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WorstMedivhKR t1_j2apvf8 wrote

Reply to comment by Cyoarp in What is our current "best guess" about how to observers that entered a black hole on opposite sides would look to each other once they crossed the event horizon? by WittyUnwittingly

> If two objects are moving near the speed of light and they happen to be moving in opposite directions then they are moving towards each other at faster than the speed of light.

That's not correct. https://en.wikipedia.org/wiki/Velocity-addition_formula

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Cyoarp t1_j2aq3y3 wrote

Yes it is. I have checked this over multiple times and even consulted multiple physicists.

But let me clarify. They move towards each other at greater than the speed of light from a third party's reference frame. From the objects own reference frame nothing can move faster than the speed of light.

What I mean to say is that from your reference for frame you are moving the speed of light you will not observe anything outside of your reference frame and time will not move at all as far as you can tell

Which is why I specifically said that from their own reference frames the two objects will never observe each other because there will never be a time where they will observe each other meeting because time dilation does not allow them to do so.

(This isn't the best way to say this but I am driving. If this isn't clear enough let me know and I will better explane)

However from a third party's reference point they will be moving towards each other at faster than the speed of light or if they're going half the speed of light then they will be going towards each other at the speed of light.

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WorstMedivhKR t1_j2e2ko9 wrote

Ok, that's correct, but still from either observer's perspective the other person is not traveling faster than the speed of light, due to relativity it is very different. It is true that they won't see each other though even if they enter at the same time, so long as the entry point is different, for reasons I don't really understand mathematically since I haven't actually taken GR but have to do with the geometry of the black hole and that the singularity doesn't actually appear small, it appears to grow larger and larger as you approach it paradoxically. So it's more like free falling onto a huge black planet would look like.

https://jila.colorado.edu/~ajsh/insidebh/schw.html

> Geometrical intuition, bolstered by pictures like this one would suggest that the center of the Schwarzschild black hole is a point. That intuition is misleading. If you and a friend fall into a black hole at the same time but at different locations (in latitude and longitude), you do not approach each other as you approach the singularity. Rather, the diverging tidal force channels the parts of your body along the inward radial direction. Far from meeting your friend at the singularity, you cannot even put out your arms to touch her.

> “The” singularity is not a point. Rather, it is a 3-dimensional spatial boundary where general relativity commits suicide. New physics, presumably quantum gravity in some form, must replace general relativity at singularities. What that new physics is remains a profound unanswered question.

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Cyoarp t1_j2enn6x wrote

First off is Specifically SAID they would never observe each other. That was the entire point of my post. Second off NO F-ING SHIT it's like falling into a planet. Did you think black holes are actually hollow?

I am sorry, I shouldn't be angry. It is fine that you don't known stuff. The reason I am upset is that you didn't know what you were talking to about but you tried to correct me. Next time, if what someone is saying doesn't make sense to you and you aren't an expert in the subject, maybe try asking questions. The answers will tell you if the person knows more than you do or if they are just full of shit.

PLUS that way if they do turn out to be full of shit you get to be the reasonable guy who really embarrassed them when you figure out why they are wrong. And if they turn out to be right you learned something and gain a lot of respect and karma.

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