5 ms·

I wouldn't be so sure there is nothing special about the duration of a second. It comes from dividing a day into two sets of 12, then those 12 into five sets of

by nonbel 10y ago

I wouldn't be so sure there is nothing special about the duration of a second. It comes from dividing a day into two sets of 12, then those 12 into five sets of 12 (12x5=60), then those 60s into 60 each. We know our bodies do follow circadian rhythms, so you have the initial link to length of day. Then everything else is split into sets of 12, a number with exceptional properties that natural selection may optimize towards: "The number twelve, a superior highly composite number, is the smallest number with four non-trivial factors (2, 3, 4, 6), and the smallest to include as factors all four numbers (1 to 4) within the subitizing range. As a result of this increased factorability of the radix and its divisibility by a wide range of the most elemental numbers (whereas ten has only two non-trivial factors: 2 and 5, and not 3, 4, or 6), duodecimal representations fit more easily than decimal ones into many common patterns, as evidenced by the higher regularity observable in the duodecimal multiplication table. As a result, duodecimal has been described as the optimal number system.[4]" https://en.wikipedia.org/wiki/Duodecimal https://en.wikipedia.org/wiki/Duodecimal http://dozenal.org/ http://dozenal.org/ Edit: Another thing is that our current system of setting the duration of a second as a constant may be non-optimal for some purposes. Other systems let the length of time units vary with the seasons. It is interesting to think that under these systems, by maintaining the same base frequency, the tone of the note would change over the course of the year and with latitude. https://en.wikipedia.org/wiki/Roman_timekeeping https://en.wikipedia.org/wiki/Roman_timekeeping

hamiltonkibbe 10y ago
According to NIST It's slightly more arbitrary than that: The second is 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 cesium 133 atom. Not sure of the numerological significance of 9192631770.
- duskwuff 10y ago
  > Not sure of the numerological significance of 9192631770. It has none. It just happens to make the new cesium-based definition of a second roughly equal to the historical definition of a second as 1/86400 of a mean solar day.
gh02t 10y ago
> I wouldn't be so sure there is nothing special about the duration of a second. It comes from dividing a day into two sets of 12, then those 12 into five sets of 12 (12x5=60), then those 60s into 60 each. That's exactly why, actually. This is what the second was once defined as, but the problem is that the length of a day varies slightly - up to ~8s depending on the time of year and other seconds. As the article mentions, the amount of time that is defined as one second is now taken as an arbitrary fraction of the decay time for Cs-137 that is close the mean value of the length of the second defined relative to the time it takes the planet to rotate. In terms of keeping time in our common lives it's not really a problem for there to be a little bit of ambiguity in how long a day/minute/second is, but this is important for things that rely on precision timing - like tuning in music. It'd also be crazy hard to keep track of how long a second is at any given moment, since some of the variation is random from tidal forces.
- nonbel 10y ago
  >"It'd also be crazy hard to keep track of how long a second is at any given moment, since some of the variation is random from tidal forces." I think you could use something like this, which may be accurate enough: https://en.wikipedia.org/wiki/Sunrise_equation https://en.wikipedia.org/wiki/Sunrise_equation It may be more accurate to use something like the JPL ephemerides to convert between the two though: https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/req/time.html#Time%20Routines%20in%20SPICE https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/req/... Finally, the current definition of a second is meant to approximate the previous definition of a second. I am saying the previous one may have some correlation with biological activity.
  - sesqu 10y ago
    If I understand you correctly, you are advocating for defining the second such that its length varies, but its connection to a day does not? And you would also introduce locality to the definition? edit: Or perhaps you meant to tune variably, and not redefine the second. That sounds more sensible, but not as practical.
    - 10y ago
syntheticnature 10y ago
Except that our day length is also changing -- very slowly, but changing it is. Further, given that the human clock, disconnected from day/night feedback, apparently treats 24.2 hours as a day.... https://en.wikipedia.org/wiki/Circadian_clock https://en.wikipedia.org/wiki/Circadian_clock
- nonbel 10y ago
  >"the human clock, disconnected from day/night feedback" I am saying the second was originally linked to length of day, so the calibrated clock should be used. Also, at some point the differences due to latitude changes, etc will be biologically indistinguishable from stuff like the effect of clouds.
- drdeca 10y ago
  So, we could say that a "circadian second" is about 1.008 seconds? (On average) How precisely is that 24.2 known I wonder..
  - jdmichal 10y ago
    From the referenced Wikipedia link: By recording the daily rhythms of hormones and body temperatures in 24 healthy young and old men and women over a one-month period, the researchers conclude that our internal clocks run on a daily cycle of 24 hours, 11 minutes. ... Researchers previously reported a range of 13 to 65 hours, with a median of 25 hours, 12 minutes. The variation between our subjects, with a 95 percent level of confidence, was no more than plus or minus 16 minutes, a remarkably small range. http://news.harvard.edu/gazette/story/1999/07/human-biological-clock-set-back-an-hour/ http://news.harvard.edu/gazette/story/1999/07/human-biologic...
vacri 10y ago
12 is a funky number, but arbitrarily grouping them into 2's and 5's takes the shine off.
anigbrowl 10y ago
I did refer to this with the Babylonian thing but I didn't want to get sidetracked into a review of ancient number bases. I love your reference about non-constant time though, most interesting.

by nonbel 10y ago

hamiltonkibbe 10y ago

According to NIST It's slightly more arbitrary than that: The second is 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 cesium 133 atom. Not sure of the numerological significance of 9192631770.

duskwuff 10y ago
> Not sure of the numerological significance of 9192631770. It has none. It just happens to make the new cesium-based definition of a second roughly equal to the historical definition of a second as 1/86400 of a mean solar day.

gh02t 10y ago

> I wouldn't be so sure there is nothing special about the duration of a second. It comes from dividing a day into two sets of 12, then those 12 into five sets of 12 (12x5=60), then those 60s into 60 each. That's exactly why, actually. This is what the second was once defined as, but the problem is that the length of a day varies slightly - up to ~8s depending on the time of year and other seconds. As the article mentions, the amount of time that is defined as one second is now taken as an arbitrary fraction of the decay time for Cs-137 that is close the mean value of the length of the second defined relative to the time it takes the planet to rotate. In terms of keeping time in our common lives it's not really a problem for there to be a little bit of ambiguity in how long a day/minute/second is, but this is important for things that rely on precision timing - like tuning in music. It'd also be crazy hard to keep track of how long a second is at any given moment, since some of the variation is random from tidal forces.

nonbel 10y ago
>"It'd also be crazy hard to keep track of how long a second is at any given moment, since some of the variation is random from tidal forces." I think you could use something like this, which may be accurate enough: https://en.wikipedia.org/wiki/Sunrise_equation https://en.wikipedia.org/wiki/Sunrise_equation It may be more accurate to use something like the JPL ephemerides to convert between the two though: https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/req/time.html#Time%20Routines%20in%20SPICE https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/FORTRAN/req/... Finally, the current definition of a second is meant to approximate the previous definition of a second. I am saying the previous one may have some correlation with biological activity.
- sesqu 10y ago
  If I understand you correctly, you are advocating for defining the second such that its length varies, but its connection to a day does not? And you would also introduce locality to the definition? edit: Or perhaps you meant to tune variably, and not redefine the second. That sounds more sensible, but not as practical.
  - 10y ago

syntheticnature 10y ago

Except that our day length is also changing -- very slowly, but changing it is. Further, given that the human clock, disconnected from day/night feedback, apparently treats 24.2 hours as a day.... https://en.wikipedia.org/wiki/Circadian_clock https://en.wikipedia.org/wiki/Circadian_clock

nonbel 10y ago
>"the human clock, disconnected from day/night feedback" I am saying the second was originally linked to length of day, so the calibrated clock should be used. Also, at some point the differences due to latitude changes, etc will be biologically indistinguishable from stuff like the effect of clouds.
drdeca 10y ago
So, we could say that a "circadian second" is about 1.008 seconds? (On average) How precisely is that 24.2 known I wonder..
- jdmichal 10y ago
  From the referenced Wikipedia link: By recording the daily rhythms of hormones and body temperatures in 24 healthy young and old men and women over a one-month period, the researchers conclude that our internal clocks run on a daily cycle of 24 hours, 11 minutes. ... Researchers previously reported a range of 13 to 65 hours, with a median of 25 hours, 12 minutes. The variation between our subjects, with a 95 percent level of confidence, was no more than plus or minus 16 minutes, a remarkably small range. http://news.harvard.edu/gazette/story/1999/07/human-biological-clock-set-back-an-hour/ http://news.harvard.edu/gazette/story/1999/07/human-biologic...

vacri 10y ago

12 is a funky number, but arbitrarily grouping them into 2's and 5's takes the shine off.

anigbrowl 10y ago

I did refer to this with the Babylonian thing but I didn't want to get sidetracked into a review of ancient number bases. I love your reference about non-constant time though, most interesting.