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Expansion mechanism

  1. May 8, 2015 #1
    Hi, This is my first post and I've joined simply to see what anyone may make of the following idea.
    Given the relatively recent depictions of the universes 3d structure as something akin to nodes with filaments connecting them. It seemed that the expansion of the universe could be explained by imagining the filaments constricting. I assume the filament-like structures are constricting, just as the galaxies in clusters are coming together e.g Andromeda and milky way). That is, while there is, at the largest scales of the universe, an expansion, there is also local adherence to the effects of gravity.
    If you constrict (under gravity) a connecting filament -what does it do? -like rolling out dough it lengthens. . if the universe structure is as has been mapped - then local gravity effects - local constriction (under gravity) of filaments and similar tightening of galaxy clusters creates an expanding structure ...does it not?
    The universe expansion then is a geometric effect of local gravity on a structure.
    This model would fit with the observation that increasing distance has increasing expansion speed (simply since there are more intervening filaments being constricted and lengthened). The accelerating universe expansion?...not entirely sure but doesn't a structural change as described here give rise to accelerating expansion since it is slightly exponential?
    If the gravity and 3d geometry then explain the universes expansion there's no need for dark energy. The expansion would seem to be a limited feature - perhaps the filaments constrict and thereby expand the universe to a point where the structure is too fine and breaks up or collapses under gravity.
    Thoughts anyone
    Thanks,
     
  2. jcsd
  3. May 8, 2015 #2

    PeterDonis

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    The "filaments" in the universe are not continuous objects, like the dough is. They are just regions occupied by stars and galaxies which are relatively long and thin, surrounded by relatively empty space. You can't treat them as "material" with properties the way you are trying to. See below.

    The filaments, as above, are not "structures" in the requisite sense; there is nothing analogous to the inter-atomic forces in a solid object that account for its behavior when a "constricting" force is applied. Also, no force is being applied to the filaments in the universe's 3d structure anyway; stars and galaxies are simply free-falling through space. They don't have anything acting on them analogous to a rolling pin rolling out dough.

    Finally, the expansion of the universe is the same in all directions; it is isotropic. If it were due to filaments constricting as you suggest, it would be different in different directions, because any given filament points in a certain direction, so it can only account for expansion in a certain direction.

    Dark energy isn't needed to account for the universe's expansion per se; it's needed to account for the fact that the expansion is accelerating.

    Also, the expansion is not "limited"; it has been happening for the entire history of the universe.
     
  4. May 8, 2015 #3
    Thank you for your reply and yes, I take your points, especially the first one that the filament of galaxies are not like dough - inter-atomic forces are absent, and therefore filaments would not lengthen as galaxies coalesce along them. Although - can galaxy radiant energy be a mild inter-atomic force equivalent? Only need be mild I assume to get those darn filaments lengthening. Or dark matter has a preferred density profile and thereby is fluid like and then filaments could lengthen?? ...If those ideas carry no weight I am sunk I think.
    Regards the isotropic expansion - it's perfect on the largest scale and not - intra galaxy cluster scale - so it could be that at this scale (intergalactic cluster) perhaps the expansion data could fit, or fit better.
     
  5. May 8, 2015 #4

    PeterDonis

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    No.

    "Perhaps" is not enough. You would have to work out what your model actually predicts, and compare it with the actual data.
     
  6. May 8, 2015 #5
    "No"? then how so kind sir. Intergalactic radiant pressure is a thing and so could that not provide my long (2 hours and counting) imagined inter-atomic force surrogate? Wiki.
    I don't see mention in that wiki article of its intergalactic effects - guess the inverse squared with distance make it a small effect. So my calculation then (cough- that's a pretty high expectation for a forum ..but okay) would have the Hubble constant rate provide a similar order of mag in the first instance with the longitudinal dispersive effect of intergalactic radiant pressures on inter galactic cluster filaments. Feels like that requires integration of forces and masses and not a few other facts and knowledge. My recollection of physics and maths from 1984 may not enable my doing this ..In any case you may provide me with the reason 'No' was your answer and so short circuit this path. And thank you again for your time and responses.
     
  7. May 8, 2015 #6

    PeterDonis

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    Calculate how much of a "thing" it is, and how much force such a "thing" could exert on a neighboring galaxy. Then you will see.

    You don't need to get too complicated; just a rough order of magnitude calculation will do. How many stars are there in a typical galaxy, how much radiation do they put out, how much pressure does that radiation exert, how much force does that add up to on the next galaxy over, and how much acceleration will that force produce on the mass of the galaxy?
     
  8. May 9, 2015 #7
    Well who'd have thought (Peter actually) an acceleration along the length of a filament of 65 MPc (got the length from a chunky looking filament from the Sloan digital survey - .02 z long) - which given Hubble constant of 70km/s gives a required acceleration over the length of filament of 4.6e6 m/s. The aggregated radiant force [edit: assuming 7e-6 N/m2 at 1AU per sun] of 81000 galaxies down the length of this filament (assuming an average of 2000 ly between them and 100e9 stars per galaxy like/averaged as the sun and a galaxy size like ours 1e5 ly D getting 208e14 N's force from one another which is then an acceleration of 17e-27m/s/s on each of galaxies) ...overall acceleration of ends of filament (and yes I guess my addition of the accelerations is invalid, but it's ...moot) 1.4e-24m/s/s.
    Needed 65Mpc x 70 (hubble constant) = 4.6e6 m/s/s.[edit2: oh dear H is a speed isn't it - not an acceleration - in which case..? not sure ..I can multiply inter galactic acceleration by the number of seconds since big bang? ...doesn't matter I guess - the numbers even at 10^16 seconds are still miles off that required]
    gulp... so that's 30 [edit - maybe 14] orders of magnitude insufficient acceleration. (and even given vastly inaccurate assumptions and/or enormous errors in calculation) that's one big hill to climb.
    Leads me to think filaments are an artifact of the expansion ..or just an artifact full stop, not (even remotely) the engine of it.
    Anyway thank you Peter, that was interesting ...almost fun. :)
    Scott.
    (further I guess ignoring the mass of the clusters/super clusters themselves - which would require accelerative force is a many orders of magnitude oversight - in the wrong direction)
    (further too -Makes me wonder how on earth the universe expansion could be accelerating - that's some seriously strong dark energy voodoo magic - which comes from where? ..maybe instead its geometric effect of constricting filaments ..oh wait)
     
    Last edited: May 9, 2015
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