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Size of the Universe.

  • 15-02-2011 10:45pm
    #1
    KoolKid
    Moderators, Home & Garden Moderators, Technology & Internet Moderators Posts: 24,789 Mod ✭✭✭✭


    Ok heres one thats bugged me for a while. Total amature point of view here , so please excuse if its silly.

    Its rekoned the universe is 15 billion light years.
    Does that mean we can see 15 billion light years in all directions, in which case the universe would be over 30 billion light years, or can we see 7.5 billion light years all round us. If thats the case it would be very presumtious to think out of this vastness we are in the middle...


Comments

  • #2
    NoQuarter
    Registered Users, Registered Users 2 Posts: 4,624 ✭✭✭NoQuarter


    You're thinking of us here on earth as the centre of the universe and we are not. think of the start of the universe as a torch and the universe as its beam of light shining out. The beam has expanded from the torch for approx 13.7 billion years, were just in the beam somewhere.

    So the universe is expanding out from a point like a torch's beam and we're just part of the beam, rather than expanding out from our point in the universe thats my interpretation of it.


  • #3
    KoolKid
    Moderators, Home & Garden Moderators, Technology & Internet Moderators Posts: 24,789 Mod ✭✭✭✭KoolKid


    That was my question
    I heard it said before that a distance of approximately 15 bn light years is the known universe as thats as far as we can see.
    So if we pick one point in the sky how fast can we see...?


  • #4
    rccaulfield
    Registered Users, Registered Users 2 Posts: 1,015 ✭✭✭rccaulfield


    We can see 13.2 billion light years(a baby galaxy) at the moment and according to the expansion evidence when you rewind the clock it starts 13.7 billion years ago which seems ok. As far as earth being in the centre well every dot on a balloon things its in the centre relative to the other dots when its being inflated! Try it!


  • #5
    The Hill Billy
    Registered Users, Registered Users 2 Posts: 22,833 ✭✭✭✭The Hill Billy


    The Wikipedia article on the Observable Universe may interest you.


    On the other hand it may confuse the hell out of you like it did me. :o


  • #6
    KoolKid
    Moderators, Home & Garden Moderators, Technology & Internet Moderators Posts: 24,789 Mod ✭✭✭✭KoolKid


    Thanks for the replys.
    What still confuses me is if the universe has expanded in all directions for 13.2 billion years is it not 26.4 billion light years across?


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  • #7
    Cú Giobach
    Closed Accounts Posts: 3,772 ✭✭✭Cú Giobach


    KoolKid wrote: »
    Thanks for the replys.
    What still confuses me is if the universe has expanded in all directions for 13.2 billion years is it not 26.4 billion light years across?

    That would be true if the universe expanded at the speed of light which it didn't.
    It was/is much faster. (the speed of light limit is only for things traveling through space).
    If you were to travel to the edge of the observable universe you would then see it as a 27 billion light year across "bubble" with you at the center and where the Earth is would then be the edge. :D


  • #8
    KoolKid
    Moderators, Home & Garden Moderators, Technology & Internet Moderators Posts: 24,789 Mod ✭✭✭✭KoolKid


    Thanks guys. Head hurting stuff, but I have a little more understanding.
    So basically , no matter how fast or how far we could travel or how far we could see we could never leave or view outside the universe. (if such a place even exists) And no matter where we go it will still be all around us?
    :confused::confused::confused:


  • #9
    Cú Giobach
    Closed Accounts Posts: 3,772 ✭✭✭Cú Giobach


    KoolKid wrote: »
    Thanks guys. Head hurting stuff, but I have a little more understanding.
    So basically , no matter how fast or how far we could travel or how far we could see we could never leave or view outside the universe. (if such a place even exists) And no matter where we go it will still be all around us?
    :confused::confused::confused:
    Yea, just think of it like a 3 dimensional version of wandering around the Earth looking for the edge. Though the Earth is finite in size no matter where you stand you are always surrounded by the circle of the horizon and can never find an edge.
    In a simplistic way thats what the universe is like, finite but without a definable edge.
    To go a bit deeper, in 4 dimensional space/time the edge of the universe is actually in the time dimension, ie 13.7 billion years away/ago. :D


  • #10
    MRPRO03
    Registered Users, Registered Users 2 Posts: 272 ✭✭MRPRO03


    A few of things that I find a little hard to understand, is

    1) If the Universe is expanding, what is it expanding in to ?
    2) If the Universe was at some point smaller, how can it become infinite ?
    3) They say that the speed of expansion of the Universe is speeding up by the observation of galaxies in all directions going away from us, but maybe the opposite is happening, in that galaxies are being pulled together but give the impression of speeding away, like jumping from a plane, the atmosphere appears to speeding away as the person falls to Earth.


  • #11
    Cú Giobach
    Closed Accounts Posts: 3,772 ✭✭✭Cú Giobach


    MRPRO03 wrote: »
    A few of things that I find a little hard to understand, is

    1) If the Universe is expanding, what is it expanding in to ?
    2) If the Universe was at some point smaller, how can it become infinite ?
    3) They say that the speed of expansion of the Universe is speeding up by the observation of galaxies in all directions going away from us, but maybe the opposite is happening, in that galaxies are being pulled together but give the impression of speeding away, like jumping from a plane, the atmosphere appears to speeding away as the person falls to Earth.

    1. Nothing, there is nothing outside the Universe even the concept of "outside the Universe" doesn't apply because there is no outside.
    This is the simplest explanation and there are theories abounding but that is the first thing to get ones head around.
    It's not expanding into anything. (don't worry, no human being can really visualise that).

    2. The Universe isn't infinite, there is no "edge" from a 3 dimensional perspective, like there is no "edge" to a finite sphere from a 2 dimensional perspective.
    As I mentioned earlier the "edge" of the Universe is actually in time, we live in 4 dimensional space/time. 3 dimensions of space and 1 of time, to get to the edge of the Universe we would have to travel through the time dimension.

    3. From your analogy the distance between the jumper and the clouds (?) is increasing and would appear so, so I don't really get where your going there.
    The distance between the Galaxies on a large scale is increasing and the speed this is happening at is increasing. If the Universe was contracting we would know about it.

    Have a read here it might give you a few ideas (or warp your brain :D).


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  • #12
    KoolKid
    Moderators, Home & Garden Moderators, Technology & Internet Moderators Posts: 24,789 Mod ✭✭✭✭KoolKid


    The 2 things that I don't think anyone can really comprehend is Nothing & Infinity


  • #13
    Cú Giobach
    Closed Accounts Posts: 3,772 ✭✭✭Cú Giobach


    KoolKid wrote: »
    The 2 things that I don't think anyone can really comprehend is Nothing & Infinity
    What about the fact that some infinities are bigger than others. :D


  • #14
    KoolKid
    Moderators, Home & Garden Moderators, Technology & Internet Moderators Posts: 24,789 Mod ✭✭✭✭KoolKid


    Where's the Panadol? :confused::eek::confused::(:mad:


  • #15
    hal9000
    Registered Users, Registered Users 2 Posts: 933 ✭✭✭hal9000


    just to mess with your head a little bit more :p
    http://en.wikipedia.org/wiki/Inflation_(cosmology)
    reading distances like 24 gigaparsecs makes my head hurt too!


  • #16
    rccaulfield
    Registered Users, Registered Users 2 Posts: 1,015 ✭✭✭rccaulfield


    Isn't infinity just a mathematical concept with no bearing in reality(devils advocate).


  • #17
    KoolKid
    Moderators, Home & Garden Moderators, Technology & Internet Moderators Posts: 24,789 Mod ✭✭✭✭KoolKid


    It depends.
    If the universe is not infinite, is what its expanding into infinite?
    If not is the universe going to hit some sort of barrier one day?


  • #18
    Moon54
    Registered Users, Registered Users 2 Posts: 1,242 ✭✭✭Moon54


    I firmly believe the Big Bang model will need to be revised soon.

    The big bang model states that the Universe began 13.7 billion years ago.
    However, new discoveries have shown that fully formed galaxies, albeit much smaller,
    have been detected out to 13.2 billion light years away. The trouble is that these
    distant galaxies have been detected with heavy elements in them.
    And there's the problem. These heavy elements can only be formed from supernovas.

    500 million years is a pretty small amount of time on the galactic time scale,
    and a lot has to happen in that time - eg - The galactic debris from the
    big bang has to collapse to form stars, the stars go supernova, the supernova
    create the heavy elements and spread the dust from which newer stars form,
    then clusters of stars form, more supernovas, the clusters go on to form galaxies and so on..................

    I have no doubt that we will detect galaxies even further back than 13.2 billion
    yrs, the new Hershel space telescope will do this, which begs the question,
    was there enough time to get everything going?     (to form what we can now
    observe in the earliest galaxies!)

    My own personal theory that I am toying with, is that the Universe is cyclic,
    ie, the Universe is infinite, and the current Big Bang is just one of an infinite
    cycle of Bangs. Of course, I can't provide proof. :)

    I don't know how everyone else will feel about it, but I'm comfortable
    with the notion of an infinite Universe.


  • #19
    Helix
    Closed Accounts Posts: 17,661 ✭✭✭✭Helix


    surely we can only see as far as light has travelled? isnt it the case that we dont actually know how big the universe is, only how much of it we can see?

    maybe im wildly off the mark here even if the universe was 10000bn light years across, we're only ever gonna be able to see back to just after photons started knocking around and creating light, so approximately the same distance we can see right now, since looking through space is looking back in time right?


  • #20
    Helix
    Closed Accounts Posts: 17,661 ✭✭✭✭Helix


    KoolKid wrote: »
    If the universe is not infinite, is what its expanding into infinite?

    does it actually need to be expanding into anything? if its a self contained system, then wouldnt it be possible that it's the same size as it always was, but rather than expanding into an external entity, it only seems like its expanding because everything is uniformly shrinking?


  • #21
    rccaulfield
    Registered Users, Registered Users 2 Posts: 1,015 ✭✭✭rccaulfield


    Helix wrote: »
    surely we can only see as far as light has travelled? isnt it the case that we dont actually know how big the universe is, only how much of it we can see?

    maybe im wildly off the mark here even if the universe was 10000bn light years across, we're only ever gonna be able to see back to just after photons started knocking around and creating light, so approximately the same distance we can see right now, since looking through space is looking back in time right?

    Accept that current theory states that at a certain distance away from the earth the space in between the earth and say a galaxy at that point is expanding so that the galaxy in question begins to move away from the earth faster then the speed of light and so will one day disappear from our horizon forever. Which leads to the problem that its not when photons started thats the observable universe, the observable universe may only be a grain of sand on a beach for all we know cos we can't see past a certain point due to the expansion of space.:eek:


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  • #22
    slade_x
    Moderators, Science, Health & Environment Moderators Posts: 1,428 Mod ✭✭✭✭slade_x


    Moon54 wrote: »
    I firmly believe the Big Bang model will need to be revised soon.

    500 million years is a pretty small amount of time on the galactic time scale,

    The current model of the big bang theory doesnt satisfy much but that of a possible start of inflation. The big bang theory has been losing ground for years. It doesnt answer anything, just leaves us with more and more questions. mind boggling ones in fact

    500 millions years may seem like nothing to a star like ours but to a massive giant its a very long time. if anything the earliest galaxies had the most amount of matter with which to form, which would exponentially increase star formation and not to mention of those stars that have to endure supernova conditions only burn for a relatively short amount of time. 10 millions years would possibly be old age for such a star


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