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Re: Finite Matter, Infinite Density...

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Posted by John/">John on March 2, 1999 19:36:06 UTC

: : : : According to theory, Black Holes have infinte mass and infinte gravity. : : : : How then, can there be an event horizon? If the force of gravity from the Black : : : : Hole is infinite, then it would not dissipate with distance and therefore would be : : : : the same everywhere, for an infinite distance. If my understanding of infinity is : : : : correct, then Black Holes must have a finite mass and gravity if there is to be an : : : : an event horizon.....right?

: : : actually I think you have the theory off a bit.

: : : BH have (at their singularities) infinite density, : : : not infinite mass; for the reason you state in the : : : latter portion. : )

: : : this is why there are different sizes of BH as well.

: : : For instance the gravitational field surrounding a : : : BH may as well be the mass of 50 of our suns, and : : : the event horizon be 1500 feet across.

: : Thanks, the finite mass aspect clears a few things up.

: : It still doesn't deal with the infinite gravity though. : : How is it possible to measure the dimensions of a : : gravitational field under conditions of infinite gravity?

: A BH does not have infinite gravity whatsoever. : I'm not sure where you heard this from.

: Let me give you an example...

: Take for instance a massive star in its dying phase. : As the nuclear fusion begins to slow, the equalibrium : balance of the force of fusion expelling outwards falls : below the force of gravity collapsing inwards.

: As the crushing force is creating a denser mass, keep : in mind the mass does not change, thus the gravitational : field has not changed.

: Now, imagine the star has collapsed to the critical size : called the, "Schwarzchild radius". This is the diameter : of the star where space has become "potentially" infinitely : curved. Thus light cannot even escape this boundary. : IOW, the escape velocity required to escape this event horizon : becomes infinitely close to the speed of light.

: Now, lets take a step back and look at this BH. Has : its gravity increased? No... In fact, imagine this : particular BH side by side with its earlier form as : the star. The BH and star have exactly the same mass (accounting : the BH hasn't drawn anything in) as the star does. (in its early, : pre-collapse stage) The only thing that has increased : is the density. If you measured the gravity attraction : of the BH at a given distance, you would measure the : same gravity measurement of the same star at the same : distance...

: -nåte

Thanks nate, you obviously know alot more about this than I. I got the infinity thing from a show on the Discovery Channel. The guy who was their "expert" described a BH as having infinite mass and infinite gravity. The logic of that didn't seem to fit, thus the posting on here. Infinite space, I can almost deal with, but infinite mass seemed to have much graver implications.

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