Evidence of past CMB (split from steady state universe)

[michel123456]

There is one key factor you missed. In the steady state universe the temperature is constant. The matter creation maintains the same energy density so according to the ideal gas laws the eternal steady state universe would not show a change in temperature. This is one of the why the CMB disproved the steady state model. The temperature of the CMB is roughly 3000 kelvin today it 2.73 kelvin which shows that the average energy density is decreasing due to expansion with a finite amount of mass energy per volume.

Excuse my ignorance but what evidence have we that 10 billion years ago the CMB was measured more than it is measured today?

Edited October 26, 2014 by michel123456

[swansont]

Excuse my ignorance but what evidence have we that 10 billion years ago the CMB was measured more than it is measured tofay?

 

The several-thousand-K temperature is that at recombination, when the universe became more or less transparent

http://en.wikipedia.org/wiki/Recombination_(cosmology)

[michel123456]

 

The several-thousand-K temperature is that at recombination, when the universe became more or less transparent

http://en.wikipedia.org/wiki/Recombination_(cosmology)

That is not evidence.

[swansont]

I don't really know how to respond to that. You can't demand a specific set evidence, because that's not how science works; not all of science is a direct measurement of some phenomenon. So I can't really ask what evidence you want. There is a larger picture you have to look at — that we understand how plasmas work, and what happens when the electrons and protons recombine and what conditions are required to have a reasonable mean free path of photon travel.

 

Plus the context of the thread that this came from, that there is probably no reason to expect any particular CMB temperature in a steady-state condition.

[michel123456]

I don't really know how to respond to that. You can't demand a specific set evidence, because that's not how science works; not all of science is a direct measurement of some phenomenon. So I can't really ask what evidence you want. There is a larger picture you have to look at — that we understand how plasmas work, and what happens when the electrons and protons recombine and what conditions are required to have a reasonable mean free path of photon travel.

 

Plus the context of the thread that this came from, that there is probably no reason to expect any particular CMB temperature in a steady-state condition.

O.K.

We are measuring today that the CMB has a specific temperature. That is an evidence.

We cannot measure what temperature of the CMB a long time ago, that is a lack of evidence and I understand that we are obliged to work out a model with that lack of information.

I also understand that any proposed model must "insert" the fact that the CMB has the specific temperature.

But I understand also that the only fact that we really know, the only evidence we have at hand, is today's CMBR temperature.

We cannot say: the CMB was higher in the past and thus blah blah blah.

We must say that our model "predicts" a higher CMB temperature in the past.

IOW the higher temp of CMB in the past is not an element that supports our current model, it is an assumption that derives from our model.

For example

 

the very fact that there is a CMB is proof of a hot dense past.

Is a false assumption. Edited October 26, 2014 by michel123456

[Mordred]

Our understanding of particle physics and thermodynamics predicted the existence of the CMB. The CMB is a result of particles dropping out of thermal equilibrium from higher temperatures when the universe cooled down enough. If the temperature is too high stable reactions cannot occur so heavier elements cannot form with stability. This is what thermal equilibrium means. At high enough temperatures quarks and gluons cannot even combine to form Hydrogen. The CMB is a direct result of particles being able to combine with stability to form hydrogen and lithium.

 

Keep in mind Big Bang nucleosynthesis predicted the CMB long before we discovered it

http://www.wiese.itp.unibe.ch/lectures/universe.pdf

 

the process is described in this textbook style article

Edited October 26, 2014 by Mordred

[Strange]

 

Keep in mind Big Bang nucleosynthesis predicted the CMB long before we discovered it

 

And that is why it was the death blow to the steady state theory. There is no other model that can produce the observed CMB (and that also fits all the other evidence).

[swansont]

O.K.

We are measuring today that the CMB has a specific temperature. That is an evidence.

We cannot measure what temperature of the CMB a long time ago, that is a lack of evidence and I understand that we are obliged to work out a model with that lack of information.

I also understand that any proposed model must "insert" the fact that the CMB has the specific temperature.

But I understand also that the only fact that we really know, the only evidence we have at hand, is today's CMBR temperature.

We cannot say: the CMB was higher in the past and thus blah blah blah.

We must say that our model "predicts" a higher CMB temperature in the past.

IOW the higher temp of CMB in the past is not an element that supports our current model, it is an assumption that derives from our model.

For exampleIs a false assumption.

If that's what you want, then you have to throw out a lot of science.

[Strange]

IOW the higher temp of CMB in the past is not an element that supports our current model, it is an assumption that derives from our model.

 

If it derives from a model then it isn't an assumption, by definition.

[michel123456]

If it derives from a model then it isn't an assumption, by definition.

Lets put it otherways.

 

Do you agree with the following statement:

 

the very fact that there is a CMB is proof of a hot dense past.

 

[Strange]

Do you agree with the following statement:

 

Given the only current model we have, yes.

 

With, of course, the usual caveats on the use of the word "proof" in science; in other words, the existence of the CMB with the predicted temperature, spectrum, isotropy, and other properties confirms the predictions of the model.

[michel123456]

 

Given the only current model we have, yes.

 

With, of course, the usual caveats on the use of the word "proof" in science; in other words, the existence of the CMB with the predicted temperature, spectrum, isotropy, and other properties confirms the predictions of the model.

I prefer your last statement.

Edited October 26, 2014 by michel123456

[Strange]

I prefer your last statement.

 

That is what "proof" means in science.

[michel123456]

 

That is what "proof" means in science.

You have a model that predicts there are fishes in the sea.

You fish a dolphin.

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To say it otherwise.

If I build a model that predicts CMB but my model says that temp is a sinusoidal function (raising and lowing), would CMB become a "proof" of my model?

[Strange]

Sorry, I don't understand the question.

[elfmotat]

You have a model that predicts there are fishes in the sea.

You fish a dolphin.

-----------------------

To say it otherwise.

If I build a model that predicts CMB but my model says that temp is a sinusoidal function (raising and lowing), would CMB become a "proof" of my model?

 

If your model correctly predicts bunch of phenomena, and it also predicts some related yet untested phenomenon, then it's reasonable to assume that your model will also accurately describe the untested phenomenon. Is it "proof" that it definitely will describe it accurately? Of course not, but it's more useful to assume the usual rules work (until they don't).

[Strange]

You have a model that predicts there are fishes in the sea.

You fish a dolphin.

 

Catching a dolphin would falsify the model if it predicts that there should be no dolphins.

If the model said nothing about dolphins, then you may need to modify or extend the model. (See also: dark matter.)

[MigL]

Thermodynamics predicts that an EXPANDING universe with a CMB is proof of a hotter past.