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. H

    I Can an object fall into a black hole at faster that the speed of light?

    I am wondering if an object can fall into a black hole at faster that the speed of light. I have heard that the expansion of the universe can make distant galaxies appear to recede from one another at velocities faster than the speed of light.

 Intuitively, this makes sense to me. I am...
  2. mousheng xu

    I Black Holes: Time Bidirectional?

    I just watched a youtube video saying that somewhere in a black hole, time is bidirectional (can go to the future and can go to the passed), but space is one-directional. Any introduction material on this subject? Thanks in advance!
  3. JuniorAlcala

    B Black hole gravitational pull

    Do all black holes have the same gravitational pull yes or no, and if not, is it possible that if space and time bends on itself and connects two black holes that the one with the strongest pull will continue as a black hole and the weakest will turn into a white hole considering the amount of...
  4. Deepblu

    B What A White Hole Will Look Like?

    White Holes may not exist, but if we discover that they are real and we find one, then: What a white hole will look like? How it will behave? What will be its characteristics (such as gravity, mass, size ..etc) in relation with it's parent black hole? What will be it's effect on nearby stars...
  5. K

    I What happens to the inertia of a mass falling into a black hole?

    What happens to the inertia of a mass falling into a black hole? I am not even sure if I frame the questions correctly. Will this mass reach the center or is mass distributed within the black hole? Is the singularity the whole volume of the black hole or is it a point in the center? If a large...
  6. park

    Please give me some clues about the calculations for a non-rotating black hole

  7. S

    I Accelerating into a black hole?

    I'm sure this has been asked before, but it's lost to me among all the false positives... If falling into a black hole would lead to you being spaghettified, and moving relativistically towards it would contract your length / etc., is there a speed at which they balance out? Seems calculable but...
  8. DrClaude

    B A different take on the M87 black hole

    From Randall Munroe (http://xkcd.com). It left me speechless.
  9. N

    B Black Hole Evaporation: What's Left?

    Suppose a black hole isn't sucking in any new material. Then it is doomed to evaporate due to Hawking radiation and become smaller and smaller over time. Is there anything left when it's done evaporating?
  10. haael

    A What does the image of the black hole say about general relativity?

    We all heard about the "photo of black hole". My question is: did this image show any hints of physics beyond general relativity? I read once (not sure where) that the apparent size of black hole shadow is very sensitive to corrections to general relativity. Add some minor correction and the...
  11. D

    Photovoltaics and time near a black hole (as a key story element)

    I'm a physics student and science fiction writer, and I've never been to this section of PF before! But I have an idea I think is cool for a novel or short story and I'd like some input on the physics involved. As I'm not overly worried about this idea being stolen I'm going to provide a short...
  12. Harperchisari

    The energy conservation issue with parallel charged plates with a hole.

    A while back I thought of an issue with parallel charged plates. Imagine this: a set of opposite charged resistive plates with holes in the center. In theory, there is a finite amount of energy required to push a positive charged particle through the hole in the positive plate (in theory it...
  13. Hey

    I Exploring the Gravitational Pull of Black Holes: A Perspective on Safe Distances

    I was wondering recently what a black hole's tug/pull/ sucking effect would feel like if you could stand on a planet at a totally 'safe' distance, for example, or fly by perpendicularly. I came up with 2.5 trillion miles or .43 light years, give or take. I compared the diameter of the sun...
  14. aabottom

    I M87 Black Hole Photos and the Spin Orientations

    M87 Black Hole Photos and the Orientations the Angular Momentum of the Black Hole and that of the Accretion Disk. I’m trying to understand the orientations the angular momentum (let’s call it spin) of the black hole and that of the accretion disk. Veritasium has good video on the topic [1], but...
  15. BWV

    I Can black hole studies shed any light on dark matter

    Curious if the ongoing studies of black holes at the centers of galaxies, like the Event Horizon Telescope, might provide some clues about the nature of dark matter. Tried googling this, but all I get is articles debating, mostly to the negative, the hypothesis that dark matter might be...
  16. A

    I Falling Into a Black Hole: Time Dilation & Hawking Radiation

    I know that has been discussed elsewhere but never could find for a satisfying answer, so I try this here again. Let us not take into account that an observer (an astronaut or a clock or just let us take both: an astronaut with a clock) falling into a black hole (BH) will be killed and torn...
  17. wolram

    B First ever look at black hole?

    I do not know if this image is a true image but for scientists to see a black hole is some thing. https://www.sciencedaily.com/releases/2019/04/190410091028.htm
  18. S

    If photons can't escape a black hole, how come gravitons can?

    It would seem that they both must observe the laws of General Relativity.
  19. E

    I Black hole image: What are those "lobes"? [M87 10April2019]

    Lobes Did anyone hear an explanation of the appearance of the lobes visible in the published image? I only caught part of the Q&A. (Visible most prominently at at eleven o'clock and four o'clock positions, and to lesser degree at three and nine) Do these type of observations generate "lense...
  20. M

    I Observation of the Messier 87 Super Massive Black Hole

    This week, leading up to the release of the pictures of the super massive black hole Sagittarius A* at the center of the milkyway, I have done a bit of background research on the topic and learn that they are also looking at trying to get an picture of the super massive black hole at the center...
  21. P

    A Dark Matter Accretion Disk for Black Hole (Neutron Star)

    Hello! Dark Matter (if exists)(if it is in form of particles - collisionless) could also be attracted by Black Holes (or Neutron Stars) and form accretion disk. I would like to discuss possible properties of such hypothetical object. DM particles could be trapped and settled in around...
  22. P

    The Physics of De Sitter Black Hole Heat Capacity

    I am reading the paper https://arxiv.org/pdf/0801.4591.pdf , says "Fortunately, the fact that the heat capacity of the cosmological horizon be positive permits to foresee the evolution of the space in absence of any external source. Taking the correct signs for the temperatures one can notice...
  23. S

    A Penrose diagram of black hole with a changing event horizon

    Dear all, I have a question on Penrose diagrams. Consider a collapsing star that forms a black hole with a Schwarzschild radius normalized to 1. What happens in the Penrose diagram when additional matter falls in? I suspect the diagram then has to look like this : When the outer shell (second...
  24. A

    I Black hole orbital mechanics questions

    What are some of the challenges associated with calculating orbital parameters of objects around a black hole (I.e. Orbital velocity, period, semi major axis, kinetic energy). At what point can classical physics no longer provide accurate results?
  25. Lord Crc

    B Exploring the Mystery of Black Hole Ringdown

    I thought I'd create a new thread rather than derail. In https://www.physicsforums.com/threads/if-quark-stars-exist-why-do-neutron-stars-become-black-holes.937452/#post-6143231 it was explained to me that gravitational waves do not escape the interior. The reason I thought they did is that we...
  26. N

    B Star Lifespan Near Black Hole: Time Dilation & Energy

    I would like to know, how much a stars life would appear to lengthen relativisticly as observed from earth, if the star was in a close orbit around a supermasive black hole. If the stars lifespan is longer from our perspective than a star of its size should be, would it also appear to be...
  27. L

    A Quantum amplitude for a particle falling into a black hole

    Here we consider a black hole formed by gravitational collapse classically. We also consider a scalar massless Klein-Gordon field propagating on this background. To quantize the field we expand it in appropriate modes. The three sets of modes required are: The incoming modes, appropriate for...
  28. K

    B What happens to the matter inside a black hole?

    What happens to matter after it falls into a black hole? Are electrons pushed closer to the nucleus? Do electrons combine with protons to form neutrons? Are there nuclear reactions occurring in the process? Since no light can escape from a black hole and cool it, then how can a black hole...
  29. G

    Air flow through a hole in a submerged pressure tank

    Hello! I will try to formulate myself as clearly as possible, but english isn't my main language. I'm having trouble solving this problem that should be relatively easy to solve. Let's say we have a submerged pressure tank, constantly fed with air through a compressor, so it's maintained at a...
  30. Arman777

    B Naked Singularity, Black hole mass limit

    I came across a question on PSE. I am not sure its a violation to ask the same question here, but there's no answer to the question in there so I wanted to ask it here. Quoting his question,"Since the universe has a positive cosmological constant, there is an upper limit on the mass of the...
  31. Joshua Guyette

    I Supermassive black hole eating a stellar black hole

    I'm trying to visualize what a fast spinning supermassive black hole slowly eating a stellar black hole should "look" like; how would the mass flow between the two? Could enough mass be removed from the stellar black hole, that it loses it's event horizon before entering the supermassive black...
  32. CalcNerd

    I Measuring Charge & Angular Momentum in Black Holes

    It is stated that a Black hole has only mass, angular momentum and charge for properties, but since it is black ie no light escapes its event horizon and charge E/M is related (same speed) as light (photons), how can unbalanced charge be detected? And since many Black holes have electron...
  33. A

    I Negative Mass & White Holes: Does It Create?

    does somebody with a negative mass create a white hole instead of a black hole because of its anti gravity property.
  34. K

    B Beyond the Black Hole Singularity

  35. PeterDonis

    A Interior volume of a black hole

    This paper by Christodolou and Rovelli discusses how to define the interior volume of a black hole: https://arxiv.org/abs/1411.2854 I'll try to condense their basic argument into a (heuristic) form that makes it easier to raise the issues I want to raise. The basic idea is to start with the...
  36. S

    I Black Hole Stability Conjecture: Why Is It Important?

    I am working on a presentation for a course in general relativity and my topic is the stability of black holes. In many of the references and articles that I have found, the author asserts the importance of the conjecture but offers no reason. So I ask: Why is the black hole stability conjecture...
  37. P

    B Black Hole Paradox: Exploring Theories

    Just a question: Can anybody give any information regarding the black hole paradox? There are so many theories behind it. Which one should we believe? Just a general question.
  38. J

    B Tidal Forces When Falling into a Black Hole

    So, if the Earth moves slowly through a large hula hoop, sensors attached on the hoop will measure some stresses, which we might call tidal forces. The faster the Earth moves relative to the hoop the larger those tidal forces are. So, if a person falls into a black hole, there are some tidal...
  39. P

    Black Hole Temp: Calculate Specific Heat

    Homework Statement Compute the specific heat of black hole Homework Equations ##T=\frac{2}{r_+}-3/2048 r_+^2-\frac{6r_+^3M^2}{(M+r_+^6)^2}## ##f(r)=1-\Big (\frac{r^2}{64}+\frac{Mr^4}{M+r^6} \Big ) ^{1/2}## ##r_+## is the horizon where ##f(r=r_+)=0##. The Attempt at a Solution I tried to...
  40. H

    I Can Atoms & Baryons Exist Inside a Black Hole?

    In the way I naively imagine a black hole's interior there are event horizons all the way down, and any material object of whatever size will straddle many event horizons. So, with both atoms and baryons, there cannot be any interaction between their components. Consequently, at the moment of...
  41. S

    I Creating a Dark Matter Black Hole: How it Differs from Ordinary Black Holes

    let's imagine that we can create a black hole from dark matter. Is it going to be different from the ordinary black hole(which is created by ordinery matter)?
  42. Joe591

    Possible Causes for Hole in Radiator Tank

    What would cause a hole to form in the top aluminium tank of a radiator of an earthmoving machine. The tank material is 6mm thick and is made from 1050 aluminium plate. The material around the hole has bubbles almost like pitting corrosion or like somebody went and took a flame to it. The rest...
  43. Stu-W

    I Black Hole Singularity: Discussing Quantum Theories

    Hi, I'm new on here and this is my first post, so forgive me if I don't master the threads instantly :) - right, now that's out of way: I want to open a discussion on the singularity in Black Holes, namely in regards to the well known issue of Special Realitivity breaking down at the...
  44. J

    Schwarzschild Singularity & Black Hole: Same or Different?

    Are a Schwarzschild singularity and a black hole the same thing?
  45. Milsomonk

    I Lorentz Symmetry at Black Hole Event Horizon

    Hello people, I have been thinking about a concept that I was taught whilst learning GR, If I understand correctly it is that Lorentz symmetry becomes local when we consider GR. This makes sense to me as then the metric is generally speaking not Minkowski, only for a...
  46. FallenApple

    I Understanding Black Hole Entropy: Consistency Across Reference Frames

    Is entropy consistent from all reference frames? For an observer at the surface of a black hole, a finite amount of time would pass, but the observer would observe an unbounded amount of time passing for the outside universe, hence from his/her reference frame, information, entropy of the...
  47. H

    I How certain are we about black hole mass density?

    The Wikipedia entry on "White dwarf" has a table listing the densities (in kg/m3) of various objects/substances, and states that an earth-mass black hole has a critical density of 2 x 1030, about 13 orders of magnitude denser than atomic nuclei. Has such an enormous density been calculated...
  48. Ryan Walsh

    I Audio question about black hole

    I was wondering if someone can help explain to me what is happening in the image. Black holes have Light paths or something so i read here more accurate description is that within this horizon, all lightlike paths (paths that light could take) and hence all paths in the forward light cones of...
  49. B

    Model pressure loss vs time for air in a cylinder w/ hole

    Related to an engineering project I will be working on. The situation is that essentially I will have a closed cylinder (5.5 in x 26 in) with a small 15mm hole on the side (not on a circular face), which allows the air inside to be at equilibrium pressure/temperature with the outside. Then a...
  50. G

    Rate of Air Loss Through a Hole in a Spaceship

    Homework Statement We want to calculate the rate of air loss from a space vehicle (module) if a meteoroid punches a hole in it. Assume the module is sealed off from other modules. It is shaped like a cylinder roughly 4 m in diameter and 10 m long. The hole's area is a cm2. The hole is punched...
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