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Any solid theories re: where it all came from?

  1. Jun 30, 2015 #1
    As I understand it, the BB says the universe came from a tiny ball of stuff.

    Is it correct that no one has an explanation as to where the ball of stuff came from? Is it also correct that the BB is still speculation and subject to revision, even potentially discarding altogether?
     
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  3. Jun 30, 2015 #2

    jfizzix

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    All scientific theories are subject to revision, and possible discarding when new data comes in.

    That being said, there are very good reasons that the big bang theory is as popular as it is.

    Namely:
    - It makes sense of why galaxies further away are moving faster away from us than galaxies closer by
    - It makes sense of why at large distance scales galaxy clusters are scattered more or less uniformly
    - It makes sense of the cosmic microwave background radiation seen in all directions in space

    There are even widely speculative ideas about where that ball of stuff came from.
    One is that the big bang is a big bounce, and the universe endlessly oscillates from big bang to big crunch, and back again
    We may never know, but as we get better data from better space telescopes, we can get better at guessing at these theories too.
     
  4. Jun 30, 2015 #3

    e.bar.goum

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    It's important to note that the big bang theory tells us what happens after the time at which the universe was 10−43 seconds old (the planck epoch). It's silent as to what happens before that time.

    The big bang theory is one of the most successful physical theories to date, some of the reasons jfizzix outlined. It is unlikely it will be thrown out, so much as modified in the future. It is certainly not speculation, no more than any other well grounded physical theory.

    ETA: See https://en.wikipedia.org/wiki/Big_Bang#Observational_evidence
     
  5. Jul 1, 2015 #4

    bapowell

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    The "big bang theory" is a model that describes how the universe evolved from an early, hot, dense state to the present. Measurements of the Hubble expansion, the presence of the cosmic microwave background, and the abundances of the light element are in agreement with a smoothly expanding universe and lend strong support the big bang model. But scientific theories are always open to revision; they are never certain.

    There are many things that the "big bang theory" does not explain. It does not describe the origin of the universe. It does not fix its geometry, or explain where matter came from, or why there is more matter than antimatter. Some of these facts are purely empirical at present, and some depend on inputs from other fields, like particle physics.
     
  6. Jul 2, 2015 #5
    But still highly speculative, correct?
     
  7. Jul 2, 2015 #6

    e.bar.goum

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    The phrase "one of the most successful physical theories" by definition precludes it being called "highly speculative". So no, not correct.

    Perhaps we are using different definitions of "successful physical theory" or "speculative". Concordance (∧CDM) cosmology very well reproduces the universe that we see, and as such, is well grounded - not speculative. There are speculative (not tested or not supported by the evidence) extensions to the concordance cosmology, but the plain old vanilla model of the big bang does very well. There are details that require ironing out (see bapowells post), but those details are unlikely to involve an entirely new cosmology.
     
  8. Jul 2, 2015 #7
    You would bet your life and the life of your most cherished loved ones that no new revelations will ever come to light to alter thinking on it?

    "There are details that require ironing out" sounds like there's speculation involved.
     
  9. Jul 2, 2015 #8

    e.bar.goum

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    I'm not sure you understand how physics works. There's a long way between (for example) "the abundance of 7Li produced during BBN is twice as much as we expect" and "we need to throw away the concept of a hot big-bang". Of course physical theories alter over time, but that doesn't mean that theories that have a wealth of supporting evidence get thrown out - they evolve. Newtons laws aren't "wrong" -- they're just "approximate". If you look at the link I posted earlier, you can see some of the wealth of evidence for a hot big-bang.

    There have been a lot of studies looking for alternates to a hot-big bang model. None of which have the same support of observation evidence behind them. Otherwise we would have changed the model.

    Look - the most successful physical theories of all time are General Relativity and QED (QED people would argue QED is the most successful, GR people the opposite, but either way, they're tremendously accurate). You can use either to make predictions to many many significant figures, and they match experiment. We know that they're incomplete - QED and GR are mutually exclusive, but we know there are places in the universe they need to work together. Therefore, QED and GR need to evolve. That doesn't make either theory "speculative" or "wrong" - it makes them incomplete. But in almost every experiment you can do, they look pretty much perfect, so any new model must make pretty much the same predictions on lab scales as GR and QED do.

    The same goes for the big bang. Any new model must look "pretty much like" a hot big-bang, because it must reproduce the results of observations, all of which look like a hot big-bang.

    See also: this xkcd, and this:
    Planck_power_spectrum_625.jpg
    From the 2013 Planck data release. The data points are measurements, the line is the accepted Big Bang model. Pretty good, huh?
     
  10. Jul 2, 2015 #9

    Drakkith

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    There are details that require ironing out out involving our theories describing how supernovas explode, but I'd bet my life that a supernova is an exploding star. Just because a theory doesn't perfectly predict everything does not mean that it is incorrect. Our observations lead us to believe that a supernova is an exploding star. Similarly, our observations lead us to believe that the big bang theory correctly describes the universe. If the big bang theory, as it currently stands, is so wrong that even its broadest statements and predictions are incorrect, then the universe is a very, very strange place and any new theory would be far stranger and more unacceptable to many people than the big bang theory already is.
     
  11. Jul 2, 2015 #10
    Al lot of the answers to your questions depends on how you define terms like "universe" and "big bang". these terms can have varying definitions and so you can get different answers depending upon which definition you use.

    Question: Was the universe a tiny ball?

    Firstly lets look at the word "universe" sometimes people use this in the sense of "observable universe" about 93 billio light years in diameter.
    https://en.wikipedia.org/wiki/Observable_universe
    However other times people use the word "universe" as everything that exists including things beyond our horizon.
    We do not know the size of the universe beyond our horizon, but measurements of the geometry of space tell us that it must be much bigger than the observable universe and may even be infinite in size. What cosmology tells us is that the past was hot and denser than the present. If the whole universe is infinite in size now it was infinite in size in the past, so it was not a tiny ball. However the observable universe is finite so it was a tiny ball.

    Question: Is the big bang speculation and subject to revision?
    Everything in science is subject to revision, thats the nature of science.

    Question: is the big bang speculation?
    Again depends on what you mean by the term "big bang" one way to use the term is to say the observable universe evolved from a incredibly hot dense state. This is not speculation and is supported by multiple lines of evidence. see here :
    http://www.damtp.cam.ac.uk/research/gr/public/bb_pillars.html
    However another way to define the big bang is that the universe arose from a state of infinite temperature, density etc. IS that speculative? Depends on how you define the word speculative. Its based on rigorous mathematical singularity theorems proven by Hawking and Penrose. However all theorems have assumptions and one of the assumptions in these theroems is the Einsteins theory of general relativity is a good description of gravity all the way to the moment of the singularity.
    This assumption is not taken seriously by most cosmologists. However the search for a improved theory of gravity ( one that take quantum effects into account) is a difficult one. which leads us on to you next question:

    Question: Does anyone have an explanation of where the ball came from?
    There are no shortages of ideas as to what might have happened before the big bang. These ideas are often generated from attempts to combine Einstein's theory of gravity with quantum theory. You will usually hear phrases such as " a quantum theory of gravity". The most popular of such theories are string theory and loop quantum gravity. Generally these ideas predict the universe did not begin with the big bang 13.8 bio years ago, but the big bang was really a transition in a longer possibly infinite history. A common prediction is that the big bang is really a bounce from a previous collapsing stage, although there are many other ideas some not relying on quantum gravity but on other principles. "Eternal inflation" is another idea that seems popular in the community.
    However none of the ideas on quantum gravity have been put to the test empirically and so we cannot say if they are right or wrong.
    In science empirical testing is the ultimate judge and so we have to wait and see if someone can achieve this for the competing ideas for the true nature of the big bang
    A series of films ( and there will be more) exploring some of these competing ideas is on youtube, if you would like to watch the link is here:
    https://www.youtube.com/playlist?list=PLANt-1sb3M3o82YWDDm3oiFwToHVj07Vo
     
  12. Jul 2, 2015 #11
    The big bang theory is NOT a theory about where everything came from, that is a very common misunderstanding though.
    BBT explains how the observed universe has arrived in it's present condition from having been in a much hotter and denser state billions of years ago.
    It can't be said to be 'speculative' because not only does it describe very well what we actually see, it also has made predictions of what we should be seeing before we found a way to see it! - lookup 'Cosmic Microwave Background'.

    There ARE theories of how the hot dense Universe could have come into being in the first place, (like string theories), and those could fairly be called speculative because we don't as yet have sufficient data on which to base conclusions.
     
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