From: Georgi Guninski <guninski@guninski.com>
   >To get it, you use the network which is of unknown latency (unless you
   >sniff it).
   >To get the system time you must know:
   >1. When you got the time
   >2. When you received the time
   >Something like Eisenstein's theory about impossibility to synchronize
   >clocks with super-light speed. Sometimes I wonder what is so special
   >about the speed of light and if humans were blind per design and
   didn't
   >know what light is, would they replace "speed of light with 'speed of
   >fastest thing they can measure", explaining relativity with "the fast
   >thing slows down near `matter'" ;) (this paragraph is just trolling).
   As I recall, it is impossible to (perfectly) synchronize a rotating
   assemblage of clocks.
   Since Earth is rotating, that means all clocks on it (except at the
   poles) are rotating, too.
   This is related:
   [1]https://en.wikipedia.org/wiki/Einstein_synchronisation
   Interesting side-side-issue:
   [2]https://en.wikipedia.org/wiki/Quantum_entanglement
   Scientists have continued to experiment with the use of optical fibers
   to study quantum
   entanglement.
   [3]http://phys.org/news/2008-06-world-largest-quantum-bell-spans.html
   (no relation, of course)  They generated photon-pairs which were
   quantum-entangled,
    sent them in opposite directions, made their measurements far away,
   and found
   (as they kinda-sorta expected) that the first measurement somehow
   affected the second
   measurement many kilometers away.
   I read a few years ago, somewhere, that in such a test they were able
   to exclude the
   possibility of a direct-communication effect manipulating the results
   unless it were
   at a speed of at least 10,000 c (10,000x the speed of light in a
   vacuum.)
   Perhaps this system could be used to synchronize clocks.  Although,
   since the speed
    of light in an optical fiber is very constant over time (assuming the
   temperature isn't
   changing) then very good results can obviously be obtained using the
   far more mundane
   system.
   Interesting tidbit:  A 1 centimeter change in the altitude of a clock,
   at about the Earth's
   surface, changes the rate of that clock by about 1 part in 10E18.   (My
   own calculation:  It
   might be a factor of 2 off.)    Experimental clocks of approximately
   this accuracy exist.
   [4]http://www.nature.com/nature/journal/vaop/ncurrent/abs/nature12941.h
   tml?message-global=remove
   In addition, "nuclear clocks" are talked about.  (although they are
   somewhat hard to
   Google-search because of term confusion with the "Doomsday Clock".
   here's an example:
   [5]http://www.forbes.com/sites/chadorzel/2016/05/17/why-do-physicists-w
   ant-a-nuclear-clock/#2dc823e1d0b5
                 Jim Bell

References

   1. https://en.wikipedia.org/wiki/Einstein_synchronisation
   2. https://en.wikipedia.org/wiki/Quantum_entanglement
   3. http://phys.org/news/2008-06-world-largest-quantum-bell-spans.html
   4. http://www.nature.com/nature/journal/vaop/ncurrent/abs/nature12941.html?message-global=remove
   5. http://www.forbes.com/sites/chadorzel/2016/05/17/why-do-physicists-want-a-nuclear-clock/#2dc823e1d0b5