[Bored chemist]

oxyacetylene gas torch

This also has several things that didn't appear in the Big Bang, like the OH, CH, C₂ and C₃ species.

Which makes things worse.
With no molecular species, only atomic transitions were available.
Neither hydrogen nor helium can give a black body spectrum at 3000K except under pressure.

[HelpMe929 (OP)]

Now I'm interested again, with more advanced questions, if that's allowed.

The conversation seems to imply the CMB generation was quite a short phase (when the universe was a 3000k plasma). If its effects are still saturating the universe after 13.7bn years (due to its photons filling cubic meters of space as fast as they leave it), then the volume of this plasma must have been.... 'large'. But, why dont we see other radiation that must have been emitted before and after this 3000k period? Why isn't this still filling up cubic meters of space as fast as they leave it like the cmb? Or is this the dark matter that ppl are still looking for?

[Halc]

The conversation seems to imply the CMB generation was quite a short phase (when the universe was a 3000k plasma). If its effects are still saturating the universe after 13.7bn years (due to its photons filling cubic meters of space as fast as they leave it), then the volume of this plasma must have been.... 'large'. But, why dont we see other radiation that must have been emitted before and after this 3000k period?

There was light before then, but the universe was opaque, so the light never got far before hitting something.
There is light since then.  That's all the stars and whatnot, most of them brighter than the CMB.

Why isn't this still filling up cubic meters of space as fast as they leave it like the cmb? Or is this the dark matter that ppl are still looking for?

It does fill space as fast as it leaves it, else the stars would not shine continuously.  There's nowhere you can be (except in places like clouds that obstruct light) where galaxies cannot be seen, so their light fills all space, same as the CMB.

[Colin2B]

The conversation seems to imply the CMB generation was quite a short phase (when the universe was a 3000k plasma). If its effects are still saturating the universe after 13.7bn years (due to its photons filling cubic meters of space as fast as they leave it), then the volume of this plasma must have been.... 'large'. But, why dont we see other radiation that must have been emitted before and after this 3000k period?

To add to what @Halc said, I’m giving a very simplified analogy.
Think about a light bulb, lots of very bright light. Switch it off and you will see the light fade quickly and the filament still glow red for a while. Now touch the glass, still very hot, move the bulb 100m away and a thermal imaging camera will still pick up that heat (infrared) radiation.
Now imagine a universe filled with light bulbs (lets ignore for the moment the inflation that put them there) if they are all switched off together they begin to cool, but still radiating. When the ones next to us have cooled, all of them will have cooled, but the radiation reaching us from the ones billions of light years away was emitted when they were still quite hot - less hot than IR and was down to microwave frequencies.

[HelpMe929 (OP)]

Thanks everybody for the explanations

They all make perfect sense and fit in with the logical laws of physics as I understand them. But there's still my original question that even now I cant get my head around.

I'll come back to it in a moment, because evan_au mentioned that the early universe was opaque due to the ultraviolet radiation. I must have misunderstood him because otherwise the universe would still be opaque due to ultraviolet radiation wouldn't it (or at least the more distant/older swathes of it would still be opaque?)

But forgetting that, I still dont understand WHY anything as old as 13bn years is still visible to us. The only way I can understand that is if the universe as early as one hour old (just to pick a sensible timeframe) was already as big as our visible universe now is, big enough so that anything travelling at lightspeed would still take 13bn years to travel between two given points in it.

If it wasn't already this big then common sense would sugest that  its expansion rate (in order to explain the 13bn year 'lag') would be too high for gaseous material to coalesce into stars and solar systems.

So was the Universe already universe sized very early in its life?

Have I just answered my own question...? (other than the ultraviolet bit).

Many thanks

[Colin2B]

evan_au mentioned that the early universe was opaque due to the ultraviolet radiation. I must have misunderstood him

Yes, slightly.
Not opaque due to UV, but the temperature at that time was below the UV level and so there wasn’t much around to excite the H & He.

If it wasn't already this big then common sense would sugest that  its expansion rate (in order to explain the 13bn year 'lag') would be too high for gaseous material to coalesce into stars and solar systems.

No it wasn’t already size of current universe, but locally the force of gravity was still strong enough to pull the material together.

[HelpMe929 (OP)]

Apologies Colin for the confusion.

I'm asking if there's a reason (yet) for this 13bn year delay in the cmb reaching our neck of the universe.

[Halc]

But forgetting that, I still dont understand WHY anything as old as 13bn years is still visible to us.

Light doesn't decay.  If I emit a photon thataway, assuming it hits nothing, it will go forever at that speed and energy, so 13 BY is nothing to that process.
Problem is, when it is finally measured by something, that something is probably very far away and moving away from the source (here) of that photon, so that receding detector will measure a very red-shifted photon.  That's why the CMB currently appears so red-shifted from its original frequency: because we're moving just stupid fast away from the source atom of that photon.

The only way I can understand that is if the universe as early as one hour old (just to pick a sensible timeframe) was already as big as our visible universe now is, big enough so that anything travelling at lightspeed would still take 13bn years to travel between two given points in it.

It takes less time for light to travel between points closer together, else we'd not see the light of our sun.  So sure, points that far apart might take that long for light to travel between them.
All of the CMB today comes to us from some identical distance.  If the light was emitted closer by, it has already passed by us, and if emitted from further away, it hasn't reached us yet.  How far away that distance is depends very heavily on how one measures distance (what sort of coordinate system is used).

If it wasn't already this big then common sense would sugest that  its expansion rate (in order to explain the 13bn year 'lag') would be too high for gaseous material to coalesce into stars and solar systems.

The universe doesn't have an edge and thus a meaningful finite size.  Space has expanded some 40,000 times the distances that were between things back when the CMB was emitted.

So was the Universe already universe sized very early in its life?

That's the model, yes.  It's like dividing an unbounded size by 40,000, which isn't a meaningful thing to do since said size isn't a finite number.

I'm asking if there's a reason (yet) for this 13bn year delay in the cmb reaching our neck of the universe.

There's no delay.  It was always here, and will always be here, since the light is everywhere at all times.  We're just observing from a position where it has been 13 billion years since that light first flooded all space.

[HelpMe929 (OP)]

I'm asking if there's a reason (yet) for this 13bn year delay in the cmb reaching our neck of the universe.

There's no delay.  It was always here, and will always be here, since the light is everywhere at all times.  We're just observing from a position where it has been 13 billion years since that light first flooded all space.

haha. OK. Enough questions I think.

Many thanks

[evan_au]

why don't we see other radiation that must have been emitted before [and after] this 3000k period?

We don't see light emitted before this period because the plasma was opaque before this era.
- In a plasma (before this era), electrons are not attached to atoms, and so they can have every possible energy
- As electrons approach positive nuclei (or negative electrons), they are accelerated/decelerated by the electric field
- This produces "Braking Radiation" (with the German name "Bremsstrahlung") which can absorb and produce light of every possible energy level - but in thermal equilibrium, it will have a distinctive spectrum
https://en.wikipedia.org/wiki/Bremsstrahlung

In atoms (after this era), electrons can have specific energy levels, and thus produce a line spectrum
- Cosmology suggests that there was an even later phase (150 million to 1 billion years after the Big Bang), where hydrogen fusion started in early stars, which produced lots of UV light, causing hydrogen & helium to again become a plasma
- With larger telescopes, we are now able to see quasars that were active towards the end of this period in the early universe
- These have high red-shift (z=6 to 20), but not nearly as much as the big-bang radiation (z=1089)
- They do have many atoms beyond hydrogen and helium, since nuclear fusion produced them, and supernovas spread them into space
- Astronomers are hoping that the James Webb Space telescope will be able to see a lot more of these infra-red =high red-shift quasars which were active earlier in this reionization phase (if and when it is successfully launched & commissioned)
- But the universe was much less dense during the reionization phase than in the pre-3000K era, so we can still see the CMB at microwave frequencies through the infra-red haze of radiation from this later phase (and the visible-light of today's stars and galaxies).

See: https://en.wikipedia.org/wiki/Reionization

[yor_on]

In a way it's a mystery HM. What we see is 13.8~ billion years away from us. That's the time of light existing. When it comes to the universe itself it may be infinite though. We have our 'bubble' of light and as we 'move' through the universe that 'bubble' still won't grow. One reason why there is no definite 'place' for the universe to start, although we still set a 'time' to it locally defined.
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and yes, a good argument for the universe actually being 'infinite'.
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Another thing is how we came to be, and how 'light' itself came to be. One idea that I like is the one of 'spontaneous pair productions' of particles. That one goes out from the vacuum itself having a ability to transform into particles. The vacuum has a time relation to what can be said to 'exist' as well as it can be under so called 'pressure'. If you imagine the original state of a universe as something under a tremendous 'pressure' as defined 'dimensionally' then this spontaneous pair production has a excellent chance to start. If you then also define 'c' as a 'universal constant' then that is the rate of 'information' connecting it to become our universe.  In such a case the universe didn't exist until the pair production started.
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Sorry, forgot one most important part of that recipe :)

You need to add a 'inflation' at that origin, faster than the rate of information, which I hope we agree on being 'c'. Otherwise the pair production will just be a fluctuation recombining under a time limitation, unable to become 'real'. Then we just need those patches of 'space' to become united into a universe. And that is where this idea of 'information' helps us. If you think of quantum entanglements they are 'instantly connected' although outside 'c', but that is allowed due to their inability to transmit information, just as a spontaneous pair production is limited through a time relation (which I would define as Planck time). So we really need a inflation for it to work..

https://www.universetoday.com/79418/planck-time/
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and yes, I think that would make the dimensions (universe) we define something constructed, non existing until information united it. The idea of 'pressure' creating 'pair productions' can be altered to 'energy densities' if you like, aka Hawking radiation.

[yor_on]

https://en.wikipedia.org/wiki/Pair_production

" Pair production is invoked to predict the existence of hypothetical Hawking radiation. According to quantum mechanics, particle pairs are constantly appearing and disappearing as a quantum foam. In a region of strong gravitational tidal forces, the two particles in a pair may sometimes be wrenched apart before they have a chance to mutually annihilate. When this happens in the region around a black hole, one particle may escape while its antiparticle partner is captured by the black hole.

Pair production is also the mechanism behind the hypothesized pair-instability supernova type of stellar explosion, where pair production suddenly lowers the pressure inside a supergiant star, leading to a partial implosion, and then explosive thermonuclear burning. Supernova SN 2006gy is hypothesized to have been a pair production type supernova. "

One problem with those ideas is that we don't get a answer to what makes a 'photon'. Because 'photons' are what makes 'pair productions' exist. Then again, I don't know anything describing the idea of 'energy' better than just 'photons'. Then you also need to remember that all you see and experience is secondhand, as a result of outcomes. Photons are not footballs, you can't follow their propagation. I think Collin put it quite nicely in

So the question is this, is light an independent entity or is it somehow an observed effect of a larger mechanism.

It all depends what level you are talking about. Clearly, light is just a part of the overall electromagnetic spectrum, which is an effect of oscillating electric/magnetic fields. So you would say that light is an observed effect of the laws of electromagnetism. Remember, Einstein’s first paper on relativity dealt with a specific problem in electrodynamics (moving electromagnetic fields) that had been puzzling scientists; it was in that paper where he suggested light does not behave as if propagated in a medium so it’s measured speed is not affected by the emitter or observer. This speed also comes from Maxwell’s equations which are based on the findings of Amper, Faraday, Coulomb and Gauss - all leaders in electromagnetic theory.

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Another difficulty with it is that if we imagine different patches uniting, then shouldn't there be a time difference?  Meaning that patches further away would have time to evolve? Then again, if we set a origin at null, would it matter? All patches would then be equivalent from some 'global perspective'?  But would they be it relative my local clock? Actually that difficulty is baked in into the theories we use normally too, if we define it relatively.

[HelpMe929 (OP)]

In a way it's a mystery HM. What we see is 13.8~ billion years away from us. That's the time of light existing. When it comes to the universe itself it may be infinite though. We have our 'bubble' of light and as we 'move' through the universe that 'bubble' still won't grow. One reason why there is no definite 'place' for the universe to start, although we still set a 'time' to it locally defined.

If the universe (during the period of its CMB emition) was infinite, then wouldn't there be evidence of it in its red-shift? Wouldn't there be quite a large fluctuation in red-shift values for the CMB?

Is it possible to determine the size of the CMB universe from its red-shift fluctiaions? Assuming that it had a physically recognizable 3 dimensional shape...

and assuming that it has red-shift fluctuations.....................................

[evan_au]

assuming that [CMBR] has red-shift fluctuations

There is one aspect of the CMBR which does represent a red shift; this "dipole anisotropy"  appears be due to the motion of our galaxy within the local cluster: 370 km/sec towards Leo.
See: https://en.wikipedia.org/wiki/Cosmic_microwave_background#Features

Apart from this, the CMBR does have variations, but they are very small - around 1 part in 100,000.
- This is a small variation on something which is pretty close to absolute zero ...
- A different red-shift would produce a black-body spectrum with an effective different temperature.
See map at: https://en.wikipedia.org/wiki/Cosmic_microwave_background#Microwave_background_observations

The variation in CMBR temperature is usually interpreted as differences in matter density in the early universe.
- By interpreting these spots and blotches, scientists are inferring many details about the early universe.
See: https://en.wikipedia.org/wiki/Cosmic_microwave_background#Primary_anisotropy

Roger Penrose has even controversially suggested that ring-like structures in the CMBR are relics of objects from before the Big Bang...
Listen:

[HelpMe929 (OP)]

thanks for the video

It wasn't the easiest explanation to follow as he seems to keep drawing on a level of knowledge in his listeners that I don't have, and I seemed to miss a lot of patches in his theory. The death of one universe being the birth of another... with the implication of photons being the common denominator in the deaths and births of universes, and the evaporation of black-holes supplying the energy for the new births (eek).

But a really fascinating idea, and one which would seem to explain a high entropy universe evolving (or devolving) into a low "boring" one before its rebirth (low entropy because everything is so dispersed that there are no more configurations available).

But this is why I asked the question about red-shift fluctuations in the CMBR. Wouldn't a uniform red-shift indicate the CMBR was generated from just one very small area and time? There should be CMBR from the moment when space lost its opacity, and CMBR from the time when it stopped radiating and started 'forming'. Surely between these two periods the redshifts of the CMBR would have increased due to the intervening inflation? A uniform redshift suggests a sudden burst of energy from a flat surface!

[yor_on]

I'm not sure. If you think of a origin as having no specific place even if we can set a time to it. Then it seems to have started 'everywhere' and if so a redshift/ blueshift should be due to different galaxies (stellar objects) relative motion versus each other, and inflation and its subsequent expansion. What strikes me in such a scenario is that there is a defined time zero for it all to happen, and that one we're pretty sure about as we constantly are in (relative) motion versus the rest of the universe, at least the way I think about it. If we use the skin of a expanding ballon then? I don't know, the ballon analogy is a halting one but if we used it we would need to think of it as a sphere as it seems to me, to keep a equivalent zero time? I might be wrong about this but that's how I think of a 'zero time being equivalent everywhere'. Wrinkles and a uneven form should be able to translate to a different time, ahem, sort of :)
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If we leave the balloon we could also imagine it as a sheet of a even tension as it seems to me. But it is pretty strange if we assume a infinite universe, isn't it? Then again, the size doesn't matter for it, it's still strange to me. The blue and redshift we  find have two reasons, one being between different objects (as suns) in relative motion versus each other, the other a (cosmic) redshift due to the inflationary period, and subsequent accelerating expansion. That one is a major effect and seems to be the same more or less everywhere on a large scale. There is one thing more that is strange and that is the idea of a vacuum expanding. How does it do it?
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You could also ask yourself how we would create CBR if we now could. It's as if the universe came to be in all 'spots' possible, and at a same time? And the same must go for the vacuums expansion, it comes also to be in all spots simultaneously? The problem with that , let's call it a question, is that simultaneity doesn't exist in relativity as far I know. But if I would be to assume that the vacuum expanded unevenly we should notice it from the CBR (cosmic background radiation).

And just for the fun of it. A expansion means that you're shrinking :) Relative the 'size' of the universe at least.

[Halc]

But this is why I asked the question about red-shift fluctuations in the CMBR. Wouldn't a uniform red-shift indicate the CMBR was generated from just one very small area and time?

If it was generated from one small area in a small time, it would appear to us as a flashbulb on a camera going off at one random instant in time.  It would only be noticed if 1) There were humans around at the time, and 2) Somebody was looking in the exact correct place at the time.  So there would be no CMB.
No.  The CMB was emitted from everywhere, all at once, and as I said before, all of the CMB today comes to us from some identical distance.  If the light was emitted closer by, it has already passed by us, and if emitted from further away, it hasn't reached us yet. Being from an identical distance in all directions, it is uniform in all directions (or at least would be if we were comoving.  See the anisotropy that Evan discusses above), and forms the 'flat surface' you mention below.

There should be CMBR from the moment when space lost its opacity, and CMBR from the time when it stopped radiating and started 'forming'. Surely between these two periods the redshifts of the CMBR would have increased due to the intervening inflation?

The two periods are quite close together, and the CMBR is not cleanly one frequency, but a narrow range, partially due to this brief bit of inflation that took place between these two periods.  It wasn't an instantaneous flash, but a brief one nonetheless.

A uniform redshift suggests a sudden burst of energy from a flat surface!

That it does, and all points at some uniform distance from us is that flat surface, which actually appears as the inside of a sphere as viewed from the center.  It's curved, not flat, since light from a flat surface would get to us first from the point on that surface closest to us.

[HelpMe929 (OP)]

If it was generated from one small area in a small time, it would appear to us as a flashbulb on a camera going off at one random instant in time.  It would only be noticed if 1) There were humans around at the time,

The CMB was emitted from everywhere, all at once, and as I said before, all of the CMB today comes to us from some identical distance.  If the light was emitted closer by, it has already passed by us, and if emitted from further away, it hasn't reached us yet.

According to the Big Bang model, the radiation from the sky we measure today comes from a spherical surface called the surface of last scattering. This represents the set of locations in space at which the decoupling event is estimated to have occurred[15] and at a point in time such that the photons from that distance have just reached observers

Sorry, but the above means I have to ask my question 'again'
Why the 13bn delay in the CMB reaching us?

It isn't like the big bang was an event that happened 'to somebody else'. We were there when it happened. We were in the middle of it. We've been part of the inflation, and it seems photons travelling at the speed of light from that place where we started from have only just caught us up... HOW?

I dont expect an answer because it seems everybody has a different 'explanation'.

[Halc]

Sorry, but the above means I have to ask my question 'again'
Why the 13bn delay in the CMB reaching us?

There's no delay.  It is everywhere and has been here since it was formed and will be here for as long as you want.  It didn't just now 'turn on', so there's no delay to it.

It isn't like the big bang was an event that happened 'to somebody else'.

No, but it happened everywhere, not in just some spot.  The CMB is not from the big bang.  It's from when the universe was a bit more than a third of a million years old.

We were there when it happened. We were in the middle of it. We've been part of the inflation, and it seems photons travelling at the speed of light from that place where we started from have only just caught us up... HOW?

The CMB we see didn't come from 'here'. Similar light did, but the light that originated here is heading away from us, hitting perhaps some observer maybe 45 billion light years away (comoving distance).  So the light we see now is similarly coming from the birth of hydrogen atoms that are currently (comoving coordinates again) 45 BLY away.  It wasn't that far away when it was emitted.  That material is 'now' well outside our event horizon and any light emitted from there now will never ever reach us.

[yor_on]

It's tricky. There are two ways to find out how old the universe might be. The most recommended is using the redshift we measure from the 'earliest' light reaching us, then extrapolate it in time, backing up its 'history'. Doing so the light that has been 'stretched' gains energy until it reach a point in where its energy is 'infinite', and that energy coincidence with the shrinking of our universe as we play the cosmic movie backwards. At that point we have a origin, at least for the most distant light we are able to find and measure. The other way is to use 'cosmic ladders' as astronomers have a good idea of what type of stars that existed at different stages of the universe's time evolution and then defining how far away they are from us. Those furthest away from us fits very well in age with the first method described. And defining how far those stars are from us is by using 'standard candles', an idea from https://www.famousscientists.org/henrietta-swan-leavitt/ at a time when only men was expected to invent new methods :)
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Ok, 'infinite is a pretty strong word for it, before the light we can see it is supposed to have been a hot and dense plasma without radiation. There is one thing though, How do we guarantee that this redshift hasn't disappeared into oblivion? The only way you can be sure of that, as it seems to me, is by finding that there could be even more redshifted light that we would be able to measure, if it existed. That should be the answer to that one I think? (Not that the plasma couldn't radiate but as far as I got the idea it was more or less 'soaked up' before it could leave.)