[LEAPSECS] Letters Blogatory

[Kevin Birth]

Solar time is good for humans, but as everyone on this list knows, solar time is not the same as mean time or UTC.

>From a chronobiological perspective, mammals have a small cluster of neurons at the base of the hypothalamus called the suprachiasmatic nucleus (SCN).  There are two parts to this structure.  The medial portion has a robust free-running rhythm of around 24 hours plus or minus about 15 minutes.  The two ventral portions connect to the optic nerve and have no strong rhythm.  Instead, the ventral portions work to reset the dorsal part so that the @24 hour rhythm always anticipates the next sunrise regardless of seasonal variations in the length of the daylight period (or the equation of time).  One could say that the SCN is an evolutionary adaptation to Earth's foibles.

The SCN then operates quite differently from representations of solar time, mean or apparent, which chart the rotational day.  In fact, the SCN works much like some old forgotten systems of timekeeping like Bohemian or Italian time, which reset every day.

The features of UTC that we celebrate--continuity, uniformity and standardization--are features that are useful for measuring biological cycles but warp our understanding of those cycles if we begin to think of those cycles as having the same features of uniformity as UTC.  This is true whether or not there are leap seconds.  One of the shortcomings of modern chronobiology and psychophysics of time perception is that as they move more and more into laboratory settings from field settings the cycles are clock controlled, i.e., uniform.  As a result, a lot of current biological science of timing is actually studying how well organisms adapt to humanly created time cycles rather than environmental cycles tied to the Earth's rotation and weather conditions.  

Since many human activities are now structured by UTC and not circadian rhythms, many of those activities are, in fact, unhealthy.  In a sense, with regard to what Folkman worries about in his blog, the horse has left the barn and galloped to the border, cleared customs, and now is in another country and most people still don't know the barn door is open much less the horse is gone.  The disconnect between social rhythms, human biology, and apparent solar time began hundreds of years ago when preference in timekeeping shifted in favor of mean time and 24 hour days beginning at midnight, and this disconnect has been exacerbated by artificial lighting.  

Cheers,

Kevin







________________________________________
From: LEAPSECS [leapsecs-bounces at leapsecond.com] on behalf of Tom Van Baak [tvb at LeapSecond.com]
Sent: Wednesday, March 11, 2015 2:04 PM
To: Leap Second Discussion List
Subject: Re: [LEAPSECS] Letters Blogatory

Brooks,

> Overall he seems to make a good philosophical argument why solar time is
> good for humans. But his conclusion seems confused.

Quite correct. Solar time is good for humans. That's why no one except the United Kingdom can use UTC for their daily activities. Every other nation has a way to circumvent UTC and use their own local time instead.

UTC, with or without leap seconds, is still solar time -- plus or minus a couple of hours, plus or minus a couple billion people, plus or minus a thousand years. Noon at 12:00 is an extremely loose assumption.

I would not worry or argue what happens beyond 1,000 years or 10,000 years. Knowing what little I do about earth dynamics, and how science, technology, culture, and politics [d]evolves, it would be irresponsible for anyone in the year 2000 to dictate the details of atomic or civil time in the year 2500 or 3000.

>
> "... let the airlines and the Internet companies use TAI".

Ok, let's say the airplane runs on TAI. What about the pilot's watches? Their navigation iPads? Then what about ATC? Do you really want the plane running TAI and the tower running UTC? And just big planes but general aviation too? Crop dusters should also run TAI then? And not just one ATC tower but every tower in the world. What about collision avoidance systems? What about the employees of ATC. Should they use local time or UTC while the planes use TAI? What about the weather reports. Or emergency services? Or their wall clocks? Should the ticket reservation system run TAI then too? How about the entire airport ground infrastructure? Do you want fuel and baggage and security running a different timescale as ATC and pilots and planes? What about realtime telemetry? Or in-flight WiFi? Should all contracts involving the airplane industry be tied to TAI instead of UTC? Where does this lawyer draw the line? What is and isn't an "airline"?

The entire purpose of UTC is to provide a single timescale for all human-related activity. That includes transportation.

You can run through the same thought experiment for "internet companies". Do we want ATT to use TAI? All time-stamps going into and out of ATT are TAI. While Verizon uses UTC? What about Google? Or Microsoft? Should Facebook use TAI or UTC? Should local time be based on a hour offset from TAI then? Should all routers be required to use TAI instead of UTC? Where does this lawyer draw the line? What is and isn't an "internet company"?

The entire purpose of UTC is to provide a single timescale for all human-related activity. That includes the internet.

It sort of doesn't matter what that timescale is. Or where its midnight Meridian is historically located. It works extremely well to have one timescale for 99.9999% of human activity. Yes, there are some 0.0001% niche timescales for highly specific scientific purposes. But UTC runs the world. This must not change. Fortunately, neither the pro/con arguments for leap seconds propose a change in UTC's role in this regard. What is scary is when a lawyer jumps into the 15-year game and propose a third alternative: that certain major technology sectors of the planet switch to TAI, as a way to "solve" the leap second issue.

/tvb
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