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Looking for some help understanding the Big Bang.

  1. Apr 21, 2013 #1
    Hello, as the title states I'm looking for some help understanding some things about the Big Bang that I'm sure the people here would know. I apologise if this is posted in the wrong section -- I wasn't quite sure where to make it.

    It's said that the Universe, immediately after the big bang, was incredibly hot and began to expand rapidly. What temperature was it, immediately after the big bang? And, how was such a thing calculated? How fast did it begin expanding, and how was that calculated also?

    I guess, I'm generally asking for anything to read or watch that could really extend my knowledge of the Big Bang. I definitely welcome as many maths calculations and equations as possible. :smile: Anything would help, really. Thank you.
  2. jcsd
  3. Apr 21, 2013 #2


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    The temperature decreases rapidly after the big bang, so of course it depends on how long "immediately" is. http://www.astro.ucla.edu/~wright/BBhistory.html gives the figure 10^32 at the time 10^-43 seconds, which is about as soon after the big bang as I can fathom. The universe cools adiabatically as it expands, so we can estimate what the temperature was in the past if we know what the scale of the universe was compared to today's scale. We need to know the adiabatic index, which was about 4/3 in the radiation-dominated early universe. We can make a rough estimate of the scale by projecting the Hubble constant backward. The big bang is at the time when the scale goes to zero. For a more accurate result, we also need to factor in gravity and dark energy. Unfortunately, inflation complicates things and we really don't know too many details about inflation, and it's still somewhat speculative in my opinion. Certain assumptions have to be made.
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