"Charles" wrote in message
...
| On Thu, 25 Aug 2005 01:41:00 GMT, "Androcles" Androcles@ MyPlace.org
| wrote:
|
|
| "Charles" wrote in message
| .. .
| | On 24 Aug 2005 17:55:15 -0700, "Yousuf Khan"
| | wrote:
| |
| | Here's a question that's been puzzling me. If the universe is
| | expanding, and the further an object (e.g. a galaxy) is away from
us,
| | the faster it is moving away from us. Are there parts of space so
far
| | away from us that it's expanding away from us *faster* than the
speed
| | of light? From what I understand the speed of light limitation
| doesn't
| | apply to the expansion of space itself.
| |
| | Therefore the Cosmic Microwave Background Radiation isn't the
cloak
| | that surrounds the secrets of the Big Bang, but just the curtain
| around
| | a part of the universe that is now out of contact with us. An
| endlessly
| | expanding universe sure, but one that never had a beginning?
| |
| | Yousuf Khan
| |
| |
| | If we never know, does it matter?
|
| To whom?
|
| Androcles.
|
|
| us

I don't think Yousuf Khan is part of us, or he wouldn't be asking that
question.
Androcles

Yousuf Khan wrote:
If the universe is
expanding, and the further an object (e.g. a galaxy) is away from us,
the faster it is moving away from us. Are there parts of space so far
away from us that it's expanding away from us *faster* than the speed
of light?

You have to be careful of what you mean by "speed". It has units of distance
over time, but it's not the same as speed in special relativity. With that
caveat, the answer is yes.

Therefore the Cosmic Microwave Background Radiation isn't the cloak
that surrounds the secrets of the Big Bang, but just the curtain around
a part of the universe that is now out of contact with us.

The "speed" of the CMBR, in units of comoving distance over cosmological
time, is much larger than the speed of light. I think it's about 3.2c. This
means essentially nothing, since the speed of light has no special status
when talking about cosmological recession velocities.

-- Ben

N:dlzc D:aol T:com (dlzc) wrote:
Are there parts of space so far
away from us that it's expanding away from us *faster* than
the speed of light?

We expect so, yes.

Okay great, then assuming by some discovery we find out how much of the
universe is outside of our viewing range, will that affect the
calculations for the age of the universe?

Isn't it possible that given only what we can observe, we will always
come up with a finite age for the universe, and it will always be the
same age limit no matter when we do the calculation? For example if
we're calculating the age of the universe to be somewhere around 15-20
billion years old now, then a 100 billion years from now another set of
observers will look at what they can see in the universe at that time,
and they too will come up with 15-20 billion years rather than 115-120
billion?

In fact, wasn't there an observation made at one time, that some of the
oldest stars seem to be older than the age of the universe itself? I'm
not sure if that's been resolved or not.

Therefore the Cosmic Microwave Background Radiation isn't
the cloak that surrounds the secrets of the Big Bang,

It is believed to be, yes. Choose a different word than
"isn't"...

but just the curtain around
a part of the universe that is now out of contact with us. An
endlessly expanding universe sure, but one that never had
a beginning?

It is also expected to have had a beginning. The current
distribution of matter around us is not pure iron, which an
inifnite Universe would produce. Nor are there iron to hydrogen
conversion engines predicted or observable, with anywhere near
the amounts required.

Well, how do we know the distribution of matter isn't highly iron? We
don't even know what dark matter is composed of yet. What if all of the
stuff out in the galactic halos are long dead star cores (including
neutron stars and stellar blackholes), which somehow migrate out into
the halo over time? Separated out by gravity in some sort of natural
galactic centrifuge. Afterall it seems like the laws of gravity are
starting to undergo modifications these days as we do more detailed
observations of the rest of the universe -- perhaps a galactic
centrifuge is a quite logical outcome of the laws that we will
eventually discover?

As for an iron to hydrogen conversion engine, why do we need one?
Doesn't matter just pop up out of nowhere in the vacuum? Near a
blackhole its anti-particles could get swallowed while the particles
would get boosted right out of the blackhole's vicinity in the jet. The
new particles could go into refreshing the galactic gas clouds for new
star formation. And mass and energy conservation would be preserved in
the universe by the fact that every year, more parts of the universe
become inaccessible to us as they go "beyond the rim".

Yousuf Khan

Yousuf Khan wrote:

Isn't it possible that given only what we can observe, we will always
come up with a finite age for the universe, and it will always be the
same age limit no matter when we do the calculation? For example if
we're calculating the age of the universe to be somewhere around 15-20
billion years old now, then a 100 billion years from now another set of
observers will look at what they can see in the universe at that time,
and they too will come up with 15-20 billion years rather than 115-120
billion?

We estimate the age of the universe to be about 13.7 billion years.
As the universe expands faster and faster, our observable horizon
will begin to shrink and we will no longer be able to "see" the early
universe.

No Center
http://www.astro.ucla.edu/~wright/nocenter.html

Also see Ned Wright's Cosmology Tutorial
http://www.astro.ucla.edu/~wright/cosmolog.htm
http://www.astro.ucla.edu/~wright/cosmology_faq.html

WMAP: Foundations of the Big Bang theory
http://map.gsfc.nasa.gov/m_uni.html

WMAP: Tests of Big Bang Cosmology
http://map.gsfc.nasa.gov/m_uni/uni_101bbtest.html

Ben Rudiak-Gould wrote:
Yousuf Khan wrote:

If the universe is
expanding, and the further an object (e.g. a galaxy) is away from us,
the faster it is moving away from us. Are there parts of space so far
away from us that it's expanding away from us *faster* than the speed
of light?


You have to be careful of what you mean by "speed". It has units of
distance over time, but it's not the same as speed in special
relativity. With that caveat, the answer is yes.

Therefore the Cosmic Microwave Background Radiation isn't the cloak
that surrounds the secrets of the Big Bang, but just the curtain around
a part of the universe that is now out of contact with us.


The "speed" of the CMBR, in units of comoving distance over cosmological
time, is much larger than the speed of light. I think it's about 3.2c.
This means essentially nothing, since the speed of light has no special
status when talking about cosmological recession velocities.

-- Ben

I'm not sure I understand: Does that mean that there are portions of
the universe that we can never see because they are in effect moving
away from us faster than the speed of light? I thought that was
impossible--that the light just got more red-shifted at greater
distances.

Sam Wormley wrote:
We estimate the age of the universe to be about 13.7 billion years.
As the universe expands faster and faster, our observable horizon
will begin to shrink and we will no longer be able to "see" the early
universe.

Okay, then wouldn't we then be calling whatever we can still see to be
the "early" universe? And therefore wouldn't we then be saying that the
universe is always 13.7 billion years, since that's as far out into
that we can see?

Yousuf Khan

Yousuf Khan wrote:
Sam Wormley wrote:

We estimate the age of the universe to be about 13.7 billion years.
As the universe expands faster and faster, our observable horizon
will begin to shrink and we will no longer be able to "see" the early
universe.


Okay, then wouldn't we then be calling whatever we can still see to be
the "early" universe? And therefore wouldn't we then be saying that the
universe is always 13.7 billion years, since that's as far out into
that we can see?

Yousuf Khan



Why do you not think that in one billion years we will estimate
the age of the universe to be 14.7 billion years?

The restriction of observable horizon won't kick in for a while?

In the near term, our observable horizon is expanding about one
light-year every year.

John Graeme wrote:
The "speed" of the CMBR, in units of comoving distance over cosmological
time, is much larger than the speed of light. I think it's about 3.2c.
This means essentially nothing, since the speed of light has no special
status when talking about cosmological recession velocities.

-- Ben

I'm not sure I understand: Does that mean that there are portions of
the universe that we can never see because they are in effect moving
away from us faster than the speed of light? I thought that was
impossible--that the light just got more red-shifted at greater
distances.

Yeah, the light speed limit is only the limit of matter or energy
*moving* inside space. There is no such speed limit when it comes to
how fast space itself grows or shrinks inside itself. I always throught
of it like a bunch of boats in water, if the boats have a maximum speed
of 10 knots, then there's nothing that says you can't have a 20 knot
current in the water which moves them faster. Think of the boats as
matter or energy, and think of the water as space.

Yousuf Khan

"Yousuf Khan" wrote in message
ups.com...
Sam Wormley wrote:
We estimate the age of the universe to be about 13.7 billion years.
As the universe expands faster and faster, our observable horizon
will begin to shrink and we will no longer be able to "see" the early
universe.

Okay, then wouldn't we then be calling whatever we can still see to be
the "early" universe? And therefore wouldn't we then be saying that the
universe is always 13.7 billion years, since that's as far out into
that we can see?

Possibly. We can estimate the age of the universe (within obvious margins or
effort) through other means though, and generally these are consistent with
the age of the universe being around 12-17 billion years old.

Even our saying "13.7 billion years old" is to a massive (by Human
standards) margin of error - around 49 million years either way would still
be "13.7 billion years."

Sam Wormley wrote:
Yousuf Khan wrote:

Isn't it possible that given only what we can observe, we will always
come up with a finite age for the universe, and it will always be the
same age limit no matter when we do the calculation? For example if
we're calculating the age of the universe to be somewhere around 15-20
billion years old now, then a 100 billion years from now another set of
observers will look at what they can see in the universe at that time,
and they too will come up with 15-20 billion years rather than 115-120
billion?

We estimate the age of the universe to be about 13.7 billion years.
As the universe expands faster and faster, our observable horizon
will begin to shrink and we will no longer be able to "see" the early
universe.

The portion of the early universe (by which I mean the universe at the
time the CMBR was emitted) that we can see must always be expanding (by
which I mean we that in the future, we see things that were further
away). For this region to shrink, light which has already reached us
would have to reach us again. It is possible, however, for the part of
the early universe we can see to asymptotically approach some bound.