Stephen Hawking helped develop current theories on black holes—but now, he's saying there aren't any. New Scientist explains his thinking, focusing on what's known in physics as the "firewall paradox," which deals with a black hole's event horizon. That's an "invisible boundary" that prevents anything that crosses it from escaping, Nature explains. The theory of general relativity suggests that an astronaut passing through an event horizon wouldn't even notice it. Quantum theory, however, says that an event horizon would be packed with energy—something an astronaut would definitely notice, since she'd be burned alive.
The conflict is known as the "firewall paradox," and Hawking's new theory addresses it. The theory favors "apparent horizons" over event horizons. Apparent horizons hold matter and energy but later release them "in a more garbled form," as Nature puts it. Per Hawking: "The absence of event horizons means that there are no black holes—in the sense of regimes from which light can't escape to infinity."