Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What caused the bang?

  1. Nov 6, 2008 #1
    Hi all

    My question is, what has caused the big bang?

    Could be vacuum fluctuations? or collisions between two other universes, or big creature that caused it ?!!

    Thank you
  2. jcsd
  3. Nov 6, 2008 #2


    User Avatar
    Science Advisor

    Any of the above. There doesn't seem to be any way to test these ideas, so the question of what caused the big bang is purely speculative.
  4. Nov 6, 2008 #3


    User Avatar
    Staff Emeritus
    Science Advisor

    Note that the popular definition of the "Big Bang" is not what professionals think of. The Big Bang theory really only tells us that there was a time when the universe was a lot hotter and denser than it is today.
  5. Nov 7, 2008 #4
    hotter and denser but not smaller? yes the portion that we can see out to the cmb was smaller (verry small) but is that just a subset portion of the universe, a finite portion of all that there is? So is there more matter, galaxies etc. farther away than the CMB 45gl even though we cant see any farther than that, I mean, do the three dimensions stretch out in all directions infinitely even at the moment of beginning? so in the beginning the singularity was one of density and not of size? or is that wrong? or is it known or unknown?

    There is the concept that some infinities are larger or smaller than others for example the infinity of all primes is smaller than the infintiy of all integers because there is not a one to one correspondence so it must be conceptually ok for a universe to be smaller at some point in the past and yet at the same time be infinite and expanding i.e. getting larger?

    Keep in mind, this is just a layman trying to get a grasp of the concept.
  6. Nov 7, 2008 #5


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    That is put very clearly. It is a good question. What you present is one possibility---infinite spatial volume filled with infinite matter.
    An initial state of very high density. This is the version of the standard cosmic model that is most often used for calculation.

    The standard model is LCDM (lambda cold dark matter) and it comes in several versions, most commonly there is the spatially infinite LCDM with overall zero curvature (so-called flat version) and the spatially finite LCDM with slight positive curvature, nearly flat.

    If you look in Ned Wright's cosmology FAQ he says clearly we don't know which is right, all we know is that (finite or infinite) space is really really big.

    The easiest version to calculate with and to fit data to is the flat---spatial infinite---version. But the professionals when they fit their data and make their estimates they recognize they dont know so they put extra columns in the table and allow for various cases.

    it is simpler than that, you don't have to resort to comparing infinities and saying some infinities are larger---that is barking up the wrong tree.

    the fact is that when they say universe expanding they mean a pattern of increasing distances that can take place inside a spatial infinite universe with no defined size, and can also take place in a spatial finite universe which has some definite size.

    We aren't talking sophisticated set-theoretical infinities, we are talking about ordinary spatial volumes, and an infinite volume has no mathematically defined size---so it cannot get larger.

    As cosmologists use the word, expanding does not mean getting larger----it refers to an internal process of things getting farther apart.

    so, in the spatial infinite version LCDM, the thing starts out infinite and stays infinite----meanwhile the density thins out.

    in the spatial finite version, there is a well-defined total volume so it makes sense to speak of the volume increasing, so yes in that case it gets larger-----but so far we don't know the volume so we focus on the density thinning out (which it does just like in the infinite case)
    Last edited: Nov 7, 2008
  7. Nov 7, 2008 #6
    hopefully I'm not qouting too much out of context. I like the phrase of 'decreasing density' it helps aleviate my tendency to think of the 'fabric' of space time stretching.
  8. Nov 11, 2008 #7
    Knowing what caused the bang means to know what was before it, in this case was not the bang the origin of our universe but just a next step part of it.
    Continuing in this way it could be easily demonstrated that the universe exists, in different forms or dimensions, all along.
  9. Nov 11, 2008 #8
    Considering the theoretical work that is being done on the possibility of us humans creating a baby universe in the laboratory. The one option you didn't mention is perhaps a physicist in another universe pressed a button on a high energy particle accelerator and created our universe.? and so on ad infinitum
  10. Nov 11, 2008 #9
    Seemingly more relevant than what caused the big bang is what caused the singularity that the universe originated from to even form...? Hmmmmmmm
  11. Nov 11, 2008 #10
    I am relativly new on this subject. and i am only 14 years mind you.
    The object of the big bang was an atom that was infinitly dense and and very very very tiny.
    For some reason unexplained it was disrupted and expanded. it expanded into what we know to be the known universe. This explosion caused many things to happen. brian greenes theory called the string theory says that if we had a microscope able to look at something smaller than a quark(so far known to be the smallest thing in the universe) you would see a 2 dimentional string that would look like a rubber band. this string is what was released by the big bang. when these different kind of strings connected they formed matter. so they formed into quarks., quarks to atoms, atoms to well everything else. no one is sure about what happened to make this explosion. if you look at the universe as a video. we can rewind it all the way back to the point of 1 second AFTER the big bang. for some odd reason we cant go any farther than that. so what happened between that 1 second. The universe is enough to drive anyone crazy. hell ive only been thinking bout it for 5 days. thats when we turn to religion=]]
  12. Nov 12, 2008 #11
    Two words... Big Crunch
  13. Nov 12, 2008 #12
    hmmm... and I've only been thinking about since I was 6, that was 41 years ago,(yeah I was a strange kid). Back then I had the idea that the whole universe was just a mere speck of dust floating around on a planet in someone else's universe, lol. You would think I would have learned a thing or two in all that time, but then time is just relative to the inertial reference frame of the observer eh?
  14. Nov 12, 2008 #13
    Were free thinkers=]]Did you try to hold your breath to kill yourself when u were a child only to figure out you couldn't do it. i know i did and some others
  15. Nov 13, 2008 #14


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    As a rule, if you make flat statements like this you are expected to provide some evidence. Not just popularized mass-market accounts like Brian Greene books but some scientific journal papers or something equally solid.
    The best way to back things up is with online sources so we can all see where your quotes come from.

    I don't know of any scientific evidence that the universe began as something "very very tiny" and "infinitely dense". Do you have an online source? Maybe you misunderstood something you read.

    In standard cosmology (scientists talking to scientists) the event called Big Bang does not refer to an explosion. That is a popular misconception. I have some links in my sig that it might help you to read. The princeton.edu link is to a Scientific American article dealing with popular misconceptions about the big bang (that's its title!)
    The einstein-online link gives you a fairly up-to-date overview of the current picture in mainstream cosmology.

    I strongly urge you to forget what you have learned from popular mass market stuff and assimilate a bit of what scientists who study the universe actually are saying, and what there is evidence for.

    Quite a lot remains unknown and we have to recognize where issues are unresolved. For instance the size and density of the universe at the start of expansion is not known. There are several different models and an ongoing effort to find ways to test, and exclude and select those that best fit observation.

    It could well be that at the time expansion began the universe was several miles across, or several lightyears across, and not very tiny. It may turn out that it had some finite density, not infinite. We don't as yet know. The expansion may have been preceded by a contracting phase, as some models indicate. Again we don't know. But a lot IS known and more is being learned all the time.

    If you want to understand what's going on in the field you would be well-advised to read the stuff at einstein-online that deals with cosmology. Ned Wright's website is also good, but some of the material is older and not quite as up-to-date. If you want to follow up, google Ned Wright, or look for the einstein-online link in my sig.
  16. Nov 13, 2008 #15


    User Avatar
    Science Advisor
    Gold Member

    'Size' is a misleading term. The universe has always been very large [possibly infinite] from the perspective of any observer who ever existed anywhere in time or space. It was hotter and denser [compared to now] in the past, but that does not make it any more, or less finite. The trouble with being an observer within the universe is it has always and will forever be observationally finite.
  17. Nov 14, 2008 #16
    Hi all, I'm new to this so please be gentle. I am simply a fan of Cosmology and Physics and the like.

    I had a question/theory on the "Big Bang", please feel free to tear it apart since it will just be a learning experience for me...I have no evidence or links to back anything up...

    Anyway...could our universe be the result of a massive black hole? Maybe at the end of our universe there is a black hole that is sucking in another universe or body of mass and spitting it out the other end...thus creating our universe. I'm not positive what happens in a black hole but from what I've read, I assume that everything gets broken down to its smallest part. Maybe that happens and then as everything is spit out the other end of the black hole it continues to gather mass as it travels outward. Not so much of a big bang...but more of a recycling of another universe. And our universe gradually ceases to expand...the further away we get from the "origin".
  18. Nov 14, 2008 #17


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    Certainly that is possible. It is a common idea and quite a lot has been written about it. The interesting thing is how to TEST ideas like that. How to derive predictions from such models that fairly put them at risk if you look for what they predict and don't see it. It's how we judge if a model is likely to be true or not.

    There are basically two versions:
    1. collapse of just part of a prior region, forms a black hole, resulting in a bounce that initiates a new expanding tract of spacetime
    2. collapse of an entire prior region (if you like, a whole universe), forms a big crunch, resulting in a bounce that initiates a new expanding tract of spacetime.

    It's quite clear that #2 is possible in the context of present ideas. A straightforward quantized version of the standard classical cosmo model leads to a standard quantum cosmology that has a bounce, and is so far consistent with all observational data. This interests people, so an increasing number of researchers are working on how to TEST such models. There is a thread listing recent research in that area (looking for quantum cosmology effects that you can check against data expected to come in during the next few years.)

    The bounce in #2 is a robust result. Computer simulations based on quantum cosmology models are run, varying the parameters and trying lots of different cases---they nearly always get a bounce. There are a lot of studies done of this---let me know if you want links to professional journal articles or stuff like that.

    The bounce in #1 is NOT a robust, well-studied thing. It is still not clear how to quantize the black hole. In the professional literature, some quantum black hole models have a bounce, and others do not. Some of those that bounce initiate a queer expanding spacetime which is different from ours---that may even have a lower dimensionality than our 4D world. Just yesterday two new papers came out about this. The quantum theory of black hole collapse is being actively worked on, but it is not as well developed. Again, if you want links, let me know. The quantum black hole research literature is not especially easy to read, I find. But they are moving ahead. Eventually there may be some clearer understanding.

    In a curious way #1 may be testable even if it is not as well understood. That's really topic for a second thread. In that department there is Smolin's popular-written book The Life of the Cosmos, and a bunch of research papers about testing the idea that universes arise from black holes in prior universes. Oddly enough this is testable because it could have an evolutionary effect. If variation occurs, then features favoring reproductive success would be selectively favored. You can see if your local library has a copy of The Life of the Cosmos, or look it up on Amazon. Interesting idea.
    Last edited: Nov 14, 2008
  19. Nov 21, 2008 #18

    Apparently the model of the universe is currently that all matter came from the big bang, no one knows how it happened but it did and now everything is flying out in all directions and everything is getting furthur and furthur away from everything...is that right?

    I don't know but it seems to me that if they guy is blowing into the balloon, and you included in the diagram the lungs of the guy that are being used to expand the balloon, then you would also notice that when the balloon expands the LUNGS CONTRACT.

    Every action has an opposite and equal reaction.

    Could it be that the vacuum has a structure that contracts into infinity just as matter expands into infinity? Creating equalibriam for the dynamics of a scaling structure .........
  20. Nov 22, 2008 #19


    User Avatar
    Science Advisor
    Gold Member

    Probably not. Observational evidence [like WMAP] paints a different picture.
  21. Feb 23, 2009 #20
    So the Stephen Hawking view is now redundant?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook