1. Subscribersonhouse
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    24 Jan '09 12:43
    About something he calls 'dark flow', where clusters of clusters are moving independently of the rest of the universe and at a group velocity way above anything in our present day understanding of how these clusters can move in one direction in aggregate. There are multiverse theories galore presented here to account for this new discovery. If confirmed, which has already been done twice by independent teams but more work is going on about this new discovery, it would be on the order of the discovery of galaxies a few decades ago. The article is very interesting in itself but the comments at the end of this long piece is just as interesting, very interesting links to alternate theories about this and a very good discussion by the posters, with of course the usual ad hominems but not as much as usual. All in all, an A+ piece.:
    http://www.newscientist.com/article/mg20126921.900-dark-flow-proof-of-another-universe.html?full=true
  2. weedhopper
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    15 Feb '09 19:521 edit
    Very interesting. But that last part, how the universe is 13.7 billion years old, yet the farthest object we can (could?) observe is 45 billion light years away? because of the constant expanding of the universe throughout it's lifetime?? AAggghhh! I can't get my head around itπŸ™„
  3. Germany
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    15 Feb '09 20:27
    Interesting, I have an oral exam in cosmophysics in a few weeks so we'll have something to discuss. πŸ˜‰
  4. Standard memberScriabin
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    23 Feb '09 21:17
    Interestingly, according to modern astronomers, space is finite. This is a very comforting thought-- particularly for people who can never remember where they have left things.
  5. Subscribersonhouse
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    24 Feb '09 04:19
    Originally posted by PinkFloyd
    Very interesting. But that last part, how the universe is 13.7 billion years old, yet the farthest object we can (could?) observe is 45 billion light years away? because of the constant expanding of the universe throughout it's lifetime?? AAggghhh! I can't get my head around itπŸ™„
    The thing to remember is the BB theory says there was a period, very short time frame, where the infant universe went from basically a dot the size of a proton (MaybeπŸ™‚ to something the size of a basketball in something like 10E-34 th of a second. Whether that happened for real is still being debated and other theories say maybe not, but the rest of the expansion is going faster than the speed of light even if it is not as fast as it was in the beginning, assuming the BB theory is correct, of course. Remember, space itself does not follow the same rules as matter, space can expand and contract a lot faster than matter because there is no mass involved. So in the past 14 odd billion years the actual size can be 45 billion Light years across, making the average expansion about 3 times the speed of light. So there are parts of the universe people will never see because it is beyond the light horizon. Only if you can exceed the speed of light someway or another could you actually visit the outer parts of our universe.
  6. weedhopper
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    24 Feb '09 05:06
    Well, is there any theory that light may not always have traveled at the speed it does today? I think some scientist named Guth was lecturing on inflation theory and brought that up on one of the science shows.
  7. Cape Town
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    24 Feb '09 11:42
    It must be noted that even if the universe expands at 3 times the speed of light that does not in any way equate to traveling faster than light, nor does it mean that when looked at on a small scale that expansion is taking place faster than light.
    If you have a long rubber band and it is stretching at say 1cm per metre per year, if the band is long enough the ends will move away from each other faster than light. This is not possible for an ordinary object in space time, but when it is space itself that is expanding then it is possible.
  8. Standard memberScriabin
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    24 Feb '09 17:59
    glad you introduced the rubber band concept.

    always thought we had only two outcomes to the universe:

    1. the big crunch -- you let go of the rubber band when it won't stretch any further and it snaps back in on itself;

    2. the big freeze -- the rubber band won't expand any more because it has lost its elasticity, everything burns out, and things just sit there quietly, too far from each other to either get back together or even make enough players for a bridge game;

    Now I read about something new being kicked around:

    3. the big rip -- the rubber band keeps expanding, but stresses build up as dark energy within the rubber band become proportionally greater the thinner the rubber band gets -- so the whole thing tears apart and all you have left is anyone's guess.

    Gee, thanks NASA, made my day there.
  9. Standard memberDeepThought
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    24 Feb '09 19:06
    Originally posted by Scriabin
    glad you introduced the rubber band concept.

    always thought we had only two outcomes to the universe:

    1. the big crunch -- you let go of the rubber band when it won't stretch any further and it snaps back in on itself;

    2. the big freeze -- the rubber band won't expand any more because it has lost its elasticity, everything burns out, and things ju ...[text shortened]... tears apart and all you have left is anyone's guess.

    Gee, thanks NASA, made my day there.
    The analogy with rubber bands has some weaknesses. Space-time doesn´t get thinner or snap. For one thing space-time is static in the big rip scenario - what happens is that geodesics diverge from one another. Locally nothing moves faster than light, but because the geodesics diverge things can end up moving faster than light relative to one another because of the global geometry. The reason for the rip is that the rate of divergence of geodesics becomes so huge that even a small seperation is enough to overcome attractive forces between particles. It´s a speculative theory and is probably not going to happen.

    In the Friedman-LeMaitre-Robertson-Walker model (relevant in this epoch) space-time actually is expanding because there is a time dependent scale factor. Space-time does not get thinner or snap in this scenario either, it´s not like a rubber band in any material sense.
  10. Germany
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    24 Feb '09 19:13
    Originally posted by twhitehead
    It must be noted that even if the universe expands at 3 times the speed of light that does not in any way equate to traveling faster than light, nor does it mean that when looked at on a small scale that expansion is taking place faster than light.
    If you have a long rubber band and it is stretching at say 1cm per metre per year, if the band is long enou ...[text shortened]... rdinary object in space time, but when it is space itself that is expanding then it is possible.
    I don't understand how this results in speeds larger than c, care to elaborate?
  11. weedhopper
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    25 Feb '09 04:15
    Aha! The Universe episode I was refering to was just on the tube. The moderator pointed out that only one thing could break the law of speed limit of the speed of light, and that is the expansion of space itself. Apparently space can expand faster than the speed of light.

    Now, what that means to physics, metaphysics, astrogation, or religion, I don't know. But it sure sounded cool.
  12. Subscribersonhouse
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    25 Feb '09 04:532 edits
    Originally posted by KazetNagorra
    I don't understand how this results in speeds larger than c, care to elaborate?
    Just remember, if you strap a rocket to your asss, all the energy of the universe, if you could do that, would not get you even TO the speed of light, much less exceeding it, just extremely close, and what really happens is you make your own 2 dimensional world where you are flatter than a pancake, even though you don't feel it and time goes by inside your craft but the outside world has a different time flow and from their viewpoint, they think you are now immortal, till you slow down to sub relativistic velocities.

    Now the idea that distant parts of the universe is separating 3X faster than light just means that space is in some sense 'thinning out' even though it has been pointed out that is a limited analogy.

    If you imagine two treadmills that are close together but going in opposite directions and stuff is on both treadmills, the parts will separate but there is no acceleration of the parts, the treadmill is like space, the distance between parts gets greater with no acceleration of the matter at the two distances.

    It's almost like space is being 'pumped' in between each atom at the same time, and gives the effect like I mentioned with two treadmills going in opposite directions. As far as the boxes on the treadmils are concerned, they have had no energy added in terms of kinetic energy but they are still separating in distance.

    In fact, if you had a billion light year long cord, and had it hooked up to a generator where each end has a large mass, and you have a lot of cord left over, you could in theory generate energy by the simple fact that the cord is being pulled apart, therefore if you resist the unwinding by hooking it to a generator you would get free energy thanks to the expansion of the universe.

    The concept of a variable speed of light has been debated also and so far not much change is seen from 10 billion years ago to today, but even a tiny shift would be seen as new physics in action. News at 11πŸ™‚


    I saw a talk given by Guth a few decades ago and I asked him that same question about exceeding the speed of light, I had used his figures of starting out as essentially a point source and expanding to something say the size of a football (now there is debate over that footballs' shape) in I think it was 10E-34 second. I did a quick calculation and during Q&A I told him that came out to an expansion 22 orders of magnitude greater than the speed of light and he responded and I quote " You did your arithmetic right" and then went into how it was space expanding taking matter with it which IS allowed, space does not have a speed limit.

    Of course all that said and done, it has not been absolutely proven that his inflationary theory is correct, it just takes care of most of the observations made on how the universe is actually behaving, where for instance, the MBR (microwave background radiation) is so almost perfectly smooth across the sky, to within one part in 100,000 or so, that could not happen if things had just popped out of the universe at even the speed of light, one side of the sky would start accumulating huge differences because photons or other forms of energy would not have enough time to interact so everthing in the universe would have been independent of one another which is in fact what we do NOT see, so inflation solves that conundrum.

    Whether something else comes along that solves the same problems without requireing that kick start is another story. That's what the alternative theories about the variable speed of light is supposed to address, the idea that light went a lot faster in the early days of the universe would also account for the same observations we see today. Problem with that is as best as can be determined as of this date, no such change has been seen. So inflation so far wins by default.

    The universe expands faster than the speed of light but matter doesn't care because it has not been given direct kinetic energy to do so like two planets separating because a big rocket was installed on each planet and they separate because of the added kinetic energy, that's the difference.
  13. Cape Town
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    25 Feb '09 06:20
    Originally posted by KazetNagorra
    I don't understand how this results in speeds larger than c, care to elaborate?
    The speed of light is approximately 3 x 10^8 m / s.
    If space were expanding at the rate of 1cm / metre per year.
    Then the expansion per light year is approx 3 x 10^6 m / year.
    If we take a year to be approx 3 x 10 ^ 7 s then expansion per light year is 0.1 m / s.
    So over 3 x 10^9 light years the two ends will be traveling away from each other at the speed of light.
    So if our universe is larger than 3billion light years (it is) then and expansion of 1cm/m per year would result in some parts moving away from each other at greater than light speed.

    Does anyone know what the approximate expansion is?
  14. Subscribersonhouse
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    25 Feb '09 08:34
    Originally posted by twhitehead
    The speed of light is approximately 3 x 10^8 m / s.
    If space were expanding at the rate of 1cm / metre per year.
    Then the expansion per light year is approx 3 x 10^6 m / year.
    If we take a year to be approx 3 x 10 ^ 7 s then expansion per light year is 0.1 m / s.
    So over 3 x 10^9 light years the two ends will be traveling away from each other at the s ...[text shortened]... m each other at greater than light speed.

    Does anyone know what the approximate expansion is?
    You can tell by the size of the estimate they give, 45 billion light years across as the size of the actual universe and the part we can see is only 13.7 Billion LY at most, so just divide the two, comes out at about 3 times the speed of light. 3.28X and change. I don't think it's any more complicated than that.
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    25 Feb '09 08:39
    Originally posted by sonhouse
    You can tell by the size of the estimate they give, 45 billion light years across as the size of the actual universe and the part we can see is only 13.7 Billion LY at most, so just divide the two, comes out at about 3 times the speed of light. 3.28X and change. I don't think it's any more complicated than that.
    Where do the 45 billion of light years come from?
    Is it across the 3-dim universe or across the 4-dim? Is the curvature accounted for?

    I think it's more complicated than that...
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