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What are black holes made of?

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#26 EJN

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Posted 27 April 2019 - 02:53 PM

If time approaches zero near the event horizon, doesn't that mean that the events that happen in the event horizon aren't a part of the history of the universe?

 

Time approaches zero only in one specific frame of reference, a stationary observer distant from

a black hole. From the frame of reference of matter falling into a black hole, no time dilation

happens at all and you fall through the event horizon quite quickly. For a distant outside observer

moving with respect to the black hole, that is a frame of reference intermediate to the two

diametrical cases above.

 

The 2 extreme frames of reference might seem like a paradox, but the distant stationary

observer frame of reference is an inertial reference frame, and the frame of reference of infalling

matter is an accelerated reference frame due to the strong spacetime curvature, and the 2 are

not interchangeable. The dynamics of black holes are normally described in the accelerated

reference frame, since strong spacetime curvature is the defining characteristic of black holes.


Edited by EJN, 27 April 2019 - 03:09 PM.


#27 PXR-5

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Posted 27 April 2019 - 05:38 PM

Stay away from black holes, they are dangerous.

#28 bitnick

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Posted 30 April 2019 - 07:01 AM

From the frame of reference of matter falling into a black hole, no time dilation
happens at all and you fall through the event horizon quite quickly.

What does the outside world look like according to the infalling matter? If, according to an outside observer, it takes an infinite time for matter to pass the event horizon, does that mean the infalling matter "sees" literally all the future events that will ever happen outside the black hole as it reaches the EH? If so, and if Hawking radiation exists (or some other mechanism that "evaporates" black holes over arbitrary time frames), then wouldn't that mean that, from its own perspective, it gets instantly radiated away before passing any distance inside the horizon?



#29 Jim Davis

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Posted 30 April 2019 - 08:13 AM

What does the outside world look like according to the infalling matter? If, according to an outside observer, it takes an infinite time for matter to pass the event horizon, does that mean the infalling matter "sees" literally all the future events that will ever happen outside the black hole as it reaches the EH? If so, and if Hawking radiation exists (or some other mechanism that "evaporates" black holes over arbitrary time frames), then wouldn't that mean that, from its own perspective, it gets instantly radiated away before passing any distance inside the horizon?

Here is a good explanation of time inside a black hole from PBS Space Time: https://www.youtube....h?v=KePNhUJ2reI



#30 bitnick

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Posted 01 May 2019 - 12:37 PM

Thanks, PBS Space Time's videos are great!

 

Here's one that directly answers my question: https://youtu.be/mht-1c4wc0Q?t=495

 

In short: You'd need to hover above the event horizon to see the universe go by in fast forward.



#31 ColoHank

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Posted 04 May 2019 - 07:32 PM

According to Wikipedia, the Black Hole of Calcutta was a prison in Fort William in which British prisoners of war were incarcerated for a three-day period in June,1756.  The facility was small and so crowded that 143 of 164 prisoners confined therein died of suffocation and heat exhaustion.  Thus, at least one black hole is known to have contained a bunch of unfortunate humans long before Einstein or Hawking ever gave the topic any thought.



#32 rowdy388

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Posted 05 May 2019 - 02:45 PM

According to the Big Rip theory even black holes get torn apart.  If so they must be part of our universe??

Yes, no, maybe? A black hole ripping apart would be in the form of Hawking Radiation presumably?




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