All this talk of light pressure gives me gas.

In article ,
dlzc writes:
[the CMB] is hundreds of watts per square meter, since it
is a whole sky source.

The above is off by about 8 orders of magnitude. (270 K gives
300 W/m^2.) Also, only the _difference_ in flux in opposite
directions gives a net force. That's about 1% of the total for a
peculiar velocity of 3000 km/s (which is much larger than any
relevant velocity I can think of).

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On 04/11/2011 10:25 AM, dlzc wrote:
Dear Yousuf Khan:

On Nov 3, 11:39 pm, Yousuf wrote:
On 01/11/2011 8:23 PM,dlzcwrote:

If we have neutral atoms / molecules in intergalactic space,
won't light pressure tend to brake them to average neutral
speed wrt the Universe at large?

Neutral gas is too diffuse to be braked by light pressure.

Diffuse neutral gas has the same laws of physics as non-diffuse, at
least until a Bose-Einstein state is set up. As a discrete diffuse
gas, it will suffer "friction" with the CMBR, since most molecules
interact with microwaves.

The molecules do interact with microwaves through the primary
electromagnetic force. But the light pressure is a secondary effect of
the electromagnetic force that requires a lot of molecules in close
proximity pushing and shoving each other as one big interconnected body.
Gaseous things like Gas Giant Planets, stars, brown dwarfs. Liquid and
solid things like terrestrial planets, asteroids, etc. Neutral gas
spread between the galaxies don't act as one cohesive body.

Macroscopic objects that are dense balls of gas or liquid,
or solid be the only things affected by light pressure.

Why? Light is discrete, as are the bits "objects" are made of. Even
LeSage gravitation (which light could be the actor for, in some sense)
works on both the large and the small. Or do you imagine the universe
around smaller objects is not expanded, while for larger it is?

Yeah, I do think smaller low-density objects don't feel the light
pressure, like larger high-density objects do. Once small objects start
grouping into larger more coherent objects, then they can feel the
effects of light pressure. Basically anything that is opaque (or at
least translucent) to light is a candidate to be affected by light pressure.

I think light pressure might have been what drove inflation when the
universe was still dense enough to be considered one large dense and
opaque object (i.e. pre-CMB). When the universe became diffuse after the
CMB era, the light pressure didn't have as much effect. Once the
reionization era was upon us, then smaller groups of dense objects
started appearing, like stars and galaxies, and light pressure once
again started taking hold.

I am not trying to make fun of your (current favorite) idea here. I
am following a parallel path is all. This thread isn't about
"expansion", but about a possible "preferred background" established
by the CMBR itself. And if the "preferred background is detectable in
some way, can be validated by heliopause and stellarpause (maybe even
"galacticpause") measurements, then we can find out how much neutral
gas there is on average. I really don't think there is much, or we
could not see as far as we do. Also, if it were present, I think it
would tend to strip other neutral gas from passing galaxies...

But heliopauses and other x-pauses are driven by stellar winds, not
stellar light pressure. So it's not really the same thing as what I'm
talking about anyways.

So what exactly do you see in this paper about Luminous
Infrared Galaxies that you think is relevant to light pressure?

Gas that doesn't move significantly, that may not be entirely
uniformly distributed, would be free to form luminous structures later
in the Universe's history. Brightness then would be expected to
increase with time, as the structure loses energy, and falls into even
tighter arrangements.

Not saying the above paper even talks about good candidates for this.
I am reminded of a really cool (as in not very bright, infrared)
galaxy we had completely overlooked, right in our neighborhood, that
was announced a few years ago, but didn't try really hard.

I'm pretty sure that the intergalactic gas will form new galaxies in
distant future once the current crop of galaxies start fading away.
There is enough material in the intergalactic medium to form several
times more galaxies than we have now. Some of the intergalactic gas,
that is near some galaxies will fall into those galaxies, and
re-energize star formation in them. Some will stay far away from all
other galaxies, and they will get squeezed to form a new separate galaxy
of its own. Of course that means that a supermassive blackhole will have
to form in its center, or it would have to capture a cast-off
supermassive blackhole leftover from a previous galaxy merger. This
would then lead to the object capturing some the cluster's dark matter
(whatever that is).

Yousuf Khan

Dear Yousuf Khan:

On Nov 4, 10:20*pm, Yousuf Khan wrote:
On 04/11/2011 10:25 AM, dlzc wrote:
On Nov 3, 11:39 pm, Yousuf *wrote:
On 01/11/2011 8:23 PM,dlzcwrote:

If we have neutral atoms / molecules in intergalactic space,
won't light pressure tend to brake them to average neutral
speed wrt the Universe at large?

Neutral gas is too diffuse to be braked by light pressure.

Diffuse neutral gas has the same laws of physics as non-diffuse, at
least until a Bose-Einstein state is set up. *As a discrete diffuse
gas, it will suffer "friction" with the CMBR, since most molecules
interact with microwaves.

The molecules do interact with microwaves through the primary
electromagnetic force. But the light pressure is a

.... [larger but] ...

secondary effect of the electromagnetic force that requires a
lot of molecules in close proximity pushing and shoving each
other as one big interconnected body. Gaseous things like
Gas Giant Planets, stars, brown dwarfs. Liquid and
solid things like terrestrial planets, asteroids, etc. Neutral gas
spread between the galaxies don't act as one cohesive body.

Macroscopic objects that are dense balls of gas or liquid,
or solid be the only things affected by light pressure.

Why? *Light is discrete, as are the bits "objects" are made
of. *Even LeSage gravitation (which light could be the actor
for, in some sense) works on both the large and the small.
*Or do you imagine the universe around smaller objects is
not expanded, while for larger it is?

Yeah, I do think smaller low-density objects don't feel the light
pressure, like larger high-density objects do. Once small
objects start grouping into larger more coherent objects, then
they can feel the effects of light pressure.

Seriously, I don't want to convert my thread into yours.

Basically anything that is opaque (or at least translucent) to
light is a candidate to be affected by light pressure.

I think light pressure might have been what drove inflation
when the universe was still dense enough to be considered
one large dense and opaque object (i.e. pre-CMB). When
the universe became diffuse after the CMB era, the light
pressure didn't have as much effect. Once the reionization
era was upon us, then smaller groups of dense objects
started appearing, like stars and galaxies, and light pressure
once again started taking hold.

I am not trying to make fun of your (current favorite) idea
here. *I am following a parallel path is all. *This thread isn't
about "expansion", but about a possible "preferred
background" established by the CMBR itself. *And if the
"preferred background is detectable in some way, can be
validated by heliopause and stellarpause (maybe even
"galacticpause") measurements, then we can find out how
much neutral gas there is on average. *I really don't think
there is much, or we could not see as far as we do. *Also,
if it were present, I think it would tend to strip other neutral
gas from passing galaxies...

But heliopauses and other x-pauses are driven by stellar
winds, not stellar light pressure.

*CMBR electromagnetic force* pressure, using the inflections you try
and impress.

So it's not really the same thing as what I'm
talking about anyways.

Sorry, I cannot grasp the difference you keep trying to produce. A
failing on my part, and since I'd given up, I've started this
unrelated thread.

Note that our heliosheath is aligned with our motion wrt the CMBR
dipole, not our motion wrt the Milky Way's center. And even if were
exactly that, why is that gas not rushing outwards, in orbit too, or
somewhere in between?
http://encyclopedia2.thefreedictiona...+through+Space

What is braking the gas, if not light? Is there any such neutral
gas? Would it be indicative of being in a galaxy, is it about this
value across the Universe, in this epoch?

David A. Smith

In article ,
dlzc writes:
Note that our heliosheath is aligned with our motion wrt the CMBR
dipole, not our motion wrt the Milky Way's center.

Reference please? I can't even figure out what it means for the
heliosheath to be aligned with anything or how one would measure it.

The various directions of motion are well known. It's the alleged
alignment of the heliosheath I don't understand.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

Dear Steve Willner:

On Nov 7, 2:44*pm, (Steve Willner) wrote:
In article ,

*dlzc writes:
Note that our heliosheath is aligned with our motion wrt
the CMBR dipole, not our motion wrt the Milky Way's
center.

Reference please? *I can't even figure out what it means
for the heliosheath to be aligned with anything or how
one would measure it.

Distance to "boundary", in heliocentric frame.
http://arxiv.org/abs/0707.2970
.... probably more, but if I don't use the *exact* search terms, and in
order, I cannot find the one I noted a couple of days ago.

The various directions of motion are well known. *It's the
alleged alignment of the heliosheath I don't understand.

And not really clear if it is anything more than happenstance. Is it
likely that intergalactic neutral gas impinges on us? If so, so what?

Really can't tell much (I guess), unless we can image other star's
sheaths...
http://www.dailymail.co.uk/sciencete...ears-long.html

David A. Smith

In article ,
dlzc writes:
Distance to "boundary", in heliocentric frame.
http://arxiv.org/abs/0707.2970

That looks interesting, though it seems not to have been accepted for
publication. I'm not qualified to comment on possible reasons for
non-acceptance.

The point in the paper about the CMB was not that the CMB influences
the heliosheath but rather that heliosheath irregularities might
contaminate measurements of the CMB. Given that the CMB is measured
at many wavelengths, and contamination ought to be wavelength-
dependent, I'm skeptical, but I'm not qualified to have a real
opinion.

And not really clear if [orientation] is anything more than happenstance.

Yep.

Is it likely that intergalactic neutral gas impinges on us?

Interstellar, not intergalactic, but yes. One thing that interested
me (referenced in the paper, not part of its results) is that the
Sun's velocity with respect to the local ISM is determined from
Ulysses measurements of neutral helium atoms from the ISM.

http://www.dailymail.co.uk/sciencete...ers-discover-=
star-tail-13-light-years-long.html David A. Smith

Great picture! Mira was long known to be losing mass and have an
extensive shell of dust and gas. Apparently some of the shell is
being lost to the ISM as Mira travels through it. Isn't Mira a Pop 2
star with a large space motion?

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

"Steve Willner" wrote in message
...
| In article
,
| dlzc writes:
| Distance to "boundary", in heliocentric frame.
| http://arxiv.org/abs/0707.2970
|
| That looks interesting, though it seems not to have been accepted for
| publication. I'm not qualified to comment on possible reasons for
| non-acceptance.
|
| The point in the paper about the CMB was not that the CMB influences
| the heliosheath but rather that heliosheath irregularities might
| contaminate measurements of the CMB. Given that the CMB is measured
| at many wavelengths, and contamination ought to be wavelength-
| dependent, I'm skeptical, but I'm not qualified to have a real
| opinion.
|
| And not really clear if [orientation] is anything more than
happenstance.
|
| Yep.
|
| Is it likely that intergalactic neutral gas impinges on us?
|
| Interstellar, not intergalactic, but yes. One thing that interested
| me (referenced in the paper, not part of its results) is that the
| Sun's velocity with respect to the local ISM is determined from
| Ulysses measurements of neutral helium atoms from the ISM.
|
|
http://www.dailymail.co.uk/sciencete...ers-discover-=
| star-tail-13-light-years-long.html David A. Smith
|
| Great picture! Mira was long known to be losing mass and have an
| extensive shell of dust and gas. Apparently some of the shell is
| being lost to the ISM as Mira travels through it. Isn't Mira a Pop 2
| star with a large space motion?
|
13 light years long.
Speed say 0.0001c
time = 13/0.0001c = 130,000 years
Still "glowing", nothing to illuminate it, only visible in UV,
must have a long half-life.
On the other hand, Daily Mail...

Dear Steve Willner:

On Nov 10, 2:16*pm, (Steve Willner) wrote:
In article ,

*dlzc writes:
Distance to "boundary", in heliocentric frame.
http://arxiv.org/abs/0707.2970

That looks interesting, though it seems not to have been
accepted for publication. *I'm not qualified to comment on
possible reasons for non-acceptance.

The point in the paper about the CMB was not that the
CMB influences the heliosheath but rather that
heliosheath irregularities might contaminate measurements
of the CMB.

The point of me linking it, is it states the orientation of the
heliosheaths "long axis", as relates the CMBR.

*Given that the CMB is measured at many wavelengths,
and contamination ought to be wavelength-dependent, I'm
skeptical, but I'm not qualified to have a real opinion.

Your opinion is suitable, more than suitable at this distance. Likely
why it wasn't accepted.

And not really clear if [orientation] is anything more than
happenstance.

Yep.

*Is it likely that intergalactic neutral gas impinges on us?

Interstellar, not intergalactic, but yes.

Why would our heliosheath be oriented towards the CMBR, rather than
Milky-Way- radially symmetric or circumferentially symmetric?
http://iopscience.iop.org/0004-637X/.../70114.web.pdf

*One thing that interested me (referenced in the paper,
not part of its results) is that the Sun's velocity with
respect to the local ISM is determined from Ulysses
measurements of neutral helium atoms from the ISM.

Ignorance on my part... "ISM" = "Inter Stellar Medium"?

snip link now broken by Google.Groups

Great picture! *Mira was long known to be losing mass
and have an extensive shell of dust and gas. *Apparently
some of the shell is being lost to the ISM as Mira travels
through it. *Isn't Mira a Pop 2 star with a large space
motion?

That brightens the stellarsheath up to the point we can see it. We
really didn't know we had one for the longest time. If the lion's
share of general stars just traveling in orbit (as if that were really
clear cut) around the Milky Way, would their stellarsheaths be
oriented towards the CMBR dipole?

The question might balance on how fast a neutral medium equilibrates
to neutral CMBR motion. Based on Mira (for lack of a good statistical
sample), something on the scale of a few multiples of 11 light years,
would brake anything we'd plow into... be that interstellar or
("recently") intergalactic. Of course it also would sweep much of the
contents out of the Milky Way, unless it was being replaced equally
fast... solar systems like mostly-empty atoms drifting unawares
through an aether... not that is anything more than a poorly chosen
simile.

I don't know if this is worth pursuing... and your opinion is better
than mine here.

David A. Smith

dlzc wrote in
:

[...stuff on the CMB dipole moment...]

Do you realize that the only reason we have a measurable CMB dipole is
because we are moving with respect to the reference frame in which the CMB
was created?

Dear eric gisse:

On Nov 11, 8:18*pm, eric gisse wrote:
dlzc wrote :

[...stuff on the CMB dipole moment...]

Do you realize that the only reason we have a measurable
CMB dipole is because we are moving with respect to the
reference frame in which the CMB was created?

Did you not notice that our heliosheath is aligned with our motion wrt
the CMBR, and not so much our motion wrt the Milky Way? Or did you
miss that?

David A. Smith