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Why do really fast speeds keep you from aging or feeling time ? 
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#1
Oct1809, 10:12 AM

P: 2

I started reading Orson Scott Card's "Speaker for the Dead" yesterday and I was struck by the fact that being able to communicate instantly with any point in the universe (as one can in Card's scifi world) is completely at odds with the ability to travel at nearlight speed (as on also can in the Ender series).
I know, it's science fiction, but I want to know if there's something in REAL science that I'm overlooking that makes this scheme at least moderately plausible. The thing that gets me as that, in Card's world, you can transmit 3000 years worth of communications to someone who has only "felt" eight years of time. So my real question is, what is time dilation supposed to be like? If you are traveling through space at super super fast speeds, why is it that you experience less time than someone on Earth? How is it that their 20 years is your 1 year, or whatever? If you were traveling at 0.99 of light speed and someone was sending you messages with some kind of laser communicating device, and hence the messages would catch up to you, how would "experience" those messages, if you were traveling for a period long enough for ALL the messages to arrive (catch up), but that the messages spanned over more Earthtime than "space traveler" (relativistic) time? Thanks for any help you can give! bn 


#2
Oct1809, 01:17 PM

P: 362

do a google search for
signal reaching speeding spaceship you'll find many answers 


#3
Oct1809, 01:36 PM

P: 362

to be more specific
http://www.mathinst.hu/pub/algebrai...etime113.pdf 


#4
Oct1809, 01:58 PM

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Why do really fast speeds keep you from aging or feeling time ?
The same thing happens with time. Two different paths between event A and event B in spacetime simply have different durations. 


#5
Oct1809, 04:07 PM

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#6
Oct1809, 04:30 PM

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Then if you turned around and were traveling back towards the Earth at 0.99c, now you would each receive each other's messages at a speededup rate, because of the Doppler effect (now each successive signal is sent from a smaller distance, so it has less distance to cover to reach you than the previous one), which shortens the time between signals being received by a greater factor than time dilation lengthens it. So, in this sense things are symmetrical during the inward journey too. There is an asymmetry over the entire journey though: if you spent the same amount of time traveling away from the Earth as traveling back towards it (same speed on both the outward and inward legs of the journey), then you would see the Earth's signals go from sloweddown to spedup exactly halfway through the journey, while the Earth would see your signals sloweddown through most of the journey and spedup for less than half of it, which is one way of explaining why you have aged less (sent less total signals to Earth than they sent to you) by the time you return. This is explained in the Doppler Shift Analysis section of this excellent page on the twin paradox, and in the Too Many Analyses section they also offer a nice spacetime diagram, with time on the vertical axis and space on the horizontal axis, the signals sent from Stella (the rocket traveler) to Terence (the guy on Earth) shown on the left, and the signals sent from Terence to Stella shown on the right. You can see on the left side that Terence is receiving sloweddown (redshifted) signals for more than half the time between Stella leaving and Stella returning, whereas the right side shows that Stella is receiving sloweddown signals for exactly the same amount of time she is receiving spedup (blueshifted) signals (for her the switch from one to the other happens at the midpoint of her journey when she turns around, the curved section of her worldline in the diagram). 


#7
Oct1909, 05:25 AM

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The equation for the relativistic Doppler effect is Fo = Fs / sqrt((1+v/c)/(1v/c)) where Fo is the frequency the observer measures and Fs is the frequency of the source. v is the velocity of the source relative to the sender and c is the speed of light. If the source and observer are heading towards each other the signs for v in the equation have to be reversed. See http://en.wikipedia.org/wiki/Relativ...Doppler_effect 


#8
Oct1909, 06:14 AM

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However, I feel I should point out that no speed will "keep you from aging or 'feeling time'". In your own coordinate system, no matter how fast you are going relative to others, you will age and "feel time" at exactly the rate you always do.



#9
Oct1909, 06:06 PM

P: 117

*See Twin Paradox 


#10
Oct2109, 06:10 PM

P: 2

Thanks everyone!
bn 


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