I have heard/read evidence that galaxies are observed accelerating
away from us (and each other). Given that the Earth is not "special",
if we were experiencing even minute acceleration, we should be able to
detect it (variation in gravity in particluar direction of
acceleration). Since we don't (right?) then this "proves" the universe
is steady state? Comments?

Hi Barry, 

Fascinating question!  Let me start by letting you know that I’m no
cosmologist; I merely have a deep interest in astronomy.  However,
just last Friday, cosmologist Robert Kirshner appeared with Ira Flatow
on NPR’s Talk of the Nation Science Friday.  He discussed the
concepts, not only of the expanding Universe, but of the accelerating
expansion of the Universe.  His writing should interest you especially
because the title of his new book is “The Extravagant Universe:
Exploding Stars, Dark Energy, and the Accelerating Cosmos”.  You can
listen to the segment with RealAudio here:
http://www.sciencefriday.com/pages/2003/Jan/hour2_013103.html

Another great resource is the Cosmology FAQ at:
http://www.astro.ucla.edu/~wright/cosmology_faq.html
But there is no specific Question that addresses the issues brought up
in yours.

Specifically, the reasoning of your initial question is flawless if
the expansion of the Universe is considered as being in one direction
from some central point.  However, this is not the case.  In present
THEORY, there is no central point in the Universe that everything else
is expanding away from.  Everything is expanding away from everything
else at an equal rate, so *each point* in the Universe can be thought
of as a center.  Since expansion is occurring throughout the Universe
constantly in *all* directions, there is no apparent *motion*
detectable to us here on Earth that would indicate a direction of
expansion.

Think of it this way:  You are observing the universe from point A
within a spheroid, (with no implied center), which is moving away from
points B and C within that same spheroid, each of which are 180
degrees from point A. Each of those three points are in turn expanding
away from every other point and each other at the same rate. With the
Universe expanding in *all* directions, there wouldn’t be a
directional gravitational anomaly on Earth to measure.

Mr. Kirshner also has an interview on the BBC you can read through at
this site:
http://www.bbc.co.uk/science/space/spacechat/livechat/bob_kirshner.shtml
One of the questions asked is:  “My dad says the Universe is
expanding. If it is getting bigger can we tell where it first started
and is this the centre of the Universe?”
Bob Kirshner answers: "Your Dad is right. The Universe is expanding
but it's expanding everywhere. We don't think we're at the centre and
we don't think [anything else] is at the centre. Somebody on a distant
galaxy would have the same view of the expanding Universe that we do.”

In one of the comments below, the issue of the rate of cosmic
expansion is brought up.  Here’s another question and answer from the
same interview:
At what rate is the Universe still expanding?
Kirshner answers: "Astronomers use funny units to describe the way in
which the Universe is expanding. We say the expansion rate is about 70
km per second per megaparsec. What this really means is that the
Universe is stretching out by one part in 14 billion every year. The
distances between the galaxies are growing in a way that depends on
their distance. This is what we observe as the expanding Universe."

When we speak of expansion in terms like these, it is habitual to
assume that there are boundaries to the thing that is expanding, but
in the case of the Universe, there are no outward boundaries.  This is
hard to grasp, and that’s the problem that vexes cosmologists and
folks like us trying to understand it.  Only by understanding that
there isn’t a boundary to the Universe is it possible to “understand”
everything expanding from everything else.

There is a discussion of this subject matter at Starstuff.org that
contains  this information:
http://www.starstuff.org/default.asp?cover=/articles/792.asp

“Hubble was able to show a linear relationship between the velocity of
the galaxies and their distance -- the farther the galaxy, the faster
it was receding.

“Hubble's Law is a linear relationship, so every observer at every
point in every galaxy of the Universe sees him or herself to be at the
center of expansion, when there really is no center.

“Sir Arthur Eddington (another physicist/astronomer of the period)
devised an analogy of the surface of a balloon painted with dots. The
curved surface of the balloon is a two-dimensional analogy for the
three spatial dimensions of the Universe. If you're standing on one of
these dots and look out as the balloon is inflated, it will appear
that all the other dots are moving away from you, but every person
standing on every dot will see the same thing!”
___________________________________

I realize that there are only a few references given in the body of my
answer, however this question, dealing with the realms of theory as it
does, invites further discussion.  Please ask for clarification of any
point.

--Kutsavi

---

Request for Answer Clarification by barryn56-ga on 04 Feb 2003 05:40 PST

Hi Kutsavi-ga,

and thanks for trying to answer this difficult question, which I think
you've had a good stab at. However, I still think there is a deal of
confusion between expansion and acceleration. Much of the commentary
is about expansion - there is no problem with expanding in all
directions, with everything moving away from everything else, but in
order to accelerate away, you need to have a force - this is even
mentioned and required (the anti-gravity component, for example).
Then, there is no avoiding it - if there is a force, then it must have
a direction.

Let's say, for example, the Moon is accelerating away from the Earth,
which it is. As the moon is rotating and also orbiting the Earth, the
acceleration would be "in all directions" from the viewpoint of an
outsider looking at the system - the moon is essentially on a spiral
path with the gaps getting wider faster. But standing on the Moon, if
I measure the force of gravity each time the Earth is over head, it
would be at a minimum compared to when I am at an angle to the Earth,
and a maximum when on the opposite side. In other words, the force
would be through the centreline between the Earth and Moon, and in the
direction away from the Earth.

I don't know where this is leading, but I am thinking this force may
indeed exist, but is difficult to measure due to the other influences.
Perhaps, for example, it might account for the variation in the
magnetic field of the Earth due to force on the molten core? There is
an interesting project looking into this, and it uses gravity meters
around the Earth in various laboratories. An interesting comment from
one site is:

"But they (gravity variations) are more precisely detected by the
associated disturbances in the locations of distant stellar radio
sources relative to the Earth, as measured by radio telescopes. This
technique, called very-long-baseline-radio-interferometry (VLBI for
short), was actually developed in Canada over 30 years ago. Dr.
Rochester is currently trying to track down the reasons why the theory
of such wobbles predicts one of them to have a period significantly
different from the value deduced from VLBI data."

Anyway, I will take this as an answer for now, and be interested to
have nay further comments.

Regards,

Barry

---

Clarification of Answer by kutsavi-ga on 04 Feb 2003 16:47 PST

Hello again! 

You wrote:
"I still think there is a deal of
confusion between expansion and acceleration."

Not confusion so much as the fact that acceleration isn't really a
necessary issue to talk about when trying to determine whether the
effects of Universal expansion can be detected on Earth.  Acceleration
of the Universe is the newest "thing" in cosmology.  Apparently, the
Universe actually slowed its expansion up until about 7 billion years
ago, when "something" happened to trigger the present acceleration. 
This is attributed to what is known as a "dark force", for lack of a
better term.

An Accelerating expansion of the Universe was first posed by a team of
cosmologists at Lawrence Berkeley National Laboratory in January,
1998, led by Saul Perlmutter.  Their work was duplicated
simultaneously by another team of scientists working at the Cerro Tolo
Inter-American Observatory in Chile.  Prior to these scientists'
findings, it had been theorized that the expansion of the Universe was
slowing due to the forces exerted by stars' gravity.  Perlmutter's
team, while attempting to determine the rate at which expansion was
*slowing*, discovered by observing light emission from Type 1A
Supernovae, that the opposite was in fact the case; the Universe is
accelerating its expansion.

From an article appearing on MSNBC's website reporting on Science
Magazine's 1998 pick for the most important science discovery of the
year: (Science Mag. charges to view their archived articles, but the
issue is Feb. 27, 1998; "COSMOLOGY: Astronomers See a Cosmic
Antigravity Force at Work, Science 1998 279: 1298-1299")
http://www.msnbc.com/news/224520.asp?newguid=B431A1A48F55423794D9E4E56AFCE18E&cp1=1#BODY
___________________________
(by Alan Boyle) "In 1929, astronomer Edwin Hubble announced that the
universe appeared to be expanding based on his observations of faraway
galaxies. He noticed that the characteristic signature of starlight
from distant sources appeared to be shifted toward the red end of the
spectrum — meaning that the light waves had been stretched during
their journey to Earth. The implication was that during the
intervening time, the entire universe had been stretched by a
corresponding amount.
    "Such “redshift” observations have been confirmed repeatedly in
the nearly 70 years since then, cementing the idea of an expanding
universe as a fundamental pillar of modern astronomy. But many
theorists assumed that the gravitational attraction of all the matter
in the universe would slow down an expansionary tide that came in the
wake of the primordial Big Bang.
    "To shore up that assumption, scientists looked for a standard
yardstick that could be used to measure the distance from a light
source. Using such a yardstick, they could match up various known
distances with redshift values and calculate how the expansion rate
has changed over time. Light that started its journey from a
relatively distant source — say, 10 billion years ago — might exhibit
a redshift different from light that was thrown off just 1 billion
years ago.
    "Perlmutter and  others found such a yardstick in a particular
kind of exploding star known as a Type 1A supernova. Over the course
of several years, the astronomers developed a model to predict how
bright such a supernova would appear at any given distance.
Astronomers recorded dozens of Type 1A supernovae and anxiously
matched them up with redshifts to find out how much the universe’s
expansion was slowing down.
    "To their surprise, the redshift readings indicated that the
expansion rate for distant supernovae was lower than the expansion
rate for closer supernovae, Perlmutter said. On the largest scale
imaginable, the universe’s galaxies appear to be flying away from each
other faster and faster as time goes on."
_______________________________

The driving force behind this apparent acceleration, (which has more
to do with decreasing density of the Universe than actual
acceleration, by the way), is a "dark force", somewhat related to
"dark matter", which has been much-talked of lately.  (The two are not
synonyms, and "anti-gravity" is not the accepted term, either.)  This
Dark Force acts as a counter to gravitational attraction and "snaps"
the Universe outward.  This would be a fifth force at work in the
Universe, on top of the four now accepted by physicists: the strong
force, which holds the nucleus of an atom together; the weak force,
which causes atomic decay; electromagnetic force, which holds
electrons in orbit in an atom; and gravity.
  
But all this talk of acceleration and decay seems to be a red herring
when trying to address your question of measuring simple expansion
from an Earth-based perspective.  It seems more logical to address the
issue of expansion first.

You wrote: "...with everything moving away from everything else, but
in order to accelerate away, you need to have a force - this is even
mentioned and required (the anti-gravity component, for example).
Then, there is no avoiding it - if there is a force, then it must have
a direction."

Agreed on a Euclidean basis, but as I attempted to purvey in my
answer, all this accelerating and expanding is taking place from *our
perspective* here on the blue ball.  Everything is expanding away from
us, leaving us a stationary object in the Universe...HOWEVER...it is
assumed that this observation would be the same no matter your vantage
point in the Universe.  Hence, we perceive no apparent motion, and
least of all, no direction.  But this doesn't mean we are the center
of the Universe!  Each point in the Universe is receding from every
other point at the same time.

I guess I have to pose a question to you in order to explain this:  If
everything in the Universe is expanding away from you, and you are on
a body expanding from everything else in the Universe, how do you
determine what direction you are going?  There can't *be* one
direction of expansion or acceleration, because in fact if you are
inhabiting that one point, you are traveling away from everything else
in the universe at the same time...it borders on the theological.

I assume that you've heard of the loaf of bread with raisins in it
baking in the oven.  As the bread rises, all the raisins move away
from each other.  In so doing, the raisins mimic stars in the
Universe.
____________________________________________

You also wrote:  "Let's say, for example, the Moon is accelerating
away from the Earth, which it is."

Is it?  One would think that it would eventually stray from the
Earth's gravity and no longer be a moon if this were the case. 
Granted, in an expanding Universe, this would have to the the case,
but gravity still has its effect, keeping the moon in its orbit and
even electrons and other sub-atomic particles in orbit around their
nucleus, otherwise, none of the other forces of nature would apply,
and atoms would cease to exist, and so we would cease to exist.

I don't think that the moon is expanding away from the Earth at the
rate that the Universe is expanding...strange but true.  Gravity must
still hold true for the whole Universe to expand.

The case for the expanding Universe acts only on a HUGE scale, which
operates to leave the other forces of physics in tact.  You used the
above example of the moon to explain why the forces of expansion and
acceleration should be measurable from Earth.  However, and to
belabour the point, Universal expansion and acceleration only makes
sense if you assume that the Universe as a whole is expanding from
each and every point in the Universe.  This is the point at which
logic breaks down, and everything we've learned or know comes up
against the Cosmos, and, I assume, why you asked your question ;-)

You also mention the molten core of the Earth as being an indicator of
the direction of the expansion of the Universe.  Belabouring the point
yet again, there isn't any reference point on Earth, nor even in the
Solar System, that will serve as a directinal vector to enable you to
determine which direction Universal expansion is progressing toward. 
THERE SIMPLY ISN'T ANY DIRECTION THAT ANY BODY IS NECESSARILY
EXPANDING TOWARD.

This of course doesn't completely answer your question either, but at
least addresses a couple of your points.  Feel free to ask further
clarifications of the point.  I'm out of breath and need to get dinner
started ;-)  Thanks for a great physical and metaphysical question.

-- Kutsavi

Hi Barry

  The answer is obviously 'Two cultures' misunderstanding. 
  HTTP://dannyreviews.com/h/The_Two_Cultures.html

To get a technical answer it may be necessary 
(and justified) to
"Ask for a refund" , as described in 
 HTTP://answers.google.com/answers/help.html

It may also be necessary to elaborate your 
reasoning a bit. 
There is is slight anisotropy, 
HTTP://map.gsfc.nasa.gov/m_uni.html
 but how would that or any  locally measured acceleration 
support steady state models???
 
hedgie

Hedgie, you might want to look your comment over in the context of the
June 6th newsletter.  You can find it in the Newsletter Archive tab of
the Researcher Center.

Thanks.

--Missy

Now, I could be wrong, but are you sure that you heard "accelerating"
away from us/each other?  Not just moving?  If it is the former, it is
news to me and I'd like to know your source.  My understanding is that
it is the latter, that all points in the universe are moving apart,
and further, that the speed of recession is proportional to their
distance - this is Hubble's Law, and appears to argue against a
"steady state" universe.

The vexed question is - will this expansion continue forever, or will
gravity eventually cause its reversal into a "big crunch".  Last I
heard, the jury was still out on this, but recent work on "dark
matter" and esoteric theoretical particles like WIMPs, may mean that
the crunch is coming.

Also - there is debate over whether the gravitational constant has
always been a constant!  Observations of distant quasars, when
considered in the light of Hubble's Law, suggest that they are older
than the Universe - clearly not possible.  One suggestion is that in
the very early Universe, gravity was weaker(?) than it is now, and
thus the light we see from these distant objects was emitted when G
differed.

Of course, I could be way off base, and if it is acceleration you are
talking about, then Newton tells us f=ma, so we need to find a force
to account for it.  If it is an attractive force, then this requires
that its source be "outside" the Universe - again not really possible.
 Therefore we need a repulsive force.  There is a possibility here
that at extreme distances, the inverse-square law of gravitation
breaks down in the face of an as yet uncharacterised fifth natural
force.

xarqi-ga,

thanks for the comment, but I do mean accelerating - there's lots now
about Einstein's gravitational constant and the idea of a repulsive
force (solar pressure?), but there are lots of recent work indicating
an accelerating universe - as I said, just do a search for that term
in Google... However, this is the point of my question - how do
cosmologists support this theory and yet not allow the force to be
measured on Earth? Either we happen to be moving at a constant speed -
neither accelerating nor decelerating at detectable levels (i.e. less
than a few tenths of a metre per second squared) - which has
interesting implications for the Big Bang theory - how can some
universes be accelerating and others not? - Or, if we keep a
consistency, then no universes are significantly
accelerating/decelerating or - is there another explanation - that's
what I'd like to know. So really need a cosmologist who thinks the
acceleration is real to explain why we don't feel it here...

Hedgie-ga,

by "Steady State" I guess I mean Pseudo-Steady State, where everything
is acting in the same way (i.e. all moving apart at constant
conditions) rather than some accelerating (+ or -) and others not. We
can easily measure the effect of acceleration due to our planet
rotating by measuring the difference between weight at the equator and
poles, despite the cancelling effect of the planet's equatorial bulge,
so the fact we don't feel directional variations means our nett
acceleration through space must be below a certain (pretty low, I
should guess) limit - what value would that be?

Regards,

Barry

For missy

         Thank you for your comment. 
  I did look at the newsletter and appreciate your point.

  There may be some misunderstanding here, though.
  My comment was about a  totally different answer.
  You may note that date on my comment od feb 02.
  This answer is dated Feb 03. 
  I certainly would not make such comment on this answer.

   Technically, one may saythe policy applies to any answer,
   but I believe that if you would see that original answer
   you would agree it is a question of degree.


   I think that when editors pull the answer, they should pull
   the comments too, to prevent such misunderstandings.

Hi Barry

   'everything is acting in the same way' - meaning there are no 
    special places or directions - that is called The Cosmological
Principle

"... The starting point for these theories is what is termed
cosmological principle: Viewed
on sufficiently large distance scales, there are no preferred
directions ..."
csep10.phys.utk.edu/astr162/lect/cosmology/cp.html

and that is  assumed. The problem I still have with 
understanding your interesting idea is this

   Earth is in free orbit
    (so is Earth Moon system, Solar system, etc.)
    That means that (with some qualification) we do not feel
     the accelrations and gravity pulls.
   The total gravity field determines the orbit so, that inertia
effect
    balances the pull of total gravity, right?

 So, we do not feel (or can measure directly) pull of the Sun. It is
revealed
 by shape of our orbit. Now (and that's the qualification) we can
measure
 the tides. Due to the Sun, moon, other planets, and even weaker
effect
 of the other objects - nearby galaxies. But does that, let's say
tides
due to near galaxy, says anything about the Cosmological Principle?

i dont have any specific answers but there is one book that does
explain our univers, if only people would bother to read it. check out
the bible and these scriptures in it. ecclesiastes 1:4,  psalms 104;5,
 2 peter 3:5-7,   genesis 7:23,   matthew 24:34,37,39   2
thessalonians 1:6-9   revelation 7:9,14. i know this is a scientific
question, but who better to ask about a bit of gear than the builder.
and god built the earth and all the universe. if you disagree, prove
to me who else did. thanks for the opportunity.

Hi Kutsavi - yes, the moon is leaving us (and has been for a long
time) and I guess, as it gets further away, it will leave faster,
although other say it will stabilize, see
http://itss.raytheon.com/cafe/qadir/q1282.html. This will affect the
Earth's rotational velocity, of course...leading to all manner of
interesting effects no doubt, but not before the Sun explodes...

Many people mention expanding ballons/bakery items and I would point
out that, if standing on one of those raisins, you would experience a
different force on one side (the side away from the centre of
expansion, compared to the other side. Assuming a rotating raisin, if
you had gravity (acceleration) measurements on each side of the raisin
and compared them, the difference between them would change as the
raisin rotated relative to the "direction of expansion". OK, I keep
harping on about a direction, but there has to be one for an
individual particle, like the Earth.

And are you sure we can't measure directly the Sun's gravitational
effects - I'm pretty sure we can (like the moon) - it is just a lot
farther away. There are borehole gravity tools which specifically
require correction for the presence of the moon, for example, and the
Sun isn't anything special to not be detectable with a sensitive
enough instrument.

As I mentioned, we can certainly detect the effect of acceleration due
to the earth's rotation (difference in gravity between equator and
poles).

And what about the anomlous positions of the cores of some of the
outer planets? Displaced from the centre and at a weird angle to the
planet's rotational axis...

Maybe I need to find a Bulletin Board to discuss this!

Barry

>And what about the anomlous positions of the cores of some of the
>outer planets? Displaced from the centre and at a weird angle to the
>planet's rotational axis...

Can you elaborate on that, please? I know Uranus' axis of rotation is
at an unusual angle, but I've not heard of that before.

Ian G.

Iang-ga,

there's a great review here:

http://astronomy.nju.edu.cn/astron/AT3/AT31305.HTM

Regards,

Barry

Barry

Thanks for that! I don't think it's the cores themselves that are off
centre, it's the line joining the magnetic poles. It's still strange,
though!

Cheers

Ian G.

Hey Barry, 

Quite the discussion you've fomented here!

I've written to Professor Kirshner at Harvard with your question, and
am waiting to hear back from him.  I will post his reply here if I
receive one.

Yeah, the baked goods analogy is poor, but it's the one most widely
used to explain the expansion.

Once again, fascinating question and I'm not done with it yet...for
that matter, science isn't done with it yet ;-)

As far as measuring the sun's gravity being measured from Earth, yes,
of course it can.  In reading through my posts to this question, I
can't find where I said that it couldn't be...any help?

Let me throw out the postulation that examining things as small as one
planet or even our solar system, is a bit like counting the number of
fleas to determine the size of the dog.  Earth and the solar system
are such a small part of the Universe that measuring an effect like
Universal expansion from that perspective may be a bit short-sighted. 
I understand what you're trying to ask/find out, but my hunch is that
this issue must be inspected from a larger frame of reference.

--Kutsavi

Hi Kutsavi-ga, yes - sorry, it was Hedgie-ga who made the Sun comment.

Interesting point on size issue - this is one thing that acceleration
is somewhat "immune" to, I think, as it affects everything in the
system in the same way, but agree that the interference due to local
(gravity and rotation) effects may be overwhelming. Your comment gave
me the thought of the analogy of an atomic nucleus on a train that
accelerates from rest. Despite the high rate of acceleration, what
does the nucleus feel? If it is vibrating around anyway, it might be
really tough to detect, but still possible if the acceleration is long
lived. I guess this is what NMR relies upon.

Regards,

Barry

Hey Barry,

Heard back from Professor Kirshner today.  First of all, this is what
I wrote to him yesterday:

"[I said] essentially that the expansion and rate of acceleration
can't really be measured by Earth-based gravitational anomalies
because the Universe is expanding in all places equally as measured
from each point in the universe.  This means that a direction is
impossible to determine because each point is moving away from every
other point, so your particular position appears stationary as the
Universe expands/accelerates all around you.  Additionally, there is
no central point that the Universe is expanding *from*, and so the
expansion is essentially directionless."

Here is Prof. Kirshner's response re. expansion and accleration:
_________________________
"Thanks for your note.  I think you did pretty well for the Google
questioner.

"The central idea is that what we are calling "acceleration" doesn't
have a
direction (unlike the usual meaning in Newtonian mechanics).  We mean
"the rate
of cosmic expansion is speeding up."  The way we measure that is by
looking at
large distances where the light from exploding stars was emitted long
ago to
compare the relation of velocity and distance seen back then with the
relation
(Hubble's Law) that we see nearby.

"The other important idea you nailed right on the head--we think the
view from
Earth is like the view from any other place.  A little more
forcefully, we'd say that, when you average over big enough chunks
(about 300 million light years), one part of the Universe is pretty
much like another.

"But the Universe has been changing over time.  The Universe today is
much
different from what it was like 14 billion years ago, and we can see
that in our observations of distant galaxies and quasars, to say
nothing of the cosmic
microwave background.  The steady state idea suggested you wouldn't
see any
changes over time, and that is just plain wrong."
________________________

So, directionless expansion and acceleration having to do with the
rate of that expansion speeding up, as opposed to single particles
expressing acceleration.  All this being observed over vast distances
of time and space.  Sounds like the opening of a movie.

Mindboggling at least.

I've bought a copy of Kirshenr's book "The Extravagant Universe", and
plan on a long weekend of cosmic theorizing ;-)

--Kutsavi