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Nature of Dark Energy and a cracker in the sand

  1. Oct 13, 2011 #1
    I have a question of sorts.

    I was taught that the universe formed from the Big Bang, which was a unique event. Much later I learned about the hypothesis of a multiverse, and the prospect that the Big Bang and our universe might not be as unique. This has off course has yet to be proven. Later we have also been introduced to the concepts of dark matter and dark energy.

    What I want to get around to is an idea of the nature of dark energy. As I understand it, dark energy is necessary to make the math add up with an accelerating universe, which should not be happening if our universe was unique. Dark energy seems to me a Ad Hoc solution.

    The question that keep coming back to me is: "What if there was a infinite space filled with stars, galaxies, black holes, the works, before the big bang?" What would it look like after the shockwave of the big bang passed through? What would happen to a black hole?

    If you detonate a cracker in the sand, it will create a crater. The shockwave pushes the sand in front of it. In the case of matter and mass, we know that it behaves much the same way as sand would, and would probably be dragged along with the shockwave. Mass, as I know it, makes a curvature in space. If there was a perfectly good universe in place before the cracker detonated, would we not se a similar accumulation og mass along the edge of the shockwave, which then gets left in place when the wave looses momentum. If this is the case, then it is not unlikely, for me, that there could be a significant sphere of mass surrounding what we perceive to be the universe. Sort of like a crater. If that is true, then what amount of mass would be required to create the effects we see, and how distant would it be?

    Regards
    Hammer76
     
  2. jcsd
  3. Oct 13, 2011 #2

    mathman

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    Dark energy is being used to explain an experimental result (~1996) where it was discovered that the expansion of the universe is speeding up, rather than slowing down. What the nature of dark energy is still very much an open question. Einstein's cosmological constant is the usual explanation, but the physics underlying this idea has many difficulties.
     
  4. Oct 13, 2011 #3

    PAllen

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    An what are those difficulties? The general Lagrangian for GR has exactly two free parameters, G and lambda. For G, we are happy to accept experimental determination. For lambda, experimental determination causes conniptions and is declared out of order. Why?
     
  5. Oct 13, 2011 #4

    marcus

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    :rofl: Conniptions is right! Why indeed? It can be argued that people should just accept the lambda constant the way they do Newton's G, and get over it.

    Mathman, there is a paper debunking the alleged "difficulties" surrounding the cosmological constant which is by one of the top people in Quantum Gravity. It might be interesting for you to read.

    You can get it simply by googling "Why all these prejudices against a constant?"

    Free online PDF. Should be the first hit. Let us know if you have any difficulty finding it. Or any questions. A lot is pretty straightforward, so I don't imagine it will give you any trouble.
     
    Last edited: Oct 14, 2011
  6. Oct 13, 2011 #5

    Drakkith

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    First of all, welcome to PF Hammer!

    Now, it seems you have some very common misconceptions about the Big Bang. Mainly about the "explosion" part of it. The current view is that the Big Bang was an explosion OF spacetime and not an explosion IN pre existing spacetime. There is currently no reason for us to believe there was a pre existing universe, and in fact it would probably be very suprising if there turned out to be one like you imagine it.

    So after saying that, there isn't any way to answer most of your questions as they don't even match with current theories.
     
  7. Oct 13, 2011 #6
    it would have to be a very big bang hence the name but how big was it?
    regards awsomness
     
  8. Oct 14, 2011 #7

    marcus

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    Hammer,
    a good way to start learning expansion cosmology is to learn about the standard model, the picture that most working cosmologists use.
    "Big bang" is a name someone who hated the idea applied to it. It is misleading. The standard picture is not of an explosion. But the name sounds jazzy and it stuck so that is what we often call it (even if misleading.)

    A good thing to read is a 2005 article in the Scientific American called "Misconceptions about the Big Bang"

    It is by a worldclass Australian cosmologist named Charles Lineweaver. I have the link in my signature at the end of this post. It is the "charley" link.

    He and his co-author go into all the misconceptions and confusions people have. They use simple language and pictures to get across the right ideas.

    So you could try that. If you click on that link be sure you scroll down. The first page is blank so it may look as if nothing loaded.

    Let us know if you have any trouble. Standard expansion cosmology is not like an explosion blowing material from some central location out into the surrounding empty space.

    Nor is it at all like an explosion in the midst of an already existing universe with planets stars galaxies producing a crater.

    Both those pictures involve material flying outwards from a well defined central location in space. This we do not observe happening. We have tons of observational data of many sorts. The model we use is a model which that data FITS. It fits remarkably well. The model has no central point anywhere in space with stuff flying outwards from there as in an explosion. The explosion idea is a non-starter. You are invited to start learning about the standard model of expansion cosmology. It may not be right but it is the best fit to the data we have so far.
     
    Last edited: Oct 14, 2011
  9. Oct 14, 2011 #8

    Chronos

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    The multiverse is an exercise in quantum philosophy to explain why the universe in which we reside happens to possess the constants we happens to measure. It might be the right idea, but, appears unlikely to ever garner any observational support. I consider it scientifically irrelevant.
     
  10. Oct 14, 2011 #9
    Hey, and thank you for the response. It’s always hard to jump into a field that others have discussed thoroughly before you arrive. My point of putting forward the question was to challenge my understanding of this subject. That being said, I would like to explain where my thoughts are going, and why.

    I've read the FAQ, Wikipedia, and then some, but I would not presume to say I have my head wrapped around it. Again, thats why i'm doing this.

    The first assumption for my argument seems to revolve around a big bang at a singular point. I accept and understand the notion that it was our universe "exploding", in full. Most of what I’ve read suggests that our universe was much smaller at that time, hence the balloon analogy of the universe. If the universe didn’t expand, we could not be. I also know that the big bang theory does not explain what happened before the initial rapid expansion. This indicates to me that for an external viewer, the big bang could have a singular and localized area. In our current model of the universe tho, there could be no external viewer, because nothing could exist outside our universe?

    Let’s say that in the first "boom" the balloon started expanding. The surface of the balloon IS our universe. As I understand it, that does not preclude an existing universe before the boom. Our balloon is just our relative system, or our reference system. I am aware that it is not just a regular explosion with matter traveling in the x, y z plane. It seems to me that the vector of the expansion is beyond our senses, tho we can observe its effect.

    Another analogy. If an ant crawls into a pack of C4, and it detonates, let’s say for the sake of argument that it survives, can observe and report. Also for the sake of argument the shockwave travels out with more than the speed of light, considering the expansion of the universe. Standing at a point on top of the balloon, the ant would never be able to observe the edge, because of the nature of the expansion. It would just be sitting in the middle of a void with remains from the "boom".

    The relevance off course is where we are going, long term. It was easy when we were looking at a big crunch or that the universe would just keep going, in a Newtonian sense, but.. we are not just "going" along the path, we are accelerating. That is where Dark Energy, as I understand it, enters the picture. The effect of DE is similar to a falling slope in space that, like mass falling into a gravity well.

    "The crater" I refer to would not be like the shell of a supernova remnant or anything close, Since the universe, or space, is expanding I have å hard time visualizing the result.

    I'm not sure this makes my thoughts clearer. In Norway we have a saying, that "its better to keep quiet and let people think you are dumb, than to speak and remove all doubt."
     
  11. Oct 14, 2011 #10

    Drakkith

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    There is no "shockwave" Hammer. At an infinitesimal length of time after the big bang space was infinite in size yet very very very dense and hot. Two points in space that were 1 lightyear, 10 lightyears, or 100 billion lightyears apart all see expansion take place exactly the same, meaning that everything expands away from them from their point of view. There is no edge, no shockwave, no vector, and nothing for the universe to expand into. It is simply that the distance between every object in the universe increased and is still increasing. The best way to start to visualize it is to completely do away with any notion of an explosion as we know it.

    As for dark energy, I'm not sure what you are asking.
     
  12. Oct 14, 2011 #11

    mathman

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    The particular concern I have is that the size of the cosmological constant hasn't been satisfactorily explained by any physical mechanism. The most common attempt seems to be vacuum energy. However, estimates as to size end up 120 orders of magnitude too large.
     
  13. Oct 14, 2011 #12

    marcus

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    These are exactly the questions that Bianchi and Rovelli are responding to in the paper I mentioned.
     
  14. Oct 14, 2011 #13

    phinds

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    Yes, that's a good understanding; no outside, no surface, nothing to "explode into". There ARE other hypotheses but until you grasp the current model fully you're best off working on doing so before you get off into the really unlikely stuff.
     
  15. Oct 15, 2011 #14
    So you all firmly believe in the cosmological principal, and take it for granted that it is correct?
     
  16. Oct 15, 2011 #15

    phinds

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    I would not go along with "take for granted". I for one did NOT "grant" it, I looked at the evidence and I believe it correct. There is not at present any evidence to contadict it so if you think it wrong, I have to ask, WHY?
     
  17. Oct 15, 2011 #16

    Drakkith

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    I firmly believe that the cosmological principal is the best description we currently have to explain the observations and evidence available. If it turns out tomorrow that it is incorrect, I will change my view accordingly.
     
  18. Oct 15, 2011 #17
    Well, I am a economist, not a cosmologist, so I have no basis for concluding either way. My take on cosmology is probably more philosophical than physical. Reading the forums, some people seem very adamant about a certain world view, more so than I think a theory based on assumptions, however probable, merits. I realize that my original question contradicts the current pardigm. There are some concepts I have a hard time with, so I ask questions. :) I get that some of the veterans in this field will get tired of newcomers asking irrelevant questions, based on wrong assumptions.

    Anyway, the cosmological principal is going to be very hard to disprove considering we can only observe a limited area of the universe.
     
    Last edited: Oct 15, 2011
  19. Oct 15, 2011 #18

    Drakkith

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    Realize that just like any scientific theory currently accepted, this model is simply the most accurate we have currently. No one here will ever argue that our model is the only possibly correct one and that it is 100% accurate and infallible. It is simply the best one that fits our observations and data.
     
  20. Oct 15, 2011 #19

    Drakkith

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    Energy has mass. The difference in mass between 4 individual protons before fusion and after they fuse to form helium will be radiated out as light and neutrinos. No mass is lost anywhere, it is simply moved around in one form or another. Note that while light doesn't have REST MASS, it's energy does in fact contribute to gravity.

    Edit: Also I recommend reading the rules for PF, as personal theories are not allowed, and for good reason.
     
  21. Oct 15, 2011 #20

    phinds

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    TheZness, your theory is full of holes. Just to start with, how do you propose that the reactions in the core of stars create a uniform effect spread out over large numbers of light years?

    This is a really great forum and folks here will be happy to help you if you have questions about science, but the moderators have a low tolerance for personal theories, EPECIALLY when they are promoted as true. If you plan on sticking around, you'd best read the rules.

    EDIT: I see drakkith already recommended your reading the rules about personal theories.
     
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