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 kurious Aug3-04 07:18 PM

definition of a clock in relativity theory

What is the definition of a clock in relativity theory?

an object that measures the rate of time flow.

 pervect Aug5-04 01:09 PM

Quote:
 Quote by Perfectly Innocent Typically, the meaning of a clock is not defined in relativity. No reason to worry. Logically, it's OK to just have blind faith that "ideal clocks" really do exist conceptually.
The quest for a good clock has developed slowly and empirically over time. A rather interesting show on the topic is "Longitude", in which the first naval chronometer was developed. The goal wa simple - to develop a clock that could be taken to sea, and still keep good enough time so that a person could determine their latitude by measuring the time at which the sun reached it's high point in the sky.

As a practical matter, we do have a definition for a "good clock" nowadays. But it's not a theoretical definition, it's one from a standards comission. I refer, of course to the SI second. And, to tie it in with my pervious comment, our "good clock" nowadays is also very small - it's an atom.

Quote:
 The second is the duration of 9 192631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom. [13th CGPM (1967), Resolution 1]
It is a good thing, in my opinion, that we define our clocks empirically (through standards comittee's) rather than through theory. Defining a clock theoretically is not productive, as science has to be based ultimately on observation.

 pmb_phy Aug5-04 01:30 PM

Quote:
 Quote by kurious What is the definition of a clock in relativity theory?
A friend of mine is a GR expert. He wrote an article on the nature of time and what is meant by a "clock". Its a great article and a good read. See

http://www.wfu.edu/~brehme/time.htm

Pete

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