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## Summary:

- New mode of travel in a one-way 'twin's paradox. Is this method valid?

## Main Question or Discussion Point

I have always had an interest in relativity theory, though have struggled to wrap my head around it. But, now that I have retired, I thought I should try once again to understand its intricacies.

Following the discussions in 'One Way Twin', initiated by Buckethead on 16th June last year, has recalled a problem I had in previous attempts at comprehension.

My enquiry starts off like the 'One Way Twin', but instead of travelling to a distant plant (Mars), my 'twins' live on a very long, flat planet, called 'Home', adjacent to which is another long, flat planet, known as 'Northbound, which whizzes past at 3c/5 - I chose that value as it makes the maths easy.

Twins Tim and Tom have top quality watches, which tick in synchronisation with each other, and display the same time. The watches are also extremely shockproof.

My understanding is that if one of them leaves Home at 3c/5, travelling for four minutes on his watch, then returns at the same speed, he will 'lose' two minutes when they compare watches, that is when the traveller's watch displays three o'clock, the stay-at-home's will display two minutes past three.

Tim steps onto Northbound, and waits for four minutes to elapse on his watch, then leaps back onto Home.

What I should like to know is: what is the difference between their watches? As suggested in the 'One Way Twin' discussion, this can be discovered. Tom could use triangulation to measure how far away Tim is, if Tim provides two signalling devices at a known separation.

Once Tom knows how far away Tim is, Tim sends a light signal when his watch is at exactly three o'clock. Tom will see the signal, note the time on his watch and as he knows haw far away Tim is, he can calculate how long it took the light to come from Tim. Thus he can say "the time on my watch when Tim's watch was at 3:00 was... and that should allow Tom to work out how Tim's time varied with respect to his on his one-way trip.

Can you tell me what the answer will be please, and obviously more importantly, why?

Of course, that's the easy bit; my real puzzle comes once I get this information.

My apologies if this seems very simple stuff.

Following the discussions in 'One Way Twin', initiated by Buckethead on 16th June last year, has recalled a problem I had in previous attempts at comprehension.

My enquiry starts off like the 'One Way Twin', but instead of travelling to a distant plant (Mars), my 'twins' live on a very long, flat planet, called 'Home', adjacent to which is another long, flat planet, known as 'Northbound, which whizzes past at 3c/5 - I chose that value as it makes the maths easy.

Twins Tim and Tom have top quality watches, which tick in synchronisation with each other, and display the same time. The watches are also extremely shockproof.

My understanding is that if one of them leaves Home at 3c/5, travelling for four minutes on his watch, then returns at the same speed, he will 'lose' two minutes when they compare watches, that is when the traveller's watch displays three o'clock, the stay-at-home's will display two minutes past three.

Tim steps onto Northbound, and waits for four minutes to elapse on his watch, then leaps back onto Home.

What I should like to know is: what is the difference between their watches? As suggested in the 'One Way Twin' discussion, this can be discovered. Tom could use triangulation to measure how far away Tim is, if Tim provides two signalling devices at a known separation.

Once Tom knows how far away Tim is, Tim sends a light signal when his watch is at exactly three o'clock. Tom will see the signal, note the time on his watch and as he knows haw far away Tim is, he can calculate how long it took the light to come from Tim. Thus he can say "the time on my watch when Tim's watch was at 3:00 was... and that should allow Tom to work out how Tim's time varied with respect to his on his one-way trip.

Can you tell me what the answer will be please, and obviously more importantly, why?

Of course, that's the easy bit; my real puzzle comes once I get this information.

My apologies if this seems very simple stuff.