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Is there a contradiction here.

  1. Jan 24, 2012 #1


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    list of contradictory situations.
    1. Age of universe is determined by rate of proton decays at some place taking into consideration half life of proton.
    But since ALL protons were created after big bang, how can protons even decay. Considering the fact that their half life is greater than present life of universe.

    2. Everyone knows that radius of universe in terms of speed of light (more than 13billion yrs) meanins that it takes light more than 13 billion years to reach curcumference from centre. is definite larger than age of universe. It implies that objects/stars at boundry travelled faster than light. Is not here too another contradiction.

    Any ideas.
  2. jcsd
  3. Jan 24, 2012 #2

    Simon Bridge

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    1. the half-life of the proton is the amount of time it takes for the number of protons in the Universe to reduce by half. A half-life greater than the best-estimate age of the Universe just means that more than half of the protons the Universe started out with are still around.

    proton decay is highly speculative and has not been observed - therefore has not formed part of our knowledge of the age of the Universe.
    See age of universe for three common methods. These are discussed, and the uncertainties of each accounted for in a final estimate.

    2. That is the radius of the observable Universe - it is how far we can see from here.
    The rest of the statement is not clear -
    ... what was your question? What is bigger than who?
    Last edited: Jan 24, 2012
  4. Jan 24, 2012 #3


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    sorry for unclear language.
    A. Universe started as singularity or near singularity.
    B. Matter at the edge of universe travelled from O or approx. O radius to present 46 billion light years radius in 13 billion years.
    C. Light takes 46 billion years to cover same distance.
    D. Does this mean matter had to travel/expand faster than light to reach to the present horizon of universe from r=0 position.
  5. Jan 24, 2012 #4

    Simon Bridge

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    Gotcha - 14bil years ago some light got send towards us from point P, 14bil ly away.
    14bil years later, point P is 46bil ly away and we get the light.
    this gives an average speed of 46-14/14=2.3c

    But this is faster than the speed of light!!! :)

    from wikipedia.
    There are a few things that can go FTL without violating relativity.
    Space-Time is one of them. Well spotted.

    your point B seems to suggest expansion from a center - there is no center to expand from.
    Last edited: Jan 24, 2012
  6. Jan 24, 2012 #5


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    As Simon points out, relativity forbids objects locally from moving at > c wrt each other. It does not forbid the expansion of space between distant objects causing them to recede at speeds > c.
  7. Jan 24, 2012 #6


    Staff: Mentor

    In addition to the comments above, I would like to point out that in modern cosmology there is no boundary/edge to the universe.
  8. Jan 24, 2012 #7


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    @dalespam. sorry for that error

    can i deduce then that the spacetime continuum even long after big bang/perhaps even today is/was highly distorted to allow matter to travel faster than light and hence expansion of universe is far complicated than expanding balloon.

    Excuse me if i appear idiotic here.
  9. Jan 24, 2012 #8
    no...space expanded FTL.

    also no, it's the [new expansion] space between that is causing the apparent speed.....

    Spacetime in the observable universe is generally pretty flat and uniform...not within solar systems and galaxies and their attendent dark matter and dark energy necessarily, but at intergalactic distances.
  10. Jan 24, 2012 #9
    Here's an online article about Cosmology from Scientific American that is good:

    http://space.mit.edu/~kcooksey/teaching/AY5/MisconceptionsabouttheBigBang_ScientificAmerican.pdf [Broken]
    Last edited by a moderator: May 5, 2017
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