Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Bianchi I LQC, Kasner transitions and inflation

  1. Mar 26, 2013 #1


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    Slides and audio for this talk by Brajesh Gupt were posted online today.

    LQC bounce creates conditions for inflation. It's important to extend the quantum bounce model to anistropic cases, such as Bianchi I. Anisotropy can affect what one expects from the ensuing inflationary episode. Here are the questions posed and addressed in the talk.

    ==quote slide#3==
    Kasner Transitions:
    • What is the relation between the geometrical nature of spacetime in pre and post bounce regime?
    • Are there transitions from one type to other?
    • Are some transitions favored over others? If yes, depending on what?
    • Does anisotropy prevent inflation?
    • How does LQC modify the dynamics and the amount of inflation?
    • How is the amount of inflation affected as compared to the isotropic spacetime?

    Here are the conclusions drawn in Brajesh's talk:

    ==quote slide#18==
    • There are Kasner transitions across the bounce in Bianchi-I spacetime
    • These transitions follow a pattern and depending on anisotropy and matter content some of them are favored- “selection rule”
    • Inflation takes place irrespective of the initial anisotropic shear
    • Anisotropy may enhance or reduce the amount of inflation depending on the initial conditions on the inflaton velocity
    • Bianchi-I spacetime widens the window of the value of inflaton at the bounce, for a given number of e-foldings

    Last edited: Mar 26, 2013
  2. jcsd
  3. Mar 28, 2013 #2
    It is said that a Kasner's metric has something to do with the study of gravitational chaos. Can the "Kasner's exponents" (see the link) be compared with some probabilities (the sum must be 1) or with some probabilities of existence (the sum of the squares must be 1)? My underlying question -perhaps a little bit unclear and, I am sorry, at the frontier of actual physics- is: if, what is called a "wave" in Quantum physics would "only" be series of states taken in that gravitational chaos, then would this picture make our theories incoherent?
  4. Mar 28, 2013 #3


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    If anyone wants to look the background paper for Gupt's talk

    Hi Blackforest, I'm glad to see you back again and appreciate your comment on this. I think of Bianchi I cases as a sort of toy model to study anisotropy. They are some of the simplest anisotropic cases, where you have 3 different directions which can contract, bounce, expand at different rates.

    If expansion is much more rapid in one direction than in the other two, you could describe it as "cigar type"
    (think long and skinny.)
    If expansion is much slower in one than in the other two, you could call it "pancake type" (think thin and spread out.)

    In the LQC bounce Singh and Gupt found that the type could change. You could have contraction of one type that somehow bounces resulting in expansion of a different type. I haven't studied this and can't explain it. So I won't be able to respond to your question. They found that some transitions are allowed but not others.

    I think what this amounts to is studying the anisotropic bounce in simple toy model cases so as to make gradual incremental gains in understanding. A realistic bounce would be much more complicated, but one can learn something by studying these simple cases.

    It's late here. You got me interested in the and I stayed up long past bedtime. :-) Time to turn in.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook