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Stupid Questions about the big bang

  1. Jun 15, 2012 #1
    I attended a theistic high school and did not receive much of an education on the big bang theory. My question is was there any sort of matter or energy at the start of the big bang, and if so where do scientist hypothesize its origin?
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  3. Jun 15, 2012 #2


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    "big bang" really has two meanings

    (1) t=0 / the singularity / the start of it all --- this meaning of the big bang is most appropriately described as "the place where our theories break down and we have not idea what was going on".

    (2) Everything SINCE the singularity, after one Plank Time. At this point, there was energy in a dense hot plasma beyond our imagination, which expanded (turning into matter along the way) to create the current universe.

    See: www.phinds.com/balloonanalogy
  4. Jun 15, 2012 #3
    Is there anyplace i could read about what is known (or hypothesized) about the singularity?
  5. Jun 15, 2012 #4


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  6. Jun 15, 2012 #5
    Thank you Marcus, that was quite interesting. And would I be correct if I concluded between t=0 and the inflation phase scientist are unsure of what was going on?
  7. Jun 15, 2012 #6

    yes, that's pretty close depending on what you mean.....call it 10-32 seconds after the bang [approximate]

    Wikipedia does a good job explaning here:


    I'm reading Alan Guth's book about inflation right now [he is generally credited with the inflationary hypothesis] ,,,..maybe I'll learn more!!!
  8. Jun 15, 2012 #7
    Apparently the inflationary period lasted from about 10-36 sec to about 10-32seconds after the bang....so I'd said we can go back to the beginning of that.

    PS: what's a "theistic high school "....
  9. Jun 15, 2012 #8


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    Grant, you can save yourself some confusion down the road if you start off right. I don't know that most cosmologists working today think of singularities as real occurrences in nature. Technically speaking, an S. is a feature of a particular model. In cosmology some mathematical models break down and fail to give meaningful numbers right near or at the start of expansion. Other models (sometimes called nonsingular models) continue on back in time and describe conditions BEFORE the start of expansion.

    A singularity is a failure, breakdown, blow-up of a particular man-made mathematical model. Whether you see a singularity (say at the start of expansion) will in general depend on which model you are using.

    The word comes from the use of the word "singular" to describe something or somebody who is odd, weird, eccentric, peculiar. "What a singular occurrence!" or "What a singular fellow that Mr. Toad is!" So singularity means weirdness that you don't know what to make of. Mathematical singularities happen, for example, when a formula accidentally divides by zero and blows up, giving no meaningful result. A better word might be "glitch".

    Historically when singularities appear in physics formulas they eventually get cured by fixing or replacing the formula, or the equation model. That is what is currently happening in cosmology. Some of the models currently being developed and studied do indeed go back before the start of expansion, or in other words back before what used to be called
    "the Big Bang singularity".

    I can't give you a good short answer to your initial question. But one thing you could do is watch (with me and probably others of us) what the lineup of talks are going to be at next months MG13. I will get a link. Have to go out now. Back later
  10. Jun 15, 2012 #9
    It was a christian high school so we did not learn anything about the big bang theory.
  11. Jun 15, 2012 #10


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    but that's fine. In an ordinary high they wouldn't learn much of anything either (at least anything up-to-date) about models of the start of expansion. This is all work in progress. And in science nothing is certain, it is only the best most reliable that the best people can do for the time being. Models eventually get refined corrected improved and/or replaced, as a rule, after a while. Understanding evolves.

    I have to go out but still have a moment. I will get some links to some of the sessions at a big international conference that is coming up. These links go to the session-leader who is supposed to post a list of the talks, but so far they mostly just give brief descriptions of what the session is going to be about. This may not mean much for starters but I'll try to explain more later. Here are the links
    Some of the chairmen have so many people coming to give talks that they have been assigned two 4-hour sessions, on separate days.

    Parallel Session: QG1a and QG1b - Loop Quantum Gravity, Quantum Geometry, Spin Foams

    Parallel Session: QG3 - Asymptotic Safeness and Symmetry Breaking in Quantum Gravity

    Parallel Session: CM4 - Quantum Cosmology and Quantum Effects in the Early Universe

    Parallel Session: QG4a and QG4b - Loop quantum gravity: cosmology and black holes

    Parallel Session: CM3 - Nonsingular Cosmology

    Parallel Session: QG2a and QG2b - Quantum Gravity Phenomenology

    These all have to do with non-singular models and with testing by observation (phenomenology) of such models, but only one of them is TITLED "nonsingular". You could click on that one and see the chairman's general description.
    A lot of these models are bounce models where expansion is preceded by a contraction.
    http://www.icra.it/mg/mg13/parallel_data_grid_2012_06_14.pdf [Broken]
    Last edited by a moderator: May 6, 2017
  12. Jun 15, 2012 #11
    "It was a christian high school so we did not learn anything about the big bang theory."

    Maybe you should tell your teachers that the big bang theory was first proposed by a christian priest (http://en.wikipedia.org/wiki/Georges_Lemaître). This was actually a huge obstacle to the scientific acceptance of the theory. Many scientists believed the big bang theory was an attempt to bring religion into science. Pope Benedict also welcomed the big bang theory (http://www.reuters.com/article/2011/01/06/us-pope-bigbang-idUSTRE7052OC20110106).
  13. Jun 15, 2012 #12
    With regard to your question about energy:

    It seems more and more likely from observations (such as WMAP) that the universe is flat - that is, it has no overall curvature. This leads to the possibility that the universe has zero total energy - the energy of matter is counterbalanced by its negative gravitational potential energy.
  14. Jun 15, 2012 #13
    The link listed by Marcus in post #4 has this to say in part:

    “At this moment, all the galaxies that we see around us today were compressed into a region of zero volume - to a single point in space.”

    If the OP does not mind, I have my own stupid question. Often on this forum various posters say the big bang “happened everywhere.” At other times it is described as in the above quote…happening at a single point. Is this a contradiction or am I missing something?
  15. Jun 15, 2012 #14
    No, it isn't a contradiction - it means that the universe itself was zero size. Not just the matter in it, but space itself. To understand what that means, imagine the universe was one lightyear in size. This would mean that travelling one light year from your position in any direction would return to your starting position. This is similar to the surface of the earth, or like an old arcade game where you go off of one side and return to the other.

    Now, the universe could be infinite - so it has always been infinite size.

    The purpose of saying the universe was zero volume at the big bang is to highlight the fact the everything in the universe would be zero distance away from everything else - even in an infinite universe. This demonstrates the fact that treating the big bang purely with general relativity leads to this 'singularity', and that we need quantum gravity to treat the situation. Loop quantum cosmology and string cosmology both attempt to resolve the singularity this way.
  16. Jun 15, 2012 #15


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    I checked and it does NOT imply that actually was the case. You missed the qualification. What he is explaining is what is wrong with GR and why people are working on improving it.

    If we simply follow the predictions of Einstein's theory of general relativity for the evolution of a simple expanding, homogeneous universe filled with matter and radiation, then our journey into the past will eventually come to an end - a point in time where we cannot go back any further. At this moment, all the galaxies that we see around us today were compressed into a region of zero volume - to a single point in space. Since density is defined as mass divided by volume, the density was infinite. In Einstein's theory, matter influences the way that the geometry of space and time is distorted, and at this moment of infinite matter density, the curvature of spacetime was infinite, as well. Within the simple cosmological models based on general relativity, there is no possibility to go to any earlier times than this. Such a boundary of time (or, more generally, of spacetime) is called a singularity...​

    You missed the "If we simply follow..." Do you see Chiclayo?

    Farther down the page, he says:
    Most cosmologists would be very surprised if it turned out that our universe really did have an infinitely dense, infinitely hot, infinitely curved beginning. Commonly, the fact that a model predicts infinite values for some physical quantity indicates that the model is too simple and fails to include some crucial aspect of the real world. In fact, we already know what the usual cosmological models fail to include: At ultra-high densities, with the whole of the observable universe squeezed into a volume much smaller than that of an atom, we would expect quantum effects to become crucially important... ​

    In other words Einstein's original 1915 predicts infinite density, so it is probably too simple and fails because it overlooks something, namely the quantum effects that kick in at very high density. Indeed when you move to a quantum version of GR it seems likely that at very high density quantum effects cause gravity to repel. A collapsing region would be unable to get down to a volumeless point, and would rebound. Infinite density does not happen IOW.

    The universe may be spatially finite or infinite (we don't yet know which and may perhaps never) but in either case what we can see occupies a finite volume which, if you could stop expansion to give yourself a chance to measure, would have radius 45 to 46 billion LY. The expansion ratio is estimated to have been such that this volume would have begun very small---nearly zero volume.

    According to the standard cosmic model space is boundaryless, edgeless, there is no space outside of space. And this has always been the case.
    This leads to the simplest best fit math model that we have so far. Any geometric properties (like curvature) and any geometric processes can only be experienced from INSIDE. By noticing that triangles don't add to 180 degrees or that distances between stationary objects increase according to some largescale average pattern. There is no "outside" space that space "expands into", and no "center" of expansion that we can point to. It turns out to be mathematically clean and convenient to model that way, the fewest extra assumptions. After all we have no evidence of a boundary or edge or center, so including them would just mess things up needlessly.

    As far as we know whenever and however expansion began it began at every point in space.
    There is no evidence that it began at different points at different times. (Although some people IMAGINE that may have happened, just too far away for us to know about.) So the simplest cleanest assumption is that expansion began at all points at once. That's built into the model, which has a kind of uniformity assumption. ("homogeneity")

    the proof of the pudding is in the eating. The simple model (called LCDM) gives a remarkably good fit to the data! So there is a strong motive to not mess things up by adding extra features.
    Last edited: Jun 15, 2012
  17. Jun 15, 2012 #16
    I see that I did read it out of context. Thanks Marcus
  18. Jun 16, 2012 #17
    No one really knows anything about the instant that the BB started. When you hear things like "X amount of time after the BB the universe was the size of a grapefruit" What they really mean is that all the matter in out observable universe was compressed into a volume the size of a grapefruit. There is more out there beyond our observable universe. In fact the universe may be infinite. It would be more accurate to say "X amount of time after the big bang the universe was filled with a very dense soup of matter and energy which extended indefinitely throughout all of space. As space expanded, a spherical volume of this soup the size of a grapefruit expanded into a spherical volume 43 Gly in radius. That is as far as we can see so we call this volume the observable universe."
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