Nib asked for
Falling into a black hole
You would cross the event horizon without feeling anything special, but near the center tidal forces would stretch you apart, and nothing you could do would bring you back out.
7 steps, drawn by Nib. Read it here, or watch him draw it. Updated .
1far away
Picture yourself drifting feet-first toward a black hole. Far away, nothing is unusual: you simply fall, as any object falls toward any large mass. Your own sense of things stays ordinary, because falling freely feels like floating, the same weightlessness astronauts feel in orbit.
Free fall feels like floating, even toward a black hole.
a common mix-upThat you would feel a violent pull dragging you in from afar.
Would you feel a tug or a jolt as you fall freely toward the black hole from far away?
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No. Free fall feels like weightlessness; you feel nothing special.
2the horizon
Then you reach the event horizon, the boundary from page 4. For a large black hole, nothing marks the moment: no wall, no flash, no change in how your body feels. Space there looks and feels like space anywhere else. But you have just crossed the point of no return, and you cannot know it by sensation alone.
The horizon is a threshold you cannot feel yourself crossing.
a common mix-upThat the horizon is a physical surface you would hit or burn up against.
What would you notice at the instant of crossing the horizon of a large black hole?
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Nothing special; the change is in what is now impossible, not in what you feel.
3no way out
Once inside, the geometry works against you: every possible path leads toward the center, the way every path through time leads to the future. Firing rockets, struggling, or turning around cannot help, because going outward would require going faster than light, which nothing can do. The most you can change is how long the trip takes.
Inside the horizon, every direction leads to the center.
a common mix-upThat a strong enough engine could always haul you back out.
Could a powerful enough rocket carry you back out from inside the horizon?
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No. Leaving would require exceeding light speed, which is impossible.
4tidal stretch
What finally hurts you is the difference in pull across your body. Gravity gets stronger closer to the center, so your feet, nearer in, are pulled harder than your head. Near a black hole this difference is enormous, and it stretches you lengthwise while squeezing you sideways. These are tidal forces, the same kind of effect the Moon has on the oceans, vastly magnified.
Tidal forces: nearer parts are pulled harder, stretching you.
a common mix-upThat you would be crushed all at once by a single overwhelming force.
Why are your feet pulled harder than your head as you fall feet-first?
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They are closer to the center, where gravity is stronger.
5tidal stretch
Gravity is stronger closer in, so your feet are pulled harder than your head. That difference stretches your body out, like pulling taffy.
6stretched
Your body is stretched thin, like taffy. The black hole's pull is the same; only the difference between your head and feet stretches you.
7big vs small
How soon this happens depends on size. A black hole a few times the Sun's mass stretches you apart before you even reach the horizon, because its gravity changes so sharply over short distances. A supermassive black hole, millions of times the Sun's mass, like those at galaxy centers, is so large that the stretching is gentle at the horizon, and you would only be torn apart later, deeper inside.
Bigger black holes are gentler at the horizon; you still lose in the end.
a common mix-upThat all black holes would tear you apart at the same moment.
Which gives you a gentler crossing of the horizon: a small black hole or a supermassive one?
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A supermassive one; its gravity changes more gradually across your body.
So falling in is quiet at the threshold and brutal at the end: you cross a line you cannot feel, then cannot return, then are stretched apart.