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

I Infinity and the beginning

  1. Jul 17, 2016 #1
    Since the success of the Penrose Hawking singularity theorems many people have claimed that the universe must have a beginning . In recent years though people have explored models of the universe that resolve the singularity and imply the universe may have existed before the big bang. In such models the universe may exist forever into the past.
    Of course nobody knows which models are correct, was there a singularity or is it just an artificat of pushing Gr beyond its regime of applicability.?But it seems to me whichever answer is correct some form of infinity is very hard to avoid. if there is a singularity then the temp. pressure, density, curvature etc are all infinity. if there is no singularity for example as is claimed in LQC and many other models then the past is infinite. So it seems to one way or another infinity is almost inevitable. ( i say almost as there may be ways to have a finite past without a singularity but such models have their own problems ).
    Is this a fair summation or do you see an error somewhere?
     
  2. jcsd
  3. Jul 17, 2016 #2

    phinds

    User Avatar
    Gold Member
    2016 Award

    You seem to misunderstand the meaning of "singularity" and are taking it to be a physical thing. It is not. "Singularity" is just shorthand for "the place where the math model breaks down and we don't know WHAT is/was happening".
     
  4. Jul 17, 2016 #3
    I understand that and I agree with it. nevertheless many cosmologists talk about the universe having a beginning or being 13.8 bio years old and their rational for doing so is believing the singularity is real. I agree the singularity is unlikely to be real and is likely to be replaced with something that resolves it. My point is it seem on either scenario ( ir the singularity is real or the singularity is resolved) there is likely to be an infinity somewhere.
     
  5. Jul 17, 2016 #4

    phinds

    User Avatar
    Gold Member
    2016 Award

    Not necessarily. The universe could be finite but unbounded and with a start at t=0, in which case there is no infinity.

    Now, mind you, No matter WHAT the case is, I find it mind blowing because there only seem to be two possibilities. Either the universe (whether finite or infinite) popped into existence out of absolutely nothing or it is infinitely old and had no beginning. I can't comprehend either one but don't see how you get around one of them being the case. People like Lawrence Krause are perfectly happy saying that according to QM you can have something popping out of nothing but I don't get it.
     
  6. Jul 17, 2016 #5

    Ken G

    User Avatar
    Gold Member

    Even when people like Krause talk about something popping out of nothing, it isn't really nothing-- there must be the laws that say the something can pop out of the nothing, or the claim has no authority. So they do not escape the fundamental question of where did the universe come from, they just reframe the question into where did the laws come from, and where did the nothing-that-isn't-nothing come from, and so on. I would say the basic problem here is that there is simply no escape from mystery. It is clear in all cases that our scientific discoveries simply replace more superficial and varied mysteries by more profound and unified ones, and the Big Bang model is no exception. Indeed, it is the mother of all examples of that phenomenon. If that bothers us, perhaps we need to consider more carefully what it is that we get to know.
     
  7. Jul 17, 2016 #6

    phinds

    User Avatar
    Gold Member
    2016 Award

    It's turtles all the way down.

    I'm sticking with that.
     
  8. Jul 17, 2016 #7
    Turtles all the way up as well?
    Where is the infinitely huge turtle we can't see? Is it a "We can't see the forest for all the trees around?" ...for all the little turtles around?
    One turtle is all we need to be concerned with. He is the beginning and the end. He just eats 2pi-es.
     
    Last edited: Jul 17, 2016
  9. Jul 21, 2016 #8
    One of the things that I took away from reading Alan Guth, is that nothing just isn't what it used to be.

    diogenesNY
     
  10. Jul 21, 2016 #9
    An infinite loop of turtles might solve that.
     
  11. Jul 22, 2016 #10
    Might as well use snakes then.
     
  12. Jul 22, 2016 #11

    phinds

    User Avatar
    Gold Member
    2016 Award

    Or the worm Ouroboros
     
  13. Jul 22, 2016 #12
    Dear windy miller,

    You are right, of course, the Universe existed forever or had a beggining. Lawrence Krauss showed that a beggining from nothing is possible, but nothing shows that it occurred 13,8 billion years ago, as It could be cyclic. A matter very difficult to decide, if the decision will be possible at all.
    But the fact is that infinities are mathematical concepts, Mathematics deals rather well with them, not Physics. When they appear, it seems to me this only indicates that the mathematical tool used has reached a limit and ought to be abandoned. So, we must forget singularities, such things are impossible in the real world.
     
  14. Jul 22, 2016 #13

    phinds

    User Avatar
    Gold Member
    2016 Award

    Yes, that's why they are called singularities. You seem to be under the impression that a singularity is something that is supposed to be physical but that's not true. "Singularity" does not mean "point" or "infinite",it just means "the place where our math model breaks down and we don't know what's going on", so saying a singularity is not physical is redundant.
     
    Last edited: Jul 22, 2016
  15. Jul 23, 2016 #14

    Fervent Freyja

    User Avatar
    Gold Member

    There are some analogies using geodesics that may be helpful in helping you understand the numerous definitions for the term singularity on this website. It's important to recognize the various ways and reasons that the term is used, or you will get confused again...
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Infinity and the beginning
  1. In the beginning (Replies: 3)

  2. In the beginning (Replies: 9)

Loading...