[time-nuts] Absolute time (was Time of death-Again)

Marshall Eubanks tme at americafree.tv
Thu Oct 28 17:23:26 UTC 2010


On Oct 28, 2010, at 11:33 AM, Bill Hawkins wrote:

> If a far future observer was to make any sense of a date, quite
> a lot would have to be known about the culture, including how to
> read its markings.
> 
> It would be impractical to carve a map of the sky showing the
> location of a stellar beacon on each tombstone, and then adding
> some number of rotations of the Earth around the sun to it. How
> would you describe leap seconds? Or seconds?
> 

All of that is irrelevant IMHO. You are saying that something happened on this date, and trying to give sufficient information so
that people (?) much later could independently determine the elapsed (TAI) time.

The best behaved msec pulsars - see http://arxiv.org/pdf/1003.0418 and http://arxiv.org/pdf/0908.0244 and many other papers - have
period dot accuracies on the order of 10^-20 s/s, and no real evidence for a period double dot (acceleration). There are Pulsar glitches 
which might mess up any individual pulsar, so doing an array would be better than doing one.

1 Million Years (T) is ~ 3 x 10^13 seconds and order 10^16 periods, so the period error would 
be order sigma(P) ~ T * sigma(P_dot) ~ 3 x 10^-7 seconds in that time, so 
(if they could do radio or X ray astronomy) they should be able to figure out which pulsars then correspond to the ones now. (Of course,
giving coordinates would help a lot there.)

WHo knows what the timing error would be after that long, but if I am doing my math correctly it would be order(years). That's a lot worse than
a Hydrogen maser would do, but it would require no maintenance of equipment (or civilization) during the intervening period.

Regards
Marshall



> The use of BC and AD pervades our culture. What's needed is a
> Rosetta Stone that has a lengthy description of the relation of
> astronomical events to the year 0, after first describing the
> time system (Y, M, D, H, M, S). Perhaps radioactive dating by
> isotope ratios would be easier than describing years, using a
> stellar event to pin down the base ratio to absolute time.
> 
> Any understanding of a culture includes an understanding of its
> religions. Perhaps the Mayan calendar would be discovered first.
> Too bad it stops in December 2012.

It's cyclical, with multiple cycles embedded in each other. The long count is 144,000 days, and will roll over December 20, 2012, ending the
13th b'ak'tun. The next day is just the first day of the 14th b'ak'tun.

> 
> Bill Hawkins
> 
> 
> -----Original Message-----
> From: Raj
> Sent: Thursday, October 28, 2010 9:17 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Time of death-Again
> 
> T=0 could be a recent supernova for a secular short measurement span
> considering the life span of Earth.
> OR
> T=0 could also be a local solar system event that is easily determinable on
> Earth. 
> 
> For someone measuring events on Earth a million years from now, give or take
> a ppm :-) or they may not care!
> 
>> I think this is a sort of relativity question, isn't it?  That is, you just
> have to pick some place/time, and reference everything else to that.  So
> which astronomical event do you want use as your reference (e.g. a T=0
> epoch)and is it sufficiently well determined that you can figure it out
> later?  It's all well and good, for instance, to use noon on January 1st,
> 1900 or something as your time zero, but that's hardly a universally
> available reference point.
> 
> -- 
> Raj, VU2ZAP
> Bangalore, India. 
> 
> 
> 
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