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Thread: The big bang and infinity? (and other things)

  1. #1 The big bang and infinity? (and other things) 
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    Hello, this is my third (first "real") post. I have a lot of questions and am here in hopes of learning.
    So, before I start I would like to say there is a good chance I have no idea what I'm talking about, if I'm totally and utterly wrong please criticize me, but please don't flame.

    So I've been thinking about this a lot lately: What IS the universe? Did the big bang create it? What IS time and did it exist before the big bang?

    I have heard quite a few people state that time did not exist before the big bang, it was created by it along with the universe. I have to say I don't understand this. Surely, both time and the universe must be infinite in all respects? Because of the definition of the "universe" : "All existing matter and space considered as a whole; the cosmos." surely it can have no edge, because whatever is beyond said edge, even void would be considered part of the "universe." Therefor I can only conclude that the big bang happened WITHIN the universe, and simply created/released matter and energy, and that it's likely that, out in the universe, other big bangs have occurred?

    As for time; is time not a human construct? To my knowledge it doesn't really "exist" therefor it cannot have beginning or an end, right? Furthermore in a system, if there is no time, there can be no change; surely this would mean that in order for the big bang to have happened time must have existed prior to it?

    And lastly: Is the matter, energy, IPM etc that was created by the big bang infinite, if so, why? I'm not saying I would know better but, why would it be? I also don't understand this. Surely it would just be extremely large but finite?

    The way I've always thought about it is that the universe and time are both infinite in all respects (after all if the universe is finite, what is beyond it? And why isn't that, even if it is just nothingness considered to be a part of it), the big bang simply happened at a finite point within the universe, and generated a finite amount of energy and matter: Which is our particular, "Local universe," (for want of a better expression.) Beyond which is, well, whatever was there before the big bang, and beyond that probably an infinite number of other "Local Universes" created by similar events.

    Also I have heard of the idea that, no matter where you are in the universe, things appear to be moving away from you. How can this be? If two people were on opposite sides of the same body (say a planet or large rock,) for this to hold true, they must both observe the body moving towards the other one. Even if they are both also moving with the expansion of the universe how can they both be observing the same body to have direct opposite velocity's?

    That's all for now, I'm sure I'll be back later to further terrorize people with my scientific ineptitude.


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  3. #2  
    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by VincentProud View Post
    What IS the universe?
    Starting with the easy ones, eh?

    Did the big bang create it?
    I guess the only real answer to this is: we don't know. We can trace back the apparent expansion of the universe to a very hot dense state early on. We don't know what happened before that (at "time zero"). The may have been a "creation" event or some sort of continuation from an earlier state.

    What IS time and did it exist before the big bang?
    Time is defined in various, not very useful but pragmatic ways: it is what clocks measure; it is what stops everything happeing all at once. I don't think that you can get much better than our intuitive understanding of what time "is". However, Relativity theory gives us a precise way of relating time to space.

    Did it exist before the big bang? Hmmm... Personally (and I am no expert) I would say yes because the big bang theory describes the evolution of space. This is based on General Relativities description of the universe as being made up of a space-time "manifold" (4 dimensional "surface"). This space-time manifold must have always existed for the big bang and subsequent evolution of space to have occurred. (But maybe someone with more knowledge will have another view.)

    Surely, both time and the universe must be infinite in all respects?
    Again, we don't know for sure. The universe could be curved back on itself. Imagine the universe had only two dimensions (instead of three) like the surface of a ball. There is no edge/end/boundary to that universe. On the other hand, the universe could be like an infinitely large sheet of paper.

    Also I have heard of the idea that, no matter where you are in the universe, things appear to be moving away from you. How can this be?
    The expansion is better though of as a change in scale of distance. For example consider a series of points equally spaced:
    A .. B .. C .. D .. .. Z ..

    If the space between each point expands:
    A ... B ... C ... D ... ... Z ...

    Then the distance between A and B will increase by 1 unit. The distance between B and C will increase by 1 unit. But the distance between A and C will increase by 2 units. The distance between any 2 points will increase by an amount proportional to their separation. Therefore, everyone will see the things around them receding at a speed proportional to distance. Everyone will appear to be in the centre of a sphere of expansion. (It may take a bit of thinking to get your head round that!)

    Hope that helps a bit ...


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    A number of philosophers have concluded that time doesn't exist, and this conclusion does seem odd at first. They are not denying that change exists - it obviously does. By "time", they are referring to the ways of thinking that have been developed to describe and quantify change. These could be seen as mental constructs rather than entities which actually exist in the real world. Notions such as that time flows are hard to justify, as becomes evident as soon as one asks, "how quickly does it flow?". Despite this, Isaac Newton's statement which has been widely criticised didn't prevent him from developing an extraordinarily useful treatment of dynamics. Newton's view of time - "Absolute, true and mathematical time, of itself and from its own nature, flows equably without relation to anything external". I doubt that any physicist would accept this today. Block time, which is closely related to time as it appears in space-time does not involve time flowing, but it has its own difficulties which don't appear to have been resolved. No one seems to fully understand time.
    Last edited by JonG; November 22nd, 2012 at 02:15 PM. Reason: typographical error
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    Did it exist before the big bang? Hmmm... Personally (and I am no expert) I would say yes because the big bang theory describes the evolution of space.
    from my rudimentary knowledge of GR, time would not have existed if space had not. they are inexorably linked together by that theory.
    so the BBT describes the evolution of spacetime not just space.

    Surely, both time and the universe must be infinite in all respects?
    from the WMAP probe results we are pretty sure, with a 0.5% accuracy, that the universe is flat, infinite and unbounded.

    Cosmology

    will give you a bit of a help.
    Sometimes it is better not knowing than having an answer that may be wrong.
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    Quote Originally Posted by Chrispen Evan View Post
    Did it exist before the big bang? Hmmm... Personally (and I am no expert) I would say yes because the big bang theory describes the evolution of space.
    from my rudimentary knowledge of GR, time would not have existed if space had not. they are inexorably linked together by that theory.
    so the BBT describes the evolution of spacetime not just space.
    Interesting: So, without time, how could it have been that anything changed or moved? If nothing could change, then how did whatever "started" TBB do whatever it is that it did, surely if anything did exist, without time it simply would have been entirely inert? I'm confused >.<

    Quote Originally Posted by Chrispen Evan View Post
    Surely, both time and the universe must be infinite in all respects?
    from the WMAP probe results we are pretty sure, with a 0.5% accuracy, that the universe is flat, infinite and unbounded.

    Cosmology

    will give you a bit of a help.
    Thanks Also I know we describe the universe as flat to help us understand some theorys, but your saying that it is ACTUALLY flat? How can that be? I can personally move in 3 dimensions, as can everything else? :O
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    Quote Originally Posted by VincentProud View Post
    Thanks Also I know we describe the universe as flat to help us understand some theorys, but your saying that it is ACTUALLY flat? How can that be? I can personally move in 3 dimensions, as can everything else? :O
    "Flatness" has a special meaning in cosmology. I strongly recommend Ned Wright's pages for the lay reader: Frequently Asked Questions in Cosmology

    He also has a tutorial.
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  8. #7  
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    Time and is a concept of man and infinity is undefined. have fun with that.
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    Interesting: So, without time, how could it have been that anything changed or moved? If nothing could change, then how did whatever "started" TBB do whatever it is that it did, surely if anything did exist, without time it simply would have been entirely inert? I'm confused
    dunno, but the quantum world moves in mysterious ways and the start of this universe was a quantum event. of some sort. we haven't got a theory as yet of how this universe started as that will require a quantum theory of gravity. we only have GR at this time and that can't deal with the quantum world but works very well for the current big bang theory which doesn't deal with the beginning.

    PS Ned Wright does a good job.
    Sometimes it is better not knowing than having an answer that may be wrong.
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  10. #9  
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    surely it can have no edge
    It doesn't have an edge; it has a pole. Take as an analogy the surface of the earth - what is north of the north pole ? It is immediately obvious that this question is meaningless, because when you stand at the north pole all directions are south, no matter where you are facing. Yet there is obviously no edge either, the earth continues to be smooth and continuous at the north pole.
    Likewise at the Big Bang - time has a pole at the Big Bang, so no matter how you are "oriented", all possible world lines will face into just one direction - the future. Therefore, the question as to what was before the Big Bang is meaningless, just as meaningless as it is to ask what is north of the north pole. Once can say that at the point of the Big Bang no "past" existed.
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    So, without time, how could it have been that anything changed or moved?
    <br><br>Those who deny the existence of time are not claiming that change and motion don't happen. They are saying that the description of these things using the current notion of time is inconsistent.
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    Quote Originally Posted by Markus Hanke View Post
    surely it can have no edge
    It doesn't have an edge; it has a pole. Take as an analogy the surface of the earth - what is north of the north pole ? It is immediately obvious that this question is meaningless, because when you stand at the north pole all directions are south, no matter where you are facing. Yet there is obviously no edge either, the earth continues to be smooth and continuous at the north pole.
    Likewise at the Big Bang - time has a pole at the Big Bang, so no matter how you are "oriented", all possible world lines will face into just one direction - the future. Therefore, the question as to what was before the Big Bang is meaningless, just as meaningless as it is to ask what is north of the north pole. Once can say that at the point of the Big Bang no "past" existed.
    At the risk of arguing with someone who knows a lot more about maths/physics than myself I have to say I'm not convinced by the analogy. Over the years we have been informed by several scientists, in books and other media, that the question of what happened before the BB is "meaningless". I could accept the description "pointless" but find it difficult to agree with the word "meaningless".
    Recently there was a programme (it may have been a repeat) in the Horizon series on BBC Television. The programme ( What Happened before the Big Bang?) was aimed at the interested layperson and did include a lot of speculation: a certain amount might have been tongue in cheek.
    Nevertheless the programme considered the views of a number of top scientists such as Roger Penrose, Neil Turok, Andrei Linde, Param Singh and Lee Smolin. None of these individuals gave the impression they regarded the question as "meaningless" and, in fact, Penrose actually used the word when he stated that in recent years his opinion had changed and he was no longer convinced that such a question was "meaningless".
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    Quote Originally Posted by Markus Hanke View Post
    Likewise at the Big Bang - time has a pole at the Big Bang, so no matter how you are "oriented", all possible world lines will face into just one direction - the future.
    Ah, that is the bit I was missing in my mental model. Is it required that all world lines end at another pole/singularity? Some will, I assume end at the singularity of a black hole. But I assume it is a possibility that time can extend into the infinite future.
    ei incumbit probatio qui dicit, non qui negat
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    Quote Originally Posted by Halliday View Post
    Nevertheless the programme considered the views of a number of top scientists such as Roger Penrose, Neil Turok, Andrei Linde, Param Singh and Lee Smolin. None of these individuals gave the impression they regarded the question as "meaningless" and, in fact, Penrose actually used the word when he stated that in recent years his opinion had changed and he was no longer convinced that such a question was "meaningless".
    My (again, very limited) impression is that Penrose, for example, thinks there was an earlier universe which ended at the point ours "started". So this would be analogous to having the south pole of another planet just touching the north pole of ours. You could go "further south than south" by passing through the singularity and ending up in a new universe. (I'm sure Markus can express that better. )
    ei incumbit probatio qui dicit, non qui negat
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    I could accept the description "pointless" but find it difficult to agree with the word "meaningless".
    i think they mean "meaningless" in regards to this universe. the BB was the creation of this universe and as such there was nothing before. now, this doesn't mean that there wasn't something before but it has nothing to do with what we live in now.

    hope that makes more sense to others than it does to me.

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    Quote Originally Posted by Strange View Post
    Is it required that all world lines end at another pole/singularity?
    I don't think world lines are required to end at a pole at all. Do grid lines end at the north pole ? No.
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    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by Strange View Post
    Is it required that all world lines end at another pole/singularity?
    I don't think world lines are required to end at a pole at all. Do grid lines end at the north pole ? No.
    Good! That was my intuition.
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    Quote Originally Posted by Halliday View Post
    At the risk of arguing with someone who knows a lot more about maths/physics than myself I have to say I'm not convinced by the analogy. Over the years we have been informed by several scientists, in books and other media, that the question of what happened before the BB is "meaningless". I could accept the description "pointless" but find it difficult to agree with the word "meaningless".
    Recently there was a programme (it may have been a repeat) in the Horizon series on BBC Television. The programme ( What Happened before the Big Bang?) was aimed at the interested layperson and did include a lot of speculation: a certain amount might have been tongue in cheek.
    Nevertheless the programme considered the views of a number of top scientists such as Roger Penrose, Neil Turok, Andrei Linde, Param Singh and Lee Smolin. None of these individuals gave the impression they regarded the question as "meaningless" and, in fact, Penrose actually used the word when he stated that in recent years his opinion had changed and he was no longer convinced that such a question was "meaningless".
    Yes, I kind of take your point here. Please note that I lay no claim to the truth - when all is said and done we simply don't know what goes on at the time of the Big Bang. We are still missing a crucial bit of information, and that is a consistent model of quantum gravity. Who knows, perhaps that model will be so radical that it completely turns our understanding of space and time upside down. I sure hope so - it would be interesting times
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