Expansion of Space, Where is it expected to start?

[Tyler Dresden]

How many light years away is the expansion of Space expected to start?
Also, At that point, would that not mean space time is not "Flat" any
more?

[jacob navia]

Le 31/03/12 21:07, Tyler Dresden a écrit :

> How many light years away is the expansion of Space expected to start?
> Also, At that point, would that not mean space time is not "Flat" any
> more?

OK.

Space "expands". But... into WHAT is space "expanding"?

Into more space obviously. Space expands into more space. But...

Was this space already there for the old space to be able to "expand"
into it?

Or it is created out of nothing?

Now you ask (no, I will not laugh)

How many light years away is the expansion of space?

How many light years of space you mean?

So, reformulating your question you are asking about the space that lies
between us and the space that is being swallowed by the new space?

:-)

Nobody has been able to answer conclusively what objects are pushed away
by the new space appearing out of nothing. We know that we aren't
expanding (even if I have weight problems, but that is another problem).

Humans do not expand. Nor the earth nor the solar system since the
orbits of the planets look stable. Nor the galaxy since it is a
gravitationally bound object.

Do galaxies in clusters expand? Apparently since redshift measurements
to other galaxies have an "expansion" already. Mr Hubble discovered the
redshift and the explanation advanced was the space expansion so
galaxies must be feeling the space expansion since a long time.

So, the answer should be that space expansion is several hundred
thousand light years away, more or less.

Or not? Should clusters of galaxies dissolve since the expansion of
space breaks them apart? Aren't the galaxies in there gravitationally bound?

Personally I am convinced that space "expansion" is absurd. Space can't
expand since "expansion" means an object increases its volume occupying
space previously empty. And space can't have more volume since it
encompasses ALL the volume there is.

BY DEFINITION of space.

All this conceptual problems are happily forgotten, and astronomers say
that:

https://www.cfa.harvard.edu/~huchra/hubble/

the value is 160 KM/sec /million light years.
For a single light year this is:
160 000 meters / 1 million --> 16 cm
In one second 16 cm, in a year 5045.76 KM.


So, each second, a light year of space creates 16 cm of new space,
around 5Km each year. 5Km of real estate out of nothing. Isn't expansion
wonderful?

[jacob navia]

Le 01/04/12 09:21, jacob navia a écrit :

Sorry but I forgot several points:

>
> So, each second, a light year of space creates 16 cm of new space,
> around 5Km each year. 5Km of real estate out of nothing. Isn't expansion
> wonderful?

What is a light year?

Is the time light travels in a year but WITH those 5Km of space
expansion? Or without them?

If you measure the light year between the sun and alpha centauri, space
is NOT expanding within the galaxy so the 5km aren't included.

But if you measure in inter-galactic space the 5Km should be included so
we would have that light speed is greater there since it swallows 5Km
more in a year.

Or is light speed measured in non-expanding units?

But space metrics should be independent of the size of the measuring
units. If I want to use a unit

U = space traveled by a light ray in 1 million years

I can't have a non expanding unit since there are no galaxies bigger
than 500 000 light years. Would that mean that I can't have any units of
measure bigger than the size of a galaxy?

Another big problem (for me) is the new space that is being created out
of nothing.

Is it created continuously in the light year?

Or it is created in a "bump" in the middle (say) of the light year?
Or is it created in pieces of (say) 500 meters regularly spaced in the
light year?

How is the distribution function of the new space?

And many other questions appear:

Suppose that out of the quantum foam two virtual particles are emitted.
They decay immediately and disappear again.

But, once a year, one of the virtual particles is emitted but falls into
the new space that is being created out of nothing and can't recombine
again with its sister particle and... well it rests in the new space. A
new particle is being created out of nothing.

Can this happen?

(This is a similar reasoning to the black hole evaporation argument)

I will stop here since thinking about this makes for a headache :-)

jacob

[Phillip Helbig---undress to reply]

In article <mt2.0-23365...@hydra.herts.ac.uk>, Tyler Dresden

<tiler....@gmail.com> writes:

> How many light years away is the expansion of Space expected to start?

The expansion of space is an approximation. It does not start at a well
defined point. In general, one can say that it starts when the
expansion velocities are large compared to the peculiar velocities.
More detail is complicated, but not needed.

> Also, At that point, would that not mean space time is not "Flat" any
> more?

Do you mean space-time being flat or space being flat. In either case,
the answer has nothing to do with the question above.

[Tyler Dresden]

On Apr 1, 4:24 pm, Phillip Helbig---undress to reply
<hel...@astro.multiCLOTHESvax.de> wrote:
> In article <mt2.0-23365-1333220...@hydra.herts.ac.uk>, Tyler Dresden

>
> <tiler.dres...@gmail.com> writes:
> > How many light years away is the expansion of Space expected to start?
>
> The expansion of space is an approximation.  It does not start at a well
> defined point.  In general, one can say that it starts when the
> expansion velocities are large compared to the peculiar velocities.
> More detail is complicated, but not needed.
>
> > Also, At that point, would that not mean space time is not "Flat" any
> > more?
>
> Do you mean space-time being flat or space being flat.  In either case,
> the answer has nothing to do with the question above.

But Spacetime cannot be separated into space.... and ....time. except
at an event horizon Correct?

So it does have something to do with the above question does it not?

ok if you say it has nothing to do with the above question.......

[Tyler Dresden]

On Apr 1, 2:21 am, jacob navia <ja...@spamsink.net> wrote:
> So, each second, a light year of space creates 16 cm of new space,
> around 5Km each year. 5Km of real estate out of nothing. Isn't expansion
> wonderful?

But I bet that it would also work like Compound interest.
expanding the previously expanded space time. exponentially

Thank you very much for checking. :-)

[Mod. note: entire quoted article trimmed -- mjh]

[Phillip Helbig---undress to reply]

In article <mt2.0-2517...@hydra.herts.ac.uk>, jacob navia

<ja...@spamsink.net> writes:

> What is a light year?
>
> Is the time light travels in a year but WITH those 5Km of space
> expansion? Or without them?

It is the speed of light multiplied by a year. The relationship between
this and other units of distance in cosmology is well understood.

> If you measure the light year between the sun and alpha centauri, space
> is NOT expanding within the galaxy so the 5km aren't included.

Right.

> But if you measure in inter-galactic space the 5Km should be included so
> we would have that light speed is greater there since it swallows 5Km
> more in a year.

Right. But the relative increase in distance to other objects (such as
the destination of the light) is the same.

> Is it created continuously in the light year?

Yes.

[Tyler Dresden]

On Apr 1, 2:21 am, jacob navia <ja...@spamsink.net> wrote:

> Le 31/03/12 21:07, Tyler Dresden a écrit :
>
> > How many light years away is the expansion of Space expected to start?
> > Also, At that point, would that not mean space time is not "Flat" any
> > more?
>

> So, each second, a light year of space creates 16 cm of new space,
> around 5Km each year. 5Km of real estate out of nothing. Isn't expansion
> wonderful?

So space expands .00000005333333336177777779295 percent each second?
or Time slows .00000005333333336177777779295 percent each second?
or light slows .00000005333333336177777779295 percent each second?

Or maybe Space expands (.00000005333333336177777779295 / 2) percent
AND Time slows (.00000005333333336177777779295 / 2) percent each
second "Squared"

[Jonathan Thornburg [remove -animal to reply]]

Tyler Dresden <tiler....@gmail.com> wrote:
> But Spacetime cannot be separated into space.... and ....time. except
> at an event horizon Correct?

No, any "reasonable" spacetime can be viewed as a 1-dimensional
"stack" of 3-dimensional "spaces". An analogy might help here: suppose
we have a pile of 500 sheets of paper. We can view this as a 3-dimensional
block of paper (the analogy with 4-dimensional spacetime), or as a
1-dimensional stack of 500 individual 2-dimensional sheets (the analogy
with 3-dimensional space).

This really has nothing to do with event horizons.

--
-- "Jonathan Thornburg [remove -animal to reply]" <jth...@astro.indiana-zebra.edu>
Dept of Astronomy & IUCSS, Indiana University, Bloomington, Indiana, USA
"Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral."
-- quote by Freire / poster by Oxfam

[jacob navia]

Le 03/04/12 02:19, Phillip Helbig---undress to reply a écrit :

Thanks for answering Mr Helbig. Your answers leave me a bit perplexed
though:

Isn't the speed of light a *constant*?

Well, it is not, since it is greater in intergalactic space (5KM/year
faster) than inside a galaxy.

The other problem that I hinted to was the effects of space creation out
of nothing in the quantum foam. If we assume (as you propose) that space
is created continuously, quantum foam should "feel" the effects of space
creation: some virtual particle could fail to return to the "foam"
because it would be sucked by the appearing space.

I understand that this questions look stupid but they aren't. The
"expanding space" concept is full of this kind of stuff.

[Phillip Helbig---undress to reply]

In article <mt2.0-20945...@hydra.herts.ac.uk>, jacob navia

<ja...@spamsink.net> writes:

> Isn't the speed of light a *constant*?

Yes, but only when measured locally.

> The other problem that I hinted to was the effects of space creation out
> of nothing in the quantum foam.

Note that the idea of the expansion of space is a purely classical one,
which was along before anyone thought about quantum foam.

> I understand that this questions look stupid but they aren't. The
> "expanding space" concept is full of this kind of stuff.

In the end, the only thing that matters is whether you get the correct
answer in your calculations. Whether the picture you have in your mind
corresponds to reality or not is secondary. Think of Feynman diagrams:
they are extremely useful, but not an accurate description of reality
per se. Or think of the Bohr model of the hydrogen atom: it gives the
correct results, even though we know it is wrong.

Personally, I think the idea of expanding space is very useful in that
it gives intuitive answers to questions and these answers are correct.
Perhaps that is because I am more of a visual person. However, it is
possible to get the same correct answers without the expanding-space
concept. See, for example, E. F. Bunn & D. W. Hogg, Am. J. Ph., 77,
688, 2009, also at http://arxiv.org/abs/0808.1081, and references
therein.

[Steve Willner]

In article <mt2.0-26738...@hydra.herts.ac.uk>,

Phillip Helbig---undress to reply <hel...@astro.multiCLOTHESvax.de> writes:
> > Isn't the speed of light a *constant*?
>
> Yes, but only when measured locally.

Suggesting it's not constant measured over a large distance? Is it
really variable if you use strictly metric distance? No doubt you
will get a varying light speed if you use something like luminosity
distance divided by time to measure it, but that seems an odd thing
to do.

> In the end, the only thing that matters is whether you get the correct
> answer in your calculations.

Yep! A point often overlooked by those who try to understand things
conceptually without ever doing any calculations.

By the way, in SI units the exact value of a light year is
299792458*365.25*86400 meters (if I haven't made a copying mistake).
This cannot vary in time or space unless fundamental constants vary.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123 swil...@cfa.harvard.edu
Cambridge, MA 02138 USA

[Phillip Helbig---undress to reply]

In article <mt2.0-23090...@hydra.herts.ac.uk>, Steve Willner

<wil...@cfa.harvard.edu> writes:

> In article <mt2.0-26738...@hydra.herts.ac.uk>,
> Phillip Helbig---undress to reply <hel...@astro.multiCLOTHESvax.de> writes:
> > > Isn't the speed of light a *constant*?
> >
> > Yes, but only when measured locally.
>
> Suggesting it's not constant measured over a large distance?

It's not well defined.

> Is it
> really variable if you use strictly metric distance?

It depends on how one measures it, what a "measurement" is and what an
inferred quantity is etc. Certainly in cosmology the distance by
light-travel time is in general not the same as the proper distance.

> No doubt you
> will get a varying light speed if you use something like luminosity
> distance divided by time to measure it, but that seems an odd thing
> to do.

Agreed.

> > In the end, the only thing that matters is whether you get the correct
> > answer in your calculations.
>
> Yep! A point often overlooked by those who try to understand things
> conceptually without ever doing any calculations.
>
> By the way, in SI units the exact value of a light year is
> 299792458*365.25*86400 meters (if I haven't made a copying mistake).

No copying mistake, but since when is a year 356.25 days? 365.2422 is
closer. But tropical year, sidereal year,...?

> This cannot vary in time or space unless fundamental constants vary.

Agreed. But without any theoretical baggage, how can one distinguish
between a varying speed of light and expansion of space? Yes, within a
theory, things are clear (if one understands the theory), but if one
takes a purely phenomenological approach, it becomes more difficult.

[jacob navia]

Le 05/04/12 08:53, Steve Willner a écrit :

>
> Yep! A point often overlooked by those who try to understand things
> conceptually without ever doing any calculations.
>

Science is about understanding and not just calculating without any
understanding.

As far as I understood science.

OK, astronomy today is in a state of disarray because we start realizing
we have no clue: "dark" matter, "dark" energy, "dark" flow,
too much "darkness".


So it is easy to just give up trying to understand and limit
yourself to calculating some stuff, and seeing if the ad-hoc
mathematical rules give some "meaningful" i.e. observable results.

This will work of course, since you evacuate all understanding of
concepts away, leaving only some equations with nothing behind them,
i.e. no *concepts* !

Now, you say that a light year is *exactly*:

<quote>

the exact value of a light year is

299792458*365.25*86400 meters

<end quote>

but you accept that this value changes by +5045 meters if light is
traveling between galaxies because space expansion.

Then you say:

"This cannot vary in time or space unless fundamental constants vary."

(!!!!)

And then you wonder that I do not follow you :-)

But OK, let's agree to our disagreement.

jacob

[Steve Willner]

In article <mt2.0-24204...@hydra.herts.ac.uk>,

jacob navia <ja...@spamsink.net> writes:
> Now, you say that a light year is *exactly*:

> 299792458*365.25*86400 meters

Yes.

> but you accept that this value changes by +5045 meters if light is
> traveling between galaxies because space expansion.

No, I don't accept any such thing. A lightyear is a unit of
distance, exactly defined in SI units and invariant unless the meter
itself varies due to "new physics."

Expansion of space means that the distance (at least metric distance)
between distant galaxies will become greater -- more lightyears -- as
time passes.

To Phillip: for better or worse, the IAU has defined the lightyear
based on the Julian year, 365.25 days. I guess they had to pick
something, and it probably doesn't matter what as long as everyone
agrees.

As to distinguishing variable speed of light from expanding space,
that's part of the general question of whether physical constants
vary with time. Some variations can be ruled out (or more
accurately, given upper limits) observationally. For example, the
fine structure constant, which involves the speed of light, can't
have changed much. There are similar limits on other constants, but
I'm not sure it would be impossible to invent a scheme where many
constants change in coordinated way that is consistent with
observation. I've never seen a scheme like that, though, and I'm
sure it would be complicated. Of course if no possible observation
can distinguish such a scheme from conventional cosmology, the choice
isn't really a matter of science.

[Dr J R Stockton]

In sci.astro.research message <mt2.0-23090...@hydra.herts.ac.uk>
, Thu, 5 Apr 2012 06:53:47, Steve Willner <wil...@cfa.harvard.edu>
posted:

>By the way, in SI units the exact value of a light year is
>299792458*365.25*86400 meters (if I haven't made a copying mistake).
>This cannot vary in time or space unless fundamental constants vary.

It cannot vary even then. Those numbers are all exact, by definition.
The value can only be changed by redefiners - and none of them are
likely to be redefined. The SI second will almost certainly be
redefined some day, and will change in size by an unmeasurable amount -
then, the value of the light year will be unchanged, but its size will
change in proportion.

--
(c) John Stockton, near London. *@merlyn.demon.co.uk/?.?.Stockton@physics.org
Web <http://www.merlyn.demon.co.uk/> - FAQish topics, acronyms, and links.
Correct <= 4-line sig. separator as above, a line precisely "-- " (RFC5536/7)
Do not Mail News to me. Before a reply, quote with ">" or "> " (RFC5536/7)

[Phillip Helbig---undress to reply]

In article <mt2.0-22298...@hydra.herts.ac.uk>, Steve Willner

<wil...@cfa.harvard.edu> writes:

> To Phillip: for better or worse, the IAU has defined the lightyear
> based on the Julian year, 365.25 days. I guess they had to pick
> something, and it probably doesn't matter what as long as everyone
> agrees.

Indeed. Certainly the differences between different types of year are
much less than the measurement errors of such distances.

Is there a similar official definition for the parsec (i.e. fixing the
AU and specifying which, if any, trigonometric approximations are used)?
Again, in practice it won't matter.

[Steve Willner]

In article <mt2.0-4249...@hydra.herts.ac.uk>,

Phillip Helbig---undress to reply <hel...@astro.multiCLOTHESvax.de> writes:

> Is there a similar official definition for the parsec (i.e. fixing the
> AU and specifying which, if any, trigonometric approximations are used)?

Sort of. The IAU definition of the AU (apparently from 1976) is at
http://www.iau.org/public/measuring/

The AU is defined as "the distance from the center of the Sun at
which a particle of negligible mass, in an unperturbed circular
orbit, would have a mean motion of 0.01720209895 radians/day." In
other words, this is the value of the "Gaussian gravitational
constant." The distance corresponding to this definition has to be
determined by observations, which nowadays are quite precise, but it
is not an exact distance in meters. As far as I can tell, it
corresponds to a year of 365.257...(many digits) SI days. I don't
know why the correspondence isn't to something closer to 365.25, but
maybe it was to leave some prior AU value unchanged.

The reference frame in which the orbit time is measured is apparently
not specified; I'm not sure how much uncertainty this leads to.

The conversion I've seen in several places from AU to parsec is
pc = AU/tan(1 arcsec)
but I don't know that it's official. The value of the trig function
is, of course, a transcendental number, but it can in principle be
calculated to any desired precision. I'm sure the old 4-digit trig
tables printed on paper are more than good enough for any practical
purpose, and of course any modern calculator or math library will do
far better than that. And of course the approximation that the
tangent of a small angle is equal to the angle is plenty good enough.

[Bill Owen]

Steve Willner wrote:
> In article <mt2.0-4249...@hydra.herts.ac.uk>,
> Phillip Helbig---undress to reply <hel...@astro.multiCLOTHESvax.de> writes:
>> Is there a similar official definition for the parsec (i.e. fixing the
>> AU and specifying which, if any, trigonometric approximations are used)?
>
> Sort of. The IAU definition of the AU (apparently from 1976) is at
> http://www.iau.org/public/measuring/
>
> The AU is defined as "the distance from the center of the Sun at
> which a particle of negligible mass, in an unperturbed circular
> orbit, would have a mean motion of 0.01720209895 radians/day." In
> other words, this is the value of the "Gaussian gravitational
> constant." The distance corresponding to this definition has to be
> determined by observations, which nowadays are quite precise, but it
> is not an exact distance in meters. As far as I can tell, it
> corresponds to a year of 365.257...(many digits) SI days. I don't
> know why the correspondence isn't to something closer to 365.25, but
> maybe it was to leave some prior AU value unchanged.

Gauss's gravitational constant k is defined to be exactly 0.01720209895.
Gauss calculated that number to 10 significant digits from the
then-accepted value of the length of the sidereal year, and by
convention k has been held fixed ever since. Subsequent determinations
of the length of the sidereal year have indicated that Gauss was off by
a little bit -- but since k is fixed, the mean value of the earth's
semimajor axis is not exactly 1 AU but a few parts in 10^8 greater.

One can compare Gauss's equation of motion to Newton's and see trivially
that
k^2 = G * M_sun.
This means that units of k are not radians/day but rather AU^{3/2}/day.

We can measure the right-hand side of the equation very accurately
thanks to radio tracking of interplanetary spacecraft, and we get a
value for the sun's GM in units of km^3/s^2. Then it's merely a
question of converting units:
1 AU = cube root [(GM_sun measured in km^3/s^2) * (86400 s/day / k)^2]
JPL's planetary ephemeris DE410 has GM_sun = 1.3271244003502E11
km^3/s^2, hence 1 AU = 149597870.697 km. These values are subject to
adjustment. DE421 has ...004094 and ...870.700.

> The reference frame in which the orbit time is measured is apparently
> not specified; I'm not sure how much uncertainty this leads to.

Any inertial (non-precessing) reference frame will do. And that
historically has been the rub: to determine the rate of the earth's
precession well enough to transform observations made in true-of-date
coordinates to an inertial system.

-- Bill Owen

[Phillip Helbig---undress to reply]

In article <mt2.0-28039...@hydra.herts.ac.uk>, Steve Willner
<wil...@cfa.harvard.edu> writes:

> In article <mt2.0-4249...@hydra.herts.ac.uk>,

> Phillip Helbig---undress to reply <hel...@astro.multiCLOTHESvax.de> writes:

> > Is there a similar official definition for the parsec (i.e. fixing the
> > AU and specifying which, if any, trigonometric approximations are used)?
>

> Sort of. The IAU definition of the AU (apparently from 1976) is at
> http://www.iau.org/public/measuring/
>
> The AU is defined as "the distance from the center of the Sun at
> which a particle of negligible mass, in an unperturbed circular
> orbit, would have a mean motion of 0.01720209895 radians/day." In
> other words, this is the value of the "Gaussian gravitational
> constant." The distance corresponding to this definition has to be
> determined by observations, which nowadays are quite precise, but it
> is not an exact distance in meters. As far as I can tell, it
> corresponds to a year of 365.257...(many digits) SI days. I don't
> know why the correspondence isn't to something closer to 365.25, but
> maybe it was to leave some prior AU value unchanged.

Probably.

I found that the AU is officially (IAU definition) 149597870691 meters,
from the above definition.

> The conversion I've seen in several places from AU to parsec is
> pc = AU/tan(1 arcsec)
> but I don't know that it's official.

That's essentially the definition, of course.

> The value of the trig function
> is, of course, a transcendental number, but it can in principle be
> calculated to any desired precision. I'm sure the old 4-digit trig
> tables printed on paper are more than good enough for any practical
> purpose, and of course any modern calculator or math library will do
> far better than that. And of course the approximation that the
> tangent of a small angle is equal to the angle is plenty good enough.

Right.