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  1. Nov 7, 2011 #1
    *The following philosophical statement is as far as i know, based on nothing and surely wrong*
    Hi, I would simply like your input into the following. I know its not much.

    Space the indescribable something that the universe(matter) sits in is infinite. Whilst matter being finite is dispersing into infinity. Discuss.
     
  2. jcsd
  3. Nov 7, 2011 #2

    marcus

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    First let's be clear this forum is about the professional research area called cosmology which is a mathematical science. That means there are math models (not verbal models) and folks collect observational data and adjust the models to get the best fit.

    In this forum people ask questions and give answers related to the standard mainstream model, discuss, explain, help each other understand.

    In the standard cosmo model matter is approximately uniformly distributed throughout space. Matter and space are co-extensive. And there is no boundary. The model basically has two versions: finite and infinite.

    So far the data fits both about equally well, so we maintain and use both. You really can't tell the difference.
    In the finite case space has no boundary, is finite volume, and matter is finite.
    In the infinite case space has no boundary, is infinte volume, and matter is infinite.

    So what you are starting out with does not fit in with what we normally discuss here.

    It seems to be your own personal conception (or misconception of what cosmology is about.)

    I would encourage you to LEARN THE STANDARD PICTURE FIRST and understand regular mainstream cosmology. Then branch out from there, if you want to, and propose your own private vision. But don't start proposing your private scheme and arguing for it UNTIL YOU UNDERSTAND the standard picture.

    That's just a bit of friendly advice based on how I've seen things go, over the years.

    You could start by reading the "charley"--link article in my signature. It has served as a good introduction to cosmology for a lot of people. It is a SciAm article from 2005. Let me know if the link doesn't work for you :smile:
     
  4. Nov 8, 2011 #3
    Wow, marcus, the 'charley' link was incredible reading!
     
  5. Nov 8, 2011 #4
    OK, I admit I'm an amateur cosmologist, with tendency to philosophise. Resulting in assumptions that ignore the standard model.I also find it easier to use words rather than mathematics to explain things, but that is duly to my own shortcomings in maths I guess. It was my understanding that the standard model doesn't work, it is just the best fit to what we can observe. Theories like 'dark matter', 'dark energy'. We don't know what they are or even if they exist, they are purely additives in an attempt to make an ill fitting model work. Isn't that correct?

    Taken from one of your links marcus, I can now see that my original post was premature. It appears that the general consensus is that space and matter was at an infinite density at minuscule size at cosmic time zero.

    How can space be stretched, when essentially it is nothing? The distance between two atoms is the same 'space' between Earth and Mars, or the Milky way and Andromada.
    Or am i wrong and space is something?

    Forgive my ignorance, I simply just want to learn
     
  6. Nov 8, 2011 #5
    The constants are not added to make an ill-fitting model work, they are the opposite. They are required to fit so the model does work - we just do not know what they are.

    Imagine a box we know weighs 10KG in total including its contents (which we partially know), we know it has 9KG of lead and the box weighs 0.5KG, now without opening the box we know we have 0.5KG of "dark matter". This does not ascribe any distinct properties to the dark matter it is just unknown what that the "dark matter" is. Dark Matter can be directly observed due to the lack of any electromagnetic interaction with normal particles - this can be seen in colliding galaxies.

    Space doesnt stretch. The geometric distances between gravitationally unbound objects grows with time - this is the scale factor. As for space being an independent object I think it better to view space as geometry. The homogeneity of expansion is accounted for by the geometry of space.


    Also it is not adviseable to talk about "time at point zero" or t=0 as this is essentially the singularity and most physicists wont discuss t=0 but t>0 or more specifically t>planck time
     
  7. Nov 8, 2011 #6

    Drakkith

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    Do you realize that ALL scientific models are inaccurate to some extent? Cosmology is no different. The nature of the universe means that we must passively observe things from extreme distances with no way to interact with them. It is no surprise that there are a great many things that remain unanswered.
     
  8. Nov 8, 2011 #7
    The big bang was like a bomb going off at a certain location in previously empty space.
    In this view, the universe came into existence when matter exploded out from some particular location. The pressure was highest at the center and lowest in the surrounding void; this pressure difference pushed material outward.

    How do we know that this is inaccurate over the idea that the big bang happened everywhere at once?

    I know the standard model. I'm just questioning it. Isn't that what science(besides the pursuit of knowledge) is, challenging the widely accepted 'facts'.

    What I can't get my head around is that there was no space(or geometry, as cosmo novice described it) before the big bang
     
  9. Nov 8, 2011 #8
    The big bang happened everywhere not just an explosion in one place.
     
  10. Nov 8, 2011 #9
    There was no pre-existing space. Space was created along with the entirety of the Universe as we know it at the BB.


    We know this is inaccurate becauses it contradicts a fundamental principle in cosmology - isotropy. Isotropy dictates that (barring local differentiation) the Universe is pretty much the same everywhere. This means there is no "leading edge" to expansion and no "center" - because if the Universe had either of those then it would fail to be isotropic - and parts of the universe would be fundamentally different. We know this is not the case through observations. Specifically the CMBR shows the Universe is uniform 1/1000 and this shows the Universe is isotropic.

    The Big Bang is not an explosion of matter in a pre-existing background - it does not have a priori. The Big Bang is the expansion of EVERYTHING; time, space, energy and matter. Essentially the expansion of reality.

    I would highly reccomend you to look into curvature of space and topology as this may help solidify your current understanding.
    Hope this helps

    Cosmo
     
    Last edited: Nov 8, 2011
  11. Nov 8, 2011 #10
    cool, i'll look into that.
    Got any links for it?
     
  12. Nov 8, 2011 #11
    Try:

    http://en.wikipedia.org/wiki/Shape_of_the_Universe
    Is probably a good start. Once you have a bit more information on the "flavours" of the different topologies.

    There are also a few good forum pieces in physics forums which are worth a look. I am in no means an expert but there are experts on this site and very well educated laymen.

    If you have a good read through what you can find and then create a new topic on your revised questions - should you have any deeper questions which I think you will :smile:

    Cosmo
     
  13. Nov 8, 2011 #12

    marcus

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    I don't think there is any scientific reason to suppose that ("no space"..."no before"...etc.) So you don't need to "get your head around it". For sure on the one hand some math models of the U break down as you go back in time and get close to the start of expansion. (those are the older models)

    But on the other hand some math models of the U do not break down at that point as you go back in time. So for example there may continue to be space or geometry (as cosmo novice correctly says, I think) but it is just contracting. So the model is of a contraction and a sudden rebound, followed by the expansion picture that we are used to. BB is simply the start of expansion, not necessarily the start of the universe.

    You get that in a research area called quantum cosmology. Quantum effects may make gravity repel at extremely high densities, so a U that looks like it is going to crunch may actually bounce. This idea still has to be tested but no reason to rule it out so far. Possible.

    So one cannot as a scientist honestly say that there was no "before" or that there wasn't any geometry and matter before the start of expansion. That would be to make an unfounded claim.

    Nor can one say that there was. Some models say was, some models say wasn't. The observational evidence is not yet adequate to decide.
     
    Last edited: Nov 8, 2011
  14. Nov 9, 2011 #13
    Yes Marcus this is correct so thanks for clarifying - I was not stipulating theres was no time/space before the BB, merely that it cannot be defined properly using current metric. I hope this makes sense shifty88/marcus.

    It is very difficultt expressing essentially mathemtical theorems using english - things get lost in translation so I try to be very careful with my wording.
     
  15. Nov 9, 2011 #14

    marcus

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    I suppose that whether or not it can be properly defined depends on what mathematical model you are using. In some, for example Loop quantum cosmology, there is no problem with pre-BB. One has both computer simulations and equation models that can be started before BB and run through the bounce and into the expansion period.

    for a taste, try googling "Ashtekar loop cosmology overview" and sample some of Ashtekar's papers.

    But if by "current metric" you mean vintage 1915 General Relativity, and the cosmological models derived from that, then you are quite correct: pre-BB can NOT be properly defined with those particular tools.

    I guess it depends on what you call "current" :smile:
     
    Last edited: Nov 9, 2011
  16. Nov 10, 2011 #15
    Haha, yes. I was reffering to "current" metric as 1915 GR! I have skimmed over some of the Ashtekar papers - the math is above my head a little but I can understand the flavour. I find the idea of a LQG bounce beautiful in simplicity AND it does not mean inventing new math as it avoids the singularity which is an inevtiable failure in GR.

    I will look on Google thanks :smile: If you have any additional reading links on LQG (at begginer level) I would be very interested in them as this is a topic I am actively studying. (Studying at laymens level)
     
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