1. Standard membervivify
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    15 Jun '14 11:14
    What is causing the universe to expand?

    Also, for the universe to expand, wouldn't that imply that there's something larger outside of the universe? For example, a balloon can expand if there's more space outside of the balloon to expand in; doesn't this apply to the universe?

    Thanks for your inputs.
  2. Germany
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    15 Jun '14 11:38
    Originally posted by vivify
    What is causing the universe to expand?

    Also, for the universe to expand, wouldn't that imply that there's something larger outside of the universe? For example, a balloon can expand if there's more space outside of the balloon to expand in; doesn't this apply to the universe?

    Thanks for your inputs.
    What is causing the universe to expand?

    This is an active field of research. I don't know the details, but there are several theories that describe cosmic inflation and the current expansion of the universe.

    Also, for the universe to expand, wouldn't that imply that there's something larger outside of the universe?

    No. The expansion is self-contained.
  3. Standard membervivify
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    15 Jun '14 12:07
    Originally posted by KazetNagorra
    [b]What is causing the universe to expand?

    This is an active field of research. I don't know the details, but there are several theories that describe cosmic inflation and the current expansion of the universe.

    Also, for the universe to expand, wouldn't that imply that there's something larger outside of the universe?

    No. The expansion is self-contained.[/b]
    What do you mean when you say the expansion is self - contained?
  4. Standard memberDeepThought
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    15 Jun '14 12:10
    As Kazet said, the expansion does not require a space to expand into. Given two points in the universe what me mean by expansion is that the rule that gives us the distance between them is an increasing function of time.

    The dominant theory for a long time was that the expansion wasn't driven. There was the initial Big Bang and the universe has been increasing in size by coasting ever since. Measurements, however, indicate that the expansion of the universe is accelerating. This can be built in to Einstein's gravitational theories using a term in the equation called a cosmological constant - ironically Einstein first put this in to keep the universe static!

    There are a number of ideas about how a cosmological constant could come about, it should really be called a cosmological term since in most of these models it isn't a constant. Dark Energy is the catch all phrase to express it.
  5. Cape Town
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    15 Jun '14 12:38
    Originally posted by vivify
    What is causing the universe to expand?
    Dark energy. In other words, energy that we have not yet identified. It is possible that empty space has a certain amount of energy, so as space expands the total amount of energy in the universe goes up, thus causing accelerated expansion.

    Also, for the universe to expand, wouldn't that imply that there's something larger outside of the universe? For example, a balloon can expand if there's more space outside of the balloon to expand in; doesn't this apply to the universe?
    If you were on the surface of the balloon, you would not see it as expanding into something, you would always remain on the surface of the balloon, but points on the balloon would get further apart. The analogy is not perfect because the two dimensional balloon surface sits in three dimensional space whereas three dimensional space is not necessarily expanding in a four dimensional universe.
    Instead think of the cartesian plane, then try applying an enlargement to the whole plane. Everything gets bigger, and adjacent points move away from each other, but because the plane is infinite, it does not expand into somewhere else.
    I don't think it is known whether or not space if finite, but it does seem likely that it is self contained.
  6. Subscribersonhouse
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    15 Jun '14 16:33
    Originally posted by twhitehead
    Dark energy. In other words, energy that we have not yet identified. It is possible that empty space has a certain amount of energy, so as space expands the total amount of energy in the universe goes up, thus causing accelerated expansion.

    [b]Also, for the universe to expand, wouldn't that imply that there's something larger outside of the universe? ...[text shortened]... k it is known whether or not space if finite, but it does seem likely that it is self contained.
    But still, the universe seems to be actually growing larger, like right now you can peer back in time with telescopes to a bit under 14 billion years but since the universe has been and is still expanding faster than the speed of light, that means the real universe, the part we can NEVER see has to be several times as large as what we CAN see, maybe 100 billion light years across. I wonder what we would see if we had a spacecraft that could go a trillion times the speed of light? It seems likely we would come back to the place we just left as in the balloon surface analogy but that trip would probably be several hundred billion light years long. At a trillion c, you could do that whole thing in a few months🙂 Wouldn't THAT be a mind boggling voyage!
  7. Cape Town
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    15 Jun '14 17:271 edit
    Originally posted by sonhouse
    It seems likely we would come back to the place we just left...
    As I said, I don't think there is any evidence as to whether the universe is finite or infinite, and if it is finite, exactly how big it actually is.

    http://en.wikipedia.org/wiki/Universe#Size.2C_age.2C_contents.2C_structure.2C_and_laws
    The size of the Universe is unknown; it may be infinite.
  8. Standard membervivify
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    15 Jun '14 18:301 edit
    Originally posted by sonhouse
    But still, the universe seems to be actually growing larger, like right now you can peer back in time with telescopes to a bit under 14 billion years but since the universe has been and is still expanding faster than the speed of light, that means the real universe, the part we can NEVER see has to be several times as large as what we CAN see, maybe 100 bil ...[text shortened]... lion c, you could do that whole thing in a few months🙂 Wouldn't THAT be a mind boggling voyage!
    The universe is expanding faster than light? Doesn't that break the laws of physics? I thought c was sort of like the universal speed limit.
  9. Standard membervivify
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    15 Jun '14 18:30
    Originally posted by twhitehead
    Dark energy. In other words, energy that we have not yet identified. It is possible that empty space has a certain amount of energy, so as space expands the total amount of energy in the universe goes up, thus causing accelerated expansion.

    [b]Also, for the universe to expand, wouldn't that imply that there's something larger outside of the universe? ...[text shortened]... k it is known whether or not space if finite, but it does seem likely that it is self contained.
    Okay. Thanks so much for your help.
  10. Standard memberDeepThought
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    15 Jun '14 18:52
    Originally posted by vivify
    The universe is expanding faster than light? Doesn't that bresk the laws of physics? I thought c was sort of like the universal speed limit.
    Imagine a series of rulers each 1 light year long, initially laid end to end all the way to the edge of the observable universe. As space expands gaps will appear between the rulers. Suppose the rate of expansion is such that the gap increases by 1 light second every billion years (~1 foot per year). We sit at the centre of one of the rulers and look at particles that are at the centre of each ruler. The closest one will be moving away from us at a rate of 1 a foot per year, the next one at twice that rate, the one after that at 3 times that rate and so on. The most distant one at the edge of the observable universe (50 odd billion light years away) will move away at the speed of light. This produces something called a cosmological event horizon. Light from there can never reach us. It doesn't matter how fast it is moving relative to us since the region is causally disconnected from us. Relative to each other particles in that region all go slower than light. It is the space they are in that is "moving" faster than light, not the particles themselves.

    Note, be wary of the numbers in this - I haven't checked it all adds up properly!
  11. Standard membervivify
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    15 Jun '14 19:14
    Originally posted by DeepThought
    Imagine a series of rulers each 1 light year long, initially laid end to end all the way to the edge of the observable universe. As space expands gaps will appear between the rulers. Suppose the rate of expansion is such that the gap increases by 1 light second every billion years (~1 foot per year). We sit at the centre of one of the rulers and look ...[text shortened]... themselves.

    Note, be wary of the numbers in this - I haven't checked it all adds up properly!
    Excellent explanation. Thanks.
  12. Standard memberKellyJay
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    15 Jun '14 20:46
    Originally posted by KazetNagorra
    [b]What is causing the universe to expand?

    This is an active field of research. I don't know the details, but there are several theories that describe cosmic inflation and the current expansion of the universe.

    Also, for the universe to expand, wouldn't that imply that there's something larger outside of the universe?

    No. The expansion is self-contained.[/b]
    Expansion is self contained? It expands into itself? How does that work
    since when something expands it typically moves into previous areas it
    wasn't before?
    Kelly
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    15 Jun '14 21:08
    Originally posted by KellyJay
    Expansion is self contained? It expands into itself? How does that work
    since when something expands it typically moves into previous areas it
    wasn't before?
    Kelly
    Expansion is self contained?

    correct
    It expands into itself?

    what does that mean?
    How does that work
    since when something expands it typically moves into previous areas it
    wasn't before?

    but this is not 'typical' expansion i.e. not expansion like you would see on a smaller scale in your everyday life but rather a expansion on a much larger cosmic scale caused by space itself expanding thus, regardless of whether objects actually do move through space, no need for objects to move through space for this expansion happen (actually, whether something is moving depends on your personal chosen frame of reference because there is no absolute space -just hope you understand that! )
  14. Standard memberRJHinds
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    15 Jun '14 21:381 edit
    Originally posted by vivify
    What is causing the universe to expand?

    Also, for the universe to expand, wouldn't that imply that there's something larger outside of the universe? For example, a balloon can expand if there's more space outside of the balloon to expand in; doesn't this apply to the universe?

    Thanks for your inputs.
    Could Occam's_razor be applied here as it was with the following example from the wikipedia article?

    The motions of the sun, moon and other solar system planets can be calculated using a geocentric model (the earth is at the center) or using a heliocentric model (the sun is at the center). Both work, but the geocentric system requires many more assumptions than the heliocentric system, which has only seven. This was pointed out in a preface to Copernicus' first edition of De revolutionibus orbium coelestium.

    Occam's razor states that among competing hypotheses, the one with the fewest assumptions should be selected. Other, more complicated solutions may ultimately prove correct, but—in the absence of certainty—the fewer assumptions that are made, the better.

    The application of the principle often shifts the burden of proof in a discussion. The razor states that one should proceed to simpler theories until simplicity can be traded for greater explanatory power. The simplest available theory need not be most accurate. Philosophers also point out that the exact meaning of simplest may be nuanced.

    http://en.wikipedia.org/wiki/Occam's_razor
  15. Subscribersonhouse
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    15 Jun '14 22:56
    Originally posted by RJHinds
    Could Occam's_razor be applied here as it was with the following example from the wikipedia article?

    [b]The motions of the sun, moon and other solar system planets can be calculated using a geocentric model (the earth is at the center) or using a heliocentric model (the sun is at the center). Both work, but the geocentric system requires many more assumpt ...[text shortened]... hat the exact meaning of simplest may be nuanced.

    http://en.wikipedia.org/wiki/Occam's_razor
    And your conclusion based on all that?
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