What would you wonder if you could only know the answer to one question about the Universe? More than anything else, what would you like to know? So the other day, my son asked me about it, and it was an interesting one. If you fall through a black hole, what happens?
Let me explain, firstly, how black holes come in. As a result of stellar death, black holes may form. Once a star runs out of fuel to burn, and can thus no longer sustain itself by radiation pressure, all the metal layers fused to that stage would crash down into the core. In the creation of a supernova, the stellar center can either implode or, as is the case with more massive stars, collapse and then form a black hole.
If the clutches of a black hole can not avoid massless photons, so surely neither will we. But if you were to find yourself falling into a black hole, what would happen to you? We can predict the particulars of what will happen to us without having to go through it ourselves, thanks to Einstein’s theory of general relativity, a framework that lets us understand how space and time behave in the presence of strong gravity.
You can think of it the same way you think of an astronaut comfortably floating in space: free in the sense that there is no ground to drive you up, no air molecules to rush towards you, no chair to sit on, no other people to touch you. In the Universe, you are free. But it also implies that you are free to be driven around by gravity, even though we don’t think about it all that much.
Sure, you may not notice it, but you are still pulled by gravity. The power that you feel here on the surface of the Earth? That’s not gravity; it’s gravity balanced by the forces that hold you up from the chair, ground, or other surfaces. Take away those powers, as you feel when you leap off the ground, and the sudden sensation of weightlessness is what it is like to be in free-fall or to be alone without the influence of gravity.
There are masses all over the place in our natural Universe, though. Planet Earth is mass, the Sun is mass, and there are masses of all the planets , stars, and galaxies in the Universe. It wouldn’t just be a perfectly flat grid if you were able to imagine space itself; it would be distorted by the existence of all these masses. The warped grid will decide how you moved as you moved through the Universe under the influence of gravity alone.
We treat space and time as continuous in General Relativity, but all sources of energy, including but not limited to mass, lead to spacetime curvature. The way that space warps in the presence of mass (and energy) and the impact it has on other objects (like you) that exist in that space is what gravity is:
Don’t be fooled, either, by this static image. As masses pass across it, the fabric of space is continuously shifting. The warping of space shifts as the earth orbits the Sun. The curve of space varies as the Sun travels across the galaxy. The fabric of space shifts as stars shape and live and burn and die.
All of this is part of the Great Celestial Dance, and part of the Gravity Tale. As the masses move about and shift, the fabric of space shifts as the Universe expands, as a whole slew of processes take place in the Universe. Yet gravity remains real despite it all, and keeps pulling on all of us as if we were falling freely.
If you travel from the right position with adequate speed and in the right direction, you can establish a stable orbit around any mass in the Universe. But if there’s anything wrong with you, you’ll collapse back to whatever mass you try to orbit. Without enough velocity, launch a rocket and it’ll fall back to Earth. Slow down so much of the earth, and it’ll sink into the Sun. An spinning star slows down, and it will fall to the middle of a galaxy.
And in the most extreme scenario, you can fall into a black hole if you have the incorrect properties. The ultimate mass is a black hole: one that is so dense, so huge and so compact that once it falls in, nothing can get out. And at the universe’s absolute speed limit, the speed of light, you can not escape.
There is a very, very good explanation why you can never get out once you hurtle through the invisible barrier. The fabric of space is less curved when you are very far away from a black hole. In fact, when you’re really far from a black hole, you can’t discern its gravity from any other mass, be it a neutron star, a normal star, or just a diffuse gas cloud. Spacetime can be curved, but all you can say is that it is due to the presence of a mass, not what the properties or distributions of that mass are at your distant spot.
You will literally slide, openly, the same as if you had substituted something else for that black hole. It would just look different: it would look like a black hole. You would feel something odd as you started to get close: a force pulling on your body. You would experience a stretch from head to toe while your feet were closer to the event horizon than your head was, while your sides would get squeezed. These are tidal forces, the same forces which cause the oceans of the Earth to bulge.
The only thing is, a black hole is much, much stronger, and the closer you get, its tidal forces will stretch and compress you extremely badly. They’d work to draw you into a thin , long strand; they’d transform you into a noodle effectively. Scientists have known this for a long time, and to explain what happens to an entity when it falls into a black hole, we actually have one of the most fun terms of all: spaghettification!
The explanation is clear. Yes, spacetime mass curves, but as you get closer and closer to an incredibly dense and massive mass, like a black hole, space curvature becomes more and more serious. This definitely raises the tidal, spaghettifying powers on you, but it also increases the amount of bending of light from across the black hole. The event horizon will start to look gigantic in comparison to its real physical dimensions! In the distance, distant stars will seem to be disastrously out of shape with their positions bent, and the event horizon will begin to take over your entire frontal field of view.
But you somehow aren’t doomed! At this point, you can still get out, having not yet crossed the event horizon. You could escape its gravity and make the Universe go back to your healthy, far-away-from-the-black-hole, asymptotically flat spacetime if you provide ample acceleration away from the event horizon. Your gravitational sensors will inform you that towards the middle of the blackness and away from the regions where you can still see starlight, there is a strong downhill gradient.
And then… blackness. Nothing. From inside the event horizon, no light from the outside Universe hits your spaceship. No matter how you fire your engines, no matter what you do, there’s no way out. What you’d see wouldn’t be a reflection of where you were headed: the singularity would be in front of you no matter which direction you went in.
But you wouldn’t actually see that singularity, because of how weird this severely curved space was. There’s actually light from the outside world following you into the black hole, crossing the event horizon before you, after you, and with you. The video below shows what happens if you allow the light from the outside Universe to fall into the black hole all around you, exactly as it does in real life.
It would only take seconds, from the moment you crossed over the black hole’s event horizon, for you to be crushed to bits. But in the largest black holes, there’s a chance that they lead somewhere else: to a white hole, to another Universe, or to a new physical reality that’s shrouded behind an event horizon we cannot see past. From the outside, we cannot obtain any information about what lies inside the event horizon. All we have are our theories.
If you can help it, please don’t fall into a black hole, because the most probable scenario is that you will actually be ripped apart and crushed. But if you went inside, you would be the only human being in life to know what it was like for certain. You will be the first person to discover the secrets kept inside a black hole. You will chose not to do so, and that is arguably the wise option. But in this world, you have to risk everything to find out whether you want to be the first one. Perhaps one of you out there, reading this, would definitely be the first to hear.
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