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Why do we live in a Friedmann universe?

  1. May 17, 2006 #1


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    You may have heard people say that we live in a Friedmann universe. Why do they say that instead of saying "deSitter universe" or "Lemaître universe"

    didnt these other people also come up with an expanding universe solution to Einstein's 1915 equation?

    all these various universe you hear about are just special solutions to the Einstein Equation of Gen Rel.

    I don't happen to know the historical details so maybe someone can sort it out for us and explain.

    I don't think Friedmann had connections. Maybe he was just better looking than the other guys. There is a picture of him on that biography webpage I put a link to.

    It is possible that he has precedence because he found out MORE than the other guys. Or maybe he was the one who wrote down a particularly beautiful EQUATION (called the "Friedmann equation") which is a child ot the 1915 Einstein Equation and involves an elegant simplification that makes it easy to solve which the Einstein Equation is not. Or maybe he is more famous than them because he devised a DISTANCE FUNCTION, called the "Friedmann metric", for using in that universe.

    Or maybe the other guys actually did all that too, with the simplified equation and the metric, and history is simply unfair to them.

    In any case the date for Alexandr Friedmann finding his universe is 1922 and he was living in Saint Petersburg, Russia (which happened to be called something else at the time)

    if anybody wants to take the trouble to give us the full story on this it would be good

    I like George Lemaître because he went to Rome one time for the express purpose of telling the Pope not to confuse the singularity of his theory with anything to do with creation or God. Singularities do not exist in nature. A singularity is a place where a theory fails to compute, so it is a purely manmade thing in a manmade theory. Singularities often go away as theories get improved. Well George Lemaître was a serious Roman Catholic so he was quite embarrassed when he heard people confusing his singularity with creation or some other act of God.
    He requested an audience with the pope and advised him not to mix things up like that. the pope agreed and made an official statement soon afterwards saying people should not mix up theology with big bang theory, which seems like what a sensible pope should say. So George Lemaître is admirable and very much OK too. But for some reason Friedmann just slightly takes precedence. Or is it just alphabetical order?
  2. jcsd
  3. May 17, 2006 #2
    Probably because no one got it right completely!
    de Sitters universe was static and empty. As soon as he put even the tiniest pece of matter in it the whole thing collapsed! so he does not get the glory.
    Le Maitre took Einsteins equations and removed the cosmological constant. That is all. So how can he get the glory for proof reading someone else's theory? Besides, do you really believe all that about:
    Me thinketh he protesteth too much!
    That leaves friedman. He was the one who realised that it was space itself that was expandng and therefore the man of the moment.
    Unfortunately he 'caught cold ' and died.
    Dying is not good for a scientist. it leaves the field open for others to promote ones theories and claim them as their own.
    The reason we do not have a Friedmann universe is that Friedman caught a cold and died.
    Any up and coming scientists out there - keep healthy!
  4. May 17, 2006 #3


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    George Lemaître , is my kind of guy, but Marcus i am sure (all) theese mathmatical models are only a human concepts and that the best cosmo
    rulers are made of jello.
  5. May 17, 2006 #4
    why because he wore a frock?
    Einstein told him that his physics was all wrong!
    Lemaitre had as preconceved programme - creation!
  6. May 17, 2006 #5


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    Take as an example an aircafts wing, (if) math is such a powerful tool it
    (should) be able to design the wing, but tell me if i am wrong, there has never been an aircraft wing that has been designed with (only) maths.
  7. May 17, 2006 #6
    Yep, you are wrong.
    As a point of fact, "during the war" Friedmann mathematically, worked out bomb trajectories and he tested his theories on the Austrians by droppng bombs on them!
    Fredmann held the record for the highest balloon ascent.
    Without mathematics we are nothing!
    Quote - ratfink.
  8. May 17, 2006 #7


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    ratfink is a good person to take charge of this thread
    he has ideas about history and knows that Friedmann did high-altitude ballooning
    ratfink has a reasonable idea of why we live in a Friedmann universe, the answer to the question
    if you want to know anything ask him and if you dont like his attitude try to argue him down

    have fun, and in the meantime dont believe anybody else's distance function (especially not traveltime "distance"). use only genuine FRW metric: accept no substitutes :smile:
  9. May 17, 2006 #8


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    So mathmatics (alone) perfected the wing ?
  10. May 18, 2006 #9


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    There have in fact been wings derived from equations (mathematical physics) without wind testing. But since wind tunnels are available there's no reason to do such a "stunt".

    On the other hand, look up Joukowsky airfoil (I think that's how it's spelled).
  11. May 18, 2006 #10
    Growth can be described mathematically, and evolution is a form of recursion. A birds wing is therefor mathematical.

    Maybe physics is more like DNA, its just the code we pass on to the next generation to start building wings with, and hopefully improve on them.
  12. May 19, 2006 #11


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    The wind argument is a bit misguided . . . there is a correction factor called 'turbulence' that plays a role.
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