| Craville Studies Forum » Physics » Viewing Topic: Time Dilation |
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  Posts: 22 Group: Admin Skin: Default | Ok, time dilation is simple enough when all you have to do is calculate the elapsed time etc using the formula supplied on the formula sheet. But trying to understand it can be much more difficult.
As most would already know, time dilation is when an observer, stationary in relation to another object, sees time appear 'slower' than an observer in the same frame of reference as the moving object. As an example, take for instance a car moving at half the speed of light (0.5c). Say the driver of the vehicle sneezes and it takes him one second to sneeze as recorded by himself. A stationary observer watching the car go past however, observes that sneeze to take longer. Now, in trying to understand this, many relate it back to light. We all know that our eyes see images in frames. Frames that are travelling from a source at the speed of light. If we think about it logically, a car moving away from us at 0.5c will put a bigger space between its frames. Say for instance a stationary object is projecting its light, the frames that our eyes see are exactly the way they should be. However, an object that is moving away from us at 0.5c has the following breakdown at each frame: In each frame: The object has moved 0.5c away from us, then the light has come back at 1c. This goes on for each frame. Following this logically, the frames are 1.5 times further apart than if it was stationary. This is called the relativistic Doppler effect. How Stuff Works has a picture of this under Fig 7 at http://science.howstuffworks.com/relativity3.htm. Whilst this theory sounds good, it falls down in many ways. Firstly, the above example was made on the assumption that the object was moving away from the stationary observer. Following the logic from above, if the object was then to turn and come towards us, time would actually speed up, which we know doesn't happen. Secondly, the formula that has been shown to accurately predict time dilation does not produce the same result as simply saying the frames are 1.5 times further apart. And thirdly, this idea means that as soon as the object stops moving, its time would be reset, which we know doesn't happen as a result of experiments. Experiments such as sending atomic clocks around the world in jet aeroplanes to see if their time had slowed proved time dilation to be true. So, if the idea of frames of light doesn't fit, what does? Does time actually slow? Wikipedia has a very good article on time dilation at http://en.wikipedia.org/wiki/Time_dilation. The article details many of the experiments that have shown time dilation to exist. According to wikipedia, and many other sources, time dilation means that humans could theoretically live for thousands of years. The only way this is possible is if the ageing of the human body actually slowed. However, this throws up the strange possibility: A human watching from earth would see time on the spacecraft slow, meaning living for a long time is possible. However, we know that an observer in the same frame of reference sees time as normal. That means that an observer on earth could see the person in the spacecraft as living (because time has slowed) but on the spacecraft the person is dead (because time has not slowed in that frame of reference). However, since time dilation works conversely, it also works the other way around. ie: the person on the spacecraft sees the person on earth as living, but the person on earth is dead. So, if the ageing of the human body cannot actually be slowed, that puts time dilation back into the category of a 'trick of light slowing down.' But this fails to explain the dilemma with the two atomic clocks not being synchronised after one was flown around in a jet aeroplane. I know that all of this is confusing, which is why in many cases it is best to not even try to understand it, just be able to do the time dilation questions using the formula. However, Craville Studies would love to see some people out there try and understand it and get back to us in this topic. Good luck. ----------------- Craville Studies The Site for HSC subject links, tips and resources www.craville.110mb.com |
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Post #1 - 08.05.07
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Posts: 2 Group: Member Skin: Default | Wow! That's incredibly confusing, but it does come up with some good points. 
I'd love to see someone clarify this. ----------------- |
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Post #2 - 08.06.07
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Posts: 7 Group: Member Skin: Default | Shotgun being the guy on the spacecraft who lives.
I like it when i gain time from time dilation. Does that mean that a fast 100m sprinter times himself to go faster than someone watching in the stands? ----------------- |
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Post #3 - 08.07.07
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Posts: 22 Group: Admin Skin: Default | QUOTE:
Yes. However, the effect is minimal because a sprinter is realistically not travelling at that high a speed. However, in a race that comes down to milliseconds, it is important so that is why the new systems use lasers to record the time as they have no problem with time dilation. ----------------- Craville Studies The Site for HSC subject links, tips and resources www.craville.110mb.com | |
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Post #4 - 08.14.07
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Posts: 2 Group: Member Skin: Default | "A human watching from earth would see time on the spacecraft slow, meaning living for a long time is possible. However, we know that an observer in the same frame of reference sees time as normal. That means that an observer on earth could see the person in the spacecraft as living (because time has slowed) but on the spacecraft the person is dead (because time has not slowed in that frame of reference). However, since time dilation works conversely, it also works the other way around. ie: the person on the spacecraft sees the person on earth as living, but the person on earth is dead."
This scenario is, I think, known as the Twin Paradox. Our teacher gave us a booklet on space which had this. Apparently Einstein disproved the Paradox, by, instead of applying the Special Theory of Relativity, applying the normal Theory of Relativity. As such, the only slowing down of time happens when one is accelerating away from the planet in the spaceship and when accelerating back.... In that case the age difference would be minial, unless you're accelerating in space as well. I'm guessing this is something to do will inertial & non-inertial frames of reference. I can't really expand on it either, because I'm just recalling something from the back of my head. Oh, and also, if the acceleration thing is the case, if you're accelerating back to Earth, would that cancel out the time dilation achieved when levaing Earth?? This is pretty confusing, but i doubt they would ask anything about the Twin Paradox. ----------------- |
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Post #5 - 02.08.09
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