Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The Percentage of dark matter

  1. Nov 27, 2011 #1
    I have a theory about what dark matter and dark energy is and so far my theory can explain the % of dark matter, atoms and dark energy for the present universe and the 380 000 old universe base on the Wilkinson Microwave Anisotropy Probe findings
    but I need to be sure, I need more confirmations that it will work for any age of the universe

    If anyone can help me, I am looking for the %s of the dark matter, atoms and “dark energy or/and photons” in a 6x10^9 years old universe‏, my problem is that I am not an astrophysicist; I cannot work the equations. Anyway I need the %s to verify my theory.
    I calculated the %s for the 6x10^9 years old universe:
    47.838% dark matter, 9.112% atoms, 43%"dark energy or/and photons"

    Last edited: Nov 27, 2011
  2. jcsd
  3. Nov 27, 2011 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You should know that overly speculative posts and personal theories are both against PF rules and that this thread will probably get locked.

    Theories in the physical sciences are mathematical models. There is no other way to describe nature unambiguously. If you don't have any equations, then you don't have a theory.
  4. Nov 27, 2011 #3
    It is not overly speculative post; I just said my calculations (or theory) so far are verified by the findings of the Wilkinson Microwave Anisotropy Prob.
    And I have a mathematical model, I posted my findings base on my theory for the %s of the dark matter, atoms and “dark energy or/and photons” in a 6x10^9 years old universe.
    ‏ 47.838% dark matter, 9.112% atoms, 43%"dark energy or/and photons"

    My equations are very simple and are based on my theory of the geometry of time, and so fare they work, I just need to help to verify it, I do not claim anything, I do not claim that I am right but maybe I just found something.

    I understand your skepticism but science is about discovery too, and imagination leads to discovery.
    Albert Einstein quote:“Imagination is more important than knowledge. For knowledge is limited to all we now know and understand, while imagination embraces the entire world, and all there ever will be to know and understand.”
  5. Nov 27, 2011 #4


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    To answer your question we can use the standard cosmic parameters
    assuming spatial flatness, matter fraction 0.27, and Hubble rate 71 km/s per Mpc.

    Google "cosmo calculator" and verify that redshift z = 0.984 corresponds to the age you mention---6 billion years.

    So you are talking about distances being 1/1.984 what they are today. About half.

    Taking ordinary matter and dark matter together, the matter density would be about 8 times what it is today.

    As long as you are just asking questions about past conditions according to the standard model everything is fine and folks will try to answer. You should probably think about explaining your own theory on some other discussion board though---our focus is on understanding mainstream cosmology.

    The estimated Hubble constant with those parameters, at redshift 0.984, would be 119.62 instead of 71 km/s per Mpc. So bigger by what factor?
    Bigger by a factor of 119.62/71.

    The square of that is 2.84

    That means the critical density was 2.84 times what it is now.

    But the matter density which is .27 of critical now was 8 times bigger so as a fraction of critical it was .27*8/2.84

    I get that the matter fraction was 76% of critical then!

    Or putting in 1.984 instead of 2, for a little more precision I get 74%

    So according to me at least, your model fails this test. You say the matter fraction at age 6 billion years should be 57%

    I say that according to standard cosmology at 6 billion years of age the matter fraction was not 57% but rather it was around 75% (my rough estimates were around 74-76)

    I could have made a mistake though! Hopefully someone else will confirm, or else correct me if I made an error.
    Last edited: Nov 28, 2011
  6. Nov 28, 2011 #5
    Interesting 75% (Dark matter + Atoms) it is the same percentage base on the Wilkinson Microwave Anisotropy Probe findings for a 380 000 years old universe.

    If you are right for the first 6 billion years of the universe, the % stayed the same, 25% dark energy or/and photons and 75% atoms/dark matter until dark energy started to accelerate the expansion of the universe..?
    Today %s are 72% dark energy, 4.6 atoms and 23 dark matter.
  7. Nov 28, 2011 #6
    That chart looks odd to me. I think that someone was vastly oversimplifying things. In particular, the baryon/photon ratio and the baryon/neutrino ratio shouldn't change much after freeze out. So I don't see how they are getting the numbers they got.

    Also, you are looking at two data points. There is a ton of other data that comes in from WMAP.

    The other problem is that most of the universe today does not consist of "atoms" but rather "ions". The probably mean "baryons".
  8. Nov 28, 2011 #7
    Also some things that we expect:

    1) the ratio between dark matter and ordinary matter should have remained constant for the last several billion years.

    2) dark energy is a recent thing. There was no evidence of dark matter at the time of the CMB.

    Also if you are proposing that photons and neutrinos turned into dark energy, there are several reasons why that won't work. One is that if photons were interacting to create dark energy, then the early universe would have looked "fuzzy."
  9. Nov 28, 2011 #8
    It seems that the amount of visible normal matter is changing significantly over time - and becoming non visible normal matter:

    http://www.cosmosmagazine.com/news/4653/galaxies-are-running-out-gas [Broken]

    I also read recently that many more wandering brown dwarf failed stars than normal stars are now believed to exist - hopefully not in our backyard!

    I dont know if any of this causes a change in the ratios discussed above.
    Last edited by a moderator: May 5, 2017
  10. Nov 28, 2011 #9

    Cepheid, Is this really strictly correct, if you have no equation, you have no theory?

    Well fortunately I recently discovered a Math program which can create equations for almost any plot of interdependant values there is.
    I am not sure it adds to the Physical understanding of what is responsible though, it just helps me calculate a value from the other values.
  11. Nov 28, 2011 #10
    1) If the ratio between dark matter and ordinary matter have remained constant for the last several billion years, it is a problem for my theory, in my model the % of dark energy has been growing faster than the % of dark matter.

    2) I do not think dark energy is a recent thing, if it is; it means that Dark energy appeared from nowhere and it is not believable to me.

    I am not proposing that photons and neutrinos turned into dark energy, in the 380000 year old universe you cannot see/observe dark energy because the size of the universe at the time and the amount of photons and neutrinos, in another words dark energy was hiding “behind” the % of photon and neutrinos.
    I believe dark matter was present from the beginning of the universe as dark energy, you cannot see/observe it in the 380000 year old universe because the size of the universe at the time and the difference with dark energy is that dark matter was “hiding behind” the % of mass or atoms.

    (The term dark in dark matter and dark energy comes from the realization that in the today universe we are missing 96% of it and we cannot explain it. The 96% missing universe was always there, we cannot see it in the early universe and in the today universe.
    We call it “dark” because again we do not know what it is, if “dark” did not exist at the beginning it does not exist today, “nothing can appear from nothing”)
  12. Nov 28, 2011 #11
    I am sure that we cannot see/observe all the "visible" matter in the universe but if the not seen "visible" matter is only 1% of the total of matter in the universe it doesn’t really “matter”.
    Last edited by a moderator: May 5, 2017
  13. Nov 28, 2011 #12


    User Avatar
    Gold Member
    2016 Award

    Are you sure about that? If it didn't exist, how did it arise spontaneously? Now we have the UNIVERSE arising spontaneously (by some theories) AND we have dark energy arising spontaneously.

    I thought it was simply the case that the EFFECT of dark energy only started overcoming gravity about 7 billion years ago, not that dark energy came into existence at that time.
  14. Nov 28, 2011 #13


    User Avatar
    Gold Member

    For a fairly accurate ΛCDM formula for the expansion factor, a = 0.713[sinh(1.28t/t0)]2/3, where t0 is the present age. This assumes that ΩΛ now is 0.73, so that matter (including DM) is now 0.27 of the total. (from 1 Gyr and later, photon+ neutrino energy density was I think <1% and the formula ignores this contribution). This also normalizes to a = 1 at the present.
    In the time range you're talking about, the matter density was proportional to 1/a3, while the "DE" density was constant and photon+ neutrino energy density was negligible (but prop to 1/a4).
    Although this formula arises from the ΛCDM model, it's very accurate at matching supernova data, etc., so whatever the actual formula ends up being, it's very close to the above.
  15. Nov 28, 2011 #14


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I was trying to make the point that in physics, a "theory" that amounts to little more than a vague verbal description of natural phenomena that doesn't have any quantitative, testable predictions is not useful or even meaningful. Furthermore, any new theory should be able to explain what existing theories are able to explain, at least as well as they do, if not better. Yes, I stand by the statement that physical theories are mathematical models that describe nature. No other form of description is precise enough, and I would argue that any other form of description lends itself to too much ambiguity.

    It's really not clear what your point is here. Maybe I am misinterpreting you, but your point seems to be, "just because you have mathematical equations doesn't mean that you have a theory." Well: I never said that it did. If A = "mathematical model" and B = "physical theory", then what I asserted was that:

    (not A) ==> (not B).

    As you should know, it does NOT automatically follow that the inverse, A ==> B, is true, nor was it my intention to assert that.
  16. Nov 28, 2011 #15


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Yeah you're right. The dark energy density is constant with time (maybe), whereas the matter density varies inversely with the cube of the scale factor (in other words, as the universe expands, matter gets diluted). Therefore, for much of the past, the matter density has been higher than the DE density, but steadily decreasing. It is only when these two density curves cross that the universe switches from being "matter-dominated" to "dark energy-dominated" (in terms of what dominates the dynamics of the expansion). This is a transition that, according to the standard model, has just occurred more or less "now."
  17. Nov 28, 2011 #16
    It doesn't. The ratios involve the total amount of "normal matter" that is inferred from things like big bang nucleosynthesis and galaxy distribution. When cosmologists talk about "dark matter" they are talking about "weird dark matter." It turns out that there is a huge amount of "normal dark matter" that cosmologists don't worry about but which other astrophysicists do.
  18. Nov 28, 2011 #17
    You don't have a theory. You have a curve fit. That's not a theory.

    If you take some points and draw a line through those points that's not a theory. If you have an explanation that will let you draw a line through the points *without looking at the points* that's a theory.

    The ratio of dark matter and ordinary matter has to be constant or else you'd see dark matter turning into ordinary matter and vice versa. We don't.

    You are not the only one that is bothered by this, but if you look through the telescope, this is what you see. The fact that what you see isn't what you expected is why the people that first saw it, got Nobel prizes.

    There's the "principle of least weirdness" you go with the explanation that is "least weird." Right now "dark energy" is the "least weird" explanation for what people are seeing.

    So why can we see it now? One thing seems to be true about the universe is that the average conditions are the roughly the same everywhere, so there is no "behind". How does dark energy "hide behind" neutrinos and photons.
  19. Nov 28, 2011 #18
    That was an ops. I meant "dark energy". "Dark energy" is something recent and you can get perfectly good explanations for CMB without dark energy.

    Maybe. But you don't see dark energy in CMB. It could be there, but you don't see it. Also whether it was there and not seen or whether it was something that came into existence after the early universe is an open question.
  20. Nov 28, 2011 #19
    That's assuming that dark energy consists of the cosmological constant. If it consists of something else like quintessence or modified gravity or voids, then it's different.

    Now as data is coming in, it's starting to look more and more like cosmological constant.

    Which really bothers people. One rule of thumb in cosmology is "you are not special, and if it looks like you are, then something is off." The fact that the numbers are send up so that we just happen to be living in the transition is suspicious.
  21. Nov 28, 2011 #20
    That also explains what the chart was measuring. You'd expect that the ratio between photons, neutrinos, and baryons to be roughly constant, but as the universe gets hotter, photons and neutrinos end up with more energy and more pressure.

    Now if you measure mass (i.e. gravitational attraction) then things are different. Neutrinos and photons have zero rest mass, so you don't have them overwhelm baryons until things get a lot hotter.

    Also, to the OP. This is a theory. We have three components.

    Dark matter + baryons = energy proportional to 1/a^-3
    Photons/Neutrinos = energy proportional to 1/a^-4
    Dark energy = energy constant

    The first two we can observe from experiment. The last thing we are guessing. If dark energy has constant energy, then we should see a particular expansion rate (which is what we are starting to see). If it turns that we don't see something with constant energy, then we look at what we do see and then figure out what the energy dependence is.

    That's a theory......
    Last edited: Nov 28, 2011
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: The Percentage of dark matter
  1. Dark Matter (Replies: 21)

  2. Dark Matter (Replies: 4)

  3. Dark matter (Replies: 6)

  4. Dark Matter (Replies: 3)

  5. No dark matter (Replies: 59)