Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Expanding Space

  1. Dec 4, 2008 #1


    User Avatar

    I was reading http:/arxiv.org/abs/0810.0153 by Yu and Baryshev on expanding space and a question came to mind.

    The far galaxies are accelerating away from us. The amount of space that’s “created” each day, causing this acceleration, is much more than was needed the day before to cause the previous days expansion. This expansion must require ever increasing amounts of energy to “push” it’s way into the already existing space. Where is this energy coming from? Come to think of it, where is this “space” coming from?

  2. jcsd
  3. Dec 4, 2008 #2
    As I understand it, Einstein showed with General Relativity that matter and energy are interchangeable. Further, that both have mass and that space-time is “curved” by mass. Mass has a property called gravity and the more gravity you have, the greater the curvature of space-time that occurs as a result. This curvature allows for the formation of stars, galaxies, planets, you and me. At the microscopic level, space-time is not an empty vacuum, but instead is alive like a field of energy. Virtual pairs of matter and antimatter particles borrow energy from this field, and then annihilate returning the energy to the field. This constant interchange creates a “negative pressure” at a tiny or quantum level throughout the whole of the universe. This pressure is represented as dark energy that acts to gradually stretch space-time. The more space-time is stretched, the more dark energy has an effect. At present, gravity is stronger than dark energy in galaxies, so space-time is only stretching in the Inter-Galactic Medium (IGM). However, the effect may continue to grow until dark energy overcomes local gravity, causing a “Big Rip”.
  4. Dec 4, 2008 #3


    User Avatar
    Gold Member

    I have only quickly scanned the reference: http:/arxiv.org/abs/0810.0153 so my comments may be out of place until having spent more time reading through the details. However, it seems to be more of a definition of the problem space rather than the solution. Presumably this is why you still raised the questions:
    Excellent questions. Please let me know if you find an answer.
    In another thread https://www.physicsforums.com/showthread.php?t=267808, there was a figure of 2.7 put on the energy increase between decoupling and now. See posts #11 & #12. If the analysis is right, it seems to imply that the additional energy must be accessible to each unit volume of space because there doesn’t seem to be any net flow of energy into or out of each unit volume at the macroscopic level.
    This seems to be a very logical line of thought. Is it suggesting that the vacuum energy is some sort of energy reservoir accessible to each unit volume of space as it expands? However, one of the problems in a basic energy density model is that it doesn’t account for any vacuum energy other than possibly in the form of dark energy. However, the negative pressure of dark energy only appears an effective source of expansion after some 6-7 billion years based on an EoS where w=-1. Prior to this gravity seems to win hands down unless some other form is active. Basically, I am interested in understanding what cosmologist’s believe continued the expansion after inflation within the 1st second of existence until dark energy around 6-7 billion years?

    Doesn’t anybody know whether any extended energy density models have ever been tried out? For example, if you simply look at the symmetry of the EoS in the basic energy density model, we have:

    Matter:…….. w=0, a^3
    Radiation:…. w=+1/3, a^4
    Curvature:…. w=-/1/3, a^2
    Dark Energy: w=-1, a^0

    What about these possibilities?
    Do they make any sense?

    Dark X: w=-2/3, a^1
    Dark Y: w=+2/3, a^5
  5. Dec 4, 2008 #4

    According to Guth, inflation didn’t just stop after the first second. A less spectacular inflation mechanism continued, gradually slowed by gravity, until the effect of dark energy “took over”. I read that it was fueled by the energy released by the separation of the Superforce. So a patch of negative pressure with the mass of a gram “bangs”, the Superforce separates causing explosive inflation, this event “shuts off” after 10^-35 second but inflation continues. Negative pressure, in one form or another, is the culprit throughout.
  6. Dec 5, 2008 #5


    User Avatar
    Gold Member

  7. Dec 5, 2008 #6
    Could you model the universe as some sort of expanding wavefront in some sort of medium?

    What sorts of waves in what sorts of media might exhibit variable local accelerations?

    As the wavefront propagates away from the original disturbance (this is the source of any energy in the volume bounded by the front), would the recession of objects closer to the front appear to be accelerating from the frame of objects closer to the source?

    Maybe some sort of heterogeneous medium?
  8. Dec 6, 2008 #7

    Expanding space?

    How can space expand?

    What does the expansion?

    How can you create more space?
  9. Dec 7, 2008 #8


    User Avatar
    Gold Member

    I am not sure whether some of the following is relevant to the sort of questions you are trying to raise. Equally, some more qualified members may wish to correct some of my comments, but for what it's worth….

    Are you assuming the wavefront is moving at constant velocity defined by the medium? Would the energy be dissipated over an ever-expanding wavefront defined by an expanding sphere? In many cases, energy sets the frequency [f], but the medium sets the propagating velocity [v] and wavelength = v/f. However, this seems to pre-suppose the existence of some sort of medium. If the wavefront acts more like a blast wave then a taylor-sedov solution is often considered, but have been told it gives a different result for the radius as a function of time in comparison to the Friedmann equation. The Friedmann solution is said not to describe an explosion because it describes a uniformly expanding sphere at any point in time. The uniformly expanding sphere idea seems to be supported by the cosmological principle of homogeneous and isotropic space. Not sure what scope this leaves for what is implied as the `original disturbance`.
    With reference to my comments above, observations appear to suggest that the universe is essentially homogeneous and isotopic on the large-scale and expanding. This seems to lead to the qualification that states that the big bang was not an explosion, hence the need for the expanding space idea where two points in space, i.e. distant galaxies, move apart due to space between them expanding. The uniform expansion of each unit volume of space would also seem to explain how superluminal speeds can exist without violating special relativity. On the other hands, much of 20th century science refutes the existence of space as a propagating medium, i.e. no aether, in the conventional sense and therefore light (EM) waves are considered self-propagating in a vacuum. Of course, this may only seems to underline your questions. As far as I know, cosmology cannot directly answer your questions and you may have to turn to quantum or string theory for an answer, at least, in respect to the possibility of the vacuum having some sort of energy structure that might then explain how space expands and where it gets the energy to support this expansion.

    However, as indicated at the outset, some more qualified members may be in a position to clear up the confusion I have suggested.
    Last edited: Dec 7, 2008
  10. Dec 8, 2008 #9
    G'day from the land of ozzzzzz

    Hello mysearch

    This is interesting link

    Scaling Regimes as obtained from the DR5 Sloan Digital Sky Survey
    Authors: Reuben Thieberger, Marie-Noëlle Célérier

    (Submitted on 4 Feb 2008)

  11. Dec 8, 2008 #10
    If space is created as the universe expands , can it be destroyed as well?
  12. Dec 8, 2008 #11


    User Avatar
    Gold Member

  13. Dec 8, 2008 #12
    lots of info i will check it out ... thanks
  14. Dec 8, 2008 #13


    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    Good paper, the less-technical first 3 pages have a nice introductory summary of ideas, and although it gets more mathy later it tries to remain pedagogical throughout.

    Alan Rendall is at Golm's Max Planck Institute for Gravitation Physics, the same outfit that hosts the Einstein-Online site on the web---a great outreach source for modern cosmology and relativity.
    Last edited: Dec 8, 2008
  15. Dec 8, 2008 #14


    User Avatar
    Gold Member

    Thanks to Wolram and Sundance for both references. Here is a link to Sundance reference for anybody interested: http://arxiv.org/PS_cache/arxiv/pdf/0802/0802.0464v1.pdf

    Given my limited background in cosmology, both papers will require some work on my part to digest. However, in the meanwhile I would like table a more basic issue that I am also trying to resolve concerning expansion. Is it reasonable to breakdown the expansion of space into 3 phases?

    1. Guth-like inflation
    I have only just started to read up on inflation, but most papers seem to discuss this phase in terms of scalar fields, which although said to be associated with the concept of energy density and pressure and still linked to the idea of kinetic and potential energy, it seems all very abstract. Does anybody know of any good introductory papers?

    2. Post inflation up until +7 billion years
    The whole issue of what drive expansion after inflation for the next 7 billion years seem very ambiguous. The standard model based on the Friedmann equations just doesn’t seem to explain anything and seems to rely on some unspecified ‘initial condition’ that I am struggling to understand in terms of any specific energy density, i.e. it is not dark energy [w=-1]. See posts #4 & #5. Therefore, would really appreciate any insight on this specific phase that could be modelled as the cause of expansion.

    3. +7 billion years up until now
    While dark energy is speculative, it does seem to, at least, provide a viable explanation of the accelerated expansion and makes up the critical density required, if k=0 in a spatially flat universe. However, recently there seems to be a number of proposals suggesting that dark energy maybe unnecessary. Does anybody know whether these proposals, in general, also explain the critical density/k=0 issues?

    If we don't really understand inflation, can't explain post inflation expansion and cannot position dark energy within the current definition of particle physics, might we be on thin-ice when it comes to any hard & fast ideas about the beginning or the end of the universe?
    Last edited: Dec 9, 2008
  16. Dec 9, 2008 #15
    G'day from the land of ozzzzz

    oops I forgot to link my last reference
    Either way arXiv search will do the trick.

    Thank you for the links

    From welram

    my search

    I have read them before, but! I will need to re read them for better understanding.

    THis also may be of interest

    Its a list of 7 papers by
    Ari Brynjolfsson


    Have a look at the ABS and let me know what you think.


    As for expansion and acceleration of the universe, I just cannot find any evidence to support it. Particularly observations.
  17. Dec 9, 2008 #16


    User Avatar
    Gold Member

  18. Dec 10, 2008 #17
    Thanks mysearch. I'm not assuming anything yet. Just enjoying the thread(s) and trying to find the time to learn more about the behavior of various waves in various media.

    Although SR obviated ether models, and experiments didn't find evidence of the sorts of ether(s) they were designed to detect, I think that it's inevitable that some sorts of ether theories will be developed and proposed, especially in light of the apparent expansion acceleration.

    It just makes sense to me to model the universe as some sort of wave expanding in some sort of medium, with the dominant energy and force being related to the expansion. Maybe the properties/topography of the universal medium can be adjusted to produce the sorts of variable internal and front expansion velocities that would provide an understanding of sorts of observable expansion accelerations in a universe that is otherwise generally slowing down and dissipating toward equilibrium with the medium.

    Of course, reconciling such a model with current mainstream physics isn't likely. But it might provide a useful heuristic, perhaps obviating an internally produced dark energy.
    Last edited: Dec 10, 2008
  19. Dec 11, 2008 #18


    User Avatar
    Gold Member

    Hi ThomasT,
    If my own learning curve in cosmology has taught me anything, so far, it is that there still seems to be plenty of scope for new ideas. As a slightly tangential reference that may not be accepted as suitable topics of discussion for this forum, have you looked into the idea of the wave structure of matter as first outlined by Milo Wolff? This idea appears to have been taken up by Gabriel LaFreniere in recent years, although remains well outside mainstream thinking. Anyway, good luck with your own search.

    <<links deleted>>
    Last edited by a moderator: Nov 20, 2011
  20. Dec 12, 2008 #19

    Nice links on matter wave.

    As for the scope of ideas.

    Mate we have not even know a fraction of the workings of the universe.
  21. Dec 12, 2008 #20
    Thanks mysearch. As a parting post to this thread (though I'll continue to monitor it as well as others), the original poster, 81+, wrote:

    "This expansion must require ever increasing amounts of energy to “push” it’s way into the already existing space. Where is this energy coming from? Come to think of it, where is this “space” coming from?"

    It doesn't seem likely that an explanation for this is going to emerge by considering only the internal structure(s) of the universe and the rules describing their evolutions.
    The question of where the energy originally came from is of course an unanswerable one (though one can fiddle with certain scalars and mechanisms to generate some idea of magnitudes and internal structures). But it's quite reasonable to assume that the dominant energy of the universe is the kinetic energy of the expansion, and that all internal behavior (including gravitational) is a byproduct of that -- then, the so called dark energy doesn't seem quite so strange or mysterious or require some sort of exotic particle interaction to 'understand' its apparent existence.


    I happened on a book by Milo Wolfe a few years ago, and I vaguely remember that there was some reason or reasons why I didn't like the whole package that he presented (even though some of his basic ideas seemed to make sense).

    A cursory glance at LaFreniere's site indicates that it might be interesting. The standing wave idea wrt particles is pretty mainstream I think. Many sorts of bounded (stable) patterns can be produced using macroscopic (eg., vibrational) phenomena as analogies for submicroscopic states. It's reasonable to assume that submicroscopic wave mechanics is essentially the same as macroscopic wave mechanics.

    Thanks again.
    Last edited by a moderator: Nov 20, 2011
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Expanding Space
  1. Expanding space ? (Replies: 4)