Expanding Space

"Jack" wrote in message
oups.com...
Can anyone explain to me what "expanding space" (a la Big Bang theory)
actually means? If we notice 2 objects moving away from each other we
don't say space is expanding so why is this any different when the
objects are 2 galaxies or all galaxies? Surely it's more appropriate to
say that the physical universe (matter, energy and what not) is
expanding - into space. Why do we say that space itself expands?
Pre-Einstein space seemed fairly intuitive but now it seems to have
been materialized/physicalized.

If space itself were indeed expanding would that not mean that the
length "1 meter" is ambiguous unless a time is specified? Would we even
be able to detect space expanding if all out instruments are expanding
with it?


The reasons why physicists assert that space is doing the expansion instead
of the galaxies are moving apart by themselves as follows:
1. The age of the universe is determined to be 14 billions years old.
2. The current observed horizon of the opposite regions of the universe is
28 billion years apart.
3. This means that these opposite regions of the universe cannot possibly be
in contact with each other and at the same time preserves that the postulate
of SRT that no massive object can move faster than the speed of light. This
is known as the horizon problem. This would mean the refutation of the
standard Big Bang model.
4. To save the BB model cosmologist came up with the idea that the expansion
of the universe is due to that space itself is doing the expansion and that
space expansion is not subject to the limitation imposed by the speed of
light c.
5. Alan Guth then came up with the isea of inflation to resolve the horizon
problem. Inflation says that when the universe is 10^-35 seconds old it
experienced a period of inflationary expansion. This resolved the observed
horizon problem and at the same time not violating the SR postulate.

I have a paper entitled "Unification of Physics" that resolves the horizon
problem without resorting to the ad hoc inflation hypothesis in the
following website:
http://www.geocities.com/kn_seto/index.htm

Ken Seto

On Wed, 24 Jan 2007 20:40:38 -0500, "kenseto"
wrote:


The reasons why physicists assert that space is doing the expansion instead
of the galaxies are moving apart by themselves as follows:
1. The age of the universe is determined to be 14 billions years old.
2. The current observed horizon of the opposite regions of the universe is
28 billion years apart.
3. This means that these opposite regions of the universe cannot possibly be
in contact with each other and at the same time preserves that the postulate
of SRT that no massive object can move faster than the speed of light. This
is known as the horizon problem. This would mean the refutation of the
standard Big Bang model.
4. To save the BB model cosmologist came up with the idea that the expansion
of the universe is due to that space itself is doing the expansion and that
space expansion is not subject to the limitation imposed by the speed of
light c.


If you could have galaxies moving apart faster than the speed of
light, provided that they are not moving relative to space faster than
the speed of light (because its expanding) wouldn't that imply that
speed relative to space is physically meaningful?


-- Surfer

Dear Surfer:

"Surfer" wrote in message
...
....
If you could have galaxies moving apart faster than
the speed of light, provided that they are not moving
relative to space faster than the speed of light
(because its expanding) wouldn't that imply that
speed relative to space is physically meaningful?

No, because you cannot measure motion with repect to "space" nor
"spacetime". What you could be moving with respect to is other
local matter and light that is travelling in your vicinity.

David A. Smith

On 25 Jan, 01:40, "kenseto" wrote:
"Jack" wrote in ooglegroups.com...

Can anyone explain to me what "expanding space" (a la Big Bang theory)
actually means? If we notice 2 objects moving away from each other we
don't say space is expanding so why is this any different when the
objects are 2 galaxies or all galaxies? Surely it's more appropriate to
say that the physical universe (matter, energy and what not) is
expanding - into space. Why do we say that space itself expands?

It is described that way because it best conveys in non-technical
language what our theories (mathematical models) suggest actually
happens. Observations are consistent with the large scale universe
being pretty homogenous, that is having a uniform density everywhere
when averaged over large enough volumes. If one part expanded then
it would imply that surrounding areas were being squeezed but in fact
it appears that the whole universe is expanding.

Pre-Einstein space seemed fairly intuitive but now it seems to have
been materialized/physicalized.

That is perhaps clearest when considering gravitational radiation,
ripples in the geometry of spacetime that carry energy. Hulse and
Taylor observed a binary pulsar system and showed that the rate
at which energy was being removed matched that predicted for
gravitational radiation so it appears to be a real phenomenon.

If space itself were indeed expanding would that not mean that the
length "1 meter" is ambiguous unless a time is specified?

No, "expansion" means distances are increasing relative to the metre.

Would we even
be able to detect space expanding if all out instruments are expanding
with it?

We do detect it, we see it as the Hubble red shift which stretches the
wavelength of light.

The reasons why physicists assert that space is doing the expansion instead
of the galaxies are moving apart by themselves as follows:
1. The age of the universe is determined to be 14 billions years old.
2. The current observed horizon of the opposite regions of the universe is
28 billion years apart.
3. This means that these opposite regions of the universe cannot possibly be
in contact with each other and at the same time preserves that the postulate
of SRT that no massive object can move faster than the speed of light. This
is known as the horizon problem.

snip - see below

5. Alan Guth then came up with the isea of inflation to resolve the horizon
problem. Inflation says that when the universe is 10^-35 seconds old it
experienced a period of inflationary expansion. This resolved the observed
horizon problem and at the same time not violating the SR postulate.

Ken's reply above is quite reasonable. The bit I snipped was:

This would mean the refutation of the
standard Big Bang model.

It wouldn't mean that, just that we need to find out why the CMBR
is so uniform, but the existence of the CMBR would still indicate
a hot dense period in the past which is what the Big Bang model
describes.

4. To save the BB model cosmologist came up with the idea that the expansion
of the universe is due to that space itself is doing the expansion and that
space expansion is not subject to the limitation imposed by the speed of
light c.

That is not correct, Ken's earlier comment on inflation is related
to the horizon (and flatness) problems but the description of
space expanding comes directly from the solutions to general
relativity which accurately model the observed Huble red shift
and other evidence.

HTH
George

"Surfer" wrote in message
...
On Wed, 24 Jan 2007 20:40:38 -0500, "kenseto"
wrote:


The reasons why physicists assert that space is doing the expansion
instead
of the galaxies are moving apart by themselves as follows:
1. The age of the universe is determined to be 14 billions years old.
2. The current observed horizon of the opposite regions of the universe
is
28 billion years apart.
3. This means that these opposite regions of the universe cannot possibly
be
in contact with each other and at the same time preserves that the
postulate
of SRT that no massive object can move faster than the speed of light.
This
is known as the horizon problem. This would mean the refutation of the
standard Big Bang model.
4. To save the BB model cosmologist came up with the idea that the
expansion
of the universe is due to that space itself is doing the expansion and
that
space expansion is not subject to the limitation imposed by the speed of
light c.


If you could have galaxies moving apart faster than the speed of
light,

But galaxies cannot move apart faster than the speed of light.

provided that they are not moving relative to space faster than
the speed of light (because its expanding) wouldn't that imply that
speed relative to space is physically meaningful?

Speed wrt space is already meaningful. The perceived horizon problem does
not exist. See my paper entitled "Cosmology Based on Absolute Motion" in the
following website:
http://www.geocities.com/kn_seto/2005Cosmology.pdf