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Few questions about universe

  1. Mar 8, 2005 #1
    after watching the elegant universe a few questions popped into my head. im a fresheman in high-school so dont flame plz.

    How big is the universe? its hard to find the right words to ask what is in my head, but is there just a brick wall at the end of the universe? understand what im asking now? ok another question: how did we get here? (please leave out religious beliefs) try to think of a situation where nothing exists...where there is no matter... i dont know i guess im going crazy but those thoughts were stimulated after watching that movie. thanks in advance
  2. jcsd
  3. Mar 8, 2005 #2
    How big is the universe? We don't know. Is there a physical edge to it? We don't know. How did something come from nothing? If indeed that is what happened ... you guessed it ... we don't know.

    We have theories (for which there is good evidence) that describe a part of those questions (e.g. Big Bang cosmology, natural selection), and sophisticated speculations (which lack any hint of evidence) that try to go a bit further (e.g. string theory), but nothing more than that. Do not expect to find final answers to the big questions in science, or in any other vocation in life. Maturity in both an individual and a species lies in rationally and responsibly dealing with incomplete and uncertain knowledge.
  4. Mar 9, 2005 #3


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    Current theory puts the observable universe at about 45 billion light years. It does depend on how you define the universe, though. That's just the limit of what we can see...and it's even a little more complicated than I may be leading you to believe.

    At the end of the observable universe, we presume that there's just more stuff which we can't see. Beyond that, we simply don't know.

    I'm afraid that religion is the only thing that's claiming to answer that question right now.
  5. Mar 9, 2005 #4
    Should we ask how did everything begin or why did everthing begin ? if its not why then why is it so ?
  6. Mar 9, 2005 #5


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    There will always be some point at which science is not going to be able to give you an answer. I don't know if, when you were a kid, you ever played that game with your parents where every time they'd answer a question, you'd ask "why?". You really can go indefinitely with that line of questioning. Our mortality prevents us from learning any "final" reasons. Perhaps its even unreasonable to think that the universe has a final explanation or purpose. Maybe it just is.
  7. Mar 9, 2005 #6
    This is true for contingencies, objects whose creation we can ask about. But if the physical world can be derived from principle alone, then the questions stop when the answer is that it is the only logical explanation. We can question things until it becomes obvious that the answer rests on the principles of reason itself. For if we start to question reason and logic itself, then there can be no answers. There can be no answers when there is no principles of reasoning. Therefore, the answer is that there are principles of reasoning.
  8. Mar 9, 2005 #7


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    We can't know if the universe can be derived from principle alone, so we'll never be sure when we can stop. In practice, we'll probably stop when we no longer can find anything to explain, but there's no way to guarantee that we've reached the limit of possible understanding, particularly since we can't guarantee the constancy of physical laws in time.
  9. Mar 9, 2005 #8
    Metaphyisical theories

    Your questions about the universe is properly addressed in the philosophy forum because the questions you ask are unanswerable by science alone and where science stops philosophy begins.
    Other people who have posted in this thread correctly state that some of your questions are not known from a scientific point of view. We know roughly how big the "observable" universe is but there is probably more to the universe than can be detected by humans.
    The famous physicist Stephen Hawkins says in his famous book, "A Brief History of Time" that the universe is "probably" finite but unbounded, like the surface of the earth, though I doubt he is implying that the universe is shaped like a sphere. Like the surface of the earth, there are no "edges" to it and if you travel far enough in the universe, like here on earth, you will end up back where you started.
    The strange world of quantum mechanics is starting to show us that our everyday experience of time and space is an illusion. Euclidean geometry is a concrete idea in our minds that causes these illusions and is the origin of some of your questions.
    If the universe is hyperbolic (curved back onto itself), as some cosmologist have suggested, then one could correctly claim that the center of the universe is everywhere.

    The subject of "nothing" is brought up often in the philosophy forum and the concept of nothing can drive a person nuts when thought about deeply. Something and nothing cannot coexist. If you want to read more on the subject of "nothing" I suggest reading "The Book of Nothing" by John Barrow. He addresses your questions and goes into other areas of "nothingness" such as the topic and history of the number 0.

    I would like to comment that your mind has a mature facet to it. When I was in high school the only things going through my mind dealt with girls and substance abuse.

    The Book of Nothing : Vacuums, Voids, and the Latest Ideas about the Origins of the Universe -- by JOHN BARROW; Paperback (Rate it)
    Buy new: $10.20 -- Used & new from: $7.41
    Last edited: Mar 9, 2005
  10. Mar 10, 2005 #9


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    I like simplified versions, the universe is exactly as big as possible for us to observe. Anything beyond that is metaphysics. I'm sure that's an interesting subject, I just don't find it scientifically interesting. I prefer theories that have observational consequences.
  11. Mar 10, 2005 #10


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    I suspect our universe exhibits a qualitative change beyond our current reach of perception. That's why we have difficulty extending our understanding of it past our observational limits. I base this on the many real-world examples of "catastrophe" we see all around us. You know, the "straw that breaks the camel's back". Our world has a strange capacity to flow smoothly, reach a "critical point" (a singularity), then change drastically and qualititaively: water turning to ice, a branch being bent than abrubtly snapping, a supernova (well I suppose the last one takes some time).

    So it is with the universe as a whole I think: Concepts such as "how big?", "nothing" and "something" have meaning in our world, like viewing the earth as flat. When used to describe the universe as a whole, terms like "size", and "boundary" may not apply in a way similar to applying "flatness" to a round earth: A singularity may be involved and this changes the rules.
  12. Mar 10, 2005 #11
    motion is life, the Universe is alive because of its motion;
    thus the Universe is changing and its size is not a constant;
    it's either contracting or expanding (2 theories which are being studied nowadays)

    About the wall, you have to take it this way:
    inside a small cube there's air
    a certain room is surrounding the cube
    the room is a part of a building
    the building is a part of a city
    the city is a part of a country
    the country is a part of a continent
    the continent is a part of a planet
    a planet is a part of a solar system
    a solar system is a part of a galaxy
    THAT's what we know until now "a galaxy is a part of the Universe"
    (supposing that the Universe is the most big description)
    but IT'S NOT!!
    Time can help relying on our intelligence

    How did we get here?
    well that's a hard and complicated question.
    you can ask also why did we get here?
    or even before that: who are we?
    and you can also surely ask: do we even formally exist?
    You still have a very long way to arrive to the ultimate questions.

  13. Mar 10, 2005 #12


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    Welcome to Physics Forums, mmmmm.

    You'll find that Physics Forums are moderated and flaming is not allowed. So feel free to ask any science-related questions you may have.

    Your "ultimate questions" are not easy to answer as you see from the above responses. As for the size of the universe, there is the portion that is within our field of view (the observable universe) and the portion beyond that (not viewable yet because light from there has not reached us yet).

    Given that the universe is about 13.7 billion years old, the radius of the observable universe is at least 13.7 billion light years away from us (actually it's more...like SpaceTiger suggested...because space is expanding).

    The whole universe is either finite (limited) but boundless (no edge because the way space curves back on itself) or infinite (unlimited). Some recent evidence indicates it's infinite, but there's still a lot of research to be done.

    If it's finite, how is there no edge? Imagine walking around the world...you could walk forever and never reach an edge because the world is round (the surface curves back on itself). Space could do the same thing...except it's 3D (not a 2D surface). Now trying to imagine curved 3D space is not easy...it certainly hurts my head.

    I assume you mean "where did the Big Bang come from?" That is unknown. Big Bang Theory explains how the universe changed since its beginning, but it does not explain where it came from. It may be nearly impossible to figure out where it came from because any information from "before" the Big Bang might have been lost when the Big Bang happened. But scientists are trying to figure it out and are coming up with some interesting possibilities. The show you saw on String Theory is one possibility. However, as mentioned above, that theory is based on math and not actual experimental evidence. Stay tuned...research goes on.
  14. Mar 10, 2005 #13
    The universe might even be infinite, we dont really know
  15. Mar 11, 2005 #14
    I am not challenging anyone here, but for what U say here U must answer to my post in the below thread, i promise U wont be dissapointed on the observation factor.

    Last edited: Mar 11, 2005
  16. Mar 11, 2005 #15


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    Regarding the origin of the Big Bang: It just seems reasonable to me to conclude the Big Bang arose as a phase transition, precipitating from some pre-existence. I base this, again, on the many examples of phase transitions I see in the world and how these transitions lead to qualitatively different states and thus I conclude the pre-existence was a qualitatively different state from the current state of the Universe.
  17. Mar 11, 2005 #16
    I read somewhere that the universe is 156 billion lightyears wide.


    Of course this is speculative.

    Also, light from the Hubble Ultra Deep Field was about 13 billion lightyears away when it started travelling towards us, but the distance to those galaxies nowadays is probably 3 times that, (I dont remember the exact numbers but i read this somewhere) because of the expansion.
    Last edited: Mar 11, 2005
  18. Mar 11, 2005 #17


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    That might be closer to right. Mine was a crude estimate of the radius, so if you double it, our numbers are only discrepant by a factor of 1.7 or so.
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