That's right. Only the component from the averaged starlight is negligible. That is to say there aren't enough photons produced by starts to come close to the numbers of photons that we see in the CMB. They are of such a small number that we just cannot see them. They don't exist (well below the one part in 10^4 threshhold for the anisotropy). Models have been done for the Big Bang universe asking how many microwave photons should come from stars and the number is about 10 or 15 orders of magnitude lower than the number we see in the CMB. So, try again. No interaction because not enough photons: it's as simple as that.

Hmm... is right. You should get out a bit more and actually become FAMILIAR with the paradigm you are railing against. That might allow you a bit more integrity.

If you mean by that the DENSITY of the IGM and the wavelength.

Not quite. Of course the IGM isn't static. No one said it is (it has to be at a finite temperature above zero). Your treatment of the mean free path is fine, but the conclusions you come to are utterly bogus. You are assuming that the only two things that are interacting are the background radiation and the IGM in this limitting case. This is one of the worst approximations you could make. The IGM may be diffuse, but its self-interactions are far more important than any equilbirium processes with the CMB.

Except the IGM's temperature need not be reasonant with the CMB since there are other thermal processes. The IGM is NOT in thermal equilbrium with the CMB.

Which is to say that if the universe is less massive, we get thermal equilibrium sooner in an expanding universe. This is a legitimate answer, but doesn't make sense in the context you put it in.

<font size=-1>[ This Message was edited by: AgoraBasta on 2002-11-03 12:02 ]</font>
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You've got some very exotic and rather unphysical ideas about "photons". A photon is a particle only in event of non-elastic interaction, otherwise there's no photon, only a wave. And guess what - you can't get inelastic photon/proton or photon/electron interaction at the energies we're talking of; so you can have just any arbitrary number of "photons" out there to interact with IGM particles elastically.
Same to you...
I also mean the general nature of IGM particles.
I suspected you'd get carried that very way. I really had to make it more clear. Mean free path is of little importance, it's the integral path that matters. Interactions are elastic, so they need not be point-like. There are two fields - first, the diffuse "light" field and second, the rarefied degenerate IGM plasma/gas. Particles' motion "weaves a dense web of paths" out of the degenerate IGM plasma, increasing effective cross-section by many orders of magnitude.
Furthermore, if you admit the presence of matter flows in the IGM induced by the ULF non-thermal background, then your argument about IGM self-interactions loses almost all of its validity (since the motion is mostly ordered at the scale considered).
In the 2-20 GHz band, they have a good chance to be resonant and in equilibrium. In other bands there are other processes, which may or may not be considered as thermal - that depends on the observation scale.
It makes a perfect sense to me - protons don't come without electrons out there somewhere. So you'd better count both those components in IGM scattering of background. And if there really are crowds of neutrinos - all bets are off altogether.

<font size=-1>[ This Message was edited by: AgoraBasta on 2002-11-03 19:01 ]</font>

This isn't right. The number density of photons is a well determined quantity no matter what the energy scale. Even if your photons are more wavelike than particlelike they are still photons and are still quantatized.
Except, I'm not railing against a paradigm, I'm railing against a model that is nonstandard.

You care to make a meaningful distinction between these two things at the densities we are talking about?

But NOT detectability of such interactions. With a finite detector size and a low density you are in a needle in a haystack problem. Sure, if I could observe everything in the universe I might see the annihilation and degradation of the background, but when it's as numerous as it is, there's really no measuring such an interaction. That's the end of it. You can read more about it here or here.

Cite? I don't believe this to be true at all.

You need to be more specific. Low-energy interactions will just not be observable.

Well, we have a lower and upper bound on the mass of neutrinos which end up contributing not a significant amount to the gravitational dynamics and kinematics of the universe at the present epoch. Earlier in history, though, they certainly did.

Personally I like the Multiverse model, with many universes being constantly formed and obliterated and in all stages of formation. Most having laws of physics that don't work and occasionally some that do.

For the number of photons to be conserved, it requires total decoupling from the medium. Once they are allowed to interact - they breed like bunnies, the faster the more wavelike they are. Feed a radio wave through a degenerate plasma - enjoy the broad output spectrum all the way till wavelengths about the plasma sample size. And, btw, photons' interaction with free charges is not quantized.
Even if you ensure that photons are pointlike, there's still gravity, which means that even then they do interact and secondary photons are produced since the original ones gravitate to plasma.
Who cares of their mass? Not me, here and now that is. Them neurinos carry kinetic energy, they are very likely to have magnetic moment; if so - they interact with photons as if the photons were a slow field and happily carry away energy in tiny chunks. That's as simple as could be.

And that's exactly what has occurred, to a great level of accuracy. We're talking about foreground emmission that is insignificant in comparison to the background. The decoupling models are very well understood, you can get them from any standard cosmology text.

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Who cares of their mass? Not me, here and now that is. Them neurinos carry kinetic energy, they are very likely to have magnetic moment; if so - they interact with photons as if the photons were a slow field and happily carry away energy in tiny chunks. That's as simple as could be.
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They're decoupled too. In fact, they decoupled earlier than the photons since they are weakly interacting. A magnetic moment only slightly complicates things.

Long and the short of it: at the energy scales of the present universe we just don't get cosmic photons, cosmic neutrinos, or really anything to interact except by means of gravity. The time of last scatter is a predictive thing that gives us nucleosynthesis abudnances we see and models for the expanding universe as well as various cosmological parameters which are measureable from large scale structure, small scale structure, and cosmological dynamics. I have the feeling you're tilting at windmills here. Do you read the literature on the subject?

According to The Five Ages of the Universe by Adams and Laughlin, if there was a Big Bang in the first place, before it was nothing but chaos. In other words, space-time is a roiling and fluctuating froth constantly changing geometry every few microseconds. Out of this chaotic foam erupt bubbles of microscopic space time. While most of them recollapse within the foam, at some point the conditions are just right for it to keep rapidly expanding, and adjacent points of space are racing in opposite directions. This newly formed bubble of space time then becomes seperated from the chaotic froth, and thus begins a new universe.

__________________
The only reason for time is so that everything doesn't happen at once.
--Albert Einstein

I'm arguing against the basic premises of those standard texts. Elastic scattering had never ceased, your standard texts mostly deal with deeply inelastic processes.
That's yet another standard misconception. Interaction by magnetic moment has huge cross-section and very low momentum exchange per event, i.e. neutrinos of non-zero magnetic moment may make for a nice magnetic fluid.

Elastic scattering doesn't effect the energy signal so we don't have to worry about it. Especially since we know everything has "frozen out" and fallen out of equilibrium.

I know that the magnetic moment has a lot of implications for early-type cosmology, but at densities we're dealing with and the cross sections we have there just isn't any go with that idea. Actually, reaction cross-sections are way to small to give us available mechanisms for changing the universe's energy structure. That is the main reason why the CMB has remained a Planck spectrum after all these years (temperature goes as one over the characteristic radius in relativistic cosmology).

Fairy tales. Elastic scattering sure does affect the photon "gas" energy. Essentially, it's the same mechanism that works toward thermodynamical equilibrium in any gas mixture. Rarefaction can't extend the photons free path too far, just as I pointed out earlier.

The photons are not in equilibrium with anything. I don't know how many more ways to say it, Agora. Read about it here

This is an aggressive misinformation!
An object suspended in radiative field always tries to get in some kind of equilibrium with that field. Such equilibrium has a thermal nature for wavelengths smaller than the object's size, whilst at greater wavelengths the object becomes more point-like and its motion becomes macroscopical and thermal equilibrium is lost starting from specific scale. The overall picture changes if the the object is a point-like charged free particle; absorption and re-emission becomes impossible and interaction turns elastic and generally aperiodic at broad frequency band. Those aperiodic accelerations deliver a secondary spectrum, and if the system of particles has enough time to interact with radiative field in an effectively closed system, the result contains an equilibrium spectrum, at least as a part of total spectrum.
If you want to have a relic spectrum, you have to ensure zero cross-section for elastic interactions with the free charged particles in your system. That's quite impossible at given IGM plasma density and CMB wavelengths.
Your " here " has got nothing to do with what I'm talking about. The author has got no understanding of possible models for global equilibrium; e.g. it doesn't even cross his mind that global equilibrium may be effectively constructed of a closed chain of local non-equilibria... That's plain stoopid!

why not ask when did your favorite god begin, if gods can have no beginning it not that much harder to think that quantum fuctuations can bubble off new big bangs without beginning or end, each having their own histories closed or open, if open more likly to create in turn their own new univeces

This is exactly how I would characterize your statements. You don't seem to realize that what's going on is coupling. If you are dealing with an expanding universe than you have a horizon size dictated by 1/H (in units of time) that has to be equal to the number density times the velocity times the cross section. Even if you don't have the expanding universe as you see it, you have to have some characteristic time in order for anything to come to equilibrium. If you do the simple, simple math you will see that the time it will take for the CMB radiation to get into equilibrium with the surroundings is so ridiculously huge if we have any structure whatsoever there is no way we can have equilibrium at this point. It's just simple relic physics and you think by using terms like "global" equilibrium you can get around it because you refuse to believe in a finite age or extent to the universe.

Well, I've got news for you, you simply don't have the observational evidence on your side. The universe is not infinite simply because we know the universe is evolving and we know that steady state doesn't have a leg to stand on. But we've gone through this all before, and you are likely to just be as stubborn as previously.

The only thing is, the author knows a thing or two about cosmic abundances. Steady staters require all the Helium to be produced in stellar nucleosynthesis. Do you? If not, where did the Helium come from?

(Hint: there's not enough energy in the universe for the 25% cosmic abundance of Helium to be made in stars).

I was too harsh in my previous post, and I'm sorry for that.
But I realize and explain exactly how that coupling is there, and you refuse to realize it.
I did it two posts above, though I got it expressed in distance rather than time.
Let's ask the audience, who's the most stubborn of us two. [img]/phpBB/images/smiles/icon_razz.gif[/img]
No, I don't. I think that everything between bare protons and heaviest elements is produced with a certain weight distribution when matter accelerated in the magnetic fields in the voids smashes into accreted material structures. Stars then work on turning it all into dead iron and further. It will take some effort to quantify the process, so I could use some help from an accelerator specialist.
We don't have a clear idea of energy density in frequency bands below those we managed to measure. Most of the energy may be lurking exactly there.

[img]/phpBB/images/smiles/icon_eek.gif[/img]
Interstellar magnetic fields cause fusion? This would require a magnetic field of over 10e13 gauss.
(Solve the following equation for B:
qvB=q^2/(4*pi*epsilon0*r^2)
)

Good luck finding that field. It shouldn't be that difficult, as with that magnetic field, it will be a mighty impressive Zeeman effect.

<font size=-1>[ This Message was edited by: Zathras on 2002-11-06 18:17 ]</font>

This smacks of convenient theorizing. You're basically saying, "I can't measure the energy yet that's why I haven't seen it. There couldn't possibly be something wrong with my theory." And you accuse me of not being open-minded?

JS Princeton:

Thank you! Thank you!

ljbrs [img]/phpBB/images/smiles/icon_frown.gif[/img] [img]/phpBB/images/smiles/icon_smile.gif[/img] [img]/phpBB/images/smiles/icon_biggrin.gif[/img]

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