[HelpMe929 (OP)]

Could somebody please explain this to me better than anybody else has so far?

My understanding of the CMB is it's some kind of leftover from the big bang. But just how is that possible when 'we' (all the atoms that make up you, me and our local universe) were part of that big bang?

Isn't it like seeing a lightning strike hit your garden shed before breakfast, but not actually hearing the thunderclap until after supper!

I just dont get how my atoms have managed to get where I find them today ahead of all those other atoms/photons/whatever that other sciences would suggest have travelled umpteen billion lightyears in distance a good deal faster than my own humble bits of matter could have done.

Just WHY are we still seeing this stuff that should have TOTALLY dissipated out of eternity a few umpteen billion years ago?!?!

Any answers, please?

[Janus]

The problem is that you are thinking of the Big Bang as an explosion in space, rather than the expansion of space.
With an explosion in space, the Photons could have raced past the matter into the space beyond. But with the Big Bang, there is no "space beyond" for the photon to expand into. We are at the "forefront" of this expansion.
An analogy would be that the universe is like the skin of an expanding soap bubble. Everything in it, photons, matter, etc. is confined to the skin. When the bubble is small everything is much more crowded together and as it expands, Things on a whole move apart and it is less crowded.  With photons, when it is small their frequencies are high ( the universe is "hot"), but as the bubble expands, they are stretched out to longer wavelengths and lower frequencies ( the universe "cools"). The CMB are those early photons that have been stretched out, but still confined to the same "Bubble skin" as everything else.

[HelpMe929 (OP)]

And here was I thinking there was no such thing as magic.

The fact that we're 'seeing' this radiation is proof that it's moving through space, right? It isn't just loitering around in our vicinity with nothing better to do. So the radiation we saw last week must now be gone forever. It sounds like this radiation must have been tavelling past us and 'disappearing forever' for the last umpteen billion years. why is it STIIL travelling past us in a way that we can register with instruments?

My apologies, but to me your answer does not really answer the question at all.

[Hayseed]

Modern theory believes that mass and motion can change time.

They also believe that a change in clock tic rate, or a change in frequency is proof of a change in time.

This allows time to vary with motion.  They believe this is the only way to explain light velocity measurements.

Any theory or explanation of CMB must have these underpinnings.

So, if you capture a CMB wave, it would appear very old to us, but for the wave, it thinks it's only milliseconds old.

See what you can do with science?

[Kryptid]

The fact that we're 'seeing' this radiation is proof that it's moving through space, right? It isn't just loitering around in our vicinity with nothing better to do. So the radiation we saw last week must now be gone forever. It sounds like this radiation must have been tavelling past us and 'disappearing forever' for the last umpteen billion years. why is it STIIL travelling past us in a way that we can register with instruments?

It's true that the radiation is constantly on the move. However, that radiation is travelling in all directions at very nearly the same rate. As many photons of this radiation are entering any given cubic meter of space as are leaving it. So there is always radiation present to measure.

[Janus]

And just to add to What Kryptid already said. While the photons we detect today are different ones than the ones we detected yesterday or will detect tomorrow. The one we detected yesterday where a bit "younger" and and the one we will detect tomorrow will be a bit "older".   In other words, the CMB is still decreasing in temp as the universe continues to expand.  The decrease is very small, so it would take a long time before it became enough to be discernible by our measurement standards, but it exists.


 

So the radiation we saw last week must now be gone forever. It sounds like this radiation must have been tavelling past us and 'disappearing forever' for the last umpteen billion years. why is it STIIL travelling past us in a way that we can register with instruments?

This is like saying that because the average water molecule speed is something is in the 100's of meters per second, that a fish in a lake should not detect any water around him because the water molecules that he felt yesterday has traveled off to some other part of the Lake. New water molecules have replaced them.*

*Now it is true that with the lake being a confined body of fixed size, he can encounter the same water molecule more than once.  This is note completely inconceivable for the universe if it were of a finite fixed size.  a Photon could pass the Earth, "circumnavigate" the universe and pass it again. How long it takes between passes would depend on the size of the universe. ( in a really small "closed" universe you could conceivably look off into the distance with a telescope and see the back of your own head)
 But with an expanding universe, even if it is finite, the size and rate of expansion could be such that the "circumference" grows faster than light can traverse it, and light passing you at any given moment can never return. ( but this still doesn't mean that it won't be replaced by a different photon.)

[RobC]

It is easy to understand that the sun has already gone down 8 minutes before one sees it set but I can understand the difficulty in visualising the formation of the CMB.

[HelpMe929 (OP)]

I suppose my next obvious question has to be what has generated (or is generating) the CMB?

It must be more than from just the birth of everything...? For so much radiation to still be zipping passed us after so long, then whatever radiated the photons we're still seeing surely must have been a long way from where 'we' were at the time it was emitted.

Does that suggest the possibility of calculating the diameter of the universe at a particular moment in history? I mean, if it's possible to calculate how much total mass the entire universe holds by investigating the CMB, then why not be able to calculate how big it once was also...

[Kryptid]

I suppose my next obvious question has to be what has generated (or is generating) the CMB?

It was formed when the first atoms formed. The bonding of an electron with a proton to form a hydrogen atom releases a photon. Those protons and electrons very uniformly filled all of the Universe, so the radiation was released from pretty much all locations in space, both near and far.

[HelpMe929 (OP)]

It was formed when the first atoms formed. The bonding of an electron with a proton to form a hydrogen atom releases a photon. Those protons and electrons very uniformly filled all of the Universe, so the radiation was released from pretty much all locations in space, both near and far.

But I didn't think there was a 'far'! Wasn't all matter/energy compresseed in a high pressure / high temperature 'soup' in which the first atoms were able to bond? How can they bond in a cold / empty envrinment?

Are we even talking aboout the same thing anymore?

[Kryptid]

But I didn't think there was a 'far'! Wasn't all matter/energy compresseed in a high pressure / high temperature 'soup'

This happened when the Universe was about 380,000 years old. It was already pretty big by then.

How can they bond in a cold / empty envrinment?

It's actually easier for electrons to bind to protons when they are travelling more slowly (that is, the temperature is lower). If it's too hot, the electrons will be stripped away from the protons, forming a plasma. The environment wasn't exactly cold, though (it was about 3,000 kelvins at that time) and it was far from empty.

[evan_au]

what has generated (or is generating) the CMB?

As Kryptid said, the CMBR photons last interacted with matter when the universe had a temperature around 3000K.
- A plasma at 3000K will continually absorb and reemit light with a characteristic "black body spectrum"

At that time, the universe was mostly hydrogen, some helium, and almost nothing else.
- When the temperature drops below 3000K, hydrogen and helium can capture and hold onto electrons, so emission of the black body radiation effectively stops, and emission becomes a "line spectrum".
- Hydrogen and Helium bind their electrons tightly, so it takes very energetic photons (Ultraviolet) to excite them and allow emission of a line spectrum.
- By the time the universe dropped below 3000K, there was very little ultraviolet around, so space became transparent to this 3000K black-body radiation.

The subsequent expansion of the universe by a factor of over 1000 has dropped the effective temperature of the black body radiation from 3000K to 2.7K.
- Since we are still within the "fireball", we are being continually bombarded by this black body radiation from all directions (but severely red-shifted).

See: https://en.wikipedia.org/wiki/Cosmic_microwave_background#Relationship_to_the_Big_Bang

[HelpMe929 (OP)]

This is just going around in circles....

I'll just agree with the experts that they really do know how much mass is in the universe and that it just isn't enough, and that invisible matter really does exist (along with flying broomsticks and invisible cloaks).

Thanks everybody for their patience and attempts to explain something that only really exists in mathematics.

[Hayseed]

I would not rely on any estimate of cosmos(or even galactic) mass.  All stars spew out isolated free charge continuously.  Think about that......think how long they have been doing that.   We can find no evidence of charge recombination from our sun.  The charge from our sun is still accelerating out past Neptune.  If that charge recombined, we would detect the emission.  Think about all the charge from the sun for eons.  And eons of stars.  There could be a good chance that most of the mass(isolated charge) in the universe, is not under gravitational influence.

And a good chance that there could be much, much more mass than thought.   Naked mass might be different than gravitational mass.

How about this, we believe that high velocity makes it difficult for recombination.  What if a simple pole flip on a particle made a difference?  What if there are certain velocity and density conditions where a high velocity recombination readily occurs with an unknown emission spectrum..........such as CMB.  CMB might be fresh.  A cold spectrum.

Astronomy is an unique science.  When we photograph motion on earth, all the objects are in present time. One time stamp. But a star field is not an image of objects........it's an image of time stamps, with unknown AND different times.  This is unique. We are foreign to this dynamic.  On earth, we have never had need of this way of thinking and understanding.  That does not include recognizing star field patterns with season.  That reasoning when to the gods.

We can not see the present universe or even our present galaxy. The present universe might be dark and scattered.

It's hard to fathom that our galaxy's center could have super nova-ed thousands of years ago.

Compare the number of assumptions that astronomy uses with the number of assumptions that chemistry uses.   Astronomy needs salt to swallow.

Not that there is anything wrong with astronomy.  Like I said, it's unique. A different kind of puzzle.

[Kryptid]

This is just going around in circles....

What wasn't clear about what we said?

[HelpMe929 (OP)]

This is just going around in circles....

What wasn't clear about what we said?

the statistics :p

[Colin2B]

Thanks everybody for their patience and attempts to explain something that only really exists in mathematics.

That’s not true, it doesn’t exist in maths, it is as real as the radiation from a light bulb, we just can’t see it with our eyes.

What wasn't clear about what we said?

the statistics :p

What statistics, what maths?. I don’t see any of those here, just a genuine attempt by a number of people to help you understand what it is.

[Hayseed]

At first, it was thought to come from pigeon poop.

[Bored chemist]

- A plasma at 3000K will continually absorb and reemit light with a characteristic "black body spectrum"

Not reliably.
The flame of an oxyacetylene gas torch is a plasma at about that temperature, it emits a band spectrum.

https://rkdmb.home.xs4all.nl/rkd/flame/spectrum.html

To get a black body you either need lots of ionisation and or high pressure.
The aftermath of the BB had both.

[evan_au]

oxyacetylene gas torch

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