Interesting method. Two points. First, would this mean that X was measuring his relative velocity by reference to the part of the ruler next to him (like where X's clock is) and thus Y (by extension!) would effectively be present at X ? Second, how could this be made to work if the distance between X and Y is large - maybe light years?

First, would this mean that X was measuring his relative velocity by reference to the part of the ruler next to him (like where X's clock is) and thus Y (by extension!) would effectively be present at X ?

i dont really follow that...

X is measuring his relative velocity by reference to the part of the ruler next to him, yes, but the:

"thus Y (by extension!) would effectively be present at X"

i do not follow... when you say by extension, if you are referring to the ruler being part of Y then yes Y is present at X, but that is if the ruler is part of Y, which it isnt, i dont think!

 

Second, how could this be made to work if the distance between X and Y is large - maybe light years?

you'd need a way of measuring that distance, there must be a way, how else would scientists know that the neareast star (except our sun) is however many light years it is from us, i dont know how they'd work it out... it must be possible.

i do not follow... when you say by extension' date=' if you are referring to the ruler being part of Y then yes Y is present at X, but that is if the ruler is part of Y, which it isnt, i dont think!

[/quote']

 

I imagined that your ruler was "attached" to Y in the sense that Y had hold of the ruler and extended it towards X. Then X would be able to see the marks on Y's ruler. X could then compare any changes in his relation to the marks with those on his clock. There would be real problems if the ruler wasn't attached to Y. X wouldn't be sure whether his motion was relative to Y or relative to the ruler which had no connection with Y. Seems connection is the key.

yeah ok, so there'd have to be a connection between Y and the ruler, i mean, if i hold a ruler the ruler doesnt become part of me, although there is a connection.

 

do you understand it all now?

do you understand it all now?

 

Some' date=' not all. Thanks for your help. If you come up with any thoughts about the [b']big[/b] distance problem let me know. Perhaps you'll be able to throw some light on it.

The ruler represents the rest frame of y.

The ruler represents the rest frame of y.

 

What do you mean. What is a rest frame? Please don't say that it's a frame at rest!

What do you mean. What is a rest[/b'] frame? Please don't say that it's a frame at rest!

 

Isn't it a non-accelerating frame?