All this talk of light pressure gives me gas.

On Nov 1, 5:23*pm, dlzc wrote:
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?

They aren't terribly massive, so the (for example)
temperature difference between the "poles" of the
CMBR that we experience, should brake them in
finite time.

Note sure where I am going with this, other than it
will make capture by nearby bodies easier, or
coalescence into new galaxies possible.
http://arxiv.org/abs/1006.2166

So what is the liklihood that "light pressure" is what boosts solar
wind to the velocities we see? They are higher than corona
temperatures alone should achieve...

Or is this too little rope for a clothesline this long...

David A. Smith

On 11/18/2011 12:01 AM, dlzc wrote:
So what is the liklihood that "light pressure" is what boosts solar
wind to the velocities we see? They are higher than corona
temperatures alone should achieve...

Or is this too little rope for a clothesline this long...

Solar wind is transparent, so I doubt light pressure could boost such
small objects as hydrogen ions and electrons. However, magnetic forces
can, which is also caused by photons.

Yousuf Khan

Dear Yousuf Khan:

On Nov 17, 11:38*pm, Yousuf Khan wrote:
On 11/18/2011 12:01 AM, dlzc wrote:

So what is the liklihood that "light pressure" is what
boosts solar wind to the velocities we see? *They are
higher than corona temperatures alone should achieve...

Or is this too little rope for a clothesline this long...

Solar wind is transparent,

.... a failing of our eyes ...

so I doubt light pressure could boost such small objects
as hydrogen ions and electrons.

If they are supposed to recombine as quickly as "expected", then maybe
they are ions and free electrons largely *because* they were re-
ionized.

However, magnetic forces can, which is also caused
by photons.

The problem is "magnetic field lines" from the Sun are not oriented
roughly radially, except at the poles. Yet the solar wind travels
radially. Light travels radially too, so a couple of boosts from
(sufficiently energetic) photons, would drive solar wind radially
outwards. That isn't to say we won't find "mechanism" in the Sun's
version of an accretion disk that it the major cause. But maybe light
is that cause.

David A. Smith

On 18/11/2011 9:28 AM, dlzc wrote:
Dear Yousuf Khan:

On Nov 17, 11:38 pm, Yousuf wrote:
On 11/18/2011 12:01 AM, dlzc wrote:

So what is the liklihood that "light pressure" is what
boosts solar wind to the velocities we see? They are
higher than corona temperatures alone should achieve...

Or is this too little rope for a clothesline this long...

Solar wind is transparent,

... a failing of our eyes ...

Particles that small and sparse can hardly be anything but transparent
at all frequencies, not just for our limited visible frequencies. A
graph might reveal little spikes of absorption, but even these spikes
are insignificant fluctuations in opacity. Our various space telescopes
of various EM bands are hardly obstructed in anyway by the solar winds.

For light pressure to be effective, it really needs object that are
macroscopic in scale and with large surface areas available. Individual
particles don't apply to this definition.

so I doubt light pressure could boost such small objects
as hydrogen ions and electrons.

If they are supposed to recombine as quickly as "expected", then maybe
they are ions and free electrons largely *because* they were re-
ionized.

I'm sure the light may re-ionize the particles, especially at the UV
levels and above. But that's not the same as light pressure.

However, magnetic forces can, which is also caused
by photons.

The problem is "magnetic field lines" from the Sun are not oriented
roughly radially, except at the poles. Yet the solar wind travels
radially. Light travels radially too, so a couple of boosts from
(sufficiently energetic) photons, would drive solar wind radially
outwards. That isn't to say we won't find "mechanism" in the Sun's
version of an accretion disk that it the major cause. But maybe light
is that cause.

The ionized particles can be boosted radially by the rotating magnetic
fields.

Yousuf Khan

Dear Yousuf Khan:

On Nov 18, 8:51*am, Yousuf Khan wrote:
On 18/11/2011 9:28 AM, dlzc wrote:
On Nov 17, 11:38 pm, Yousuf *wrote:
On 11/18/2011 12:01 AM, dlzc wrote:

So what is the liklihood that "light pressure" is what
boosts solar wind to the velocities we see? *They are
higher than corona temperatures alone should achieve...

Or is this too little rope for a clothesline this long...

Solar wind is transparent,

... a failing of our eyes ...

Particles that small and sparse can hardly be anything
but transparent at all frequencies, not just for our limited
visible frequencies. A graph might reveal little spikes of
absorption,

Hence not transparent.

but even these spikes are insignificant fluctuations in
opacity. Our various space telescopes of various EM
bands are hardly obstructed in anyway by the solar
winds.

Sure.

For light pressure to be effective, it really needs object
that are macroscopic in scale

Atoms comply.

and with large surface areas available.

Negligible mass (such that eV's worth of momentum is a significant
speed), finite size / cross section.

Individual particles don't apply to this definition.

Sure do.

so I doubt light pressure could boost such small
objects as hydrogen ions and electrons.

If they are supposed to recombine as quickly as
"expected", then maybe they are ions and free
electrons largely *because* they were re-
ionized.

I'm sure the light may re-ionize the particles, especially
at the UV2 levels and above. But that's not the same as
light pressure.

You are going to have to think about what "light pressure" derives
from. It should include the various scattering mechanisms (which
would apply here), and the absorption mechanism (which should apply
here).

If you want to talk about the effects of diffraction (which could
elicit something like gravitation as an "equal and opposite
reaction"), that would be something else again. More of a "venturi
effect"...

Or are you imagining some other mechanism? Something that only
effects galaxies, but nothing smaller. How would the individual
photon discriminate between a galaxy and an arm, a nebula, a solar
system?

However, magnetic forces can, which is also caused
by photons.

The problem is "magnetic field lines" from the Sun are
not oriented roughly radially, except at the poles. *Yet
the solar wind travels radially. *Light travels radially too,
so a couple of boosts from (sufficiently energetic)
photons, would drive solar wind radially outwards. *That
isn't to say we won't find "mechanism" in the Sun's
version of an accretion disk that it the major cause.
*But maybe light is that cause.

The ionized particles can be boosted radially by the
rotating magnetic fields.

Our Sun does not produce a smooth rotation, with high enough speeds,
to generate the solar wind we measure. Occasionally, absolutely yes
it does, but not smooth like solar wind. That is another "problem"
searching for a solution, as far as I know (which isn't very far to be
sure).

David A. Smith

On 18/11/2011 11:20 AM, dlzc wrote:
Dear Yousuf Khan:

On Nov 18, 8:51 am, Yousuf wrote:
On 18/11/2011 9:28 AM, dlzc wrote:
On Nov 17, 11:38 pm, Yousuf wrote:
On 11/18/2011 12:01 AM, dlzc wrote:

So what is the liklihood that "light pressure" is what
boosts solar wind to the velocities we see? They are
higher than corona temperatures alone should achieve...

Or is this too little rope for a clothesline this long...

Solar wind is transparent,

... a failing of our eyes ...

Particles that small and sparse can hardly be anything
but transparent at all frequencies, not just for our limited
visible frequencies. A graph might reveal little spikes of
absorption,

Hence not transparent.

Close enough to transparent.

For light pressure to be effective, it really needs object
that are macroscopic in scale

Atoms comply.

The only thing that atoms would be considered macroscopic next to are
gamma rays. Not a lot of gamma rays get out of the Sun's surface.

and with large surface areas available.

Negligible mass (such that eV's worth of momentum is a significant
speed), finite size / cross section.

Sure, that gamma rays exert considerable pressure -- at the Sun's core.
By the time those gamma rays make it out of the Sun's surface, they've
been all diluted to UV or less. Won't affect solar wind speeds once
they're out of the Sun.

Individual particles don't apply to this definition.

Sure do.

so I doubt light pressure could boost such small
objects as hydrogen ions and electrons.

If they are supposed to recombine as quickly as
"expected", then maybe they are ions and free
electrons largely *because* they were re-
ionized.

I'm sure the light may re-ionize the particles, especially
at the UV2 levels and above. But that's not the same as
light pressure.

You are going to have to think about what "light pressure" derives
from. It should include the various scattering mechanisms (which
would apply here), and the absorption mechanism (which should apply
here).

Yup, all of those effects combine to create the overall light pressure
effect. But it necessarily requires an opaque body to push against to
get all of those effects working together.

If you want to talk about the effects of diffraction (which could
elicit something like gravitation as an "equal and opposite
reaction"), that would be something else again. More of a "venturi
effect"...

It tends to impart a spin on bodies rather than pushing or pulling them
completely. That is, it pushes on one side of the body while pulling on
the other side.

Or are you imagining some other mechanism? Something that only
effects galaxies, but nothing smaller. How would the individual
photon discriminate between a galaxy and an arm, a nebula, a solar
system?

No, not imagining a different effect at all. I'm talking about the exact
same effect that gets asteroids rotating, or solar sails blowing.
However, so far most of the light pressure effect has been studied
within the context of our solar system, and is pretty well understood
within that context. In fact, the equations that describe light pressure
seem to be practical engineering-style empirical equations, rather than
formalized theoretical physics-style equations.

So it seems that light pressure may not have a lot of formal theory
behind it. As such, it seems that there has been no real studies done on
light pressure effects at larger scales. That's the reason for my
original question about whether it's possible that this effect is at
work at the galaxy supercluster scale? The reason I imagine it might be
more effective at the supercluster level than at the cluster or
individual galaxy level is because of the differing levels of overall
density, surface area, and light intensity of each of these body scales.

The ionized particles can be boosted radially by the
rotating magnetic fields.

Our Sun does not produce a smooth rotation, with high enough speeds,
to generate the solar wind we measure. Occasionally, absolutely yes
it does, but not smooth like solar wind. That is another "problem"
searching for a solution, as far as I know (which isn't very far to be
sure).

Well, we also see the solar winds speeding up and slowing down with the
changing magnetic conditions of the Sun, so there's a clue right there.

Yousuf Khan

Dear Yousuf Khan:

On Nov 20, 7:08*pm, Yousuf Khan wrote:
On 18/11/2011 11:20 AM, dlzc wrote:
On Nov 18, 8:51 am, Yousuf *wrote:
On 18/11/2011 9:28 AM, dlzc wrote:
On Nov 17, 11:38 pm, Yousuf * *wrote:
On 11/18/2011 12:01 AM, dlzc wrote:

So what is the liklihood that "light pressure" is what
boosts solar wind to the velocities we see? *They are
higher than corona temperatures alone should achieve...

Or is this too little rope for a clothesline this long...

Solar wind is transparent,

... a failing of our eyes ...

Particles that small and sparse can hardly be anything
but transparent at all frequencies, not just for our limited
visible frequencies. A graph might reveal little spikes of
absorption,

Hence not transparent.

Close enough to transparent.

For light pressure to be effective, it really needs object
that are macroscopic in scale

Atoms comply.

The only thing that atoms would be considered macroscopic
next to are gamma rays. Not a lot of gamma rays get out of
the Sun's surface.

Don't need gamma rays for solar wind speeds. Don't need much more
energetic than UV.

and with large surface areas available.

Negligible mass (such that eV's worth of momentum is a
significant speed), finite size / cross section.

Sure, that gamma rays exert considerable pressure -- at the
Sun's core. By the time those gamma rays make it out of
the Sun's surface, they've been all diluted to UV or less.

Which is all that is required.

Won't affect solar wind speeds once they're out of the Sun.

Seems reasonable to me. Even seems reasonable that more than one
interaction can occur to a given proton, especially near the Sun.
Regardless of my personal fantasy, here is a good paper on "fast solar
wind"...
http://arxiv.org/abs/1003.2299

Individual particles don't apply to this definition.

Sure do.

so I doubt light pressure could boost such small
objects as hydrogen ions and electrons.

If they are supposed to recombine as quickly as
"expected", then maybe they are ions and free
electrons largely *because* they were re-
ionized.

I'm sure the light may re-ionize the particles, especially
at the UV2 levels and above. But that's not the same as
light pressure.

You are going to have to think about what "light pressure"
derives from. *It should include the various scattering
mechanisms (which would apply here), and the absorption
mechanism (which should apply here).

Yup, all of those effects combine to create the overall light
pressure effect. But it necessarily requires an opaque body
to push against to get all of those effects working together.

I'm sorry, but "opaque" really just means "has charges capable of
interacting with photons". Solar wind particles have that.

If you want to talk about the effects of diffraction (which could
elicit something like gravitation as an "equal and opposite
reaction"), that would be something else again. *More of a
"venturi effect"...

It tends to impart a spin on bodies rather than pushing or pulling
them completely.

Consider single body diffraction, say around Mercury. Outbound
photons passing near Mercury are bent around it on all sides. No
"spin".

That is, it pushes on one side of the body while pulling on
the other side.

Or are you imagining some other mechanism? *Something
that only effects galaxies, but nothing smaller. *How would
the individual photon discriminate between a galaxy and an
arm, a nebula, a solar system?

No, not imagining a different effect at all. I'm talking about
the exact same effect that gets asteroids rotating, or solar
sails blowing. However, so far most of the light pressure
effect has been studied within the context of our solar
system, and is pretty well understood within that context. In
fact, the equations that describe light pressure seem to be
practical engineering-style empirical equations, rather than
formalized theoretical physics-style equations.

So it seems that light pressure may not have a lot of formal
theory behind it. As such, it seems that there has been no
real studies done on light pressure effects at larger scales.
That's the reason for my original question about whether it's
possible that this effect is at work at the galaxy supercluster
scale?

Maybe, but it is inadequate to describe expansion. Because
superclusters and such do not have peculiar motion, just are the only
critters with members still inside their mutual Rindler Horizons.

The reason I imagine it might be more effective at the
supercluster level than at the cluster or individual galaxy
level is because of the differing levels of overall density,
surface area, and light intensity of each of these body scales.

But the Universe is overall homogeneous. So in all directions, light
pressure is on average the same. I just don't see it being more
"interesting" than Dark Energy.

The ionized particles can be boosted radially by the
rotating magnetic fields.

Our Sun does not produce a smooth rotation, with high
enough speeds, to generate the solar wind we measure.
*Occasionally, absolutely yes it does, but not smooth like
solar wind. *That is another "problem" searching for a
solution, as far as I know (which isn't very far to be
sure).

Well, we also see the solar winds speeding up and slowing
down with the changing magnetic conditions of the Sun, so
there's a clue right there.

Works for fast, not for slow solar wind.

David A. Smith

On 20/11/2011 10:00 PM, dlzc wrote:
Dear Yousuf Khan:

On Nov 20, 7:08 pm, Yousuf wrote:
The only thing that atoms would be considered macroscopic
next to are gamma rays. Not a lot of gamma rays get out of
the Sun's surface.

Don't need gamma rays for solar wind speeds. Don't need much more
energetic than UV.

UV would be small enough to knock an electron off of the electron cloud
of an atom and turn it into an ion, but it's not small enough to touch
the nucleus of an atom.

and with large surface areas available.

Negligible mass (such that eV's worth of momentum is a
significant speed), finite size / cross section.

Sure, that gamma rays exert considerable pressure -- at the
Sun's core. By the time those gamma rays make it out of
the Sun's surface, they've been all diluted to UV or less.

Which is all that is required.

The ions coming out of the Sun are hydrogen ions, i.e. meaning that
they're just single protons. Their single orbital electrons have been
blown away. You really need gamma rays to affect hydrogen ions/protons.
UV might be enough to affect complex higher-order ions like oxygen or
carbon because they still have lots of electrons orbiting them, even if
they are ionized.

Won't affect solar wind speeds once they're out of the Sun.

Seems reasonable to me. Even seems reasonable that more than one
interaction can occur to a given proton, especially near the Sun.
Regardless of my personal fantasy, here is a good paper on "fast solar
wind"...
http://arxiv.org/abs/1003.2299

The authors of the link seem to be looking at magnetic cyclotron links
for the speed function, not light pressure.

You are going to have to think about what "light pressure"
derives from. It should include the various scattering
mechanisms (which would apply here), and the absorption
mechanism (which should apply here).

Yup, all of those effects combine to create the overall light
pressure effect. But it necessarily requires an opaque body
to push against to get all of those effects working together.

I'm sorry, but "opaque" really just means "has charges capable of
interacting with photons". Solar wind particles have that.

It's more complex than that. Opaque means to me that an object has
multiple particles interacting with each other to capture, absorb,
re-emit, bounce, reflect, and block photons. Each of the particles in
the multi-particle object will share the photons with each other, and
pass it around to each other in complicated ways. Single particles
cannot interact with light this way.

If you want to talk about the effects of diffraction (which could
elicit something like gravitation as an "equal and opposite
reaction"), that would be something else again. More of a
"venturi effect"...

It tends to impart a spin on bodies rather than pushing or pulling
them completely.

Consider single body diffraction, say around Mercury. Outbound
photons passing near Mercury are bent around it on all sides. No
"spin".

That's mainly due to Mercury's gravity that the photons bend around it.
The photons aren't powerful enough to create any kind of meaningful spin
on massive Mercury, but they do tend to be powerful enough to create
small spins on asteroids in the asteroid belt.

So it seems that light pressure may not have a lot of formal
theory behind it. As such, it seems that there has been no
real studies done on light pressure effects at larger scales.
That's the reason for my original question about whether it's
possible that this effect is at work at the galaxy supercluster
scale?

Maybe, but it is inadequate to describe expansion. Because
superclusters and such do not have peculiar motion, just are the only
critters with members still inside their mutual Rindler Horizons.

Light pressure shouldn't give them any peculiar motion, just a straight
outward momentum between adjacent superclusters. It might impart a small
spin on them too, but that spin would be indistinguishable from their
mutual orbital movements.

Adjacent superclusters would impart small forces on each other, and it
may thus create a supercluster by supercluster chain-reaction movement
that would add-up over the scale of the universe to what we see as Dark
Energy.

The reason I imagine it might be more effective at the
supercluster level than at the cluster or individual galaxy
level is because of the differing levels of overall density,
surface area, and light intensity of each of these body scales.

But the Universe is overall homogeneous. So in all directions, light
pressure is on average the same. I just don't see it being more
"interesting" than Dark Energy.

The light pressure from individual superclusters wouldn't have much
effect on the overall expansion of the universe it's just too big of a
place, just the most nearest neighbouring superclusters. It's much like
how much effect the Sun's light pressure has on objects near to it vs.
objects far from it.

Perhaps a good analog might be binary or multiple star systems, all of
the members of which are shooting photons off at each other and thus
pushing each other away. The closest pairs would have a large light
pressure effect on each other, while the furthest pairs would have
negligible. While they are both alive, the light pressure (and solar
winds) keeps them from spinning into each other, but once one is a dead
star (white dwarf through blackhole), they get much closer sometimes.


Yousuf Khan

Dear Yousuf Khan:

On Nov 27, 8:34*pm, Yousuf Khan wrote:
On 20/11/2011 10:00 PM, dlzc wrote:
On Nov 20, 7:08 pm, Yousuf *wrote:
The only thing that atoms would be considered macroscopic
next to are gamma rays. Not a lot of gamma rays get out of
the Sun's surface.

Don't need gamma rays for solar wind speeds. *Don't need
much more energetic than UV.

UV would be small enough to knock an electron off of the
electron cloud of an atom and turn it into an ion, but it's
not small enough to touch the nucleus of an atom.

*The system* has to conserve momentum. The UV is more than energetic
enough to release an electron. Which means the ion and electron are
net outbound after absorption.

and with large surface areas available.

Negligible mass (such that eV's worth of momentum is a
significant speed), finite size / cross section.

Sure, that gamma rays exert considerable pressure -- at the
Sun's core. *By the time those gamma rays make it out of
the Sun's surface, they've been all diluted to UV or less.

Which is all that is required.

The ions coming out of the Sun are hydrogen ions,

Mostly...

i.e. meaning that they're just single protons. Their single
orbital electrons have been blown away.

.... but is still in close proximity.

You really need gamma rays to affect hydrogen ions/protons.

Nope. Just need conservation of momentum.

UV might be enough to affect complex higher-order ions
like oxygen or carbon because they still have lots of
electrons orbiting them, even if they are ionized.

Sorry, you are being too literal-minded. We attack nucleii with
gammas only because we need to see things break.
http://scitation.aip.org/getabs/serv...ifs=yes&ref=no
.... CO2 lasers aren't that hot, messieur.

Won't affect solar wind speeds once they're out of the Sun.

Seems reasonable to me. *Even seems reasonable that
more than one interaction can occur to a given proton,
especially near the Sun. Regardless of my personal
fantasy, here is a good paper on "fast solar wind"...
http://arxiv.org/abs/1003.2299

The authors of the link seem to be looking at magnetic
cyclotron links for the speed function, not light pressure.

As I said, it really didn't speak to my personal fantasy.

You are going to have to think about what "light pressure"
derives from. *It should include the various scattering
mechanisms (which would apply here), and the absorption
mechanism (which should apply here).

Yup, all of those effects combine to create the overall light
pressure effect. But it necessarily requires an opaque body
to push against to get all of those effects working together.

I'm sorry, but "opaque" really just means "has charges
capable of interacting with photons". *Solar wind particles
have that.

It's more complex than that. Opaque means to me that an
object has multiple particles interacting with each other to
capture, absorb, re-emit, bounce, reflect, and block photons.

Which are all accomplished at the atomic level, not the supercluster
level.

Each of the particles in the multi-particle object will share
the photons with each other, and pass it around to each
other in complicated ways.

So opaque requires heating?

Single particles cannot interact with light this way.

They can and do all but "heating". Heating is how the excess momentum
is handled.

If you want to talk about the effects of diffraction (which could
elicit something like gravitation as an "equal and opposite
reaction"), that would be something else again. *More of a
"venturi effect"...

It tends to impart a spin on bodies rather than pushing or
pulling them completely.

Consider single body diffraction, say around Mercury.
*Outbound photons passing near Mercury are bent around it
on all sides. *No "spin".

That's mainly due to Mercury's gravity that the photons bend
around it.

Then an opaque, near mass-less disk. Light would also diffract around
it, simply because of geometry.

The photons aren't powerful enough to create any kind
of meaningful spin on massive Mercury,

I'm not talking about spin. Sorry I should not have tried to touch
your pet theory. YOu and I cannot see eye-to-eye on it.

David A. Smith