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The accelerating universe

  1. Aug 30, 2006 #1
    I have heard that people say the universe is accelerating, however i cannot find direct evidence of these claims anywhere. What has led people to believe that the expansion of the universe is accelerating?
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  3. Aug 30, 2006 #2
    Type Ia supernovae (which are believed to always have the same absolut luminosity, although this is somewhat being contested currently) are dimmer than they should be unless the universe's expansion has been accelerating. There are other measurements, but that was the initial big one.
  4. Aug 30, 2006 #3


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  5. Aug 30, 2006 #4
    I don't understand how SN 1A can determine that the universe is accelerating. From what i see, the older things are the higher their redshift, which just means that things were moving faster in the past. If anything it should be slowing down since closer galaxies have blueshifts meaning that it is coming together. What we see out there is not what is actually happening now.
  6. Aug 30, 2006 #5
    It is simply a conjecture, there is no proof.

    The issue is that is appears that some objects in the universe recede from us faster than light. So something has to bend, the theory or we postulate that the universe expands in an accelerating fashion.

    It is the same with dark matter, it is a conjecture to explain the discrepancy with the theory.

    It might very well be right but so far there is no proof.

    Of course there are alternative theories but unfortunately anything that looks like an alternative to relativity theory is seen as blasphemous by many physicists and publishers. :smile:
    Last edited: Aug 30, 2006
  7. Aug 30, 2006 #6
    i see, i was hoping for a little more evidence to convince me that acceleration is the correct idea, but i guess it is just like the other theories, awaiting better observations
  8. Aug 30, 2006 #7


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    Supernovae 1a are not the only evidence for dark energy. There are basically three observations that complement each other: the flatness of space derived from the measurements of CMB anisotropies, matter as the observed energetic component of galaxy clusters and the luminosity distance of supernovae 1a.

    In future there might be possible other observations that can help to provide information about the equation of state of the dark energy component, such as the redshift distribution and evolution of galaxy clusters or the analysis of secondary anisotropies in the CMB (the ISW effect). However, to my knowledge, currently these test deliver very ambiguous results that depend on uncertainties.

    See this great article for more information.
    Last edited: Aug 30, 2006
  9. Oct 29, 2011 #8
    Please correct me but if the Universe were to be accelerating inwards i.e. into a Mega black hole -wouldnt the same acelerating attributes match i.e. the star closer to the black hole would accelerate away from those further away and those stars further away would be seen also as accelerating away from those closer (getting further distant) - so rather than explaining it as an unfathomable scenario of an endless expaning entity - it then makes sense that we are actually contracting at an acceleratiing rate , not expanding
  10. Oct 29, 2011 #9
  11. Oct 30, 2011 #10


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    Absolutely not happening. Your logic is somewhat correct, but you should read up on homogeneity and isomorphism, which would not exist if everything were being sucked back into a black hole because that would be a POINT. There IS no point for the expansion, thus homogeneity and isomorphism can exist (they don't HAVE to exist but they can and do ... under your scenario, they can't)
  12. Oct 31, 2011 #11


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    But then we wouldn't see galaxies receding from us in every direction we look: there would e galaxies receding in the direction of the black hole, and galaxies approaching us if we look in the opposite direction.
  13. Oct 31, 2011 #12


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    SN 1A can be used as a method of determining the distance to galaxies. The red shift tells us how fast the galaxy is receding. As we look at galaxies further and further away, we are looking further and further back in time. If the expansion of the universe was at a constant rate and we plotted the distance arrived at from SN 1A data to redshift, you would get a straight line. (double the distance, double the red shift etc.)

    If the expansion slowed over time, this line would curve, and if it is accelerating over time, it would curve the other way.

    Nobody ever expected the plot to be flat, but expected that mutual gravitational attraction would slow the expansion over time. It was quite a surprise when they discovered that the plot curved the other way.
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