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How the Big Bang heated?

  1. Apr 15, 2006 #1
    I'm having trouble here, will you help me out? They estimate the heat of the Universe at 1000 trillion degrees Celsius in a picosecond, nanosecond (or other fraction of a second). What body was hotter before that second to heat the universe to that degree? Or am I looking at that the wrong way? :confused:
     
  2. jcsd
  3. Apr 21, 2006 #2
    Your question is probably the biggest question in the Universe, so no one can answer it. I'd offer a possibility that precluding the BB and Inflationary epoch, there was a big crunch from out prior Universe's collapse and this condensation produced a 'singularity' that then exploded as our BB. This is wildly speculative, but at least somewhat plausible, if not provable.
     
  4. Apr 21, 2006 #3
    Annoying thing in that is that it implies that there has never been a true beginning. Not impossible, just very annoying for science.
     
  5. Apr 22, 2006 #4

    Chronos

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    The big bang did not heat, it unheated. It started impossibly hot [re: the Planck temperature] and has cooled down ever since. The question you are asking is behind the Planck wall [prior to 10-43 seconds], which is implicitly impossible to answer by physics as we know it. I agree, this is an unsatisfactory answer, from a scientific perspective, but it is the best we can do for the time being.
     
  6. Apr 25, 2006 #5
    would this suggest that the universe is still cooling off and will continue cooling forever until the collapse(if there is one)?
     
  7. Apr 25, 2006 #6

    SpaceTiger

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    Yes, on average, the universe will continue to cool as long as it expands. This is true of both the radiation and the matter.
     
  8. Apr 25, 2006 #7

    That's right, the Universe is cooling off as we speak. This is because the Universe is expanding (accelerating) outwards. This 'may' lead to a collapse eventually but that is speculative territory. At present we see an accelerating Universe that is driven by an unknown force we call 'dark energy' for lack of a better term. If this dark energy ever got depleted, gravitational collapse would be very likely. This collapse would then reheat the Universe as it got smaller and smaller. There is no reason to believe that the Universe will ever stop cooling, so make sure you have a nice toasty parka in the future or you will freeze.
     
  9. Apr 27, 2006 #8
    Me, personally, I cannot accept "nothing" before the BB. Thank you for these answers. Was "Space" there?
     
  10. Apr 27, 2006 #9
    I agree batboy, i find the bigbang-bigcrunch theory appealing for this reason. Of course, then the question becomes 'how was the cycle created?'
     
  11. Apr 30, 2006 #10
    This makes sense if we understand that heat occurs when moving atomic particles, such as electrons, collide with one another. If the density of the universe is decreasing, then there is less likelihood of collisions occurring, thus less heat.
     
  12. Apr 30, 2006 #11

    SpaceTiger

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    A system that didn't self-interact at all wouldn't cool at all, since it needs some means of releasing energy. The matter in the universe cools because more and more of its energy gets converted into radiation (by interactions) and, as the universe expands, that radiation has a decreasing probability of interacting with the matter and giving the energy back. In addition, the radiation itself is redshifting and getting less energetic as the universe expands, leading to a net cooling effect on the radiation field as well.
     
  13. Apr 30, 2006 #12
  14. May 1, 2006 #13

    hellfire

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    I don't understand this. Ideal gases, that do not have interactions and undergo elastic collisions, do actually cool when they adiabatically expand. For non-relativistic ideal gases the temperature goes as T ~ 1/a and for relativistic idea gases as T ~ 1/a2.
     
  15. May 1, 2006 #14

    SpaceTiger

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    Wouldn't that be for a gas with pressure (i.e. self-interacting)? The matter component of the universe (most of it, at least) is undergoing an essentially pressureless expansion at the current epoch, so I would think there would be no change in temperature without some form of interaction. Just by conservation of energy, free-streaming non-relativistic particles ought to retain their temperature.
     
  16. May 1, 2006 #15

    hellfire

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    Why does pressure follow from self-interaction? For example, a gas of photons does not self-interact but has pressure. Am I wrong?

    On the other hand I agree that something that is pressureless does not decrease its temperature during adiabatic expansion.
     
  17. May 1, 2006 #16
    Pressure does not require self-interaction,but there is a difference between an 'ideal gas expanding' and the universe expanding.An ideal gas expanding adiabatically does work against the walls of a container(say),loses internal energy and cools down(1st law).What does the expanding universe work against?At best it can work against its own self interactions--the universe is a non-ideal gas.
     
  18. May 1, 2006 #17

    SpaceTiger

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    I was under the impression that an ideal gas cannot be made up entirely of particles that don't self-interact (like photons) -- they'd just free-stream away. When coupled to baryonic matter, photons can be part of an ideal gas, but I would say that constitutes self-interaction of the gas particles.
     
  19. May 1, 2006 #18

    hellfire

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    Thank you for your replies. gptejms' post clarified the point.
     
  20. May 1, 2006 #19

    marcus

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    I agree with the spirit of this post. the "planck wall" someone referred to cannot be shown to be anything but a creation of our minds, and an artifact of what model we happen to be using.

    Any time anybody extrapolates backwards, they use a model.

    If you use vintage 1915 pre-quantum Gen Rel, then you get a singularity----conditions that physics can't handle.

    If you use vintage 2001 quantum cosmology, you do not get a singularity. the model keeps on running deterministically in reverse back PAST where the (classical or pre-quantum) singularity was supposed to be

    And the quantum cosmology models make predictions that CAN and eventually will BE TESTED so epistemologically we are talking the same ballgame as usual. We know the past by using a model which makes predictions and we can test, and chose to believe it or not based on the tests-----just as with an earlier generations Big Bang ideas.

    so the time prior to the former (pre-quantum) singularity is not in principle any more unknowable to us than the time right after the former singularity.

    The main issue is whether or not a person is willing to read standard up-to-date reference works like the encyclopedia.

    If you are willing to read a science encyclopedia say put out by a major science publishing house like Elsevier, then I can get a link to the article on Quantum Cosmology and you can see what the state of knowledge is at present.

    http://arxiv.org/abs/gr-qc/0603110

    This is from Volume 4, page 153 of the Elsevier Encyclopedia of Mathematical Physics

    The picture is in flux and certainly is not settled. As Chaos Bro indicated there are no definite answers as yet. In fact Quantum Cosmology has not yet made pre-quantum cosmology (based on the 1915 theory) obsolete! there are still lots of professionals doing the old kind! But the trend is for Quantum to put Classical out of business in domains where Classical doesnt work very well, like at former singularities :smile: So even though the details of the story are unsettled one can at least say that the conditions prior to expansion are NOT IN PRINCIPLE OUTSIDE OUR KEN
     
    Last edited: May 1, 2006
  21. May 1, 2006 #20

    marcus

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    You might want to check out references [2] and [3] of the encyclopedia article I mentioned

    [2] Bojowald M (2005) Loop Quantum Cosmology. Living Reviews in Relativity 8, 11.
    [ http://arxiv.org/gr-qc/0601085 ]

    [3] Bojowald M (2001) Absence of a Singularity in Loop Quantum Cosmology. Phys. Rev. Lett. 86, 5227–5230.
    [ http://arxiv.org/gr-qc/0102069 ].

    Planck temperature is about 1032 Kelvin if I remember right.
    In the quantum bounce that replaces the bang singularity, the temperature pressure and density do not go off the chart.

    Inflation occurs naturally, without having to make extra assumptions---it is generic in a range of quantum cosmology models.
    The article in LIVING REVIEWS IN RELATIVITY discusses that IIRC and should give references. It is actually probably more informative than the article in the Ensevelier encyclopedia
     
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