Hole Definition and 1000 Threads

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. 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
  2. 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
  3. R

    I Gravity at the Event Horizon of a Black Hole

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

    I Can Gravity Escape a Black Hole? | GR Learning

    I was learning GR and I got to the point where I learned about worldlines and their structure within a Schwarzschild black hole, that space-time itself is curved so that all future worldlines from an event point inward. Since a massive object cannot exert gravity into its past, how does the...
  5. W

    I In the beginning there was.... a black hole?

    When matter is dense enough (most usually because its own gravity compresses it), it collapses into a black hole. The necessary density is defined by the Schwarzschild radius of that matter: If matter is inside its own Schwarzschild radius, it will collapse into a singularity (as far as we...
  6. brotherbobby

    Water flowing out of a tank through a hole

    I assume the water to start flowing from rest at position 1, hence ##v_1 = 0##. Applying the continuity equation, ##A_1 v_1 = A_2 v_2##, we find the (wrong) result that the velocity at position 2 is ##v_2 = 0## also! (We assume that ##A_2## is small but finite) Hence, to answer the question...
  7. DennisN

    I An observer passing the event horizon of a black hole (Part 2)

    Hi all, this is a new scenario I got thinking about after having received great feedback and corrections from other PF'ers in this thread. Thanks again for the great help! This new scenario is similar to the previous one, but with a twist including a mirror. And as I said in that thread, I am...
  8. DennisN

    I An observer passing the event horizon of a black hole

    Hi all, I've just read this entire thread and watched the videos about black holes posted by @PeroK, which I liked very much (thanks @PeroK! :smile:). I am not particularly well aquainted with GR and my questions are concerning the often mentioned statement that an observer that passes the...
  9. M

    B What path does matter take after entering a black hole?

    Probably a silly question I thought of last night but would appreciate some clarification. Matter falling towards a black hole joins the disk spinning around the black hole slowly inching towards the event horizon with each orbit of the black hole. When matter passes the event horizon does it...
  10. M

    B Matter falling into a black hole

    As I understand it, as you get closer to a black hole no matter what trajectory you were on approaching it, you will get pulled into the disk of spinning matter around the black hole which I assume is around it's equator? I am just curious as to what is happening to the "space" in the disk, and...
  11. A

    I What is an electron hole pair?

    Hi, These questions may seem basic, yet, I do not have an answer for that. The density of electrons and the density of holes in an intrinsic semiconductor are equal at equilibrium. From this, it seems that holes are simply lack of electrons that are given enough (thermal) energy to escape...
  12. M

    B Fishing in a Black Hole: Can It Be Done?

    Summary:: If BH do exist, could a sufficiently small mass attached to a sufficiently strong string be lowered past the Schwarzschild radius, and pulled back out? If BH do exist (see https://arxiv.org/abs/1406.1525), could a sufficiently small mass attached to a sufficiently strong...
  13. Replusz

    I Can One Observe Anything Falling Into a Black Hole?

    1. So for an asymptotically far-away observer, something falling towards a black hole will never reach it 2. However, the thing falling in will reach the event horizon is finite affine parameter 3. The Universe has a finite age for an asymptotically far away observer a) Does this mean that one...
  14. lomidrevo

    I Is This Newly Discovered Black Hole Breaking The Rules of Stellar-Mass Limit?

    Article: https://www.skyandtelescope.com/astronomy-news/heavyweight-black-hole-find-mystifies-astronomers/
  15. Moon Shine

    B Why The Big Bang banged and didn’t collapsed into a black hole?

    Summary: The Big Band question. Why don’t we live in a black hole? Or do we? That actually might be a stupid question... so don’t hesitate to tell me that. If all mass of our universe was squeezed into something incredible small (compared the universe size) like maybe a tennis ball or maybe...
  16. Moon Shine

    B Are supernovas more likely to produce neutron stars or black holes?

    I read that after explosions supernovas can ”transform” into a neutron start or into a black hole? And now I’m curious of therer any factors which can predict what thing we’re going to get after the supernova’s explosion.
  17. Demystifier

    I A Copenhagen solution of the black hole singularity problem

    Due to strong gravitational tidal forces, any living observer will die and any macroscopic measuring apparatus will be destroyed before it reaches the black hole singularity at the center of a macroscopic black hole. Hence the black hole singularity cannot be observed, so from an experimental...
  18. PG1

    B If I were to observe a black hole....

    If I was looking at a black hole head on (from outside its Schwarzschild radius), would I be able to discern it? Would the stars etc from behind the hole be gravitationally lensed as to "obscure" the hole? Would any of this change when positioned ON, or within, its Schwarzschild radius? Excuse...
  19. Ascendant78

    I Create Black Holes with Warping EM Fields: Feasible?

    As a prior physics major (had to stop at my 3rd year of undergrad due to children and financial difficulties), there was something I was always extremely passionate about - finding feasible ways to travel faster than light. Obviously, the only feasible way seems to be to bend space-time, but I...
  20. S

    B Size of Bullet Hole: Comparing 0.000001c & .9c

    If I had two bullets one moving 0.000001 c and the other moving at .9 c for example, and they both went thru a tin foil square target, assuming they are traveling in vacuum, and that the tin foil square target will make a perfect aperture around the radius of the passing bullet, assuming the...
  21. P

    B Can Black Hole Gravity Be Overpowered?

    Summary: If a situation can exist where photons can escape black hole gravity, would “dark star” not be a more adequate name? It is commonly accepted that once there is enough material put together to create a sphere with a mass big enough to prevent light from escaping, that this object then...
  22. R

    B What Would You See Inside a Black Hole? | General Relativity

    For this assume General and Special Relativity and not some of the quantum enhancements that have been proposed for them. If I were an astronaut who just crossed the event horizon on a galaxy center type black hole (big enough so I would not be immediately spaghettified) and avoided the...
  23. Frigus

    Do two boxes expand equally with temperature if one has a Hole?

    Suppose we have two boxes of same material and same size but one have a hole in it and if we raise the temperature with equal amount then does two box expand equally?
  24. Adi6677

    Velocity of fluid flowing from a hole at the bottom of a conical shape

    My approach was that I consider the pressure of cross section A first Pa= P + dgh Now by writting Bernoulli's Equation between the cross-section A and the opening : $$ Pa + 2dgh + 2dV^2/2 = Pb + 2dV'^2/2$$ Where Pb is the pressure of the opening which is equal to the atmospheric pressure...
  25. S

    MCNP: Is it possible to make a "hole" in an fmesh tally?

    Hello, I am running a MCNP calculation where there is a source in the center of a building. I have put a fmesh tally parallel to the ground so that I can see how the particles disperse throughout the building and outside the building. However, I only really care about the results from the fmesh...
  26. AshPowers

    I How does BBT resolve away from "It should be a black hole"

    If it all started with a big bang of incredible density and energy, does that mean there must be particles that can travel faster than light? How would anything escape the grip of that kind of gravity? I was under the impression that at a certain threshold of mass/density, it turns into a...
  27. T

    I Is Planet 9 Actually a Primordial Black Hole?

    According to MIT Technology Review, the Solar System's conjectured 'ninth planet' might be a Black Hole. https://www.technologyreview.com/s/614441/is-planet-9-actually-a-primordial-black-hole/
  28. BillTre

    NASA's Black Hole Visualization/Explanation

    NASA's website has a video and annotated image of a black hole simulation. It is here. I found the explanations of some aspects of the weirdness of black hole images interesting, but I'm no expert on these things.
  29. W

    I Matter-Antimatter black hole collision

    From what I understand, a black hole can exist that was formed entirely from antimatter. If this antimatter black hole were to collide or merge with a black hole that has the exact same mass, but was made of regular matter, what would happen? Obviously the matter and antimatter would...
  30. B

    B A wormhole collides with a black hole -- what would happen?

    A wormhole collides with a black hole------------what would happen?
  31. K

    I Understanding Light from Black Holes

    Hello! I am a bit confused about the circles of light around a black hole, that were present both in simulations and in that image of a real black hole. I understand that the gravitational field is so strong around the black hole that the light is forced to move in a circular path around (from...
  32. D

    Worm Hole light years away and look at Earth through a giant telescope

    Summary: I'd like to know if anyone else thinks of these things <mentor moved to general discussion> What if one day we can "warp" x light years away from Earth, build an enormous telescope, and look back at the Earth x years ago with resolution that rivals the American flag on the moon? Do...
  33. I

    Hole in an aluminium plate and that plate is heated

    the radius of the hole should decrease from my perspective but the book says that the radius of the hole will increase. I am not able to understand why??
  34. R

    I Is the Big Bang a White Hole? Exploring Possibilities

    We know that black holes exist in the universe, but white holes don't, as far as we know, Although white holes are not an impossibility in GR. Is it reasonable to ask if the big bang singularity is in fact a white hole, and is the only white hole in the Universe? Is the place where everything...
  35. B

    B Universe Becoming a Black Hole: What Would It Look Like?

    suppose the universe started shrinking. because the density vs mass is a 1/M^2 factor, density can be made arbitrarily small given high enough mass. so it's not hard for all the mass in the universe to quickly reach black hole density. when critical density of the universal is reached, what...
  36. B

    B Rod Dipping in a Black Hole: Exploring Tidal Forces and Event Horizon Impact

    if there's a really good rocket hovering just above a super massive black hole with very low tidal force, and it dips a rod just inside the event horizon, will the rod break? it seems a certainly but the tidal forces are very weak. is it like dipping ur feet into piranha infested water? so when...
  37. Creedence

    I Appearance of a Kerr black hole from above

    How does a Kerr black hole look like from above? Is it the same as a Schwarzschild one? I could not find any convincing visualization for this question. By above I mean from a point r>0 and ϑ=0.
  38. D

    How Is Black Hole Entropy Calculated According to Bekenstein-Hawking?

    none
  39. T

    4-acceleration in a circular orbit around a black hole

    In a circular orbit, the 4-velocity is given by (I have already normalized it) $$ u^{\mu} = \left(1-\frac{3M}{r}\right)^{-\frac{1}{2}} (1,0,0,\Omega) $$Now, taking the covariant derivative, the only non vanishing term will be $$ a^{1} = \Gamma^{1}_{00}u^{0}u^{0} + \Gamma^{1}_{33}u^{3}u^{3} $$...
  40. Creedence

    I Extracting Info from a Black Hole: Robert's Hypothetical Process

    I just wandering about the following hypotetical process to get some information from the inside of a black hole. 1. Drop a satellite into the black hole on a nearly tangential orbit. 2. After it crossed the event horizon drop a large mass after it (for example a small black hole). 3. This mass...
  41. B

    B Can quantum entangled particles be split and sent into a black hole

    I am new here so apologies in advance. When a virtual particle and anti particle appear at the event horizon of a black hole, before they destroy each other, they are split with one being sucked into the black hole and the other becoming exhaust. Are these the same particles as the quantum...
  42. Marshall_Mathers

    B Possibility of Black Hole research

    Hey, If we take a hypothetical black hole with the mass of thirty billion suns which has the schwarzschild radius of roughly the orbit of the venus and let a spaceship fly into it, would it be possible for the spaceship to do some reseach on the physical nature of the singularity and then...
  43. B

    B The Physics of a Black Hole Merger: What Happens to Mass?

    What would happen if a black hole made entirely from anti-matter merges with another black hole made from normal matter? Since most of the product left over from the annihilation is in the form of light (gamma rays) would the black hole lose mass?
  44. M

    A Double copies and the black hole electron

    Because they evaporate, quantum micro black holes resemble unstable elementary particles: you can create them by smashing stable particles together, and then they will decay back into particles, as if it was all just another scattering process. Certainly in string theory, elementary particles...
  45. P

    A Hawking Radiation Inside a Black Hole: Theory & Possibilities

    It is known theoretical prediction that Black Holes must emit radiation "... its temperature and surface gravity are proportional to its mass divided by its area" (Kip Thorne). This is applied to Event Horizon (rg). But one can imagine inner Black Hole (e.g. inside r' < rg), it does not have...
  46. BlackWhole

    I Approximating a Black Hole Merger Using a Schwarzschild Model

    Summary: Can a black hole merger be approximated as a daughter Schwarzschild black hole created when two parent Schwarzschild black holes pack close enough together to trigger a local Schwarzschild radius containing their combined mass? We know that the radius of the event horizon of a...
  47. M

    B Total % of Photons Redshifted While Moving Away From a Black Hole?

    Suppose a black hole with a radius equal to the radius of the observable universe exists and a fleet of coasting spacecraft are moving directly away from the black hole (along a similar vector) at very close to the speed of light with an amount of kinetic energy A with respect to the...
  48. nn2e19

    Hole Sizing to Drain Fluids [Pressurized Container]

    Hello, I want to size my system to be able to get rid of fluids without any head buildup within the container. I am just a bit confused as to what formula I should use. My problem is summed up in the following schematic. Note that P1>P2, I have assumed H=10^(-4)m and my flow rate is 0.1 m3/s...
  49. M

    B Rest Energy and a 1 million solar mass black hole

    Suppose there is a 1 million solar mass black hole. A 1.022MeV photon near a nucleus produces an electron-positron pair a distance=A from the event horizon. The positron’s vector is directly “up” away from the singularity. It doesn’t have escape velocity. It reaches an apogee at distance=B from...
  50. H

    I Measuring Mass of a Bowling Ball Dropped into a Black Hole

    In a recent thread we discussed the idea that an object slowly dropped into a black hole, can have its rest mass recovered, as energy, if slowly brought to a halt at the event horizon. Once the object is dropped, it would be unrecoverable, and the BH would gain no new mass. I am under the...
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