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Time and length units

  1. Oct 21, 2007 #1
    a) What is the modern definition of the time unit and the length unit?

    b) How people actually Materially realize these units ?

    (a) in the wiki, it reads:

    Under the International System of Units, the second is currently defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.[1] This definition refers to a caesium atom at rest at a temperature of 0 K (absolute zero). The ground state is defined at zero magnetic field.

    Meter: Today, it is defined as 1⁄299 792 458 of a light-second.

    Would anybody like to answer question (b) ?
  2. jcsd
  3. Oct 21, 2007 #2
    I think in question b you are asking how you, I, or anyone else measures time or length. How we individually realize these units varies from person to person. I can look at a person and say oh, he is 6 feet tall. He is not actually exactly 6 feet tall, but i think he is around that height. I hope that answers your question.
  4. Oct 21, 2007 #3


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    Science Advisor

    Wiki has it correct for part (a).

    I'm not quite sure what you are asking in part (b).
  5. Oct 21, 2007 #4


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    perhaps the OP is wondering how we actually physically implement a meter, or a second.
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