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Time dilation and age difference

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Time dilation and age difference

kkiiji
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1 of 1 people found this post helpful Posted 07/13/09 - 07:09 PM: Subject: Time dilation and age difference	#1
Let's say I am in a spaceship that travels near the speed of light for a second, meaning I must have traveled near 310^8 meters. Now let's assume someone watched me travel this whole time, a second for me must have been much longer for him, let's say my one second was an hour for him. Now doesn't this mean that he watched me travel a distance of near 310^8 in a whole hour, thus to him I wasn't going all that fast? Now if we increase my traveling speed even more, wouldn't I appear to be going slower and slower to the observer eventually coming to a halt?
Heard joke once: Man goes to doctor. Says he's depressed. Says life seems harsh and cruel. Says he feels all alone in a threatening world where what lies ahead is vague and uncertain. Doctor says "Treatment is simple. Great clown Pagliacci is in town tonight. Go and see him. That should pick you up." Man bursts into tears. Says "But Doctor... I am Pagliacci." Good joke, everybody laugh. Roll on snare drum... Curtains.

Kwalish Kid
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Posted 07/14/09 - 05:22 AM:	#2
kkiiji wrote: Let's say I am in a spaceship that travels near the speed of light for a second, meaning I must have traveled near 310^8 meters. Now let's assume someone watched me travel this whole time, a second for me must have been much longer for him, let's say my one second was an hour for him. Now doesn't this mean that he watched me travel a distance of near 310^8 in a whole hour, thus to him I wasn't going all that fast? Now if we increase my traveling speed even more, wouldn't I appear to be going slower and slower to the observer eventually coming to a halt? To the observer, it would appear that your physical processes were going slower. However, the speed that you were going need not be different, because while you were travelling, you would see the distance that you were passing to be significantly less than the observer sees it. In Special Relativity, symmetry is often preserved through relationships between space and time, not simply symmetry preservation in space and symmetry preservation in time as we expect given pre-relativistic physics and geometry. Sorry if that last bit is a little unexplained, but I'm a little rushed right now and don't have enough caffeine.
"Scientific truth is always paradox, if judged by everyday experience, which catches only the delusive nature of things." - KM, V, P and P Can you pass Religion 101?

Death Monkey
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Posted 07/14/09 - 06:29 AM:	#3
To elaborate, let's say that I am here on Earth observe you to be travelling at 0.9c for 1 second. I would thus observe that you travel about 270,000 km. You, however, would only experience about 0.44 seconds of time passing, but you would also only observe that you travelled about 119,000 km. So we both agree on the relative speed being 0.9c. DM
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kkiiji
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Posted 07/14/09 - 03:30 PM:	#4
So because the space I am traveling is contracting, my velocity is the same as your measurement of my velocity? I see. Thanks. Question two: So what if while I am in my spaceship I observe the person who is measuring me? I think the theory is that his time would be slower than my time, but then if that's the case wouldn't I observe his time to pass by less than my time? When in reality his time passed by more than my time, since a second for me was more than a second for him. So why would his time be slower than mine? Shouldn't it be faster? Edited by kkiiji on 07/14/09 - 03:38 PM
Heard joke once: Man goes to doctor. Says he's depressed. Says life seems harsh and cruel. Says he feels all alone in a threatening world where what lies ahead is vague and uncertain. Doctor says "Treatment is simple. Great clown Pagliacci is in town tonight. Go and see him. That should pick you up." Man bursts into tears. Says "But Doctor... I am Pagliacci." Good joke, everybody laugh. Roll on snare drum... Curtains.

Kwalish Kid
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Posted 07/14/09 - 03:58 PM:	#5
kkiiji wrote: Question two: So what if while I am in my spaceship I observe the person who is measuring me? I think the theory is that his time would be slower than my time, but then if that's the case wouldn't I observe his time to pass by less than my time? When in reality his time passed by more than my time, since a second for me was more than a second for him. So why would his time be slower than mine? Shouldn't it be faster? The reality is that each observer is correct. Each sees the other moving slower because, in order for the laws of physics to work out (with the constant speed of light), events that one observer sees must happen at a different time than when another observer sees them, but all observers must agree on what events actually occur.
"Scientific truth is always paradox, if judged by everyday experience, which catches only the delusive nature of things." - KM, V, P and P Can you pass Religion 101?

kkiiji
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Posted 07/14/09 - 07:42 PM:	#6
That seems conflicting though. If the guy in the spaceship is observing the stationary observer the whole 1 second duration of his travel and sees that less than a second has passed by on the stationary observer's clock, how could the stationary observer have observed the pilot's travel duration of 1 second in more than 1 second? Pilot: in one second of ship clock, sees observer's clock go by less than 1 second. Observer: Sees ship clock go by 1 second in more than a second. Doesn't that seem horribly conflicting?
Heard joke once: Man goes to doctor. Says he's depressed. Says life seems harsh and cruel. Says he feels all alone in a threatening world where what lies ahead is vague and uncertain. Doctor says "Treatment is simple. Great clown Pagliacci is in town tonight. Go and see him. That should pick you up." Man bursts into tears. Says "But Doctor... I am Pagliacci." Good joke, everybody laugh. Roll on snare drum... Curtains.

Death Monkey
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Posted 07/15/09 - 01:34 AM:	#7
kkiiji, That seems conflicting though. If the guy in the spaceship is observing the stationary observer the whole 1 second duration of his travel and sees that less than a second has passed by on the stationary observer's clock, how could the stationary observer have observed the pilot's travel duration of 1 second in more than 1 second? Pilot: in one second of ship clock, sees observer's clock go by less than 1 second. Observer: Sees ship clock go by 1 second in more than a second. Doesn't that seem horribly conflicting? Only because you are assuming that both observers agree on which events were and were not simultaneous. Let's take acceleration out of the equations, and consider the following thought experiment: You have two space stations, stationary with respect to each other, and 8 light minutes apart according to their reference frame. You also have a spaceship travelling at 0.8c. It will pass station A (assume it passes arbitrarily close to the station), and then station B. Also, let's say the spaceship is 10 meters long. Let's also say that station A and the spaceship each have a clock inside them, and that the observer on station A (let's call him Adam) is watching both clocks, as is the observer on the ship (call him Steve). Now, when the ship passes station A, both Adam and Steve each reset their clocks to 0. First, let's consider the whole situation from the point of view of Adam. According to him, Steve passes station B 10 minutes after passing station A. He observes that when he sees Steve pass station B, his own clock says 18, but he knows that since station B is 8 light minutes away, that Steve actually passed B 8 minutes ago, when Adam's clock would have said 10. This matches what he would expect, since Steve travelled 8 light minutes at 0.8c. Adam also observes that when Steve passes B, Steve's clock says 6. So clearly Steve only experienced 6 minutes betwee the two events. This also matches what Adam would expect, given that he knows that due to time dilation, Steve should only experience 0.6 times the amount of time that Adam experiences. And as a final note, Adam also observes that Steve's spaceship is only 6 meters long. But he also knows that due to length contraction, Steve would observe his own spaceship to be 10 meters long. Now, let's consider the whole situation from the point of view of Steve. Steve sees two objects coming towards him, both at 0.8c. The first is station A, and the second station B. He also observes that these two stations are 4.8 light minutes apart. But he knows that due to length contraction, Adam would observe the distance to be 8 light minutes. According to Steve, station B passes him 6 minutes after station A does. This is, of course, consistent with the fact that the two stations are 4.8 light minutes apart, and are both travelling at 0.8c. Steve is also watching Adam's clock. When Steve passes B, he observes that Adam's clock says 0.72. He also knows that Adam is 4.8 light minutes away, so the light he is seeing from Adam is 4.8 minutes old. He knows that because Adam is moving at 0.8c, he is only experiencing 0.6 times the amount of time that Steve is experiencing. He thus computes that right now Adam's clock says 3.6 (0.72 + 4.8 * 0.6). So, everybody sees what they expect to see, even though both Adam and Steve say that time is going more slowly for the other one. So how is this apperant contradiction resolved? The answer is that they do not agree on the simultaneity of events. Note that Adam cannot directly observe what his own clock said when Steve passed B. He has to infer this. He can infer this in two ways. He can either infer from the fact that Steve was travelling at 0.8c that Steve will pass B 10 minutes after he passes A, or he can infer that he saw Steve pass B 8 minutes after it actually happened, from the fact that B is 8 light minutes away. Either way, implicit in this is the assertion that two events, seperated by a distance of 8 light minutes, were simultaneous. Those two events being that Steve passes B, and that Adam's clock says 10. likewise, when Steve passes B he cannot directly observe what Adam's clock says. He must infer what Adam's clock said at that time, as was already described above. Likewise, implicit in this is the assertion that two events, seperated now by a distance of 4.8 light minutes, were simultaneous. These two events being that B passes Steve, and that Adam's clock says 3.6. So the apperant contradiction follows from the incorrect assumption that simultaneity is preserved in differt reference frames. Put simply, two people in different inertial frames will not agree on which events are simultaneous with each other. This should actually be no suprise. Time dilation implicitely indicates that two people in different inertial frames will not agree on the amount of time that passes between two events. All this means is that they won't agree even when the time between those two events is (occording to one of them) zero. DM
Pseudoscience makes Baby Jesus cry.

kkiiji
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Posted 07/15/09 - 11:16 AM:	#8
Oh yeah I forgot about the simultaneity thing, that helps a lot, thank you. I assume that this means if Steve were to decelerate back to 0m/s, Adam's time would appear to travel super fast until Adam's time surpasses Steve's time, right? I also assume that due to the difference in simultaneity, Adam would NOT see Steve just kind of traveling real slowly in space while he decelerates, but instead see him decelerating normally? Edited by kkiiji on 07/15/09 - 11:22 AM
Heard joke once: Man goes to doctor. Says he's depressed. Says life seems harsh and cruel. Says he feels all alone in a threatening world where what lies ahead is vague and uncertain. Doctor says "Treatment is simple. Great clown Pagliacci is in town tonight. Go and see him. That should pick you up." Man bursts into tears. Says "But Doctor... I am Pagliacci." Good joke, everybody laugh. Roll on snare drum... Curtains.

Kwalish Kid
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Posted 07/15/09 - 02:57 PM:	#9
kkiiji wrote: Oh yeah I forgot about the simultaneity thing, that helps a lot, thank you. I assume that this means if Steve were to decelerate back to 0m/s, Adam's time would appear to travel super fast until Adam's time surpasses Steve's time, right? One of the results of relativity theory is that there are multiple paths from one event to another, and not all of these events have the same length in time. If Steve decelerates until he is not moving relative to Adam, he will have aged less than Adam. If Steve turns around and heads back, then he will probably get back to Adam and find that less time has passed for him than it has for Adam. From any perspective, Steve has performed a strange trip through time and space: in one direction, he passed a contracted space, then he travelled the contracted space back. In doing the turnaraound (even if only to slow to a stop), Steve changes from one frame of reference to another, so even though we normally would say that he could consider himself to be at rest, when he is comparing his clock behaviour to that of others, when he does the turnaround he "skips over" a chunk of time--there are events for which he either assigns one value on the way out an another on the way in or there is a big gap in the time assigned to some events and the events that happen "next" in Adam's frame. I also assume that due to the difference in simultaneity, Adam would NOT see Steve just kind of traveling real slowly in space while he decelerates, but instead see him decelerating normally? As Steve decelerates, his dilation will reduce appropriately until it reaches zero when they are not moving relative to each other.
"Scientific truth is always paradox, if judged by everyday experience, which catches only the delusive nature of things." - KM, V, P and P Can you pass Religion 101?

cosscos
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Posted 07/15/09 - 11:18 PM:	#10
When you travel to universe by speed of light, about three hundred thousand kilometres per second, your time is going to close to stop. While your friends on the planet earth spending seconds or minuets or even hours talking one another. you could travel to past or future, and get back to earth only with seconds. Then, you will be surprised how you get old, with white hair, white eyebrows, white moustache and wrinkled skin, while your friends are just spending seconds,talking one another on this planet earth. Couple of seconds in GMT would be everlasting stop in World Time over there. cc

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