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kzb
2012-May-11, 03:40 PM
If the cosmic microwave structure we can see is the highly-redshifted plasma at the time the universe first became transparent, how come it is not beyond our light horizon?

I ask this because apparently there should be galaxies beyond our light horizon -because of inflation. Since all galaxies formed after the plasma condensed into more normal matter, all galaxies should be in the foreground of the CMB, and none behind it.

So are there in fact galaxies beyond the horizon?

antoniseb
2012-May-11, 03:56 PM
That is a question whose answer beautifully shows some ideas often misunderstood by people who think of the Big Bang as an explosion into already existing empty space. Thanks.

Let me try to give a hand-waving answer. If you want detail, someone will come along soon with detail:

The light from the CMB is coming from matter that later turned into galaxies, but we see that matter as it was then.
In 100 years, we'll be seeing CMB coming from matter even further away (not much further, but I'm illustrating a point). The matter we saw today will be transparent, and further along in the process of condensing into galaxies that we will never see, because the light from that matter has already passed us.

If you could somehow see that space as it looks 13.7 billion years after the big bang, it would have galaxies of about the same maturity as what we see locally, but we'll never see them form. We will only see galaxies closer than that.

Hopefully that helps, if not ask a more detailed question to clarify what you don't see yet.

WayneFrancis
2012-May-11, 04:06 PM
The CMBR was emitted at every point in space. We just continually see a CMBR that is further and further away and as we see CMBR that originated further away from us that CMBR will be cooler but the CMBR is always more from a specific point in time rather then a specific point in space.

Now there are galaxies that are beyond our light horizon but this is something different. These galaxies started out further away then any CMBR light we can ever observe. They did form after the CMBR but since they where further away their photons will never reach us. We'll never see past the CMBR electromagnetically.

The way I think of it is the CMBR represents a soft boundary. Things beyond it in distance and after it in time are outside of our light cone and, if expansion keeps increasing, will always stay that way. Eventually the CMBR will be red shifted to near nothing.

So yes we believe there are in fact galaxies beyond our visible horizon but keep in mind that they formed after the CMBR and because of expansion we'll never be able to see them even if we tried.

I'll see if I can put together some quick diagrams

grapes
2012-May-11, 04:13 PM
There could be, we haven't seen them. :)

The CMB radiation pervaded space, it wasn't just unleashed at the boundary.

http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation

Cougar
2012-May-11, 05:48 PM
If the cosmic microwave structure we can see is the highly-redshifted plasma at the time the universe first became transparent, how come it is not beyond our light horizon? ... Since all galaxies formed after the plasma condensed into more normal matter, all galaxies should be in the foreground of the CMB, and none behind it.

Thing is, we're not seeing all of the CMB. If Guth is right, most of "our" universe is outside our light horizon, and all of that external part is also filled with CMB... and galaxies.

Jeff Root
2012-May-11, 08:27 PM
The light from the CMB is coming from matter that later
turned into galaxies, but we see that matter as it was then.

In 100 years, we'll be seeing CMB coming from matter even
further away. The matter we saw today will be transparent,
and further along in the process of condensing into galaxies
that we will never see, because the light from that matter
has already passed us.
I think you got that last part backwards.

Because of the increasing distance due to continuing
expansion, and even more, because of the acceleration of
that expansion, we will likely never see the galaxies which
condensed from the gas which gave off the CMB that we
observe now. But that light is still enroute. It hasn't
reached here yet. It hasn't already passed us.

-- Jeff, in Minneapolis

antoniseb
2012-May-11, 08:55 PM
I think you got that last part backwards.

Because of the increasing distance due to continuing
expansion, and even more, because of the acceleration of
that expansion, we will likely never see the galaxies which
condensed from the gas which gave off the CMB that we
observe now. But that light is still enroute. It hasn't
reached here yet. It hasn't already passed us.

Here's the problem... light from the CMB we see now is coming from material that is getting further from us at 1100 times the speed of light. That material will/did eventually turn into galaxies, but those galaxies are forever beyond the limit of what we will ever see...

That being said, you are right that what I wrote miscommunicated, so thanks Jeff. Light from our side of the CMB wall comes from galaxies that continue to exist and do keep sending light that we can see.

kzb
2012-May-12, 04:33 PM
Thanks for the replies everyone. Not sure if it has got me anywhere yet, I'll have to sleep on it.

kzb
2012-May-14, 12:39 PM
I can understand that the CMB wall is further away than we presently observe it to be, and that "really" some galaxies now exist that we have not seen yet. Also, these new galaxies are, in current time, situated beyond where we now see the wall.

Is this what is meant by the phrase "beyond our light horizon" ?

It seems to me though, that eventually we must see these galaxies (the wall will have moved further out by then). It also seems to me we can never observe a galaxy to be beyond the wall. All galaxies must be in the foreground to the wall at any given epoch.

Quadrazar
2012-May-24, 12:33 PM
When you look at the moon it you see it like it was about 1.5 seconds ago (because te light from the moon as to get from the moon to earth ...)
If you where looking at the sun, you see it as it was 500 seconds. (same reason the light has to reach us ...)
Looking at proxima centauri you see proxima centauri like it was 4 years ago.
Looking at some galaxy a "X lightyears" away, you see it ,be it a little more red and a little slower, 1like it was"X years" ago

Now ...
looking at te CBR you see it the universe as it was at the time when it expanded just enough for light to start shining true. (the light redshifted so far only radiowaves remain, and we observe it realy slow)

If you are hoping to see anyting beond the CBR (say 10 lightyears beond it), the light must been emmitted 10 years before the light we see in the CBR. But at that time light couldn't exist in the universe, it was to crowdy. So with the absence of emmited light, observations becomes rather dificult. :(
(you could wait for the CMBR to move further away, it would take A LOT longer then ten years before it retracted that far)



STRUCTURE

I saw you mentioned "stucture" in the tread title... . That term puzzled me for a long time. That CMB map looked to me afterall like some blue random noise. Reacently I discovered what this 'structure' is by whatching a Youtube video. I don't have the source anymore so I try to repeat it from memory:

When you got onto the ocean (on a ship) you will see big waves, turns out that these waves are regulary spaced, (they have a ceratain wavelength). When you you observe the waves closer you can see smaler waves riding on top of the big waves (these smaler waves also have a smaler wavelenght). If you had a device that counted the waves & their waveleght you coul plot these wave in a graph you would get somthing like this:



/|\
|
| ##
| ####
| # ####
| ### ######
| # ##### ########## ###
| ########## ### ### #######################
| ############################################
+----------------------------------------------->
wavelength



The two bumps (spikes) represent the big waves and smaller waves. From this graph we can conclude that this ocean has a sertain structure (the big wave - litlle wave structure).

A simular graph can be created for the "blobs" on CMB map and it turns out that there are also spikes in that graph.. This means that the CMB has a certain structure. (I beleive it is called "the large scale structure" of the universe).


Remarks
1 the further an object is the longer the lightwave travels trough expanding space.
* Moving trough expanding space stretches the waveleght. So light that started it's journey as blue light could arive as green light.

ultra violet -> blue -> green -> red -> infrared --> radiowave

* The the expanding of space, has a second consequence. The light has from distant sources has to travel an evergrowing distance to reach us.
so if two pulses (seperated by 1 second in time) are transmitted towards us over a vast cosmic distance.The second pulse has to travel a longer distance to reach us then the first pulse. When we observe the pulses they will be seperated by more then a second, this gives the impression that time over there runs slower.

kzb
2012-May-24, 05:34 PM
Thanks Quadrazar. At the moment I can't understand the following:

The red-shifted plasma wall that we currently observe is in the act of forming galaxies in its wake. The plasma at the wall is currently being observed, and in the (our) future that same matter will have formed protogalaxies.

So will we eventually observe these new protogalaxies? It seems to me we should, because we currently see the matter that they are made from, even though it is receding from us at many times the speed of light.

Also, this is just a continuation of a process that has been going on for billions of years. If we were to go back say 8 billion years into the past, presumably the red shifted plasma wall would be closer, and many galaxies that we can currently observe would not be visible, because they have not yet formed (from our perspective). Yet here we are 8 bn years on, observing galaxies that would have been behind the (current) plasma wall position then.

So is it really true that any galaxy can continue to be beyond our horizon indefinitely, or that any currently-observable galaxy can go beyond our horizon?

Jeff Root
2012-May-24, 07:01 PM
The red-shifted plasma wall that we currently observe
is in the act of forming galaxies in its wake. The plasma
at the wall is currently being observed, and in the (our)
future that same matter will have formed protogalaxies.

So will we eventually observe these new protogalaxies?
It seems to me we should, because we currently see the
matter that they are made from, even though it is
receding from us at many times the speed of light.
Probably not.

After the cosmic background radiation was emitted, the
matter in the Universe stopped emitting light for quite
a long time. When it finally resumed emitting, it was
from the surfaces of stars, which have a much, much,
much smaller surface area than the matter which emitted
the CBR. So it is possible for current-day radiotelescopes
to detect the CBR but not the first light from the first
stars. The distance is too great. We don't get enough
light from them to detect them. Future, more sensitive
telescopes should be able to detect the light from the
first stars, but if those telescopes were used a couple
of billion years from now, they probably would not be
sensitive enough to detect the even weaker first light
from the even more distant first stars in the galaxies
which formed from the matter that we currently see by
the cosmic background radiation it emitted.



Also, this is just a continuation of a process that has
been going on for billions of years. If we were to go
back say 8 billion years into the past, presumably the
red shifted plasma wall would be closer, and many
galaxies that we can currently observe would not be
visible, because they have not yet formed (from our
perspective). Yet here we are 8 bn years on, observing
galaxies that would have been behind the (current)
plasma wall position then.

So is it really true that any galaxy can continue to be
beyond our horizon indefinitely, or that any currently-
observable galaxy can go beyond our horizon?
I think both are true, given the acceleration of the
expansion. But someone else can answer this better
than I can. I mainly wanted to reply to the first bit.

-- Jeff, in Minneapolis

Jeff Root
2012-May-24, 07:17 PM
If you are hoping to see anything beond the CBR
(say 10 lightyears beond it), the light must have
been emitted 10 years before the light we see in
the CBR. But at that time light couldn't exist in the
universe, it was too crowdy.
The light certainly could and did exist in abundance.
The problem wasn't that the matter was too crowded,
but that it was too hot. It was so hot that it was
constantly emitting light. And absorbing light. When
it cooled enough to stop emitting light, it also cooled
enough to stop absorbing, so the Universe became
transparent, and the light which had been bouncing
back and forth between electrons began zooming
along without being intercepted.

Ten years might make a difference, but 100 years or
so is more like the scale of the transition from opaque
Universe to transparent.

-- Jeff, in Minneapolis

noncryptic
2012-May-24, 08:45 PM
Extrapolating into the distant future: due to expansion the Andromeda galaxy is beyond our light horizon - but there still is be a CMB to be seen.

WayneFrancis
2012-May-25, 01:24 AM
Extrapolating into the distant future: due to expansion the Andromeda galaxy is beyond our light horizon - but there still is be a CMB to be seen.
AIUI this isn't correct.

Andromeda will merge with the Milky Way long before expansion will rip apart our local cluster. At that point the CMBR would only be very cold and disperse so not sure how you'd see it. The universe has only increased in size by 1,000 since the CMBR was emitted. The point where galaxies in our local cluster would be lost beyond our light horizon indicates a huge increase in the rate of expansion and many orders of magnitude larger universe. Long before that point in time we will have stopped receiving CMBR photons. Because of the way expansion works we will have a point in time where CMBR will no longer be. For every point in space CMBR photons will have passed and before that point they'll be almost infinitely red shifted.

This is similar to the fact that if something falls into a black hole there really isn't a red shifted image of the object frozen just at the event horizon. There is a last photon emitted even before the object reaches the event horizon.

Quadrazar
2012-May-25, 07:02 AM
I can understand that the CMB wall is further away than we presently observe it to be, and that "really" some galaxies now exist that we have not seen yet. Also, these new galaxies are, in current time, situated beyond where we now see the wall.

Is this what is meant by the phrase "beyond our light horizon" ?


This might help understanding the light-horizon.

let's represent space by a rubber strip, say meter long. At one end of the strip there is an observer (the finish) and at the other end there is an Emittor (the start). It can help to imagine some subdevisions on to the rubber band. I'll asume there are 10 devisions on the rubber strip. We also need a measuring rod (1 meter long) that is solid (not expanding)

now we are going to do two things the start an experiment:
1. start stretching the rubber strip to represent expanding space.
2. place a little motorized car at the start, and let it drive towards the finish (to emulate a photon).

One thing we clearly notice is:
the speed of the little car is dictated by it's weels on the rubber, so it will take longer and longer to cross one of the 10 subdevisions on the expanding rubber strip.

Now for the light horizon part:
We gonna look at the time the cart crosses its first subdevision after it started, and measure the remaining nine subdevisions with the non stretching measuring rod. There are 3 possabilities:
A. the nine remaining devisions are smaller than one meter measuringrod. (the car will eventualy reach us)
B. the nine remaining devisions are longer than measuring rod (the car will not reach us, because in the same amout of time since te start the 9 remaining divisions should expand the same as the original ten)
C. the nine remaining devisions are equal to the 1-meter rod (the car will not reach us)

The outcome (A,B or C) is dependent on the amount of stretching aplied to the rubber. But a similar results can be achieved by a constant stretching, and by moving the startpoint closer or further away from the finish.
In this scenario a startpoint that an A-like outcome is whitin the horizon. Starting points that have a B-like result are on beyond the horizon. C-like startingpoints, are close to the horizon but behind it.


So the CMBR is whitin our light horizon. If it where outside it the CMBR photons (radiowaves) never would have got here.





At the moment I can't understand the following:

The red-shifted plasma wall that we currently observe is in the act of forming galaxies in its wake. The plasma at the wall is currently being observed, and in the (our) future that same matter will have formed protogalaxies.


the plasma was all over the unverse, actualy it was the universe. persumably it went true the same stages everywhere. Cooling down and clumping together. No mather where you would go in the universe (if you're clock said 13.5y after bigbang), you should see the same things around you, local galaxies, redshifted distant galaxies and a shell of CMBR. So the places we recieve CMBR from today would have the same skyfeatures like us. they would see our location as it was when it was in that plasma state X years after the bigbang.



So will we eventually observe these new protogalaxies? It seems to me we should, because we currently see the matter that they are made from, even though it is receding from us at many times the speed of light.


If we simplify things a bit and asume a constant expantion rate for the universe, then the Light horizon is at a fixed distance. Due to the expansion, things get pushed beyond the horizon. (to go back to the rubber strip, start and finish are moving away from eachoter, but expansion rate keeps the same, so eventualy the start wil go beyond the horizon point).

To give an anwer to your question, it's safe to presume that the matter that emmited the CMBR we currently observe went trought all stages of galaxy formations (including protogalaxies). The question then becomes: "by the time they went trough their protogalaxy-face, how far did they drifted (expanded) away from us.". In other words
did their protogalaxy-fase took place inside or outside our light horizon? I don't have the data to answer that question.


There is one remark I like to make. I the distant future, when galaxies are pushed beyond the Light horizon they will be so redshifted, they are only to be seen in as radiowaves, (due to the huge redshift). And by then they wil have such a big cosmic time dialton that their final departure moments can be viewed in "hyper slowmotion" from our point of view.

kzb
2012-May-25, 11:44 AM
It's all a bit of a headache isn't it !?

Take Quadrazars' closing statement:
by then they wil have such a big cosmic time dialton that their final departure moments can be viewed in "hyper slowmotion" from our point of view.

This was also Wayne Francis' opinion
This is similar to the fact that if something falls into a black hole there really isn't a red shifted image of the object frozen just at the event horizon. There is a last photon emitted even before the object reaches the event horizon.

In other words, going beyond our light horizon is akin to falling into a black hole event horizon. From our perspective, the infalling object slows down as it approaches the horizon. We don't actually observe the thing crossing the EH, we just see it wink out of existence with its last photon.

So the plasma we currently observe will/has produced galaxies, but bearing in mind we we can see that matter now (as plasma) can it ever be observed to go beyond our horizon?

caveman1917
2012-May-25, 08:07 PM
So the plasma we currently observe will/has produced galaxies, but bearing in mind we we can see that matter now (as plasma) can it ever be observed to go beyond our horizon?

As stated before, no. If the horizon is defined as the furthest we can observe anything, then we can't observe anything crossing it, by definition.

Cougar
2012-May-25, 08:47 PM
If you are hoping to see anyting beond the CBR (say 10 lightyears beond it), the light must been emmitted 10 years before the light we see in the CBR. But at that time light couldn't exist in the universe, it was to crowdy. So with the absence of emmited light, observations becomes rather dificult. :(

As Jeff mentioned, this is incorrect, though I'm not sure his explanation was particularly enlightening. There was plenty of light even at one second after the beginning of the expansion. In fact, there were about a billion photons for every matter particle - due to the wholesale annihilation of matter and antimatter particles. Fortunately for us, there was a very slight asymmetry in the creation of matter and antimatter, resulting in a single matter particle after a billion annihilations.

Anyway, before the time of recombination, which is when the CMB was "set free," the Universe was very dense, and it was very hot, but all the time expanding and cooling. The matter was made up of hydrogen nuclei, helium nuclei, and electrons, and that's about it. It was too hot for the nuclei to capture and hold onto the electrons to make neutral atoms. When separate, these nuclei and electrons are charged particles, and charged particles interact with photons. Due to the high density, the photons could not travel far before running into another charged particle. It must have been maddening for the photons :rolleyes: since they couldn't get going anywhere before running into another charged particle.

Finally, after about 380,000 years after the beginning of the expansion, the whole universe, which was in thermal equilibrium, cooled enough to allow the nuclei to capture and hold onto the electrons, making neutral atoms. Neutral atoms are not charged. For the most part, photons rarely interact with uncharged neutral atoms. So to a photon, it was like the Universe suddenly became transparent, and the photon was free to propagate without hindrance. Hence the CMB.

Cougar
2012-May-25, 08:58 PM
So the plasma we currently observe....

If you're talking about the CMB, the CMB is not plasma. It is microwave photons.

noncryptic
2012-May-26, 12:00 PM
As stated before, no. If the horizon is defined as the furthest we can observe anything, then we can't observe anything crossing it, by definition.

I understand it can not be observed after it has crossed the light horizon, but can it not be observed to disappear out of view?

I can think of practical reasons why it can't: the light-horizon is behind the CMB and the CMB is opaque so we can't see what happens behind it. Also it would be red-shifted so much we'd have a hard time detecting it.
But i can't think of a fundamental reason why it can not be observed to disappear out of view.



If you're talking about the CMB, the CMB is not plasma. It is microwave photons.

Likewise a star that we see is not a star, but is the photons emitted by the star.

Otoh one might argue there is a bit of a conceptual difference between "CMB" and "CMBR".

Cougar
2012-May-26, 01:10 PM
Likewise a star that we see is not a star, but is the photons emitted by the star.

I see your point, but I think you're bending too far. Certainly the star that we see is a star. If you want to talk about the light from the star, then you specify "the light from the star." Otherwise, you're talking about the star itself.


Otoh one might argue there is a bit of a conceptual difference between "CMB" and "CMBR".

In this case, the CMB is essentially short for the CMBR. The microwave background. This is different than the baryonic state of the universe prior to recombination (hot plasma). In fact, recombination is the point where most of the plasma becomes not-plasma, which is what allows the CMB to propagate.

noncryptic
2012-May-26, 02:32 PM
In fact, recombination is the point where most of the plasma becomes not-plasma, which is what allows the CMB to propagate.

Doesn't that mean most of the so-called plasma that is created on Earth is for the most part not really plasma?
Yet scientists seem comfortable calling it plasma.

caveman1917
2012-May-26, 05:05 PM
I understand it can not be observed after it has crossed the light horizon, but can it not be observed to disappear out of view?

How would you define "observed to disappear out of view"?

Jeff Root
2012-May-26, 05:07 PM
Likewise a star that we see is not a star, but is the
photons emitted by the star.
I see your point, but I think you're bending too far.
Certainly the star that we see is a star. If you want
to talk about the light from the star, then you specify
"the light from the star." Otherwise, you're talking
about the star itself.
Noncryptic's point is correct. When kzb said
"So the plasma we currently observe will/has produced
galaxies...." he was NOT talking about the CMB, he
was talking about the plasma which emitted the CMB.

-- Jeff, in Minneapolis

Jeff Root
2012-May-26, 05:17 PM
How would you define "observed to disappear out of view"?
Writing for noncryptic, since what he meant was
obvious the first time he wrote it: The plasma, or stars
and galaxies which develop from that plasma, are within
our horizon, and so are visible, and later are not visible,
because they are beyond our horizon. That's what the
word "disappear" means, to be visible at one time and
not be be visible at a later time.

-- Jeff, in Minneapolis

caveman1917
2012-May-26, 05:24 PM
Writing for noncryptic, since what he meant was
obvious the first time he wrote it: The plasma, or stars
and galaxies which develop from that plasma, are within
our horizon, and so are visible, and later are not visible,
because they are beyond our horizon. That's what the
word "disappear" means, to be visible at one time and
not be be visible at a later time.

-- Jeff, in Minneapolis

Yes that's what i first thought, however since the original question was


In other words, going beyond our light horizon is akin to falling into a black hole event horizon. From our perspective, the infalling object slows down as it approaches the horizon. We don't actually observe the thing crossing the EH, we just see it wink out of existence with its last photon.

So the plasma we currently observe will/has produced galaxies, but bearing in mind we we can see that matter now (as plasma) can it ever be observed to go beyond our horizon?

it already acknowledged the "wink out of existence with its last photon", so what was meant must have been something else, ergo my question.

But i now see that apparently noncryptic took the place of kzb for that question, so i'm not sure what exactly is meant.

Cougar
2012-May-27, 01:09 PM
Noncryptic's point is correct. When kzb said
"So the plasma we currently observe will/has produced
galaxies...." he was NOT talking about the CMB, he
was talking about the plasma which emitted the CMB.

Then he should not have said that "we currently observe" it, which was my point.

Anytime someone overuses the term "plasma," I tend to watch out for accompanying misconceptions, since:



Plasma cosmology is a term describing a loose set of non-standard ideas about cosmology. Its central idea is that the dynamics of ionized gases (or plasmas) plays a decisive role in the physics of the universe at scales larger than the Solar system. Today, almost all cosmologists and astronomers are dismissive of the idea. - wiki (http://en.wikipedia.org/wiki/Plasma_cosmology)

antoniseb
2012-May-27, 01:38 PM
... Anytime someone overuses the term "plasma," I tend to watch out for accompanying misconceptions...
I also watch out when the term comes up, but we can't just not use it. I suppose we can say that until 380,000 years after the big bang, the universe was filled with thermally ionized Hydrogen and Helium gas, and not use the word plasma... but I feel like that is losing a semantic battle in some way.

noncryptic
2012-May-27, 05:24 PM
But i now see that apparently noncryptic took the place of kzb for that question, so i'm not sure what exactly is meant.


I speak exclusively on behalf of myself, i took no-one's place.
If i happen to make the same point (correctly explained by Jeff) as someone else does, so be it.
If this revolves around what exactly "disappear" means - seems like a word game to me.

I don't think laypersons should be held to a higher standard of use of terminology than scientists are, so i'll just call it "plasma".

caveman1917
2012-May-27, 07:44 PM
I speak exclusively on behalf of myself, i took no-one's place.
If i happen to make the same point (correctly explained by Jeff) as someone else does, so be it.
If this revolves around what exactly "disappear" means - seems like a word game to me.

What i meant was that i hadn't noticed that the second question about that (which was the same as the first) was made by a different person (you) rather than the one who made the first question (kzb), which created the confusion about what was exactly meant since kzb had already agreed to the answer given the usual interpretation. So i assumed that the second question must have been meant in a different sense than the first, rather than noticing it was made by a different person.

kzb
2012-May-28, 12:25 PM
Let me reassure everyone that when I used the term "plasma" it is not because I am an Electric Universe convert. I'm simply referring to the state of matter just before the universe became transparent to photons. I don't believe it to be a totally incorrect term.

All I am trying to do is get my head around this going beyond our light horizon concept. I have no hidden agenda. If I can see the CMB, and the structure in it at the point of recombination, that is surely equivalent in the context of this discussion to seeing distant galaxies.

Jeff Root
2012-May-29, 02:13 PM
Noncryptic's point is correct. When kzb said
"So the plasma we currently observe will/has produced
galaxies...." he was NOT talking about the CMB, he
was talking about the plasma which emitted the CMB.
Then he should not have said that "we currently observe"
it, which was my point.
Of course he should have. The statement was correct,
and appropriate. He was talking about the plasma we
currently observe, not (for example) plasma that someone
might have observed from Earth a billion years ago or the
plasma that someone might observe from Earth a billion
years from now. It's exactly the same as talking about
the stars we currently observe or the galaxies we currently
observe.

-- Jeff, in Minneapolis

kzb
2012-May-30, 11:37 AM
Thanks for that Jeff. I can't see any conceptual difference in seeing the light (CMB) from structure in the matter at the point of recombination, and seeing the light from slightly nearer distant galaxies. In fact those distant galaxies formed from that structure....when it was nearer.


If I do have an axe to grind, it's with popular science books/mags/TV documentaries, which, from what people have said on here, must be giving the wrong impression.

Question: (1) if we ever see galaxies rushing off beyond our horizon, it can only be in the context of the last photon from a highly time-dilated galaxy squashed up against that horizon (for ever) ?

(2) We can't have seen any such disappearing galaxies yet, because we can still see the CMB, and that is not beyond our horizon. The scenario in (1) will only happen at some time after the last CMB photon has passed our position ?

Cougar
2012-May-30, 12:19 PM
(2) We can't have seen any such disappearing galaxies yet, because we can still see the CMB, and that is not beyond our horizon. The scenario in (1) will only happen at some time after the last CMB photon has passed our position ?

I question whether this is correct. Conceptualizing the Universe is not easy, and I don't claim to have any great insight into how that should be done. But the CMB fills the visible universe. A distant galaxy does not.

Cougar
2012-May-30, 12:37 PM
Of course he should have. The statement was correct,
and appropriate. He was talking about the plasma we
currently observe...

Perhaps this is nitpicking on a nitpick, but after giving this a little more thought, I've come to conclude that your statement is incorrect and inappropriate. We are not currently observing this so-called "plasma" that existed prior to recombination, as you claim. Never have and never will. That plasma is not the source of the microwave photons that we do observe. Those come from the matter-antimatter annihilations.

Jeff Root
2012-May-30, 04:05 PM
A couple of decades ago I asked an astronomer if any
of the CMBR originated in matter-antimatter annihilation,
and he said that some of it did. I forget whether he gave
a percentage, but he did indicate that it was a relatively
small amount. I didn't ask how it would affect the CMB
spectrum. Since I knew the CMBR is the most perfect
blackbody curve ever observed, I was surprised that he
said it could contain a matter-antimatter annihilation
component, but I asked because my ATM hypothesis
suggests it should be major, contrary to the mainstream
theory that annihilation all took place in the first fraction
of a second. The light from that annihilation should all
have been absorbed by the plasma and re-emitted,
many, many times before the moment of decoupling
some 380,000 years later.

So there are two mysteries here: How could the CMBR
contain *any* light from annihilation, and why would
you think it was *all* from annihilation?

-- Jeff, in Minneapolis

kzb
2012-May-31, 12:00 PM
Cougar wrote:
But the CMB fills the visible universe. A distant galaxy does not.

But this is why I've been mentioning the CMB structure. The CMB is plotted over the whole sphere of the sky, and it shows structure. As I understand it, this structure is held to be as it was at the point of plasma-to-gas phase change. If we look at an "item" of this structure, is it any different to looking at a distant, high-z galaxy?

That plasma is not the source of the microwave photons that we do observe. Those come from the matter-antimatter annihilations.

Like Jeff said, would we not see distinct peaks corresponding to the masses of particles annihilating? Unless the photons from such annihilations had been highly thermalised first?

Anyway, wherever the energy came from, I don't see how this affects the argument.

(Except now you've got me thinking. If all we can observe now is the thermalised plasma, in the far future, will we observe these annihilation peaks as we see further back in time?)

Cougar
2012-May-31, 12:32 PM
...would we not see distinct peaks corresponding to the masses of particles annihilating?

You may want to look again at what those peaks represent. (http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation#Primary_anis otropy)

Jeff Root
2012-May-31, 01:56 PM
Cougar,

The section of the Wikipedia page you linked to is on
anisotropy of the CMBR. Differences in intensity in
different directions. The "peaks" referred to in that
section are peaks of intensity in different directions.
The "peaks" kzb refers to would be peaks in the
spectral curve, the first graph in the Wikipedia article,
"Cosmic Microwave Background Spectrum from COBE".
If matter-antimatter annihilation were a significant
contributor to the CMBR, there would be peaks from
electron-positron annihilation and proton-antiproton
annihilation. Instead it is perfectly thermalized.

I don't get why you think the CMBR is due to matter-
antimatter annihilation. I think you must have just
got confused. A "brain fart" in some people's terms.
It would be really great for my ATM hypothesis if the
CMBR did come from matterr-antimatter annihilation,
but I'm afraid the observation rules that out.

-- Jeff, in Minneapolis

Cougar
2012-May-31, 05:15 PM
What I said was "That plasma is not the source of the microwave photons that we do observe."

Yes, there was one heck of a lot of Thomson scattering since the annihilation, which equalized the temperature of the plasma to within 1 part in 100,000.

kzb
2012-May-31, 05:53 PM
You may want to look again at what those peaks represent. (http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation#Primary_anis otropy)

Yep I read that some time back. I don't understand it really. However, the peaks are ascribed to completely different origins than annihilation peaks. Or are you implying the mainstream theory is mistaken?

But I still don't understand how this affects my question either way. Where the energy comes from is not relevant.

Jeff Root
2012-May-31, 05:53 PM
But it *was* the source. The page you linked even said so.

-- Jeff, in Minneapolis

Cougar
2012-May-31, 06:37 PM
But I still don't understand how this affects my question either way.

Yes, I believe this train has become derailed. Was there a pending question?

kzb
2012-Jun-01, 03:46 PM
Yes, I believe this train has become derailed. Was there a pending question?

See Post #34. I still don't understand what is going on, or going to happen. I still don't understand how the matter I can now see at the edge of the observable universe can become causally disconnected from me at some time in the future.