Physics Question #1538

Sarah Bosquet, a 26 year old female from Issoudun asks on August 9, 2003,

I'm writing a science-fiction novel and need information about black holes, gravitation and nothingness. Unfortunately I have no scientific education. Can you help me?

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The answer

Barry Shell answered on August 10, 2003

The single most important thing you need to know about a black hole is that it is **NOT** a hole. It's a thing. A very very dense object. It is as though our sun, which is very massive, containing most of the mass of the whole solar system including our earth, were to collapse to the size of, say, a giant boulder about 1 kilometer in size. That is: the whole sun becomes the size of a large bolder. But it would still contain the same mass. It would still be there. It would not be a "hole". This happens because the space between the nucleus of atoms and the electrons orbiting the nuclei of gasses that make up the sun collapse to nothing. Since this space takes up about 99% of the atom, the resulting thing is very very dense indeed--a neutron star, but even denser than that. Hence, the gravitational force of such a massive small thing is huge. The gravity is so huge that even light particles with almost no mass, photons, are pulled in. So nothing can "radiate" from the massive small object. So it *appears black*. It's not a hole.

By the way, another very important point about black holes: nobody has ever seen one, held one or actually observed one. Black holes are hence all conjecture and theory and imaginary. We *infer* the existence of black holes in part to explain the massive gravitational sources at the centres of galaxies, and to account for missing mass in our universe that is otherwise predicted by the big bang theory but which is not observable. But there is no actual concrete observable black hole that anyone has "laid their hands on".

An interesting science fiction story involving a small "research" black hole made on Earth that someone "drops" is David Brin's "Earth". You can get this anywhere. In his story, when the "hole" is dropped, it is so heavy and dense, it smashes right through the earth's crust and drops into the molten core of the Earth where it starts orbiting and gathering mass--kind of bizarre, but sort of plausible. Something that you can imagine happening with an object--not a "hole". You can't, for instance, "fall into" a black hole, since there is no hole there. It's a thing. It's like falling *onto* the Earth, except the gravity would crush you long before you hit. A search of google on: science fiction black hole, turns up lots of other good science fiction stories already done on black holes.

Here is a good, though somewhat esoteric, explanation from a physicist on "nothing".

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