Which statement about a black hole's event horizon is true?

• A. Nothing can escape from inside the horizon.
• B. Light can escape from just outside the horizon.
• C. A physical surface exists at the horizon.
• D. Time stops for all observers at the horizon.

Answer: (A)

The event horizon marks a boundary in spacetime beyond which nothing can affect the outside world. It’s not a physical surface you could touch; it’s a causal boundary: any path a particle or light could take from inside the horizon inevitably leads inward toward the singularity, so there’s no route out to infinity. That’s why nothing can escape once you’re inside the horizon.

Light can escape from regions just outside the horizon because those paths still lie in the exterior spacetime, but that doesn’t change the fact that inside the boundary there’s no way for signals to reach outside. There isn’t a physical surface at the horizon, so imagining a real surface there is misleading. And time doesn’t stop for all observers at the horizon—the effect is frame-dependent: a distant observer sees objects near the horizon slow down and redshift, while a freely falling observer experiences time normally.