 |
|
|
|
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Warp wrote:
> Darren New <dne### [at] san rrcom> wrote:
>>> No. Space expands, the brick doesn't.
>
>> That doesn't really make sense.
>
> It makes sense when there's a force opposing the expansion.
Warning: Underinformed rambling ahead... :-)
Hmmm. Maybe it makes sense if you're assuming that the "expansion of
space" is caused by "adding space" between other bits of space. It
doesn't make as much sense if you think of "expansion of space" in the
same terms as you think of "contraction of things going near light speed".
I.e., it's like saying "time slows down, so you get more seconds per
minute, but the seconds are the same length." How would the universe
know to keep the seconds the same but make the minutes different?
> Think about it this way: The distance between atoms in a molecule is
> determined by the bounding forces between atoms.
It's determined by electrons exchanging photons, which gives rise to
what can be interpreted as forces, yes. It certainly depends on distance
(amongst other things) or you'd stick just as readily to glue on the
other side of the room as you do to the glue on your chair. :-) But the
underlying numbers stay the same ("n" and "j", basically, with "n" being
related to the mass of the electron (equal, if random spontaneous
"virtual particles" didn't interfere), and "j" being related to the
"charge" of the electron, which is proportional to that electron's
likelihood of absorbing or emitting a photon). But the formula using
those numbers is also based on distance, due to the inverse-square law.
(Or inverse-cube, I forget which.)
E.g., it's much more likely for an electron to wind up stuck to an
adjacent atom in a molecule than it is for that electron to wind up
thirty feet away.
> These are proportional to the charge of the electrons, or whatever.
Charge (which is the probability of an electron absorbing or emitting a
photon), mass (not sure if this includes relativistic mass), and distance.
> It's a constant. It doesn't change.
> If you tried to separate the atoms of a molecule, this force would
> resist it.
Right. But would the molecules themselves be getting bigger? Would the
protons and electrons be larger? Would the photons that mediate that
force be getting red-shifted in both directions?
Or would new space be getting inserted between the protons and the
electrons? If so, I'd think your chemistry would change, in just the
same way that chlorine is more chemically active than oxygen.
> Not everything gets longer. Only intergalactic space, far away from
> the galaxies, gets longer.
That's what has me curious. How does space far from galaxies "decide"
to get larger while space between stars doesn't?
>>> AFAIK space doesn't expand inside galaxies.
>
>> OK. More weirdness. Have you heard any postulates on why that would be
>> the case? Space only expands where the gravity is sufficiently low?
>
> http://en.wikipedia.org/wiki/Hubble%27s_law
>
> "In using Hubble's law to determine distances, only the velocity due
> to the expansion of the universe can be used. Since gravitationally
> interacting galaxies move relative to each other independent of the
> expansion of the universe, these relative velocities, called peculiar
> velocities, need to be accounted for in the application of Hubble's
> law. The Finger of God effect is one result of this phenomenon
> discovered in 1938 by Benjamin Kenneally. In systems that are
> gravitationally bound, such as galaxies or our planetary system, the
> expansion of space is (more than) annihilated by the attractive force
> of gravity."
OK. That still doesn't make sense to me. As space expands between two
stars within a galaxy, the gravity between those stars gets *weaker*,
meaning they orbit more slowly and are less likely to hold together.
Maybe that's why galaxies turn from globular clusters into spirals or
something, tho.
It makes sense if what it's saying is "the expansion of space isn't
rapid enough to keep a collapsing galaxy from collapsing", but if you
have a stable orbit and then start adding "space", the orbit won't
somehow adjust to take account of that - the sign of the change is the
wrong direction.
It also makes sense if what it's saying is "galaxies moving relative to
each other due to gravity are moving at a significant speed compared to
the speed caused by the expansion of space, and thus we must account for
that." That seems to be what the "finger of god" effect is talking
about, regardless of the quote.
(http://en.wikipedia.org/wiki/Fingers_of_God)
I'm not clear on two things: (a) why, if space expands, don't the things
in the space expand, and (b) why would gravity "overcome" the expansion
of space. There's no reason for the earth, for example, to have a
"preferred distance" from the sun, gravitationally-speaking. If extra
space gets added, either the earth will spiral away from the sun or
it'll slow down (as larger orbits are slower orbits).
Now, for (a), maybe stuff in the expanding space *does* get larger. A
red-shifted photon is, in many senses, "bigger" than a blue-shifted
photon, so maybe the expansion is small/slow enough that the expanding
things *do* get bigger. But if that was the case, atoms would also be
getting bigger in proportion to "space", and your rulers would show that
space isn't getting bigger after all, so the *only* way to notice might
be from red-shifts? But if "space expands" in the same sense that "time
slows down near the speed of light", then it doesn't make sense to say
"the galaxies will hold together", as everything will nevertheless
expand too - I expect the expansion of the matter in the galaxy (if it
leads to increased mass) might exactly balance (via increased gravity)
the increased distance between objects. (I'd have to do more thinking
about this than I want to at this hour to check.) Alternately, it's
possible that the "G" in "F=G m_1 m_2 / r^2" is fractionally higher than
thought, just enough to offset the expansion of space? Dunno.
To address (b), you could be inserting "new space" between other "bits
of space", but then I can't imagine the mechanism (other than "new
space" only appearing where curvature from gravity is flat enough) that
would create "new space" between galaxies but not inside galaxies.
I don't think saying "gravity holds them together" would keep galaxies
from expanding at the same rate as the rest of the universe, and indeed
I'd expect them to expand faster as the gravity holding things together
got weaker with increasing distance and stuff started "flying apart".
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Darren New <dne### [at] sanrrcom> wrote:
> I'm not clear on two things: (a) why, if space expands, don't the things
> in the space expand, and (b) why would gravity "overcome" the expansion
> of space.
Gravity deforms space, as does the expansion of the universe. Gravity
resists the expansion.
Perhaps you are thinking about gravity as a force?
--
- Warp
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Darren New <dne### [at] sanrrcom> wrote:
> Space only expands where the gravity is sufficiently low?
Btw, this might have something to do with so-called "vacuum energy"
(in addition to the so-called "dark energy"). Existing vacuum energy
expands the universe, but can only do so if gravity is low enough
(becaues there's only a limite amount of such energy). But I'm not at
all sure of this.
--
- Warp
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Darren New nous apporta ses lumieres en ce 2008/01/03 11:59:
> Warp wrote:
>> Darren New <dne### [at] sanrrcom> wrote:
>>> Now, if space expanded and gravity pulled everything back together,
>>> that makes sense. But that still doesn't answer the question of
>>> whether (for example) a brick floating in intergalactic space would
>>> be 10% bigger if given enough time.
>>
>> I don't think the brick would expand because forces which are much
>> stronger than gravity are keeping it together.
>
> In other words, space expands, but then the brick collapses again? Sure,
> it's possible. It still doesn't explain why space expands but the matter
> in it doesn't. It's like saying "time slows down, but the spring in the
> clock keeps it running the same speed". :-)
>
> I don't think this works for celestial objects. If you added space
> between the sun and the earth without slowing the orbit of the earth (in
> absolute velocity terms), you'd make an unstable system where the earth
> would tend to move even farther from the sun.
>
Space expand where the mater density is under a treshold value. The very diffuse
gases and relative proximity from stars inside a galaxie prevent space from
expanding. Between galaxies, there is MUCH less gas and no stars, so, there is
not enough mater to "hold space in place".
The Andromeda galaxi is moving toward us as it is close enough for the mutual
gravitational pull to overcome the very weak spacial expantion in the area. The
mater density in the local group is high enough to, maby almost, maybe totaly,
cancel the expantion.
--
Alain
-------------------------------------------------
You know you've been raytracing too long when you downloaded and printed the
Renderman Interface documentation, so you'd have a little light reading to take
on holiday.
Alex McLeod a.k.a. Giant Robot Messiah
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Darren New nous apporta ses lumieres en ce 2008/01/03 23:51:
>> Not everything gets longer. Only intergalactic space, far away from
>> the galaxies, gets longer.
>
> That's what has me curious. How does space far from galaxies "decide"
> to get larger while space between stars doesn't?
It don't decide to get larger far from galaxies, galaxies prevent it to get larger.
>
>>>> AFAIK space doesn't expand inside galaxies.
>>
>>> OK. More weirdness. Have you heard any postulates on why that would
>>> be the case? Space only expands where the gravity is sufficiently low?
>>
>> http://en.wikipedia.org/wiki/Hubble%27s_law
>>
>> "In using Hubble's law to determine distances, only the velocity due
>> to the expansion of the universe can be used. Since gravitationally
>> interacting galaxies move relative to each other independent of the
>> expansion of the universe, these relative velocities, called peculiar
>> velocities, need to be accounted for in the application of Hubble's
>> law. The Finger of God effect is one result of this phenomenon
>> discovered in 1938 by Benjamin Kenneally. In systems that are
>> gravitationally bound, such as galaxies or our planetary system, the
>> expansion of space is (more than) annihilated by the attractive force
>> of gravity."
>
> OK. That still doesn't make sense to me. As space expands between two
> stars within a galaxy, the gravity between those stars gets *weaker*,
> meaning they orbit more slowly and are less likely to hold together.
> Maybe that's why galaxies turn from globular clusters into spirals or
> something, tho.
The concensus is rather that galaxies start as spiral and degenerate into
globular clusters.
Usualy, spiral galaxies are relatively young, with lots of forming stars and
interstellar gases. Globular galaxies are older, have very little or no new
stars forming and almost to totaly lack interstellar gases.
>
--
Alain
-------------------------------------------------
You know you've been raytracing too long when you've tried rendering hair with
each strand as an object.
Quietly Watching
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Warp wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>> I'm not clear on two things: (a) why, if space expands, don't the things
>> in the space expand, and (b) why would gravity "overcome" the expansion
>> of space.
>
> Gravity deforms space, as does the expansion of the universe. Gravity
> resists the expansion.
That was kind of what I was getting at with
"""
(other than "new space" only appearing where curvature from gravity is
flat enough)
"""
> Perhaps you are thinking about gravity as a force?
It *is* a force, depending on your definition of "force". :) As in
"F=ma". If you're going to argue gravity isn't a force, then magnetism
isn't a force either, nor is pushing on something.
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Alain wrote:
>> That's what has me curious. How does space far from galaxies "decide"
>> to get larger while space between stars doesn't?
> It don't decide to get larger far from galaxies, galaxies prevent it to
> get larger.
Yeah. I was asking about the mechanism, tho. Is there an actual theory
as to *why* this happens?
> The concensus is rather that galaxies start as spiral and degenerate
> into globular clusters.
Ah. This is something new (or more correct at least) than when I last
looked at it.
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
In article <477e656b$1@news.povray.org>, ele### [at] netscapenet
says...
> Darren New nous apporta ses lumieres en ce 2008/01/03 23:51:
>
> >> Not everything gets longer. Only intergalactic space, far away from
> >> the galaxies, gets longer.
> >
> > That's what has me curious. How does space far from galaxies "decide"
> > to get larger while space between stars doesn't?
> It don't decide to get larger far from galaxies, galaxies prevent it to g
et larger.
> >
> >>>> AFAIK space doesn't expand inside galaxies.
> >>
> >>> OK. More weirdness. Have you heard any postulates on why that would
> >>> be the case? Space only expands where the gravity is sufficiently low
?
> >>
> >> http://en.wikipedia.org/wiki/Hubble%27s_law
> >>
> >> "In using Hubble's law to determine distances, only the velocity due
> >> to the expansion of the universe can be used. Since gravitationally
> >> interacting galaxies move relative to each other independent of the
> >> expansion of the universe, these relative velocities, called peculiar
> >> velocities, need to be accounted for in the application of Hubble's
> >> law. The Finger of God effect is one result of this phenomenon
> >> discovered in 1938 by Benjamin Kenneally. In systems that are
> >> gravitationally bound, such as galaxies or our planetary system, the
> >> expansion of space is (more than) annihilated by the attractive force
> >> of gravity."
> >
> > OK. That still doesn't make sense to me. As space expands between two
> > stars within a galaxy, the gravity between those stars gets *weaker*,
> > meaning they orbit more slowly and are less likely to hold together.
> > Maybe that's why galaxies turn from globular clusters into spirals or
> > something, tho.
> The concensus is rather that galaxies start as spiral and degenerate into
> globular clusters.
> Usualy, spiral galaxies are relatively young, with lots of forming stars
and
> interstellar gases. Globular galaxies are older, have very little or no n
ew
> stars forming and almost to totaly lack interstellar gases.
> >
>
Was the consensus. The problem is, they have found old galaxies and new
that do *not* conform to those expectations. Its now thought that
globular systems may be missing the central black hole, or some other
factor, which would cause the tidal forces that make some galaxies spin,
and thus form spirals. Its kind of up in the air though.
--
void main () {
if version = "Vista" {
call slow_by_half();
call DRM_everything();
}
call functional_code();
}
else
call crash_windows();
}
<A HREF='http://www.daz3d.com/index.php?refid=16130551'>Get 3D Models,
3D Content, and 3D Software at DAZ3D!</A>
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
In article <477e8615$1@news.povray.org>, dne### [at] sanrrcom says...
> Alain wrote:
> >> That's what has me curious. How does space far from galaxies "decide"
> >> to get larger while space between stars doesn't?
> > It don't decide to get larger far from galaxies, galaxies prevent it to
> > get larger.
>
> Yeah. I was asking about the mechanism, tho. Is there an actual theory
> as to *why* this happens?
>
> > The concensus is rather that galaxies start as spiral and degenerate
> > into globular clusters.
>
> Ah. This is something new (or more correct at least) than when I last
> looked at it.
>
Actually, as I stating in the other post, its not really the consensus
any more, at least in new studies. And imho, it also makes no sense.
Tidal forces from a spinning black hole "could" pull stars into a
spiral. That would make sense. But... What kind of mechanism would
possibly make a galaxy start spinning, when it first formed *then* stop
spinning later? Either Alain has it backwards, or if just flat out
doesn't make any sense to me.
--
void main () {
if version = "Vista" {
call slow_by_half();
call DRM_everything();
}
call functional_code();
}
else
call crash_windows();
}
<A HREF='http://www.daz3d.com/index.php?refid=16130551'>Get 3D Models,
3D Content, and 3D Software at DAZ3D!</A>
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Patrick Elliott wrote:
> Tidal forces from a spinning black hole "could" pull stars into a
> spiral. That would make sense.
Actually, I think the problem is that the calculations show that if you
start with a somewhat symetrical distribution of stars, you wind up with
a more symetrical rather than less symetrical distribution of stars
after a couple of orbits. I.e., gravity *won't* pull a galaxy into a
barred-spiral shape, as is so common out there.
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
|
|
