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Information on Dark Matter and Dark Energy

  1. Dec 27, 2015 #1
    I am doing my undergrad research on Dark Matter and Dark Matter but have only few links of sources. Are there any online info-stores where I can get most of the discovered information on them. All related research papers and the different properties discovered about Dark Matter and Dark Energy. For eg- http://physicsworld.com/cws/article/news/2014/nov/18/is-dark-energy-eating-dark-matter
    Every response is appreciated
  2. jcsd
  3. Dec 27, 2015 #2
  4. Dec 27, 2015 #3


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    Advice: keep a balanced skeptical perspective. There is no scientific evidence that DM and DE are related. Don't let the names people use fool you--the fact that both names include the word "dark".

    So you would not necessarily find a good "online info-store" that simultaneously treats DM and DE. Searching for a solid introductory article that deals with BOTH might not get you much---besides wild speculation about some imagined interconnection or interaction---"what-iffery".
  5. Dec 27, 2015 #4


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    The evidence for DM is pretty straightforward and solid. We can see clouds of it and map their density contours. Google "bullet cluster". DM is essential to standard simulations of structure formation. By gathering into regions of higher density it helped the less abundant ordinary matter OM to collect and clump, forming clusters of OM galaxies (with surrounding DM clouds). And of course DM explains rotation curves of spiral galaxies, but that is only one of many ways that it is consistent with observations.

    By contrast, there is no scientific evidence that "DE" corresponds to anything we would normally call an ENERGY. or that it interacts/interchanges with any of the real normally-dealt-with forms of energy. As others here (PeterDonis, Chalnoth) have often pointed out, the SIMPLEST way to understand "DE" is as an alias or code name for the cosmological constant Lambda Λ. Lambda is a constant CURVATURE which shows up in the 1917 Einstein GR equation which is our standard equation for gravity.
    The cosmological curvature constant belongs in the GR equation because allowed by the symmetry of the theory---the way a constant of integration belongs in your answer when you do an integral in college calculus--you get graded off a point if you don't include it.

    So far "DE" acts exactly like a spacetime curvature constant, as per the 1917 GR equation. Maybe some day people might detect an interconversion between it and some known form of energy, so they might discover that the curvature Λ actually arises (all or in part) from an energy! That hasn't happened so far--it acts just like a curvature constant (the reciprocal of a constant area, i.e. a number per unit area). So calling it "dark energy" is, in a way, going off "half cocked". People got very excited in 1998 when it was discovered that Einstein's curvature constant wasn't zero and started calling it that and the name stuck.
  6. Dec 27, 2015 #5
    Good prior posts from Marcus.
    Several papers below echo his cautions regarding dark energy....

    Here are some notes I made from, discussions in these forums....
    "Is it a case of an accelerating universe at this moment in time at all points in the universe?
    or Is it a case of an expanding universe in the past which we assume is still accelerating today based on what we see?"
    [I think these are my own interpretations:]
    Very distant points in the universe ARE moving away from each other, distances are increasing. The universe expanded really fast for a very short period of time shortly after the big bang [this is called inflation] then slowed down before picking up acceleration several billions years ago. The role of dark energy in all this remains a matter of discussion and debate....We have been in an 'energy dominated universe' for several billion years and observations confirm expansion is speeding up.

    Here are two well regarded papers which are insightful:

    Davis & Lineweaver: [good for general background]

    [There is a simplified and abbreviated version of the above paper in Scientific American, "Misconceptions about the Big Bang"....I have a copy but not a valid link. ]
    edit: Took me a while but I found it..Linewaver has all his works listed on a Berkely U website...START HERE and maybe pHinds 'Balloon Anlogy' in a post below

    "Misconceptions about the Big Bang"

    Tamara Davis thesis:

    and some experimental data:

    What have we learned from observational cosmology ? [with explicit discussion sections on dark matter, dark energy....]No one is sure about 'the role dark energy plays'....

    Why all these prejudices against a constant?
    Eugenio Bianchi, Carlo Rovelli
    (Dated: April 13, 2010)

    "The expansion of the observed universe appears to be accelerating. A simple explanation of this phenomenon is provided by the non-vanishing of the cosmological constant in the Einstein equations. Arguments are commonly presented to the effect that this simple explanation is not viable or not sufficient, and therefore we are facing the “great mystery of the nature of a dark energy". We argue that these arguments are unconvincing, or ill-founded."

    [but nevertheless it still seems a possibility.]

    Marcus of these forums explains expansion this way:

    "...{the} classical 1915 Einstein GR equation explains how expansion once started will continue without constant input of energy. The equation only allows for a gradual predictable change in the rate. There is one enormously difficult to accept, but apparently true, thing about cosmology and that is geometry has a mind of its own. It is not like what Euclid said, it is not fixed static with triangles always adding to 180 degrees. Geometry RESPONDS to the flow of matter and to its own past. If it gets started growing, it will continue at least for a while. If it gets started bending (say because of a flow of some matter) it will continue at least for a while. And bending makes triangles add up to something besides 180.

    We have to accept this because it is also our law of gravity, that turned out to be more successful than Newtons. Gravity=dynamic geometry. We don't have anything better than this at present. It has been tested a lot, in all sorts of ways, at many different scales (earth, solar system, other stars, distorted lensing effects of clusters of galaxies and unseen clouds, and (yes) expansion of distance. It is all part of the same thing, the same simple equation that WORKS. And it is the best law of gravity we have so far. So it puts our intuitions in a bind. Our intuitions say that geometry cannot be dynamic and influenced by flows of matter, it has to be fixed exactly the way Euclid said.

    So in addition to looking at 'dark energy searches', searches involving 'cosmological constant' might be of value.
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