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Big bang, explain please?

  1. Nov 1, 2014 #1
    hi,

    1. radiation travels faster than matter.
    2. our earth was formed much after the big bang.

    The big bang goes like this. At some point in time and in some point in space (witch we cannot determent so we just leave the location open and say it could have happened anywhere) all the matter in the universe that we see today or don't see :), has been in that single point and for no reason at that point in time it started to spread out very rapidly.

    any radiation that got emitted should determine the expansion rate of that bubble. radiation gets emitted outside of the current matter boundary of the bubble and the pressure expands any lumps of matter or atoms that might have been formed or that were there already. all that radiation would have surely went much faster when any matter expansion. so does it seem logical to you that we still can see an event that preceded our own existence by so much and that we can see it in any direction we look??
     
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  3. Nov 1, 2014 #2

    russ_watters

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    No, not "anywhere", everywhere. Since the Big Bang was the creation of space, every point in space was compressed at least very close together (we can't actually prove it was a single point).
    There is no bubble or boundary. Since the Big Bang happened everywhere and the universe is curved, the early radiation just zips around in all directions in the universe.
    No pressure.
    Yes, it is perfectly logical once you get your arms around the admittedly difficult geometry of a curved 3d space. It isn't something we can actually picture, but we can use 2d or 1d analogues: like the edge of a circle or surface of a sphere. If you are standing on earth, no matter which way you walk, you'll never get off the earth.
     
  4. Nov 1, 2014 #3

    phinds

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    As russ has already pointed out, it is not correct that the big bang happened at a point in space, but you should not feel badly for having believe it because it is probably THE most common misconception in cosmology and it is something you hear on EVERY TV show that shows a "popularized" version of science. You do not read it in physics texts, however.
     
  5. Nov 1, 2014 #4
    ok so no bubble or boundary is supposed to mean that space just suddenly flattened out? from being a point to being something else? or better said just from being very dense to not being so dense anymore?

    please if you don't mid sharing your explanation of the big bang?
     
  6. Nov 1, 2014 #5
    the same goes for this signal bubble of radio and tv transmissions right? there is no way that these signals can go very far into space but I don't know why they persist in almost every tv show that aliens could pic up hitlers speeches or what not :D
     
  7. Nov 1, 2014 #6

    Orodruin

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    What is happening is that space itself is expanding and stretching out - this still happens. You can find more information in our https://www.physicsforums.com/threads/where-did-the-big-bang-happen-would-that-be-the-center-of-the-universe.506991/ [Broken] and on http://en.wikipedia.org/wiki/Big_Bang. If you have specific questions once you have read this and introductory texts on the subject, we will be happy to assist you and straighten out any misconceptions.
     
    Last edited by a moderator: May 7, 2017
  8. Nov 1, 2014 #7

    russ_watters

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    I'm not sure I understand what you mean by "flattened out". It went from being a point to expanding into what we have now (which is still expanding). Have you read any of the analogies people often give? The balloon analogy (we have a thread dedicated to it), the raisin bread analogy? What sources have you read (did you read the wiki article? A Brief History of Time?)?
     
  9. Nov 1, 2014 #8

    russ_watters

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    The geometry of tv and radio signals is very different from the big bang. TV and radio signals do indeed propagate in a finite radius, expanding sphere. However, I'm not sure why you think it is being portrayed wrong in the media. The movie Contact cited Hitler's 1936 Summer Olympics opening ceremony speech being picked-up by aliens near Vega. You should do the math on whether that is valid...
     
  10. Nov 1, 2014 #9
    well a balloon's surface Is flattened out when you blow it up that's what I mean, also the curvature of space-time at the big bang was infinite and then it got less as a result of expansion, or space-time got flatter. I did read all kinds of stuff im just trying to be very simple on the subject, also I forgot to ask in the first post:

    if all galaxies are accelerating from each other more and more as we look further and further out, then why is it necessary that all space has to have been a singularity isn't it more simple to assume that all of that matter came out of a black hole witch is a singularity in a already nice and flat space-time just like the once we encounter today??

    what I meant by that, has nothing to do with the big bang. the guy in the replay said that tv shows explain things wrong about the big bang so I just motioned something else that tv shows do wrong :).
    the bubble of radio signals could never get picked up even at the nearest star it would just become so weak that any massage encoded would be lost and interpreted as noise if even detected. but all tv shows show that it could expand forever and get picked up even in Andromeda hehe :D.
     
  11. Nov 1, 2014 #10

    phinds

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    This continues the misconception that it was a point in space. Is that really what you think it was? If so, why is there no preferred frame of reference with the original point at the center?
     
  12. Nov 1, 2014 #11
    One issue with that is it would mean the matter currently furthest from that source would be moving faster than c, a limitation that expansion of the Universe itself doesn't have. A second is that while black holes may be able to evaporate, matter can't come out of them.
     
  13. Nov 1, 2014 #12
    I don't understand why the first reason would be true, why would it have to move faster than c, but the second one I would rather imagine then imagine that the whole universe popped out of nothing and that it happened out of a singularity.
     
  14. Nov 1, 2014 #13

    russ_watters

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    No, I was referring to the singularity. Where every point in space was laid over top of each other. That's most certainly not a re-statement of the "center of the universe" misconception: It can't be claimed that one point is the center since all points were the center.
     
    Last edited: Nov 1, 2014
  15. Nov 1, 2014 #14

    russ_watters

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    I'm not seeing much difference between those two options.
    That math is a little more difficult, but we can walk you though it as well if you want. Suffice to say, the SETI project would have a pretty fundamental flaw if it weren't capable of picking-up a TV transmission from a few light years away.
     
  16. Nov 1, 2014 #15
    what do you mean, SETI is not supposed to pick up alien tv and radio transmissions but directed and amplified EM signals.
     
  17. Nov 1, 2014 #16

    Nugatory

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    No, the same does not apply to radio and television transmissions. A radio transmission at some point in space will propagate as an expanding sphere in space, just as the ripples from a stone dropped into a pond will propagate as expanding rings.

    The expansion implied by the big bang is something completely different.
     
  18. Nov 2, 2014 #17

    Fredrik

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    If we're talking about solutions to Einstein's equation in which the big bang is an initial singularity, then it doesn't make sense to talk about curvature (or anything else) at the big bang. Every event in spacetime has a time coordinate t>0, and the big bang is the funny things we see when we consider the limit t→0. In particular, for each positive real number M, there's a t>0 such that the curvature at t was greater than M.

    Because our universe is homogenous and isotropic on large scales. If matter was spewed out from any kind of object located somewhere in space, the average density of matter would be higher in regions closer to that object than in regions far away from it.

    The original big bang theory is simply the idea that the large-scale behavior of matter in the universe is approximately described by a solution to Einstein's equation that describes spacetime as sliced up into homogeneous and isotropic 3-dimensional "spacelike hypersurfaces" that can be thought of as representing space at different times. It turns out that all such solutions involve an initial singularity.
     
    Last edited: Nov 2, 2014
  19. Nov 2, 2014 #18

    Chronos

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    TV signals, as in 50,000 watt transmitters, would be overwhelmed by background noise from even our nearest neighbor - alpha centauri. Only directed signals from high power radar stations, or radio telescopes would be intelligible beyond a few light years. It is difficult to comprehend the vastness of interstellar distances - much less intergalactic distances. Assuming ET intelligence is even somewhat rare, how many such civilizations do you think would invest heavily in SETI type projects? As I recall, we have invested less than about 10 seconds in broadcasting realistic strength ET signals over the last 50 years.
     
  20. Nov 2, 2014 #19
    so the only difference for someone living in a universe very close to the big bang singularity and us living in our universe would be the temperature and density of matter and deadly radiation? there is no intrinsic way of saying, oh im in a more curved space than I have to be, other than the one I mentioned?
     
    Last edited by a moderator: Nov 2, 2014
  21. Nov 2, 2014 #20
    yes indeed but can you believe that in every tv show about space they are talking about a radio bubble that could be picked up by aliens, and they do that for about 50 years even today.
    isn't that funny :)
     
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