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

I have a crude understanding of dark energy and the relativist universe.

  1. Oct 25, 2011 #1
    Hi there:),

    I've always been interested in the notion of an expanding universe. It seems like such a hand wavey thing to say. Over the past few years of my life I've done some thinking (with minimal scientific backing) about how and why the universe expands. I've come up with some pretty cool ideas but I'm sure they are ill-founded. So allow me to list the things that I think are true, and tell me if I'm missing any important concepts or if I'm wrong altogether. (And don't be afraid to scold me :tongue2:)

    1) The universe is thought/known to expand because the doppler shift between earth and stars around it is proportional to the distance from the earth

    2) Dark energy is an unmeasurable energy that causes or contributes to the expansion of the universe. This energy is theoretically uniformly distributed about the universe which suggests that it repulses itself.

    3) Entropy represents the idea of spontaneity in the context of a reaction. Reactions are in general spontaneous, and this implies that they release energy (since reactions that require energy wont happen)

    Now that that stuff is out of the way, I have a thought.

    What if the universe only seems to be expanding because all of the matter inside of it is "compressing"? It only makes sense to me that if the universe began at a singularity of energy, it would end that way as well. Matter seems like a process of energy recollection. Not only is matter the most dense form of energy known(cite that dacruick...geeze), but it can also accumulate kinetic energy.

    If the earth is rotating around the sun, and the sun is rotating around the galaxy centre, and our galaxy is rotating around...you get the point, wouldn't there be a system of centripetal accelerations? Couldn't that explain the doppler shift? ...Hmm then why wouldn't we see some blueshift?...Well, what if its not the space between galaxies that is expanding, what if its the time? What if our acceleration towards a prospective singularity is ever increasing that in the time it takes for light to travel between a star and Earth, time has expanded enough to cause redshift from every target. If time dilation is indeed independent of direction then I don't see how this should be a problem conceptually. If we are approaching a singularity at relativistic speeds (which isn't a mind blowing hypothesis since we already think the universe is expanding at relativistic speeds) are there any of my claims that can be ruled out? I mean, dark energy is a concept used to reconcile the distribution of space that we only assume to be there since we think the universe is expanding. It seems like the wrong direction to go (pun intended for sure).

    I don't want to get caught up in the fantastical side of my idea, but isn't it valid to believe that the Universe goes through cycles. Why should we think otherwise?

    Let me know what you guys think!

  2. jcsd
  3. Oct 25, 2011 #2
    Hi there.... Just from the looks of things, it seems that galaxies are basically the result of an explosion of a self-rotating object, hence the helicoid arrangement-shape.... That brings me in mind, as I have read, black holes, which explode under their gravity etc. What that means, is that galaxies are continuously expanding, and as such, there are not going to become the same "singularity" again; as it has already been seen, galaxies can collide, or the outer parts can be seperated at some time from the "mothe" galaxy.... Those free parts, but especially galaxies colliding, are very prone, at least to my understanding, to form new black holes, and there you are again.......... That is basically my understading, as I said, just by the looks of it, though, I always have in mind that all those speculations may stand true, but also there may be many other things that we can not perceive, because I find knowledge is like atoms: you can divide them infinitely, and there will always be something more to divide; you can know much, but there will always be room for more knowledge.....
  4. Oct 25, 2011 #3
    I don't see why black holes exploding rules out the possibility of approaching a singularity. That just means that the circumstances surrounding that particular black hole are not sufficient. I'm just trying to establish the idea that there could be a cyclic aspect of the universe, and I'd like concrete reasoning to be at the core of these responses. If you could tell me why every black hole will explode under its own gravity then that's different. I'm being speculative and a devils advocate to consolidate my understanding, I would appreciate not to be met with speculation in response. I should have made that more clear in my original post. I just feel that your response didn't meet the depth of my question. And I don't mean to be rude I am very sorry if I am being perceived that way, I just want to be clear about my goals :)
  5. Oct 25, 2011 #4
    Hehe, you are right that I did somehow missed the heart of your question.... which is I believe that "It only makes sense to me that if the universe began at a singularity of energy, it would end that way as well" and similarly "isn't it valid to believe that the Universe goes through cycles". My initial post was instead about "If the earth is rotating around the sun, and the sun is rotating around the galaxy centre, and our galaxy is rotating around...you get the point", in order to insist to the fact that our knowledge is limited - you do not and either I do not know if galaxies are rotating around anything - and all our speculations originate from our experience... hence I said "by the looks of"..... since we do not have a clear picture (photo) if our universe is rotating around a singular point, the point of the bing bang, we could assume that either this point was either stationary, which is more propable, judging from the random placing of the elements (galaxies etc.) in our universe as of our current knowledge. It is also possible that this point was rotating, although we are not having enough information so far about the look of our universe in its wholeness, or also that there are many bing bangs around, maybe many universities, each with it's own rules and/or magnitudes of the same phenomena (for example, different magnitude of the mechanism of gravity), and those universities collide with each other etc. etc.
    But before going even further, I am coming back to what, as I said, feel that is your original wondering.... does the universe comes back in singularities, where it is supposed to come from? Well, I think I would not risk much saying, that if there was a bing bang, even a stationary or rotating one, then it is very propable, and if it does not collide or interact with another universe(s), that matters will come back to the same singularity... Why? After the big explosion, parts are moving in the outer space with a startup velocity..... but this velocity is only a first "push", that ceases to exist aftewards; then the only force existing between those parts will be their mutual gravity.... Now, if those parts are flowing in a spherical shape arranged in the empty space, althought they can be in random placing, statistically the gravitational forces between them will bring all parts back together to the original center... So, as you said, first it goes grande.... and then comes back.... How could we know that? I guess, observing a blue shift, as you are suggesting....
    Last edited: Oct 25, 2011
  6. Oct 25, 2011 #5
    I am not suggesting that if we saw a blueshift we would be going in the opposite direction. I'm suggesting that the universe is compressing as opposed to expanding, and the reason we don't see a blueshift is because of time dilation. If your "first push" analysis of the big bang is accurate, why is the expansion of the universe increasing? This is what doesn't make sense to me. The concept of dark energy is needed to reconcile the amount of space with the amount of matter, but I don't see the hypothesis behind the expansion of the universe to be concrete enough to start making up 75% of mass-energy density of the universe. If space is expanding at all times, and the amount of matter stays the same, wouldn't dark energy have to be continuously created? It just doesn't make sense does it?
  7. Oct 25, 2011 #6
    I have not any knowledge of dark eneyrgy, so I will not comment on this, at the moment, at least.... As for the first push, I envisage this as an explosion, in which some small parts are going more far than some others.... Then, in the empty space, at some time the distance between the heavy and the lighter parts will seize to increase and they will start coming bαck together.... Then, instead of observing a red shift someone will start observe blue-shifts (not blue colour, but red becoming green and so on)... The reason that we are now seeing red shifts is because the things around us are going more far, and that is just an observation.... Of course I maybe be wrong with the physics (movement especially) of explosions, but I leave aside time dillation, in which I have much to comment, but not at the moment.... I am just saying that I consider that there are some misconceptions in the overall SR theory, and I will come back to them at sometime, but the Doppler effect is a right assumption at its base.....
  8. Oct 25, 2011 #7


    User Avatar
    Science Advisor

    This is a rather incorrect view of the big bang and early universe evolution. The big bang was not an explosion occurring in a pre-existing space. While of course the properties of the big bang itself re not known, the big bang model, which considers the expansion of the universe from a hot dense initial phase, describes a homogeneous and isotropic expansion of space -- the big bang happened everywhere at once and involves the expansion of space itself. See the balloon analogy in the FAQ or sticky at the top of the cosmology forum.
  9. Oct 25, 2011 #8


    User Avatar
    Science Advisor

    Dark energy is only hypothetical -- it is a proposed cause of the observed accelerated expansion of the universe. It is indeed theoretically uniformly distributed throughout the universe, but this is not a result of the accelerated expansion (or repulsion if you prefer to think of it that way). Rather, it's the cause of this gravitational behavior. Strange, I know.

    I'm not sure how useful this definition is for physics and cosmology. In these contexts, entropy is most usefully understood as the amount of disorder present in a system -- a quantity that depends on the number of available states of the system.
  10. Oct 25, 2011 #9
    excuse me, some more comments.....
    I must say that I agree, at a first glance (that is, without making any mathematical calculations) that this is a possibility, maybe the expansion has ceased, although we can not see it already, as we can only see what happened in the past (light has finite speed etc.)

    Just before, you said that you are thinking that there may be not expansion anymore and now you are saying that you are sure that the expansion continues.... I prefere not to be sure in those things, as it is nearly impossible to be sure for the actual current state of the entire university

    The ask of existence and what that is, is so big and so unknown.... So you can think of anything that suits your observations and thinking, dark energy, kids bearth, anything really.....
    Last edited: Oct 25, 2011
  11. Oct 25, 2011 #10


    User Avatar
    Science Advisor

    Too bad that science is based on evidence, not from the "looks of things". I know you've given the caveat that much of what you say is your speculation, but this a science forum, where, unsurprisingly, we discuss accepted scientific viewpoints.

    Black holes do not explode "under their own gravity" -- they explode in a fit of Hawking emission. If they explode at all -- we have no observational evidence for this process.
    This is not true according to modern particle physics.
    Last edited: Oct 25, 2011
  12. Oct 25, 2011 #11


    User Avatar
    Science Advisor

    You know, it would probably be a good idea to actually learn a bit about the science that you are discussing on these pages before you, um...discuss it. Instead of making grand and nebulous claims about the lack of evidence for dark energy, I have a crazy idea. Google "dark energy". Or try wikipedia. People on this forum are asking honest questions about honest science; you do a disservice to them by giving misleading and false answers.
  13. Oct 25, 2011 #12
    I don't understand how my claim that the universe isn't expanding isn't being addressed here. Maybe my original post isn't being read in its entirety?
  14. Oct 25, 2011 #13


    User Avatar
    Science Advisor

    If the universe was uniformly contracting, we'd see blue shifts in accordance with Hubble's Law. We don't.
  15. Oct 25, 2011 #14
    You didn't read my post it its entirety did you? I proposed a reason why we might not see blueshift. And I certainly don't claim it uniformly contracts.
  16. Oct 25, 2011 #15


    User Avatar
    Science Advisor

    Well, because in the very sentence where you are supposed to explain the lack of blue shift you start talking about an expanding universe again. And special relativity isn't applicable in the presence of gravity, so ideas like time dilation due to relative motion cannot be made precise. Instead, you must use general relativity to understand how time passes for observers in the universe. Lastly, you haven't developed a mathematical understanding of your idea, at least you haven't shown one. My guess is that if you were to succeed in doing this, it would be a rather contrived set up and probably significantly more complicated than the concordance cosmological model, which is based only on general relativity (a well-supported gravitational theory) and the assumptions of homogeneity and isotropy (a well-motivated assumption based on observations).
  17. Oct 25, 2011 #16
    I talk about a time expansion not an expansion of space. Are they not different? Are they the same because of things like length contraction?
    Last edited: Oct 25, 2011
  18. Oct 25, 2011 #17


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2016 Award

    At some point, this thread has gone from asking a question, to making unsubstantiated speculation, which is in clear violation of the PF Rules.

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: I have a crude understanding of dark energy and the relativist universe.
  1. Relativistic energy (Replies: 7)

  2. Relativistic energy (Replies: 10)