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Penrose: there was a universe before this one

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lightly
On October 12, 2020 at 1:48 AM, Imaginarynumber1 said:

Nope. Black holes slowly evaporate through hawking radiation 

You might be able to explain this.....    I was reading about black holes evaporating, and 'it' was saying that sometimes, some of the  radiation/evaporation was in the form of photons.   (light).   'It' was saying that if a positive particle was absorbed, a negative particle was ejected/evaporated ....and vise-versa.     I was surprised because ,haven't we been told that NOTHING can escape the pull of a black hole,  even light/photon.  ?       Thanks in advance.

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Imaginarynumber1
On 10/15/2020 at 8:19 AM, lightly said:

You might be able to explain this.....    I was reading about black holes evaporating, and 'it' was saying that sometimes, some of the  radiation/evaporation was in the form of photons.   (light).   'It' was saying that if a positive particle was absorbed, a negative particle was ejected/evaporated ....and vise-versa.     I was surprised because ,haven't we been told that NOTHING can escape the pull of a black hole,  even light/photon.  ?       Thanks in advance.

We've known for some time about Hawking Radiation and the evaporation of black holes. Your basic explanation is correct, but involves virtual particles and various quantum effects. 

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Rolci
On 10/10/2020 at 1:55 PM, Taun said:

Thanks for your explanation! The only question I have about it is your opening line. Isn't the very definition of a "Black Hole" an object that is so gravitationaly powerful that even light (photons) cannot escape it's gravity? Hence it's name? Perhaps that is what "Dark Matter" actually is? (Or am I opening a new can of worms?) Granted a "low mass" black hole would have a correspondingly smaller area of effect - but still be extremely strong. Unless I'm confused (always a possibility :))

I will say that your understanding is not incorrect. I would invite you to research how small that area of effect would be in the case of, for exampe, a black hole the mass of the Earth. You will find some very simple equations if you do. And if you do the calculations you will find that the area of effect is so small that pretty much nothing gets that close to it as it has a low mass, therefore, again, a low gravitational field - the same as the Earth's. Meaning that it will only attract stuff with the same force the Earth does, which is really low. You probably recall some space rocks that pass us with a near miss reported in news every now and then. They're rare, and even they miss. Most objects don't even get close. If you replaced the Earth with an Earth-mass black hole, the exact same situation would be the case.

If you want to get into the thick of it and grasp the fundamental difference between the effect of the two objects (Earth and the Earth-mass black hole) you will do well to imagine getting closer to the black hole than our current distance from the center of the Earth. This is where the differences start. As you get closer to the center of the Earth (say you go down an imaginary elevator) there will be more and more material (mass) "above" you, pulling you "up", effectively canceling out some of the pull "down". When you get to the center, G=0 as there is as much mass "above" as "below" (indeed, all around). With the black hole, all the mass is always "down". What that means is that you can get infinitely close to it, and the closer you get the stronger the gravitational field. No surprise then that even a black hole the mass of an ant will have a strong force close enough, strong enough to pull light back - because it's a black hole. But in the case of an ant-mass black hole the Schwarzschild radius will be on such a small scale that the effect on the external world will be practically 0 and it won't be gaining mass at any observable speed. It will still be an ant-mass black hole in a zillion years, unless it is pulled into a star or something, in which case it will eat it up. But keep in mind, it was the star that pulled the black hole and not the black hole that pulled anything because "it had a strong gravitational field". It did not. It does not. Small mass - weak field - tiny effect on the world.

Hope this helped.

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