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Big Bang theory

  1. Jun 20, 2007 #1
    I was discussing the Big Bang theory with a friend, but couldn't answer a question he asked. Why is it that people believe that the Big Bang is true? Is there any scientific proof to it?
     
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  3. Jun 20, 2007 #2

    cristo

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    A theory like the big bang theory cannot be "proven," but there is evidence which points towards the big bang theory as being correct.

    1. The Cosmic Microwave Background Radiation-- since the early universe must have been very hot, we expect remnant heat left behind from the big bang. In 1965, this radiation was observed. (I can't remember who discovered it, although I'm sure a google search would tell you, however I do know that it was discovered by accident-- at first the scientists thought it was pigeon crap affecting the observations!)

    2. Edwin Hubble discovered that galaxies were all receding from us (by observing the red shift of the light emitted from these sources). Therefore, in the past the universe would have been smaller. So, we can conjecture that there was a time in the past when it was infinitesimally small-- agreeing with the big bang theory.

    3. The abundance of "light elements" observed is more or less exactly the percentage that the big bang model predicts.
     
    Last edited: Jun 20, 2007
  4. Jun 20, 2007 #3
    Thanks! :smile:
     
  5. Jun 21, 2007 #4

    Chronos

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  6. Jun 21, 2007 #5
    Did you know that the Big Bang was supposed to prove Genesis in Christianity?
     
  7. Jun 21, 2007 #6
    So, what existed before the Big Bang?
     
  8. Jun 21, 2007 #7

    marcus

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    the latest on that question will be in an article written for the journal called *Nature Physics* by a leading quantum-cosmologist, Martin Bojowald. I think this is to appear in the July issue.

    I'll get some references to earlier stuff---work on this question has progressed quite a bit in the past two years, so I would not bother with any sources from before 2005. It is a good question. Have to go now but will check in later.
     
    Last edited: Jun 21, 2007
  9. Jun 21, 2007 #8
    I think that Stephen Hawkings said that before big Bang the universe was very very very very very very very very very very very very very very very very very dense...... all the matter was so closed together and the pressure was probably so great that it could not handle it anymore so Big Bang and then all the matter started to pile up together to make the planets and stars we have today.......
    I think thats what he said... I read the book like 4 years ago..
     
  10. Jun 22, 2007 #9

    marcus

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    I think that part is not controversial Pak,
    the study of these things is part of a fairly young field called Quantum Cosmology.

    (it has origins with work of Hawking back in the 1980s, and other earlier like DeWitt and Wheeler in 1970s----but since 2001 with work of Bojowald it has grown and changed considerably)

    The Oxford University and Elsevier publishing houses have cooperated on making a standard reference work called "Encyclopedia of Science". they got Martin Bojowald to write the article on Quantum Cosmology because he is a top expert on it.

    His QC article for Oxford/Elsevier was in 2005 and is already out of date.

    If you want the latest thinking about pre-Bang, you can't do better than read what Bojowald has written. Unfortunately much of it is technical, uses equations, but at the beginning and end of most technical articles you can find summaries in ordinary non-mathematical English. For starters, Pak, look just at these titles:

    http://arxiv.org/find/grp_physics/1/au:+Bojowald/0/1/0/all/0/1

    these are 78 QC articles by bojo, of which 18 are in the last two years (2006 and 2007)
    In 2006 alone he published 4 of them in Physical Review D, and several more in other top peer-review journals like PRL, CQG, GRG etc.

    To a large extent the game (in Quantum Cosmology) is to develop a model which one can test in the present, by empirical observations, which one can run back in time to probe the past before the big bang.
    Some versions of the model have be implemented in computer, as numerical simulations of the contracting and re-expanding universe. One wants to then study what the model says about conditions before the moment of maximum density and pressure.
    This has become a mainstream research field with some 20 (or more) active researchers working on it.

    The publication rate of new results is high. Another important figure in this field is a theoretical physicist from Bombay, by the name of Abhay Ashtekar. Here are 85 of his professional papers

    http://arxiv.org/find/grp_physics/1/au:+Ashtekar/0/1/0/all/0/1

    in 2006 he got 3 in Physical Review D, plus several more in other top journals like PRL, etc. (I am showing you a quick easy way to estimate activity and mainstream standing, to get an idea who the major figures in a field are. It isn't 100 percent accurate but it can be helpful.)
     
    Last edited: Jun 22, 2007
  11. Jun 22, 2007 #10
    Thanks Marcus I will read those articles... I am new to all this.
     
  12. Jun 22, 2007 #11

    marcus

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    No, Pak baby, noooo!!!!

    don't read all those articles! I just wanted you to glance at the recent TITLES of the articles to get an idea of top-level recent research in Quantum Cosmology.

    It would be too hard to read most of those articles. Only a few are written for the general audience---the interested non-specialist.

    I would like to try to help you find an article by either Bojowald or Ashtekar that is easy to read.
    and which is recent----so it gives an up to date picture of their ideas.
     
    Last edited: Jun 22, 2007
  13. Jun 22, 2007 #12

    marcus

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    I am hoping that in a few days the July issue of NATURE PHYSICS magazine will come out.
    http://www.nature.com/nphys/index.html
    Everybody knows the journal NATURE and it has a specialized auxiliary publication called *Nature Physics*, which has asked Bojowald to contribute an article called "Beyond the Big Bang".

    This could appear as early as the July 2007 issue and will be written for the general educated (non-specialist) audience. It will not be too technical! It will give an up-to-date view. He is the world number one QC expert right now (altho Ashtekar is a close second, I would say).

    Sometimes these articles are FREE to download, although sometimes they are only for subscribers. If it is not free maybe we can still get some exerpts.
     
    Last edited: Jun 22, 2007
  14. Jun 23, 2007 #13
  15. Jun 23, 2007 #14
    But they are very outdated i guess...
     
  16. Jun 23, 2007 #15

    Chronos

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  17. Jun 23, 2007 #16

    malawi_glenn

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    rather the opposite. Before Big Bang was the paradigm of natural science, the "steady state universe" was the ultimate proof against the Genesis in Christianity.
     
  18. Jun 23, 2007 #17

    malawi_glenn

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    i. Will never be possible to prove what existed before big bang empirichaly and scientificly

    ii. All models / theories on what happen before big bang is ad hoc and meta physical.
     
  19. Jun 23, 2007 #18

    marcus

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    I doubt what you say. When we look back at what happened on earth in the past we implicitly use models which we can test in the present.
    We never SEE or TOUCH past events, we always extrapolate back using some model of causality (e.g. the chemistry by which dinosaur bones fossilize). To scientifically infer past conditions and events we have to rely on some model which has proven trustworthy in other contexts.

    Even though inference about the past may not satisfy some naive idea of direct "proof", we habitually make scientific inferences about stuff NOT in our lightcone (the events we are currently getting direct signals from).

    These inferences are NOT normally considered "metaphysical" or "ad hoc". they are part of science.

    If you use a quantum cosmology (QC) model that does not break down at the start of expansion, as classical models do, then the epoch before the big bang is simply an extension of the past.

    The point is that these QC models, which extrapolate back to conditions prior to the start of expansion, are not intrinsically "metaphysics"---they simply need testing. Predictions have to be derived from them about what we CAN observe in our current lightcone----observable features of the microwave background and largescale structure. These predictions then have to be checked.

    Only in this way can the epoch prior to expansion become generally accepted as part of our past.

    AFAIK cosmology divides into two parts. there is CLASSICAL cosmology based on the 1915 theory of spacetime geometry called Gen. Rel. and there is QUANTUM cosmology which began to be developed in the 1970s but did not make much progress until Bojowald's work starting in 2001, and is now entering the mainstream.

    In classical cosmology, the model breaks down at the start of expansion and you cannot run it back any farther in time. so prior to expansion there is no past.

    In quantum cosmology, the newer models (post 2001) do not break down. so there is a pre-expansion past.
     
  20. Jul 12, 2007 #19
    so, sorry, im such a noob, and couldn't find the answer, but basically, along with the theory, what did it all start as, and are we going on the belief that all matter has already been created, so no more is bieng made? thanks
     
  21. Jul 12, 2007 #20

    marcus

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    it isn't known
    I picture mankind as just being at the beginning of a drive to understand the universe---and the big bang models are just a first step

    there are different models.
    some include a prior contracting phase that preceded a kind of bounce
    some include "inflation scenarios" of various kinds involving exotic matter called "inflatons" that no one has ever seen

    they don't make up this stuff for fun, or to impress people, they make it up because they can't think of any simpler way to explain the observational data.

    all we can do is construct models of the past and check them against what they say should be observable in the present. it's hard. none of the models AFAIK is able to answer all the questions. none AFAIK is perfectly consistent and in perfect agreement with the data.

    but they are improving rapidly at this stage---ever since 1998 cosmology has been on a roll largely because of technical improvements in the instrumentation---so stay tuned :smile:
     
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