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Thread: The Shape of the Universe

  1. #1
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    Default The Shape of the Universe

    It's easy to flip through pages and pages of speculation, but it's harder to get an insight into what most physicists actually believe on this question. So I gotta ask: What are the most popular theories among experts about the large-scale structure of the universe?

  2. #2
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    Default Re: The Shape of the Universe

    The current widely accepted belief, largely based on the Wilkinson Microwave Anisotropy Probe (WMAP) survey which examined the temperature spectra and distribution of the Cosmic Microwave Background and foreground radiation (i.e. that from radiating matter), is that the curvature of the universe is slightly negative and increasing in magnitude, so that it will not only continue to expand but will accelerate until the expansion of space between two points is moving so fast i.e. that it will not be possible to communicate from one non-local point to another. We can already see this at the Cosmic Event Horizon, 78 Bly away, where light is redshifted to effectively zero frequency. The WMAP survey indicated (per current assessment) that no region of space is repeated, so if the universe is bounded the bounds are larger than this. We assume that space is simply connected (i.e. there is a one-to-one correspondence between points which has only causal, future-directed vectors) except about mass-energy singularities (black holes) from which there is no egress. Here is a conceptual view (of a two dimensional surface expanding along a time axis representing a 3+1 dimensional Minkoski space. You can see how the shape flutes out in future time, indicating accelerated expansion.

    There is much curiosity about the actual structure of cosmic objects (clusters, filaments, walls, et cetera) as the anisotropy (non-uniform structure) doesn't fit in with the existing Standard Model of Cosmology. We would expect objects to be much more uniform and smaller if we assume space is uniform everywhere; instead, we find massive structures that are too large for existing models of formation and gravitational influence to explain. The current theories include large scale anisotropies forming during cosmic inflation due to perturbative influences, or cosmic strings, domain walls, and other topological "defects" which seeded these structures. The Great Attractor (a large, highly influential gravity source in the direction of Hydra toward which all nearby clusters, including the Local Group which we belong to, is flowing) may be caused by one of these defects and its influence on local matter.

    Stranger
    Some people just aren't happy unless the world is about to come to a bloody and fiery end.- Diana

  3. #3
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    Default Re: The Shape of the Universe

    Thanks, Stranger. Informative as always. Let me see if I understand the basics:
    Quote Originally posted by Stranger On A Train
    The current widely accepted belief, largely based on the Wilkinson Microwave Anisotropy Probe (WMAP) survey which examined the temperature spectra and distribution of the Cosmic Microwave Background and foreground radiation (i.e. that from radiating matter), is that the curvature of the universe is slightly negative and increasing in magnitude, so that it will not only continue to expand but will accelerate until the expansion of space between two points is moving so fast i.e. that it will not be possible to communicate from one non-local point to another.
    In other words, light traveling from one non-local point won't ever reach the other because the expanding universe will increase the gap between the two points faster than the light waves can traverse the distance.
    Quote Originally posted by Stranger On A Train
    We can already see this at the Cosmic Event Horizon, 78 Bly away, where light is redshifted to effectively zero frequency.
    And the whole reason that the Cosmic Event Horizon (the edge of observable space) is 78 Bly away, and not 13.7 according to the time since the Big Bang, is precisely because the universe is expanding.
    Quote Originally posted by Stranger On A Train
    The WMAP survey indicated (per current assessment) that no region of space is repeated, so if the universe is bounded the bounds are larger than this. We assume that space is simply connected (i.e. there is a one-to-one correspondence between points which has only causal, future-directed vectors) except about mass-energy singularities (black holes) from which there is no egress.
    So as far as we can tell, given the great difficulties in making these observations, it doesn't look to be like a giant torus or Klein bottle or anything like that.
    Quote Originally posted by Stranger On A Train
    Here is a conceptual view (of a two dimensional surface expanding along a time axis representing a 3+1 dimensional Minkoski space. You can see how the shape flutes out in future time, indicating accelerated expansion.
    This increased expansion relates to the dark energy people talk about, which has caused new interest in investigating the cosmological constant that Einstein wanted to use for a theory of a stationary (non-expanding) universe. It's back, this time in conjunction with the weird increased rate of expansion.
    Quote Originally posted by Stranger On A Train
    There is much curiosity about the actual structure of cosmic objects (clusters, filaments, walls, et cetera) as the anisotropy (non-uniform structure) doesn't fit in with the existing Standard Model of Cosmology.
    There's a bunch of weird shit out there.


    That about wrap it up, or do I have any major misconceptions?

  4. #4
    Oliphaunt
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    Default Re: The Shape of the Universe

    Quote Originally posted by Hellestal
    There's a bunch of weird shit out there.
    "Something unknown is doing we don't know what." — Arthur Eddington

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