| Topic: |
Religions > Atheism |
| User: |
"Elroy Willis" |
| Date: |
05 Jul 2005 06:41:00 AM |
| Object: |
OT - Expanding Universe Questions |
If the universe is expanding, and even accelerating as it expands,
which seems to be the case according to current observations, then how
can galaxies actually collide with each other?
One of the popular visual models of the universe depicts it as a loaf
of raisin bread that's rising and expanding, with all the raisins
getting further and further apart as the bread bakes in the oven. Do
individual raisins actually collide inside a loaf of cooking raisin
bread?
Another model I've seen is the balloon example, with dots drawn on an
uninflated rubber balloon, and when the balloon is blown up, the dots,
which represent stars and galaxies, get further and further apart, but
none of them actually collide with each other, since the surface of
the balloon is continually stretching bigger and bigger...
Are both these pictorial models inaccurate or lacking in some way, and
what is a better one to use these days?
Hubble has taken some excellent pictures of colliding galaxies, and
it's said that the Andromeda galaxy is moving towards our own Milky
Way galaxy, not away from it, and one day they'll collide with each
other, or pass through each other, causing some distortions in both of
them in the process...
The fact that they're moving towards each other indicates that
localized gravity has overtaken the expansive force of the big bang,
and if that's the case, why are cosmologists looking for a bunch of
"dark matter" which is required to keep the universe from expanding
forever?
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
--
Elroy Willis
www.elroysemporium.com
.
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| User: "Walking on Glass" |
|
| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 06:17:07 PM |
|
|
And lo, it came to pass that did attempt to esape
burning at the stake, by proclaiming in alt.atheism:
If the universe is expanding, and even accelerating as it expands,
which seems to be the case according to current observations, then how
can galaxies actually collide with each other?
One of the popular visual models of the universe depicts it as a loaf
of raisin bread that's rising and expanding, with all the raisins
getting further and further apart as the bread bakes in the oven. Do
individual raisins actually collide inside a loaf of cooking raisin
bread?
Another model I've seen is the balloon example, with dots drawn on an
uninflated rubber balloon,
The 'dots' example neglects the fact that galaxies *do* in fact move
relative to each other. The 'dots' example is only usually used as an
analogy to demonstrate the effects of expansion of space-time (viz. the
dots move further apart as the balloon inflates). In reality, the dots
are also moving around *very slowly* relative to each other (galaxies
have a speed in the hundreds of miles per second range, which compared
with their size and typical separation means it takes a long time - many
hundreds of millions of years for them to close the gap between each
other).
Therefore, in reality, there are two types of motion - expansion of
space-time, which enlarges distance between two objects over time, and
the intrinsic motion of those objects relative to each other. If the
objects are moving towards each faster than the space between them
expands, they will collide at some point in the future.
--
Stuart
AA #2053
.
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| User: "Fred Stone" |
|
| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 06:57:31 AM |
|
|
Elroy Willis <elroywillis@swbell.net> wrote in
news:igrkc1t4imbtqrovfv6tlvoe8mc3osg74e@4ax.com:
If the universe is expanding, and even accelerating as it expands,
which seems to be the case according to current observations, then how
can galaxies actually collide with each other?
One of the popular visual models of the universe depicts it as a loaf
of raisin bread that's rising and expanding, with all the raisins
getting further and further apart as the bread bakes in the oven. Do
individual raisins actually collide inside a loaf of cooking raisin
bread?
The "raisins" are actually galactic clusters with their own internal
dynamics. While the clusters get farther apart as the universe expands,
they are themselves gravitationally bound and their individual parts
orbit around each other. Occasionally those internal orbits intersect.
Another model I've seen is the balloon example, with dots drawn on an
uninflated rubber balloon, and when the balloon is blown up, the dots,
which represent stars and galaxies, get further and further apart, but
none of them actually collide with each other, since the surface of
the balloon is continually stretching bigger and bigger...
Are both these pictorial models inaccurate or lacking in some way, and
what is a better one to use these days?
Hubble has taken some excellent pictures of colliding galaxies, and
it's said that the Andromeda galaxy is moving towards our own Milky
Way galaxy, not away from it, and one day they'll collide with each
other, or pass through each other, causing some distortions in both of
them in the process...
The fact that they're moving towards each other indicates that
localized gravity has overtaken the expansive force of the big bang,
and if that's the case, why are cosmologists looking for a bunch of
"dark matter" which is required to keep the universe from expanding
forever?
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
When they look at the orbital parameters of galaxies and galaxy
clusters, and then they look at the amount of energy output and estimate
the total mass from that, they find a discrepancy. The orbits of the
stars in the galaxy and the galaxies in the cluster would seem to
require more mass to produce more gravity than they can account for by
their standard models of mass to brightness. Something in the models
doesn't add up, and they call that "dark matter".
--
Fred Stone
aa# 1369
"Metaphysics is almost always an attempt to prove
the incredible by an appeal to the unintelligible."
[H.L. Mencken, "Prejudices"]
.
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| User: "Elroy Willis" |
|
| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 07:46:02 AM |
|
|
Fred Stone <fstone69@earthling.com> wrote in alt.atheism
Elroy Willis <elroywillis@swbell.net> wrote in
news:igrkc1t4imbtqrovfv6tlvoe8mc3osg74e@4ax.com:
If the universe is expanding, and even accelerating as it expands,
which seems to be the case according to current observations, then how
can galaxies actually collide with each other?
One of the popular visual models of the universe depicts it as a loaf
of raisin bread that's rising and expanding, with all the raisins
getting further and further apart as the bread bakes in the oven. Do
individual raisins actually collide inside a loaf of cooking raisin
bread?
The "raisins" are actually galactic clusters with their own internal
dynamics. While the clusters get farther apart as the universe expands,
they are themselves gravitationally bound and their individual parts
orbit around each other. Occasionally those internal orbits intersect.
Where is the dividing line between all those individual clusters,
which keeps one cluster from interacting with another,
gravitationally?
Another model I've seen is the balloon example, with dots drawn on an
uninflated rubber balloon, and when the balloon is blown up, the dots,
which represent stars and galaxies, get further and further apart, but
none of them actually collide with each other, since the surface of
the balloon is continually stretching bigger and bigger...
Are both these pictorial models inaccurate or lacking in some way, and
what is a better one to use these days?
Hubble has taken some excellent pictures of colliding galaxies, and
it's said that the Andromeda galaxy is moving towards our own Milky
Way galaxy, not away from it, and one day they'll collide with each
other, or pass through each other, causing some distortions in both of
them in the process...
The fact that they're moving towards each other indicates that
localized gravity has overtaken the expansive force of the big bang,
and if that's the case, why are cosmologists looking for a bunch of
"dark matter" which is required to keep the universe from expanding
forever?
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
When they look at the orbital parameters of galaxies and galaxy
clusters, and then they look at the amount of energy output and estimate
the total mass from that, they find a discrepancy. The orbits of the
stars in the galaxy and the galaxies in the cluster would seem to
require more mass to produce more gravity than they can account for by
their standard models of mass to brightness. Something in the models
doesn't add up, and they call that "dark matter".
I see it as a fudge factor for some reason...
I don't see any problem with the idea of the universe eventually
collapsing back in on itself, with all of the localized galaxies being
sucked into some black holes at the centers of each of them, and then
all the black holes sucking each other in, creating some cosmic
singularity, via a big crunch, and then another big bang, and the
whole she-bang starts over again...
--
Elroy Willis
www.elroysemporium.com
.
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| User: "Fred Stone" |
|
| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 08:24:11 AM |
|
|
Elroy Willis <elroywillis@swbell.net> wrote in
news:vivkc1hv0n6t6b82gs008rt421bo3pmft8@4ax.com:
Fred Stone <fstone69@earthling.com> wrote in alt.atheism
Elroy Willis <elroywillis@swbell.net> wrote in
news:igrkc1t4imbtqrovfv6tlvoe8mc3osg74e@4ax.com:
If the universe is expanding, and even accelerating as it expands,
which seems to be the case according to current observations, then
how can galaxies actually collide with each other?
One of the popular visual models of the universe depicts it as a
loaf of raisin bread that's rising and expanding, with all the
raisins getting further and further apart as the bread bakes in the
oven. Do individual raisins actually collide inside a loaf of
cooking raisin bread?
The "raisins" are actually galactic clusters with their own internal
dynamics. While the clusters get farther apart as the universe
expands, they are themselves gravitationally bound and their
individual parts orbit around each other. Occasionally those internal
orbits intersect.
Where is the dividing line between all those individual clusters,
which keeps one cluster from interacting with another,
gravitationally?
There is no dividing line. They do interact, but the distances are so
great that the gravitational attraction no longer outweighs the
expansion.
Another model I've seen is the balloon example, with dots drawn on
an uninflated rubber balloon, and when the balloon is blown up, the
dots, which represent stars and galaxies, get further and further
apart, but none of them actually collide with each other, since the
surface of the balloon is continually stretching bigger and
bigger...
Are both these pictorial models inaccurate or lacking in some way,
and what is a better one to use these days?
Hubble has taken some excellent pictures of colliding galaxies, and
it's said that the Andromeda galaxy is moving towards our own Milky
Way galaxy, not away from it, and one day they'll collide with each
other, or pass through each other, causing some distortions in both
of them in the process...
The fact that they're moving towards each other indicates that
localized gravity has overtaken the expansive force of the big bang,
and if that's the case, why are cosmologists looking for a bunch of
"dark matter" which is required to keep the universe from expanding
forever?
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
When they look at the orbital parameters of galaxies and galaxy
clusters, and then they look at the amount of energy output and
estimate the total mass from that, they find a discrepancy. The
orbits of the stars in the galaxy and the galaxies in the cluster
would seem to require more mass to produce more gravity than they can
account for by their standard models of mass to brightness. Something
in the models doesn't add up, and they call that "dark matter".
I see it as a fudge factor for some reason...
Me too, but I don't really understand all the calculations. I've only
read technical popularizations such as in Scientific American.
I don't see any problem with the idea of the universe eventually
collapsing back in on itself, with all of the localized galaxies being
sucked into some black holes at the centers of each of them, and then
all the black holes sucking each other in, creating some cosmic
singularity, via a big crunch, and then another big bang, and the
whole she-bang starts over again...
My understanding of the current theory is that the universe is expanding
too fast for the big crunch to occur, so eventually all those galaxy-
sized black holes will evaporate via Hawking radiation.
--
Fred Stone
aa# 1369
"Metaphysics is almost always an attempt to prove
the incredible by an appeal to the unintelligible."
[H.L. Mencken, "Prejudices"]
.
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| User: "Grogs" |
|
| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 12:22:36 PM |
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|
Fred Stone <fstone69@earthling.com> wrote in
news:1120569851.24ecc8ed557051c7c3f3848f69048c7c@teranews:
Elroy Willis <elroywillis@swbell.net> wrote in
news:vivkc1hv0n6t6b82gs008rt421bo3pmft8@4ax.com:
Fred Stone <fstone69@earthling.com> wrote in alt.atheism
Elroy Willis <elroywillis@swbell.net> wrote in
news:igrkc1t4imbtqrovfv6tlvoe8mc3osg74e@4ax.com:
If the universe is expanding, and even accelerating as it expands,
which seems to be the case according to current observations, then
how can galaxies actually collide with each other?
One of the popular visual models of the universe depicts it as a
loaf of raisin bread that's rising and expanding, with all the
raisins getting further and further apart as the bread bakes in the
oven. Do individual raisins actually collide inside a loaf of
cooking raisin bread?
The "raisins" are actually galactic clusters with their own internal
dynamics. While the clusters get farther apart as the universe
expands, they are themselves gravitationally bound and their
individual parts orbit around each other. Occasionally those internal
orbits intersect.
Where is the dividing line between all those individual clusters,
which keeps one cluster from interacting with another,
gravitationally?
There is no dividing line. They do interact, but the distances are so
great that the gravitational attraction no longer outweighs the
expansion.
This is correct. Gravity has no range limit, so practically every piece
of matter in the Universe is pulling on every other. In most cases, that
pull isn't enough to significantly affect other objects, but
(astronomically) close objects, like the galaxies in a cluster, started
out closely enough and with a relatively similar initial velocity that
they were able to bond together. It's also quite likely in the case of
galactic clusters that they were all one huge cloud of matter near the
beginning of the Universe that slowly coalesced into the shapes we see
today (galaxies.)
Another model I've seen is the balloon example, with dots drawn on
an uninflated rubber balloon, and when the balloon is blown up, the
dots, which represent stars and galaxies, get further and further
apart, but none of them actually collide with each other, since the
surface of the balloon is continually stretching bigger and
bigger...
Are both these pictorial models inaccurate or lacking in some way,
and what is a better one to use these days?
Hubble has taken some excellent pictures of colliding galaxies, and
it's said that the Andromeda galaxy is moving towards our own Milky
Way galaxy, not away from it, and one day they'll collide with each
other, or pass through each other, causing some distortions in both
of them in the process...
The fact that they're moving towards each other indicates that
localized gravity has overtaken the expansive force of the big bang,
and if that's the case, why are cosmologists looking for a bunch of
"dark matter" which is required to keep the universe from expanding
forever?
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
When they look at the orbital parameters of galaxies and galaxy
clusters, and then they look at the amount of energy output and
estimate the total mass from that, they find a discrepancy. The
orbits of the stars in the galaxy and the galaxies in the cluster
would seem to require more mass to produce more gravity than they can
account for by their standard models of mass to brightness. Something
in the models doesn't add up, and they call that "dark matter".
I see it as a fudge factor for some reason...
Me too, but I don't really understand all the calculations. I've only
read technical popularizations such as in Scientific American.
'Fudge factor' is probably an accurate description, although you can see
why they'd rather not call it that. I think you've got 1 of 3
possibilities:
1) The measurements/calculations were wrong
2) Gravity works differently in other parts of the Universe
3) There's additional mass there that we can't see
#1 seems quite unlikely since the observations and calculations have been
repeated several times by several different people. #2 would require
some significant changes in the way we view the Universe (i.e. constants
aren't so constant.) There would also be other ramifications. For
example, if you increase G slightly, stars would end up being smaller,
and we would expect to find a lot more black holes. #3 seems to be most
plausible, just by the virtue of it being the simplest explanation
(Occam's Razor) and thus we call it dark matter. Recent observations
have led us to believe there is both dark matter and dark energy,
although the form of both can only be described as 'weird.'
I don't see any problem with the idea of the universe eventually
collapsing back in on itself, with all of the localized galaxies being
sucked into some black holes at the centers of each of them, and then
all the black holes sucking each other in, creating some cosmic
singularity, via a big crunch, and then another big bang, and the
whole she-bang starts over again...
My understanding of the current theory is that the universe is
expanding
too fast for the big crunch to occur, so eventually all those galaxy-
sized black holes will evaporate via Hawking radiation.
.
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| User: "Kevin" |
|
| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 10:47:12 PM |
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|
Grogs <grogs@nomail.com> wrote:
Fred Stone <fstone69@earthling.com> wrote in
news:1120569851.24ecc8ed557051c7c3f3848f69048c7c@teranews:
Elroy Willis <elroywillis@swbell.net> wrote in
news:vivkc1hv0n6t6b82gs008rt421bo3pmft8@4ax.com:
Where is the dividing line between all those individual clusters,
which keeps one cluster from interacting with another,
gravitationally?
There is no dividing line. They do interact, but the distances are so
great that the gravitational attraction no longer outweighs the
expansion.
This is correct. Gravity has no range limit, so practically every piece
of matter in the Universe is pulling on every other. In most cases, that
pull isn't enough to significantly affect other objects, but
(astronomically) close objects, like the galaxies in a cluster, started
out closely enough and with a relatively similar initial velocity that
they were able to bond together. It's also quite likely in the case of
galactic clusters that they were all one huge cloud of matter near the
beginning of the Universe that slowly coalesced into the shapes we see
today (galaxies.)
I think what he was getting at by the question about the dividing line
was the following. The overall cosmic expansion tends to move everything
farther apart from everything else. But that cosmic expansion can easily
be counteracted by the attractive force of gravity. The closer together
objects are to each other, the easier it is for the gravitational attraction
between them to counteract the overall cosmic expansion. So at what
distance does the gravitational attraction become so weak that the cosmic
expansion takes over?
That's quite a good question, and I have to confess that I'm not sure of
the answer, but I _think_ that the relevant distance is at the scale of
galactic superclusters. So a cluster of galaxies will then remain
gravitationally bound even as the universe expands, but a supercluster will
partake of the expansion of the universe as a whole. Clusters are typically
several million light-years across, and superclusters are more like several
tens of millions of light-years across.
Hubble has taken some excellent pictures of colliding galaxies, and
it's said that the Andromeda galaxy is moving towards our own Milky
Way galaxy, not away from it, and one day they'll collide with each
other, or pass through each other, causing some distortions in both
of them in the process...
IIRC, it's not known if the Andromeda galaxy is moving _directly_
towards us. There might be a sort of near miss rather than a collision.
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
As others have pointed out, the dark matter is needed to explain
the observed dynamics _within_ galaxies and galactic clusters. Ordinary
visible matter would indeed be quite capable of counteracting the expanding
effect, but astronomers just don't see enough of it to account for the
observations.
I don't see any problem with the idea of the universe eventually
collapsing back in on itself, with all of the localized galaxies being
sucked into some black holes at the centers of each of them, and then
all the black holes sucking each other in, creating some cosmic
singularity, via a big crunch, and then another big bang, and the
whole she-bang starts over again...
Twenty or thirty years ago that was considered a quite plausible
scenario, but now it has largely fallen out of favor.
My understanding of the current theory is that the universe is
expanding
too fast for the big crunch to occur, so eventually all those galaxy-
sized black holes will evaporate via Hawking radiation.
Yes, that's where the so-called dark energy comes in. At least on
the most straightforward current understanding, it is gradually causing
the universe to expand faster and faster. Eventually the expansion will
be so fast that even tightly bound objects will be torn apart. Galactic
clusters, then galaxies, and finally even solid objects like planets (if
any survive) will be destroyed in a so-called big rip.
Personally, I suspect that our understanding of dark energy has quite
a few twists and turns yet left to make, so I'm not betting on the "big
rip" scenario. Maybe there will be a re-collapse after all.
Kevin
.
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| User: "N:dlzc D:aol T:com \dlzc\ N: dlzc1 D:cox" |
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| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 11:42:37 PM |
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|
Dear Kevin:
"Kevin" <ktn3654@linux3.ph.utexas.edu> wrote in message
news:dafk80$bje$1@geraldo.cc.utexas.edu...
Grogs <grogs@nomail.com> wrote:
Fred Stone <fstone69@earthling.com> wrote in
news:1120569851.24ecc8ed557051c7c3f3848f69048c7c@teranews:
Elroy Willis <elroywillis@swbell.net> wrote in
news:vivkc1hv0n6t6b82gs008rt421bo3pmft8@4ax.com:
Where is the dividing line between all those individual
clusters,
which keeps one cluster from interacting with another,
gravitationally?
There is no dividing line. They do interact, but the
distances
are so great that the gravitational attraction no longer
outweighs the expansion.
This is correct. Gravity has no range limit, so practically
every piece of matter in the Universe is pulling on every
other. In most cases, that pull isn't enough to
significantly affect other objects, but (astronomically)
close objects, like the galaxies in a cluster, started out
closely enough and with a relatively similar initial velocity
that they were able to bond together. It's also quite
likely in the case of galactic clusters that they were all
one huge cloud of matter near the beginning of the
Universe that slowly coalesced into the shapes we see
today (galaxies.)
I think what he was getting at by the question about
the dividing line was the following. The overall cosmic
expansion tends to move everything farther apart from
everything else. But that cosmic expansion can easily
be counteracted by the attractive force of gravity.
I disagree. Gravity is not a force. If spacetime presents
accelerating expansion, it is because gravity *isn't* holding it
all together.
The closer together
objects are to each other, the easier it is for the
gravitational attraction between them to counteract
the overall cosmic expansion.
At the other end of the spectrum, if the Universe is closed, two
chunks of matter at a distance of r_U (radius of the Universe)
from each other will have no net attraction. Additionally, if
c_g (speed of gravity) = c, matter beyond our "horizon" will have
no effect on curvature (aka. gravity) here. Quantum gravity may
add something to this, of course.
So at what
distance does the gravitational attraction become so
weak that the cosmic expansion takes over?
That's quite a good question, and I have to confess
that I'm not sure of the answer, but I _think_ that the
relevant distance is at the scale of galactic
superclusters. So a cluster of galaxies will then
remain gravitationally bound even as the universe
expands, but a supercluster will partake of the
expansion of the universe as a whole. Clusters are
typically several million light-years across, and
superclusters are more like several tens of millions
of light-years across.
A well reasoned response.
Interesting... superclusters are tens of million light years
across, just as the CMBR (which filled the early Universe) was
tens of million light years across when it stopped glowing at
~3000 K. I bet the "correlation" is not accidental...
Hubble has taken some excellent pictures of colliding
galaxies, and it's said that the Andromeda galaxy is
moving towards our own Milky Way galaxy, not away
from it, and one day they'll collide with each other, or
pass through each other, causing some distortions in
both of them in the process...
IIRC, it's not known if the Andromeda galaxy is moving
_directly_ towards us. There might be a sort of near miss
rather than a collision.
If localized galaxies can attract each other through
gravity and counteract the expanding effect, what
need is there for some actual mysterious or
missing "dark matter?"
As others have pointed out, the dark matter is
needed to explain the observed dynamics _within_
galaxies and galactic clusters. Ordinary visible
matter would indeed be quite capable of
counteracting the expanding effect,
.... as would the Dark Matter ...
but astronomers just don't see enough of it to
account for the observations.
And same here. Not enough of either kind of matter.
I don't see any problem with the idea of the
universe eventually collapsing back in on
itself, with all of the localized galaxies being
sucked into some black holes at the centers
of each of them, and then all the black holes
sucking each other in, creating some cosmic
singularity, via a big crunch, and then
another big bang, and the whole she-bang
starts over again...
Twenty or thirty years ago that was considered
a quite plausible scenario, but now it has largely
fallen out of favor.
My understanding of the current theory is that
the universe is expanding too fast for the big
crunch to occur, so eventually all those galaxy-
sized black holes will evaporate via Hawking
radiation.
Yes, that's where the so-called dark energy
comes in. At least on the most straightforward
current understanding, it is gradually causing
the universe to expand faster and faster.
Eventually the expansion will be so fast that
even tightly bound objects will be torn apart.
Galactic clusters, then galaxies, and finally
even solid objects like planets (if any survive)
will be destroyed in a so-called big rip.
Personally, I suspect that our
understanding of dark energy has quite a few
twists and turns yet left to make, so I'm not
betting on the "big rip" scenario. Maybe
there will be a re-collapse after all.
I suspect the "Big Rip" is currently visible as what we call the
CMBR. The rest "we'll" know in many tens to a few hundreds of
billion years.
Your response was well reasoned. Excellent!
David A. Smith
.
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| User: "Iain" |
|
| Title: Re: OT - Expanding Universe Questions |
07 Jul 2005 04:02:08 AM |
|
|
Kevin wrote:
Grogs <grogs@nomail.com> wrote:
Fred Stone <fstone69@earthling.com> wrote in
news:1120569851.24ecc8ed557051c7c3f3848f69048c7c@teranews:
Elroy Willis <elroywillis@swbell.net> wrote in
news:vivkc1hv0n6t6b82gs008rt421bo3pmft8@4ax.com:
Where is the dividing line between all those individual clusters,
which keeps one cluster from interacting with another,
gravitationally?
There is no dividing line. They do interact, but the distances are so
great that the gravitational attraction no longer outweighs the
expansion.
This is correct. Gravity has no range limit, so practically every piece
of matter in the Universe is pulling on every other. In most cases, that
pull isn't enough to significantly affect other objects, but
(astronomically) close objects, like the galaxies in a cluster, started
out closely enough and with a relatively similar initial velocity that
they were able to bond together. It's also quite likely in the case of
galactic clusters that they were all one huge cloud of matter near the
beginning of the Universe that slowly coalesced into the shapes we see
today (galaxies.)
I think what he was getting at by the question about the dividing line
was the following. The overall cosmic expansion tends to move everything
farther apart from everything else. But that cosmic expansion can easily
be counteracted by the attractive force of gravity. The closer together
objects are to each other, the easier it is for the gravitational attraction
between them to counteract the overall cosmic expansion. So at what
distance does the gravitational attraction become so weak that the cosmic
expansion takes over?
That's quite a good question, and I have to confess that I'm not sure of
the answer, but I _think_ that the relevant distance is at the scale of
galactic superclusters.
It's a question of escape velocity -- "How far can a galaxy be thrown
by the big bang before being pulled back by the gravity of the rest of
the universe" -- the answer to the queastion about distance I don't
know -- but it's just a boring number -- there is such a distance.
~Iain
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| User: "" |
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| Title: Re: OT - Expanding Universe Questions |
07 Jul 2005 11:20:47 AM |
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Kevin wrote:
Yes, that's where the so-called dark energy comes in. At least on
the most straightforward current understanding, it is gradually causing
the universe to expand faster and faster. Eventually the expansion will
be so fast that even tightly bound objects will be torn apart. Galactic
clusters, then galaxies, and finally even solid objects like planets (if
any survive) will be destroyed in a so-called big rip.
Personally, I suspect that our understanding of dark energy has quite
a few twists and turns yet left to make, so I'm not betting on the "big
rip" scenario. Maybe there will be a re-collapse after all.
Note that in the ekpyrotic scenario
(http://arxiv.org/abs/hep-th/0111098), the "new" expansion starts along
one of the extra dimensions, thus you can have a recycled universe
without a big crunch.
Karl M. Syring
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| User: "Masked Avenger" |
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| Title: Re: OT - Expanding Universe Questions |
08 Jul 2005 06:29:27 AM |
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wrote:
Kevin wrote:
Yes, that's where the so-called dark energy comes in. At least on
the most straightforward current understanding, it is gradually causing
the universe to expand faster and faster. Eventually the expansion will
be so fast that even tightly bound objects will be torn apart. Galactic
clusters, then galaxies, and finally even solid objects like planets (if
any survive) will be destroyed in a so-called big rip.
Personally, I suspect that our understanding of dark energy has quite
a few twists and turns yet left to make, so I'm not betting on the "big
rip" scenario. Maybe there will be a re-collapse after all.
Note that in the ekpyrotic scenario
(http://arxiv.org/abs/hep-th/0111098), the "new" expansion starts along
one of the extra dimensions, thus you can have a recycled universe
without a big crunch.
Karl M. Syring
wow .... that article is amazing ...... it certainly explains a lot
...... I always had a sneaky feeling the Universe would turn out to be
cyclical ............ if the Theory holds up .... it will make me feel a
bit vindicated .....
--
Masked Avenger
aa#2224
EAC Chief Technician in charge of remotely rigging Fundie 'Spell
Checkers' so they all look like hick home schooled yokels
Does Schroedinger's cat have 18 half lives ?
.
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| User: "Elroy Willis" |
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| Title: Re: OT - Expanding Universe Questions |
10 Jul 2005 09:42:22 AM |
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Masked Avenger <cootey_59@yahoo.com> wrote in alt.atheism
syring@email.com wrote:
Kevin wrote:
Yes, that's where the so-called dark energy comes in. At least on
the most straightforward current understanding, it is gradually causing
the universe to expand faster and faster. Eventually the expansion will
be so fast that even tightly bound objects will be torn apart. Galactic
clusters, then galaxies, and finally even solid objects like planets (if
any survive) will be destroyed in a so-called big rip.
Personally, I suspect that our understanding of dark energy has quite
a few twists and turns yet left to make, so I'm not betting on the "big
rip" scenario. Maybe there will be a re-collapse after all.
Note that in the ekpyrotic scenario
(http://arxiv.org/abs/hep-th/0111098), the "new" expansion starts along
one of the extra dimensions, thus you can have a recycled universe
without a big crunch.
wow .... that article is amazing ...... it certainly explains a lot
..... I always had a sneaky feeling the Universe would turn out to be
cyclical ............ if the Theory holds up .... it will make me feel a
bit vindicated .....
Since so many different things in the universe have cycles, it
wouldn't surprise me to find out that the universe itself is cyclical.
That said, it doesn't mean that people can actually escape its
cyclical nature and live forever. So if the universe does end up
recycling itself, that doesn't mean that mankind and our own egos will
survive to observe it all happening again.
--
Elroy Willis
www.elroysemporium.com
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| User: "" |
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| Title: Re: OT - Expanding Universe Questions |
11 Jul 2005 03:56:38 AM |
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Masked Avenger schrieb:
syring@email.com wrote:
Kevin wrote:
Yes, that's where the so-called dark energy comes in. At least on
the most straightforward current understanding, it is gradually causing
the universe to expand faster and faster. Eventually the expansion will
be so fast that even tightly bound objects will be torn apart. Galactic
clusters, then galaxies, and finally even solid objects like planets (if
any survive) will be destroyed in a so-called big rip.
Personally, I suspect that our understanding of dark energy has quite
a few twists and turns yet left to make, so I'm not betting on the "big
rip" scenario. Maybe there will be a re-collapse after all.
Note that in the ekpyrotic scenario
(http://arxiv.org/abs/hep-th/0111098), the "new" expansion starts along
one of the extra dimensions, thus you can have a recycled universe
without a big crunch.
Karl M. Syring
wow .... that article is amazing ...... it certainly explains a lot
..... I always had a sneaky feeling the Universe would turn out to be
cyclical ............ if the Theory holds up .... it will make me feel a
bit vindicated .....
Not to mention that the black holes are assumed to survive the cycles.
Something is in there and waits to come out and get us ... muhahah
Karl M. Syring
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| User: "Masked Avenger" |
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| Title: Re: OT - Expanding Universe Questions |
12 Jul 2005 04:52:07 AM |
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wrote:
Masked Avenger schrieb:
wrote:
Kevin wrote:
Yes, that's where the so-called dark energy comes in. At least on
the most straightforward current understanding, it is gradually causing
the universe to expand faster and faster. Eventually the expansion will
be so fast that even tightly bound objects will be torn apart. Galactic
clusters, then galaxies, and finally even solid objects like planets (if
any survive) will be destroyed in a so-called big rip.
Personally, I suspect that our understanding of dark energy has quite
a few twists and turns yet left to make, so I'm not betting on the "big
rip" scenario. Maybe there will be a re-collapse after all.
Note that in the ekpyrotic scenario
(http://arxiv.org/abs/hep-th/0111098), the "new" expansion starts along
one of the extra dimensions, thus you can have a recycled universe
without a big crunch.
Karl M. Syring
wow .... that article is amazing ...... it certainly explains a lot
..... I always had a sneaky feeling the Universe would turn out to be
cyclical ............ if the Theory holds up .... it will make me feel a
bit vindicated .....
Not to mention that the black holes are assumed to survive the cycles.
Something is in there and waits to come out and get us ... muhahah
Karl M. Syring
That would explain the 'sneaky' feeling .......... but gee it's taking
its bloody time ..... I mean 13.7 billion years to get to this point and
a few trillion more until the big Crunch ....... I just can't wait that
long ......
--
Masked Avenger
aa#2224
EAC Chief Technician in charge of remotely rigging Fundie 'Spell
Checkers' so they all look like hick home schooled yokels
Does Schroedinger's cat have 18 half lives ?
.
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| User: "John C. Polasek" |
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| Title: Re: OT - Expanding Universe Questions |
11 Jul 2005 10:59:59 AM |
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On Wed, 6 Jul 2005 03:47:12 +0000 (UTC), Kevin
<ktn3654@linux3.ph.utexas.edu> wrote:
Grogs <grogs@nomail.com> wrote:
Fred Stone <fstone69@earthling.com> wrote in
news:1120569851.24ecc8ed557051c7c3f3848f69048c7c@teranews:
Elroy Willis <elroywillis@swbell.net> wrote in
news:vivkc1hv0n6t6b82gs008rt421bo3pmft8@4ax.com:
Where is the dividing line between all those individual clusters,
which keeps one cluster from interacting with another,
gravitationally?
There is no dividing line. They do interact, but the distances are so
great that the gravitational attraction no longer outweighs the
expansion.
This is correct. Gravity has no range limit, so practically every piece
of matter in the Universe is pulling on every other. In most cases, that
pull isn't enough to significantly affect other objects, but
(astronomically) close objects, like the galaxies in a cluster, started
out closely enough and with a relatively similar initial velocity that
they were able to bond together. It's also quite likely in the case of
galactic clusters that they were all one huge cloud of matter near the
beginning of the Universe that slowly coalesced into the shapes we see
today (galaxies.)
I think what he was getting at by the question about the dividing line
was the following. The overall cosmic expansion tends to move everything
farther apart from everything else. But that cosmic expansion can easily
be counteracted by the attractive force of gravity. The closer together
objects are to each other, the easier it is for the gravitational attraction
between them to counteract the overall cosmic expansion. So at what
distance does the gravitational attraction become so weak that the cosmic
expansion takes over?
That's quite a good question, and I have to confess that I'm not sure of
the answer, but I _think_ that the relevant distance is at the scale of
galactic superclusters. So a cluster of galaxies will then remain
gravitationally bound even as the universe expands, but a supercluster will
partake of the expansion of the universe as a whole. Clusters are typically
several million light-years across, and superclusters are more like several
tens of millions of light-years across.
Hubble has taken some excellent pictures of colliding galaxies, and
it's said that the Andromeda galaxy is moving towards our own Milky
Way galaxy, not away from it, and one day they'll collide with each
other, or pass through each other, causing some distortions in both
of them in the process...
IIRC, it's not known if the Andromeda galaxy is moving _directly_
towards us. There might be a sort of near miss rather than a collision.
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
As others have pointed out, the dark matter is needed to explain
the observed dynamics _within_ galaxies and galactic clusters. Ordinary
visible matter would indeed be quite capable of counteracting the expanding
effect, but astronomers just don't see enough of it to account for the
observations.
I don't see any problem with the idea of the universe eventually
collapsing back in on itself, with all of the localized galaxies being
sucked into some black holes at the centers of each of them, and then
all the black holes sucking each other in, creating some cosmic
singularity, via a big crunch, and then another big bang, and the
whole she-bang starts over again...
snip
Kevin
You might like to see a diagram of my model of expansion of the
universe as paper #3 on my website(below).
The diagram tries to show 4 dimensions, the xyz of our universe all
being contained on the outer arc marked D. The radius R is the 4th
dimension and is expanding at velocity of light c. The Galaxy and Us
are separated by distance D and by angle theta which remains constant
forever as we expand.
So dD/dt = theta*(dR/dt = c) is the Hubble velocity. The red shift
factor z is equal to theta. Eq. 6. Hubble is Rdot*theta/D or Ddot/D.
Gravity acting in our xyz world could cause "proper motion" (small
change in theta) toward each other as eq. 7 shows. But it would not
have any effect on the expansion rate which is independent.
John Polasek
http://www.dualspace.net
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| User: "Harry F. Leopold" |
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| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 04:48:28 PM |
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On Tue, 5 Jul 2005 12:22:36 -0500, Grogs wrote
(in article <Xns968A88B5FBD9Fgrogsnomailcom@216.168.3.30>):
snip
When they look at the orbital parameters of galaxies and galaxy
clusters, and then they look at the amount of energy output and
estimate the total mass from that, they find a discrepancy. The
orbits of the stars in the galaxy and the galaxies in the cluster
would seem to require more mass to produce more gravity than they can
account for by their standard models of mass to brightness. Something
in the models doesn't add up, and they call that "dark matter".
I see it as a fudge factor for some reason...
Me too, but I don't really understand all the calculations. I've only
read technical popularizations such as in Scientific American.
'Fudge factor' is probably an accurate description, although you can see why
they'd rather not call it that. I think you've got 1 of 3 possibilities:
1) The measurements/calculations were wrong
2) Gravity works differently in
other parts of the Universe
3) There's additional mass there that we can't see
In reference to 3: that is exactly what they are talking about with "dark
matter." They aren't stating what it is, only that it can't (yet) be seen and
does not seem to be regular matter, if it were it would almost certainly show
itself.
--
Harry F. Leopold
aa #2076
AA/Vet #4
The Prints of Darkness
(remove gene to email)
Cthulhu saves our souls and redeems them for valuable coupons later.
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| User: "Grogs" |
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| Title: Re: OT - Expanding Universe Questions |
06 Jul 2005 10:48:06 AM |
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Harry F. Leopold <hleopold@coxyx.net> wrote in
news:0001HW.BEF06A5C008DD9E3F0284550@news.central.cox.net:
On Tue, 5 Jul 2005 12:22:36 -0500, Grogs wrote
(in article <Xns968A88B5FBD9Fgrogsnomailcom@216.168.3.30>):
snip
When they look at the orbital parameters of galaxies and galaxy
clusters, and then they look at the amount of energy output and
estimate the total mass from that, they find a discrepancy. The
orbits of the stars in the galaxy and the galaxies in the cluster
would seem to require more mass to produce more gravity than they
can account for by their standard models of mass to brightness.
Something in the models doesn't add up, and they call that "dark
matter".
I see it as a fudge factor for some reason...
Me too, but I don't really understand all the calculations. I've
only read technical popularizations such as in Scientific American.
'Fudge factor' is probably an accurate description, although you can
see why they'd rather not call it that. I think you've got 1 of 3
possibilities:
1) The measurements/calculations were wrong
2) Gravity works differently in
other parts of the Universe
3) There's additional mass there that we can't see
In reference to 3: that is exactly what they are talking about with
"dark matter." They aren't stating what it is, only that it can't
(yet) be seen and does not seem to be regular matter, if it were it
would almost certainly show itself.
I don't think anyone really knows. There was a theory a few years back
that called the theoretical dark matter particles 'WIMPs' for Weakly
Interracting Massive Particles. The 'weakly interracting' part of the
name implied that they wouldn't react with the strong nuclear, or
electromagnetic forces, but only with the 'weak force' and gravity.
Since gravity is so incredibly weak compared to the other forces, and
poorly understood (at a subatomic level) detecting such particles in a
laboratory would be difficult. AFIAK, the detectors they're trying to
use are similar to those used to detect neutrinos, i.e., they have to be
far underground, and even then it's very difficult to pick the signal out
of the noise. According to a quick glance at the Wiki, no WIMP's have
been detected to date, so it's entirely possible they're not what we're
looking for.
As a footnote, I should add that, not to be outdone, a 2nd group of
scientists theorized that what we were looking for was actually
nonluminescent (normal) matter concentrated in globs in galactic halos.
The dubbed these 'MACHOs' for Massive Compact Halo Objects. Experiments
to date suggest that these could account for a small portion of the
required dark matter, so to paraphrase old Obi Wan: "This is not the dark
matter you're looking for."
The most honest answer to your question is probably just "We don't
know." We know what dark matter *IS NOT* but that still leaves a wide
range of possibilities for what it could be.
.
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| User: "nobody" |
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| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 09:02:22 AM |
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Elroy Willis <elroywillis@swbell.net> wrote:
Fred Stone <fstone69@earthling.com> wrote in alt.atheism
The "raisins" are actually galactic clusters with their own internal
dynamics. While the clusters get farther apart as the universe expands,
they are themselves gravitationally bound and their individual parts
orbit around each other. Occasionally those internal orbits intersect.
Where is the dividing line between all those individual clusters,
which keeps one cluster from interacting with another,
gravitationally?
Nowhere. Everything interacts gravitationally. It's just the scale.
Even though universe is expanding, we have automobile accidents. Why?
At that scale, other forces (basically the electromagnetic one) are so
much more relevant that the expansion can be completely ignored in the
noise. At larger and larger scales, other forces attenuate rapidly.
Gravitation, by nature of being only attractive, and not both
attractive and repulsive like electromagnetism, becomes the dominant
force, although its strength too diminishes with distance (in
proportion to square distance, aamof). Expansion happens everywhere,
even within your own body, but is only noticable over long distances.
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| User: "Llanzlan Klazmon" |
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| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 11:39:46 PM |
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Elroy Willis <elroywillis@swbell.net> wrote in
news:igrkc1t4imbtqrovfv6tlvoe8mc3osg74e@4ax.com:
If the universe is expanding, and even accelerating as it expands,
which seems to be the case according to current observations, then how
can galaxies actually collide with each other?
Galaxy clusters remain gravitationally bound. The expansion is on a much
greater scale.
http://www.astro.ucla.edu/~wright/cosmolog.htm
http://www.astro.ucla.edu/~wright/cosmology_faq.html
http://math.ucr.edu/home/baez/physics/Relativity/GR/expanding_universe.h
tml
One of the popular visual models of the universe depicts it as a loaf
of raisin bread that's rising and expanding, with all the raisins
getting further and further apart as the bread bakes in the oven. Do
individual raisins actually collide inside a loaf of cooking raisin
bread?
The raison in bread model breaks down when you have to consider the
gravitational interaction between the raisons. Galaxies in clusters
interact via Newtonian gravity near enough. I.e the galaxies are
orbiting each other. Their behaviour is quite different to stars because
galaxies are large extended objects. The probably of collision of two
galaxies in a cluster is much higher than the probability of two stars
colliding in a gallaxy. The raison model makes a bit more sense if you
think of the raisons being galaxy clusters rather than individual
galaxies.
Another model I've seen is the balloon example, with dots drawn on an
uninflated rubber balloon, and when the balloon is blown up, the dots,
which represent stars and galaxies, get further and further apart, but
none of them actually collide with each other, since the surface of
the balloon is continually stretching bigger and bigger...
Again this is only illustrating one aspect of the full picture. The
equation G=8piT explains everything you did or didn't want to know.
Are both these pictorial models inaccurate or lacking in some way, and
what is a better one to use these days?
Both of these models illustrate the expansion of the universe but are of
no help illustrating the interaction of galaxies in clusters or stars in
gallaxies.
Hubble has taken some excellent pictures of colliding galaxies, and
it's said that the Andromeda galaxy is moving towards our own Milky
Way galaxy, not away from it, and one day they'll collide with each
other, or pass through each other, causing some distortions in both of
them in the process...
Maybe or could be a near miss.
The fact that they're moving towards each other indicates that
localized gravity has overtaken the expansive force of the big bang,
and if that's the case, why are cosmologists looking for a bunch of
"dark matter" which is required to keep the universe from expanding
forever?
Dark matter is required explain the rotation curves of stars within
spiral galaxies. The outer stars are orbiting at much higher speeds than
one would expect from the quantity of visible matter observed in the
galaxies. This same issue applies to galaxy clusters as a whole, which
can be analysed using the virial theorem. Even when the dark matter
assumed to cause these rotation speeds is taken into account there is
still a problem when one looks at the dynamics of the universe on very
large scales. To explain that, they throw in something called 'dark
energy' which is required to balance the books. This is equivalent to
adding a constant onto the equation above.
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
As explained above, the orbital speeds of stars in galaxies are too high
to be explained by the quantity of visible matter in the galaxies.
Visible matter (including dark dust and gas clouds which are visible at
infrared and microwave wavelengths) are made of ordinary or Baryonic
matter - i.e the same sort of stuff that the earth is made of. "Dark
matter" cannot be of this sort otherwise we would be able to detect it
easily. Some of the dark matter consists of the sub atomic particles
known as neutrinos. However for a number of reasons these must only be a
fairly small percentage of the total dark matter. What the rest of it is
composed of is a msytery. One type of elementary particle that might fit
the bill is the hypothetical neutralino.
http://en.wikipedia.org/wiki/Neutralino
Klazmon
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| User: "nobody" |
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| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 08:47:18 AM |
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Elroy Willis <elroywillis@swbell.net> wrote:
One of the popular visual models of the universe depicts it as a loaf
of raisin bread that's rising and expanding, with all the raisins
getting further and further apart as the bread bakes in the oven. Do
individual raisins actually collide inside a loaf of cooking raisin
bread?
Another model I've seen is the balloon example, with dots drawn on an
uninflated rubber balloon, and when the balloon is blown up, the dots,
which represent stars and galaxies, get further and further apart, but
none of them actually collide with each other, since the surface of
the balloon is continually stretching bigger and bigger...
Are both these pictorial models inaccurate or lacking in some way, and
what is a better one to use these days?
Obviously. If the universe could be accurately modeled with a raisin
loaf, we would fire all the physicists and hire bakers instead to
answer all our cosmological questions.
.
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| User: "Iain" |
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| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 06:50:33 AM |
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Elroy Willis wrote:
If the universe is expanding, and even accelerating as it expands,
which seems to be the case according to current observations, then how
can galaxies actually collide with each other?
One of the popular visual models of the universe depicts it as a loaf
of raisin bread that's rising and expanding, with all the raisins
getting further and further apart as the bread bakes in the oven. Do
individual raisins actually collide inside a loaf of cooking raisin
bread?
Another model I've seen is the balloon example, with dots drawn on an
uninflated rubber balloon, and when the balloon is blown up, the dots,
which represent stars and galaxies, get further and further apart, but
none of them actually collide with each other, since the surface of
the balloon is continually stretching bigger and bigger...
Are both these pictorial models inaccurate or lacking in some way, and
what is a better one to use these days?
Hubble has taken some excellent pictures of colliding galaxies, and
it's said that the Andromeda galaxy is moving towards our own Milky
Way galaxy, not away from it, and one day they'll collide with each
other, or pass through each other, causing some distortions in both of
them in the process...
The fact that they're moving towards each other indicates that
localized gravity has overtaken the expansive force of the big bang,
and if that's the case, why are cosmologists looking for a bunch of
"dark matter" which is required to keep the universe from expanding
forever?
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
Because Andromeda and the Milky Way are moving toward eachother but
outward from the supposed centre of the universe nonetheless.
~Iain
.
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| User: "Elroy Willis" |
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| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 07:47:57 AM |
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Iain <iain_inkster@hotmail.com> wrote in alt.atheism
Elroy Willis wrote:
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
Because Andromeda and the Milky Way are moving toward each other but
outward from the supposed centre of the universe nonetheless.
Then parts of the universe have already overcome the initial explosive
force of some "big bang," correct?
--
Elroy Willis
www.elroysemporium.com
.
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| User: "Iain" |
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| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 08:12:20 AM |
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Elroy Willis wrote:
Iain <iain_inkster@hotmail.com> wrote in alt.atheism
Elroy Willis wrote:
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
Because Andromeda and the Milky Way are moving toward each other but
outward from the supposed centre of the universe nonetheless.
Then parts of the universe have already overcome the initial explosive
force of some "big bang," correct?
If you fire two magnetic cannonballs into the air, and they become
attracted to one another, why must their attraction to one another slow
them down?
~Iain
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| User: "duke" |
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| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 05:33:04 PM |
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On Tue, 05 Jul 2005 12:47:57 GMT, Elroy Willis <elroywillis@swbell.net> wrote:
Iain <iain_inkster@hotmail.com> wrote in alt.atheism
Elroy Willis wrote:
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
Because Andromeda and the Milky Way are moving toward each other but
outward from the supposed centre of the universe nonetheless.
Then parts of the universe have already overcome the initial explosive
force of some "big bang," correct?
It's called the back side of the explosion going backwards.
duke
*****
"The Mass is the most perfect form of Prayer."
Pope Paul VI
*****
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| User: "Iain" |
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| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 05:46:24 PM |
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duke wrote:
On Tue, 05 Jul 2005 12:47:57 GMT, Elroy Willis <elroywillis@swbell.net> wrote:
Iain <iain_inkster@hotmail.com> wrote in alt.atheism
Elroy Willis wrote:
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
Because Andromeda and the Milky Way are moving toward each other but
outward from the supposed centre of the universe nonetheless.
Then parts of the universe have already overcome the initial explosive
force of some "big bang," correct?
It's called the back side of the explosion going backwards.
By George, I think His Grace has finally cracked it!
~Iain
.
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| User: "duke" |
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| Title: Re: OT - Expanding Universe Questions |
06 Jul 2005 05:55:02 PM |
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On 5 Jul 2005 15:46:24 -0700, "Iain" <iain_inkster@hotmail.com> wrote:
duke wrote:
On Tue, 05 Jul 2005 12:47:57 GMT, Elroy Willis <elroywillis@swbell.net> wrote:
Iain <iain_inkster@hotmail.com> wrote in alt.atheism
Elroy Willis wrote:
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
Because Andromeda and the Milky Way are moving toward each other but
outward from the supposed centre of the universe nonetheless.
Then parts of the universe have already overcome the initial explosive
force of some "big bang," correct?
It's called the back side of the explosion going backwards.
By George, I think His Grace has finally cracked it!
You didn't know this???????
duke
*****
"The Mass is the most perfect form of Prayer."
Pope Paul VI
*****
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| User: "Tim McGaughy" |
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| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 09:04:23 PM |
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Iain wrote:
Elroy Willis wrote:
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
Because Andromeda and the Milky Way are moving toward eachother but
outward from the supposed centre of the universe nonetheless.
Ehhhh.
Talking about the center of the universe is a bit like talking about the
center of the earths surface.
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| User: "John Popelish" |
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| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 11:43:26 AM |
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Elroy Willis wrote:
If the universe is expanding, and even accelerating as it expands,
which seems to be the case according to current observations, then how
can galaxies actually collide with each other?
One of the popular visual models of the universe depicts it as a loaf
of raisin bread that's rising and expanding, with all the raisins
getting further and further apart as the bread bakes in the oven. Do
individual raisins actually collide inside a loaf of cooking raisin
bread?
Another model I've seen is the balloon example, with dots drawn on an
uninflated rubber balloon, and when the balloon is blown up, the dots,
which represent stars and galaxies, get further and further apart, but
none of them actually collide with each other, since the surface of
the balloon is continually stretching bigger and bigger...
Are both these pictorial models inaccurate or lacking in some way, and
what is a better one to use these days?
They are both lacking, but in different ways. I think the raisin
bread model is pretty good as long as you stay in the middle of the
loaf, but the crust does not correspond to some edge of the 3
dimensional universe. The balloon model drops one spacial dimension
(dots only on a local 2 dimensional surface, rather than being
embedded in 3 dimensions) so that the third dimension can represent
the curve of space necessary to close it rather than showing it with
an edge or "crust". The difficulty is trying to visualize a 4
dimensional space time that includes curvature of some of thew
dimensions, using Euclidean 3 dimensional geometry. Something must be
missing in such a model. So you must be clear on what has been left out.
Hubble has taken some excellent pictures of colliding galaxies, and
it's said that the Andromeda galaxy is moving towards our own Milky
Way galaxy, not away from it, and one day they'll collide with each
other, or pass through each other, causing some distortions in both of
them in the process...
Yes. On the rather tiny scale (compared to the whole universe) of a
few galaxies, gravity rules.
The fact that they're moving towards each other indicates that
localized gravity has overtaken the expansive force of the big bang,
and if that's the case, why are cosmologists looking for a bunch of
"dark matter" which is required to keep the universe from expanding
forever?
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
I think the dark matter hypothesis is an attempt to explain why
galaxies are rotating too fast without flying apart, based on the
gravity of the visible matter in them.
The expansion hypothesis is based on velocity measurements (via
Doppler shift of their light) of very distant objects, with the
distances inferred from assumptions about the intrinsic brightness of
those objects. Both the velocity and distance values include quite a
few assumptions, any of which may turn out to be mistaken.
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| User: "Josef Balluch" |
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| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 07:16:00 PM |
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In a message sent 'round the world, Elroy Willis poured fuel on the fire
with the following:
If the universe is expanding, and even accelerating as it expands,
which seems to be the case according to current observations, then how
can galaxies actually collide with each other?
Galaxies have other motions besides that produced by the expansion of
the universe. Galaxies are gravitationally bound in clusters and
superclusters, and they move around some center of mass.
One of the popular visual models of the universe depicts it as a loaf
of raisin bread that's rising and expanding, with all the raisins
getting further and further apart as the bread bakes in the oven. Do
individual raisins actually collide inside a loaf of cooking raisin
bread?
Another model I've seen is the balloon example, with dots drawn on an
uninflated rubber balloon, and when the balloon is blown up, the dots,
which represent stars and galaxies, get further and further apart, but
none of them actually collide with each other, since the surface of
the balloon is continually stretching bigger and bigger...
Are both these pictorial models inaccurate or lacking in some way, ...
Yes. Both models assume that galaxies have no other motion except for
that produced by the expansion of the universe.
... and
what is a better one to use these days?
Depends on your requirements. Both models are adequate for understanding
the overall expansion of the universe. Calculating the detailed motion
of a cluster of gravitationally bound objects is currently beyond the
capabilities of any of our computers.
http://tinyurl.com/cresr
Hubble has taken some excellent pictures of colliding galaxies, and
it's said that the Andromeda galaxy is moving towards our own Milky
Way galaxy, not away from it, and one day they'll collide with each
other, or pass through each other, causing some distortions in both of
them in the process...
The fact that they're moving towards each other indicates that
localized gravity has overtaken the expansive force of the big bang,
and if that's the case, why are cosmologists looking for a bunch of
"dark matter" which is required to keep the universe from expanding
forever?
"Localized" gravity produces only a local halt in the expansion of the
universe. On the largest scales the expansion continues.
It is thought that the density of the universe is at the critical value
which will just prevent the universe from experiencing a collapse.
However, there is not enough visible mass to produce this critical
density.
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
Galactic clusters rotate much more quickly than would be expected, when
the visible mass in the cluster is totaled up.
Regards,
Josef
.... all knowledge of reality starts from experience and ends in it.
-- Albert Einstein
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| User: "Lars Eighner" |
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| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 09:48:50 AM |
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In our last episode,
<igrkc1t4imbtqrovfv6tlvoe8mc3osg74e@4ax.com>, the lovely and
talented Elroy Willis broadcast on alt.atheism:
If the universe is expanding, and even accelerating as it expands,
which seems to be the case according to current observations, then how
can galaxies actually collide with each other?
One of the popular visual models of the universe depicts it as a loaf
of raisin bread that's rising and expanding, with all the raisins
getting further and further apart as the bread bakes in the oven. Do
individual raisins actually collide inside a loaf of cooking raisin
bread?
The problem with this analogy is that rasins don't basically
have any momentem on their own. It would be better to consider
the rasins as points in space, rather than physical objects.
Obvious there are attractive forces and things can move toward
one another (or gravity wouldn't work, for example, or you
couldn't hit a comet with a rocket, thereby releasing deadly
intergalictic space viruses).
Another model I've seen is the balloon example, with dots drawn on an
uninflated rubber balloon, and when the balloon is blown up, the dots,
which represent stars and galaxies, get further and further apart, but
none of them actually collide with each other, since the surface of
the balloon is continually stretching bigger and bigger...
Are both these pictorial models inaccurate or lacking in some way, and
what is a better one to use these days?
Obviously both have some limitations. I think you are expecting
a little too much out of kitchen-table analogies. The real
answer is in the math. When you have outgrown the analogies,
which are really meant for small children, it is time to do the
math.
Hubble has taken some excellent pictures of colliding galaxies, and
it's said that the Andromeda galaxy is moving towards our own Milky
Way galaxy, not away from it, and one day they'll collide with each
other, or pass through each other, causing some distortions in both of
them in the process...
The fact that they're moving towards each other indicates that
localized gravity has overtaken the expansive force of the big bang,
and if that's the case, why are cosmologists looking for a bunch of
"dark matter" which is required to keep the universe from expanding
forever?
If localized galaxies can attract each other through gravity and
counteract the expanding effect, what need is there for some actual
mysterious or missing "dark matter?"
A point made by both the balloon model and the raisin bread
model is that points which are far apart move farther apart
faster than point that are near to begin with. The fact that
two local objects can be sufficiently attracted to cause them to
collide in no way suggests that there is enough mass in the
universe to draw the farthest objects back.
--
Rev. Lars Eighner ULC Atheist #1965 http://www.larseighner.com/
I don't see posts from or threads started from googlegroups.
"No falsehood is so fatal as that which is made an article of faith."
--Thomas Paine
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| User: "Meteorite Debris" |
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| Title: Re: OT - Expanding Universe Questions |
05 Jul 2005 08:56:47 AM |
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On Tue, 05 Jul 2005 11:41:00 GMT the ET form known as Elroy
Willis<elroywillis@swbell.net> sent a radio signal across the vast
expanse of deep space -._.--._.--._.--._.--._.--._.
If the universe is expanding, and even accelerating as it expands,
which seems to be the case according to current observations, then how
can galaxies actually collide with each other?
One of the popular visual models of the universe depicts it as a loaf
of raisin bread that's rising and expanding, with all the raisins
getting further and further apart as the bread bakes in the oven. Do
individual raisins actually collide inside a loaf of cooking raisin
bread?
Another model I've seen is the balloon example, with dots drawn on an
uninflated rubber balloon, and when the balloon is blown up, the dots,
which represent stars and galaxies, get further and further apart, but
none of them actually collide with each other, since the surface of
the balloon is continually stretching bigger and bigger...
Are both these pictorial models inaccurate or lacking in some way, and
what is a better one to use these days?
Hubble has taken some | |
