The CMB, how is that possible?

[michel123456]

Here is the question

 

At the Big Bang, the universe were created and started expanding. The universe includes us, the Earth, the Milky way galaxy, and also the CMB.

So the question is: how is it possible for us to observe a radiation that was emitted at the time we were born?

It looks like the archer running faster and being killed by its own arrow.

[StringJunky]

"Space is big. Really big. You just won’t believe how vastly hugely mindbogglingly big it is. I mean you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space." - D. Adams

 

What you are seeing, when you observe it, is photons that are interacting for the first time with your instrument since they were emitted... the rest just carry on their merry way to the next observer or interaction. It happened all over and they are travelling all over. Not much different to the expansion happening all over.

[Strange]

The "surface of last screaming" analogy might help:

http://ned.ipac.caltech.edu/level5/March03/Lineweaver/Lineweaver7_2.html

[swansont]

Here is the question

 

At the Big Bang, the universe were created and started expanding. The universe includes us, the Earth, the Milky way galaxy, and also the CMB.

So the question is: how is it possible for us to observe a radiation that was emitted at the time we were born?

It looks like the archer running faster and being killed by its own arrow.

 

If the archer took up all of space, how would s/he avoid being hit by the arrow? (or run anywhere for that matter)

[Strange]

At the Big Bang, the universe were created

 

There is no evidence for that.

[MigL]

Let me see if I can clarify what some of the others have said...

 

Consider the early universe. A seething mass of energy and particles appearing and disappearing, as the universe is expanding ( this is after the inflationary period ). As it expands the temperature drops. When it drops enough for the familiar particles to have precipitated out ( disregard matter predominance over anti-matter ) they collide with each other. If the temperature is still too high, they have too much energy and don't stay captive, but at a certain temperature they do 'stick'. Hydrogen, helium and some lithium is formed ( that's all ) and the universe keeps cooling.

 

At this point the universe consists of energy, free floating electrons and the lightest atomic nuclei, The free electrons collide with the nuclei, but don't 'stick', since their temperature or energy is higher than the ionization energy. The whole universe is a glowing plasma, like the Sun is, it is opaque and it is glowing with the black body spectrum appropriate to its temperature.

 

When it expands enough that its temperature drops to approx. 4000 deg., electrons are finally able to 'stick' to the light nuclei and form atoms. This is when the universe becomes transparent, and it occurred approx. 300 milyrs after the big bang.

 

What we are 'seeing' as the CMB, is the 4000 deg. glow from that time, but red shifted by the expansion of the universe by a factor of about 1500 times ( gas laws, V is inversely proportional to T ), to a present day temperature of approx. 2.7 deg.. And we see it everywhere because it was everywhere.

[zapatos]

Does anyone have any idea when all of the CMB photons that are capable of reaching us will have done so? That is, when will we no longer see the CMB?

[elfmotat]

Does anyone have any idea when all of the CMB photons that are capable of reaching us will have done so? That is, when will we no longer see the CMB?

 

The rest of the observable universe, save the local group, will be out of reach in 100 billion to 1 trillion years, CMB included.

[michel123456]

The "surface of last screaming" analogy might help:

http://ned.ipac.caltech.edu/level5/March03/Lineweaver/Lineweaver7_2.html

No that does not help really.

 

If the archer took up all of space, how would s/he avoid being hit by the arrow? (or run anywhere for that matter)

We are the archer, The cmb is the arrow.

Rephrasing the question:

If the CMB was emitted a long time ago at the same time with the matter that the universe is made up. how can we see it? Imagine switching a light bulb on, then switch it off, then go on travelling for 12 billion years and catching the photons from the light bulb.

Edited November 2, 2014 by michel123456

[swansont]

We are the archer, The cmb is the arrow.

Rephrasing the question:

If the CMB was emitted a long time ago at the same time with the matter that the universe is made up. how can we see it? Imagine switching a light bulb on, then switch it off, then go on travelling for 12 billion years and catching the photons from the light bulb.

 

Your analogy doesn't portray the scenario properly.

 

The universe was ~380,000 years old when the universe became transparent, so the CMB could propagate. "We" (if you mean the earth system) were created almost 10 billion years later. Another 4.5 billion if you literally mean us. So "we" haven't had to move at all to see photons from some other part of the universe get to us. Even though the expansion of the universe can happen at speed that exceed c.

 

IOW, the universe was not a point when the light was able to propagate, so there is no single "light bulb", and we didn't have to race any photons across the universe.

[michel123456]

Let me see if I can clarify what some of the others have said...

 

Consider the early universe. A seething mass of energy and particles appearing and disappearing, as the universe is expanding ( this is after the inflationary period ). As it expands the temperature drops. When it drops enough for the familiar particles to have precipitated out ( disregard matter predominance over anti-matter ) they collide with each other. If the temperature is still too high, they have too much energy and don't stay captive, but at a certain temperature they do 'stick'. Hydrogen, helium and some lithium is formed ( that's all ) and the universe keeps cooling.

 

At this point the universe consists of energy, free floating electrons and the lightest atomic nuclei, The free electrons collide with the nuclei, but don't 'stick', since their temperature or energy is higher than the ionization energy. The whole universe is a glowing plasma, like the Sun is, it is opaque and it is glowing with the black body spectrum appropriate to its temperature.

 

When it expands enough that its temperature drops to approx. 4000 deg., electrons are finally able to 'stick' to the light nuclei and form atoms. This is when the universe becomes transparent, and it occurred approx. 300 milyrs after the big bang.

 

What we are 'seeing' as the CMB, is the 4000 deg. glow from that time, but red shifted by the expansion of the universe by a factor of about 1500 times ( gas laws, V is inversely proportional to T ), to a present day temperature of approx. 2.7 deg.. And we see it everywhere because it was everywhere.

That covers the question.

That the CMB is a radiation coming from a plasma at an epoch before atoms were created, everywhere.

And that our galaxy, the Sun & the Earth were formed roughly where we are today in order to be able to receive this radiation that was emitted so long ago at a distance we could not have been able to travel from.

 

The rest of the observable universe, save the local group, will be out of reach in 100 billion to 1 trillion years, CMB included.

Don't you find this result completely insane?

That future observers will have no way to detect the CMB, or even to detect the universe?

[swansont]

Don't you find this result completely insane?

 

That's completely irrelevant.

[zapatos]

 

Don't you find this result completely insane?

That future observers will have no way to detect the CMB, or even to detect the universe?

It is no more insane than the fact that future observers will have no way to detect you.

[michel123456]

It is no more insane than the fact that future observers will have no way to detect you.

I know you may find it natural that in the history of the universe everything is changing, random events occur. The Big Bang happened 13 billion years ago so what, we are only a small blue dot lost in the immensity. So far, so good.

 

But to imagine that we are placed in such a position that we can today observe & measure a phenomena related to the birth of the universe, and argue that future observers will not be able to observe not only the CMB, but the next galaxies, is totally insane.

 

If our theory states that we are in a better position than them, then our theory is wrong.

[Strange]

If our theory states that we are in a better position than them, then our theory is wrong.

 

Why? Look out your window - are there any mammoths or dodos? Our ancestors saw them but we can't. Does that make history wrong?

[elfmotat]

If our theory states that we are in a better position than them, then our theory is wrong.

 

This assertion is wrong, not the theory.

[MigL]

No, you're still thinking of the CMB as an event that happened at a particular place, and radiation has to travel to us for us to 'see' it.

That is not the case. The hot, opaque plasma which gave rise to the CMB happened here, and everywhere, throughout the universe.

We are not expanding or racing away from a surface ( that's why I don't like last surface analogies ), because the photons are still here. They've just been red-shifted by the expansion to the microwave length.

 

We will never expand or outrace the CMB for the same reason. It will always be there, only red-shifted to longer and longer wavelengths, making its detection harder.

I wonder, had our civilization developed much later, and say the universe had expanded by a further factor of 10 or 100, such that the CMB was only 0.27 deg. or 0.027 deg, would we have considered it just background noise ?

Might it have gone undetected ?

[michel123456]

 

This assertion is wrong, not the theory.

I say that any random observer should observe roughly the same thing,should establish mathematically the same laws of physics and should conclude the same things about the universe.

When I say random, I mean absolutely random:

that means 10 billion years in the future, 10 billion years in the past, anywhere. (because usually we think of randomness of position "now" and we forget about randomness in space and in time).

Since the current accepted theory describes things differently, it means to me that we are not random observers.

No, you're still thinking of the CMB as an event that happened at a particular place, and radiation has to travel to us for us to 'see' it.

That is not the case. The hot, opaque plasma which gave rise to the CMB happened here, and everywhere, throughout the universe.

We are not expanding or racing away from a surface ( that's why I don't like last surface analogies ), because the photons are still here. They've just been red-shifted by the expansion to the microwave length.

 

We will never expand or outrace the CMB for the same reason. It will always be there, only red-shifted to longer and longer wavelengths, making its detection harder.

I wonder, had our civilization developed much later, and say the universe had expanded by a further factor of 10 or 100, such that the CMB was only 0.27 deg. or 0.027 deg, would we have considered it just background noise ?

Might it have gone undetected ?

Sorry that bold part I cannot understand.

The photons of the CMB that we catch are travelling to us at SOL and come from far away and a very distant past. The photons that you say "are still here" are the one coming from far away.

In our place where we are today, there were once upon a time a plasma that emitted a huge radiation that observers some billion light years from us receive today as CMB. Now the plasma is gone and there is no emitting source of the CMB here today.

Edited November 2, 2014 by michel123456

[pzkpfw]

Drop observers on random Earth locations. One reports "its a desert" another reports "it's all water". Why should it all be the same?

This line (about the cmb) seems like the " significance" some people put on the apparent size of the Moon re the Sun and eclipses. The Earth-Moon distance changes - that we now see a different thing than others did or will do is nothing amazing.

Edited November 2, 2014 by pzkpfw

[elfmotat]

I say that any random observer should observe roughly the same thing,should establish mathematically the same laws of physics and should conclude the same things about the universe.

When I say random, I mean absolutely random:

that means 10 billion years in the future, 10 billion years in the past, anywhere. (because usually we think of randomness of position "now" and we forget about randomness in space and in time).

Since the current accepted theory describes things differently, it means to me that we are not random observers.

 

I know what you're saying, and I'm telling you that it is wrong. It's fundamentally incompatible with a universe that changes size over time. Are you really willing to ignore nearly a century's worth of data on the expanding universe in favor of an ad-hoc "principle" that you made up?

[MigL]

Every single point in the universe emitted these photons.

As the universe expands we may not be able to see the ones that came from a great distance, but we'll still be able to see the ones that came from closer distances.

Even after the universe has expanded a billionfold more than it has since the big bang, we'll still be able to 'see' those photons that originated a short distance away, say down the street. I say 'see' because the photons will have red-shifted a billion times more, and will be undetectable.

[elfmotat]

Every single point in the universe emitted these photons.

As the universe expands we may not be able to see the ones that came from a great distance, but we'll still be able to see the ones that came from closer distances.

Even after the universe has expanded a billionfold more than it has since the big bang, we'll still be able to 'see' those photons that originated a short distance away, say down the street. I say 'see' because the photons will have red-shifted a billion times more, and will be undetectable.

 

Any photons created in this region of the universe near the big bang have long since traveled far away from here or been absorbed. The CMB photons we see come from billions of lightyears away. You won't be able to see the CMB once the rest of the universe is too far away.

[zapatos]

Every single point in the universe emitted these photons.

As the universe expands we may not be able to see the ones that came from a great distance, but we'll still be able to see the ones that came from closer distances.

Even after the universe has expanded a billionfold more than it has since the big bang, we'll still be able to 'see' those photons that originated a short distance away, say down the street. I say 'see' because the photons will have red-shifted a billion times more, and will be undetectable.

 

How will we be able to see the ones that originated a short distance away? There were a fixed number of photons generated, and eventually all of them that are directed at us and capable of reaching us must pass us by.

Edited November 2, 2014 by zapatos

[michel123456]

 

I know what you're saying, and I'm telling you that it is wrong. It's fundamentally incompatible with a universe that changes size over time. Are you really willing to ignore nearly a century's worth of data on the expanding universe in favor of an ad-hoc "principle" that you made up?

No I don't want to ignore a century's worth of data.

 

I dare to suggest that there is incompatibility because we have not made the correct interpretations.

The Theory (Relativity) may be correct, the data's may be correct and support the Theory, there is still a huge gap to cover, which is interpretation.

 

For example, we can observe a spaceship flying away from us at huge velocity and really observe the spaceship experiencing time dilation and length contraction while the spaceship's captain experiences nothing.

In this case, the fact that time dilation physically occurs is part of interpretation. We have thus made experiences and find out that time dilation occurs, indeed.

 

When we use this kind of Theory, which is fundamentally relative, in order to explain the Universe, we should keep in mind that all (ALL) results will be relative and not absolute.

 

So it may be that the Universe appears expanding, relative to us, that the Big Bang happened 13 billion years ago, relative to us, etc.

Similarly, I am suggesting that for an observer 10 billion years ago, it may be that again the universe appeared expanding to him, and that the Big bang happened 13 billion years before him.

It may be that an observer 10 billion years in the future would also observe the same things than we do, and conclude exactly the same, that the Big Bang occured 13 billion years from him.

 

IOW that the phenomenas that we call the Big Bang, and the CMB, are phenomenas explained by Relativity and as such, are horizons. IOW they are relative to the observer and have nothing to do with what an observer like the spaceship's captain, would have observed 13 billion years ago.

 

What we have done till now is getting the data's, applying the Theory, and driving the conclusion that the data's were different in the past and will be different in the future (because it is said so from our Theory). But that is relative.

Edited November 2, 2014 by michel123456

[elfmotat]

No I don't want to ignore a century's worth of data.

 

I dare to suggest that there is incompatibility because we have not made the correct interpretations.

The Theory (Relativity) may be correct, the data's may be correct and support the Theory, there is still a huge gap to cover, which is interpretation.

 

So are you saying the universe is not really expanding?

 

 

For example, we can observe a spaceship flying away from us at huge velocity and really observe the spaceship experiencing time dilation and length contraction while the spaceship's captain experiences nothing.

In this case, the fact that time dilation physically occurs is part of interpretation. We have thus made experiences and find out that time dilation occurs, indeed.

 

Time dilation is not an interpretation, it's a measurable effect. There is never any ambiguity as far as how much time a particular clock will measure.

 

 

When we use this kind of Theory, which is fundamentally relative, in order to explain the Universe, we should keep in mind that all (ALL) results will be relative and not absolute.

 

I don't know why you're so intent on this. Not everything is relative. It's silly to argue from a position that is demonstrably wrong.

 

 

So it may be that the Universe appears expanding, relative to us, that the Big Bang happened 13 billion years ago, relative to us, etc.

Similarly, I am suggesting that for an observer 10 billion years ago, it may be that again the universe appeared expanding to him, and that the Big bang happened 13 billion years before him.

It may be that an observer 10 billion years in the future would also observe the same things than we do, and conclude exactly the same, that the Big Bang occured 13 billion years from him.

 

That just fundamentally makes no sense at all. You can't simultaneously age and not age. Plus it's completely made up. Perhaps this would be better suited for a discussion in the speculations forum, because you're very far off track from mainstream science.

 

 

IOW that the phenomenas that we call the Big Bang, and the CMB, are phenomenas explained by Relativity and as such, are horizons. IOW they are relative to the observer and have nothing to do with what an observer like the spaceship's captain, would have observed 13 billion years ago.

 

What we have done till now is getting the data's, applying the Theory, and driving the conclusion that the data's were different in the past and will be different in the future (because it is said so from our Theory). But that is relative.

 

Events can't both happen and not happen. This is true in any physical theory. You're just making up logically inconsistent ways the universe could conform to the ridiculous principle that everything is relative.

Edited November 2, 2014 by elfmotat