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Another B.Forums blooper: It grows at the speed of light

  1. Aug 24, 2003 #1


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    another B.Forums blooper: "It grows at the speed of light"

    Wolram said:
    if our universe is finite what is it bounded by?
    best wishes.

    B.Forums replied:

    Bounded by the speed of light. It grows at the speed of light.

    B.Forums is a wonderful stimulus because he says one wrong thing after another in a blithely confident, firmly authoritative tone of voice.

    By the U "growing" is meant the expansion of space, the increasing distances between galaxies---local movement discounted

    Lots of PF folk have seen Lineweaver's article, I know, and some have mentioned printing it out. In particular we've used Figure 1 of that article as a reference several times. So I take it as known.
    You can see just by inspection from that figure (similar to some at Ned Wright's cosmology site but more carefully drawn) that the light from
    anything we see at redshift 3 or greater
    was emitted when the thing
    was receeding from us at faster than c.

    (because the redshift 3 curve is entirely outside the hubble sphere as drawn in the figure)

    Well quasars with redshifts like 6.4 have been observed and there are scores of objects observed with z greater than 3

    So there are scores of objects you can see whose light left them when that object was receding faster than c. It really is routine. sorry. And that light, even though it was headed towards us, was originally swept backwards in the general expansion and the distance to that packet of light was actually INCREASING for a while even tho it was headed towards us. And finally it overcame the expansion and got here.

    This is not my story. This is standard contemporary cosmology and there are a bunch of good web references. I recommend printing the whole Lineweaver article, all 34 pages, because the guy knows how to communicate clearly better than anyone except maybe Ned Wright

  2. jcsd
  3. Aug 24, 2003 #2
    Marcus - I apoligize but I've had to use the report button a few times, and I'm sure others have. I definetely consider this a personal attack and have asked that it be removed. I would think one who is so sure of themself would rather teach someone else than attempt to attack them.
  4. Aug 24, 2003 #3


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    Oh yeah, I forgot to say----B.Forum is WAY out to lunch.
    He claims the U expansion is "bounded by the speed of light" that is,
    it only expands at the speed of light

    and when cosmologists talk about expanding they dont mean the "radius" as you normally understand it because an infinite thing may not have a welldefined radius

    the distance scale that expands is better thought of as the "average distance between galaxies" it is actually a scalefactor built into the spatial part of the metric but it is pretty common to say "average distance between galaxies" as an intuitive handle

    So think of an infinite (thats the simplest) expanding space

    BForum is trying to say that the greatest possible recession speed is the speed of light!!!! No way guy. Points in space are receding much much much faster than that, and have been for as long as space has been expanding.

    Most of the space we can observe is receding far more rapidly than c.

    Many of the objects we can observe were receding faster than c at the very moment that they let loose the light that is now reaching us.

    General relativity is very different from the 1905 "special" relativity according to which objects in the same room of your house cannot move relative to each other faster than c. Special relativity does not apply, surprise surprise, at large scale. So in GR, which has been around since 1916, distances can grow at rates greater than c. Where have we been for the past 97 years since 1916? There are still people who think expansion of U is limited by c.

    If you did not know this before you can read it from Lineweaver's figure 1. His is the closest thing I know to a general audience readable exposition.
  5. Aug 24, 2003 #4
    I am attempting to find someone who can explain why I am wrong. I am in no way claiming I'm right. However, because of your personal attacks I don't find myself interested in reading your posts on the matter.

    If someone else wants to seperately explain I would be happy to learn. But with the attitude that you need to create columns degrading people for not knowing something is really poor on your part.
  6. Aug 24, 2003 #5


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    Now you are beginning to sound reasonable. In previous threads you were going against mainstream science in a blithely cocksure tone of voice.

    I think it is fine if you want to voice unorthodox opinions---I am all for it. But please drop the misleading tone of authority. It confuses people---they may be taken in by it.

    Obviously you have an extremely idiosyncratic personal conception of the big bang and the expansion of space. If you want to persist in that, this is fine with me and I believe everyone. We will just have fun arguing with you. This is a very open place.

    If you want to learn more orthodox cosmology there are lots of people here who will coach you---many willing and enthusiastic teachers abound. IF YOU ARE OPEN TO LEARN.

    Btw, have you printed out Lineweaver's article yet? If you are allergic to formulas then read what he says in between the formulas.

    Until 2003 the absolute flat-out best communicator in cosmology was Ned Wright (check his website out!) but Lineweaver is even better.

    Cosmology is blessed with some authentic world class authorities who really know how to draw diagrams and explain stuff. Maybe the revolutionary change in the past 3 or 4 years stimulates them to better than average communication skills. for whatever reason, take advantage! Dont read anything prior to 1998.
    Last edited: Aug 24, 2003
  7. Aug 24, 2003 #6


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    you say you are attempting to find someone to explain why you are wrong.

    What particular thing is it that you have said that you would like to have explained why it is wrong?

    I would be happy to explain why it is wrong, just tell me!
  8. Aug 24, 2003 #7
    Sorry Marcus but with your previous actions I'm no longer interested in recieving information from you. If you remove this column yourself and continue the discussion in the normal column (the need to create a column to single a user out isn't nice at all) I will certainly listen to you. Until then I am unable to. I've also asked the section moderator to do it, anyway it is done I will continue.
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