Is there a universal time?

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Eric Flesch

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Jul 13, 2022, 6:49:53 AMJul 13
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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.

In scientific jargon, take 2 places 100LY apart -- they each fire a
photon at the other at the "same time". An intermediate place at the
50LY midpoint intercepts the photons simultaneously thus showing that
the clocks at the source locations were correctly synchronized.

But so what? If space-time is truly constrained by c, then
clock-synchronicity is a pointless charade, because it unifies
nothing. It always takes you at least 100 years to cross 100LY even
if to you it happens in an instant. You can't tie this place to that
place in any meaningful way. Space is like a dense syrup with c
retarding the propagation of every effect. Molasses, my friend, space
is like molasses.

That is, unless we too can warp around as in the TV shows. But just
as we were once ground-bound, now we are c-bound. We have taken zero
baby steps in freeing ourselves of this constraint. We don't even
have anything theoretical. Fish in water, that's us.

Galaxies rotate in this molasses-like space with every part retarded
from every other part. Wonder if their peculiar rotation curves are
somehow addressing (or even countering) this constraint.

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.

Phillip Helbig (undress to reply)

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Jul 13, 2022, 11:55:42 AMJul 13
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In article <62ce8389....@news.aioe.org>, er...@flesch.org (Eric
Flesch) writes:

> 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.

That idea makes more sense in our Universe than in an arbitrary
universe, since one can define the time as the temperature of the CMB.

> 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.

Not sure what you mean here. Do you mean no time dilation with the warp
drive? If so, then I follow you. One doesn't need hugely advanced
technology to travel so fast that even crossing the galaxy is possible
in a few years, but if one then returns to home base thousands of years
will have passed.

> In scientific jargon, take 2 places 100LY apart -- they each fire a
> photon at the other at the "same time". An intermediate place at the
> 50LY midpoint intercepts the photons simultaneously thus showing that
> the clocks at the source locations were correctly synchronized.

OK, but not really necessary since the can just agree on the time by
measuring the CMB temperature.

> But so what? If space-time is truly constrained by c, then
> clock-synchronicity is a pointless charade, because it unifies
> nothing. It always takes you at least 100 years to cross 100LY even
> if to you it happens in an instant. You can't tie this place to that
> place in any meaningful way. Space is like a dense syrup with c
> retarding the propagation of every effect. Molasses, my friend, space
> is like molasses.

In other words, it has limited practical value (especially since any
communication to do something at a particular time would be limit by the
speed of light).

> That is, unless we too can warp around as in the TV shows. But just
> as we were once ground-bound, now we are c-bound. We have taken zero
> baby steps in freeing ourselves of this constraint. We don't even
> have anything theoretical. Fish in water, that's us.

Star-Trek--style warp drives are probably not possible and almost
certainly not practical.

> Galaxies rotate in this molasses-like space with every part retarded
> from every other part. Wonder if their peculiar rotation curves are
> somehow addressing (or even countering) this constraint.

Very probably not.

> 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.

I think that Milne's concept of the World Map and World Picture are
relevant here. The World Picture is what an observer sees; the World
Map is a birds-eye view at a specific instant of cosmic time. Such
ideas help us to understand the Universe. Perhaps not as practical as
warping about the Galaxy and going where no man has gone before, but not
worthless.

Jonathan Thornburg [remove -color to reply]

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Jul 14, 2022, 2:55:48 AMJul 14
to
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.

People have studied a related set of ideas extensively in general
relativity. These are questions like:
* Is there a global time coordinate /t/ such that
(a) every event has a finite /t/ coordinate,
(b) the set of events {t = constant} is 3-dimensional,
(c) the set of events {t = constant} is spacelike (i.e.,
any distinct pair of events with the same /t/ coordinate
are spacelike-separated), and
(d) /t/ is consistent with the causality, i.e., if A and B are
distinct events such that event B is in the causal future
(i.e., within the future light-cone) of event A, then t(B) > t(A)
(a) and (b) are "easy", but (c) and (d) are non-trivial, and there
are "wierd" spacetimes where it's impossible to choose any time
coordinate which satisfies all of these properties. So, we'd like
to know aht conditions spacetime must satisfy in order for us to be
able to prove that such a /t/ does exist. (As Phillip Helbig noted
in another message in this thread, in our universe 1/CMBR_temperature
can serve as such a global time coordinate.)
* More generally, what causal properties does spacetime have?
* Are there closed timelike curves, i.e., if you live long enough,
can you eventually meet up with your great-great-grandparents,
i.e., are your great-great-grandparents in your future light cone?
If this is true (which it is in certain "wierd" spacetimes"), then
we do NOT have any reasonable notion of causality. So people often
pose this question in terms of what things do we need to know/assume
in order to be able to prove that there are NOT any closed timelike
curves. (In our universe, we think there do NOT exist closed timelike
curves.)
* Are there (spacelike) Cauchy hypersurfaces? E.e., if you want to
solve a simple scalar wave equation on spacetime, does there exist
a spacelike "Cauchy surface" (roughly speaking, a t=constant surface)
where you should pose "Cauchy" initial data in order for the wave
equation's solution to exist and/or be unique everywhere to the
future of that surface? [In practice, if there's one such surface
there are probably infinitely many of them, but we can ignore that
here.] This is a desirable property for spacetime to have if you
want to do physics in/on that spacetime, e.g., it's not too hard to
extend "simple scalar wave equation" to something like Maxwell's
equations for electromagnetism; with more (a *lot* more mathematical)
work you can even extend this to "weak" gravitational waves.
(In our universe, a CMBR_temperature=const survace works fine as
as a spacelike Cauchy hypersurface.)

There is a huge mathematical-relativity literature on these topics.
A good search term to find out more is "global hyperbolicity", and the
Wikipedia article
https://en.wikipedia.org/wiki/Globally_hyperbolic_manifold
is a good (if somewhat technical) starting point.

--
-- "Jonathan Thornburg [remove -color to reply]" <dr.j.th...@gmail-pink.com>
Dept of Astronomy & IUCSS, Indiana University, Bloomington, Indiana, USA
currently on the west coast of Canada
"Sick of people calling everything in crypto a Ponzi scheme. Some crypto
projects are pump and dump schemes, while others are pyramid schemes.
Others are just standard issue fraud. Others are just middlemen skimming
off the top. Stop glossing over the diversity in the industry.
-- Pat Dennis, 2022-04-25"

Nicolaas Vroom

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Jul 20, 2022, 1:23:47 PMJul 20
to
Op donderdag 14 juli 2022 om 08:55:48 UTC+2 schreef Jonathan Thornburg:
> 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.
> > SNIP 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.
> People have studied a related set of ideas extensively in general
> relativity.

This reply is an effort to give the concept 'universal time' a more
physical interpretation involving an experiment

A more basic question around universal time is: What means time? or
Is there something, that exists, that we can call time?
IMO the answer is No. 'Time' does not exist.
What exists is a universe. The universe exits now, at a certain moment.
We can multiply time with a speed, defining a distance.
Neither the time, nor the speed nor the distance exist.

A different opinion is that a clock indicates time. A clock is a physical
process based around a mechanism that physical oscillates. As a result,
a clock shows a certain number of (a for ever) increasing number of counts.
These counts can be used to measure time (intervals).
A clock exits.

The concept 'now' is a universal concept. All the events, that are
happening now, anywhere in the universe, are happening simultaneous, now.

Consider two simultaneous events at two different locations.
The problem is how to set up two clocks at these two locations that also
run simultaneous. These two clocks are the closest to indicate something
that you can call, universal time.
The first rule is to use one coordinate system. That means that the position
and specific the distance between the two clocks should always be the same.
The second rule is that the coordinate system is considered at rest.
This implies that the speed of light is the same in all directions.
The third rule is to synchronize both clocks from a central point half way
between the two clocks.

The final step is to perform an experiment to decide if both clocks are truly
at rest. We call the points considered as A and B. We place a third clock
C at A. We synchronize clock C with A and we 'move' clock C from A to B.
When the count from clock C is less than B, we conclude that clock C runs
slower. This is the normal physical behaviour of a moving clock, using an
oscillating light signal, compared to a clock at rest, because the light
path of a moving clock becomes longer.
When the count from clock C is higher than B, we can conclude that clock C
runs faster. That means the coordinate system currently used is not at rest.
Our new strategy should be to define a new coordinate system using clock C
Clock C should be used to define a new universal time valid for the whole
of the Universe. Etc.

Nicolaas Vroom
http://www.nicvroom.be/

[[Mod. note -- Related issues are discussed a lot in the classic book

P. W. Bridgman
"A Sophisticate's Primer of Relativity", 2nd edition
Wesleyan University Press (Distributed by Harper & Row)
1962, 1983
ISBN 0-8195-6078-2 (paperback)

He goes into a lot of discussion on what we *mean* by words like
"event" and "time" and "frame of reference".
-- jt]]

Martin Brown

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Jul 21, 2022, 11:40:55 PMJul 21
to
On 20/07/2022 18:23, Nicolaas Vroom wrote:

> The concept 'now' is a universal concept. All the events, that are
> happening now, anywhere in the universe, are happening simultaneous, now.

Simultaneous events or "now" is only well defined for events that are
happening at the same x,y,z coordinates in spacetime.

Observing physically separated events the times that you observe for
each event depend on your speed relative to those events own reference
frame. We are not used to travelling fast enough for this to matter but
at relativistic speeds the effect cannot be ignored.

ISTR you can establish a frame of reference for clock time fairly easily
by moving clocks synchronised at your reference point of origin out into
the universe at a walking pace (where relativistic corrections can be
conveniently ignored). The errors made can be made arbitrarily small by
moving them more slowly to their final position.

Not ideal experimentally but it would get the job done (eventually).

>
> [[Mod. note -- Related issues are discussed a lot in the classic book
>
> P. W. Bridgman
> "A Sophisticate's Primer of Relativity", 2nd edition
> Wesleyan University Press (Distributed by Harper & Row)
> 1962, 1983
> ISBN 0-8195-6078-2 (paperback)
>
> He goes into a lot of discussion on what we *mean* by words like
> "event" and "time" and "frame of reference".
> -- jt]]

This reminds me of an introductory Relativity textbook from my youth
that I read in the school library circa 1976. I cannot remember its name
but it contained a wonderful graph of the speed of light with error bars
from the initial efforts of Romer right through to present day.

It was notable because it showed how as newer more precise refined
techniques became possible the error bars narrowed and number of digits
precision increased. But that for one notable period I think in the
1960's the accepted value was several sigma away from the true value
because a famous experimentalist had applied the correction for an
imperfect vacuum in the wrong sense (and everybody subsequently did the
same). NBS nailed the value down in 1972 so I think that puts bounds on
the date of publication. I have tried and failed to find this book.

It was only when a new technique took over that the mistake was
discovered. Does anybody recognise the book from this description?

Or failing that able to point me to such a graph of speed of light in
vacuum c with error bars as a function of time since the 1600's. This is
the closest I have been able to find with the obvious search terms.

https://interestingengineering.com/a-brief-history-of-the-speed-of-light

Sadly it lacks the all important graph...

--
Regards,
Martin Brown

[[Mod. note -- I remember a paper in the American J of Physics around
20 or 30 (?) years ago on a similar theme, looking at historical data
for the CODATA fundamental constants and how they had changed over time.
As I (dimly) recall, the conclusion was that experimenters typically
had larger error bars than they actually thought, on average by a factor
of O(1.4) or so. Alas, I've been unable to find that paper any time in
the past decade. :(

One can see similar effects in historical estimates of the Hubble constant.
Here I can actually give a reference ((locates book on bookshelf and opens
it to a bookmark)):

William H Press,
"Understanding Data Better with Bayesian and Global Statistical Methods"
chapter 3 (pp 49-60) in
John N Bahcall & Jeremiah P Ostriker, Eds,
"Unsolved Problems in Astrophysics"
Princeton U.P. 1977
ISBN-10 0-691-01607-0 (hc) or 0-691-01606-2 (pb)

Press considers the problem of how to combine multiple estimates of what
should be the same quantity, which might have systematic errors (which
he models in a Bayesian sense by multiplying the claimed error bars by
some factor > 1). He derives a Bayesian method to simultaneously estimate
the true value and the parameters of the systematic-error model. He
demonstrates the method on a dataset of 13 published Hubble-constant
measurements (ranging from 45 to 87 km/sec/Mpc). He shows a graph of
the posterior distribution for H0, with a 95% CI of 74 +/- 8 , with most
of the published H0 measurements having an ~75% chance of being "correct"
(correct erorr bars) and ~25% chance of having much larger error bars.

Returning to what Martin Brown wrote about "correlated experimental
errors" (where experimenter #1 makes a mistake, and then experimenters
#2-#N all follow), some experimental groups go to great lengths to do all
their analyses "blind" to avoid just such problems. For example,
https://arstechnica.com/science/2019/09/physics-not-broken-after-all-were-clo
se-to-resolving-proton-radius-puzzle/
includes the description
> [[the experimenters]] deliberately made a blind measurement to ensure
> against any bias, finally revealing the value they had measured over
> eight years just a few weeks prior to submitting their paper for
> publication. "The difficulty is making sure we're not influenced by
> anything that could complicate or shift energy states in our measurement,"
> said group leader Eric Hessels
> <https://www.physics.yorku.ca/faculty-profiles/hessels-eric/>. "A lot of
> the eight years [were] spent taking great care in understanding all aspects
> of the measurement so that we can carefully eliminate possibilities of
> having made mistakes."

Similarly, before announcing the first direct detection of gravitational
waves (an event detected in 2015, announced in early 2016), the LIGO
Science Collaboration did multiple "blind injections" wherein a small
subgroup (of the ~1000-member collaboration) would deliberately "inject"
a simulated binary-black-hole-coalescence signal into the LIGO data
stream, as a check on how the rest of the collaboration did at finding
it. The "blind" is that only the injection subgroup knew precisely
where in the data stream the blind injections were, or how many blind
injections there were. The rest of the LSC analyized the data stream
blind, not knowing whether any given event might be real or might be
a blind injection. In one famous case the LSC got as far as writing
a Nature paper before "unblinded" and learning this event was in fact
a blind injection. Harry Collins (a sociologist who studies the processes
of scientific research, particularily in gravitational-wave detection)
has written a book about this blind injection and the shifts in opinion
within the analysis groups,

Harry Collins
"Gravity's Ghost and Big Dog:
Scientific Discovery and Social Analysis in the Twenty-First Century"
U Chicago Press, 2011
paperback ISBN-13 978-0-226-05229-8, e-book 978-0-226-05232-8

Of course, experimentalists aren't the only ones vulnerable to "following
the crowd". Theoreticians and computational researchers can be just as
vulnerable.

Around 2006-2007 a friend of mine organized a collaboration of all the
major research groups in the world working on "numerical relativity"
simulations of the gravitational waves from the decay and merger of
orbiting binary black hole systems, to inter-compare their results.
Here each group's calculation involves a large custom-written computer
code of ~100K to ~500K lines of mostly C/C++/Fortran 90, with some
important bits in Mathematica/Maple, months of supercomputer time, and
extensive data postprocessing, so one worries a lot about software bugs
as well as "groupthink". I was very impressed when they published a
joint paper [arXiv:0901.2437 = Phys Rev D79, 084025 (2009)] showing the
results from five different groups' calculations (based on different
formulations of the Einstein equations & different independently-written
computer codes), all agreeing beautifully to within their claimed error
bars!

And just last month I presented some research of mine at a conference,
and explained in my talk that a key reason why people should be interested
in <<method I used>> even though it's more expensive, less accurate, and
in some ways harder to do than <<method many other people use>> is that
we need independent computations to validate against each other before we
can really trust our results.
-- jt]]

Jonathan Thornburg [remove -color to reply]

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Jul 22, 2022, 12:05:44 AMJul 22
to
In a moderator's note earlier in this thread
(article <tbb22q$c8d$1...@gioia.aioe.org>), I referred to the book chapter

William H Press,
"Understanding Data Better with Bayesian and Global Statistical Methods"
chapter 3 (pp 49-60) in
John N Bahcall & Jeremiah P Ostriker, Eds,
"Unsolved Problems in Astrophysics"
Princeton U.P. 1977
ISBN-10 0-691-01607-0 (hc) or 0-691-01606-2 (pb)

I'm sorry, slight garble there. The publication date was 1997, not 1977.

--
-- "Jonathan Thornburg [remove -color to reply]" <dr.j.th...@gmail-pink.com>
Dept of Astronomy & IUCSS, Indiana University, Bloomington, Indiana, USA
currently on the west coast of Canada
"C++ is to programming as sex is to reproduction. Better ways might
technically exist but they're not nearly as much fun." -- Nikolai Irgens

Nicolaas Vroom

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Jul 23, 2022, 11:20:22 AMJul 23
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Op vrijdag 22 juli 2022 om 05:40:55 UTC+2 schreef Martin Brown:
> On 20/07/2022 18:23, Nicolaas Vroom wrote:
>
> > The concept 'now' is a universal concept. All the events, that are
> > happening now, anywhere in the universe, are happening simultaneous, now.

The main reason why I write this is because all the events that are
happening now are happening simultaneous and cannot physically influence
each other.
All these events can be influenced by previous events, which happened in
the past at a certain now in the past.
The same events can influence other events which will happen in the
future at a certain now in the future.
It is important that all these influences are physical processes. The
next issue how to use a clock in these circumstances, which by itself is
also a physical process.

> Simultaneous events or "now" is only well defined for events that are
> happening at the same x,y,z coordinates in spacetime.

This creates two new concepts x,y,z coordinates and spacetime.
The concept x,y,z coordinates 'I solve' by only using one coordinate
system for the whole of the universe.
The concept of spacetime I try to prevent, by using the idea that all
the positions of the objects identified in a coordinate system are
events at the same now.

> Observing physically separated events the times that you observe for
> each event depend on your speed relative to those events own reference
> frame. We are not used to travelling fast enough for this to matter but
> at relativistic speeds the effect cannot be ignored.

The conversion of the observed positions and time of physical events, to
time and position of the coordinate system in use (considered at rest)
is a very complex process.
The reverse conversion in opposite direction from calculated positions
to observed positions involves the same complexity.
To get an idea about this complexity consider our position on earth,
which rotates around the sun, while we try to observe the planet
Jupiter. Assuming that the coordinate is centred around the Sun and at
rest, makes all the calculations much simpler.

> ISTR you can establish a frame of reference for clock time fairly easily
> by moving clocks synchronised at your reference point of origin out into
> the universe at a walking pace (where relativistic corrections can be
> conveniently ignored). The errors made can be made arbitrarily small by
> moving them more slowly to their final position.

If you move a clock from A to B in small or large steps does not solve
the issue that your light path will be longer, and the moving clock will
tick slower, compared with a clock which is (assumed) not moved.

> Not ideal experimentally but it would get the job done (eventually).

Nicolaas Vroom
https://www.nicvroom.be/

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