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universe

  • 28-08-2007 12:55am
    #1
    ronbyrne2005
    Closed Accounts Posts: 3,494 ✭✭✭


    is it expanding at speed of light? is it 15billion lighyears wide?


Comments

  • #2
    Son Goku
    Closed Accounts Posts: 1,475 ✭✭✭Son Goku


    ronbyrne2005 wrote:
    is it expanding at speed of light?
    No, it's a good bit slower than the speed of light.
    ronbyrne2005 wrote:
    is it 15billion lighyears wide?
    74 billion light years wide.


  • #3
    Kevster
    Closed Accounts Posts: 2,980 ✭✭✭Kevster


    I'm not doubting you Son Goku, but where did you get the 74 billion figure from? The most recent source I read stated a figure less than half of that; but they mentioned that no-one can be really sure.


  • #4
    Son Goku
    Closed Accounts Posts: 1,475 ✭✭✭Son Goku


    Kevster wrote:
    I'm not doubting you Son Goku, but where did you get the 74 billion figure from? The most recent source I read stated a figure less than half of that; but they mentioned that no-one can be really sure.
    The WMAP studies. However I am giving the lower bound on the diameter and using certain definitions of size. With General Relativity it is difficult to define the "size of the universe at a given moment". If you use a comoving volume definition it is 92.94 (+- 0.2) billion light years. Again it depends on how you define "volume at an instant".

    If you are interested in such things, the upper bound on the size of the universe in directions we can't see, (in other words the size of extra dimensions) is 123 nanometers.


  • #5
    Kevster
    Closed Accounts Posts: 2,980 ✭✭✭Kevster


    I heard about those extra dimensions being that size alright. That's all part of string / superstring theory, right?

    Regarding WMAP, I had no idea that they released their results. Is the study finished?


  • #6
    Son Goku
    Closed Accounts Posts: 1,475 ✭✭✭Son Goku


    Kevster wrote:
    I heard about those extra dimensions being that size alright. That's all part of string / superstring theory, right?
    Those would be the main theories that use them, although there are more theories that use extra dimensions. The term for any general extra dimensional theory is a Kaluza-Klien Theory.
    Kevster wrote:
    Regarding WMAP, I had no idea that they released their results. Is the study finished?
    Yes, although the observations are still being fully understood. Although one of the main implications is the General Relativity is far more accurate than many people guessed, being accurate to the 16th decimal place.


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  • #7
    Kevster
    Closed Accounts Posts: 2,980 ✭✭✭Kevster


    Son Goku wrote:
    one of the main implications is the General Relativity is far more accurate than many people guessed, being accurate to the 16th decimal place.

    That either shows the genius of Einstein... ... ...or his amazingly good luck.


  • #8
    ronbyrne2005
    Closed Accounts Posts: 3,494 ✭✭✭ronbyrne2005


    so at some stage the universe expanded at a speed by more than the speed of light if its 70billion light yrs "wide"? I heard the expansion/inflation of the universe is accelerating? If its accelerating then it may have been a lot less in past yet at some stage the expansion exceeded speed of light?


  • #9
    Son Goku
    Closed Accounts Posts: 1,475 ✭✭✭Son Goku


    Kevster wrote:
    That either shows the genius of Einstein... ... ...or his amazingly good luck.
    Most likely a combination of the former with certain restraints on possible theories. For instance, any classical theory of gravity, in which all inertial obersvers agree on the laws of Maxwell's electromagnetism, is always mathematically similar to General Relativity. Really "curved spacetimes" are the way to describe gravity on the classical scale.
    ronbyrne2005 wrote:
    so at some stage the universe expanded at a speed by more than the speed of light if its 70billion light yrs "wide"? I heard the expansion/inflation of the universe is accelerating? If its accelerating then it may have been a lot less in past yet at some stage the expansion exceeded speed of light?
    In intuitive terms, yes. However the "speed of space's expansion" is a ill-defined concept.


  • #10
    Kevster
    Closed Accounts Posts: 2,980 ✭✭✭Kevster


    Son Goku wrote:
    In intuitive terms, yes. However the "speed of space's expansion" is a ill-defined concept.

    That's as I understand it too, yeh. I read that the Universe has expanded so rapidly that no light could have spanned the entire 'width' of it [the Universe].

    This would be related to the theory on Inflation, I guess. The Universe underwent an enormous rate of expansion in the first few seconds of its birth and, if you believed the 'supercooling' aspect of inflation, Einstein's infamous 'Cosmological Constant' represents the energy that works against gravity to ensure the continual expansion of the Universe.

    ... ...right?


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