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Distance to Farthest Quasars

  1. Oct 13, 2006 #1
    I am just a layman who read that the farthest quasars (based on redshift) are about 13 billion light years away. Is that true?

    I also read that the age of the universe is less than 14 billion years and that the overall shape (from observations of background radiation) is that of a flat manifold.

    There seems to be contradiction or something that I am not understanding. :confused:
  2. jcsd
  3. Oct 13, 2006 #2


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    The light from the furthest quasars has travelled about 13 billion light years to reach us, but the quasars themselves are about 30 billion light years away at the present time (remember, the universe has expanded since the light left the quasars).

    The part of the universe we can see is consistent with being flat and about 13.7 billion years old.

    Where do you see a contradiction?
  4. Oct 14, 2006 #3
    I assume that the big bang started with all of the astronomical objects condensed in the same place (singularity) at the same time. How could they possibly travel so far in such a short time (13.7 billion years)?
    Last edited by a moderator: Oct 14, 2006
  5. Oct 14, 2006 #4


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    Google or wiki on Inflation. And remember that the distance grows without the objects travelling. Besides which, they didn't exist at the singularity or for a long time after it. First the universe was opaque, then the particles condensed, and then,.... Oh well, read up on it instead of trying to imagine what it says.
  6. Oct 15, 2006 #5
    I understand that. However, I thought that the distance between 2 objects could not increase at rates greater than c even when the expansion of space itself is considered. I was about to commit heresy by saying that the universe could be much older.

    On that note, is there a way to know how this rapid expansion of the manifold would affect the electrical permitivity and magnetic permeability of free space? I am now curious because I think that this would affect the speed of light along with other subsequent parameters such as the planck length.
  7. Oct 15, 2006 #6
    The speed of light is defined as "299,792,458 meters" / "9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom" or "1 meter" / "30.663319 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom". If the electrical permitivity and magnetic permeability of freespace were greater in the past, what would happen to relative permittivity and relative permeability? What about subatomic and brownian motion? Wouldn't that slow down? Wouldn't everything slow down? Maybe we wouldn't notice it even if we were in it! What if it appeared to us as time dilation and nothing more? If that's the case, we wouldn't say that the permittivity and permeability of free space were greater, we would claim that we've discovered time dilation of distant objects and would explain it through general relativistic effects...
    Last edited: Oct 15, 2006
  8. Oct 16, 2006 #7


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    It is easy to picture how expansion has no effect on P&P. If, as Einstein did, you assume there is no 'aether', attempting to ascribe 'it' properties is an exercise in futility.
  9. Oct 16, 2006 #8
    I am no expert on cosmology and I did not mention or intend to imply anything about 'aether'. However (assuming you are referring to free space):

    1. The electrical permittivity of free space has a distinct value which is different from that of many dielectric materials.

    2. The magnetic permeability of free space has a distinct value which is different from that of many ferromagnetic materials.

    Based on these facts, how can electrical permittivity and magnetic permeability not be considered properties of free space? :confused:
    Last edited by a moderator: Oct 16, 2006
  10. Oct 17, 2006 #9


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    They could be ascribed to Eistein's replacement for the classical aether - the gravitational field. Permittivity and permeability reside on the spacetime manifold, whereas gravity is the spacetime manifold.
  11. Oct 17, 2006 #10
    I was never a physics major but I always thought that what we call gravity was curved spacetime due to the mass/energy and momentum flux.

    I started this thread was because I was surprised by how rapidly astronomical objects appeared to be drifting away from each other. I was initially predisposed to conclude that current science may have either overestimated these distances and/or underestimated the age of the universe. Although this would still account for the red shift and the CMB, I decided to follow the explanation (that spacetime was expanding) which was given to me. I understand expansion to mean an increase in size, scale, or dimension. My next question was that if spacetime was changing in size or scale, then what else about spacetime could be changing. This line of thought led me to consider the electrical permittivity and the magnetic permeability of free space.

    I am now told that electrical permittivity and magnetic permeability are not properties of free space. However, the descriptive nature of these nouns implies that they are not free standing entities and that they must be the electrical permittivity and magnetic permeability of something. If not of free space/space/spacetime, then of what?

    However, I will follow this explanation for now and assume that these values along with planck length and planck time cannot be changed. This forces me to conclude that the expansion of space between 2 objects can only manifest itself as an increase in the number of planck lengths that separate them. I must also conclude that when 2 objects are moving apart, then the number of planck lengths between them is also increasing. This leads me to the inevitable question:

    What is the fundamental difference which distinguishes the expansion of space between 2 objects (number of planck lengths between them increasing), and relative motion of 2 objects away from each other (number of planck lengths between them increasing)?
    Last edited by a moderator: Oct 17, 2006
  12. Nov 30, 2010 #11
    One of many differences is that if the two objects are moving away from each other at more and more rapid speeds without spacetime expanding then they the two bodies or at least one of them is accelerating. If the space inbetween them is expanding they do not have to be accelerating and will still grow further from each other. If you're asking acceleration relative to what, look up newton's bucket. It may help provide an answer better than I can explain
  13. Nov 30, 2010 #12


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    It's a good question---what's the most distant quasar detected so far, or galaxy for that matter. The original poster is not around to talk to, but others might be reading and want to know.

    The current most distant galaxy is at redshift 8.6. It was reported in October 2010.

    If you want to translate a redshift into lightyears, google "wright calculator" or "cosmo calculator"

    You just type 8.6 into the box and press "general".

    It will give several measures, one is the light travel time, how long it took the light to get here. For redshift 8.6 the calculator will say that the light took 13.1 billion years. Or equivalently, that the light got started when expansion was 0.6 billion years old. We see the galaxy as it was when the expansion age was 600 million years.

    The next thing it gives, in the line below that, is the "now" or "freezeframe" distance which you would measure if you could stop expansion at this moment---make everything hold still---and measure by any conventional means, radar, yardsticks, tapemeasure... As it says there, this is the distance that is used in stating the Hubble law.

    The galaxy they found had just barely formed. Hadn't had time to develop into a quasar. To become a quasar you need time to accumulate a massive central black hole. The farthest galaxies we see are still in their early stages.

    In my signature to this post I have a link to another equally good calculator Morgan's "cosmos calculator".
    It gives the rates of distance increase, at two separate epochs (when the light left on its journey to us, and when it arrived).
    To use that one you need to first type in three numbers (.27, .73, and 71) which are the parameters of the standard universe model. But then it should give the same "freezeframe" distances, and light travel times, plus a little extra information
    Last edited: Nov 30, 2010
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