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Universe expansion VS speed of light

  1. Oct 26, 2006 #1

    taylaron

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    is it possible that the reason why we think that the universe is expanding is because that the light from the objects in space (eg, stars, galaxies, planets. etc...) their light isnt reaching our planet untill a sertain point in time. so, we it takes time for the light to travel to our planet. possibly making them "appear out of thin air" possibly thinking the univese is expanding.
    am i right?
     
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  3. Oct 26, 2006 #2

    mathman

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    The main evidence for the expansion of the universe is the fact that light from distance galaxies is red shifted (Doppler effect), with the amount of red shift indicating that these galaxies are moving away from us at a velocity proportional to distance. This was first observed by Hubble in the 1920's.
     
  4. Oct 27, 2006 #3

    taylaron

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    right, i learned that in school,
    but dispite that fact, does this pose as any explination to anything along "my" lines??
    im simply trying to figure out what would be explained by my concept.
     
  5. Oct 27, 2006 #4

    selfAdjoint

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    I would say you are not even wrong. This "reason" makes no sense.
     
  6. Oct 28, 2006 #5

    marcus

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    over the next billion years, as time goes on, more and more galaxies will be seen because their light will have had a chance to reach us

    so what is called the "observable universe" (the part of the universe containing objects whose light has had time to reach us) is constantly becoming more POPULOUS. It contains more and more objects as time goes on.

    so in this sense you are correct-----because of light finite speed the observable universe becomes more populated, more numerous, more teeming with galaxies, with time. You could say that they "appear out of thin air".

    THIS EFFECT HAS NOT BEEN NOTICED YET because we have only been cataloging galaxies using decent telescopes for a few decades, so our observable universe is only a few tens of lightyears larger now than when we started. Improvement in telescope techology is much more significant in extending our horizon.

    But even though the effect has not been noticed, everybody knows it is going on.

    However THIS IS NOT WHAT IS MEANT BY EXPANSION.
    What astronomers mean by expansion is that DISTANCES BETWEEN THINGS ARE INCREASING.

    this is a totally different thing from what you are talking about (you are talking about there getting to be more galaxies we can see------astronomers are talking about distances between ones we can see are measurably increasing----they are measurably getting farther and farther apart).

    this is why your question does not make sense----you do not make a correct use of the word "expanding" as normally understood in cosmology.

    I agree with selfAdjoint----what you say is disconnected from talk about the expansion of the universe (i.e. "not even wrong"---just off in another direction)
     
    Last edited: Oct 28, 2006
  7. Oct 28, 2006 #6

    wolram

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    Marcus, (everyone knows whats going on)? i wish that were true, the fact is we only observe what we can (see), and the observers try to the very best of thier ability to decode thier observations, what we see is not the end game, not even the opening move, I see difficulties ahead for QLG, if i am right where do we go?
     
  8. Oct 29, 2006 #7
    When people hear about the universe expanding, it's a common misconception to think of a finite object increasing in size in a larger space. However what cosmologists mean by the universe expanding is that the things in it are getting further apart.

    What you are describing is our current particle horizon - the part of the universe from which signals would now have their first chance to reach us.

    Note however, that if we saw such signals, they would not be pictures of fully formed galaxies, but of the matter just after the big bang. We can't see that far back as the CMBR material gets in the way.

    Also, we are getting to the stage where we can see stuff almost all the way back to the origin of the galaxies so it's not a case of being able to see further into space. Eventually, if we want to see any new galaxies, we will have to wait for a billion years or so as they form out of the CMBR material.

    See my web page Cosmological Horizons for more information on horizons. You might also take a look at Expanding Confusion by Lineweaver and Davis
     
  9. Nov 5, 2006 #8
    It's a really good question.

    See answer at www.cosmictime.net. You can download a simulation of
    a paper I have in press in Physics Essays, Vol. 19, No. 4 (Dec 2006).
     
  10. Nov 5, 2006 #9

    taylaron

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    you are correct

    thanks marcus for correcting my use of expansion. i sould've thought of a better word to use. or something alon those lines.
    you all have explained alot to me. i do agree that we are just at the beginning of a long journey do discovering the universe.
     
  11. Nov 6, 2006 #10

    Chronos

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    If my recollection is correct, the inflation model proposes all objects in our observable universe were causally connected [i.e., visible to each other] in the 'beginning'?
    I object on grounds it suggests empty space expands faster than objects embedded in it.
    I would argue the effect has not been noticed because it does not exist.

     
  12. Nov 6, 2006 #11
    I read in "Science News" at one time that the opposite it true, i.e., that as time goes on, more distant objects that are visible now will no longer be visible. It struck me as odd, although I seem to recall figuring out why that would occur. But now I don't recall why. Any comments?
     
  13. Nov 7, 2006 #12

    Chronos

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    In the 'heat death' model of the universe, galaxies currently observable [to us] will eventually redshift and time-dilate into oblivion, but never pass some imaginary horizon and 'wink' out of existence. Nor will 'new' galaxies ever 'wink' into existence. Any new galaxies we observe in the future will evolve from progenitor masses already visible [at least theoretically] to us. This takes a very long time, so it is no surprise we do not observe such events.
     
  14. Nov 7, 2006 #13
    Reference please

    I was intrigued by what you said about the heat-death theory. Pretty interesting how we would be able to see less and less of the universe. Could you refer me to some book in which i would find reference to this stuff and have a better understanding of the theory.
     
  15. Nov 8, 2006 #14

    Wallace

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    The key question to ask in finding out particle horizons (how far away from us is the stuff we can see) is not so much that the universe is expanding (the first derivative of the scale factor) but whether it is accelerating (the second derivative). In an accelerating universe, which is what the current theory suggests we are in, particle horizons shrink as time goes on, so a galaxy we see now will, in the future, be invisble to us. If we lived for billions of years we would eventually no longer see the galaxy, even though it is still there.

    But the key point again is the fact that the universe is expanding dosn't tell you what will happen, you have to know whether it is accelerating, decellerating or 'coasting'. For more details see The Long Term Future of Space Travel (Don't be fooled by the whimsickle title, it's hard science).

    For a detailed look at what happens in expanding universes see either Davis and Lineweaver as suggested above or Joining the Hubble Flow a more recent paper that points out some flaws in Davis and Lineweaver.
     
  16. Nov 8, 2006 #15

    Chronos

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    I'm not aware of any books dedicated to the subject, but a number of relevant papers have been written:

    http://arxiv.org/abs/astro-ph/9701131
    A Dying Universe: The Long Term Fate and Evolution of Astrophysical Objects

    http://arxiv.org/abs/hep-th/0410270
    Spontaneous Inflation and the Origin of the Arrow of Time
     
  17. Nov 8, 2006 #16
    "distances between things" can be misleading.Yes expansion creates distance between things but so does peculiar motion.Of the two,the first is space moving and takeing objects with it.These are static objects said to be co-moving in expanding space.The second are objects moving Thru space. Well,thats my two cents!
     
  18. Nov 9, 2006 #17
    Now if the universe accelerates in its expansion, then everything accelerates away from everything else. And the Unruh effect says that with acceleration comes a thermal bath of particles. In other words, particles are observed for accelerating observers where inertial observers observe no particles. OK, so as the universe accelerates shouldn't we expect to see particles come into existence in thermal equilibrium? Wouldn't this be just another kind of Inflation phase where acceleration ended in particle creation?
     
  19. Nov 11, 2006 #18

    Chronos

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    Only local observers perceive the Unruh effect, and they see it only in passing. It is a horizon thing that has no objective reality.
     
  20. Nov 12, 2006 #19
    hi everyone, looks like a great site, with alot of smart people.
    hopefully i have the right thread, and i will try to make myself clear.

    ive been having an argument with a work mate, about when an actual event occures. arising from the unit of distance measure of LIGHTYEAR.

    my argument is this: that if an object a number of lightyears away, DOES NOT mean that that event occured that many earth years ago.
    you see all the time, quotes like: "this object is 2000 lightyears away" therefore it occured 2000 earth years ago.

    my opinion is: ALL EVENTS occur sometime in the past, AND (therefore) ALL EVENTS since the big bang are OCCURING NOW at some point in the universe.
    what we observe through our telescope is OCCURING NOW, (to us), but happend sometime in the past, (NOT x years ago).

    i dont think it is possible to view an object 13.5 billion lightyears away, that is 13.5billion years old. (earth years), because 13.5 billion years ago, the universe was not that large. (A paradox ??)..

    (if you ask the photon how long the trip took, or how far travelled, it would not have a clue what you are talking about, as time and space have no meaning to a photon {time dilation ?}

    so if you could send an atomic clock from the object you view (2000 LY away), and read the time elapsed (of the photon) you are views, it would read ZERO Seconds, and zero distance.

    does it make sense to say every event that has occured since (and including) the big bang IS happening NOW. and that you just have to be in the right place in the universe to experience it.
    (we can still view the big bang itself with CBR)

    thanks, all.
     
  21. Nov 12, 2006 #20

    Chronos

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    Agreed in the sense that simultaneity is an illusion. What happens here stays here . . . until observed by a remote observer. Most people get confused when they assume the clock strapped to their wrist is always right.
     
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