The moronic trolling bigot Chris L Peterson [email protected]

On Sun, 26 Jul 2009 12:45:36 +1000, "Peter Webb"
wrote:

This raises a couple of questions for me ....

1. The equations for black body radiation do not involve the physical nature
of the radiating body.

Don't they? The equations rely on the emissivity of a material, which is
surely a parameter that describes its physical nature. A true black body
has an emissivity of one. Anything less and the equations become
approximations, or otherwise need modification. So what do you have if
dark matter has an emissivity of zero?

As an additional complication, can DM have a temperature above 0K? I
don't know the answer to that, but if it doesn't absorb any EM, how is
energy transferred to it? By definition, a black body absorbs 100% of
the EM that hits it. Nearly by definition, DM absorbs none.

Are you claiming that a macroscopic body composed of
DM would not emit radiation as per the black body equations?

I think that describes the commonly accepted viewpoint, where DM is
assumed to consist of non-baryonic particles. There's certainly no
evidence

2. On the other side ... I have always just accepted bb radiation as a fact
of hot bodies. Now I have to think about this. I assume that the coupling
between heat and EM derived from the existence of charged particles
(electrons and atomic nuclei) in the radiating body which ultimately accept
EM waves, turn them into electric potential (physical separation of positive
and negative charges) which re-appears as thermal energy, and vice versa.
Note that this is all mediated by charged particles being accelerated by the
E component of the EM wave, or in reverse the acceleration of charged
particles causing EM waves. Thinking about it, how does this work for
neutron starts, which have no charged particles? They absorb and emit bb
radiation, right? If so, what is the physical mechanism for the exchange of
energy between an EM wave and uncharged matter?

I'm not sure of the answer here, but my first thought is that the
mechanism depends on force carriers, but is not necessarily limited to
simple charged particles.
_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

"Chris L Peterson" wrote in message
...
On Sun, 26 Jul 2009 12:45:36 +1000, "Peter Webb"
wrote:

This raises a couple of questions for me ....

1. The equations for black body radiation do not involve the physical
nature
of the radiating body.

Don't they? The equations rely on the emissivity of a material, which is
surely a parameter that describes its physical nature. A true black body
has an emissivity of one. Anything less and the equations become
approximations, or otherwise need modification. So what do you have if
dark matter has an emissivity of zero?


Emissitivity doesn't affect black-body radiation. What it does affect is how
much of the EM energy that is incident upon it is absorbed as heat.

Pick a simple example - glass. Transparent, emissivity zero. Heat it up to
5000K and it still glows white hot. Similar deal for the gasses in
fluorescent tubes.

Indeed, a completely white object - reflects all light - still glows only
red hot if heated in a dark oven.


As an additional complication, can DM have a temperature above 0K? I
don't know the answer to that, but if it doesn't absorb any EM, how is
energy transferred to it? By definition, a black body absorbs 100% of
the EM that hits it. Nearly by definition, DM absorbs none.


Well, if you are talking about individual particles in space, then one
observer's temperature is just another observer's relative kinetic energy.

If DM consists of more than one particle bound together, then it can
certainly have a temperature, being the difference between the kinetic
energy of the object as a whole and the kinetic energy of the constituent
particles.


Are you claiming that a macroscopic body composed of
DM would not emit radiation as per the black body equations?

I think that describes the commonly accepted viewpoint, where DM is
assumed to consist of non-baryonic particles. There's certainly no
evidence



Why does "non-baryonic" matter? Is there something in the formulation of BB
radiation that is somehow tied to baryons?


2. On the other side ... I have always just accepted bb radiation as a
fact
of hot bodies. Now I have to think about this. I assume that the coupling
between heat and EM derived from the existence of charged particles
(electrons and atomic nuclei) in the radiating body which ultimately
accept
EM waves, turn them into electric potential (physical separation of
positive
and negative charges) which re-appears as thermal energy, and vice versa.
Note that this is all mediated by charged particles being accelerated by
the
E component of the EM wave, or in reverse the acceleration of charged
particles causing EM waves. Thinking about it, how does this work for
neutron starts, which have no charged particles? They absorb and emit bb
radiation, right? If so, what is the physical mechanism for the exchange
of
energy between an EM wave and uncharged matter?

I'm not sure of the answer here, but my first thought is that the
mechanism depends on force carriers, but is not necessarily limited to
simple charged particles.

I suspect that DM woule emit BB radiation if it was hot, the same as
everything else does. Its just that (if it exists) is consists of individual
particles - which cannot have a temperature in the traditional sense, or its
all floating around in space and very cold, or it does emit BB radiation and
we can observe it, its just that we incorrectly ascribe the radiation to
normal matter.

Hell, for all we really know, the Sun could be 10% DM, and 10% of the BB
radiation we see from the Sun could be caused by DM.

As to the nature of the physical coupling between heat energy and BB
radiation ... maybe someone else here can enlighten us.



_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On Sun, 26 Jul 2009 15:14:49 +1000, "Peter Webb"
wrote:

Emissitivity doesn't affect black-body radiation. What it does affect is how
much of the EM energy that is incident upon it is absorbed as heat.

But emissivity does affect black body radiation. It is the ratio of
energy emitted to energy absorbed, and provides that link to physical
materials you were questioning.

Pick a simple example - glass. Transparent, emissivity zero. Heat it up to
5000K and it still glows white hot. Similar deal for the gasses in
fluorescent tubes.

Glass has a very high emissivity- over 0.9. If you want a material with
low emissivity, you have to look to something very reflective. Of
course, if you can manage to heat such a material up, it will still emit
radiation. But it becomes very hard to actually heat it up.

Gases don't normally show black body radiation unless they are under
very high pressure- much higher than found in fluorescent tubes. The
light you see there is coming from atomic emission lines, which are also
broadened by high temperatures.

If you had a material with an emissivity of zero, it would not convert
any absorbed radiation into black body radiation.

Indeed, a completely white object - reflects all light - still glows only
red hot if heated in a dark oven.

Only because there is no such thing as a material that reflects all the
radiation striking it, over the range of input wavelengths your dark
oven produces.

Well, if you are talking about individual particles in space, then one
observer's temperature is just another observer's relative kinetic energy.

Yes, but particles are not black body radiators. For that, you need the
object size to exceed the wavelength of the emitted radiation. For cold
bodies, this can become very large. The CMB is 1.9mm wavelength, so you
won't see it emitted by dust.


If DM consists of more than one particle bound together, then it can
certainly have a temperature, being the difference between the kinetic
energy of the object as a whole and the kinetic energy of the constituent
particles.

DM is assumed to be cold, in part because it can't absorb EM. So what
mechanism is left to heat it up? Of course, if it somehow carried heat,
what mechanism would allow it to cool down? Since it doesn't interact
with EM, it shouldn't be able to radiate, either. Maybe it's hot and we
can't tell, because it doesn't radiate.

Of course, even if it did radiate, we wouldn't see if unless it was in a
form that was large compared to the long wavelength of cold radiation-
millimeters.

Why does "non-baryonic" matter? Is there something in the formulation of BB
radiation that is somehow tied to baryons?

Yes. Black body radiation is observed and described for a class of
particles. Electrons, neutrinos, and other non-baryonic particles do not
behave the same as baryonic material. Assuming (as most do) that DM is
made up of some type of non-baryonic material, there is no reason to
expect it to interact with EM the same way baryonic matter does.
_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On Jul 26, 4:25*pm, Chris L Peterson wrote:
On Sun, 26 Jul 2009 15:14:49 +1000, "Peter Webb"

wrote:
Emissitivity doesn't affect black-body radiation. What it does affect is how
much of the EM energy that is incident upon it is absorbed as heat.

But emissivity does affect black body radiation. It is the ratio of
energy emitted to energy absorbed, and provides that link to physical
materials you were questioning.

Pick a simple example - glass. Transparent, emissivity zero. Heat it up to
5000K and it still glows white hot. Similar deal for the gasses in
fluorescent tubes.

Glass has a very high emissivity- over 0.9. If you want a material with
low emissivity, you have to look to something very reflective. Of
course, if you can manage to heat such a material up, it will still emit
radiation. But it becomes very hard to actually heat it up.

Gases don't normally show black body radiation unless they are under
very high pressure- much higher than found in fluorescent tubes. The
light you see there is coming from atomic emission lines, which are also
broadened by high temperatures.

If you had a material with an emissivity of zero, it would not convert
any absorbed radiation into black body radiation.

Indeed, a completely white object - reflects all light - still glows only
red hot if heated in a dark oven.

Only because there is no such thing as a material that reflects all the
radiation striking it, over the range of input wavelengths your dark
oven produces.

Well, if you are talking about individual particles in space, then one
observer's temperature is just another observer's relative kinetic energy.

Yes, but particles are not black body radiators. For that, you need the
object size to exceed the wavelength of the emitted radiation. For cold
bodies, this can become very large. The CMB is 1.9mm wavelength, so you
won't see it emitted by dust.

If DM consists of more than one particle bound together, then it can
certainly have a temperature, being the difference between the kinetic
energy of the object as a whole and the kinetic energy of the constituent
particles.

DM is assumed to be cold, in part because it can't absorb EM. So what
mechanism is left to heat it up? Of course, if it somehow carried heat,
what mechanism would allow it to cool down? Since it doesn't interact
with EM, it shouldn't be able to radiate, either. Maybe it's hot and we
can't tell, because it doesn't radiate.

Of course, even if it did radiate, we wouldn't see if unless it was in a
form that was large compared to the long wavelength of cold radiation-
millimeters.

Why does "non-baryonic" matter? Is there something in the formulation of BB
radiation that is somehow tied to baryons?

Yes. Black body radiation is observed and described for a class of
particles. Electrons, neutrinos, and other non-baryonic particles do not
behave the same as baryonic material. Assuming (as most do) that DM is
made up of some type of non-baryonic material, there is no reason to
expect it to interact with EM the same way baryonic matter does.
_________________________________________________

Chris L Peterson
Cloudbait Observatoryhttp://www.cloudbait.com

It must be a talent among empiricists to talk about nothing as if it
is something,the guy who wrote that 'dark' this or that is merely a
symptom of a problem will e drowned out by people who truly believe
whatever their imaginations tells them.So where did all this problem
start of filling space up with hypothetical junk -

"The fictitious matter which is imagined as filling the whole of space
is of no use for explaining the phenomena of Nature, since the motions
of the planets and comets are better explained without it, by means of
gravity; and it has never yet been explained how this matter accounts
for gravity. The only thing which matter of this sort could do, would
be to interfere with and slow down the motions of those large
celestial bodies, and weaken the order of Nature; and in the
microscopic pores of bodies, it would put a stop to the vibrations of
their parts which their heat and all their active force consists in.
Further, since matter of this sort is not only completely useless, but
would actually interfere with the operations of Nature, and
weaken them, there is no solid reason why we should believe in any
such matter at all. Consequently, it is to be utterly rejected."
Optics 1704

Oh ,wait a minute,didn't they dump aether on Newton as 'absolute
space' -

"In order to be able to look upon the rotation of the system, at least
formally, as something real, Newton objectivises space. Since he
classes his absolute space together with real things, for him rotation
relative to an absolute space is also something real. Newton might no
less well have called his absolute space ``Ether'';" Albert 1920

So,Newton rejects an aether,medium or whatever 'dark' thing you call
it,Albert dumps aether back on Newton as 'absolute space'and rejects
someting Isaac "utterly rejected" in the first place.Like squirrels
running around a celestial sphere cage,nobody ever wants to get off
and look at the cage itself,that 'inertial space' is simply the
astrological framework on which Newton built his agenda,it is not a
thing in itself but was supposed to act as a common framework for
absolute/relative space -

"For to the earth planetary motions appear sometimes direct,
sometimes stationary, nay, and sometimes retrograde. But from the sun
they are always seen direct.." Newton

I can't say that you are poor lost souls who can't find your way out
of the forest Newton built for you as you seem content to believe
whatever you need,if you were talking relativity space would be
empty,if the 'big bang' it is full of something but ultimately you ae
talking about nothing and giving this 'nothing' a tremendous amount of
details and properties.

Again,anyone care to get off the treadmill of aether/dark matter and
allow astronomy to emerge again will be rewarded a thousand times
over.