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Expanding universe, big bang question

  1. Aug 23, 2014 #1
    I've always been curious about about the big bang because (from what I've read) it's a point we're not able predict before. Is there a possibility that our view of an expanding universe just means we can't see beyond the big bang? Or is there a reason that is ruled out and that everything outside of our view is expanding as well?

    On that note, I am also unclear on whether the big bang theory is supposed to be a theory of how our universe started, or how our "known" universe started? I am assuming the latter.
     
  2. jcsd
  3. Aug 23, 2014 #2

    Chronos

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    What universe did you have in mind, other than the one in which we reside?
     
  4. Aug 23, 2014 #3
    Well the universe is everything, the known universe is only what we can see. I hope this clears things up.
     
  5. Aug 24, 2014 #4

    Drakkith

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    We can only make useful predictions of the observable universe, but I see no reason why much of this cannot be applied to the rest of the universe that we can't see. Of course, there are other possibilities, such as our observable universe being different than the rest of the universe for some reason, but since there's no way to ever know for sure I see little point in talking about it.
     
  6. Aug 24, 2014 #5
    I don't understand though, how can it apply to the rest of the universe if we can't see it? Can you explain what you mean by this?
     
  7. Aug 24, 2014 #6

    Drakkith

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    It's the idea that the laws of physics are the same everywhere. As far as we can tell this is true within the observable universe, so it makes sense to apply it to the whole universe. But since we can't see the whole universe, it's possible that the laws of physics are different elsewhere.
     
  8. Aug 25, 2014 #7
    I'm not asking about the laws of physics or if they are different elsewhere. I'm asking about the expanding universe and big bang theory. I think I will have difficulty finding an answer from someone who cannot understand the question being asked. More likely, I think your personal vendetta against me is getting in the way of your forum judgement. It might be time to step down if you can't check your emotions at the door.
     
  9. Aug 25, 2014 #8

    Drakkith

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    I think there's been some sort of misunderstanding here. I attempted to answer your questions, but if I've misunderstood them I apologize. Let's take a look at your original post.

    Let's talk about what "see beyond the big bang" means. The big bang isn't a location in space, it is a point in time, so to "see beyond it" means that we would need to see light that has been traveling since before the big bang. But this isn't possible. The very early universe consisted of high-temperature, high-density plasma that is opaque to EM radiation (light). It wasn't until about 378,000 years after the big bang that something called "recombination" occurred and this plasma was converted into neutrally charged hydrogen and helium, allowing light to finally propagate without being absorbed.

    Since prior to 378,000 years after the big bang the universe was opaque, there is literally nothing to see. There is no light from this point in time in the universe today.

    Because the universe is a finite age, and because light has a finite speed, we can't see beyond a certain radius from Earth, about 46 billion light years. It's important to understand that this is a distance in space, unlike "seeing" the big bang, which is a point in time. Since we can't see beyond 46 billion light years, we can't tell what the universe is like past this distance. So as far as we know, the universe could behave differently past this distance and we wouldn't know about it.

    The big bang theory explains how our universe evolved over time, going from an initial high-temperature high-density state at the time just after the big bang to the low-temperature low-density state that it is in now. It does not explain the ultimate origin of our universe, or explain what was before the big bang, if anything.

    Does that answer your questions? If not, just say so.
     
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