wrote:
Infinite universe Jim?
It had a beining and is expanding at a finite rate.
You can't get infinity out of that.

It would have to be infinite in the beginning.

John Sefton wrote:
wrote:
Space stretches and this is the cause of the light stretch.

What is your explanation?

Uniform stretch everywhere doesn't work.
This is why shells grow in spirals.

Take 3 towns,; A, B, and C.
B is 10 km north of A. C is 10 km
north of c.

Now double all the distances
in one unit time.

B is now 20 km north of A.
C is now 20 km north of B.

So what?

Well, B moved 10 klicks.
How far did C move? (Hint: B is now
where C used to be.)

Well, B moved 10 klicks. How far
did C move in equal time? What about
D, E, F.....all originally at 10 klick
intervals? Get the picture?

John

That's why the velocity of galaxies away from us is proportional to
their distance (until relativistic effects kick in, and their relative
velocity compared to us becomes ambiguous).

T Wake wrote:
wrote in message
ups.com...
Let me take the oportunity to use this post for which
it was orignally intended twake:

Ok, a novel approach for you.....

If a closed universe is expanding there is no edge.

Well, it depends how you use closed. The general cosmological use for a
"Closed Universe" is one which has a finite amount of expansion possible. It
is still infinite in size.

If the universe is anything but infinite in size, it has an edge.

Instead the space inbetween the galaxies is stretching.

No. Stretching is a bad analogy as it implies things which aren't so.

The balloon model is not the real thing. It is an analogy to help people
understand some of the concepts.

What is interesting is that in cosmology the light
transversing this space is also stretched. It gets
longer and less energetic. This redshift is how we
determine their distances.

Where does the energy go?


If there is no boundary the universe can be seen to
be the surface of a hypersphere.


Nope.

Mitchell is right here about a finite universe not necessarily having a
boundary. This is the case if space has a positive curvature (assuming
it is isotropic and homogenous).

See, for example:
http://map.gsfc.nasa.gov/m_uni/uni_101bb2.html

Such a space is generally referred to as "closed." The
cold-dark-matter model of cosmology implied that if and only if there
was enough matter in space to make it closed, there was enough to make
it recollapse. However, the discovery of the accelerating expansion of
the universe indicated that there is more to the behavior of space-time
than the gravitational influence of ordinary and cold dark matter.
Thus, the statement that a closed universe must necessarily collapse is
no longer true, if you use "closed" in the usual way.

Jim Black wrote:
John Sefton wrote:

wrote:

Space stretches and this is the cause of the light stretch.

What is your explanation?


Uniform stretch everywhere doesn't work.
This is why shells grow in spirals.

Take 3 towns,; A, B, and C.
B is 10 km north of A. C is 10 km
north of c.

Now double all the distances
in one unit time.

B is now 20 km north of A.
C is now 20 km north of B.

So what?

Well, B moved 10 klicks.
How far did C move? (Hint: B is now
where C used to be.)

Well, B moved 10 klicks. How far
did C move in equal time? What about
D, E, F.....all originally at 10 klick
intervals? Get the picture?

John


That's why the velocity of galaxies away from us is proportional to
their distance (until relativistic effects kick in, and their relative
velocity compared to us becomes ambiguous).

Which is fine if we are the center.
John

John Sefton wrote:
Jim Black wrote:
John Sefton wrote:

wrote:

Space stretches and this is the cause of the light stretch.

What is your explanation?


Uniform stretch everywhere doesn't work.
This is why shells grow in spirals.

Take 3 towns,; A, B, and C.
B is 10 km north of A. C is 10 km
north of c.

Now double all the distances
in one unit time.

B is now 20 km north of A.
C is now 20 km north of B.

So what?

Well, B moved 10 klicks.
How far did C move? (Hint: B is now
where C used to be.)

Well, B moved 10 klicks. How far
did C move in equal time? What about
D, E, F.....all originally at 10 klick
intervals? Get the picture?

John


That's why the velocity of galaxies away from us is proportional to
their distance (until relativistic effects kick in, and their relative
velocity compared to us becomes ambiguous).

Which is fine if we are the center.
John

Watch what happens if we simply change reference frames:

time
^
| * * * *
| * * * *
| * * * *
| * * * *
+------------------------ position

time
^
| * * * *
| * * * *
| * * * *
| * * * *
+------------------------ position

time
^
| * * * *
| * * * *
| * * * *
| * * * *
+------------------------ position

time
^
| * * * *
| * * * *
| * * * *
| * * * *
+------------------------ position

Every galaxy sees the other galaxies moving away from it at a rate
proportional to their distances.

But what about galaxies beyond the causal horizon? What are they
doing? Does NASA have a mission planned to go visit them? Mommy, will
Humanity ever live in peace?????????

- Donsky Oatsky, The Nut (Pecan) Ranch

Watch what happens if we simply change reference frames:

time
^
| * * * *
| * * * *
| * * * *
| * * * *
+------------------------ position

time
^
| * * * *
| * * * *
| * * * *
| * * * *
+------------------------ position

time
^
| * * * *
| * * * *
| * * * *
| * * * *
+------------------------ position

time
^
| * * * *
| * * * *
| * * * *
| * * * *
+------------------------ position

Every galaxy sees the other galaxies moving away from it at a rate
proportional to their distances.

True. In fact, Hubble's law is nothing more than Distance = Rate *
Time: You can verify this by checking the units.

Hubble's Constant * Distance = Velocity

50 km/second per MegaParsec is equal to somewhere around 1/13 billion
years.

The diagrams you have drawn show a Galilean Transformation, showing a
fairly small change in speed, less than ten percent of the speed of
light. This would cover the area within a billion light years of
Earth; within 10% of the radius of the universe.

When we get outside that range, if Hubble's Law still holds true, we
need to use a Lorentz Transformation, as the Galilean transformation is
only an approximation.

But the d=r*t law remains true not only in the Galilean transformations
you have shown, but is also true with Lorentz Transformations. Observe
the following animation, showing a Lorentz Transformation, similar to
the Galilean Transformation you have shown.

http://casa.colorado.edu/~ajsh/sr/wh...pacetime_wheel

Notice, when the lines are nearly vertical, they are fairly similar to
those you've drawn with ASCII above. The lines at the edges, on the
other hand, are squeesed in extremely tightly.

Though the lines get squeezed in together, they do not change their
linear quality. They are straight lines, indicating a linear
relationship, preserving Distance=Rate*Time.

John Sefton wrote:
wrote:
Space stretches and this is the cause of the light stretch.

What is your explanation?

Uniform stretch everywhere doesn't work.
This is why shells grow in spirals.

Take 3 towns,; A, B, and C.
B is 10 km north of A. C is 10 km
north of c.

Now double all the distances
in one unit time.

B is now 20 km north of A.
C is now 20 km north of B.

So what?

Well, B moved 10 klicks.
How far did C move? (Hint: B is now
where C used to be.)

Well, B moved 10 klicks. How far
did C move in equal time? What about
D, E, F.....all originally at 10 klick
intervals? Get the picture?

John

So it would seem, B moved 10, C moved 30, D moved 50, E 70, F 90, to
infinity, so of course it looks like somewhere along the way something
must be moving at faster than the speed of light.

However, if you know your Special Relativity, you know that F is both
time dilated and length contracted. G is more so, H is more still, I,
more still, etc. Until you get out to Y which is moving 99.999% of the
speed of light, has experienced, for all intents and purposes, no time
at all, and is still adjacent to Z.

Yes, one second has passed for you, but one second has not passed for
"the universe"

The universe looks like this:
http://www.spoonfedrelativity.com/fi...l-big-bang.gif

Not like this
http://www.spoonfedrelativity.com/fi...lileanreal.gif

Jim Black wrote:

That's why the velocity of galaxies away from us is proportional to
their distance (until relativistic effects kick in, and their relative
velocity compared to us becomes ambiguous).

Relative velocity does not become ambiguous when relativistic effects
kick in. There might be a bit of extra work involved in establishing
precisely when and where the relative velocity happened or how long it
lasted, it is all very definable and not ambiguous at all.

Events can be described in space and time very precisely according to
an agreed upon reference frame, just as we on earth all describe time
on earth according to GMT.

Cosmology of space expansion in closed universe
only works if the space stretch inbetween the galaxies
is equivalent to them moving away *through* space.

Space stretch stretches light just like velocity does.

Mitch -- Light Falls --