Time Dilation: Explaining the Basics for a Sci-Fi Story

[CakeOrDeath?]

Hi all.

I'm working on writing a sci-fi story and I'm really just getting into researching relativity and time dilation. I'm a layman, but the ideas excite me, so I'm trying to figure these things out the best I can.

Here is my hypothetical: Say someone were to have a vehicle that could travel the speed of light, and on the front of it, a video camera was affixed to relay the image to a television set in real time. The man in the light speed vehicle travels such a distance that he returns to find everyone 20 years older, while he has barely aged. 1) What do the observers watching the television see once the craft is traveling at light speed? Do they see exactly what the man in the vehicle is seeing? 2) Would the image keep going for all 20 years, and as these people aged they could keep watching the image of lightspeed travel?

Obviously, the scenario is ignoring the time it would take for the television image to be broadcast to the television. That would make things much more complicated. I think I know the answer to this question, but I want to run it by the people who know a thing or two.

Please explain in the simplest possible manner! Thanks in advance.

 

[bcrowell]

Hi, CakeOrDeath,

Welcome to Physics Forums!

Relativity says you can't travel at the speed of light, so relativity doesn't have an answer to your question.

-Ben

 

[CakeOrDeath?]

But this is just a hypothetical. Besides, doesn't dilation occur at all high speeds? Even if you went half the speed of light, dilation would still occur, would it not?

 

[yuiop]

But this is just a hypothetical. Besides, doesn't dilation occur at all high speeds? Even if you went half the speed of light, dilation would still occur, would it not?

Hi, CakeOrDeath. Welcome to PF. Just don't mention traveling at the speed of light or the point of view of a photon or you will get an answer like #2 and every other aspect of your question will be ignored

Lets say the traveller is traveling at a relative velocity that is some significant fraction of the speed of light, such that 10 years of proper time passes for him, while 20 years of proper time passes for the observers that stayed on Earth. Now if the traveller had a webcam inside his spaceship filming his everyday activities and transmitting them back to the Earth, then the transmitted film would look like a video being played back in slow motion (for most of the journey) as far as the Earth watchers are concerned. Eventually after about 15 years Earth time, the Earth observers would see the film speed up for the final few years of the travellers journey, but overall they only see a total of 10 years of the travellers life transmitted.

Now if the traveller was watching Earth events on his TV, then the film would appear to play in slow motion to the traveller and at the turnaround pint he will only have seen about 2 years of news events pass on his TV at his turnaround point (5 years on his clock) and when he turns around he immediately sees the Earth film speed up and he sees of 15 years of Earth news broadcasts pass in the final 5 years of his journey back, so that overall he sees 20 years of Earth life transmitted during his journey.

The figures above are not exact as I am too lazy at the moment to work out the Doppler shifts, but the general idea is correct. The important thing is that the traveller sees Earth events speed up as soon as he turns around, while the Earth observers are not even aware he has turned around until he nearly home and they only see a small portion of the travellers film speeded up at the end.

 

[CakeOrDeath?]

yulop, that is a fantastic answer and exactly the type of response I needed. Thanks a million!