Einstein's light clock thought experiment

[David CLayton]

I'm an engineer who has an amateur interest in physics. I have been reading about Einsteins light clock experiment. I understand the principal that when a light clock on a train etc is moving relative to a standing still observer then the light must travel a longer distance per tick. given that that the speed of light is the same for all observers, this means that time will pass at a slower rate for the person on the train.
My question is this, would the light clock with the stationary observer on the platform appear to be moving to be moving relative to the person on the train giving the same effect as the light would appear to be traveling in a triangular motion. My basic understanding was that we could not determine who was at absolute motion.
Apologies if this is a basic error I am making but I cannot get my head around this.

 

[PeterDonis]

would the light clock with the stationary observer on the platform appear to be moving to be moving relative to the person on the train giving the same effect

Yes. The light clock on the train appears to run slow to the observer on the platform, and the light clock on the platform appears to run slow to the observer on the train.

My basic understanding was that we could not determine who was at absolute motion.

That's correct.

 

[Ibix]

If Peter's reply seems like it leads to contradiction, google "relativity of simultaneity".

 

[David CLayton]

Why is it that someone traveling at speed away from the Earth on a ship would age slower than the people left behind on the planet when to the person traveling on the ship would observe the clocks on Earth traveling at a slower rate too.
I have been told that if someone could travel near the speed of light away from the Earth for 5 years or so and then turns around and returns, hundreds of years would have passed on the earth. If is true that the person traveling at speed would observe the Earth's clock to be running slowly then I cannot understand why a greater time would of passed.

 

[Nugatory]

Why is it that someone traveling at speed away from the Earth on a ship would age slower than the people left behind on the planet when to the person traveling on the ship would observe the clocks on Earth traveling at a slower rate too.
I have been told that if someone could travel near the speed of light away from the Earth for 5 years or so and then turns around and returns, hundreds of years would have passed on the earth. If is true that the person traveling at speed would observe the Earth's clock to be running slowly then I cannot understand why a greater time would of passed.

That is the "Twin Paradox", well explained by http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_paradox.html

It actually has very little to do with the time dilation that is demonstrated by Einstein's light clock.

 

[Orodruin]

Why is it that someone traveling at speed away from the Earth on a ship would age slower than the people left behind on the planet when to the person traveling on the ship would observe the clocks on Earth traveling at a slower rate too.
I have been told that if someone could travel near the speed of light away from the Earth for 5 years or so and then turns around and returns, hundreds of years would have passed on the earth. If is true that the person traveling at speed would observe the Earth's clock to be running slowly then I cannot understand why a greater time would of passed.

See post #3 and my signature...

 

[Ibix]

Why is it that someone traveling at speed away from the Earth on a ship would age slower than the people left behind on the planet when to the person traveling on the ship would observe the clocks on Earth traveling at a slower rate too.

They don't. They both agree that the other's clocks are ticking slowly.

I have been told that if someone could travel near the speed of light away from the Earth for 5 years or so and then turns around and returns,

Turning round and returning is different. As Nugatory says - look for the twin paradox, which is the scenario you are describing. It can't be resolved just by thinking about time dilation, because that's not really the relevant factor.

 

[Orodruin]

That is the "Twin Paradox", well explained by http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_paradox.html

It actually has very little to do with the time dilation that is demonstrated by Einstein's light clock.

I would say that the paradox itself has everything go do with the time dilation as it arises as an apparent paradox due to failing to apply it correctly (ie, taking relativity of simultaneity into account).

 

[David CLayton]

thank you all for your comments. the twin paradox is something i need to read on however a basic look has proved very helpful.

 

[Nugatory]

I would say that the paradox itself has everything go do with the time dilation because...

Ah... Yes, I'll buy that :)