelerated frames, and the twin paradox is specifically treated: http://xxx.lanl.gov/pdf/gr-qc/0006095 Tom Link to comment Share on other sites More sharing options...
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