A Few Questions:

1) Since it is determined that our universe is expanding at an
accelerated rate. What is the source of energy for this acceleration?

2) As this accelerated expansion proceeds over billions of years
wouldn't matter and energy get stretched so thin that we are left with
nothing but a massive universe that is virtually empty?

3) What's the big deal over trying to detect gravity waves? Haven't
we already done this with our oceans? The tides are created by the
moon's gravitational field. Is this any different than the gravity
waves we are trying to detect from other sources?

Thanks for your input on the above.

"Bob Carlson" wrote in message
om...

2) As this accelerated expansion proceeds over billions of years
wouldn't matter and energy get stretched so thin that we are left with
nothing but a massive universe that is virtually empty?

Yes... but "we" won't be around any more anyway. g

Bob Carlson wrote:
1) Since it is determined that our universe is expanding at an
accelerated rate. What is the source of energy for this acceleration?

In General Relativity, energy is not necessarily conserved...
http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html


2) As this accelerated expansion proceeds over billions of years
wouldn't matter and energy get stretched so thin that we are left with
nothing but a massive universe that is virtually empty?

Essentially, yes. However, things that are bound together (like
ourselves, planets,
galaxies and even small groups of galaxies) will stay together - only
the space between them will grow very large.



3) What's the big deal over trying to detect gravity waves? Haven't
we already done this with our oceans?

No.

The tides are created by the
moon's gravitational field.

Yes. However, that is an effect of an essentially *static* gravitational
field. What we look for us an oscillating gravitational field which
propagates through space at (very probably) light speed.


Is this any different than the gravity
waves we are trying to detect from other sources?

Yes, there is a huge difference.


Thanks for your input on the above.

I hope I could help...


Bye,
Bjoern

"BF" == Bjoern Feuerbacher writes:

BF Bob Carlson wrote:

2) As this accelerated expansion proceeds over billions of years
wouldn't matter and energy get stretched so thin that we are left
with nothing but a massive universe that is virtually empty?

BF Essentially, yes. However, things that are bound together (like
BF ourselves, planets, galaxies and even small groups of galaxies)
BF will stay together - only the space between them will grow very
BF large.

At the risk of becoming excessively technical, this isn't entirely
clear. In technical terms, what happens in the future depends upon
the "equation of state" of dark energy; less technically, what happens
in the future depends upon the characteristics of what is causing the
acceleration.

In the classical general relativity scheme, in which the acceleration
is caused by a cosmological constant, what Bjoern says is correct.
However, people have considered other variations. In some, the rate
of acceleration is increasing with time. In that case, the Universe
could face a "Big Rip" in which everything eventually ends up being
disassociated.

(For more details, try doing a Web search on "Big Rip," dark energy
equation of state, or w parameter.)

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

Joseph Lazio wrote:
"BF" == Bjoern Feuerbacher writes:


BF Bob Carlson wrote:


2) As this accelerated expansion proceeds over billions of years
wouldn't matter and energy get stretched so thin that we are left
with nothing but a massive universe that is virtually empty?


BF Essentially, yes. However, things that are bound together (like
BF ourselves, planets, galaxies and even small groups of galaxies)
BF will stay together - only the space between them will grow very
BF large.

At the risk of becoming excessively technical, this isn't entirely
clear. In technical terms, what happens in the future depends upon
the "equation of state" of dark energy; less technically, what happens
in the future depends upon the characteristics of what is causing the
acceleration.

In the classical general relativity scheme, in which the acceleration
is caused by a cosmological constant, what Bjoern says is correct.

However, people have considered other variations. In some, the rate
of acceleration is increasing with time. In that case, the Universe
could face a "Big Rip" in which everything eventually ends up being
disassociated.

(For more details, try doing a Web search on "Big Rip," dark energy
equation of state, or w parameter.)

Yes. I was talking only about that one case, since all the other
scenarios proposed so far look quite speculative to me. Simply assuming
that the dark energy is due to the cosmological constant is the most
easy explanation so far (although it opens a fine-tuning problem).



Bye,
Bjoern