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I Cosmological constant

  1. May 27, 2016 #1
    hi, I have been watching some "world science festival" videos on youtube, also there were a conversation pertain to whether or not the cosmological constant should be a constant. As far as I know, our universe is expanding with a positive acceleration measuring the red shifts, and it implies that net total energy should not be constant in a given time. Nevertheless, there was a situation that a guy in videos said that data they had acquired resembled the cosmological constant. Is not there a contradiction???????. Because they say both the our universe is expanding and data they had acquired resembled the cosmological constant (static universe, net total energy is constant).
     
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  3. May 27, 2016 #2

    Bandersnatch

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    No, there isn't a contradiction. The universe could be expanding without a cosmological constant whatsoever.
    Presence of dark matter causes the expansion to accelerate, and if it's in the form of a cosmological constant, this acceleration is constant.
    Models with changing dark matter result in acceleration of acceleration of the expansion.
     
  4. May 27, 2016 #3
    I would like to add that as far as I know we add cosmological constant to ensure the derivative of energy tensor equals zero. I mean, if cosmological constant (even if the dark matter result in it) is constant, then Does not the derivative of energy tensor equal zero????? ( static universe )
     
  5. May 27, 2016 #4

    Orodruin

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    No, the presence of dark energy causes acceleration. Dark matter is a regular matter component which causes deceleration. Dark matter and dark energy are very different concepts.

    Einstein's introduction of the cosmological constant was to get a static universe. However, this only occurs for a very particular value for the cosmological constant and the solution is anyway unstable. There is no contradiction in having a cosmological constant and an expanding universe.
     
  6. May 27, 2016 #5

    Bandersnatch

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    A slip of mind. An embarrassing one nonetheless.
     
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