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Homework Help: Can massless particles reach the boundary at z=0?

  1. Dec 5, 2016 #1
    1. The problem statement, all variables and given/known data
    We're working in 2-d Anti-de Sitter space with metric: \begin{eqnarray*}ds^2 = \frac{1}{z^2}(-dt^2 + dz^2)\end{eqnarray*} with 0<=z.

    The solution is: \begin{eqnarray*}z^2 = (t+c)^2 + B\end{eqnarray*} And we've been asked to plot this (I think its a parabola with minima at t=-c, z=(B)1/2 (told that B>0). (I'm not sure if the c in this case is the speed of light or just a constant, it hasn't been said)
    The last part asks if massless particles can reach the boundary z=0?

    2. Relevant equations

    3. The attempt at a solution
    I don't really understand this to be honest. I know that the geodesic L=0 for massless particles but I don't really know the physics implications for a massless particle. I assume it's to do with the fact that massless particles travel at the speed of light so perhaps theres a consequence at the boundary?

    Thanks for any help, I'm a little confused!
  2. jcsd
  3. Dec 10, 2016 #2
    Thanks for the thread! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post? The more details the better.
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