What is the significance of the cesium-133 atom in defining the second?

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Discussion Overview

The discussion revolves around the significance of the cesium-133 atom in defining the second, focusing on the historical context of time measurement and the precision of atomic clocks. Participants seek clarification on the technical details related to the definition of the second and the performance of atomic clocks.

Discussion Character

  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant notes the historical definitions of the second, mentioning its evolution from a fraction of the mean solar day to the ephemeris second, and finally to the current definition based on cesium-133.
  • Another participant explains the precision of atomic clocks, specifically the NIST-F1, stating it is accurate to within about 1 second over 60 million years, and discusses the implications of the precision measurements (5 parts in 10^16).
  • There is a clarification regarding the meaning of "5 parts in 10^16," indicating that this relates to potential time discrepancies over extensive periods, with examples provided for context.

Areas of Agreement / Disagreement

The discussion does not present any explicit disagreements, but it reflects a lack of initial responses to the original query, indicating that participants may have different levels of engagement or understanding.

Contextual Notes

Participants express uncertainty about the technical details from the textbook, highlighting the complexity of the topic and the need for further explanation.

Who May Find This Useful

This discussion may be useful for individuals interested in the definitions of time measurement, the workings of atomic clocks, and the historical context of timekeeping in physics.

Dandy Candy
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Hi all,

I am a new member in your forum and I am very pleased to join it. This my first theard in this great forum.

My Q.:

The unit of time was originally defined as 1/86400 of the mean solar day. Because of irregularities in the Earth roatation, the definition was changed to the '' emphemeris second '', i.e., 1/31556925.9747 of the tropical year 1900. In 1967 , this definition was replaced.

the second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine of the ground state of the cesius-133 atom.

The definition is based on the atomic clock. One of the best atomic clocks ( NIST-F1) is precise to within about 1 second in 60 million years, or 5 parts in 10^16. Commercially available atomic clocks are precise to within 3 parts in 10^12.

I didn't understand this paragraph .. it's from my textbook !

Concepts in Engineering
Second Edition
Mark Holtzapple and W. Reece
McGraw-Hill
2008Would you mind explaining it, please?
 
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no reply ?!

:(
 
Dandy Candy said:
The definition is based on the atomic clock. One of the best atomic clocks ( NIST-F1) is precise to within about 1 second in 60 million years, or 5 parts in 10^16. Commercially available atomic clocks are precise to within 3 parts in 10^12.

I didn't understand this paragraph .. it's from my textbook !

It means that if you set the clock "exactly", and then wait 60 million years, it could be reading the wrong time. But, it will only be off by about 1 second or so, after all that time.

"5 parts in 10^16" means the time could be off by 5 seconds after having run for 10^16 seconds (that's about 300 million years).

Or it could be off by 5 nanoseconds after having run for 10^16 nanoseconds (that's 16.5 weeks). A nanosecond is a billionth of a second or 10^-9 seconds.

no reply ?!

Many of us (in USA) were sleeping when you first posted.
 
Redbelly98

Thanks a lot !

: )
 

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