What happens inside a black hole: the final 7 minutes

2019

Imagine you're approaching a stellar-mass black hole, one of about 10 solar masses. What happens?

First, the tidal effect. Gravity isn't uniform: it pulls harder on your feet (closer to the black hole) than on your head. This difference stretches you like a strand of spaghetti. Physicists actually call this "spaghettification." For a small black hole, spaghettification would kill you long before reaching the event horizon.

But if the black hole is supermassive (like TON 618), the event horizon is so large that the gravitational difference between your head and feet is negligible. You could cross the horizon without feeling anything special. That's the paradox: the moment from which you can never escape would be completely unremarkable from your perspective.

Once past the event horizon, all paths lead to the center. It's not about a force pulling you; it's about the geometry of spacetime itself. Your future literally points toward the singularity. Try to go "up"? That's still toward the center. Space and time swap roles: the singularity isn't a place in space; it's a moment in time. An inevitable moment.

How long does it take? For a stellar-mass black hole, from the moment you cross the horizon to the singularity, you'd have approximately 0.0001 seconds. But for a supermassive black hole, the time extends. For one with a mass of billions of suns, you could have several minutes: some calculations suggest around 7 minutes for a black hole like those at the centers of large galaxies.

What is the singularity? This is where current physics breaks down. General relativity predicts a point of infinite density and zero volume. But "infinite" in physics usually means "our equation no longer works here." We need a theory of quantum gravity, a fusion of quantum mechanics and general relativity, which we still don't have.

From outside, an observer watching you fall would see something completely different. As you approach the event horizon, the light you emit shifts increasingly toward red (gravitational redshift). You appear to slow down, fade, and freeze at the event horizon, never crossing it. From their perspective, you would exist forever as an ever-dimmer image at the edge of the black hole.

This asymmetry between the falling person's experience and the observer's experience is one of the most profound lessons of relativity: time doesn't flow the same for everyone.