We say that atomic clocks are the most accurate clocks ever made, they may lose or gain $x$ seconds in $y$ years. How do we find this uncertainty because we do not have an ideal clock to compare with the clock that we made?
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1$\begingroup$ We measure multiple clocks against each other and compare the statistical errors. This assumes that the clocks do not have the same systematic errors, of course. In practice this is controlled by using different technologies with different systematic errors and by having multiple clocks of the same technology built and operated by different groups of people in different locations of the world. In addition we are also comparing against precision clocks provided by nature, like pulsars. While those are not quite as accurate as our atomic clocks, they are guaranteed to be independent of us. $\endgroup$– CuriousOneCommented Dec 18, 2014 at 14:31
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$\begingroup$ @CuriousOne we are also comparing against precision clocks provided by nature, like pulsars. How is this possible? They are far away from us, aren't they? $\endgroup$– RogUECommented Dec 18, 2014 at 14:38
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$\begingroup$ The nearest known pulsars are hundreds of lightyears away. In cosmic terms that's the front yard. $\endgroup$– CuriousOneCommented Dec 18, 2014 at 14:40
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1$\begingroup$ @CuriousOne All the clocks that we posses will not keep the correct time and we do not have an ideal clock, then what's the point in comparing these clocks with each other, if this is the way we use to estimate the accuracy of our clocks, then there must be error in the estimated error(or accuracy) of a clock. $\endgroup$– RogUECommented Dec 18, 2014 at 14:59
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1$\begingroup$ @CuriousOne I am really sorry. Just because of curiosity, I asked this much. Thanks for your 'comments'. $\endgroup$– RogUECommented Dec 18, 2014 at 15:08
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The nearest we have to a standard is International Atomic Time. This is:
TAI as a time scale is a weighted average of the time kept by over 200 atomic clocks in over 50 national laboratories worldwide.
The errors in individual clocks can be assessed by comparing them to the weighted average.
Re the mention of pulsars in your comment, pulsars slow down over time and indeed atomic clocks are used to track their slowing. Also pulsars occasionally glitch. So atomic clocks are more accurate than pulsars are.
answered Dec 18, 2014 at 18:06
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1$\begingroup$ Regarding the pulsar glitch phenomenon: physics.stackexchange.com/a/781603/226902 $\endgroup$– QuilloCommented Dec 17, 2023 at 23:08