62qP3 - Results

1. What is meant by saying, "A black hole has no hair?" (J. Hedstrom)

This saying refers to the fact that black holes can be completely described by three numbers: mass, angular momentum, and electrical charge. There are no other attributes or adornments.

• It means that any sort of purturbation in the spherical symmetry of a black hole would stay for long due to the gravitational effects of the singularity. This also holds true even in the ring singularities. (Casey Bauer)
• The stars which form a black hole are left determined by only three numbers, mass, spin, and charge...no distinguishing features. (Jason Evans)
• black holes have no other attribute other than mass, nagular momentum, and electric charge. (Jason Brudvik)
• This means that whatever goes into a black hole loses its identity. If you look at a black hole you will not be able to get any information about what the mass of the black hole was initially made of. (Gianpaolo Carosi)
• A black hole can be completely described by three numbers: its mass angular momentum and electric charge. It has no other attributes, so we say it has no hair. (Yinan Song)
• A black hole has no distinguishing characteristics other than its mass, angluar momentum and electric charge. (Jim Frinier)
• A black hole can be completely described by three numbers: mass, angular momentum, and charge. It has no other attributes -- ie, hair. (Anna Clower)
• A black hole emits no radiation. (Jenica Nelan)
• this means that black holes can be descibed by just three numbers, mass angular momentum, and electric charge. black holes have no other attributes. (Christian Baude)
• Translates from nerdspeak to mean that there ain't nothin' very individual about black holes. A black hole can be completely described by figures for its mass, angular momentum, and charge. So black holes are really (kinda) just big particles! (Justin Radick)
• it can be described completely by its mass, angular momentum and electric charge since they have no other attributes or adornments. (Jenni Voelmeck)
• a black hole can be completely described by thre numbers: its mass, its angular momentum, and its electric charge (Jonathan Hedstrom)

2. What would be the approximate lifetime of a primordial black home of about 10^{-20} solar masses? (C. Simpson)

1. (0) 100,000 years
2. (10) 1,000,000 years
   {Christian Baude, Jason Evans, Anna Clower, Justin Radick, Yinan Song}
3. (1) 100,000,000 years
   {Nathan Miller}
4. (2) 10,000,000,000 years
   {Gianpaolo Carosi, Jenica Nelan}

3. Describe qualitatively what the ergosphere of a rotating black hole is. (G. Carosi)

The ergosphere of a black hole is caused by frame dragging. When a massive object spins it induces a rotation in the surrounding spacetime, called frame dragging. Near a rotating black hole, frame dragging is so severe that there is a non-spherical region outside the event horizon called the ergosphere where any particle must move in the same direction that the black hole rotates. Spacetime within the ergosphere is rotating so rapidly that a particle would have to travel faster than the speed of light to remain at the same angular coordinate used by a distant observer. The outer boundary of the ergosphere is called the static limit, so named because once beyond this boundary a particle can remain at the same coordinate as the effect of frame dragging diminishes.

• I rotating black holes, the motion of the spacetime frame severely distorts spacetime just outside of the event horizon at Rs also. This area (nonspherical) would cause any particle to move in the direction of the rotation of the black hole. (Casey Bauer)
• The ergosphere captures the spacetime surrounding a black hole in a "frame" and drags it around quite quickly, so that a particle captured within it, cannot stop the rotation. (Jason Evans)
• It is the region outside the event horizon of a black hole where frame dragging is severe and particles must move in the same direction that the black hole rotates. (Jason Brudvik)
• The ergosphere of a rotating black hole is caused by the frame shifting which a massive body puts on the space surrounding it. Inside the ergosphere objects mucst rotate around the black hole. They cannot stay stationary with respect to an observer at infinite distance because the would have to be going faster then the speed of light. (Gianpaolo Carosi)
• The ergosphere is where any particl must move in the same direction what the black hole rotates. (Yinan Song)
• The ergosphere is the nonspherical region of spacetime that is dragged around with the rotation of the black hole. (Jim Frinier)
• The nonspherical region outside the event horizon where particles must move in the same direction that the black hole rotates (b/c a massive spinning object induces rotation in the surrounding spacetime) (Anna Clower)
• A nonspherical region near the black hole where any particle must move in the same direction that the black hole rotates. (Jenica Nelan)
• the ergosphere is a nonspherical region outside the event horizon of a black hole where any particle must move in the same direction that the black hole rotates (Christian Baude)
• It's like a region of vortex space where anything inside is forced to spin with the black hole. Like the water of spacetime in a whirlpool. (Justin Radick)
• as the black hole rotates, it drags a piece of space-time around with it. so that any particle within that area (the ergosphere) has to move with it, and those out of it, don't have to. (Jenni Voelmeck)
• the ergosphere is the area surounding the spinning black hole in which all inertial frames are caught up in the rotation by the frame dragging effects. (Jonathan Hedstrom)
• glowing sphere of material being sucked into black hole (Nathan Miller)

4. Most succinctly, what is the black hole information loss problem? (J. Evans)

Two possible answers: (1) the accretion of matter into a black hole violates the laws of quantum mechanics, (2) the information inherent in matter is absorbed into the few known quantities of a black hole.

• Once a black hole "evaporates", can we ever tell what went inside it, i.e. is that information lost? (Casey Bauer)
• The information contained within accreted particles is lost in the hairlessness of a black hole. (Jason Evans)
• From within the event horizon of a black hole nothing can escape, including light, so that no information may pass to the outside. Anything that passes the horizon can never escape. (Jason Brudvik)
• Any information that goes into a black hole will be lost forever. (Gianpaolo Carosi)
• Objects fall into black holes. The information it contains now is contains in the black hole. But the black hole evaporates by Hawking radiation which is random and doesn't contain any information. Consequently, Information is lost after the black hole is radiated away. (Yinan Song)
• A system of mass before it falls into a black hole is described by a PURE state, and after the black hole is radiated away it is a described by a MIXED state. In the non-unitary transfer from a PURE to a MIXED state, information is lost thus violating the laws of quantum mechanics. Probability is no longer preserved. (Jim Frinier)
• A quantum system in a pure state (described by a large array of numbers) thrown into a black hole will eventually "evaporate" into a thermal system, described by only one number (temperature); therefore, information has been lost. I think Hawking's lecture (at Caltech) made more sense to me; he talked about how a black hole eventually fades away to nothing, so any wavefunctions trapped inside of it will be "lost" since they never have a chance to escape. (Anna Clower)
• Knowing whether or not information can be transmitted somewhere else after falling into a black hole. (Jenica Nelan)
• once an object reaches the event horizon it appears to remain at rest, however according to the object it will continue to move. This information of motion nat the event horizon is lost (Christian Baude)
• Heh heh heh. I think that was the question of what happens to materials trapped beyond the blue event horizon of a black hole. You'd suppose they'd be trapped there forever due to the Schwartzchild metric. But Hawking says: even black holes ain't forever. When they finally evaporate, where does the information go? (Justin Radick)
• imagine a black hole of mass M. after you throw in something of mass m and then wait until it evaporates back to the original M, the system has become a thermal system. however, by changing from a pure state to a mixed (thermal) state, we lose information accroding to quantum mechanics. (Jenni Voelmeck)
• when matter forms into a black hole, information is lost that cannot be regained when the black hole evaporates (Jonathan Hedstrom)
• quantum pure state turned into thermal state - probability not conserved (Nathan Miller)