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Ramafications to flatness

  1. Jul 9, 2009 #1
    This has likely been asked before but my attempts at searches did not yield what I was looking for.

    Assuming the universe is perfectly flat (so far that seems very possible), what are the ramifications?
    Such as to:

    1) Inflation
    2) Dark Matter
    3) Dark Energy
    4) Nature of Gravity
    5) Applicability of General Relativity to the Cosmological Problem

    Much of the above all seem to be intertwined with the use of General Relativity AND the assumption that gravitational force is acting on the universe as a whole (in what seems to be the 'time coordinate' or directly related to it). It would seem that a perfectly flat universe would not need GR. It could be possibly be more simply explained as an initial 'big bang' with the 'pieces' (our universe) being expelled at a constant velocity (less than the speed of light?).

    It is my understanding of the other forces that a 'transport particle' can be used to describe how the forces come about. For the electromagnetic force (in QED) these are photons (with spin-like properties), etc. For gravity a 'graviton' has been proposed (a zero rest mass -- speed of light particle). This is one factor that I understood to mean that something like 'inflation' was needed in order to get around the 'horizon' problem -- one related to a finite transport velocity.

    The arguments for dark matter and dark energy were also based on the view that gravity effects need to be 'balanced' in various ways. But if there were no gravity effects at the very large cosmology scale -- would all this still be needed?

    If still needed, then in what way ... how changed? Likely someone has recently put out a book on all this (too obvious not to) -- but what is a good one? Or is that too early to tell too.

    I seems to me that a known 'flat universe' -- and if assumed to be the normal stable condition -- puts many assumptions in jeopardy.
  2. jcsd
  3. Jul 10, 2009 #2


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    Actually, space is flat, not spacetime. You need GR to handle curved spacetimes.
  4. Jul 10, 2009 #3
    OK -- I'll bite.

    Why would spacetime still need to be 'curved'? Seems to me that a simpler solution would be to say that there are no gravity forces constraining the expansion (in time). Then the flatness would be explained -- and not as a 'coincidence'.

    When I try to visualize this situation, I see an expansion along what seems to be a 'time coordinate'. While the expansion makes sense, a force acting along this coordinate does not.
    Other forces can be modeled by particle exchange. A graviton has been proposed for gravity. But wouldn't a force along the 'time coordinate' imply a particle exchange in that coordinate -- meaning gravitons would travel back and forth in time? Doesn't make sense.

    What then does make sense is that there is no gravity force in this direction -- and therefore no curve -- and flatness.

    Added note: the expansion effect of Hubble's Law could be easily explained by 'us' and all pieces of matter in the universe having a common origin -- at the Big Bang. The 'bang' simply expelled matter in all directions and its been coasting out (at something less than the speed of light) -- no curvature needed?
    Last edited: Jul 10, 2009
  5. Jul 14, 2009 #4


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    If there were no gravity, and the universe were expanding, spacetime would be flat and space (as defined in the FRW metric) would be negatively curved. That doesn't seem to be the case.
    Curvature needed. There is evidence that the universe does not behave like an explosion with no further interaction.
  6. Jul 14, 2009 #5
    Good -- what evidence?
  7. Jul 15, 2009 #6


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    Ample evidence.

    There are some really good cosmology tutorials in the web. I'd recommend Ned Wright. An empty universe means Omega=0, compare that with observational constraints.
  8. Jul 15, 2009 #7
    Read -- long ago.

    It is entirely dependent on the model. No evidence that stands outside the model.
  9. Jul 16, 2009 #8


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    What "it"?
  10. Jul 16, 2009 #9
    The reference to:
    Assuming such issues as the "horizon problem" -- which is really only a problem with models like GR.
  11. Jul 17, 2009 #10


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    Yeah, I guess models like http://en.wikipedia.org/wiki/Flying_Spaghetti_Monster" [Broken]have no problem with "it". What's your point?
    Last edited by a moderator: May 4, 2017
  12. Jul 17, 2009 #11
    A valid model needs to do more than solve problems created by the view of the model.

    In short, it proves nothing.
    Last edited by a moderator: May 4, 2017
  13. Jul 17, 2009 #12


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    Look, I'm getting tired of this. Instead of vaguely, cryptically uttering platitudes with some alleged, but obscure, bearing on today's cosmology, why don't you simply say what you think? This could shorten the "discussion" considerably.
  14. Jul 17, 2009 #13
    I think the problem with General Relativity is several fold:

    1) Its based on a geometry solution -- ASSUMING 3 spacial dimensions and one time coordinate. When it was developed that was all that was conceived. Particle physics was in its infancy. But little of that has changed GR.

    2) My view is that 'dimensions' are a perception -- in effect they are determined by the problem' and how it is measured -- not a given.

    3) The horizon problem is much more broad than has been addressed. I do NOT see how gravity or any acceleration or deceleration can be imposed EXACTLY simultaneously throughout the universe. And it MUST be EXACTLY 'in-sync' including all matter and all energy (and photons) else the matter and energy would drop out of our universe or even possibly drop in from a previous 'out'. This would appear to happen because the expansion is also being forced to occur in the time coordinate as well. Somehow we are expected to believe that light and other objects can move backward in time in order to maintain their apparent appropriate ordered 'presence' in our view of the past.

    4) Note: if no acceleration or deceleration is possible -- or if its just not needed, then there is little need for General Relativity -- in fact it then cannot be used as a explanation for the perceived redshift -- if we accept the Cosmological Principle.

    5) The Cosmological Principle would indicate that at sufficiently large scale gravitation between the 'clumps' of matter is ineffective in causing further clumping -- i.e. no anisotropic or inhomogeneous effects are seen. At this scale the apparent only source for the cosmological redshift is actual continuing expansion -- no gravitation and therefore GR should not be needed to explain this (the cosmological redshift).

    6) I do believe that the 'simple solution' (not so simple in practice) is that there is NO acceleration or deceleration along the time coordinate needs more consideration. That is this expansion is at a constant rate. There may have been some initial 'events' -- series of them as the universe progressed to its current more (expanding) stable state -- that had large changes. Much of that will mostly remain theory. We can only pick up at the point we can start to measure -- with MATTER and a constant expansion velocity.

    7) There is NO real evidence that photons -- and possibly other leptons -- are 'effected' by gravitation. This is not even required by General Relativity.

    8) GR will give good results in situations it was designed to address -- such as limited to 3 spacial dimensions. It is usually applied with the spherical metric (F..RW etc.) so that is often another requirement. What it cannot handle -- (as normally used) -- is uncertainty of the dimensions or cases where the effect of gravity may not exist.

    9) If the transport particle idea for gravitation is correct, then that is just another reason why gravitation cannot be considered to 'oppose' (or aid) in the expansion of the universe.
    Assuming the universe isn't expanding into a 'sea of gravitons'.

    These are just the simple statements on my concerns with the current GR mainstream approach. I'm sure you and other can make arguments against them. That is not really the point. We can all make arguments for our perceived cases. What is needed is solid data to make determinations with.

    And that is another problem with the current mode used in mainstream to make such determinations -- the way the very limited data is handled. We have very few reliable data measurements. Largely due to the many years between any new significant results, many ideas and theories are worked on. So when data comes in we have models designed to incorporate many possibilities. My background is data analysis and data fitting. One thing I learned long ago putting too many variables into a data fit will just about guarantee some support for nearly any parameter. Want is needed is situation with only a limited number of possibles -- then real choices can be made (for the moment). Unfortunately we don't have 'lab universes' to do much of the kind of testing we need. So we do the best we can. But I believe its best to keep it simple UNTIL it has to get complicated -- not start off complicated just to cater to every concept.

    Since the specifics of what I'm working on are not considered appropriately mainstream -- nor for that matter do I fully have them worked out -- or even accept myself -- I must decline to give further posted details. If you want to exchange emails for more detail please let me know.
  15. Jul 17, 2009 #14
    Wanna elaborate with some maths maybe?

    From wiki:
    Do we have reason to believe there are dimensions where gravity does not exists? Evidence please.
  16. Jul 17, 2009 #15
    Since we do NOT really know what gravity is, I don't see how that can be definitely answered. That is actually the point.

    However, the current GR model assumes that the universe is expanding in all dimensions -- three spacial -- one time. The expansion in the spacial dimension are 'perpendicular' (lacking a better term at the moment) to the time coordinate. The effect of gravity in the three spacial coordinates is to cause matter to 'attract' or 'clump' together. (Pick your math model.)

    With only 4 dimensions and the expansion source not in the 3 spacial then any changing 'force' must be along the 4th -- time -- HOWEVER, THERE CAN BE NO DIRECT EFFECT FROM GRAVITY IN THE TIME COORDINATE. This is consistent with both Special Relativity and with flat General Relativity. (There have been many papers written on this -- one good one from Russia -- Moscow Institute -- drawing a blank on the name -- I'll try to find it.) Further a changing force in the time coordinate would cause havoc with many ideas (causality, horizon problems, time reversal, etc.)

    So the options appear to be:

    1) Constant expansion rate in the time coordinate -- no forces at all.
    2) Or we need to add more dimensions

    Note, while there is no direct -- or changing -- effect of gravity in the time coordinate, gravity may have 'set' the expansion rate -- likely in the 'proton era'. The 'birth' of the baryons likely coincides with the 'birth' of gravity -- and the defining of the gravitational parameter (relation). i.e. when gravity first started to 'work'. But that is just my idea -- others may have better ones.

    I prefer to try to make the simple constant rate expansion work -- so additional dimensions are not needed -- but no proof just my personal whim.


    Please note, I'm trying to describe what I believe to be problems. I'm specifically not offering my guesses at solutions -- that would be very 'non-mainstream' and not really the point of the forum. If you want more detail on my ideas please leave a message or email.
  17. Jul 17, 2009 #16
    I know there as people that will not agree with me, but logic says that an infinite thing can not expand. If the universe is 'flat' then it is infinite, therefore no inflation.
  18. Jul 17, 2009 #17
    What? Time is the fourth (or the fifth) dimension of space. Give us a reference that even suggests this.
  19. Jul 17, 2009 #18
    The horizon problem has nothing to do with gravity, it has to do with the speed of light. Where are you getting this crap? GR is real whether you need it or not.
  20. Jul 18, 2009 #19


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    So I think we're done with this thread.
  21. Jul 18, 2009 #20
    It's a valid thought process to postulate what 'might' be but in general unsubstantiated speculation does not constitute scientific rigor.

    My desk is flat and it is not infinite. I think you are mixing up somethign having curvature with something being bounded.
  22. Jul 18, 2009 #21
    Your desk is not the universe. Do some research. Start http://www.esa.int/esaSC/SEMR53T1VED_people_0_iv.html".

    From the above link:
    "ESA: ‘Flat' seems to have a different meaning to non-scientists. By 'flat' we understand to be like a table, which has width. Does the Universe have width?

    Joseph Silk: Flat is just a two-dimensional analogy. What we mean is that the Universe is 'Euclidean', meaning that parallel lines always run parallel, and that the angles of a triangle add up to 180o. Now, the two-dimensional equivalent to that is a plane, an infinite sheet of paper..."

    Boldness is mine
    Last edited by a moderator: Apr 24, 2017
  23. Jul 18, 2009 #22
    The horizon problem is only a problem due to the assumption that things could be different in the separate horizons. If there is no gravity -- or any force acting differently -- then there is no problem. More to it than just the speed of light.

    This was also my understanding of how inflation addressed the issue.

    Never said that GR wasn't 'real' -- in fact said just the opposite. I was questioning whether it actually applied to the cosmological scale.

    Bottom line is that even with todays increasing and improving data, the data quality is not good enough -- yet -- to have a verified conclusion on many issues.
  24. Jul 18, 2009 #23
    I don't see how. Google "horizon problem" and any link talks about light travel time (heat radiation) as the problem. They don't mention gravity.

    I absolutely agree.
  25. Jul 18, 2009 #24
    Well, I don't see how light travel time is an issue unless there exists a difference to be balanced. Different viewpoints I guess.
  26. Jul 18, 2009 #25
    I'm well aware of the topological definitions for curvature. Perhaps my point was poorly stated: You're concerned about something globally infinite expanding, which for starters is a slippery slope as one can consider "small infinity" and "big infinity". Do some research, start http://en.wikipedia.org/wiki/Hilbert%27s_paradox_of_the_Grand_Hotel" [Broken] =) Sorry, couldn't help myself.

    The point is if i take an infinite rubber sheet and stretch it, its expanded but its still infinite. The question is what is it expanding into, and well thats more philosophy than science at the moment.
    Last edited by a moderator: May 4, 2017
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