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The big bang

  1. Jan 4, 2010 #1
    If there is room for space to expand, hasn't the space already expanded?
  2. jcsd
  3. Jan 4, 2010 #2
    Why is a legitimate, testable, and falsifiable theory like the Big Bang being placed in the skepticism section? I was under the impression that this is the forum for debunking pseudoscience.

    Anyway, to answer the question, I think the fallacy here might be in talking about the "room" for the space to expand. The universe isn't expanding into anything. Rather, the distance between any two point in space is what is expanding. The balloon analogy is helpful here. If the universe were the surface of a balloon, then filling it with air would increase the distance between two points on the balloon. But you're not adding more rubber to the balloon. Now, this analogy (like all analogies) breaks down since balloons exist in a larger-dimensional space, but you get the idea.
  4. Jan 5, 2010 #3
    Well we're here aren't we?
  5. Jan 5, 2010 #4


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    The big bang theory is a proper scientific theory, and it makes certain predictions.

    Some of those predictions are testable now, and others will be testable when we have better technology. :wink:
  6. Jan 5, 2010 #5
    As much as the 'skeptics' (read anti science people) would like the peons to think, we don't acutally have to directly see something to know it's there. To test the big bang, we don't need a mini expanding universe in the lab to look at. The model creates predictions and explains many discoveries made about the universe.

    You don't have to observe the entire thing to build a picture of it. The testability comes from performing experiemnts that test an area of the model.

    So CMBR, redshift. These are all indicators of an expanding universe, which effectively killed off the steady state model.

    It's not only the cosmological scale (the very large) we look at to explain the big bang model. We also look at the very small, particle physics helps us to understand what happened st the birth of the universe. The BB predicts a very hot very dense start to the universe, where even the 4 fundamantal interactions were not seperate.

    So the LHC, testing for particles and phenomena that would occur during a hot start.

    Ultimately we may found out that a 'big bang' model is incomplete/incorrect. But for the moment it is by far the best explination we have for how to universe came to be in it's current state.
  7. Jan 5, 2010 #6
    But being that a medium is not required in order for an object to move, if one were to be at the edge of the universe and were to throw a baseball towards the part of the universe that hadn't expanded yet, the ball certainly would not run into a wall. I know this is not possible being the universe expands at the speed of light, but rather its a theoretical question. If nothing needs to be there in order for an object to move about, then that object wouldn't need to wait for space to expand in order to move through it.
  8. Jan 5, 2010 #7
    Spacetime doesn't expand like this. There is ho hard edge to space in 3D. You could pick any direction you wanted, and arrive back where you started. In 3D terms there is no centre nor an edge of the universe, we can see the same distance in all directions.

    The baloon example can be used again.
    An ant walking on a balloon may never reach the 'edge' or 'centre' as it lives on a 2D surface expanding in a 3rd dimension.

    This is not the expansion of something within space, its expansion of space itsself.
    So forexample if we cuold move fast enough and set off in 1 direction from the earth, we would travel a certain distance before coming back to earth. If we did the same trip again we would have to travel further becuase space time had expanded.
    Last edited: Jan 5, 2010
  9. Jan 5, 2010 #8
    I see where my lapse in visualization was, the universe is not 3d, you explained that quite well.
  10. Jan 6, 2010 #9
    Again you failed to understand what the expansion of the universe actually means. Please go read up on the subject and then come back and ask the question again.
  11. Jan 6, 2010 #10
    This is absolutely correct. If the Universe is indeed finite and unbounded, what that would mean is that no matter what direction you travel in (any direction) you will eventually come back around the other side. In such a model, it is impossible for the Universe to have a center or an edge. Now how can such a Universe expand you ask? Well that's actually pretty easy to imagine. Suppose for the sake of argument, that the distance it takes to loop back around (from any direction) is 100 light years. Let's say some time later it takes 101 light years to come around from the other side (from any direction), space has expanded. The distance it takes to come back around the other side is expanding It's as if there's more space being added to our Universe. Now can you see that space is not expanding into anything, it's just um...expanding?
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