From the perspective of an observer on a spaceship near a black hole, how long would it appear to take for a spacewalking astronaut to reach the event horizon?

• A. Millions to billions of years
• B. Seconds
• C. Minutes
• D. Hours

Answer: (A)

The core idea here is how clocks and signals behave in strong gravity. Near a black hole, time runs differently depending on how deep you are in its gravity well. As the spacewalking astronaut nears the event horizon, the gravitational time dilation becomes extremely strong, and the light carrying information about the fall is increasingly redshifted and spaced further apart.

From your viewpoint aboard a spaceship close to the hole, this means you’d see the astronaut’s progress slow down dramatically. The astronaut’s clock appears to tick more slowly, and the light you receive signaling that they’re crossing the horizon becomes so stretched and delayed that the crossing seems to take an incredibly long time—so long that, in observational terms, it could be described as millions to billions of years. Of course, in the astronaut’s own frame the crossing happens in finite, much shorter time, but that finite event is observed with extreme delay due to the strong gravity.

So the reason this appears to take such an enormous duration is the combination of gravitational time dilation and the redshifted, time-stretched signals near the horizon.