Baby Astronaut Posted November 24, 2011 Share Posted November 24, 2011 (edited) If one person A is accelerating to (or traveling at) a very high speed relative to person B, do their views of each other work like this?... Person A sees the actions of person B speeding up AND vice versa: person B sees the actions of person A speeding up. Person B sees the aging process slowing down for person A, who in turn sees the aging process speeding up for person B. So person A sees the other age quicker and move quicker. While person B sees the other age slower and move quicker. Edited November 24, 2011 by Baby Astronaut Link to comment Share on other sites More sharing options...
granpa Posted November 25, 2011 Share Posted November 25, 2011 http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html Link to comment Share on other sites More sharing options...
swansont Posted November 25, 2011 Share Posted November 25, 2011 If at constant velocity, each will see the other's clock as running slow. Link to comment Share on other sites More sharing options...
Baby Astronaut Posted November 25, 2011 Author Share Posted November 25, 2011 (edited) To clarify fully, does that mean each person would see the other aging slower, when in reality just one of them is? Edited November 25, 2011 by Baby Astronaut Link to comment Share on other sites More sharing options...
granpa Posted November 25, 2011 Share Posted November 25, 2011 it means you have to factor in relativity of simultaneity http://en.wikipedia.org/wiki/Relativity_of_simultaneity each observer will also see the other one as shrunk. this is possible because the length of an object is the distance from front to back at one simultaneous moment. Link to comment Share on other sites More sharing options...
Baby Astronaut Posted November 25, 2011 Author Share Posted November 25, 2011 I still don't get it. (What about my last question?) Link to comment Share on other sites More sharing options...
granpa Posted November 25, 2011 Share Posted November 25, 2011 how would we know? Link to comment Share on other sites More sharing options...
Mike-from-the-Bronx Posted November 25, 2011 Share Posted November 25, 2011 in Special Relativity: To an inertial observer time for any inertially moving body or any accelerating body always runs SLOWER. To an accelerating observer time for any inertially moving body always runs FASTER. To an accelerating observer time for any other accelerating body may run FASTER or SLOWER. It's more complicated. 1 Link to comment Share on other sites More sharing options...
between3and26characterslon Posted November 25, 2011 Share Posted November 25, 2011 If one person A is accelerating to (or traveling at) a very high speed relative to person B, do their views of each other work like this?... Person A sees the actions of person B speeding up AND vice versa: person B sees the actions of person A speeding up. Person B sees the aging process slowing down for person A, who in turn sees the aging process speeding up for person B. So person A sees the other age quicker and move quicker. While person B sees the other age slower and move quicker. http://www.einstein-online.info/spotlights/dialectic Link to comment Share on other sites More sharing options...
swansont Posted November 25, 2011 Share Posted November 25, 2011 To clarify fully, does that mean each person would see the other aging slower, when in reality just one of them is? They are both aging slower, according to the other observer. To break this symmetry, one of them has to accelerate. You can only say one of them is older/younger "in reality" if you have a single reference frame from which you can make the measurements. If they are both in inertial frames, you have two. Link to comment Share on other sites More sharing options...
granpa Posted November 28, 2011 Share Posted November 28, 2011 how would we know? -1 Link to comment Share on other sites More sharing options...
IM Egdall Posted November 28, 2011 Share Posted November 28, 2011 how would we know? If A and B meet and compare watches. In one example, imagine person A remains in uniform motion but person B accelerates --that is she/he changes speed and /or direction so as to arrive where A is. They meet, compare watches, and find B's watch has run slower than A's. And B has aged less than A. Why? Because only B has experienced acceleration. Link to comment Share on other sites More sharing options...
granpa Posted November 29, 2011 Share Posted November 29, 2011 I created this thread specifically for beginners to relativity http://www.physicsforums.com/showthread.php?t=314080 Link to comment Share on other sites More sharing options...
Baby Astronaut Posted November 29, 2011 Author Share Posted November 29, 2011 In one example, imagine person A remains in uniform motion but person B accelerates --that is she/he changes speed and /or direction so as to arrive where A is. They meet, compare watches, and find B's watch has run slower than A's. And B has aged less than A. Why? Because only B has experienced acceleration. Ah, that's where I've been making an error. I usually hear people traveling near c age slower, but in reality it's people who accelerate continually for a long time that would age slower. If they jumped directly into light speed (not accelerating once) they wouldn't age slower. Correct? Link to comment Share on other sites More sharing options...
swansont Posted November 29, 2011 Share Posted November 29, 2011 Ah, that's where I've been making an error. I usually hear people traveling near c age slower, but in reality it's people who accelerate continually for a long time that would age slower. If they jumped directly into light speed (not accelerating once) they wouldn't age slower. Correct? Both observers would age slower, as measured by the other. Motion is what causes the clocks to run slow. Acceleration is what breaks the symmetry when they compare measurements. Link to comment Share on other sites More sharing options...
Baby Astronaut Posted November 29, 2011 Author Share Posted November 29, 2011 Both observers would age slower, as measured by the other. Motion is what causes the clocks to run slow. Acceleration is what breaks the symmetry when they compare measurements. Ok, but when the moving person returns just one of them is going to be older (or more aged). So what the slower frame person observed had been an illusion. Link to comment Share on other sites More sharing options...
swansont Posted November 29, 2011 Share Posted November 29, 2011 Ok, but when the moving person returns just one of them is going to be older (or more aged). So what the slower frame person observed had been an illusion. It's not an illusion. What you measure depends on your frame, and when you change frames, what you measure changes. Link to comment Share on other sites More sharing options...
granpa Posted November 29, 2011 Share Posted November 29, 2011 during the acceleration some strange things happen. this is what lead to the idea general relativity. read the thread that I gave a link to Link to comment Share on other sites More sharing options...
IM Egdall Posted November 29, 2011 Share Posted November 29, 2011 (edited) One way to see why the person who experiences acceleration is the one who ages more slowly is with the twins paradox. Swanson is correct. Both A and B see the other's time running more slowly. But the acceleration breaks this symmetry. This can be explained using time dilation and the doppler effect. See my write-up: Click on http://marksmodernphysics.com/ then on Its Relative, Archives, The Twins paradox. Hope it helps. (For some reason the direct link below does not work) http://marksmodernphysics.com/Mark's%20Modern%20Physics/Musings/index.html Edited November 29, 2011 by IM Egdall Link to comment Share on other sites More sharing options...
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