This is not exactly a question about physics, but, I was wondering, what would be a clever new definition of second, which 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

By clever I mean that would yield advantages, for example to the way we count hours (or I don't know, make g= 10 m/s). I'm not smart enough to figure this out on my own. I know it would be impossible for this to happen in practice, since it would mess up all our measurements and maybe our perception of time, but just out of curiosity I was wondering what other think about this.

I'm not sure if this is the right forum to post this question or if it should be in science fiction or somewhere else. In that case let me know and I'll move it.

  • $\begingroup$ Are you asking about actually changing the duration of 1 second or just what we use as a baseline for measuring it? $\endgroup$
    – Jaywalker
    Commented May 5, 2017 at 14:09
  • $\begingroup$ Actually changing the duration. $\endgroup$
    – gionni
    Commented May 5, 2017 at 14:16
  • $\begingroup$ You really need a good reason to do so. 'Clever' does not count. $\endgroup$
    – Jon Custer
    Commented May 5, 2017 at 14:19
  • $\begingroup$ Related physics.stackexchange.com/questions/243144/… $\endgroup$
    – Farcher
    Commented May 5, 2017 at 15:03

1 Answer 1


Surely that number 9 192 631 770 with its 10 significant figures shows you the lengths to which scientists did not want to change the duration of a second as measured with apparatus prior to the change of definition of the second?

For whatever reason human being do not like being tied up in straitjacket of rules.
However it is realised that the second might not be of the right order of magnitude and in such circumstances other units like the minute $(= 60 \,\rm s)$, the hour $(= 3600 \,\rm s)$, the day $(= 86 400 \,\rm s)$, the Planck time $(=5.3912\times 10^{−44}\,\rm s)$, the natural unit of time $(=1.2880886677(86)\times 10^{−21}\,\rm s)$, the atomic unit of time $(=2.418884326505(16)\times 10^{−17}\, \rm s)$, . . . . . . are defined and used.


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