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. Q

    What happens when you fall in an evaporating black hole?

    Here's the best of my understanding of the official explanation of what happens when O' fall in a black hole. eternal black hole For an outside observer O, O' slow down more and more as you approach the event horizon, at the event horizon time seems to completely stop. In the reference frame...
  2. I

    Could High speeds create a black hole?

    As you guys probably know, as an objects speed increases, so does its mass. I was wondering if a black hole could be induced by speeding up a neutron star or some other massive object with high density to high speeds? Also, what is the equation that explains this phenomena? Also, if this is...
  3. S

    Star Trek (2009) and black hole planet collapse

    Hi. I was wondering about this. In the "Star Trek" movie of 2009, the destruction of the planet Vulcan is shown, by a black hole being formed in its core. I'm curious: supposing you had some means to create, or collapse part of the planet to form, a black hole in its core, what would, according...
  4. Quarlep

    Exploring the Energy of Black Holes: A Curious Mind's Guide

    Hello? I have a doubt about black holes energy.I am curious about that.What is the Black Holes energy? Thanks for Help
  5. I

    Would a single black hole form in the big crunch scenario?

    In the big crunch scenario, matter would clump together faster and faster, could a blob of this matter form a black hole, even if it had the necessary energy to maintain fusion or if it had no energy to burn up the matter? If the big crunch were to happen, and a single blob of mass existed at...
  6. P

    How Much Force is Needed to Keep a Drilled Cylinder at Rest?

    Homework Statement A uniform cylinder of radius R and mass 8kg has an off-axis hole drilled through it at 2R/5. Its new mass is 6.5kg. The hole and cylinder are parallel with their centers being the same height. What horizontal force, F, must be applied on the top to keep the cylinder at rest...
  7. C

    Water Flow in Free Fall: Observing the Equivalence Principle

    Homework Statement When a container full of water with a small hole in the side is at rest on a table, water flows out of the hole and follows an approximately parabolic arc before hitting the table. Suppose the same container is dropped down a mine shaft so that it is in free fall. Air...
  8. J

    Consequences of an Oversized Pulley Bore Hole in Conveyor Systems

    What would happen if the bore hole of a pulley in a conveyor was significantly larger than the shaft like in the figure below: I would imagine if the RPM was high, the whole system would shake violently. However, what if the RPM was around 30 RPM. Would the conveyor still function properly...
  9. E

    Mass: Accretion Disk vs. Black Hole

    I asked a question recently about orbiting black holes. Thanks for the answers. So if I'm correct in my thinking, long before the event horizons of orbiting black holes become close to each other, the two accretion disks get mightily disrupted and much of the mass of the two disks would fall...
  10. A

    Hole conduction vs electron conduction

    So recently I took a blow to my understanding of how hole conduction works. Like many others I had the idea that the hole i just an absence of an electron and when it moves the collection of electrons move opposite direction of it like in the analogy where the electron hole is an empty seat in...
  11. Saitama

    Electric field at centre of hole

    Homework Statement A hollow insulating sphere of radius R is charged uniformly to a charge of Q. There is a small hole on this sphere. What is the electric field strength at the centre of this hole? Homework Equations The Attempt at a Solution I think I have to use Gauss's law...
  12. anorlunda

    Heavy atoms in black hole jets.

    A recent APOD page discussed jets ejected from black holes. It said, "Recent evidence indicates that these jets are composed not only electrons and protons, but also the nuclei of heavy elements such as iron and nickel." What is thought to be the mechanism of production of these heavy nuclei?
  13. Saitama

    What Is the Incorrect Statement About the Dynamics of a Falling Chain?

    Homework Statement One end of the chain falls through a hole in its support and pulls the remaining links after it in a steady flow. If the links which are initially at rest, acquire the velocity of the chain suddenly and without frictional resistance or interference from the support or from...
  14. haael

    Is the Big Collapse a Black Hole?

    In the "closed" Friedmann model, there is a Big Bang in the past and Big Collapse in the future. Big Bang singularity is something different than a Black Hole singularity. Now my question: is the Big Collapse singularity mathematically equivalent to a Black Hole (localized) singularity, or is...
  15. O

    Find mass of black hole in center of galaxy given eccentricity+

    Homework Statement Astronomers believe that there is a massive black hole at the center of the Milky Way galaxy. What evidence is there for that? A group of astronomers have observed a star "S2" in a 15.2-year orbit around the center of the galaxy. They measured the period of revolution T =...
  16. Superposed_Cat

    Black Hole & Wormhole: Questions Answered

    Hi, two questions A) If a black hole travels into a wormhole would it collapse the wormhole? B) If a wormhole travels through another wormhole what would happen? Thanks for any help.
  17. D

    Post in Hole Problem: Characterizing Forces at Interface

    Supposing there is a metal cylinder that fits into a perfectly machined hole in a block of metal with the cylinder protruding some length from the block. If you place a force on the edge of the part of the cylinder that is protruding in a direction perpendicular to the hole, is there a...
  18. A

    What's on the other side of a black hole?

    Can a black hole be a portal to another dimension?
  19. A

    Conceptual problem on black hole singularity

    I've read that there's a point in a black hole where matter is infinitely dense. There is zero volume but infinite density. How is it possible for something to have zero volume but have an infinite density at the same time?
  20. B

    Infinite Time Dilation at the Surface of a Black Hole?

    I've never fully understood how anything can actually fall into a black hole without the black hole evaporating first. Since time dilates exponentially as I fall into a black hole, a point will come where a few seconds for me will be millions of years in the outside world...trillions in fact...
  21. B

    Calculating Accretion Rate and Luminosity of Black Holes

    Homework Statement This is the original problem for part 1 A) Suppose that a black hole of mass M accretes mass at a rate ##\dot{M}##. Further suppose that accretion of mass Δm leads to the radiation of energy ##\Delta E= \eta Δmc^2##, for some effeciency of energy conversion, ##\eta##. What...
  22. B

    Black hole Accretion Luminosity

    Homework Statement Suppose that a black hole of mass M accretes mass at a rate ##\dot{M}##. Further suppose that accretion of mass Δm leads to the radiation of energy ##\Delta E= \eta Δmc^2##, for some effeciency of energy conversion, ##\eta##. What is the luminosity of emitted radiation in...
  23. E

    Observing a cube approaching a black hole

    If a distant observer were to observe a large cube made of strong material approach a black hole, what would he see? ISTM that if one of the faces of the cube were to be the nearest approaching portion, he would see the four edges of the face become shorter and curved, and he would see the...
  24. Superposed_Cat

    Light Entering Black Hole: Hawking Radiation Explained

    Hi all, I was wondering if, when a beam of light is pulled towards a black hole , because it can't accelerate, it is blueshifted? Thanks in advance.
  25. R

    Eletric potential inside charged sphere with hole inside

    Homework Statement Consider a charge density of ρ=k/r , k>0 , located between a sphere surface of r=a and another sphere surface of r=b, b>a. I'm supposed to find the electric field on all space, which I did. Now I have to find the electric potential in all space, which I also did for r>b...
  26. Philosophaie

    Black Hole and Electric Charge

    A galaxy is many many light years away. All Electric Charge, Q, must be dissipated. How do you tell if charge exists and what magnitude.
  27. zrek

    Why the photon is disturbed by a hole?

    Please help me to understand why the path of the photon changes when travels close to a material (for example the edge of a hole)? I'm aware that the path of the photon can be calculated by the QM principles as a probability wave and by this the change of the wavefront follows the...
  28. J

    Light that is directed towards the center of a black hole

    If a beam of light is on a trajectory that is perfectly tangent to the event horizon of a black hole (or a little below tangent, allowing it to "dip" into the EH for a moment), is it possible that that photon could be pulled into a never ending orbit around the black hole? Or is the gravity too...
  29. Phy_enthusiast

    Is black hole a theoretical concept or a natural phenomenon?

    is black hole a theoretical concept or a natural phenomenon?
  30. T

    Consumption of a galaxy by its central black hole

    I was thinking about the supermassive black hole that is theorized to be at the center of our galaxy, and indeed, at the center of most galaxies. If that black hole is continuously consuming the stars, planets and gas around it, given enough time, will it not consume the entire galaxy that...
  31. U

    Rewinding a black hole - Can a spinning black hole become a star?

    "Rewinding" a black hole - Can a spinning black hole become a star? I couldn't fit all the important prerequisites and context in the title, so I'll set up the thought experiment here. Some of these assumptions are also questions, and might be easily refuted, thus answering the main question...
  32. J

    Can Extra Dimensions Solve the Central Singularity of Black Holes?

    I was watching a documentary about the universe and it claimed that black holes were sometimes as small as 2 kilometers across. Now before this, my general understanding of a black whole was that it had no physical extent in space, that it was just a 1 dimensional singularity, and the black...
  33. Islam Hassan

    How Much Mass Energy Does a Black Hole Re-Radiate?

    Given a massive object that has entered a BH's accretion disk, what percentage of its mass is typically re-radiated away as i) accretion disk radiation and ii) polar jet radiation/particle streams before ever getting to the event horizon? How much does a black hole *not* consume of its...
  34. AdrianHudson

    Black Hole Equations: Unraveling the Mystery - Adrian

    Hello, I would first just like to introduce myself I'm Adrian and I am a grade 11 student so this type of stuff is way out of my league in terms of mathematical complexity.. but are there equations that define a black hole (What is happening to particles when they enter the event horizon.. etc)...
  35. marcus

    Goodbye Big Bang, hello black hole?

    Holographic BB out of prior BH (stringy version of BH bounce) http://arxiv.org/abs/1309.1487 Out of the White Hole: A Holographic Origin for the Big Bang Razieh Pourhasan, Niayesh Afshordi, Robert B. Mann (Submitted on 5 Sep 2013) While most of the singularities of General Relativity are...
  36. J

    Black hole radius and universe

    The Schwarzschild equation for a black hole's event horizon is rsh = 2GM/c2 or (1.48 x 10-27 m/kg) x M. Thus, the ratio of mass to radius is 6.7 x 1026 kg/m for all black holes. If the mass and radius of the universe are calculated as follows, Mass of the gravitationally connected universe...
  37. Saitama

    "Solving Rope Through a Hole Physics Problem

    Homework Statement A rope of mass M and length ##l## lies on a friction less table, with a short portion, ##l_0## hanging through a hole. Initially the rope is at rest. a. Find a general solution for x(t), the length of rope through the hole. (Ans: ##x=Ae^{\gamma t}+Be^{-\gamma t}##...
  38. T

    Entropy of a black hole after evaporation

    Black holes have an entropy, but they evaporate. At the end of the evaporation, the entropy is greater than the entropy at the beginning of the evaporation. I am looking for an example of a quantitative result for the entropy of the black hole after evaporation (or the entropy difference...
  39. S

    Where should a second hole be placed in order for the light [ ]?

    "Where should a second hole be placed in order for the light [...]?" Homework Statement The problem and the solution are attached as jpg files. (Given that the problem depends on the drawing, I think it's more convenient for the reader to view the text in the image as well.) Homework...
  40. S

    Light wavelenths longer than diameter of black hole?

    I was under the impression that one of the ways of representing a black body (for explaining the ultraviolet catastrophe) is as a 'resonant box'. Frequencies lower than the dimensions of the box cannot be contained within and the black body is thus 'transparent' to those frequencies of light...
  41. D

    Is Black hole complementarity incompatible with Block Time?

    As I understand, complementarity approach claims that there are 2 different stories, for an infalling observer and an observer @ infinity, they are different, but no observer can confirm both. But it violates the Block Time/Eternalism, where time is a dimension, the whole world is a static...
  42. Y

    Tall rotating cylinder near a black hole

    Imagine we have a very tall vertical cylinder like a very elongated telegraph pole, that is rotating at 200 rpm about its long axis on near perfect bearings. Initially the cylinder is sufficiently far from a black hole, that differences in gravitational time dilation between the top and bottom...
  43. jtbell

    Cosmology The Black Hole War by Leonard Susskind

    Author: Leonard Susskind Title: The Black Hole War Amazon Link: https://www.amazon.com/dp/0316016411/?tag=pfamazon01-20 (submitted by jedishrfu)
  44. Ookke

    Will photons fry an object falling into black hole?

    For outside observer, an object falling into black hole seems to freeze at event horizon and never cross the boundary and proceed inside the black hole. This is of course not the case in the falling objects own reference frame. Depending on the size of the black hole, a falling object may not...
  45. T

    Kilonovas caused by black hole neutron star mergers

    I thought readers would be interested in this interesting article today on black hole and neutron star mergers and the very small possibility of instantaneous sterilization and extinction of all life on earth:http://www.space.com/22231-gamma-ray-bursts-neutron-stars.html...
  46. S

    Inner and outer horizon of black hole

    hi some black holes are inner and outer horizon! what's this means? inner and outer? what happen between them?
  47. S

    Recognize Black Hole: Metric Conditions & Features

    consider have a metric ds^2=f(r,t)dt^2+g(r,t)dr^2+k(r,t)dΩ^2 if g(r,t) =0, we have black hole? any metric that has this condition, are black hole? or not this is first clue to determine black hole and we should check some other features! solution of g(r,t)=0, may have some roots, for example...
  48. Ookke

    What if Earth crossed the event horizon of a supermassive black hole

    From previous threads I have understood that crossing the event horizon of a supermassive black hole is nothing very unusual for the falling observer locally. Usually in these considerations the falling observer has been thought as a "point" without much dimension. How about if Earth (and...
  49. Drakkith

    Is This Description of Falling Into a Black Hole Correct?

    From here: http://www.reddit.com/r/askscience/comments/f1lgu/what_would_happen_if_the_event_horizons_of_two/ (About a page down from the top. You can't miss it.) Imagine, just for a moment, that you are aboard a spaceship equipped with a magical engine capable of accelerating you to any...
  50. atyy

    Effective field theory, black hole evaporation, firewalls

    Arkani-Hamed, Dubovsky, Nicolis, Trincherini, and Villadoro argue in section 2.2 of A Measure of de Sitter Entropy and Eternal Inflation that the effective field theory description of black hole evaporation fails after a time tev, even though the curvatures are small. Almheiri, Marolf...
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