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Expansion of universe/what rate?

  1. Aug 8, 2011 #1
    I was watching a science program explain how once we discovered the Universe was expanding, it was a "simple" matter to imagine it rewound; and, to reach the "obvious" conclusion that it must have started from a single point. It went on to explain that the universe expanded to the size of an orange in one trillionth of one trillionth of a second. After 100 seconds the universe had expanded to several thousand light years. Oh, really?

    How did the universe expand to several thousand light years in 100 seconds if the speed of light is the velocity limit for anything and everything? And if you call this a "singularity" isn't that just a cop out word and a confession that we don't really know what is going on?

    Or, is popular science programs on television just misinformed? Many of them feature prominent physics such as Dr. Michio Kaku or Steven Hawlings.

    So, did (and/or) does the universe continue to expand at a velocity greater than that of the speed of light? I think physics is a total zoo right now- and apparently some of the theories have escaped and are running wild on television shows.

    But, if the universe is expanding faster than the speed of light and the expansion is accelerating, then it would appear that if we pointed our telescopes out to the visible edge, we might be able to detect a galaxy whose speed away from us is at a threshold. At some point it should "blink out", as it accelerates and overcomes the speed of light. Is that an observation that is technically possible?
     
    Last edited: Aug 8, 2011
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  3. Aug 8, 2011 #2

    Chronos

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    There is always a catch, GR only forbids matter from moving at superluminal velocity, it does not forbid the vacuum from expanding at any speed it pleases. Just because particles are being distanced from one another faster than light does not mean they are actually moving with respect to their own local reference frame.
     
  4. Aug 8, 2011 #3
    Fair enough, the universe (space and time I guess) expanded, continues to expand, and in fact, accelerates faster than light. So if that is true, what is the rate of expansion? Can it be measured, or even calculated, from known facts?
     
  5. Aug 8, 2011 #4
    (Sorry, I was writing this and you posted another before I could get this to post.)

    That doesn't matter(haha), there is no such thing as an intrinsic frame of reference whatsoever. There are only relative frames of reference. No entity with mass can appear to move at the speed of light, much less faster, from any frame of reference.
    It is not technically possible for anything to blink out that way.
    I've wondered the same things, Lorentz T. If a star is at the edge of expanding space, it must be emitting light away from us. I've now read a couple of times that the diameter of the universe is 42 billion light years.
    I just know that nothing can blink out because it reaches and then exceeds the speed of light because that is impossible according to special relativity. Its light will become extremely red shifted, that's all I know.
    AFAIK, inflation - the period of expansion that was faster than light - stopped when matter condensed, which means that nothing was moving apart faster than, or exactly at, the speed of light anymore, so that everything was observable, and that can't have changed.
    Yeah, just thinking, how could there be anything that we couldn't theoretically observe? Can there be anything but the observable universe?
     
  6. Aug 8, 2011 #5
    That's the diameter of the observable universe. Who knows what is beyond that, probably a lot more of it. The observable universe is a special subregion of the universe, in the sense that we are at the centre. So the edges of this observable region are no more special than the Earth's location (ie. not special at all and totally arbitrary from a purely physical perspective).

    Lorentz. T: the expansion can be measured using some complex methods, observing redshifts of various astronomical objects and comparing that to other data from them (eg. angular diameter, intensity of light). But you can't compare expansion to the speed of light. Expansion has different units. It is the speed at which two points 1m away will separate, so its units are s^-1. Two points 2m away will move away at twice this speed. The expansion is uniform in space, and only varies with time.

    To say "the universe is expanding faster than the speed of light" is inaccurate. From where you stand, there are numerous nearby objects whose movement away from you, due to cosmic expansion, is far less than the speed of light (eg. me, the sun, and the Andromeda galaxy). But if you go far enough away, there will be objects which are moving away from you faster than the speed of light (because expansion is uniform, the further you go away, the faster the recession). The line, or 'shell', dividng these two regions is the boundary of the observable universe, because once something is going away from you faster than light (due to expansion!), you can't observe it anymore. In a sense the amount of new space being generated between you and these objects increases faster than the light can travel.

    Hope this helps,
     
  7. Aug 8, 2011 #6
    Thanks mikmik, then I would want to know what is it about the condensation of (or to) matter that put the brakes on expansion or at least the incredible rate of expansion of the early universe?

    And let's assume the diameter of the universe is 42 billion light years as you read. How does that square with the accepted age of the universe of 13 billion years?
     
    Last edited: Aug 8, 2011
  8. Aug 8, 2011 #7

    phinds

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    it's been expanding for 13 billion years and due to the expansion the observable universe is now much bigger than 13B light years. The light we see at the edge of the observable universe was emitted 13Billion years ago but the objects that emitted it were, and still are, moving away from us.

    Local clumps of matter such as solar systems, galaxies, and galactic clusters are gravitationally bound and they remain together as a unit
     
  9. Aug 8, 2011 #8

    phinds

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    By the way, most popular science programs are not exactly misinformed, they just tend to be sensational and present ideas that are on the fringes of actual science as though they were things that are going to happen tomorrow. Dr. Kaku is particularly guilty of such sensationalism. He was an outstanding physicists at one time but he is now a popularize of the worse sort, making misleading statements about the likelihood of some things occurring in the near future. He was trashed pretty badly in a thread here a couple of months ago.

    Some programs, such as "Through the Wormhole" actually make statements that are absolutely incorrect and blatantly so. The most recent example that I saw was a serious misrepresentation of entanglement in which they had Morgan Freeman saying that it is possible to transmit information faster that the speed of light.
     
  10. Aug 8, 2011 #9

    Chronos

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    For discussion on ftl recession velocities, see:
    http://curious.astro.cornell.edu/question.php?number=575 [Broken]
     
    Last edited by a moderator: May 5, 2017
  11. Aug 8, 2011 #10
    The Hubble constant , the expansion rate of the universe, is currently ~74 km/sec/megaparsec. The "condensation" of matter was not what put the brakes on inflation. Inflation stopped because the negative pressure vacuum energy density, the "inflaton field", that drove inflation dropped below a certain level. These articles will explain:

    http://en.wikipedia.org/wiki/Hubble_constant
    http://en.wikipedia.org/wiki/Inflation_(cosmology [Broken])
     
    Last edited by a moderator: May 5, 2017
  12. Aug 8, 2011 #11
    Chronos

    The link you posted is saying that some distant galaxies are moving away from us faster than the speed of light... well here it is:

    "perhaps more surprisingly, some of the galaxies we can see right now are currently moving away from us faster than the speed of light! As a consequence of their great speeds, these galaxies will likely not be visible to us forever; some of them are right now emitting their last bit of light that will ever be able to make it all the way across space and reach us (billions of years from now). After that, we will observe them to freeze and fade, never to be heard from again".

    September 2003, Dave Rothstein
     
  13. Aug 9, 2011 #12

    Drakkith

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    Lorentz, the galaxies are moving away from us faster than c, yes. However in their own local area of space they are NOT moving faster than c. The effect is due to the expansion of spacetime. At such huge distances the small amount of expansion per meter of space adds so many times that the galaxy is "riding the expansion" faster than c away from us. Its velocity THROUGH space is not faster than c.
     
  14. Aug 9, 2011 #13

    Chronos

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    Er, did I mention this was a discussion of ftl [faster than light] recession velocities?
     
  15. Aug 10, 2011 #14

    chasrob

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    At some point over the last year I glanced over a paper at arxiv (unknown date:not about the steady-state universe) that stated that space was "created"; it doesn't actually expand elastically. I can't turn up the reference. Anyone remember anything about this?
     
  16. Aug 10, 2011 #15

    phinds

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    I don't know specific references but from what I have read I believe that yes, it is created, it does not "stretch" although given the weirdness of what seems to happen, I'm not sure that this distinction is more than semantics. (I DO understand that the words don't mean the same thing at all.)
     
  17. Aug 10, 2011 #16

    chasrob

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    Yes, its difficult to understand, though the scientist/author was adamant--it was created, not stretched. My guess is that its like someone blowing up a balloon--space is forced into a region. Since space is composed of fields, it happens at every point in the region.
     
    Last edited: Aug 10, 2011
  18. Aug 26, 2011 #17
    I am drawing a conclusion now. My conclusion is that there is nobody living on Earth today who has the slightest idea of what the universe is, much how it was created and where it is going. I think it is time for me to go back to inclined planes and pulleys.
     
  19. Aug 26, 2011 #18

    Drakkith

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    Nonsense. We can easily see what is happening with the universe and make logical decisions about what happened in the past based on our current understanding of the laws of nature.
     
  20. Aug 26, 2011 #19

    phinds

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    Uh, dude, this is the kind of crap post that can get you banned here. The mods are touchy about this kind of nonsense. The is a serious physics forum.
     
  21. Aug 26, 2011 #20
    OK, fair enough. But I am not talking crap. I admire all of you who are rigorously seeking the truth. But I think so many theories are so speculative that they stray into at best, metaphysics, and at worst fantasy. I am not a physicist. I am an engineer. I may have wandered too far into unfamiliar waters. But when I read how nonchalantly it is accepted that the universe is expanding faster than the speed of light, for me, it was the right time to go back a few spaces.

    Good luck in your quest gentleman. Maybe in a few years I'll revisit the sight and see what develops. But before I leave, I would like you to understand this: a challenge to a way of thinking isn't nonsense or crap- it is simply a challenge.
     
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