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*Big Bang*

  1. Feb 10, 2008 #1
    Hey guys and girls,

    I have few questions regarding the-famous Big Bang.

    - From where do the particles come from that originated the Big Bang...?

    - This may be one of the-most-asked question, but how is it possible to say that our universe is expanding? And into what? For example, for matter to expand, it must have a certain space to expand into, right?

    Also, why do most scientist think of the existence of dark matter and dark energy? Could be that there might be some errors in few theories or models? Beside, if that matter was to exist and if it does represent the majority of our universe, would'n't that mean that it is even present in our own solar system, then how come we 'cant' detect/see it?

    o.0 hmmmmmmmmm.......
  2. jcsd
  3. Feb 10, 2008 #2
    Also, is it fair to say that space itself is not expanding, but simply galaxies are getting farther from each other due to unknown reasons(or,possibly because of dark matter/energy)? In this case, there suppose to be a certain limit to where they expand...
  4. Feb 10, 2008 #3


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    questions like this are normally posted in the Cosmology forum. there are several different models under study that involve conditions before and during the beginning of expansion. If one goes by what research has the most peer-reviewed publication and is most widely cited, then the most prominent approach to understanding the Big Bang has it preceded by a contracting universe phase.

    A prior stage of the universe collapses, reaches a critical density at which gravity becomes becomes repellent due to quantum effects, and begins re-expanding rapidly.

    The equations that describe gravity allow spacetime to be curved, which means that distances need not be static. Distances between otherwise stationary objects can decrease or increase. this is what is meant by "space contracting" or "space expanding".
    Space is not imagined to be a material that actually expands and contracts----it is simply that distances between things can change dynamically in a systematic way described by the main equation of GR.

    Our universe can expand without having a surrounding space to expand into. All that expansion means is that distances between things increase. You should try not to think of our space as a material---the analogy will confuse you. Indeed for matter to expand it must have a surrounding space. But distances within our space can increase without the surrounding presence of any larger space.

    Last edited: Feb 10, 2008
  5. Feb 10, 2008 #4
    ...? o.0
  6. Feb 10, 2008 #5
    Um, arent you simply repeating my post, Marcus? o.0

    Or, are you pointing something =.= ...?
  7. Feb 10, 2008 #6
    And since we're stacking up Big Bang questions here: It is frequently said that a common misunderstanding is that the Big Bang was like an explosion throwning mass away from a central point. Is a corollary to that that near the point of the Big Bang, say when everything was still the density of plasma, the universe may already have extended infinitely in every direction?
  8. Feb 10, 2008 #7
    The Big Bang theory states that there was a certain point where there was a huge pressure(or density?,right?) between particles that it simply 'exploded'. Matter couldn't have originated out of no where and appeared into that particular center where matters simply collided with each other, right?
    Last edited: Feb 10, 2008
  9. Feb 10, 2008 #8


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    Big Bang theory does not state that matter exploded into surrounding empty space
  10. Feb 10, 2008 #9
    Aside space, from where did those matters originate? I beleive theres not really an explanation to that, right?
  11. Feb 10, 2008 #10
    If your question is really “What was there before the Big Bang?” I think the answer is “science does not have any way of knowing or even guessing at this point.”

    My understanding is that the universe probably extended infinitely in all directions even at the point of the Big Bang. Or at least that modern Cosmology is compatible with that. I'd love to get some confirmation on that if anyone knows...
  12. Feb 10, 2008 #11
    I've read somewhere that scientist found black holes aged about 13 billion years. Wouldn't that mean black holes are formed much rapidly then we expect? And, eventually, will they even take over the universe, thus the end? In this case, if there was to be many black holes, there would likely be an emergence betweent them, or between many of them. What would happen in this case?
  13. Feb 10, 2008 #12
    And is it even possible for two black wholes to collide? I think it would be the same scenarios as with galaxies collision, right?
  14. Feb 10, 2008 #13


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    Not right.
    There are several very interesting explanations which people are studying now.
    One of the outstanding research questions is how to check the models to see which is most likely to be correct.

    In none of these models does matter suddenly come into existence right at the moment called the "big bang"-----there is in each case always some kind of space and some kind of matter BEFORE that moment.

    The researchers who study this use both computer modeling and analytical modeling with equations. The simplest models have the space and matter before the bounce be a contracting version of the familiar kind of space and matter that we know about.

    According to widely studied quantum theory of gravity, gravity changes from attraction to repulsion when a critical density is reached, so there can be a rebound---which starts a new expanding phase.

    There are other expanations, but this is probably the simplest and the most widely cited in recent (post 2002) research literature.
  15. Feb 10, 2008 #14
    Hmm, let's say the universe was to face The Big Crunch, that would mean that eventually the Big Bang would begin again right? If so, is it fair to say that the current universe may have originated from a Big Crunch in the past. That would mean that the universe always existed, is existing and will exist?
  16. Feb 10, 2008 #15
    Also, since dark matter/energy really make most of the universe, did they play significant role in Big Bang? Or, was it some new matter originated by somehow to maintain a certain balance in our universe?
  17. Feb 10, 2008 #16
    Here it goes....*bump*..... :D
  18. Feb 10, 2008 #17


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    that is certainly one of the possibilities being actively worked on. It makes a lot of sense once you have a quantized cosmology model. but these ideas are not yet tested. one has to find things that the bounce models predict that we can look for and either observe or not. that's also something people are working on and write papers about: how to test

    strictly speaking all it would mean is that time didn't begin at the start of expansion ("big bang") but goes back further.

    sure it could go back indefinitely. that's possible. but that is not the issue right now. right now the aim is to understand conditions better at the start of expansion.

    if you want to read some research articles. let me know. I'm busy today and don't have enough time to paraphrase for you what you could read directly from an article by Abhay Ashtekar
  19. Feb 10, 2008 #18
    Thank You for your reply! I am certainly interested in reading some articles regarding basic cosmology, if possible, I would also like to read articles regarding planetary movements( angular momentum) and other few basic astronomy books. Sorry if I am asking for lots of stuff!

    Thanks a bunch!
  20. Feb 10, 2008 #19


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    What you may be thinking of are primordial black holes. These are black holes which are not formed in the "usual" way (that is, they are not formed by a collapse of a star) but are formed in the extreme conditions of the early universe. They are entirely theoretical objects and thus may not exist. In fact, if they do exist, I think they should be starting to evaporate now, and so we should be able to detect their radiation pretty soon.
    I know nothing about astronomy, but a nice place to start reading some introductory cosmology would be Ned Wright's cosmology tutorial, available on the web:http://www.astro.ucla.edu/~wright/cosmolog.htm.
  21. Feb 10, 2008 #20
    Thanks cristo.
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