In places where gravity is very strong, time as we understand it can break down completely. At the edge of black holes, for example, the powerful gravitational pull slows time dramatically, says Prescod-Weinstein. And upon crossing the black hole’s point of no return, known as its event-horizon, she says space and time flip. Far from the Earth, time gets extremely weird. Black holes can cause it to stretch and even break down entirely.
“You end up in a region where space now has an arrow, and it’s one direction … and time doesn’t have an arrow like it did before,” she says. “There’s really no sense of time.” -[Source](https://www.opb.org/article/2022/12/28/researchers-say-time-is-an-illusion-so-why-are-we-all-obsessed-with-it/)
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Typically space-time is represented as a joint fabric because of how gravity impacts time. If you think about how time works, it flows in one direction, only forward.
When you cross the event horizon and they say this gets ‘flipped’, it means gravity is now so strong, there’s no way you can escape the blackhole any more because light can’t even escape at this point. Because of the ridiculous amount of gravity, time essentially ceases to exist as a concept.
You’ve probably heard this or similar but as an example, if an astronaut fell into a blackhole with a blinking LED on their suit, while their partner was watching from a safe distance in the shuttle, the astronaut falling into the blackhole wouldn’t notice anything different about their light blinking, however to the observing astronaut in the shuttle, their light blinks would get stretched out becoming longer and longer, until eventually it just appears completely lit and no longer blinking. This is the concept of time of slowing (and eventually stopping / ceasing to exist) due to gravity.
As you continue being pulled into the blackhole, and that time slows to a standstill, space now only flows one direction – which is through the blackhole.
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