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. F

    Time at the center of a black hole?

    Sorry if I am woefully uninformed, but I am really curious. What happens to time at the center of a black hole according to general relativity?
  2. S

    Find Solutions to Black Hole Questions

    hi if you want to find the black hole solutions, what do you do? has any solutions of $R_\alpha\beta=0$ a black hole? thanks
  3. P

    Black Hole Destination: Final Stages, Next Steps, Reasons

    what is the final stage of black hole mean what its the next stage turning to be (in what form ) why black hole is created?
  4. PeterDonis

    Black Hole Complementarity Question

    In a thread some time back on black hole firewalls, one of the papers linked to was one by Bousso in which he argues that (as the paper is titled--note that this is a revised version, the original was quite a bit dfiferent) "Complementarity is Not Enough". I'm not trying to start a general...
  5. S

    The Central Region of Black Holes: Composition, Energetics, and Equilibrium

    What is the central region of the so called black hole composed of? Are there intense energetic waves caused by thermonuclear fissile processes? Does the high intensity ray conflagration coupled with immense crushing cause electron repulsion?Does this process also cause nuclear disintegration...
  6. michael879

    Calculating M from Charge & Angular Momentum in Black Hole

    Ok so this has always confused me and I still can't seem to find an answer anywhere! A general black hole has parameters M, Q, and J which are given the meaning of mass, charge, and angular momentum. My question is what what is the contribution to M by Q and J?? Presumably if you start with a...
  7. M

    Relativistic Effects of a Black Hole

    So, I was thinking about this the other day. If we watch material approaching near the event horizon of a black hole get scattered all over the place, then would the opposite be seen for an observer falling into a black hole? Instead of us seeing them scattered all over the place, would they see...
  8. Baluncore

    Is The Big Bang still a Black Hole.

    Following a Big Bang, if the Universe expanded at the speed of light, then the Laws of Physics would have come into play long before the radius of the Universe passed it's own Schwarzschild radius. Does that mean the Universe cannot keep expanding forever ? or maybe that we exist inside a...
  9. G

    (Almost) Black Hole = Fast Space Ship?

    Hello, I am new to this forum! I have only just completed my first physics class, but I like to learn about some of the more advanced topics in physics on my own time. I was watching a video about black holes and I noticed a part of the video that stated "any matter that enters this...
  10. F

    Verifying a 2.5mm Hole: IR Light Sensor Solution?

    I have a part with a 2.5mm hole that sits inside a fixture (I need to verify hole presence), the hole can move anywhere around the slotted area due to part flexing, install force, etc. One idea I had was point an 850nm InfraRed light from the other side at the hole, then mount an IR light...
  11. tom.stoer

    Realistic black hole in Friedmann universe

    I had a discussion regarding the region of spacetime visible to an observer falling into aSchwarzschild black hole. Using Eddington-Finkelstein coordinates this is rather straightforward, at least graphically. However the situation is rather artificial b/c the BH exists externally. So my...
  12. M

    Understanding Black Holes: Questions, Equations, and Theories

    I think black holes are amazingly interesting and I hope we get some answers about what they are in the future. I have a question I hope someone can help me with. The Schwarzschild radius is the radius at which the gravity becomes so strong there is no going back right? Is there an equation...
  13. A

    Why would a black hole be a gateway to another universe?

    I'm reading Einstein's Cosmos by Michio Kaku, and he describes Kerr black holes; which are apparently rings of matter stabilized by centrifugal force. Anyway, Kaku throws out that if you go through the event horizon of a black hole, you will be transported to another universe; he says this as if...
  14. E

    Difference between black hole solutions and wormhole solutions

    How do we know which one is a black hole solution(metric) or a wormhole solution(metric)? what is its feature?
  15. A

    Can anyone tell me how the hole will move after this?

    Here is a set of pictures showing the ways electrons and hole move under electric field. Can anyone tell me how the hole will move after this? I mean that where the hole will move after the final image.
  16. M

    When a black hole is formed officially?

    When a black hole is formed officially from a collapsing star (consider the simplest case of spherically symmetric collapse of non-rotating spherical star)? I see two possible answers: 1) At the moment when the radius of the star crosses the event horizon (##r_{star}=r_s##) , but the...
  17. A

    Something I Don't Understand about Black Hole density.

    So I always hear that the density of a black hole is infinite, because it's volume is zero. How can this be if, in mathematics, n/0 ≠ ∞? Would it be more correct to say a black hole's density is undefined or indeterminate? I also hear that some people say that a black hole's volume is...
  18. H

    What is the Velocity of Water Exiting a Hole in a Bucket?

    Homework Statement This was a problem on a test today, and it is driving me nuts that I cannot figure it out. We were told that we had a bucket 1 meter off of the ground with a 3.5 mm hole in the bottom. The water sprayed a horizontal stream 60 cm from the bucket. We are asked to find the...
  19. T

    Why do I never hear that the BB was caused by a collapsing black hole?

    Even before I had seen a Kaku documentary on black holes creating new universes, perhaps with different physics on the other side of them, I had had this image that the Big Bang was caused by a collapsing point singularity in a parent galaxy. Surely there must be something wrong with this...
  20. O

    Semiconductor has electron and hole, why not conductor has hole?

    For intrinsic semiconductor, the know its conductivity=2 neμ , where his the number of electron per cubic meter, e is the charge of an electron, μ is the electron mobility. But if I want to calculate the conductivity of a conductor= neμ. Why not consider the hole in? Electron leaves its...
  21. DHF

    What gives a Black Hole its tremendous gravity?

    I have been fascinated by stars and Black holes for most of my life but one of the things I can't get a satisfactory explanation on is what gives a Black Hole it's mind boggling gravity. We know that a Black Hole cannot be seen because it's gravity is so great that not even light can escape it...
  22. B

    What groundbreaking discoveries has Reinhard Genzel made in astrophysics?

    I have a basic question. It is well known that according to "our" time (time measured by an observer in flat space-time), an object falling into a black hole will never cross the event horizon (though, of course, according to its "proper time" it will fall into the singularity in a finite time)...
  23. J

    LQG Black Hole Model: Sources, Status & Puzzling Quantum States

    I am currently working myself into black hole physics and I am interested in their possible quantum geometric description by means of LQG. Can anybody please tell me good sources to start with? Since black holes were studied in this framework for a longer time, what is the most recent...
  24. S

    How Does Heat Affect the Size of a Hole in a Metal Plate?

    I have a very simple question. If a hole is made at the center of a metal plate and it is heated to increase its temperature, will the hole increase in size or decrease?
  25. B

    What is the shape of a Black Hole?

    I want to know what is the shape of a Black Hole? Is it round like a globe, or is it flat or oval shaped?
  26. G

    Black hole evaporation, where does it all go?

    I hear that black holes evaporate, but does it all get converted into Hawkins radiation? And what role do white holes play in evaporation?
  27. E

    I'm standing on a black hole, is light approaching red or blue?

    Little thought experiment. Hypothetically let's say I'm standing on the surface of an imaginary black hole and not completely crushed to death, or better yet, I'm in the center of the thing (never mind the singularity) and looking outward into deep space. Is the light coming toward me red or...
  28. Saladsamurai

    Simple Stress Analysis: Flat Plate with Hole

    Hello All, I have a fixture that is used for lifting an engine. See attached image for the part in question. You can see in the 'front' view the hole where a pin passes through the part and the lifting lug of the engine. You can also see the loading. We want to machine the part down such...
  29. A.T.

    Can Colliding Stars Form a Black Hole Made of Light?

    If two stars, both slightly above their Schwarzschild radius collide, can a joint horizon form before they come in contact? What if one is matter, and the other the same amount of antimatter? Will they annihilate each other completely to pure radiation, which stays within the horizon? Would...
  30. N

    White Hole in Universe: Is the Center Expanding?

    white hole in universe! isn't the center of universe a white hole?( i think)As the center of universe is throwing matter radially(if it is a white hole) outwards at high speed,we are moving away from the centre.This is nothing but the term "expanding universe". does this make sense? thanks.
  31. K

    Free falling into a black hole that evaporates by Hawking Radiation

    The solution of Einstein's field equations for a simple black hole show a slowing of time as you get close to the black hole. Time stops at the event horizon. An observer in flat spacetime far from the hole would see an astronaut fall slower and slower as he approaches the event horizon. It...
  32. P

    Calculating Stress Area at Hole Edge of Tube & Rod

    I have a tube with a rod inserted into it at a set depth. The rod is held in place by a round pin that passes through a hole in the side of the tube and into the rod. Assuming the pin and hole are the same diameter or very close, I'd like to know how to calculate the stress area on the edge of...
  33. A

    Will a Sun Collapse Form a Black Hole?

    When the sun is collapsed will it form a black hole?
  34. D

    Can a Black Hole's High Entropy State Coexist with Supercondensed Matter?

    How can a black hole have a high entropy state if the matter inside it is in a supercondensed form with maximum density,which means less degrees of freedom therefore less entropy than normal matter.Like in neutron stars we have low entropy with the neutron degenerate matter and yet a black hole...
  35. chasrob

    Can We Make Contact with an Anti-Matter Black Hole?

    Is there any such thing? Or is it unphysical? If it's physical, would making contact with a matter black hole result in E=mc^2? Thanks.
  36. A

    How can two Black holes fusion and consist a supermassive Black Hole

    How can two Black holes fusion and consist a supermassive Black Hole ?!
  37. D

    Reaction force for force exiting a tank through a clean hole

    Homework Statement Determine the reaction force from water flowing through a clean 0.02cm (Diamater assumed) hole in tank depth 3m Homework Equations P = rho.g.h A = Pi.R^2 P=F/A The Attempt at a Solution P = rho.g.h = 29400 Pa A = Pi.R^2 = 0.00031415 m^2 P = F/A -> F = PA =...
  38. H

    Can Intraband Transitions Produce Holes in the Conduction Band of Metals?

    Could intraband transition (in metals) of an electron in the conduction band produce a hole there?
  39. T

    Black Hole Singularity of a Universe

    In a recent lecture by Stephen Hawking he mentions that our universe started as a singularity. Can this singularity be caused by energy from a Black hole in another space and time? This in turn would mean that an infinite number of universes can be and are created.
  40. P

    Bulging Black Hole caused by approaching object?

    Hi I just listened to Leonard Süsskind Lecture 7 on youtube about General Relativity in the following link. At 1:28:00 he mentioned, that if a object is very close to the surface of a black hole, then the matter at this point would bulge out until it get completely absorbed. I don't...
  41. O

    Light emission from a hole in a cavity

    Homework Statement Sethna 7.7 Assume that the hole of area A is is on the upper part of the cavity, perpendicular to the z axis. The vertical component of the velocity of each photon is therefore vz= c cos(θ), where θ is the angle between the photon velocity and the vertical. The photon...
  42. S

    Exploring the Transparency of Black Holes: A Relativity Question

    Hey, before people start throwing rotten vegetables at me, I'm not any good in general relativity! So my question is: are black holes transparent to electromagnetic waves of wavelengths on the same order as the Schwarzschild radius of the BH?
  43. L

    Why wouldn't black hole singularity evaporate before it can form?

    I assume people much more knowledgeable then me must have already thought this through, but the following line of thought has me very curious. I'm making a lot of intuitive leaps here though, so I am sure there is a lot of places I could have gone drastically wrong. Hawking radiation is...
  44. A.T.

    Black Hole : Infalling Observer looking back

    What blue shift of distant light would you observe, while free falling into a black hole. It seems that hovering at the horizon (which is not possible), would result in infinite blue shift. But what about the observed blue shift in free fall, as a function of the radial Schwarzschild coordinate?
  45. E

    Black hole growth and evaporation

    What is the maximum approximate black hole size that would have negative growth rate as a function of average local mass density (and/or any other relevant parameters)? In other words, when does an evaporating black hole become a growing black hole and vice-versa? Cheers Eric
  46. N

    A small black hole goes thru a toroidal hole.

    If a small round black hole is traveling normal to the center of the major plane of a larger toroidal black hole, is it possible any energy will "get thru" to the other side of the toroid? . It's said that once you wander into a BH, you can't get out. It's like a tar pit but worse. Maybe...
  47. mrspeedybob

    Black Hole Formation: Susskind's Scenario Explained

    This scenario is described by Lenard Susskind in a lecture on general relativity starting at time stamp 44:23 in the following video. The scenario is that a spherical shell of radiation is directed inward to a point. The shell contains enough energy to form a black hole. He states that...
  48. P

    Is there such a thing as a neutral hole?

    Most explanations of doping, coupled with the simple definition of hole as positive charge carrier, and reinforced by classic graphic illustrations of P- and N-doped regions full of little plus and minus signs respectively, makes for a common point of confusion when learning basic semiconductor...
  49. H

    Mystery of the Pushed Away Black Hole

    i heard when 3 black hole crash one which come latter will pushed away and two wil become one big black hole here, why black hole pushed away?? im korean so i cannot write exactly sorry
  50. U

    How Strong is the Gravity of a Black Hole Compared to Earth?

    Gravity on Earth is 9.8m/s² and on the moon I believe it's 1.6m/s² so I'm wondering how much gravity a black hole has? What is the minimum force of gravity needed to bend space-time, do we know? Is there a formula? Also how far from the black hole would you have to be before you no longer feel...
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