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. wolram

    B The big bang singularity and black hole singularity

    In the big bang model the singularity is all ways quoted as being the start of the universe, but AFAIK scientists do not accept the singularity as real, the same with the black hole singularity, what is proposed to be in their place? from Wiki. The initial singularity was the gravitational...
  2. Cobalt101

    I Time to Form Black Hole? | Observer Slows Time at Event Horizon

    Is it correct that, from the perspective of an observer, time slows down and ultimately stops at the event horizon of a black hole, implying that no black holes have had time to form in the universe ?
  3. Q

    A Derivation of Black Hole Entropy: Hawking & Beckenstein's Arguments

    I am looking to walk trough hawking and beckenstien's arguments for the proportionality of bh entropy to surface area to better understand black hole entropy. Does anybody know where I can find this calculation? I have taken relativity and qft so I am comfortable with this level of difficulty.
  4. wolram

    B How did direct collapsing black holes form so early in the universe?

    How are thees black holes formed so early in the universe, weighing millions of suns after only 1 billion years after the big bang?
  5. K

    Solution of plate with a hole

    Homework Statement Physical understanding about the variation of hoop stresses in a plate with a hole Homework EquationsI have been reading about the solution of stresses in solution of plate with a hole from here: http://www.fracturemechanics.org/hole.html . I’m unable to physically...
  6. Markus Hanke

    I Inside Black Holes: Unraveling the Kerr Metric Structure

    I have two questions regarding Kerr black holes, which I am hoping some of you might be able to shed some light on for me. 1. What is the physical significance / meaning of the inner ergosurface, the one beyond the inner horizon ? If considered as a boundary surface, what would it separate from...
  7. S

    B Observeving Black Hole and Time Dilation Question

    Hello all, Thank you for taking time to read my question. I am curious, what happens if following criteria is met; 1. Place a indestructable stopwatch inside the black hole set it to 5 second 2. Place another stop watch outside of black hole and set it to 5 second 3. Place a...
  8. G

    Water spray from a pipe hole

    Homework Statement How far will water shoot from a hole in a pipe knowing the pipe pressure, hole size, and exit liquid velocity and flow rate. It is assumed that the hole is located such that the water is sprayed at a 45 deg angle from the horizontal. Homework Equations Basic projectile...
  9. Einstein's Cat

    I Does Black Hole Evaporation Violate the Second Law of Thermodynamics?

    Hawking showed that black holes dissipate energy when virtual particles are "emitted" by black holes and therefore black holes evaporate. However it seems to me that a shrinking black hole means a decrease in entropy and thus a violation of the second law of thermodynamics; is this the case?
  10. R

    Finding Mass Center of a Circular Disc with Hole & Weight

    Why do we take the Center of mass to be on the right side rather than on the left? A uniform circular disc of radius 4a with a circular hole of radius 2a made in the disc. The mass of L is m and a particle of mass km is now fixed to L at the point P. The system is now suspended from the point S...
  11. Rishi Tharun

    B What Happens to the Singularity Inside a Black Hole When It Evaporates?

    Hello Friends... I just need a help... I want to kno what happens to the Singularity inside the black hole when it evaporates... Help me out[emoji5] [emoji5] [emoji5]
  12. V

    B Deriving Electron Wave Function from Hole Wave Function

    Assume that i have a wave function of holes in a solid, can we derive the wave function of electrons? If can then how?
  13. T

    B Could a black hole involve a phase transition?

    The reason I ask is that the singularity involves a region of spacetime composed of a different order of magnitude than i suppose the region outside the singularity.
  14. F

    I Black Hole & Spacetime Curvature: Can Mass Decrease It?

    Since a black hole goes to a singularity, theoretically wouldn't added mass to that point decrease the spacetime curvature by increasing of the circumference, and then not have a loss in information.
  15. MichaelLujan

    Writing: Input Wanted What would it take to crawl out of a black hole?

    As I understand it, the crux of the issue is: how is information preserved across the event horizon, in this case, the arrangements of subatomic particles, atoms, etc right on up through the individual parts, etc., of the creature in question. That, and the relativistic escape velocity required...
  16. haushofer

    A John Norton on the Hole Argument

    Dear all, I have a question on the hole argument as presented here by John Norton, http://plato.stanford.edu/entries/spacetime-holearg/ in particular section 3. The hole argument, as I understand it, can be used to show that GR is a gauge theory with the metric as gauge field and general...
  17. F

    I Opposite of Black Hole - Matter Repulsion?

    Since black holes takes matter to a singularity, theoretically could there be a hole that does the opposite? As in push everything away like negative pressure.
  18. G

    I Small back hole merging more massive body

    Hi. Let's say we have a black hole of limited mass, say a few solar masses, and it encounters a much more massive object which is not collapsed into a black hole, say a very massive star, in principle it seems that some giant stars have been detected with masses over 100 solar masses. So let's...
  19. B

    B Does time stop at the center of a black hole?

    If time does indeed come to a stop at the event horizon, how are we even able to observe it? Wouldn't it cease to exist to someone moving through time the moment time comes to a halt on the event horizon?
  20. Gonzalo Chumillas

    B What Does it Mean When a Black Hole is Spinning?

    The angular momentum is related to the rotation. And when a black hole has angular momentum, it is said that it is a "rotating black hole". But what does it mean? A black hole does not have a conventional surface, like a basketball. How should we interpret that angular momentum? I asked this...
  21. Will Langas

    B Are Larger Black Holes Less Dense Than Smaller Ones?

    What has a higher density? Black Holes or Singularities? I looked online and all I saw was that they both have infinite densities.
  22. m4r35n357

    Java JavaSCript/HTML5 Equatorial Black Hole Simulator

    Not to be confused with the full 3/4D one that I was plugging a while ago . . . this HTML5 canvas/JavaScript page was inspired by an old visual aid (requires Java plugin) that I found lacking in several areas. The improvements that I have made include: Handles spinning black holes, with...
  23. J

    I Is the universe a larger version of a black hole?

    Could there be outflows associated with the poles of a universal black hole? Could the pressure associated with the black hole’s dark energy emission cause particles of matter to form and accelerate outward? Is the timeline the time and distance from the black hole? Is this the cause of dark...
  24. praveena

    B Does Time Reverse Inside a Black Hole's Event Horizon?

    hi PF, "TIME is reversed inside the even horizon" what does it means?. My sort of opinion is that for an observor outside the event horizon,the time becomes to move slow.but inside the event horizon it does not.Is that my opinion is correct or not about time reversal?? And "the black hole...
  25. Rococo

    Spacetime diagram for black hole

    Homework Statement Consider a 2D spacetime with: ## ds^2 = g_{tt}dt^2 + g_{tx}(dtdx + dxdt)## where: ##g_{tt} = -x## and ##g_{tx}=3## Draw a spacetime diagram showing the null geodesics, including one which passes through the origin. Then show that for a massive object, when ##x## is positive...
  26. Newtonfalls

    B What is the deepest hole in the world?

    Hi, just saw an documentary about "the deepest hole in the world" on NG: <link to video deleted> Can anyone tell what it is, and what is the exact quotation to determine the height (with fricton stone-pipe)
  27. m4r35n357

    I Explore Black Hole Orbits with My Kerr Orbit Simulator on YouTube

    Now my Kerr orbit simulator is pretty much feature complete, I have started to look at producing videos . . . I have just started a channel on YouTube to accumulate some of the more interesting examples. Aside from creating the simulation, the most difficult part was to generate useful initial...
  28. EnumaElish

    B Exploring the Density of Black Holes: Common Misconceptions Debunked

    [Mentors' note: split off from this thread] Do all black holes have the same density?
  29. G

    B Can a black hole event horizon grow at the speed of light?

    Assume a spherical black hole that is eating matter from its surroundings. Then its Schwarzschild radius will increase with a speed proportional to the mass flux that enters the black hole. The question is: is this speed limited by the speed of light in vacuum c? If the event horizon is a...
  30. TheSodesa

    A sphere with a hole through it (a triple integral).

    Homework Statement A sphere has a diameter of ##D = 2\rho = 4cm##. A cylindrical hole with a diameter of ##d = 2R = 2 cm## is bored through the center of the sphere. Calculate the volume of the remaining solid. (Spherical or cylindrical coordinates?) hint: Place the shape into a convenient...
  31. phinds

    I Remote observer sees black hole evaporate

    In a couple of recent threads, I have attempted, unsuccessfully, to elicit a response to the following, which is my belief about why an observer standing well off from a black hole will in fact see the black hole evaporate (over a LONG period of time, of course, so the observer has to have an...
  32. O

    A "Observation" of Black Hole Merger

    Premise 1: From the frame of reference of the earth, observing a thing falling into a black hole (crossing the Schwarzschild radius) is impossible -> the thing is observed falling toward but never reaching the radius, i.e. the process takes an infinite amount of time. Premise 2: Observation...
  33. Einstein's Cat

    B Object's Velocity in Black Hole: Calculate Final Vel.

    What would the final velocity of an object be as it falls into a black hole? I assume you could calculate the gravitational field strength of the black hole to determine the acceleration of the object and then calculate the final velocity with the equation V(final) = gt + v(initial)
  34. O

    A Black Hole Paper Outlining Process of Singularity Formation

    Can someone point me to the seminal (or any other) paper explicitly showing and proving the formation of singularities in black holes? I'd like to learn about the exact physical processes which occur during the collapse of a star into a black hole and how the progress of those physical...
  35. jBase

    B Speed of Objects Falling to Black Hole Center

    I was wondering what is known about the speed of objects falling to the centre of a Black Hole? If a number of identical objects, initially located outside the event horizon, were propelled at varying speeds towards a black hole, would that variability be maintained as they pass through the...
  36. S

    E-field of a Semi-spherical charge distribution with a hole

    Homework Statement Using direct integration, compute the electric field at the point (0,0,Z) of a semi-espherical (z > 0) charge distribution of radius R < Z and density ##\rho=constant## having a spherical hole of radius ##r_h<R## centered at (0,0,##r_h##). Homework Equations Coulomb's law...
  37. CrackerMcGinger

    B What happens to the matter inside a black hole when it dies?

    I was wondering about this for awhile and I still don't understand what happens to the enormous amount of mass stored in a black hole when it dies. I understand this question is based on a conclusion that may be incorrect, but if anyone could shed some light on this, please do so.
  38. Allen_Wolf

    B What are the limitations of the heuristic picture of Hawking radiation?

    What happens to the energy that goes inside a black hole. Will it stay there or get converted into some other forms of energy. What will happen to it?
  39. J

    A Variance of mass inside a black hole

    HI, I need to calculate the variance of mass released when a particle jumps down or up between energy levels inside a black hole , i don't know where to begin any advice will help thanks
  40. scotty c

    Maximum air velocity through a hole

    this should be easy. suppose i have a very large spaceship holding a tremendous volume of air at 14.7psi with a density of .0023769 slug/ft^3. i put a hole in the side of my spaceship that is 6" in diameter which vents to the vacuum of outer space. what is the velocity of the escaping air? i did...
  41. P

    Lagrangian of a disk with a hole on an inclined plane

    Homework Statement A wheel consists of a circular uniform disk with a circular hole in it. The disc is of radius R and mass per unit area ρ. The hole is of radius ro and an axle of radius ro passes through it. The centre of the hole is offset radially from the centre of the disk by ro. The...
  42. Stella.Physics

    I Binary system of a neutron star with a black hole

    I am reading about mergers of a neutron star with a black hole and the association with GRB. While talking about the accretion disk, the paper I am reading says about the last stable circular orbit. Firstly I thought it was where the Roche limit lies, where mass transfer or matter ejection from...
  43. P

    Rope falling through a hole on a frictionless table

    Homework Statement A rope with uniform density ##\lambda=\frac{m}{L}## is placed on a frictionless table with an initial length ##y_0## hanging through the hole. Derive a differential equation for the position of the bottom of the rope and then using this solve for the time required for the...
  44. J

    Mean Radius of Annulus with Bolt Hole Pattern

    Hello all, I am trying to remember (I did it in Uni) how to calculate the effective mean radius of an annulus that contains a pattern of holes on a PCD. Consider the following image (pinched from: https://www.solenoid-valves.com/ ): If one was to vary the value of PCD, then the effective...
  45. K

    A Does Minimal Black Hole Entropy Suggest a Fundamental Spacetime Structure?

    If we plug the Planck mass into the Bekenstein-Hawking formula for the BH entropy, we'll get S = A/4l^2 = 4πGM^2/cħ = 4π ≈ 12.56 nat for the minimal Schwartzschild black hole. If we assume that each entropy unit is a compact area on the horizon, can we consider the minimal BH a dodecahedron...
  46. Arceus74

    B Does a Star's Fuel Running Out Lead to a Black Hole or Stellar Plasma?

    I have a question that when the fuel of star runs out there is a imbalance is temeperature-gravity equilibrium. When it collapses to a single point where mass gets compressed so much,but shouldn't the temperature at instant increase so much that the mass could not be compressed to infinite...
  47. hypermental

    Shooting Video on Planet Z Near a Black Hole

    [Mentor's note: The thread title has been edited to change the level from "A" to the more appropriate "B"] Suppose there is planet Z revolving around black hole. Astronaut from Earth go in that Planet Z and start video recording and make a DVD . Suppose they played that DVD in the computer in...
  48. Italian_Mike

    Can Light Move Inside a Black Hole Event Horizon?

    The question is as follows: suppose I throw a metal bar 1m long inside the event horizon of a supermassive black hole of 1 million solar masses. At both ends of the metal bar there is a light source. (I chose a supermassive black hole to rule out any spaghettification process: with some quick...
  49. 1

    What Happens to Mass When Black Holes Move?

    I've recently read a new article that said that the recent gravitational waves might have had 2 black holes in a star that gave me a question, because you need masses to move or accelerate to generate gravitational waves, what happens to the mass inside of the star? because black holes's space...
  50. G

    B Falling into a black hole (seen from outside)

    I refer to the time coordinate of an outside observer (ideally hoovering over the BH at large constant distance). Can (s)he actually see something falling into the hole within finite time, that means actually disappearing and making the Event horizon larger? If no, all the merging of black...
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