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Is it certain that CMBR originates from the 5% of ordinary matter?

  1. Jul 26, 2013 #1
    In standard model Cosmology ordinary matter is only 5% of the total mass - energy of content of the Observable Universe.


    Since 95% of the mass energy content of the Universe is unknown with uncertain properties, can we really be certain CMBR originates from the 5% of ordinary matter making up our Universe or could there be other possible radio sources of some kind in the remaining 95%?

    Also are there possible implications for any other theories, as a result of such a large percentage of the Universe being unknown? At face value it just seems that we know very little about what makes up the vast majority of the Unverse and so I just wonder if we may be making any assumptions.
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  3. Jul 26, 2013 #2


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    Dark matter does not emit or absorb radiation, so it can't contribute to CMB. Dark energy is a property of space itself - no interaction with photons.
  4. Jul 26, 2013 #3


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    Er, my understanding is that the CMBR isn't radiation from matter, it is what is still left of the radiation of the Big Bang - when the universe contained no matter at all.
  5. Jul 26, 2013 #4


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    The CMB was emitted from electrons and protons, ~300000 years after the big bang, when neutral hydrogen formed and the universe became transparent.
    Every photon produced before that era was absorbed by some free charge, we cannot observe them any more.

  6. Jul 26, 2013 #5
    This article is probably one of the better break downs of the early universe particle physics and the epochs involved. Granted it is a bit older so some of the ideas may have changed in it. It relies on Suzy. Quote from the aticle below

    Recombination Era (380,000 years after):
    Hydrogen and helium atoms begin to form and the density of the Universe falls. This is
    thought to have occurred about 380,000 years after the Big Bang. Hydrogen and helium
    are at the beginning ionized, i.e., no electrons are bound to the nuclei, which are therefore
    electrically charged (+1 and +2 respectively). As the Universe cools down, the electrons
    get captured by the ions, making them neutral. This process is relatively fast (actually
    faster for the helium than for the hydrogen) and is known as recombination. At the end
    of recombination, most of the atoms in the Universe are neutral, therefore the photons
    can now travel freely: the Universe has become transparent. The photons emitted right
    after the recombination can now travel undisturbed and are those that we see in the cosmic
    microwave background (CMB) radiation. Therefore the CMB is a picture of the Universe at trhe end of this epoch

    Attached Files:

  7. Jul 26, 2013 #6


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    "Fast" is relative. It took something like 30000 years.
  8. Jul 26, 2013 #7
    lol true enough thankfully thats the authors wording not mine lol
    Last edited: Jul 26, 2013
  9. Jul 26, 2013 #8
    Thanks for replies.

    I know about the standard model its just that since we know very little indeed about 95% of the Universe it is difficult to understand how we can be so 100% certain.. I cant think of a similar example of knowing so little about the whole, but claiming with certainty to know so much.

    Mathman says "Dark matter does not emit or absorb radiation, so it can't contribute to CMB. Dark energy is a property of space itself - no interaction with photons".

    Well these are characteristics that we say these things would have to have. We do not know for certain since we have never had any to measure.
    Last edited: Jul 26, 2013
  10. Jul 26, 2013 #9


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    There are no unaccounted for sources of photons in the universe today, so why would that be different in the distant past? One of the axioms of modern physics is the laws of physics do not change over time.
  11. Jul 27, 2013 #10
    As a side note on this comment, yes there is a lot we don't not know as of yet about DE and DM, as well as several other aspects of cosmology. We do know a great deal about how the two influence the structure development of our universe. Albeit through indirect influences. When you consider what science believed 100 years ago approximately to now, the advances are tremendous. My link has a website cosmology101 I've been gradually developing with some excellent historical links.
    Included further down is links related to explaining current cosmology as per the "concordance cosmology" not to say there are not other viable models, I relate to LCDM as opposed to LQC due to understanding level of the two not belief.

    The article" What we have learned from observation cosmology may be of particular use to you.

    One of the challenges of cosmology is one need a wide variety of understanding to gain the full picture. Included is GR, SR, particle physics (more specifically QFT) and QM as well as other branches of science such as perturbation theory/fields

    Most of what we can correlate about DE and DM in particular involve particle physics and QM. From particle physics we can correlate a probable chance DM formed at a certain time,as well as its predicted properties, from perturbation theory we can correlate its influences on large scale structure formation.

    The unfortunate part is that truly understanding such a wide set of studies, lead to loads of misinterpretation. (hence the reason for my site development, cut to the chase, so to speak) Those incorrect interpretations can only be rectified by correct and current understanding of all the sciences involved. (thankfully this site is a great aid in understanding)

    However it is possible with dedication, take that on faith from a self taught cosmologist aka beginner to ??
    Last edited: Jul 27, 2013
  12. Jul 27, 2013 #11

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    Nonsense. This is one thing we are sure of for dark matter. If it interacted with photons, we would see it, and we wouldn't call it "dark".

    Dark energy even more so. That's a property of space. If light were spontaneously emitted or destroyed when traveling through space, we would have noticed.

    Just because we don't know everything about something doesn't mean we don't know anything about it. (We know very little about Anne Hathaway, Shakespeare's wife, but we're still certain she did not live in 9th century China)
  13. Jul 27, 2013 #12
    The 'recent' advent of these findings, roughly the 1960's for dark matter and the 1990's or so for dark energy did not completely upset our overall view of the universe. I think it was likely Vera Rubin's work of galactic rotations that made dark matter a mainstream phenomena. But Fritz Zwicky suspected such as far back as the 1930's. So I would guess while the findings for each were a surprise, they were not unexpected by everyone.

    Let's hope there WILL be implications after we find out just what those 'dark' entities really are.
    Harvesting dark energy, for example, is science fiction for now. Perhaps dark energy might someday offer insights into vacuum energy, or vice versa. Right now, as noted in prior posts, all we can tell so far is that both are rather weakly interacting but do have gravitational effects.

    Consider reading about WIMPS as one possible description of dark matter. For dark energy, leading models are a 'cosmological constant' and 'quintessence'. Both models include the common characteristic that dark energy has negative pressure.

    edit: I believe one unresolved issue for dark energy that is still unknown is whether it is constant, as in cosmological CONSTANT, or more like a scalar field that varies over cosmological time.

    Maybe someone here will post an opinion or current observational efforts.
  14. Jul 28, 2013 #13
    Thanks for thoughtful replies.

    Please note that I am not saying I disagree with the model at all, just the absolute certainty with which we say we know something. The CMBR measurement and explanation is still only 50 years old, and when one says that we know something with absolutely certainty, then the scientific community shuts its mind out to ALL other possibilities, however remote. Being a corner stone for every part of Cosmology, if the CMBR explanation did turn out to be wrong (trillions to one chance I know) then refusing to ever consider that possibility might prevent us from EVER seeing such a mistake which would be a terrible thing.

    So I dared to mention a small voice of concern when I read that 95% of the mass energy of the Universe is relatively unknown, with unknown properties, which we are also still in the process of creating to explain other phenomenon. When I read this I also wonder just how much of the Universe is also still unknown to us. And besides this uncertainty there are also a multitude of various radio sources scattered throughout the universe in all directions, they are not difficult to make, so again I remain concerned that there is no room whatsoever for even a very small amount of doubt in the CMBR explanation.

    The universe is full of EM radiation with new sources appearing every year:
    Last edited: Jul 28, 2013
  15. Jul 28, 2013 #14
    I don't think anybody meant that.

    The best science can do is to match theories with observational measurements. The closer the better. If a new theory comes along and can make some new prediction [and match known observational measurements] which is then confirmed via new observation, voila, we have a new theory a bit better than the old.

    Here is a discussion about whether concentric circles have or have not been detected in the CMBR:


    If ever confirmed, it could add to our understanding of the universe.
  16. Jul 28, 2013 #15
    Naty this is purely hypothetical:

    100 years from now we send a probe into interstellar space and the CMBR signal is discovered to change significantly. Measurements reveal that the source of the CMBR radiation turns out to be a sphere of dust particles surrounding our solar system being heated by cosmic rays.

    Or alternatively a 100 years from now: As well as 94.9% dark matter and energy the universe is discovered to also consist of a 0.1% strange matter which produces EM radiation at the CMBR frequency when... etc etc

    Things like this have happened in the past and this is why I keep a tiny part of my mind open to other possibilities. I also get even more skeptical when I read that CCC variations in the CMBR may be caused by a universe before our own BB. Occam etc
    Last edited: Jul 28, 2013
  17. Jul 28, 2013 #16


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    They have not. I think you are really underestimating the amount of evidence for the big bang model, and how well the CMB is in agreement with that.
  18. Jul 28, 2013 #17
    All, While accepting and agreeing with everything that has been said, allow me to ask Tanelorn's question from a different perspective: given the DE results in a stretching of the space that protons pass through, and DM has a gravitational impact on the photons of the CMBR, and that the photons originate from / relate to 5% of (observable) universe, can we be reasonably sure of the conclusions that are drawn?
  19. Jul 28, 2013 #18


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    Which conclusions do you have questions about?
  20. Jul 28, 2013 #19

    What is the difference between certain, absolutely certain, and a fact?
    It does seem that there is no doubt whosoever then.

    I see that the CMBR was predicted as early as 1941. When did the explanation for the background temperature become the BB?

    I see that the redshifted CMBR frequency is still quite high 160.2GHz. My poor memory had it at 3GHz for some reason.

    Here is an interesting chart showing the full range of frequencies observed on earth and their attenuation and absorption:


    Last edited: Jul 28, 2013
  21. Jul 28, 2013 #20


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    These are not scientific words, they do not have a clear definition.
    The model how the CMB formed during recombination? Beyond reasonable doubt. It is interesting to see what other models predict, but as none of them comes close to the observations they are not a serious competition.

    I think (most of?) those predictions come from the big bang model, but you can check the references.

    I guess the numerical value comes from the temperature of 3K.
  22. Jul 28, 2013 #21
    always a good idea.

    yes. The cosmological model, Lambda CDM, or Big Bang Model has been 'tweaked'[modified] to match observational cosmology. It's not as if we have the perfect model arising from a few first principles which provides all the constants and factors necessary.

    To get an idea of actual observational and theoretical constraints, check out the first few paragraphs here: http://en.wikipedia.org/wiki/Lambda-CDM_model

    Here is a quick summary why scientists like the existing 'big bang model':
    http://www.damtp.cam.ac.uk/research/...b_pillars.html [Broken]

    The Big bang model says nothing about time zero...when we find what happened there, it will say something. Roger Penrose describes how we glue in, that is add to the earlier model, an inflationary theory to create the proper 'front end' which is now incorporated in the 'big bang model:

    This transition is the 'slow roll' version of 'inflation' described in Wikipedia....


    Look at the prior section, EARLIER INFLATIONARY MODELS, to see problems that were overcome like 'bubble nucleation'....and so those models were discarded.
    Last edited by a moderator: May 6, 2017
  23. Jul 28, 2013 #22
  24. Jul 29, 2013 #23
    (First off, this might have been addressed by a subsequent post by Naty1 and the links that he provided - I haven't had a chance to read those yet.)

    All that I was asking, is that the BB interpretation sees the ripples in the CMBR as supportive of the model (I.e. ripples in the early universe that led to the structure that we see today). However, given the gravitational impact of DM over 14by, and a magnification of any early impacts by DE, how is possible to have a non-ripply CMBR under any circumstances ... irrespective of the initial conditions?
  25. Jul 29, 2013 #24
    The CMBR is evidence of big bang nucleosynthesis. The ripples effect is historically later evidence of various processes that occured prior to last reionization. For a while after the CMBR was discovered there was conjecture as to whether or not the CMBR will retain fingerprints of earlier processes in the form of the anistrophies. Two factors combined in regard to to the CMBR are involved, one being the presence of the CMBR the other is the remnant gases ie hydrogen, lithium measurements. The BB predicted a certain % and measurements agreed. By the way a non ripply CMB would be highly unlikely, that was never expected, its the interpretation of the causes of the ripples that often comes under debate.
  26. Jul 29, 2013 #25
    Thanks Mordred. I get the link between BB nucleosynthesis and the relative / % abundance of light elements. I even get that for any CMBR to exist, there had to be initial elements / material forming inorder for a recombination event to be happening. I just hadn't made a connection between the relative amounts of the specific elements and the form of the CMBR that we see. Oh well, back to the drawing board ... again!

    Specifically in relation to the CMBR and BB nucleosynthesis / the relative abundance of light elements, could you recommend some papers or other reading?
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