Thread: Black Hole FAQ

This thread is intended to be used as a simple easy to read and itemized FAQ regarding Black Holes.

• What is a black hole?
• How big is a black hole?
• What is Information?
• How does an external hoverer observer observe something falling into a black hole?
• How does an external freefaller observer observe something falling into a black hole?
• How does a freefaller observe the universe?
• How are black holes created?
• How long to Black Holes live?
• What is the difference between a Black Hole and a Neutron Star and how are they formed?
• How do black holes evaporate?
• What is an Event Horizon?
• What is a white hole?
• What is a wormhole?
• What is a Photon Sphere?
• What is a Singularity?

Can someone help answer these questions?

• What is a black hole?
A black hole is (or rather was) an object in space whose mass is so great that the compressive force of its own gravity exceeded the repulsive force of matter (atoms resist being squashed together).
As mass and accordingly, gravity increase, the matter is squeezed more and more. Eventually fusion reactions occur. This phase is a star.
If certain conditions are met, (very large star runs out of fuel and collapses) the matter is squashed together until all the atoms are pushed together, at which point their charges cancel each other and they all become Neutrons. This phase is a "Neutron star".
If the mass of the star was great enough the collapse would not stop at the neutron phase. Instead, the atoms would be crushed to neutrons and then crushed even more to become a "Singularity". A singularity is a point in space that has infinite density and occupies zero space. Its density is complete. Its "size" is infinitely small. It has no "size" and is thus only a point. A singularity.
Matter displaces space-time. This is called gravity. The more matter, the more space-time is displaced, and the denser the matter, the stronger the displacement. A black hole is squeezed so densely that no space-time can permeate it. There is no (zero) space-time in the black hole because the mass is too dense (too tightly squeezed) to allow any space-time to permeate within. A black hole is a complete displacement point, like a drop of oil on water, where the space-time surrounds it but is a distinctly separate medium.

Because our perceived existence is bound to the 4 dimensions of space-time, anything and everything that lies within a black hole exists outside of our perceived reality. A black hole truly is a "doorway" as it is quite literally an "exit" from our perceived existence and therefore an entrance to some alternate level of existence. We know there are perhaps ~10 dimensions of reality. Therefore it follows that "existence" on or in a black hole is an existence based upon the other ~6 dimensions of reality.

• How big is a black hole?
Theoretically it has no size. It is only a singular point. However the "event horizon" may vary in size perhaps growing much bigger in diameter as the black hole gains mass.

• What is Information?
Information is an optional state of existence. That is, something that exists and can exist in more than 1 state is information. That is the principle of the binary numerical language. You cannot write down information with a single numeral. If all spaces are filled with a single numeral and no other numeral can be used, there is no information. However if you can use blank spaces or other numerals, then you can encode information.

A single point in space can exist in an infinite number of places in that space. Therefore, it can have infinite states. However, it can only signify 1 bit of information. It is only a single point. 2 points, can likewise exist in infinite places but they can also exist in infinite distances from each other. Therefore they can signify many bits of information.

The amount of different possible states of things multiplied by the amount of those things = "entropy". An empty box has significantly less entropy (information) than a box full of stuff.

The entropy of a black hole is a matter of confusion and debate. If it truly contains matter, what is the state of that matter and is it variable?

• How does an external observer observe something falling into a black hole?
You watch things fall toward the "event horizon" and the closer they get, the slower they move. Also, the closer they get, the more blurry they become. In all probability, you could sit there for 1000 years watching things slowly approach and then apparently stop frozen in place and time. The compression of space-time near the black hole causes time to slow down. All things fall slower and slower and appear to stop somewhere around the horizon forever.


• How does a faller observe the universe?
As you fall toward the black hole, the rest of the universe around you speeds up. The closer you get to the black hole, the faster the universe outside goes. The universe gets brighter and brighter, stars flash all around as they are born, grow old and die, faster and faster, galaxies spin faster and faster, nebulae swirl and boil and fade like storm clouds in fast-forward. As you approach the horizon of the black hole, the universe outside would become a hectic gyrating mess of streaking light and dizzying motion and then quickly fade to nothing as the universe expands, grows cold and fades away. It is at this point that you might see a new "big bang" if such a thing is in fact in our future. Once you reach the horizon of the black hole, you would essentially cease to exist in this universe. Where you would then exist is a mystery.

• How are black holes created?
see number one.

• How long do Black Holes live?
That depends on what you believe. If you believe in Hawking Radiation, then it is possible that black holes might eventually "evaporate". If you do not believe in Hawking radiation, then you might believe they last forever, or that they are pulled apart by the expansion of space, etc. Nobody knows.

• What is the difference between a Black Hole and a Neutron Star and how are they formed?
See number one.

• How do black holes evaporate?
According to the Hawking Radiation model, the force of gravity on the "surface" or "horizon" of the black hole is so strong that it can tear apart fundamental particles. As they are split, one half falls in and one half sling-shots away, thus causing the black hole to slowly lose mass through radiation. I don't really understand it.

• What is an Event Horizon?
The event horizon is the distance from the black hole (singularity- point of infinite density and zero volume or size) where the pull of gravity is stronger than the speed of light. Light can come close, skimming by and bending around it but if it comes too close, and goes into the "event horizon" (gets closer to the singularity than the distance of the "event horizon") then the light can never get back out.

• What is a white hole?
A white hole is a theory that the black hole is in fact 1 end of a tube or doorway and all matter/light that falls into the black hole then pours out the "other side", the other side being the "white hole" because it is a singularity that emits massive amounts of energy and/or matter from an infinitely small and dense point. Where is this white hole? Who knows. It is a theory.

• What is a wormhole?
The structure depends on who you ask, but the theory is that space-time can be distorted into a "tunnel" spanning great distances and times or even alternate realities. Some believe black holes could be wormholes. Some believe the big bang caused swirls in space-time that manifest as tunnels between different parts of space-time. We know they are possible. We also know that the amount of energy needed to make one is essentially infinite and would almost definitely cause a destructive black hole or space-time-quake that would unravel the wormhole and cause harm to anyone trying to enter it.

• What is a Photon Sphere?
A photon sphere is a spherical region of space where gravity is strong enough that photons are forced to travel in orbits. The formula to find the radius for a circular photon orbit is: r=3GM/c2. Because of this equation photon spheres can only exist in the space surrounding an extremely compact object, such as a black hole or a neutron star. The photon sphere is located farther from the center of a black hole than the event horizon. Within a photon sphere it is possible to imagine a photon that starts at the back of your head and orbits around a black hole only then be seen by your eyes.

• What is a Singularity?
It is a black hole. See number one.

Originally Posted by dedcupid

• How big is a black hole? Theoretically it has no size. It is only a singular point. However the "event horizon" may vary in size perhaps growing much bigger in diameter as the black hole gains mass.

I thought a BH is defined by its EH ... which in turn is the maximum amout of mass that can fit in a volume. And that this has to do with a bit of information somehow.