Is the popular understanding of C.M.B.R. too simplistic?

[Peter Watkins]

Contributers to this forum are no lovers of popular science magazines or TV. programs, but this is from where most 'lay' people get their information. From such sources we are given to understand that the background radiation is thought to be light, (of whatever original wave-length), from the very early universe that has been "stretched" by the expansion of the universe, making shortwaves longwaves, and high frequencies, low. Is this the case, or is this too simplistic a view?

 

[Rick88]

I would just say that the energy of the photons that are still traveling from the moment when the Universe became transparent has decreased substantially as a result of the expansion of the Universe.

But the idea was roughly right.

 

[Nabeshin]

That's pretty much it. Like the above post mentions, though, it doesn't give an idea of WHY this is the first light we can see. But as an explanation, it's pretty good (better than many other popular science explanations I've heard).

 

[Peter Watkins]

So would it be safe to say that the different frequencies of early light, x-rays, ultra-violet, visible light, etc., have been "stretched" so much that they can no longer be discerned in their original form?

 

[marcus]

I would just say that the energy of the photons that are still traveling from the moment when the Universe became transparent has decreased substantially as a result of the expansion of the Universe.

But the idea was roughly right.

So would it be safe to say that the different frequencies of early light, x-rays, ultra-violet, visible light, etc., have been "stretched" so much that they can no longer be discerned in their original form?

Peter, notice that Rick did not say anything about x-ray or ultraviolet.

But he did refer to the "moment when the Universe became transparent".

You could refine your picture by asking him (or anybody) what were conditions like at that moment or epoch, what was the estimated temperature?

For starters, maybe think of a classic tungsten-filament 100-watt light bulb. The light it gives off is more orange-ish than, e.g. daylight.

Direct unfiltered sunlight is temperature around 6000 K. Lightbulb light is around 3000 K.

It is mostly infrared, with a small percentage of visible. Almost no ultraviolet and insignificant xray.

Essentially all the xray from former hotter times would have been re-absorbed by the hot gas while it was still optically dense. Opaque in the way that the surface of a star is opaque---ionized gas absorbs most wavelengths---you can't see through the glowing surface of the star. The xray in the core of the star never make it out to us. I'm thinking of a star smaller and cooler than the sun---a star about 3000 K---more orange than the sun.

Maybe if you wake up in the middle of the night and have nothing else to think about, shut your eyes and imagine the universe around year 380,000 when it was getting transparent---when it was full of hot hydrogen gas and orange-ish light and radiant heat infrared. Gradually cooling enough so that the gas was less and less ionized---therefore less and less opaque.

 

[Peter Watkins]

So the C.M.B.R.is solely the light from the moment that the universe became transparent, the spectrum of which presumably did not resemble what we see today from distant stars, galaxies etc.

 

[marcus]

So the C.M.B.R.is solely the light from the moment that the universe became transparent, the spectrum of which presumably did not resemble what we see today from distant stars, galaxies etc.

I expect it would have resembled the black body spectrum (thermal glow of a neutral surface) at a temperature of about 3000 K
since that is the calculated temperature at which the gas is sufficiently un-ionized to permit light to travel uninterrupted from then on.

That mix of wavelengths is about the same as you get from a normal main-sequence star that is a bit smaller and cooler than the sun and has a surface temp of 3000 K.

It is a faintly orange-ish glow.

So the light, at that moment, when it started on its way to us, did resemble what we see today from a large number of stars. Stars with masses around a quarter the sun's mass are even more common than stars like the sun. So, in a sense, the ancient light was a very familiar commonplace light.

Also like the 3000 K glow of a tungsten light bulb, or the glow inside a metallurgical furnace at 3000 K.You might like to know that the REDSHIFT factor by which the wavelengths have been stretched out since transparency occurred is about z = 1100. They like to use the letter z to stand for redshift.

That is also the ratio of temperature. Nowadays the light's temperature is 2.725 K.
If you multiply that by 1100, because the light was originally 1100 times hotter, you get around 3000 K.
That is why the number 3000 K comes up. Blackbody radiation wavelength and temperature scale the same way.

My intuitive feeling about you (if you will not be insulted by my offering a wild guess) is that you might be the sort of person (like myself) who wishes to have an emotional connection with the universe---to feel something about it, besides just knowing facts.

In that case I could suggest to you that this ancient light is a very warm familiar light, a glow that you know from many places and you can feel at home with. Nothing strange or exotic about it. It is as familiar as the sun---just a factor of two different color. The sun has the same mix of wavelengths except all half as long---twice as short---twice as energetic.

The light I'm thinking of is more like the way sunlight is around sunrise or sunset, when the shorter wavelengths are somewhat filtered out by the atmosphere and the sunlight is more reddish orange. That is sort of what the CMB started out like.

The matter we are made of was once this hot gas, mostly hydrogen with some helium, and it was becoming transparent, and it was glowing hot. And our matter sent out this glow of orange-ish light. And somebody else, in a galaxy far away from here, is receiving the CMB right now. And some of the light coming to them is the glow from the matter that you and I are made of. The very same quarks and electrons, but since then rearranged into different elements and molecules.

If you want to know, I can tell you the original distance when the light set out and also the distance now, if you could stop expansion and measure it, between us (our matter as it now is) and the person in the distant galaxy who is receiving our CMB light and perhaps measuring its temperature to be 2.725 K, but in their own temperature units.

 

[Jorrie]

That mix of wavelengths is about the same as you get from a normal main-sequence star that is a bit smaller and cooler than the sun and has a surface temp of 3000 K.

It is a faintly orange-ish glow.

Hi Marcus, would 3000 K not be more of an 'infrared glow'?

 

[Calimero]

Can you see good old light bulb? Do you have infrared vision?

 

[Jorrie]

Can you see good old light bulb? Do you have infrared vision?

Yep, I think I can see the ~5% that's not IR. :)

 

[Jorrie]

Hi Marcus, would 3000 K not be more of an 'infrared glow'?

Perhaps I should put my question more technically. Since the peak intensity of 3000 K is at about 1.2 microns wavelength (double that of orange light), well inside the IR band, should we not classify the CMBR as IR at the time of emission? Or is there more to it?

I agree that if humans were around then, they would have only seen an 'orange-red-ish glow'.

 

[marcus]

Jorrie, language and concepts like peak intensity can lead you on a merry chase.
Given that the title of the thread says "popular science", I want to describe blackbody radiation at 3000 K to someone without getting technical.

The tungsten filament of an ordinary 100 watt lightbulb operates at about 3000K Indeed most of the energy from an ordinary lightbulb is in the infrared---that is why they are inefficient sources of visible light. You know all this, so why are we even talking!

Their output is roughly blackbody 3000 K radiation! And we experience it as a glow that is more orange-ish than sunlight. Call it whatever you want. Call the light from a lightbulb "invisible infrared" if you want, because the peak intensity from a lightbulb is obviously in the invisible IR, and most of the power is in the invisible IR. You are very welcome to make up more sophisticated ways of talking---decide what, for you, is the right thing to call the light from a lightbulb.

BTW isn't it neat how the human eye can gauge temperature. The way a blacksmith or pottery kiln master might. Red heat, orange heat, yellow, white hot. The colors correspond to known temperatures. The human eye does not see the PEAK of the black body spectrum, it samples the mix in the shortwave tail, in the highfrequency tail. So a blacksmith can judge the temperature by the mix in the visible part of the tail of the blackbody curve.
Likewise do I when I look at the electric stove and see that someone left the "burner" on.

My sense is in this thread I just want to talk to the OP Peter Watkins about the CMB. Unfortunately he seems to have left. You will forgive, I hope, this obstinate focus on a single (probably futile) effort at communication.

 

[Jorrie]

My sense is in this thread I just want to talk to the OP Peter Watkins about the CMB. Unfortunately he seems to have left. You will forgive, I hope, this obstinate focus on a single (probably futile) effort at communication.

Marcus, I was more interested in the spectrum of the CMB than that of light bulbs or stoves.

Maybe we should open a 'more technical' thread for that - if it has not already been sufficiently covered around here.

As I understood it, the microwaves that were observed by COBE, WMAP and others ranged from roughly wavelength 1.5 to 15 mm, giving the original emission wavelength as roughly 1.5 to 15 micron IR. If I'm not mistaken, that sits in the 'lower frequency tail' of a 3000 K blackbody source (1.2 micron), the opposite side from what our eyes can observe. Obviously, there could also have been a 'higher frequency tail', but that would possibly not be distinguishable from background (visible) light?

 

[marcus]

Marcus, I was more interested in the spectrum of the CMB than that of light bulbs or stoves.

Maybe we should open a 'more technical' thread for that - if it has not already been sufficiently covered around here.
...

Well this is Peter Watkins' thread. I was hoping he would stay around and ask some more general readership questions. But he didn't. So if you want to start a 'more technical' discussion, why not?

I doubt I personally would be want to take part, but you should be able to find others to talk to. I have little to say on the topic and it's too simple to make good conversation with:

1. when you redshift/blueshift a blackbody curve it stays a blackbody curve, just for a different temperature

2. COBE showed us an exquisitely perfect blackbody curve fit for 2.725 K

3. whatever light there was back then at z=1100 must have fitted a blackbody curve for
1100*2.725 K. Speaking approximately, call that 3000 K. You seem to agree:

...3000 K blackbody source ... Obviously, there could also have been a 'higher frequency tail', but that would possibly not be distinguishable from background (visible) light?

What "background (visible) light" are you talking about? In year 380,000 of the expansion?
Were there stars?

And I thought we agreed that essentially ALL the light that was present has come down to us and is the CMB. In principle from all sources, though I can't think of any other source besides the glowing gas.

The light pervading the universe at that moment in history was near-perfect fit of 3000 K blackbody curve. The only interesting question, then, is what that would look like to Peter Watkins. But we know that. You just have to heat some ceramic firebrick up to 3000 K and look at it. Or better, look through a door into a furnace that is at 3000 K. That is what the universe looked like then.

 

[Jorrie]

What "background (visible) light" are you talking about? In year 380,000 of the expansion?
Were there stars?

I guess I was thinking of "foreground light", but I now realize that even this makes little sense in this context. :-(

The question in my mind was: why are the CMB observations all in the "low frequency tail" and not on the other side of the blackbody curve? (But I'll start a new thread on this new question).

 

[marcus]

The question in my mind was: why are the CMB observations all in the "low frequency tail" and not on the other side of the blackbody curve? (But I'll start a new thread on this new question).

They aren't. The match is almost perfect all the way along the curve. When COBE showed the slide at a major astro conference, for the first time, there was a standing ovation. It was a historic mind-opening moment.

Have you not seen the COBE slide, matching CMB spectrum to the 2.725 K curve?
The fit is excellent all along the curve from low to high.

This is not the best picture because you can't see enough detail but it gives the idea:
http://upload.wikimedia.org/wikipedia/commons/5/5d/Cobeslide36.jpg

Smack dab for wavenumbers all the way from 2 per cm to 22 per cm.

 

[Jorrie]

Smack dab for wavenumbers all the way from 2 per cm to 22 per cm.

Thanks Marcus. The wavenumbers are quite confusing, but I now see that the http://lambda.gsfc.nasa.gov/product/cobe/about_firas.cfm" measured a band from 0.1 to 10 mm in microwaves, not 1.5 to 15 mm, as I originally thought. That surely represents "both sides" of the 2.725 K blackbody curve.

 

[Tanelorn]

Apparently CBMR, the key stone for the standard model, can all be explained away by a new form of matter known as red shift matter. Red shift matter was proposed in a similar way to dark matter, used to explain galaxy rotation.

There we are, we can all rest easy now knowing there are no more inflatron singularities or our universe flying apart! Of course I am only jesting... :)


Seasons Greetings!

 

[marcus]

...

There we are, we can all rest easy now knowing there are no more inflatron singularities or our universe flying apart! Of course I am only jesting... :)


Seasons Greetings!

And a merry Christmas to you, Tanelorn!

 

[Peter Watkins]

Thank you gentlemen for your replies, and my apologies for lack of conversation, but it takes me a while to absorb things. Here's another question that is the result of a popular science "education". The high energy big bang radiation is said to have shifted toward the low energy end of the spectrum, past the red and into the longer, lower-energy microwave section due to universe expansion and a travel time of 13.7 b.y's. over a distance of 13.7 b.l.y's. The most distant gamma ray burst yet detected was from a source that was 13.2 b.l.y's distant. Being only half a billion years younger, why weren't these also shifted into the microwave section?
In fact, of course, they are less than 200,000 years younger than that released at the point of transparancy.

 

[marcus]

Thank you gentlemen for your replies, and my apologies for lack of conversation, but it takes me a while to absorb things. Here's another question that is the result of a popular science "education". The high energy big bang radiation is said to have shifted toward the low energy end of the spectrum, past the red and into the longer, lower-energy microwave section due to universe expansion and a travel time of 13.7 b.y's. over a distance of 13.7 b.l.y's. The most distant gamma ray burst yet detected was from a source that was 13.2 b.l.y's distant. Being only half a billion years younger, why weren't these also shifted into the microwave section?
In fact, of course, they are less than 200,000 years younger than that released at the point of transparancy.

Welcome back! Glad to see you thought about stuff and came back with more questions.
A million does not equal a billion. So the GRB do not come from a time "less than 200,000 years" after the moment of transparency.

13.7 b - 13.2 b = 0.5 b = 500 million = 500,000,000 after start of expansion (redshift z = 10?)

transparency era = approx. 380,000 after start of expansion (redshift z = 1100)You might like to learn how to calculate the redshift z or "stretch factor" 1+z that corresponds to a given light travel-time. It is easy. I don't know how motivated you are to do actual calculations with a cosmology calculator. You might say if you are curious and want to see how the calculator works to relate distance and travel time to redshift.

Anyway the microwave background was longer wavelength to start with and it got much much more stretched---by a factor of 1100. So naturally it got down to the microwave.

But the gamma-burst was much shorter wavelength to start with, by several powers of ten, and got stretched much less---only by a factor of about 10.

http://www.astro.ucla.edu/~wright/DlttCalc.html
========================

BTW Peter the reason I am glad you reappeared is that it means we didn't confuse or discourage you. This is a way to gauge performance of a board like this. If we are working properly then some fraction of lay newcomers with beginner questions will not be put off, and assimilate some and come back with further questions.

 

[marcus]

Actually Peter your figure of 13.2 billion might not be right. I just checked and found that the highest redshift GRB was z = 8.2
http://apod.nasa.gov/apod/ap090429.html
I will keep checking in case my information is out of date. But 8.2 and 10 are not very different anyway.

To relate redshift to light travel time:
http://www.astro.ucla.edu/~wright/CosmoCalc.html

You could give a link if you have a source that says 13.2 billion years.

To relate travel time to redshift (the reverse):
http://www.astro.ucla.edu/~wright/DlttCalc.html
Qualitatively it is about the same----much less stretchout than the 1100 we have with the oldest light---the cmb.

http://www.nature.com/news/2009/091028/full/news.2009.1043.html

 

[Jorrie]

Actually Peter your figure of 13.2 billion might not be right. I just checked and found that the highest redshift GRB was z = 8.2
http://apod.nasa.gov/apod/ap090429.html

Peter may be thinking of http://www.eso.org/public/news/eso0723/" , the oldest star for which the age was measured so far (13.2 billion years), right here in our Galaxy.

 

[marcus]

Peter may be thinking of http://www.eso.org/public/news/eso0723/" , the oldest star for which the age was measured so far (13.2 billion years), right here in our Galaxy.

Thanks for the link. That star is estimated to be 7500 light years from us.
The Wippy has links to more articles about it: http://en.wikipedia.org/wiki/HE_1523-0901

There would be no significant redshift or (cosmological scale) light travel time---Peter was talking about objects at cosmological distance with significant redshift---like a very distant GRB. So the figure 13.2 could have crept in by accident.

But I still think we can probably find examples of very distant stars where the "lookback time" or light travel time is 13.2. So then we would be observing the object as it actually was back near the time it was formed.

Interesting how they estimated the age of that 13.2 billion year old star HE_1523-0901 right here in our galaxy! A comparative close neighbor! They apparently reckoned the age by detecting traces of some radioactive elements. I wonder how well that has stood up. I couldn't find much written about it after 2007.

 

[marcus]

Here's an October 2010 report of imaging a galaxy at z = 8.555.

http://arxiv.org/abs/1010.4312

We see it as it was when expansion was about 600 million years old.

The light has taken about 13.1 billion years to get here.

This is in some sense more definite than detecting a GRB at z = 8.6 because with a GRB alone you don't get an image. You get a flash. There may be an associated optical image, or there may not be. With a GRB you do not necessarily actually see the object.

But this recent imaging of a GALAXY at z = 8.6 is quite an accomplishment! Farthest object imaged so far.

That would actually be a good basis for what Peter Watkins was saying, and the direction of his questions, never mind the GRB.

 

[Jorrie]

But this recent imaging of a GALAXY at z = 8.6 is quite an accomplishment! Farthest object imaged so far.

If we take the result of this and also of the 'oldest star' in our Galaxy (13.2 billion years) at face value, our Galaxy must at least as old as this z = 8.6 galaxy. According the cosmo-calculators, our Galaxy with a star of age 13.2 Gyr, would be equivalent to one at redshift z > 10, formed at less than 500,000 years.

This might mean that the Hubble Ultra Deep Field (HUDF) original aim of z ~ 12 (formed at t < 400,000 yr) might not be out of reach. The galaxies might just be too faint to measure accurately at this time, but I'm quite sure it will be accomplished soon. I'm not sure that we can hope for much more than that...

 

[Peter Watkins]

It seems I got my millions and billions confused. Aging brain! Sadly the computer that had a shortcut to the site that that reported the GRB. has expired. However, GRB090423 is thought to have occurred when the universe was just 630 million years old. This is fairly close to the time of tansparency.
Another question. What is the increase in the rate of recession between one numeral and the next on the red shift scale, and what is the base figure or unit?

 

[marcus]

Another question. What is the increase in the rate of recession between one numeral and the next on the red shift scale, and what is the base figure or unit?

Peter the relation between redshift and current distance
and also the relation between redshift and current recession rate

are not linear, so there are some handy online calculators that convert redshift to other info.

Also the relation between redshift and distance depends on three parameters which people try to estimate as best they can and then plug into the formulas.

With one calculator the three numbers are already plugged in for you:
.27 for the matter fraction, .73 for the cosmol. constant fraction, and 71 for the Hubble (current expansion rate)

It is good to know these numbers anyway--- .27, .73, 71 ---even though sometimes they are put in for you. As with the calculator you get by googling "cosmo calculator".

With another calculator, the one you get by googling "cosmos calculator", they are not put in. The professor wants her students to do a little work, so they know that the results depend on parameters. She has dummy placeholder numbers in the boxes, like 1, 0, 70 instead of the right numbers .27, .73, 71.

I think that is pedagogically good and it takes only a few seconds to put in the right parameters---then you are good to go.

I recommend using her calculator---Prof. Siobhan Morgan. "cosmos calculator" I keep the URL for it in my signature. It is simple and clear and it gives not only the distance now but also the distance back then when the light started on its journey. Because of expansion the two are different.

The distance is what you would measure if you could freeze expansion at that moment (so it would not be changing while you were trying to measure it.)

Morgan's calculator also gives the then and now RECESSION RATES!
The rate that the distance was increasing back then, when the light started on its journey, and also the rate the distance to the galaxy is increasing at this moment when we receive the light and take the photograph. I like this extra feature. Not every cosmology calculator gives the rates of distance increase.

 

[Chronos]

The CMB is an entirely different beast from a GRB at 13.2 billion light years. The CMB was an extremely homogenous plasma that comprised all of the known universe ~13.7 billion light years ago. A GRB is a gravitationally bound object that detonates with far more energy than the CMB. A GRB at 13.2 billion light years would still be highly redshifted [~ z = 1000], but, would peak at a much higher EM frequency than the CMB.

 

[Tanelorn]

Anyone think that galaxies forming so soon after the BB might pose a problem?

 

[Jorrie]

. A GRB at 13.2 billion light years would still be highly redshifted [~ z = 1000], but, would peak at a much higher EM frequency than the CMB.

I do not understand what you mean by "[~ z = 1000]". Would a GRB at 13.2 billion light years not have happened at t ~ 500 million years and have a redshift z ~ 10?

 

[marcus]

Anyone think that galaxies forming so soon after the BB might pose a problem?

Early structure formation helps to confirm current ideas about dark matter.

We can image clouds of dark matter using gravitational lensing and estimate amounts of it in galaxies and clusters of galaxies---there are various was of doing that. But structure formation is one of the ways we can check estimates of the over all amount.

For results of quantitative computer modeling leading to simulations of structure formation in the early universe, google "Smoot TED" for an 18 minute general audience talk with good visuals.

In the numerical simulations, collapsing strands of dark matter serve as "seeds" of ordinary matter condensation---or as kind of "armature" for visible structure to collect on.

So galaxies as early as 500 million is consistent---essentially what one can expect given current ideas of how much DM.

I would say that new observational data is tending to guide or constrain or narrow down the model---rather than presenting "a problem". But you could think of it as potentially constituting a problem to the model if the wrong parameters are chosen. e.g. like choosing too low a DM density.

 

[Peter Watkins]

Re #28. Did all that. It seems to be that red-shift is used to calculate the age of the universe, whereas I had thought that it was a scale that measured the rate of recession of whatever galaxy was being observed. The H.U.D.F. view certainly gives the latter impression when it reports galaxies that existed 800 million years after the big bang, red-shift 7, and others that lived just 400 million years after the big bang, red-shift 12. If the numerals are indicating age and not recession rates, then this is just information duplication.
Just as an aside, red-shift cannot be used to determine age as recession rates vary according to the angle of view. This was the most important fact to emerge from some four decades of study to determine the Hubble constant, although it was not, and still isn't, realized.

 

[marcus]

Re #28. Did all that.

Good! Glad to hear that you tried out one or more of the calculators. Did you specifically experiment with Morgan's? That was the one I discussed most in post #28. The link to it is in my signature at the end of my posts.

It seems to be that red-shift is used to calculate the age of the universe, whereas I had thought that it was...

If you play around with the calculator you will see that it the estimated present age of the universe depends on the three numbers you put in at the beginning: .27, .73, 71. The age is calculated from them. Putting in a different redshift should not affect the estimated age.
So I would say that using the calculator could teach you the opposite from what you say here---the redshift of a galaxy is NOT used to calculate the present age.

Maybe you mean the age of the universe when the light was emitted by the galaxy and started on its way to us. Then what you say is right. The redshift tells the age at emission time. And also a lot else. The distance then, the distance now, the light travel time, the recession rate back then at emission time, the recession rate now...

A lot can be calculated from the redshift.

I should mention that before the measured redshift is used, it needs to be corrected for the doppler effect of solar system motion. It is standard practice to adjust the data to get rid of the effect of the solar system's motion (around 370 km/second in direction of constellation Leo) and also, if necessary, the motion of the Earth or whatever space platform relative to the solar system as a whole, which can be as much as 30 km/second.

So when we talk about the redshift of some galaxy we are assuming it is already corrected for the doppler of the observer's own motion. I've often made that point here at this forum and I expect many others of us have as well. It is well-known.

Just as an aside, red-shift cannot be used to determine age as recession rates vary according to the angle of view. This was the most important fact to emerge from some four decades of study to determine the Hubble constant, although it was not, and still isn't, realized.

Do you have a source for that, Peter? I'm curious to know where you get the information that this "was not, and still isn't, realized".

 

[Peter Watkins]

Just been looking back over old questions; seems we've been here before. There is no source for this as this is my own assertion. My reasoning is simple. The different teams endeavering to establish a "constant" kept coming up with results that did not match. The expectation was that a single figure would be found, the fact that it wasn't led to discord. What it should have led to was acceptance of the fact that different angles of view produce different rates of recession. This can be easily illustrated in two dimensions by picturing a spoked bicycle wheel representing a slice through an expanding mass of matter that extends from the hub to the rim. If an observer should be situated at a distance 55% along one of the spokes it will be self evident that recession rates will vary according to his angle of view. The inward view will appear to be moving away from him as he moves away from them, the outward view will actually be moving away from him. This is, of course, not the universe, but a loaf of raisin bread. The three dimensional view would see these "spokes" in all directions with virtually all raisins, (galaxies), exhibiting red shift at a rate that increases with distance. Collapse would produce the same view, as would inner collapse whilst the outer was still expanding. It's quite amazing what a loaf of bread will do with varying rates of gravitational restraint