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Mass required for a closed universe.

  1. Jun 21, 2014 #1
    How much mass (percentage increase) would have to be added to the Milky Way (our Galaxy) for it to become a closed universe if there were no other mass? Assuming of course the other universal mass does not change some basic physical law.

    I know a closed universe as a hole is lacking in mass but i was wondering how close we are as a galaxy.

    Thanks

    Duordi.
     
  2. jcsd
  3. Jun 21, 2014 #2

    Matterwave

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    The galaxy is not the universe. You can't make the universe closed by adding mass only to our galaxy...

    Are you asking how much mass would the galaxy have to have if it is to become a black hole?
     
  4. Jun 21, 2014 #3
    What would it take for the Milky way to be closed?

    OK,
    Here is the long description.

    I recently had discussion which revolved around what we would see if our galaxy was inside a black hole.

    The first question was, could we tell?
    Although this may seem obvious it was pointed out that in the Einsteins elevator mind experiment the man in the elevator could not tell he was in free fall if his observation was limited in distance and time.

    However if the observer is allowed to extend his test area he would find he is being stretched as his feet are falling faster then his head.
    This seemed to us to be similar to the universal expansion which is being stretched (red shifted) with our current galaxy falling into time faster then the distant galaxies from a previous time.

    In addition while falling in a black hole we are allowed to move in all directions but one, we can not go up.
    We may be able to fall zero distance if we access all the energy of the universe to do so because we would have to follow a light path at the Schwarzschild radius.

    This is similar to our universe we have four dimensions and in three dimensions we can move in positive and negative directions but in time we can only move forward.
    If we accelerate to the speed of light requiring all the energy in the universe we will experience zero movement in time but we can never go negative in time.

    These two similarities seem to indicate we are in free fall in a black hole falling forward in time
    (not length width or height).

    We also determined that if we are in a black hole all light images of ourselves must return to us so it could appear that there are distant galaxies which are just distorted reflections of our past.

    We were wondering what it would take for the Milky Way galaxy to be closed.

    How much dark matter/energy would it take?
    A billion times as much as we have or twice as much?

    Where would it have to be located at the galaxy rim or in the galaxy center?

    I assume that if I kept adding mass the galaxy would close.
    Would this added mass be detectable?

    How big would the galaxy be?
    The galaxy diameter or a million galaxy diameters?

    Andromeda looks a lot like the milky way.
    If you need black hole diameter to find the mass I would say the distance to Andromeda would be
    a good light path circumference estimate.

    I realize this may not be a question that is answerable.
    If you decide not to try to answer this I understand.

    Thanks.

    Duordi
     
  5. Jun 22, 2014 #4
    without going through all the points in your hypothesis, there is a couple of points I would like to clear up. The first point is how black holes form.

    A black hole forms when a stellar bodies mass falls below its Schwarzschild radius

    "Schwarzschild radius is the radius of a sphere such that, if all the mass of an object is compressed within that sphere, the escape speed from the surface of the sphere would equal the speed of light. An example of an object smaller than its Schwarzschild radius is a black hole. Once a stellar remnant collapses below this radius, light cannot escape and the object is no longer directly visible. It is a characteristic radius associated with every quantity of mass."

    http://en.wikipedia.org/wiki/Schwarzschild_radius

    the link above has some calculated values for you including the milky way, as you can see its the density of the mass not the amount of mass that is important. Our Earth for example is also included.


    Now as for the Universe being inside a black hole well there have been plenty of models that have tried to show this as a possibility.
    One essential problem however is inherent in those models. To define that I will have to familiarize you with two terms in cosmology.
    -Homogeneous meaning no preferred locations
    -isotropic meaning no preferred location.

    the description above
    "However if the observer is allowed to extend his test area he would find he is being stretched as his feet are falling faster then his head."

    is a preferred direction

    "In addition while falling in a black hole we are allowed to move in all directions but one, we can not go up. We may be able to fall zero distance if we access all the energy of the universe to do so because we would have to follow a light path at the Schwarzschild radius."

    again you indicated a preferred direction as well as location

    Universe from black hole models usually suffer this problem of having a preferred direction and locations, our measurements and observations strongly agree that there is no preferred direction and location (homogeneous and isotropic) expansion redshift measurements also agree with this rule.

    the other problem is that BH's typically rotate, that rotation would impart a rotation upon our universe, a rotating universe cannot be homogeneous and isotropic.

    Poplowskii's universe inside a BH is one such rotating model where he uses spin and torsion.

    http://www.nikodempo...blications.html [Broken]
    http://arxiv.org/abs/1007.0587

    reviews I've read on the model generally point out the homogeneous and isotropic problem, though I can't locate the reviews atm

    I should be clear though that this doesn't preclude the possibility of our universe being inside a BH. Its merely pointing out some of the problems associated with the BH cosmology models. Science is like that

    [crackpot link deleted]

    unfortunately I couldn't locate an arxiv paper review however as you can see from this paper that there is numerous problems and issues to be addressed
     
    Last edited by a moderator: May 6, 2017
  6. Jun 22, 2014 #5
    Thanks this is just what I was looking for.

    Duordi
     
  7. Jun 22, 2014 #6
    We seem to falling into the future, into time.
    Is time a preferred direction?

    I receive no light from the future, only from the past but I am used to this
    and do not tend to question why this is the case.
    This would seem to give time a preferred direction.

    Duordi
     
  8. Jun 22, 2014 #7
    Mordred "the other problem is that BH's typically rotate, that rotation would impart a rotation upon our universe, a rotating universe cannot be homogeneous and isotropic".

    Mass enters a black hole rotating however once it enters a black hole it can not rotate because it has to rotate with respect to something. Space time will drag with the mass inside a black hole so inside a black hole it can only rotate with respect to itself (some mass is rotating differently then other mass inside the black hole) unless you are suggesting the world outside the black hole somehow is defining the rotation inside the black hole.

    This comes back to the question about where physical properties come from. Is mass/rotation a property which would exits if no other mass existed or is mass a property defined by the quantity and properties of surrounding mass?

    Duordi
     
  9. Jun 22, 2014 #8

    Bill_K

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    Isotropic means no preferred direction.

    Black holes do not have to rotate, and there is certainly no requirement that the universe must be inside a black hole which is "typical".

    Poplawski. This model is based on Cartan's theory of gravity, not General Relativity. One of his radical ideas:

    ViXra.org is well-known as a repository for crackpots and their papers.
     
    Last edited by a moderator: Jun 22, 2014
  10. Jun 22, 2014 #9
    yeah I meant no preferred direction lol thanks for catching that, I also agree on the rest of your comments. As stated I couldn't find a better paper. Please note I stated typically rotate not that BH's always rotate.
     
  11. Jun 22, 2014 #10
    as far as that question goes I would refer you to this paper,

    http://arxiv.org/abs/1104.5499 :''Black hole Accretion Disk'' -Handy article on accretion disk measurements provides a technical compilation of measurements involving the disk itself.

    "the source of energy in this Penrose process is the rotational energy of the black hole.
    Indeed, the angular momentum absorbed by the black hole,"

    page 13, for that quote its a lengthy article, that covers how the accretion disk influences the BH's angular momentum, the Penrose process is one of the numerous influences.

    They also clearly state that BH's can be rotating or not rotating, keep in mind angular momentum must always be conserved. So a BH will conserve the angular momentum of infalling materials.

    As far as infalling material is concerned in my opinion this is also another challenge for a universe inside a BH. BH's have inconsistent feeding rates, if were inside a BH we should see variations in energy-densities due to that inconsistent feeding rate. However that is a personal conjecture in that I have never seen a peer review paper that's ever mentioned that aspect in universe in BH models or reviews

    Poplowskii is not the only model of a Universe inside a BH. Variations I've read include a 5d star, going supernova into a 4d BH.

    Out of the White Hole:A Holographic Origin for the Big Bang
    http://arxiv.org/pdf/1309.1487v2.pdf

    I think its highly unlikely that we are inside a BH, there are too many observational challenges in my opinion, however that being said I also cannot discount the possibility, the first article I posted covers some of those challenges
     
    Last edited: Jun 22, 2014
  12. Jun 22, 2014 #11
    just a personal side note question I've always had but don't think there is an answer for

    Can you have a blackhole inside a blackhole?
    Our universe does have blackholes itself
     
  13. Jun 22, 2014 #12

    phinds

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    Interesting question. Since two BHs can merge, it would seem to follow that if a really big BH and a much smaller BH merged, then in some sense the bigger would then contain the smaller. BUT ... on the other hand, once the two event horizons have merged, you really just have one BH and both masses become part of the singularity (at least I guess that's what the math would say).
     
  14. Jun 22, 2014 #13
    ah but if a BH forms an Einstein-Rosen bridge and each BH contains a universe then what would happen to the geometry of both universes?
    (Poplowskii's paper uses the Einstein Rosen bridge)
    http://www.insidescience.org/content/every-black-hole-contains-new-universe/566

    to clarify Bill_k response here is a link explaining the Einstein_Cartan theory
    http://en.wikipedia.org/wiki/Einstein–Cartan_theory
    (as you can see the Einstein-Cartan theory has its own unresolved problems to overcome)

    that's the problem with a Universe inside a BH model, there is simply too much we do not know about BH's inside the EH. When you honestly look at all the possibilities by studying our own BH's in our universe and the limits of our knowledge of those BH's in terms of what goes on inside an EH. How can we possibly treat a model of a universe inside a BH as anything other than conjectural ?

    (hopefully I've demonstrated that to the OP)
     
    Last edited: Jun 22, 2014
  15. Jun 22, 2014 #14

    mfb

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    The observer would also note his arms being pulled towards his body, as the other two dimensions feel an attractive tidal force. We don't see an attractive tidal force in the universe, so tidal gravity cannot be important on the scale of the observable universe.
     
  16. Jun 22, 2014 #15

    PeterDonis

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    Yes, that's correct.

    An Einstein-Rosen bridge doesn't connect two black holes. It connects two "universes" via a "wormhole", each of which sees the *same* black hole (i.e., people from each universe that fall into what they see as the black hole will end up in the same black hole interior region and be able to meet each other).

    Also, a "standard" Einstein-Rosen bridge, meaning the one that appears in the standard maximally extended Schwarzschild spacetime--i.e., no "exotic matter" or other speculative stuff-- (a) can't be used to cross between universes, since doing so would require traveling faster than light; and (b) isn't physically reasonable anyway, since it would require the entire spacetime to be vacuum, i.e., there would be no way for the black hole/bridge spacetime to form in the first place, since no collapsing matter could be present. If there is collapsing matter present, the spacetime doesn't contain the bridge--again, assuming no "exotic matter" or other speculative stuff.

    I don't see any reference to the Einstein-Rosen bridge in the article you linked to. It mentions the Einstein-Cartan-Sciama-Kibble theory of gravity, which is not at all the same thing.

    I think this is too pessimistic. If the interior of a BH of sufficient size to contain our observable universe can be described by GR, then we know enough to say that our universe is *not* inside such a BH. And a BH of that large a size should definitely be describable by GR well into its interior, since spacetime curvature in the interior of such a BH will be much smaller than the curvature in our own neighborhood (i.e., much smaller than the spacetime curvature due, for example, to the Earth's gravity).

    It is often said that we can't extrapolate GR inside a BH's event horizon, since we could never make any observations of what goes on there. But in fact we extrapolate our well-confirmed physical theories (of which GR is certainly one) into regimes where we can't test them all the time. If we couldn't do that, we couldn't do physics. Such extrapolation, unless the theory we are extrapolating itself predicts a limit to its validity (as GR does, for example, when the spacetime curvature becomes large enough for quantum effects to come into play), is a straightforward application of Occam's razor: why should physics suddenly start working differently in some region of spacetime just because it happens to be inside a black hole's event horizon? (It's worth noting that the event horizon is globally defined, not locally defined; there is no local measurement you can make that will tell you whether you are inside or outside the horizon.)

    Theories like the one in the Poplawski paper are based on constructing an alternative theory of gravity that matches GR's predictions in the regimes where we have tested them, but makes different predictions for regimes like the interior of a black hole. But ultimately, to establish such a theory, it will have to be tested against GR in some regime where different predictions of the two theories can be compared.
     
  17. Jun 22, 2014 #16
    Its been awhile since I last studied Poplowskii's work but one of his older models did involve at WH

    http://news.sciencemag.org/physics/2010/04/does-our-universe-live-inside-wormhole

    of course I may have gotten confused with his radial motion into an Einstein bridge paper
    http://www.nikodempoplawski.com/PLB_687_110.pdf [Broken]

    nope found the paper I knew I wasn't completely off Its been a few years since I last studied any of his works

    The universe as a black hole in isotropic coordinates
    http://arxiv.org/abs/0901.0215

    " Observers inside an Einstein-Rosen black hole perceive its interior as a closed universe that began when the black hole formed, with an initial radius equal to the Schwarzschild radius of the black hole rg, and with an initial accelerated expansion. Therefore the model of a universe as a black hole in isotropic coordinates explains the origin of cosmic inflation. We show that this kind of inflation corresponds to the effective cosmological constant Λ=3/r2g, which, for the smallest astrophysical black holes, is 10−8m−2. If we assume that our Universe is the interior of an Einstein-Rosen black hole, astronomical observations give the time of inflation 10−3s and the size of the Universe at the end of the inflationary epoch. "
     
    Last edited by a moderator: May 6, 2017
  18. Jun 22, 2014 #17
    my question was what happens when a BH merger occurs if each BH in our universe has a WH?
    each with its own universe?

    although you already answered that WH's are very unlikely, so its a pointless question lol

    as far as the last comment I was thinking of his older models when I last looked at his papers (see last post)
    personally I threw away his papers a long time ago lol (my apologies for that confusion, guess he developed a newer model)
     
    Last edited: Jun 23, 2014
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