[Python-Dev] PEP 564: Add new time functions with nanosecond resolution
wes.turner at gmail.com
Sun Oct 22 16:42:40 EDT 2017
On Sunday, October 22, 2017, David Mertz <mertz at gnosis.cx> wrote:
> I worked at a molecular dynamics lab for a number of years. I advocated
> switching all our code to using attosecond units (rather than fractional
> However, this had nothing whatsoever to do with the machine clock speeds,
> but only with the physical quantities represented and the scaling/rounding
> It didn't happen, for various reasons. But if it had, I certainly wouldn't
> have expected standard library support for this. The 'time' module is about
> wall clock out calendar time, not about *simulation time*.
> FWIW, a very long simulation might cover a millisecond of simulated
> time.... we're a very long way from looking at molecular behavior over 104
Maybe that's why we haven't found any CTCs (closed timelike curves) yet.
Aligning simulation data in context to other events may be enlightening: is
there a good library for handing high precision time units in Python
> On Oct 22, 2017 8:10 AM, "Wes Turner" <wes.turner at gmail.com
> On Saturday, October 21, 2017, Nick Coghlan <ncoghlan at gmail.com
>> On 22 October 2017 at 09:32, Victor Stinner <victor.stinner at gmail.com>
>>> Le 21 oct. 2017 20:31, "francismb" <francismb at email.de> a écrit :
>>> I understand that one can just multiply/divide the nanoseconds returned,
>>> (or it could be a factory) but wouldn't it help for future enhancements
>>> to reduce the number of functions (the 'pico' question)?
>>> If you are me to predict the future, I predict that CPU frequency will
>>> be stuck below 10 GHz for the next 10 years :-)
>> There are actually solid physical reasons for that prediction likely
>> being true. Aside from the power consumption, heat dissipation, and EM
>> radiation issues that arise with higher switching frequencies, you also
>> start running into more problems with digital circuit metastability (,
>> ): the more clock edges you have per second, the higher the chances of
>> an asynchronous input changing state at a bad time.
>> So yeah, for nanosecond resolution to not be good enough for programs
>> running in Python, we're going to be talking about some genuinely
>> fundamental changes in the nature of computing hardware, and it's currently
>> unclear if or how established programming languages will make that jump
>> (see  for a gentle introduction to the current state of practical
>> quantum computing). At that point, picoseconds vs nanoseconds is likely to
>> be the least of our conceptual modeling challenges :)
> There are current applications with greater-than nanosecond precision:
> - relativity experiments
> - particle experiments
> Must they always use their own implementations of time., datetime.
> __init__, fromordinal, fromtimestamp ?!
> - https://scholar.google.com/scholar?q=femtosecond
> - https://scholar.google.com/scholar?q=attosecond
> - GPS now supports nanosecond resolution
> > In 2015 JILA <https://en.m.wikipedia.org/wiki/JILA> evaluated the
> absolute frequency uncertainty of their latest strontium-87
> <https://en.m.wikipedia.org/wiki/Isotopes_of_strontium> optical lattice
> clock at 2.1 × 10−18, which corresponds to a measurable gravitational
> time dilation
> <https://en.m.wikipedia.org/wiki/Gravitational_time_dilation> for an
> elevation change of 2 cm (0.79 in)
> What about bus latency (and variance)?
> From https://www.nist.gov/publications/optical-two-way-time-and-
> frequency-transfer-over-free-space :
> > Optical two-way time and frequency transfer over free space
> > Abstract
> > The transfer of high-quality time-frequency signals between remote
> locations underpins many applications, including precision navigation and
> timing, clock-based geodesy, long-baseline interferometry, coherent radar
> arrays, tests of general relativity and fundamental constants, and future
> redefinition of the second. However, present microwave-based time-frequency
> transfer is inadequate for state-of-the-art optical clocks and oscillators
> that have femtosecond-level timing jitter and accuracies below 1 × 10−17.
> Commensurate optically based transfer methods are therefore needed. Here we
> demonstrate optical time-frequency transfer over free space via two-way
> exchange between coherent frequency combs, each phase-locked to the local
> optical oscillator. We achieve 1 fs timing deviation, residual instability
> below 1 × 10−18 at 1,000 s and systematic offsets below 4 × 10−19,
> despite frequent signal fading due to atmospheric turbulence or
> obstructions across the 2 km link. This free-space transfer can enable
> terrestrial links to support clock-based geodesy. Combined with
> satellite-based optical communications, it provides a path towards
> global-scale geodesy, high-accuracy time-frequency distribution and
> satellite-based relativity experiments.
> How much wider must an epoch-relative time struct be for various realistic
> time precisions/accuracies?
> 10-6 micro µ
> 10-9 nano n -- int64
> 10-12 pico p
> 10-15 femto f
> 10-18 atto a
> 10-21 zepto z
> 10-24 yocto y
> I'm at a loss to recommend a library to prefix these with the epoch; but
> future compatibility may be a helpful, realistic objective.
> Natural keys with such time resolution are still unfortunately likely to
>>  https://en.wikipedia.org/wiki/Metastability_in_electronics
>>  https://electronics.stackexchange.com/questions/14816/what-i
>>  https://medium.com/@decodoku/how-to-program-a-quantum-comput
>> Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia
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