In the coordinate system of a distant stationary observer, Hawking radiation tends to be described as a quantum-mechanical particle-pair production effect (involving virtual particles), but for stationary observers hovering nearer to the hole, the effect is supposed to look like a purely conventional radiation effect involving real particles. In the membrane paradigm, the black hole is described as it should be seen by an array of these stationary, suspended noninertial observers, and since their shared coordinate system ends at the event horizon (because an observer cannot legally hover at or below the event horizon under general relativity), this conventional-looking radiation is described as being emitted by an arbitrarily thin shell of hot material at or just above the event horizon, where this coordinate system fails.