English: Spacetime diagram for ingoing Eddington–Finkelstein coordinates (using the original (r,t') coordinates as in Eddington, A.S. (Feb 1924). "A Comparison of Whitehead's and Einstein's Formulæ". Nature 113 (2832): 192. DOI:10.1038/113192a0.) Outgoing radial null-geodesics (light trajectories) are drawn in blue, ingoing - in red. Schwarzschild radius r_s separates the region under the event horizon (black) and above the event horizon (white). Light cones are drawn in green for one point in each region. Outside the blackhole particles can move both to the right and to the left - that is, away and towards the black hole (black arrows), but inside they can move only to the left (white arrows), so the event horizon at r_s cannot be crossed from left to right (from inside the blackhole to the outside).