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Where does space end

  1. Mar 26, 2009 #1
    Hi there this is my very first post ever so be gentle with me please.Ive often wondered just how big space is, if it ends and well just where is it, by that I mean for example the film Men In Black had the cat that had a universe hanging from its collar. Could we be in something similar? Any takers on this one?.
     
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  3. Mar 26, 2009 #2

    DaveC426913

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    The observable universe is believed to be about 78 billion light years across. It has no edge; it is finite but unbounded, and there is no "beyond". Many theoires purport that it wraps around and closes in on itself.

    As for existing inside a pendant: since, by definition, we cannot see outside the observable universe, it is a question for fantasy, not science.
     
  4. Mar 26, 2009 #3
    Sorry for seeming to go into fantasy but has no one ever theorized whats out beyond our universe? What if there was a multitude of universes as many as the stars in our night sky?
     
  5. Mar 26, 2009 #4
    Hi Dave,

    I did read what I recall as being a Scientific American article on it and I recall the title as being based on the Arthur C Clarke quote "Many and strange are the Universes that drift like bubbles in the foam upon the River of time". I tried to find the article, but initially failed. Spurred on by your comments I finally found http://www.stanford.edu/~alinde/1032226.pdf" [Broken]. It seems there is something wrong with my recollection.

    Wikipedia does have an article which I did find earlier but didn't link: http://en.wikipedia.org/wiki/Chaotic_inflation_theory" [Broken].

    Anyway, the idea is certainly speculative. It is not my speculation and Linde has scholarly articles which detail his theory http://www.stanford.edu/~alinde/" [Broken] - look in "A Brief History of the Multiverse".

    I should clarify that I am not championing the theory, just saying there is a theory (that particular fact is not speculative).

    cheers,

    neopolitan

    Since my reply was deleted, this may not make sense to anyone other than Dave.
     
    Last edited by a moderator: May 4, 2017
  6. Mar 26, 2009 #5
    Well, sure that's possible, but not within the realm of empirical science. The term "observable universe" doesn't just mean everything we can observe with current technology, it means everything that is possible to observe even in theory with any future technology.

    We simply can never observe something farther away than light (or information in general) has had time to travel to us since the beginning of the universe. So any theory about anything beyond would be philosophy or theology, not empirical science.
     
  7. Mar 26, 2009 #6

    DaveC426913

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    Fair enough. Though they aren't theories; they are hypotheses. Theories are based on evidence, and there is none for this.
     
  8. Mar 26, 2009 #7
    Agreed, I was not being strict enough. It's a small 't' theory, which may more accurately be known as a hypothesis, although some would say that a hypothesis is something else again (ie a testable statement used in the process of converting an idea into a large 'T' Theory). (Being overly cautious, I provide a http://www.google.com.au/search?hl=en&q=define:hypothesis&meta=".)

    Given the nature of the original question and the vagarities of the English language, I didn't expect to get jumped on so hard with an infraction and all. Especially since I gave a link to the wikipedia page and suggested that more reading be done on what seemed to be of interest to the OP.

    Did you think that when I said "my understanding is" that I was saying that I agreed with the hypothesis and was presenting it as fact rather than my own meaning "my understanding of the hypothesis is"?

    In any event, the thread seems to be in the wrong forum. Cosmology would be better, no?

    cheers,

    neopolitan
     
    Last edited by a moderator: Apr 24, 2017
  9. Mar 26, 2009 #8

    DaveC426913

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    They gave you an infraction for that??? Sorry about that. I thought they'd simply warn you and refer you to the forum guidelines.
     
  10. Mar 27, 2009 #9

    Fredrik

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    I'm guessing you didn't really mean to have the "it" in the second sentence be a reference to the observable universe? It makes more sense if it refers to "the universe"...but in that case you just said that the universe is finite. We still don't know if it is.
     
  11. Mar 27, 2009 #10

    Fredrik

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    I'm not so sure if this is how the word "theory" is actually used by most physicists. For example, a quantum field theory about particles that don't exist in the real world is still called a quantum field theory.

    I have personally never liked the requirement that a set of statements must be supported by evidence to be called a "theory". It raises the question of "how much evidence?" which doesn't have an answer that everyone can agree on, and I also don't like that it suggests that theories are supposed to describe what the universe is like, when in fact all they can do is predict (the probabilities of) the results of experiments. It suggests that a theory is either right or wrong, and that evidence makes it more likely that its right, when in fact all theories are wrong. Some are just less wrong than others.

    Don't take this as criticism against you. I know you're just using a standard definition. I just don't think that the standard definition is sophisticated enough to be appropriate in physics, and that's been bugging me ever since I realized it.
     
  12. Mar 27, 2009 #11

    DaveC426913

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    I think you're overcomplicating it. It simply means that there are some phenomena that some independent scientist can observe that this theory predicts.

    Any scientist can observe the periodic movement of stars against the fixed stellar background. If someone creates a theory that proposes Earth is in motion, causing the parallax, then you've got a theory, "Earth moves".

    But if you speculate about what's outside the universe, there is no such observable evidence to base a theory on.
     
  13. Apr 3, 2009 #12
    hi everybody sorry for not replying sooner was working overtime.Thanks for all the information you gave Ive been reading some interesting things and have came to the conclusion that there cant be any other universe out there as we havent bumped into anything and as far as I can make out there can only ever be one singularity. I do realise now that this is the wrong forum sorry
     
  14. Apr 3, 2009 #13
    Hi Dave I would like to start studying quantum physics (no laughing please) and was wondering if you could point me in the right direction ?
     
  15. Apr 3, 2009 #14
    Post 2 addresses the observable universe. As far as is known every observer from every galaxy also is emeshed in a similar observable universe...which may or may not overlap with ours. Big bang and inflation theory suggests we can see only a tiny,tiny part of our own universe and as noted there might be an infinite number of universes.....another might start right at your nose, for example, and be undetectable. This can also be hypothesized via quantum and string theories.

    Brian Greene's FABRIC OF THE COSMOS is one non mathematical book which gives good insights to these different explanations.

    It's also interesting to note that space also ends inside a black hole where it is replaced by time...?? even future and past!!!. This is analogous to an extreme case case of relativity where two observers in relative motion each see the other a mix of space and time (if we are in relative motion, my space is a mix of your space and your time, and your space is a mix of my space and my time).

    In other words, in a sense, space might meld into time and vice versa.

    Have you ever wondered how small space is? Is it continuous or discrete? In a way that might be considered analogous to a black hole, at tiny, tiny scales (planck scale) it appears that space,time,energy lose their individuality....they are apparently not identifiable but do they decompose or instead maybe meld into a "quantum foam" of uniformity....
     
    Last edited: Apr 4, 2009
  16. Apr 3, 2009 #15

    DaveC426913

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    Many here would disagree (partly because many here have a formal education in Physics) but the book that most opened my mind was Brian Greene's The Elegant Universe. I had to read it slowly and read it twice.
     
  17. Oct 28, 2010 #16
    often wondered about that myself especially when in bed at night but i think since space is the opposite of matter and has no mass or definitions it ceases to exist. The space between a persons two fingers was always there and was always never there hope that makes some sence its still a parodox though!
     
  18. Oct 28, 2010 #17

    ghwellsjr

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    Your comments might make a lot more sense if you would capitalize correctly, spell correctly, punctuate correctly and use correct English grammar. You might save yourself a few seconds of time by not proof reading but it adds more time to everyone who tries to read what you are writing. Why don't you go back and edit your post and clean it up so that we won't have to waste time trying to decypher what you are saying?
     
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