A peek outside our Universe
  According to general relativity (GR), a universe with a cosmological constant
$\Lambda$, like ours, is trapped inside an event horizon, $r<
\sqrt{3/\Lambda}$. What is outside? We show, using Israel (1967) junction
conditions, that there could be a different universe outside. Our universe
looks like a black hole for an outside observer. Outgoing radial null geodesics
cannot escape our universe, but incoming photons can enter and leave an imprint
on our CMB sky. We present a picture of such a fossil record from the analysis
of CMB maps that agrees with the black hole universe predictions but challenges
our understanding of the origin of the primordial universe.
