What happens when you fall into a Black Hole? It’s a question I am sure we’ve all pondered at some point. Would you be instantly killed by intense heat? Would you collide with a giant star or meteor? Would you discover an alternate reality where the Lemmy is the best club in Exeter? Would you be confronted by Lionel Richie, who tells you you’re his angel? In fact, no one really knows what would happen, but we can theorise.
A black hole is the name ascribed to a geometrically defined region of spacetime, where gravity is so strong that nothing (including particles and electromagnetic radiation) can escape. It can be the result of a massive star that has collapsed under its own weight, retreating to a single immeasurably dense point: the singularity. The outermost boundary is the event horizon, and if we penetrate past this, it becomes impossible to escape the gravitational field.
So, let’s imagine you’re falling toward the event horizon, and I’m floating above it watching. As you get closer, your body appears to stretch and contort (as if I’m viewing you through a magnifying glass), and you move in slow motion. I try to signal you with light from my IPhone, but it becomes distorted and redder as the light waves are stretched. Once you reach the horizon, you would freeze in place, as the stopping of time and the fires of Hawking radiation eventually reduced you to ash. According to my perspective, you didn’t make it very far and probably died a pretty tragic death.
However, from your perspective, something baffling happens. Nothing. You keep falling, blissfully unaware you’ve passed beyond the point of no return. If it were a smaller black hole, the force of gravity would be stronger at your feet than your head, and you’d eventually be stretched out like spaghetti until a string of atoms remained. But let’s say it is a massive black hole, millions of times bigger than the Sun. If it were big enough, you’d live out the rest of your life normally until you reached the singularity.
So here’s the kicker. How can I see you perish, even if you keep falling? How can you be dead, and alive? Quantum physics demands that information (i.e. your atoms) can never be lost, which means it must remain outside the event horizon, or it breaks the laws of physics. Simultaneously, the laws demands that you sail through the horizon, or you’d violate Einstein’s theory of general relativity. You have to be in two places, but there can only be one copy of you. Physicists refer to this perplex problem as the ‘black hole information paradox’.
Leonard Susskind attempted to resolve the issue in the 1990s, stating that there is no paradox because no one sees your clone. You only see one copy of you. You and I never compare notes, and there is no third observer who can see both inside and outside the black hole at the same time. So, no laws of physics are broken, right? You fall freely, I see you die, everyone goes home happy.
Well, yes, until you demand to know which story is true? Are you really dead or are you really alive? And just like that, we’re back to where we started. What happens when you fall inside a black hole? Unfortunately, it depends on who you ask, which means no one knows the true answer. That is why it’s become one of the most antagonistic questions in fundamental physics, and why it’s such a fun concept to talk about.