Black holes aren’t the cosmic vacuum cleaners they are rumored to be, but could you still fall into one? What would happen to you? The answer to that question depends on whom you ask (thanks to quantum gravity)
Black holes are regions of space where the gravity is so thick that not even light can force its way out. Black holes can form as a result of stellar death. Once a star runs out of fuel to burn, and thus can no longer support itself via radiation pressure, the layers of metals fused up to that point will all come crashing down towards the center. The stellar core can then implode in the production of a supernova or, as is the case for more massive stars, collapse to then form a black hole.
If massless photons cannot escape the clutches of a black hole, then certainly neither could we. But what would happen to you if you were to find yourself falling into a black hole? Thanks to Einstein’s theory of general relativity, a framework that helps us understand how space and time behave in the presence of strong gravity, we can predict the specifics of what would happen to us without having to go through it ourselves.
The answer is surprising because you get a different one depending on whom you ask. You, as the faller, would experience a reality very different from what I, as an observer from the outside, would see. So, if we can’t agree, what do we think happens to you?
BLACK HOLES DON’T SUCK
First, let’s clear up a common misconception. Black holes get a bad reputation for sucking in their surroundings, like some sort of cosmic vacuum cleaner. In reality, the gravitational pull of a black hole is the same of that for a regular star—just a lot stronger.
So astronomical objects can easily stay in orbit around a black hole, just as we stay in orbit around our Sun, so long as they are moving fast enough to balance the black hole’s gravitational pull. In fact, the hundreds of billions of stars in our galaxy orbit a central, super massive black hole with a mass of 4.6 million times that of our Sun crammed into a space of less than ~100 million miles (about the distance between the Earth and the Sun).
If we were to get knocked off course by a particularly large collision (think galaxy scales here, not just a tap from an asteroid), we could in theory be sent careening towards our galaxy’s central black hole and pass the point of no escape. However, this would require a pretty significant event and so we have much more likely things to worry about (like what happens to our Sun when it runs out of fuel).
You very quickly resemble spaghetti
For smaller black holes, like those formed from collapsed stars, the gradient in the gravitational pull is so steep (i.e. the force of gravity changes rapidly as you move closer) that you would not get anywhere close to the perimeter of the black hole. The gravitational pull on your feet would be so much stronger than that on your head that you would be pulled apart like string cheese pretty quickly.
However, around a larger black hole, you would have more time to approach before being torn in two. In fact, given a large enough black hole, you’d have all the time in the universe.
Time slows so much that you never reach the black hole
As you approach a black hole, you do not notice a change in time as you experience it, but from an outsider’s perspective, time appears to slow down and eventually crawl to a stop for you. General relativity explains that an object in the presence of a strong gravitational field will pass time more slowly, a process known as time dilation, and an effect that increases the closer you get to the black hole. If you’ve seen the movie Interstellar, you probably remember the scene where two brave explorers spend only a matter of minutes on the surface of a planet near the black hole while the astronaut that stays on the ship experiences 40 years passing.
You would notice the effect indirectly, however, because you would see everything that ever fell into the black hole before you also slowly approaching the point of no return (called the “event horizon”) below you but never quite making it there.
So who is right? This discrepancy, and whose reality is ultimately correct, is a highly contested area of current physics research.
The trouble lies in reconciling quantum mechanics, which describes our universe on the very small spatial scales like those of atoms, with general relativity, which describes our universe in the presence of massive objects. While both of these theories work well on their own, a unifying explanation that combines the two, often called quantum gravity, remains elusive. Black holes provide a rare environment where these two regimes meet: an incredible amount of mass packed into a very, very small space.
One thing we would both agree on, however, is that you’d never make it back out again to tell your story. Just as time marches only forward for us while space is static, the opposite would become your reality. Time would stand still, but you would be unable to get off the train bringing you further and further towards the massive black beast.