What is Hole: Definition and 1000 Discussions

A hole is an opening in or through a particular medium, usually a solid body. Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in many fields of engineering. Depending on the material and the placement, a hole may be an indentation in a surface (such as a hole in the ground), or may pass completely through that surface (such as a hole created by a hole puncher in a piece of paper). In engineering, a hole may be blind or through if it is partial or complete depth.

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  1. Crazymechanic

    What would happen if a black hole sucked in a cloud of hydrogen gas?

    Now what I'm about to say may sound like a sort of speculation but not in the typical bad way. Now we have a black hole in universe somewhere.(Doesn't matter where for my theoretical purposes) Now we know that once a big star looses all or most it's fusion elements and some of it's mass that...
  2. A

    Black hole information paradox

    I watched this documentary about an argument involving information loss in a black hole, Stephen Hawking managed to wind everybody up by claiming information was lost and therefore broke existing laws of physics. Its an old recording so it may not be relevant anymore but one part of this...
  3. mathmaniac1

    MHB Cutting an elephant-sized hole in a sheet of paper

    Challenge: Can anyone tell me how to cut a hole in a sheet of normal Book paper the size through which even an elephant can pass...?
  4. P

    Could the LHC potentially form a black hole?

    Hey I heard from a couple differnt places on the internet that there's a possibility that a black hole hypothetically could be formed by the LHC. I thought that black holes were formed by the implosion of a huge star that keeps going in on itself due to gravity. Is it true that this could happen...
  5. O

    The Mass of a Black Hole versus its volume

    A clump of matter does not need to be extraordinarily dense in order to have an escape velocity greater than the speed of light, as long as its mass is large enough. You can use the formula for the Schwarzschild radius Rs to calculate the volume 4/3piRs^3 inside the event horizon of a black hole...
  6. Mordred

    Black hole accretion disk/jet reference

    I found this extremely handy reference on Black hole calculations and models to measure black hole accretion disk/jets. The article also covers several types of BH non rotating and rotating. Methodologies that can be used to distinquish between Neutron and black hole event horizons...
  7. S

    Good dielectric yet hole conductor?

    Is there some material that could withstand relatively high voltages before it starts to conduct electrons,but in the same time a good hole conductor? Could such material be obtained by doping some dielectric similar to SiO2?
  8. H

    How is one black hole is larger than another?

    If black holes crush things into infinite density, shouldn't they all be the same size?
  9. G

    Big Bang vs Black Hole: Exploring the Universe's Past

    If the universe was at or near a singularity in the past, why is it not a black hole now? How can part of the universe become a black hole, and not the whole universe?
  10. V

    Buckling limit of a square plate over a circular hole

    Hi, I am carrying out a series of experiments which consist of a square plate object placed over a circular hole. The experiment is done in such a way that I can apply a point force at the center of the plate and see how much force is required to pull the plate through the hole. I should add...
  11. icesalmon

    Calculating the Diameter of a Drilled Hole in a Revolved Solid

    Homework Statement A solid is generated by revolving the region bounded by y = x2/2 and y = 2 around the y-axis. A hole, centered along the axis of revolution, is drilled through this solid so that one-fourth of the volume is removed. Find the diameter of the hole.The Attempt at a Solution...
  12. B

    Where do you think a black hole leads to, or what is inside of one?

    This is a simple question, right? Well, no. Many theories have been conjured up and broken down. However, I just want to know what all of you think or theorize about the point past the event horizon of a black hole. Does it lead to a parallel universe? Does it destroy information, a breaking...
  13. Kawakaze

    Hole in reality? Very strange experience I (we) had

    I am a bit wary about posting this, as I am pretty sure what the response would be if I claimed this was paranormal or some other weird stuff. So before we start, I do not believe in ghosts, I do not follow religion, I am very much a believer in the scientific method. I am not claiming to have...
  14. PeterDonis

    How do inertial frames centered on a black hole's horizon work?

    This is a puzzle based on a purported "refutation of GR" on http://finbot.wordpress.com/2008/03/05/no-black-holes/, which is also the subject of a subthread in this Hacker News discussion. (Btw, the Hacker News discussion contains my answer to the puzzle if you scroll down enough, so you're on...
  15. PeterDonis

    Black Hole as Wormhole: Exploring the Possibility in the Paper by Poplawski

    A recent thread on Hacker News led me to this paper by Poplawski: http://arxiv.org/abs/0902.1994 The abstract says: "We consider the radial geodesic motion of a massive particle into a black hole in isotropic coordinates, which represents the exterior region of an Einstein-Rosen bridge...
  16. shounakbhatta

    Star collapse to form directly a black hole

    Hello, Does a star collapse directly to form a black hole without creating a supernova or whether a supernova forms some neutron stars which after crossing the TOV limit forms a black hole? Thanks.
  17. A

    Curious about Black hole information paradox

    Hi! I am not much of astrophysicist or something but read something about Black hole information paradox in a book. Could anybody please explain me what is the meaning of term and why does it happen? P.S. Please include Hawking's radiation as well Thank you in advance
  18. E

    Entropy and Black Hole Temperature

    Homework Statement In a previous problem I had to find the entropy of a black hole where I ended with this: S_{BH}=\frac{8 \pi^2 G M^2 k}{h c} Now I am to find the temp, given the energy of a black hole is mc2. Homework Equations T=(\frac{\partial S}{\partial u})^{-1} The...
  19. N

    Is the Big Bang Similar to a Black Hole?

    In this FAQ at the Baez website, the big bang singularity is contrasted with a black and white hole as a possible beginning of our universe. Is the Big Bang a black hole? http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/universe.html [I'm not interested in answering the title...
  20. D

    Calculating Time for Sliding Chain through Hole

    Homework Statement A flexible chain of mass M and length L lies on a frictionless table, with a very short portion of its length L0 hanging through a hole. Initially the chain is at rest. Find a general equation for y(t), the length of chain through the hole, as a function of time. (Hint: Use...
  21. A

    How Does Hawking Radiation Affect Black Hole Temperature?

    Hi, I recently came across this formula: T = \frac{\hbar c^3}{8 \pi GK_BM} As I understand it deals with the radiation that is believed to be emitted by a black hole. Does it describe the temperature of the radiation? Thanks
  22. Q

    Hawking radiation and Black hole evaportion

    When the 'evaporation' of a black hole supposedly occurs, it is always attributed to 'Hawking radiation.' As I understand it, Hawking radiation occurs when a virtual particle pair is 'split' at the exact edge of an event horizon. When this occurs, one of the particle pair escapes to 'normal'...
  23. Q

    Big Bang singularity vs Black hole singularity

    One speaks of the Big Bang initial condition as a singularity possessing an extremely low entropy (to explain the growth of entropy throughout time to our present stage of the universe). If that singularity truly possesses infinite density, that would make perfect sense, since what would become...
  24. Islam Hassan

    Black Hole Entropy/Temperature

    In thermodynamics, I assume that any closed system that can be described in terms of individual objects/particles and their associated individual momenta has both entropy and temperature. A priori a black hole seems to me to fit that description of a closed system. Why was it significant...
  25. A

    Question about the universe and a black hole

    I recently asked myself the question "If all the stars in the universe condensed together to form a black hole how big would that black hole be?" Using the information from http://en.wikipedia.org/wiki/Observable_universe I got the approximate mass to be 3x10^52kg. After that it was just a...
  26. anorlunda

    Destroying A Black Hole: Can Alice Escape?

    So we know that Alice can free fall through the event horizon of a black hole and not notice anything. Yet Passing the event horizon is a one way event; no thing and no information can ever exit. (Except Hawking radiation). As a thought experiment, suppose we bombard the black hole with...
  27. P

    Finding the electric field on a cylinder with a hole

    Homework Statement A very long, solid insulating cylinder with radius "R" has a cylindrical hole with radius "a" bored along its entire length. The solid material of the cylinder has a uniform volume charge density "ρ". In this problem, you will find the magnitude and the direction of the...
  28. J

    Black Hole - Conservation of energy?

    since energy absorbed by a BH is no longer available to the universe, why is that not a violation of the principle of conservation of energy?
  29. S

    Big Bang, result of black hole?

    I'm certainly no scientist, but I've always had an interest in Physics & Astronomy, so I read a bit here and there, watch primarily science shows on TV etc...Just an interest. I was wondering though, and figured on a site called "Physics Forums" there may be a physicist or two running around...
  30. L

    Infinity potential hole - transition to base state

    Hi! I try to figure out the probability (sure as function of parameter time) of transition particle in the hole from the first excitation state to the base state in an infinity potential hole. Because the eigenfuncion of particle there are orthogonal, the probability looks like zero -...
  31. phinds

    Is the event horizon of a black hole physical?

    In another thread, which I don't want to derail, the issue came up as to whether or not the event horizon of a black hole is physical. Some contend that it is physical but I contend that it is merely a set of coordinates (most easily represented by the spherical coordinate R). I DO...
  32. R

    Charged Sphere with a Hole - Check my work?

    Charged Sphere with a Hole -- Check my work? Homework Statement You have a spherical shell of radius a and charge Q. Your sphere is uniformly charged except for the region where θ<= 1° (which has σ = 0). Imagine that your fi eld point is somewhere on the positive z-axis (so z could be...
  33. N

    Ampere Law in a hole Should give zero?

    Hi all, I just did an exercice and there is one point that I don't understand (about Ampere's law). Homework Statement The exercice was about a cable with given diameter a, in which a small hole with diameter b is drilled in. The axis of the cable and the hole are parallel and the...
  34. C

    What happens when a black hole devours another black hole?

    What happens when a black hole devours another black hole? The bigger eats the smaller and increases in mass and size? What happens with the singularities?
  35. C

    Area of event horizon and irreversible mass of Kerr black hole

    Hi everyone, and happy new year if you happen to be reading this tomorrow. Rather than partying, I am writing up 100+ pages of astrophysics lecture notes, which I think will take infinite time as I keep getting stuck on every other line. My current problem is with the equation for the...
  36. BitWiz

    Is the growth of black holes paradoxical?

    Much of what people say about the vicinity of black holes doesn't seem to make sense. For instance, it seems to be impossible for a black hole to grow by "ingestion" by scooping up matter around it or in its path, at least in the traditional sense. Gravitational time dilation takes care of...
  37. Crazymechanic

    Hawking radiation , black hole size

    Hi. If the hawking radiation is emitted from outside the event horizon , because probably that's the last place where the particles are being able to escape, then how come huge black holes ever evaporate as the matter behind event horizon has no chance of escaping in any way as to the immense...
  38. shounakbhatta

    So the question is:Do all galaxies contain super massive black holes?

    Hello All, It says that, if we discover every galaxy, then there is a super massive black hole, present in each galactic centre. Is there any physical rule for that? I mean to say, a galaxy rotates with x,y,z...rules, the gravitational force is such and such... So, the formation of...
  39. S

    How does a black hole know how big it should be?

    I was reading an article the other day about the second largest black hole found, something around 17 billion solar masses big, with an estimated event horizon 11 times the orbit of Neptune and it got me thinking. If all the matter generating the gravity lies in the singularity, how does that...
  40. P

    Loop of pumped fluid slowly falling into black hole.

    You have this loop of water (or some other "incompressible" fluid) with a nuclear powered water pump that constantly pumps the water in a circle. This loop is slowly lowered near the event horizon of a black hole, let's even make it a super duper massive black hole to minimize tidal effects...
  41. P

    Sphere with a hole drilled in center

    Homework Statement Find volume of a sphere with radius R with a hole drilled through the center of radius b. (b<R) Homework Equations cos thera = adj / hyp The Attempt at a Solution 4\,\int _{0}^{\arccos \left( {\frac {b}{R}} \right) }\!\int _{0}^{\pi }\!\int...
  42. C

    Exploring the Effects of a Black Hole's Event Horizon on Electron B Field

    Lets say an electron crosses the event horizon of a black hole. Now as it starts speeding up when it gets closer to the center of the black hole its B field will increase. Does this increased B field exist outside the event horizon?
  43. B

    Why photon loss energy when escape from a black hole ?

    Hello all . Why photon increase energy and frequency when falls in gravitational field ? or decrease it's energy when escape from a black hole ?
  44. harrylin

    Are Finkelstein/Kruskal interior black hole solution compatible with Einstein's GR?

    Are Finkelstein/Kruskal interior black hole solutions compatible with Einstein's GR? This topic is a spin-off from a number of recent discussions: "Are "flowing space" models compatible with GR?" "Schwartzchild and Synge once again" "Oppenheimer-Snyder model of star collapse" "Notions of...
  45. S

    'Over-massive galactic black hole discovered

    'Over-massive" galactic black hole discovered http://www.nature.com/nature/journal/v491/n7426/full/nature11592.html Can someone elaborate on how this challenges current theories of galactic evolution?
  46. C

    At what point would we discover a black hole headed directly toward us?

    Say a three solar mass black hole. Would someone notice it before it reached the Kuiper Belt, or only after there were deflections of known bodies in the Kuiper Belt?
  47. A

    Black hole event horizon radius = Schwarzschild radius?

    I am under the impression that the event horizon radius of a non-rotating black hole is equal to its Schwarzschild radius. Is this correct? If yes, then I have a mixed bag of questions: Is the event horizon radius always calculated using the Schwarzschild metric, no matter what model we are...
  48. A

    Black hole accretion: angular momentum loss

    Why exactly is it necessary for angular momentum to be lost by a mass if it is to accrete around a black hole? the mass is decreasing its radius, so it speeds up: thus angular mometum is conserved. But everywhere it is saying that 99.99% of the angular momentum must be shed for accretion to...
  49. S

    Time for a Droplet of Water to Fall .25m from Hole

    Time for Droplet of Water to Fall .25m from Hole Homework Statement A cylindrical tank .7m tall is filled with water and placed on a stand (below it) that is .3m tall. A hole of radius .001 m in the bottom of tank is opened. Water then flows through the hole and through an opening in...
  50. S

    Black Hole Angular Velocity: Is Expansion Feasible?

    Could a small black hole achieve an angular velocity such that the centripetal force is >= gravity, which would expand it enough to turn into a quark star or neutron star? I realize that in order to rotate the black hole further, more mass must be added that will increase the amount of...
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