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## Main Question or Discussion Point

I am not a physics expert but have been having a discussion about the effects of the Special Theory of Relativity with a friend.

I came up with an example where time does not actually alter at high speeds, although it can be perceived to by a stationary observer because of the time it takes an image (light) to reach that observer. I am just wondering whether this example is "correct" ie - if somebody staged this experiment for real, would it work in a logical way as I am suggesting, or would there be some sort of strange result becuase of the effects of SR?

Nb. for this example you have to assume that (i) it is possible to travel at ridiculously high speeds, (ii) someone has invented an amazing telescope and (iii) a month is exactly 1/12th of a year.

Length Contraction is an almost impossible concept for me to grasp though. One of the reasons is that, to my mind, it really complicates what the speed of light itself is. I read that (using approximation here) if something travels at around 90% of the speed of light, length contracts by 50% - what appeared to be 2 light years to a stationary object becomes just 1 light year to the object travelling at 90% the speed of light. This is basically how I understand the Twin Paradox is explained. So what happens when you apply this principal of Length Contraction to light itself? Say there is a star that is 10 light years away from me. Obviously that means it takes light 10 years to travel that distance and I am seeing the star as it was 10 years ago. But, while light is travelling (at the speed of light), doesn't that distance become almost nothing... meaning that the light should arrive almost instantly? Obviously not, as we still have a concept of distance and time based on the speed of light, but it seems in my non-expert mind to defeat the theory of Length Contraction.

Sorry, I know I haven't really given a question to answer here. I have given an example of what I would expect to happen based on my logical understanding of the world then tried to explain to myself how Einstein's theory would mean the outcome is different, but not been able to grasp it because it seems to be self defeating somehow.

Any input would be appreciated -what am i getting wrong etc - but please try and keep in fairly simple terms for me!

I came up with an example where time does not actually alter at high speeds, although it can be perceived to by a stationary observer because of the time it takes an image (light) to reach that observer. I am just wondering whether this example is "correct" ie - if somebody staged this experiment for real, would it work in a logical way as I am suggesting, or would there be some sort of strange result becuase of the effects of SR?

Nb. for this example you have to assume that (i) it is possible to travel at ridiculously high speeds, (ii) someone has invented an amazing telescope and (iii) a month is exactly 1/12th of a year.

I think that one of the reasons this is supposed not to work as I have described is because of Length Contraction. ie if Dude B is travelling really fast, the distance between him and Dude A becomes less during the period he is travelling. If he keeps moving for 6 months and travels a distance of 1/4 of a light year, then he when he comes to a standstill and looks back, he has actually travelled further than that. Also, apparently according to SR theory, time is running slow for him - he will also have been travelling for longer than a "stationary" 6 months - so there are 2 factors causing him to have travelled further then simple logic would suggest.me to a friend said:There are 2 dudes floating in space, holding calendars and looking at each other through telescopes. Dude A is a light year away from the Dude B and has been there for at least a year. The date is currently 01/01/2008. When Dude A looks through his telescope at Dude B's calendar the date he sees is 01/01/2007. He is seeing Dude B's calendar as it was a year ago obviously. Right?

Now imagine that, on 01/01/2007, Dude B starts to move and spends 6 months travelling towards Dude A at half the speed of light. Well, we are now 6 months further forwards and the Dudes are only 3/4 of a light year away from each other (if you spend half a year, travelling at half the speed of light, you will have travelled a quarter of a light year in distance).

The date is now 01/07/08. Dude A looks at Dude B's calendar and sees the date 01/10/2007. (6 months have gone by and Dude B has turned the page on his calendar every day in that 6 months. He is now only 3/4 of a light year away from dude A so dude A is seeing his calendar as it was 9 months ago.)

The image Dude A is seeing of Dude B's calendar has sped up: 6 months have elapsed for Dude A but in that time he has seen Dude B turn 9 months worth of pages on his calendar.

Not only has time not slowed down for the fast-moving Dude B (it has remained the same), from his vantage point, Dude A has actually seen timespeed upfor him!

Length Contraction is an almost impossible concept for me to grasp though. One of the reasons is that, to my mind, it really complicates what the speed of light itself is. I read that (using approximation here) if something travels at around 90% of the speed of light, length contracts by 50% - what appeared to be 2 light years to a stationary object becomes just 1 light year to the object travelling at 90% the speed of light. This is basically how I understand the Twin Paradox is explained. So what happens when you apply this principal of Length Contraction to light itself? Say there is a star that is 10 light years away from me. Obviously that means it takes light 10 years to travel that distance and I am seeing the star as it was 10 years ago. But, while light is travelling (at the speed of light), doesn't that distance become almost nothing... meaning that the light should arrive almost instantly? Obviously not, as we still have a concept of distance and time based on the speed of light, but it seems in my non-expert mind to defeat the theory of Length Contraction.

Sorry, I know I haven't really given a question to answer here. I have given an example of what I would expect to happen based on my logical understanding of the world then tried to explain to myself how Einstein's theory would mean the outcome is different, but not been able to grasp it because it seems to be self defeating somehow.

Any input would be appreciated -what am i getting wrong etc - but please try and keep in fairly simple terms for me!