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The Big Bang

  1. Nov 20, 2007 #1


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    Out of curiosity, as the universe started from a point and as we look ever further into space we are also looking back in time why don't we see matter from these furthest regions clumped together more as it was shortly after the creation of the universe and why don't we see space as a sort of shrinking conelike shape as we look back further as the universe was smaller then?
  2. jcsd
  3. Nov 20, 2007 #2
    And how would that look exactly? The universe coming to a conelike shape, I mean. Remember that we are inside the universe, and the big bang lies in every direction from our point of view.
  4. Nov 20, 2007 #3


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    I've no idea which is why I asked the question :confused: I'm looking for information not trying to impart any. I only mentioned a conelike shape as it seemed the best way to describe a shrinking horizon as looking back in time equates to a smaller universe.

    One effect I imagine is possible is you would see multiple images of the same object as the light from them traversed the curved space of the then much smaller universe perhaps?
  5. Nov 20, 2007 #4


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    This is a very common misconception about the Big Bang. It it not a theory that suggests the Universe started from a point. The Big Bang happened everywhere and there is no 'centre' to the Universe (at least there is no requirement for there to be a centre).

    Have a look at http://math.ucr.edu/home/baez/physics/Relativity/GR/centre.html" [Broken] for an explanation. If you're still unsure ask for further info on whatever is confusing.
    Last edited by a moderator: May 3, 2017
  6. Nov 20, 2007 #5


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    I never mentioned a centre :confused: but I did believe the BB theory suggests the universe began with a particle smaller than an atom which went through a rapid inflation period FTL and although slowed down continues to inflate today as space expands.

    Anyway taking the balloon analogy. Looking back in time one would (I'd have thought) expect to see a smaller balloon as less expansion had taken place at that time and thus a clumping of matter as the space between the galaxies 15 billion years ago when the light we are now seeing began it's trip would be far smaller than it is today whereas the surface area of space actually appears greater the further one looks.
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  7. Nov 20, 2007 #6


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    You seem to have a good geometric intuition Art---there is infact a kind of optical distortion of apparent sizes as you look back to an earlier less-expanded universe---but the effect is not like looking into the inside of a cone (as you imagined it).

    So you haven't got it yet, although you get cheers for realizing that there is going to be a fun-house weird optic effect.

    Do you understand using the redshift z as a measure of how far something is? (there are online calculators to convert z to lightyears if you need, it is not a linear conversion so you want a calculator programmed for it.)

    Say a typical spiral galaxy is 100,000 lightyear diameter and use that as an imaginary ruler. Then what you expect is that the farther away it is the smaller it will look (the smaller ANGLE size it has in the sky). That's normal perspective we are used to. And that works in the sky OUT TO A CERTAIN DISTANCE and then it gets overwhelmed by the effect that looking back in past means seeing a less-expanded universe.

    Once a standardsize object is out as far as around z = 1.5 it looks the smallest angle that it ever gets. Past that point it actually looks BIGGER the farther away. Subtends a larger and larger angle, the farther away it is.

    the reason is it lives in a universe that was smaller, and our picture of it and its surroundings is necessarily projected all around the 360 degree sphere of the sky.

    there is no preferred direction, like with the point of a cone you imagine. the lightrays come from all directions (from that much older smaller world)
    so its standardsize objects look bigger, anglewise.

    they are dimmer all right. but the dim silhouette occupies more angle.

    that is what corresponds to your idea of looking into the inside of a cone at a diminishing size world.

    the older smaller world is ALL AROUND US. the earlier less expanded universe we can see in every direction
    as if giant shadows were projected on a distant spherical screen----but they are real galaxies not shadows
    ======some technical details in case you want===
    the point might be z = 1.6, I don't remember exactly.
    you can find it by playing with Ned Wright's cosmological calculator
    keep trying different z until you find the "maximum angular size distance" which means the same thing as the z where a standardsize object looks smallest i.e. farthest away.

    just google Ned Wright and you will find the cosmological calculator, the oldest version is the best because simplest to use.

    I googled it for you, here is the basic Ned Wright calculator
    Last edited: Nov 20, 2007
  8. Nov 21, 2007 #7


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    The distended angle of ancient galaxies is a very important point to consider.
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