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I don't believe in singularities!

  1. Oct 6, 2014 #1
    It seems to me that singularities are taken for granted as existing, otherwise there couldn't be a big bang.
    Is that so?

    To me, to believe in singularities is in no way different to believing in a God.

    Is there any reason you can think of that precludes all other scenarios from explaining existence?
    For example, could it be that creation, for want of a better word, is actually an on going process that has a source and from that source all things come and continue to come?

    Or could the contents of our Universe when run backwards from now, not all reach the central point at the same time, but be separated by one Planck time each Planck energy?

    For me the Planck energy density is absolute, no observer can detect any greater energy density, no matter what. The way I see the Universe, to exceed the PED would turn the Universe inside out and basically ruin it completely, or at the very least make a mockery out of it.

    I apologise if this topic has been covered ad nauseam already.
    But I'd love to know if this is all settled already>
     
  2. jcsd
  3. Oct 6, 2014 #2

    Chalnoth

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    Nope. Singularities are places where the theories we use cease to make sense. They're a way of showing us that our theories are incomplete, and we need to understand how the universe works better to correctly describe the region near the singularity.

    In other words, the theory (General Relativity in this case) predicts there is a singularity. But that's nonsense. So that means that General Relativity must be wrong somewhere around that singularity. We don't yet know how close to the singularity General Relativity remains correct, as we have yet to experimentally detect any deviation from the theory. But we can be quite sure it has to become incorrect at some point.
     
  4. Oct 6, 2014 #3

    Simon Bridge

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    The singularity in question is thought of as a property of the mathematics not of the Universe.
    The belief in the literal existence of singularities of this kind in Nature would, indeed, be irrational and unscientific.

    Unfortunately, nature does not care how you or I may or may not see things, so personal statements about "how I see it" are meaningless.

    It is impossible to completely rule out any particular model as long as it accounts for all observable phenomenon.
    At any time there are a lot of competing theories - the trick is to decide which to use. How you choose, absent empirical evidence, is a matter for a broader philosophy and so off-topic for these forums.

    Continuous creation forms part of "steady state" cosmology.
    http://en.wikipedia.org/wiki/Steady_State_theory
    Possibly you are thinking of a quasi-steady state theory - where some expansion goes on somehow?

    There are, indeed, good reasons that this class of model has become obsolete:
    i.e. http://www.astro.ucla.edu/~wright/stdystat.htm for some earlier objections.
    ... although it still has it's proponents, it's becomes something like the geocentric solar system - needing ever more bits tacked on as evidence rolls in just to catch up. That does not "rule it out" exactly - but it does make it hard to use and it loses it's ability to make predictions ... so we stop using it.
     
  5. Oct 6, 2014 #4
    The thing I'd like to resolve for myself the most is; when I use GRT to calculate the energy density needed for light to close its own local space-time I get the Planck energy. That is, when the wavelength of light equals pi times its own gravitational radius the energy is the Planck energy.
    If this is a correct solution then how could you possibly collapse it. You could put as many as you like side by side and still nothing would collapse. What's the point of conservation otherwise?
     
  6. Oct 6, 2014 #5

    Simon Bridge

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    Since you are getting this at the plank scale, you need a theory of quantum gravity to answer the question.
    We don't have one of those yet - so the simple answer is: nobody knows.

    I have a concern that you may be misunderstanding the calculation you did though... it sounds like you are using the terms in ways they were not intended. Please state clearly what you are trying to do, and show your working.
    Try to use standard terms in the standard way.
     
  7. Oct 6, 2014 #6
    For me it's a matter of what comes first, quantum gravity or the question that leads to it.
    I readily admit to not having a clue when all's told.

    However; are you saying that there is no way to calculate the energy at which light is pi times its own gravitational radius in GRT?
    Light curves space-time because it's energy, right?
    It does this at a rate determined by GRT and the basic pattern is that as the wavelength shortens the gravitational radius increases.
    Are you saying GRT has nothing to say about a point of convergence?
     
  8. Oct 6, 2014 #7

    Simon Bridge

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    ... well Nature does not care what it is for you or me or anyone. Right now we have plenty of questions leading to quantum gravity, but no theory has yet emerged to answer them despite there being lots of candidates. So, in this case, the questions have come first ... this is usually the case: nessecity being the mother of invention and all...

    No, I am saying that "the energy at which light is pi times its own gravitational radius" makes no sense.
    What do you mean by "light": electromagnetic fields?
    How are you calculating the gravitational radius of light?
    What is it about light that you want to be pi times this radius? The wavelength? What? You have to say.

    Aside: the plank energy is a macroscopic unit, nothing special there.
    It's 1.22x1028eV ... this is roughly the rest-mass energy of 10000 hydrogen atoms.
     
    Last edited: Oct 6, 2014
  9. Oct 6, 2014 #8
    The key point you make is taken; that the question is nonsense.
    That's the end of the story.
    Thank you all, now I can rest easy.
     
  10. Oct 6, 2014 #9
    The OT comes off as wanting to discuss magic beliefs, specifically of religion, rather than science. Say, "existence": all we see is existence, so "non-existence" would be an extraordinary claim without any evidence whatsoever. I think those are questions for MagicForums. :rolleyes:

    However, there is a legit question here:

    No, that is backwards. It was the behavior of general relativity applied to the universe that gave the idea of an initial singularity.

    "In 1927, the Belgian Catholic priest Georges Lemaître proposed an expanding model for the universe to explain the observed redshifts of spiral nebulae, and forecast the Hubble law. He based his theory on the work of Einstein and De Sitter, and independently derived Friedmann's equations for an expanding universe. Also, the red shifts themselves were not constant, but varied in such manner as to lead to the conclusion that there was a definite relationship between amount of red-shift of nebulae, and their distance from observers."

    "In 1931, Lemaître proposed in his "hypothèse de l'atome primitif" (hypothesis of the primeval atom) that the universe began with the "explosion" of the "primeval atom" — what was later called the Big Bang. "

    [ http://en.wikipedia.org/wiki/History_of_the_Big_Bang_theory ; warning: the article is bad, lacking in references. But it ought to be roughly correct re the timeline.]

    It was always a hypothesis without a test (but see below how we can claim it has failed, sort of). It's popularity stems AFAIK from among other reasons that a singularity can generate an infinite set of parameters, and also bind the all to certain values. Exactly what you want for a singular [sic!] Theory Of Everything.

    But it was a bad idea. You can't derive a singularity from the semi-classical physics we use so far.* (But see more below on the next question.) And since the LCDM cosmology we have since 2004 is semi-classical, there is no compelling reason to think there is an initial singularity around the time of the Hot Big Bang. The preceding inflationary theory may well have singularities, but it is an open question.

    "The notion that the Universe started with a Big Bang, and that this Big Bang started from a singularity — a point in space and/or a moment in time where the universe was infinitely hot and dense — is not that different, really, from assuming humans begin their lives as infinitely small eggs. It’s about over-extrapolating into the past."

    "Moreover, there’s a point of logic here. How could we possibly know what happened at the very beginning of the universe? No experiment can yet probe such an early time, and none of the available equations are powerful enough or usable enough to allow us to come to clear and unique conclusions.

    The modern Big Bang Theory really starts after this period of ignorance, with a burst of inflation that creates a large expanding universe, and the end of inflation which allows for the creation of the heat of the Hot Big Bang. The equations for the theory, as it currently stands, can be used to make predictions even though we don’t know the precise nature of our universe’s birth. Yes, a singularity often turns up in our equations when we extend them as far as they can go in the past; but a singularity of this sort is far from likely to be an aspect of nature, and instead should be interpreted as a sign of what we don’t yet understand."

    [ http://profmattstrassler.com/2014/03/21/did-the-universe-begin-with-a-singularity/ ; my bold ]

    Here is what we know (and suspect):
    universehistoryreliability2.png

    [ http://profmattstrassler.com/2014/03/26/which-parts-of-the-big-bang-theory-are-reliable/ ]

    Note that the Hot Big Bang, the classical idea of Big Bang, has no singularity and the preceding era of Cold Inflation, is an exponential expansion so indefinite in time. In so much as old ideas placed a potential singularity with superexponential expansion there, they failed the test. Of course, you can always try again. ;)


    Semiclassical physics predict such convergences - they are called "black holes". [ http://en.wikipedia.org/wiki/Black_hole ]

    Note that the event horizon, where our ability to predict semiclassical continuation stops, (the so called firewall problem; http://en.wikipedia.org/wiki/Firewall_(physics)) are as far away from the Planck scale as you want by taking large enough black holes (AFAIU).

    There is also a semiclassical convergence for wordlines going back in an expanding universe. But what happens there, or for small black holes, "should be interpreted as a sign of what we don’t yet understand".

    *Semiclassical physics is, AFAIU, relativistic quantum fields on a background of weak (roughly linear) gravity.
     
    Last edited: Oct 6, 2014
  11. Oct 6, 2014 #10

    Simon Bridge

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    Don't get me wrong, I can't tell if the question is nonsense of not - the sentence itself does not make sense.
    I think you are trying to ask about black holes made out of light in some way, but I don't want to guess what you are asking.
     
  12. Oct 6, 2014 #11
    I'm sorry I'm not being clear about what exactly my point is, if in fact I have one at all.
    Putting it as simply and concisely as I can.
    If I ask myself "is there a limit to energy density"?
    I find only one answer; the Planck energy density.
    I get a geometric picture quite clearly.
    You won't believe how much it says to me.
    For example the ratio of field strengths, grav to emf, at the event horizon is a simple ratio of the fine structure constant.
    But clearly I'm imagining it, or at least enhancing what is actually real.
    Nobody cares if there is a limit or not it seems, as it is not needed to understand the workings of our Universe.
    That's where I start building my personal Universe, to me the Planck energy is the start of any understanding.
    But that's obviously just a personal thing and has nothing to do with science or physics.

    So thank you all again.
    But I'm happy living in my own delusion for now.
     
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