Submitted by mark0136 t3_11gygda in askscience
mutandis57 t1_jazj3ym wrote
Reply to comment by purpleoctopuppy in What exactly does Spaghettification mean? by mark0136
Everything inside the event horizon must travel towards the singularity, but the speed at which they travel inwards can still be different. This allows things like "blood" or "nerve impulses" to subjectively travel "upwards", such that from your perspective you will feel physically normal, even as you cross the horizon.
Here's an example using fake units: you are falling through the horizon, at t=0 your head is 1m above it, your legs 1m below it. Your toe sends a nerve signal. At t=1, your head enters the horizon, your leg is 2m below, and the nerve signal is 1.75m below. The signal is "deeper" into the black hole than when it started, but it still travels up your leg. At t=8, your leg is 9m below, your head is 7m below, and the nerve signal finally reaches your head. You can feel you toe!
You could even have two spaceships fall in separated by 1km (a rope linking them together optional!) and you could see your buddy on the front spaceship fall in past the event horizon and wave at them and then see them wave back in response. Of course, by the time you see the response, you yourself will already be inside the event horizon and way past the point where they were when they waved back.
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