Re: Is there a universal time?

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Richard D. Saam

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Jul 20, 2022, 2:39:22 AMJul 20
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On 7/14/22 1:55 AM, Jonathan Thornburg [remove -color to reply] wrote:
> Eric Flesch <er...@flesch.org> wrote:
>> I am wondering if a popular idea about the Universe actually has any
>> meaning. It is the idea of a clock reading the same everywhere. In
>> popular space shows like Orville or Star Trek, you can warp from place
>> to place, and there is a simultaneousness of it all, that is, it can
>> be the same "universal time" in all places and you wouldn't need to
>> adjust your universal-time watch as you go from place to place.
> [[...]]
>> So my point is that in this molasses universe, the idea of
>> synchronized clocks in distant star systems has no practical value
>> apart from models. So of what use are those models? They only
>> misguide us as to the nature of space. So that is my idea, cheerless
>> though it may sound. Wonder if anyone has thought about this.
> (As Phillip Helbig noted
> in another message in this thread, in our universe 1/CMBR_temperature
> can serve as such a global time coordinate.)
Is there another?
Assuming Voyager 1, Voyager 2 and The New Horizons spacecraft
as they proceed into interstellar space
(as a measure of universal space)
may interact with some type of space oscillation,
I have subjected these spacecraft's JPL Ephemeris position time data
to integrated Fourier Discrete Sine Fourier analysis
and have viewed a common ~8 hour (1/33.8 microHz) oscillation.
https://www.facebook.com/RichardDSaam
I interpret this as a measure of a universal time?

[[Mod. note -- JPL tracks these spacecraft with 3 main antenna sites,
which are located about 120 degrees apart in longitude around the world.
So, I would worry a bit about possible systematic errors from switching
between different antenna sites; such errors might plausibly have a
roughly 8 hour period.

Beyond that, it's hard to say much without knowing the details of the
data and your analysis.
-- jt]]

Richard Livingston

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Jul 21, 2022, 5:16:59 AMJul 21
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On Wednesday, July 20, 2022 at 1:39:22 AM UTC-5, Richard D. Saam wrote:
> On 7/14/22 1:55 AM, Jonathan Thornburg [remove -color to reply] wrote:
...
> > (As Phillip Helbig noted
> > in another message in this thread, in our universe 1/CMBR_temperature
> > can serve as such a global time coordinate.)
> Is there another?
...

I'm inclined to agree with JT about the 8 hour period in the JPL data.
There is too much human and earth related effects to be confident that
that is something universal. And there is absolutely no theoretical
basis for such an effect.

The cosmic background temperature is one good possibility for a
universal time, although it would be very difficult to use it to
determine the time with any precision useful for humans. It should be
recognized that any such "time" would be a convention that everyone
concerned would have to agree to, and as such there are many
possibilities.

A little more practical and accurate would be a time scale based on the
distance between two galaxies as measured in some specified inertial
frame. Another would be based on some master clock in a single
particular location in the universe. With an understanding of special
relativity it is possible for everyone everywhere to calculate the time
on that clock for the observers location IN THE MASTER CLOCK INERTIAL
FRAME. (Sorry about yelling, but that last part is important!) This
would not be a simple calculation for any observer that is accelerating,
but in principle can be done. If the master clock is transmitting time
signals by radio, the observer can measure the distance back to the
master clock and determine the current time, again having to take into
account the observers motion wrt the master clock and the distance. Of
course at great distances when massive objects are near the line of
sight, gravitational lensing would complicate this calculation.

Rich L.

Julio Di Egidio

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Jul 24, 2022, 8:36:26 AMJul 24
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In what sense? *Proper time* is absolute/universal time, just there is no
absolute origin: so every (working) clock ticks it, just sync them and they
stay in sync. Indeed, clocks drift because of space-time travel, not
because they slow down (most presentations are simply and completely
wrong in that sense)...

Julio

J. J. Lodder

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Jul 28, 2022, 8:46:14 AMJul 28
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Richard Livingston <richali...@gmail.com> wrote:

> On Wednesday, July 20, 2022 at 1:39:22 AM UTC-5, Richard D. Saam wrote:
> > On 7/14/22 1:55 AM, Jonathan Thornburg [remove -color to reply] wrote:
> ...
> > > (As Phillip Helbig noted
> > > in another message in this thread, in our universe 1/CMBR_temperature
> > > can serve as such a global time coordinate.)
> > Is there another?
> ...
>
> I'm inclined to agree with JT about the 8 hour period in the JPL data.
> There is too much human and earth related effects to be confident that
> that is something universal. And there is absolutely no theoretical
> basis for such an effect.

Would that be an 8 hour (siderial) or an 8 hour (solar) period?

> The cosmic background temperature is one good possibility for a
> universal time, although it would be very difficult to use it to
> determine the time with any precision useful for humans. It should be
> recognized that any such "time" would be a convention that everyone
> concerned would have to agree to, and as such there are many
> possibilities.

The cosmic background temperature isn't really a clock.
It could be used to define an epoch though.
(like epoch 10 Kelvin)
In practice such an epoch would be completely useless,
since it is in practice nothing but a distance scale.
(distance away ~ distance in the past)
Or you may give the equivalent redshift.

It is nowadays feasable to actually measure
the cosmic background temperature long ago/far away
by high resolution spectroscopy.
The occupation of hyperfine levels of long-lived states
gives the cosmic background temperature that applied then/there.

> A little more practical and accurate would be a time scale based on the
> distance between two galaxies as measured in some specified inertial
> frame. Another would be based on some master clock in a single
> particular location in the universe.

Which would be time tied to that particular location,
so by definition not a universal time.

> With an understanding of special
> relativity it is possible for everyone everywhere to calculate the time
> on that clock for the observers location IN THE MASTER CLOCK INERTIAL
> FRAME. (Sorry about yelling, but that last part is important!) This
> would not be a simple calculation for any observer that is accelerating,
> but in principle can be done. If the master clock is transmitting time
> signals by radio, the observer can measure the distance back to the
> master clock and determine the current time, again having to take into
> account the observers motion wrt the master clock and the distance. Of
> course at great distances when massive objects are near the line of
> sight, gravitational lensing would complicate this calculation.

But special relativity is irrelevant here. (Lorentz invariance applies)
Gravitational effects determine the clock rates.

Typical examples: Here on Earth clock rates vary with altitude.
(more precisely, with the Newtonian potential)
This has been easily measurable for at least fifty years.

To cope with it TAI has been invented.
TAI is a weighted average, computed by the BIPM,
taking the different clock rates into account,
by reducing the rates to mean sea level.
(beware of technicalities!)
TAI is good enough for all timekeeping on Earth.

TAI is not good enough though for precision tracking of satellites,
when taking relativistic corrections into account.
So the IAU has defined TCG, which is the time of a clock
that is co-moving with the Earth, but located 'infinitely' far away.
(in practice out of the gravitational potental well of the Earth.
It sufices for 'sublunar' orbital calculations. (such as GPS)
(don't know about L2)

Again, TCG is not good enough for tracking motions in the solar system.
So, (get the pattern?) the IAU has defined TCB, which is the time
of a clock that co-moves with the solar system barycentre,
but which is out of the gravitational well of the solar system. [1]
(and next the galaxy, the local cluster, the ....,
if we lived long enough)

So 'universal time' is not possible
because gravity has an infinite range,
and you can never be free from it.
There cannot be an absolute zero of the gravitational potential,
where you could station a universal clock.

A universal clock would have to be outside the universe,
which cannot be.
So we must do with practical clocks, that are practically adequate,
for a given purpose,

Jan

[1] These corrections are huge, by modern standards.
For example, TCB runs about half a second/year fast wrt to TAI.

Phillip Helbig (undress to reply)

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Jul 28, 2022, 9:38:46 AMJul 28
to
In article <1pvpftq.icjf7g1ehi7g4N%nos...@de-ster.demon.nl>,
nos...@de-ster.demon.nl (J. J. Lodder) writes:

> Richard Livingston <richali...@gmail.com> wrote:
>
> > On Wednesday, July 20, 2022 at 1:39:22 AM UTC-5, Richard D. Saam wrote:
> > > On 7/14/22 1:55 AM, Jonathan Thornburg [remove -color to reply] wrote:
> > ...
> > > > (As Phillip Helbig noted
> > > > in another message in this thread, in our universe 1/CMBR_temperature
> > > > can serve as such a global time coordinate.)
> > > Is there another?

> > I'm inclined to agree with JT about the 8 hour period in the JPL data.
> > There is too much human and earth related effects to be confident that
> > that is something universal. And there is absolutely no theoretical
> > basis for such an effect.
>
> Would that be an 8 hour (siderial) or an 8 hour (solar) period?

An hour is an hour, 60 minutes, 3600 seconds. A siderial day is about 4
minutes shorter than a solar day. But I see what you are driving at.

> > The cosmic background temperature is one good possibility for a
> > universal time, although it would be very difficult to use it to
> > determine the time with any precision useful for humans. It should be
> > recognized that any such "time" would be a convention that everyone
> > concerned would have to agree to, and as such there are many
> > possibilities.
>
> The cosmic background temperature isn't really a clock.
> It could be used to define an epoch though.
> (like epoch 10 Kelvin)
> In practice such an epoch would be completely useless,
> since it is in practice nothing but a distance scale.
> (distance away ~ distance in the past)
> Or you may give the equivalent redshift.

The idea is that the clock is the CMB temperature as measured by a
co-moving observer. Like any measure of time, it can be converted into
distance, and vice versa, if one knows how the Universe expands.

> It is nowadays feasable to actually measure
> the cosmic background temperature long ago/far away
> by high resolution spectroscopy.
> The occupation of hyperfine levels of long-lived states
> gives the cosmic background temperature that applied then/there.

Right.

> > A little more practical and accurate would be a time scale based on the
> > distance between two galaxies as measured in some specified inertial
> > frame. Another would be based on some master clock in a single
> > particular location in the universe.

Neither is practical in any real since; they are more akin to
relativistic trains, Bell's spaceships, relativistic ladders in barns,
and so on; the principle is the point, not actually doing anything
practical withit.

With respect to the stuff I've deleted about increasingly precise time
standards, a good introduction to that and to many other aspects is

*A Brief History of Timekeeping: The Science of Marking Time, from
Stonehenge to Atomic Clocks*, by Chad Orzel (One World), 2022. Pp. 336,
19.5 x 13 cm. Price ¤15.99 (paperback, ISBN 978 0 86154 215 4).

There is also an interview with the author about the book:

https://www.youtube.com/watch/?v=eCWj5_a1fBE

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