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Thread: The Search for Dark Matter

  1. #31
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    Hum,
    i think the danger in applying that theory to the earliest moments of the big-bang is that they don't work.
    (ie, simply, the earliest moments of the bigbang were filled with radiation (rather than particles) and before say 3000 years the particles were basically thoroughly mixed by that radiation, which would not allow the small `seeds` to form the large scale structures.)
    However, computer simulations that use a mixture of cold and hot darkmatter have proved surprisingly successful in replicating the structures we see.

  2. #32
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    Quote Originally Posted by eremon View Post
    I think the idea was that something other than classical gravity is required to effect the minuscule initial agglomerations of particles that eventuated in objects large enough to exert gravitational influence. Friction between densely packed moving particles would have electrostatically produced the necessary attractive force.

    In googling I came across these:
    Gravity as the second order relativistic manifestation of electrostatic force.
    Quantum Cosmology With Decreasing Gravity.
    I think we can safely say both of these are well and truly 'against the mainstream'!

    If any BAUT member wishes to present either of these, and defend them, please start a new thread in our ATM section.

  3. #33
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    Quote Originally Posted by Blob View Post
    Hum,
    i think the danger in applying that theory to the earliest moments of the big-bang is that they don't work.
    (ie, simply, the earliest moments of the bigbang were filled with radiation (rather than particles) and before say 3000 years the particles were basically thoroughly mixed by that radiation, which would not allow the small `seeds` to form the large scale structures.).
    Perhaps not in the earliest moments. As radiation difuses and atoms condense, would their individual gravity be sufficient to produce aggregation, or could the more locally intense electrostatic forces produced by friction be instrumental?

    Aside from that, perhaps the gravitational effects of larger irregularities in the early soup might produce initial clumping. But then, do these irregularities themselves reflect some sort of clumping?
    Quote Originally Posted by Blob View Post
    Hum,
    However, computer simulations that use a mixture of cold and hot darkmatter have proved surprisingly successful in replicating the structures we see.
    I'm interested in the parameters these simulations use to represent cold and hot darkmatter. Can you illucidate a bit on this, or, failing that, provide a reference?

  4. #34
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    Quote Originally Posted by eremon View Post
    Aside from that, perhaps the gravitational effects of larger irregularities in the early soup might produce initial clumping. But then, do these irregularities themselves reflect some sort of clumping?
    Hum,
    yeah, there would be large residual irregularities (fossil remnants from inflation, or chance etc) in the hot early universe that would produce clumping - however they alone do not have enough time to form the first blackholes/stars/galaxies/large scale structures that we observe.


    Quote Originally Posted by eremon View Post
    Can you illucidate a bit on this, or, failing that, provide a reference?
    Millennium Run, Simulating the Universe

  5. #35
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    Quote Originally Posted by Blob View Post
    Hum,
    yeah, there would be large residual irregularities (fossil remnants from inflation, or chance etc) in the hot early universe that would produce clumping - however they alone do not have enough time to form the first blackholes/stars/galaxies/large scale structures that we observe.

    Millennium Run, Simulating the Universe
    From the Millenium Run simulation:
    The mass points are roughly a billion times the size of our sun, and ... are just for simulation purposes, trying to add proportionate gravity to areas of the universe where there are stellar objects.
    Sounds like this simulation isn't scaled to the more primitive stage where electrostatic forces might have been a factor, perhaps evolving into the "fossil remnants" you mention. Maybe the question is, do the earliest irregularities correllate with clumping of stuff, or are they already present prior to primal nucleosynthesis. I'd propose that all irregularities—whether observed or deduced—fall within the province of science.

    Mind you, I'm only serving as the devil's advocate in this discussion. I really don't have a position.

  6. #36
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    Hum,
    the simulations have to be predloaded with irregularities (one of the biggest problems of the inflation model used to be that it smoothed out everything, not allowing anything to form), and begins about 10 million years after the big bang. I'm not a computer scientist but i image that they tried various different ingredients and proportions to produce totally alien universes too.

    The fossil remnants, BTW, were the tiny quantum fluctuations, when the universe was the size of a turtle, that are blown up during rapid inflation.

    There are computer images at Redshift z=18.3 (t = 0.21 Gyr) HERE


    Title: The Origin of the Large-Scale Structure in the Universe: Theoretical and Statistical Aspects
    Authors: YEINZON RODR´IGUEZ GARC´IA

    We review some theoretical and statistical aspects of the origin of the large-scale structure in the Universe, in view of the two most widely known and accepted scenarios: the inflaton scenario (primordial curvature perturbation ζ generated by the quantum fluctuations of the light scalar field φ that drives inflation, named the inflation), and the curvaton scenario (σ generated by the quantum fluctuations of a weakly coupled light scalar field s that does not drive inflation, named the curvaton). Among the theoretical aspects, we point out the impossibility of having a low inflationary energy scale in the simplest curvaton model.
    A couple of modifications to the simplest setup are explored, corresponding to the implementation of a second (thermal) inflationary period whose end makes the curvaton field ‘heavy’, triggering either its oscillations or immediate decay. Low scale inflation is then possible to attain with H* (the Hubble parameter a few Hubble times after horizon exit) being as low as 1 TeV. Among the statistical aspects, we study the bispectrum Bζ(k1, k2, k3) of ζ whose normalisation fNL gives information about the level of non-gaussianity in the primordial curvature perturbation. In connection with fNL, several conserved and/or gauge invariant quantities described as the second-order curvature perturbation have been given in the literature. We review each of these quantities showing how to interpret one in terms of the others, and analyse the respective expected fNL in both the inflaton and the curvaton scenarios as well as in other less known models for the generation of primordial perturbations and/or non-gaussianities. The dN formalism turns out to be a powerful technique to compute fNL in multi-component slow-roll inflation, as the knowledge of the evolution of some family of unperturbed universes is the only requirement. We present for the first time this formalism and apply it to selected examples.


    Read more (306kb, PDF)

  7. #37
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    Quote Originally Posted by Blob View Post
    Hum,
    The fossil remnants, BTW, were the tiny quantum fluctuations, when the universe was the size of a turtle, that are blown up during rapid inflation.
    So indeed it is as the little old lady said—"turtles all the way down!"

  8. #38
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    Ok so we know nothing about astronomy =P

    First off my daughter and I love you pod casts

    We love to listen, and then think over ideas for ourselves. It's a way for me to keep my daughter interested in science and that's always good. This Dark Matter stuff has been a lot of fun. My daughter wanted me to ask a question.

    Has anyone ever thought that maybe "space" has mass (using my words) and that gravity is the surface tension of space? and that space isn't the "void" we though, but is make of something and this something like water has like heavy water?

    Again that was mostly my works and mostly her idea. She's only 8 and I'm not a rocket scientist, so go east on the flames

    Brian

  9. #39
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    Thanks for your feedback Brian, we really appreciate it. Regarding your daughter's theories, she'll need to get some funding and write a paper or two. ;-)

  10. #40
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    Paper From Ms. Huthin's 3rd grade on Quantom WHAT?

    Well, as far as funding and writing a paper. It would be hard to have her accepted by the community, when her paper is crayon and marks as well the funding will get spent on toys :do:

    We'll continue to listen to you casts, debate them, and entertain you guys with our finds

    Brian

  11. #41
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    Quote Originally Posted by SingleDad View Post
    Has anyone ever thought that maybe "space" has mass and that gravity is the surface tension of space?
    Hum,
    it is an interesting idea.
    But, recent discoveries have shown that dark matter can clump up (not into small clumps) so space cannot have mass.
    However, just this week the Hubble space telescope has discovered that dark energy has been around for most of the universes history. It is basically the opposite of mass; Space is acting like an sort of anti gravity that is expanding the universe.

    As for gravity being the surface tension of space, tell her she knows too much; this is cutting edge science that the best brains in the world are working on right now (ie, M-theory and loop quantum gravity).

  12. #42
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    Oh my goodness!! if I laugh any harder I'll wake her up. She's a very smart child (tested 120 IQ in 1st Grade). I just want to keep her on the right road. Maybe we'll can entertain you guys at the same time =p

  13. #43
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    Red face is cosmotoligist even a word??

    Quote Originally Posted by searlesgold View Post
    Hi Fraser....

    Recently I had a conversation with the very well known cosmotoligist, Russ Croman. He pitched the Question to him
    "What is Dark Matter" He promptly replied to me....
    "That's a Good Question!" and went on to say, "Nobody Knows!"

    I have posted my question about it many times and I never receive
    any replies! This is my theory about the unknown......

    I happen to believe in INFINITY! Infinity is primarally has two major componets: Endlessness and Timelyness, no beginning and no ending to either! There never has been a moment, when infinity was not existing! Why is it so difficult to believe that infinity does not have COLOR?? In other words, at night when we point our eyes away from Earth towards the sky and focus on the "Dark Matter" between any form of light, (stars,planets,etc.)
    and believe the "Darkness" is the color of Infinity...BLACK!

    The idea that the "Big Bang" theory that supossedly started the beginning of the Universe is absurd! What was existing before the Big Bang!?? Common sence tells us there had to be Something!
    If nothing else, there had to be infinity and Temporature!
    Note: the absence of heat, temporature will Drop! I don't think we know how far down temporature can drop?

    Much more, but it is after 4am and I'm ending here!

    Regards,
    Gary / searlesgold
    g-man=coin@sbcglobal.net
    First off...if space and time were infinite, then light would have had an infinite amount of time to reach us before now (even across infinite space). This would mean that every line of sight in the night sky would end on a star, and the whole sky would be as bright as the sun, EVEN AT NIGHT!

    Secondly, black is NOT a color, but rather a lack thereof, which means that when something looks black, it is not giving off ANY visible light.The "empty space" you speak of is not in fact empty at all, but rather filled with microwave radiation, which is a form of light, our eyes just can't see it.
    This microwave radiation that you refer to as BLACK is in fact the MAIN evidence that we have to support the big bang theory that you dislike so.

    Third, your notion of something existing BEFORE the big bang is completely unfounded. Time had it's beginning at the BIG BANG. It was the FIRST thing that happened, so there was no such thing as BEFORE the big bang. This also directly refutes your statement about time having no end, because the beginning is already one end, and the other end may be just around the corner.....or not....so what common "sence" were you basing this statement on?

    NOTE: the lowest temperature is called ABSOLUTE ZERO...that is how low the temperature can drop....no lower. that's the limit.period.


    thanks for reading,
    LUCKYNATE

  14. #44
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    Arrow

    Isn´t it possible that dark energy is just a relativistic effect? All the cosmic backgroud is redshifted to 3K doesn´t that mean that it is moving away from us with relativistic speed? So it´s mass should have grown to an almost infinite ammount. Couldn´t that be responsible for an increasing expansion speed?

  15. #45
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    Quote Originally Posted by GeorgeX View Post
    Isn´t it possible that dark energy is just a relativistic effect? All the cosmic backgroud is redshifted to 3K doesn´t that mean that it is moving away from us with relativistic speed? So it´s mass should have grown to an almost infinite ammount. Couldn´t that be responsible for an increasing expansion speed?
    In a word, no, it is not possible.

    First, the expanding universe - as evidenced by the Hubble relationship - fits a relativity-based cosmology well (it's called the Big Bang theory) ... so dark energy (DE) is something 'extra', that's not already in the model.

    Second, relativity doesn't work the way you summarised here ... there are some theads in BAUT's Q&A section on this topic - why not go take a look there?

    And last, welcome to BAUT, GeorgeX!

  16. #46
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    Quote Originally Posted by Nereid View Post
    In a word, no, it is not possible.

    First, the expanding universe - as evidenced by the Hubble relationship - fits a relativity-based cosmology well (it's called the Big Bang theory) ... so dark energy (DE) is something 'extra', that's not already in the model.

    Second, relativity doesn't work the way you summarised here ... there are some theads in BAUT's Q&A section on this topic - why not go take a look there?

    And last, welcome to BAUT, GeorgeX!
    so, now you gave it to me
    1st why not Q&A: I can´t find my own shoes in there, how shall I find an answer?
    Where is the mistake? There is a radiation from out there - there should be some matter(I´m beaming-so I am) - it is moving at almost the speed of light(just interrupt me when I´m going astray!)- so the mass of that matter should have increased to a quite large ammount, shall it not?- why could that
    not create a gravitational force tearing the universe apart. One awnser could be that the microwave background is too far away, but I didn´t hear that.
    So how does relativity work? Feel free to be a bit more specific or at least show me some entrys in the Q&A that explain a thing.

  17. #47
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    Dark Matter or Blind Observers?

    People who say there is dark matter have gone blind looking at the sun trying to find more matter. They say it forms a halo around anything near the mass of a black hole but dont want to admit that it may be the effects of the blackhole at the center of the precieved dark matter.

    Most things that we see and measure are atoms that reflect light - Einstein gravity.
    Black holes are made of quarks or chrushed quarks and we cannot assume that large dense quark balls called black holes can display the same precieved effects of gravity that atoms produce - MoND gravity. (I dont believe in singularities)
    The spacetime at the center of our sun is propped up by the light that it produces and we see that light because it can still escape.

    I think that anything that looks like it has dark matter around it, is the effects of something that does not allow light to escape, since blackholes are NOT comprised of atoms they give the 5:1 gravitational effect in area instead of a 1:1 like the sun and earth

    I think that the change in spacetime expansion rates around and inside the "dark matter" of a black hole distorts the light from anything outside our galaxy. If we look out our "dark matter" through into the "dark matter" of another galaxy this would be like looking through the wrong end of a refracting telescope. an example would bet the story where they say andromeda is 5 times larger then we thought it was, or how they have noticed that the Large and Small Magellanic Clouds are moving faster then previously thought.

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