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. vanhees71

    Relativity Spacetime Physics and Black Hole Physics

    I just learned from the American Journal of Physics that the two books Space Time Physics by Taylor and Wheeler and Exploring Black Holes by Tayor, Wheeler, and Bertschinger are for free now! What a nice Christmas gift! http://www.eftaylor.com/spacetimephysics/...
  2. Marilyn67

    I Unravelling the Mysteries of the Kerr Black Hole Ergosphere

    I have a problem understanding what is going on in the region called the ergosphere of a "fast" Kerr black hole. - Relativity teaches us that no frame of reference can have relative displacements greater than the speed of light, ok. - The ergosphere of a fast Kerr black hole can contain light...
  3. P

    Kinetic Theory - A gas mixture effuses through a hole, find the pressure change

    So I know Dalton's law as stated above which I think is applicable in this question. Then I know the effusion rate is ##\frac{1}{4} n \bar{v}##, and from this we can make a differential for the time evolution of the number density of the gas in the container which is: ##\frac{dn}{dt} =...
  4. I

    B Black Hole singularities in Quantum Gravity

    If singularities don't exist in QG then what prevents particles from just collapsing falling further until they collapse into a singularity? Is there a repulsive force in QG ? Is time infinitely stretched near a singularities? What else could be happening?
  5. B

    Understanding the electric field of a sphere with a hole

    Here's an image. O and O' are the respective centers, a is the distance between them, r is the distance from the center of the sphere to P, and r' = r - a, the distance from O' to P. The approach (which I don't understnad) given is to use Gauss' Law and superposition, so that we calculate the...
  6. R

    I Proper time to reach the singularity of a Schwarschild black hole

    When calculating the proper time along a timelike radial geodesic, with the initial condition that object the starts at rest at some Schwarzschild coordinate ##r_0>r_S##, i.e. \frac{\mathrm{d}r}{\mathrm{d}\tau}\Bigg|_{r=r_0}=0\;, after using the equations of motion one finds...
  7. BWV

    B Star at black hole event horizon

    Curious if the time dilation at the edge of an event horizon would have the apparent effect of prolonging the life of the star to an outside observer - so for example a blue hyper giant at the edge of an event horizon with an expected main sequence time of, say, 500 million years, would remain...
  8. Kostik

    B Paradox about black hole evaporation

    Paradoxical scenario. Suppose Jack and Jill are sitting safely a kilometer above the event horizon (EH) of a large black hole. Now suppose: Jack decides to head toward the center of the black hole, traveling at an easy pace (say 10 km per hour). Jill sees Jack (with her ultrasensitive infrared...
  9. xpell

    B How small is the smallest hole that would still allow you to see through it?

    This is not for a homework or anything, I'm just a curious person who was wondering... that: how small is the smallest hole in an opaque material that would still allow to see the "world beyond it", using your eye or any kind of existing or prospective technology? (English is not my mother...
  10. PeterDonis

    A A Proposed Black Hole Entropy Calculation

    The following paper appeared earlier this year on arxiv, entitled "Islands in Schwarzschild Black Holes": https://arxiv.org/pdf/2004.05863.pdf First, a bit of background: this paper appears to be part of a larger research effort aimed at resolving the black hole information paradox by showing...
  11. jaumzaum

    Pressure experiment with a burning straw protruding from a hole in a bottle

    Consider the following experiment: we have an open bottle, with a hole where we put a straw. We burn the outer side of the straw. We see smoke ascending outside and descending inside. Why is that? I would say the smoke has lower density than air outside, that's why it goes up. Inside the bottle...
  12. Marilyn67

    B Black hole horizon and Hawking evaporation

    Hello, I take the example of two observers : - A distant observer - A falling observer For the distant observer, the formation of the horizon is not part of his future cone of light, we agree. For the falling observer, the consensus says it is crossing the horizon. First question: the...
  13. E

    The electric field inside a hole inside a conductor is still 0?

    This is not a homework question but something that bugs me a bit. My professor has stated that the electric field inside a conductor is 0. This I understand. However, he has also said that even if the conductor has some hole in it, the electric field inside this hole is also 0 Now, two...
  14. Buzz Bloom

    I Huge Hole Found in the Universe

    https://www.space.com/4271-huge-hole-universe.html I would much appreciate any links cited to more information about this hole, especially more recent information. I would also appreciate any information to clarify the following questions. How much baryonic matter is actually present (taking...
  15. Y

    I Black Hole Event Horizon Hypothesis

    Main Question or Discussion Point Wouldn't the definition of the event horizon of a black hole be the radius at which the acceleration of gravity exceeds the speed of light, instead of the radius at which the escape velocity exceeds the speed of light?It's very clear to me that a...
  16. Vanilla Gorilla

    I Black Hole Bomb Effectiveness: Mirrors or Wormholes?

    For the Black Hole Bomb to be effective, does it need the mirrors there, or can they be replaced with wormholes, or some other quirk of spacetime?
  17. Epsilon Eridani

    Is it possible to move a black hole?

    My fascination with black holes runs very deep. I was wondering if anyone could shed some light on two questions I have: Do black holes orbit around another object, or are they "free-roaming"? If they do, what determines which object they rotate around? The place where they form, or some other...
  18. Foxy

    I What happens if a strangelet falls in to a black hole?

    Just curiosity.
  19. I

    I Observing Black Hole Collisions: Time Dilation Explained

    When something approaches black hole time dilation slows the event down from our frame of reference such that nothing seems to cross the event horizon. How is it then we can observe two black holes colliding? From our frame of reference wouldn’t it seem the event never happens?
  20. J

    B What is the definition of a black hole?

    Hi All, This is my first post, so please bare with me and if I am going all wrong about, please let me know. The definition of a black hole according NASA; 'A black hole is a place in space where gravity pulls so much that even light can not get out'. Now I am not challenging this at all...
  21. D

    I Explore How Dropping Objects Into a Black Hole Changes It

    Mentors' note: This thread has been split off from https://www.physicsforums.com/threads/can-you-even-fall-into-a-black-hole.992212/ because it's a different interesting question that deserves it's own thread That applies to a static black hole. But if something falls in it isn't static...
  22. M

    B Can You Fall Into a Black Hole? Exploring Time & Decay

    It takes infinite amount of time to cross the event horizon from an outsider's perspective. But black holes eventually decay from Hawking radiation. So if you wait long enough a black hole won't exist anymore, as it would have decayed into nothing. The in-falling observer witnesses infinite...
  23. Markus Hanke

    A Coordinate Infall Time for a Vaidya Black Hole

    Consider an observer starting a purely radial free fall from rest at infinity in outgoing Vaidya spacetime - this being a simple model for a radiating black hole. Does anyone have an explicit expression for the coordinate in-fall time (assuming purely radial motion) from infinity to event...
  24. snoopies622

    B Exploring Time Inside a Schwarzschild Black Hole

    I notice that in a Schwarzschild black hole, at r=r_{s}/2, the c dt and dr terms are exactly the opposite of what they are in external, normal flat space (Minkowski metric). That is, one gets them by multiplying both terms by negative one. I'm having trouble grasping what this means. An...
  25. U

    I Calculating Surface Area of Schwarzschild Black Hole w/Weyl Coordinates

    Recently, I was tasked to find the surface area of the Schwarzschild Black Hole. I have managed to do so using spherical and prolate spheroidal coordinates. However, my lecturer insists on only using Weyl canonical coordinates to directly calculate the surface area. The apparent problem arises...
  26. rxh140630

    Drilling a hole through the center of a solid sphere

    The volume of the sphere = \frac{32{\pi}r^{3}}{3} The answer given at the back of the book is (\frac {32}{3} - 4\sqrt{3}){\pi}r^3 To drill a hole completely through the sphere, the hole would have to have a length of 4r. To get the answer in the back of the book, it requires setting the...
  27. H

    I Black Hole Observations: What Changed?

    Hello-- I have a question about space observations. It was only 4 or 5 years ago that I was taught that nothing could escape a black hole. More recently I have seen information and images of black holes. What has changed that now we have black hole obseravtions. Most recently, a black hole...
  28. M

    B Is a Black Hole Engine Viable?

    https://phys.org/news/2020-06-year-old-theory-alien-civilization-exploit.html Do we think this makes it possible using a Black Hole? Seems highly likely that it could be used as a power source one day if we are around long enough to sufficiently advance enough to make this possible.
  29. E

    A Kerr Black Hole Angular Momentum Limit

    The Schwarzschild metric seems to model, for example, the earth’s gravity field above the earth’s surface pretty well, even though the Earth is not really a golf-ball sized black hole down at the center. Can the same be said for the Kerr metric? Does it model a rotating extended body’s gravity...
  30. bosydomo

    B Exploring the Possibilities of Time Inside a Black Hole

    If we were to sit inside a black hole, of infinite mass what would we see ? Would you see time move around you? If I shine beam of light, after 1 year , relative to me the beam of light 1 year away, however if I manage to get in front of that beam, I will be at the same point in time. Would...
  31. M

    B Descending a Rotating Black Hole: Hit the Ring Singularity?

    So I have been watching the latest edition of PBS Space Time ( I know, not a proper resource/guide,) and it seems to be a bit confusing as to whether you would hit the ring singularity at the center or not. On the one side he claims that the geodesics end there but on the other he claims you...
  32. Ryan_m_b

    B Discover the Black Hole Growth Rate: Time Frame for Consuming Planetary Mass

    If a black hole was placed at the centre of an object (like a planet) how long will it takes for the mass of that planet to be consumed? I’ve tried having a look around the internet for an answer for this (kind of silly) question but can’t find one. I thought maybe of working out the flow of...
  33. dcheme7373

    Maximum mass of a black hole

    The question, "why didn't the emerging universe collapse into a black hole" has been answered in other forums. Though I am not sure I understand the reason. But it got me thinking. Is it particularly stupid to ponder whether a black hole has a maximum possible mass? Or rather a certain mass...
  34. Z

    I Could Quantum Physics explain the singularity in a Black Hole?

    If a singularity exists in the center of a black hole, could quantum physics, instead of relativity , explain it?
  35. T

    I What happens when a Neutron Star forms a Black Hole?

    Supposing the total mass of a stationary, non rotating Neutron Star is just one Kg below the mass required to form a black hole. Based on the wiki reference below the Schwarzschild radius must be just beneath the surface of the Neutron Star sphere. Now supposing an object with a mass of one Kg...
  36. DarkMattrHole

    I Mass distribution behavior of the singularities during black hole mergers

    When two BHs collide the resulting single BH bulges and contorts until it settles down to a stable state. 1) Does this mean that during this 'settling' period the mass internal to the merged BH is not (yet) a singularity, but instead two 'singularities' spinning down around each other in...
  37. J

    B Descending a Black Hole: Spaghettification or Compression?

    I have heard from, many attractive looking physicists on Youtube, that if I fell into a black hole, as I fell, I'd be stretched out or be "spaghettified. Is this correct? It seems to me that gravity compresses the free space, and that means, any object near a black hole should be compressed. If...
  38. Unbreakabletoon

    I Exploring the Physical Properties of Human-Sized Worm Holes

    Hello Everyone in the forum: I have a theoretical question about Worm Holes. So for the sake of this question let's just assume we have the technology and the power source to fire up a small human size worm hole. My question would be regarding the edge of the worm hole. Would you be able to...
  39. R

    B What Happens When You Fall Into a Black Hole According to Stephen Hawking?

    Stephen Hawking, in his book Brief Answers to the Big Questions (2018), wrote the following (pp. 106-107): "If you fall towards a black hole feet first, gravity will pull harder on your feet than your head, because they are nearer the black hole. The result is that you will be stretched out...
  40. atyy

    B Free Online Lecture: Seeing the Unseeable - Capturing an Image of a Black Hole

    Seeing the Unseeable: Capturing an Image of a Black Hole A Free Science Lecture Led by Dr. Sheperd Doeleman, the Event Horizon Telescope (EHT) project made history by capturing an image of the event horizon of a black hole, where gravity is so strong that even light cannot escape. You are...
  41. T

    B Particle with negative mass inside a black hole horizon

    [Moderator's note: Spin off from previous thread due to topic change.] Just as an aside and not related to the OP, would a real particle with negative mass inside the event horizon follow the runaway motion? Would it be ejected?
  42. Robert Friz

    I Frame Dragging Around Spinning Black Holes: Implications

    Frame dragging around a spinning black hole is generally accepted in cosmology. Does the frame dragging result solely in space-time rotating forever around the black hole, or does frame dragging ultimately result in space-time vectoring towards and into the black hole? An additional question...
  43. P

    B Black hole movement with no time......?

    If a black hole experiences infinitely slow time (IE time stops) due to their singularity, how are they able to move/orbit? If supermassives occupy the centre of most/all galaxies. How are the galaxies moving if the black holes can't?
  44. F

    I Black Hole Energy Confinement - Exploring the Possibilities

    After binge watching Steins;Gate, it has had me thinking about black holes. In the show it mentioned the idea of microscopic black holes(CERN). That being said, if matter and energy have an "equivalence", and if the Schwarzschild radius depends on mass, then would it be possible to confine a...
  45. Prof Mark R Smith

    Insights Black Holes Are Not Empty Voids. A Black Hole at the Heart!

    Continue reading...
  46. Omega0

    B Falling Clock & Black Hole: Measure Time or Disappear?

    Hi, This question is so simple - sorry if the answer is also that simple... It is pretty clear that every matter can cross the event horzion of a black hole. It is said that this process can be even very smooth if the black hole is big enough ("the bigger, the better for you", this is how I...
  47. S

    High Energy Introductory notes on AdS/CFT or black hole thermodynamics

    I am looking for a book/notes on the topics mentioned in the title that would be accessible to an undergrad. I have a background in grad quantum and statistical mechanics, but most resources I found on those topics assume a familiarity with QFT, string theory, gauge theory, and general...
  48. H

    B If space is transparent how can we not view light from a black hole

    If space is transparent how can we not view light from a black hole
  49. Revolucien

    B Exploring the Effects of Black Hole Gravity: Blueshift

    Does the extreme gravity from a black hole cause a blueshift in light approaching the event horizon? sorry for the newb question
  50. R

    I Gravity at the Event Horizon of a Black Hole

    Acceleration due to gravity at the Event Horizon of a Black Hole.
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