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. J

    B Black Hole Firewalls: Explaining to John K Clark

    I've heard some explanations of the Black Hole firewall involving broken entanglement releasing energy that frankly I don't understand, but I have another way to think about it and I'd like to know if its even approximately correct. As I'm getting closer and closer to the Event Horizon time...
  2. quasarLie

    A Black Hole Orbit Inequality: Explained

    Hello, Here's an interesting question inspired by a homework probem (not mine), we know that circular orbit (for scjwarzchild black hole) exist only if L ≥ sqrt3 c Rsch=Lisco . Where does this inequality come from? do you have a lecture which can help me to understand? Thanks
  3. O

    B Is a Black Hole Waterproof? Exploring the Impossibility

    So the title pretty much sums it up. I'm having a heated discussion on this topic with a friend so yes/no at the end would be nice :wink:
  4. Conductivity

    Pressure just before the exit hole in a draining tank

    Homework Statement In the given picture, A cylindrical tank has a viscous fluid with density 800 kg/m^3 and viscosity of 0.8 Pa.s. A small pipe is attached to the tank with a cross sectional area of 1 cm^2. If Q = 3.12 x 10^-6 m^3/s, Find h1, h2 ,x Homework Equations Q = pi delta P a^4/(8 n...
  5. wolram

    B How did this Black Hole come to exist?

    https://www.sciencedaily.com/releases/2017/12/171206131946.htm A team of astronomers, including two from MIT, has detected the most distant supermassive black hole ever observed. The black hole sits in the center of an ultrabright quasar, the light of which was emitted just 690 million years...
  6. SWB123

    I Why is the time of formation of this Black Hole in question?

    I have to 'question' the logic asked in the 'title question' asked in this artical: https://newatlas.com/most-distant-supermassive-black-hole/52508/?utm_source=Gizmag+Subscribers&utm_campaign=2151ebbb0d-UA-2235360-4&utm_medium=email&utm_term=0_65b67362bd-2151ebbb0d-91583997 It seems to me that...
  7. tomwinwa

    Black Hole Mass and Energy Requirements for Sustainable Hawking Radiation

    This question pertains to a Sci-Fi story I am writing, using the concept of a black hole and Hawking radiation which is developed as an energy source, and I'd like to get some technical details worked out. My understanding is that an extremely small black hole will very quickly cease to exist...
  8. T

    I Can light near a black hole travel in -t in external coords?

    Many diagrams show light cones tipping over when closer to a black hole singularity, such that emitted light can have a downwards (negative time) component in the distant observer coordinate frame. e.g this diagram: or this one: or this one: However, other diagrams show that the light...
  9. L

    B Life on a planet near a black hole

    Suppose life would evolve on a planet near a black hole, like the water planet on Interstellar. And just like on Earth, they eventually discover a theory of relativity and also how to send a rocket away from planet/black hole and back. Could they take advantage of the huge time dilation between...
  10. E

    I Some suspected Black hole mergers

    As I read in May, approximately 8 candidates existed as candidates for black hole mergers. http://www.ligo.org/news.php This is no more written in this link. Are these other candidates already excluded? Are there any papers intended about these candidates?
  11. W

    B Could time move inside a black hole?

    At the event horizon for a black hole is R=2GM/C^2 This means that, as a star collapses, it gets more dense until this limit is reached. Assuming a consistent density (just an approximation as I know this will not really be the case), the Mass will reduce proportionally to the cube of R, but...
  12. nomadreid

    I Survival Time in Black Hole: Myth Debunked

    In a thread a decade ago https://www.physicsforums.com/threads/how-to-survive-in-a-black-hole-myth-debunked.170829/, there was a discussion about the paper https://arxiv.org/abs/0705.1029v1, in which the authors discuss the way to maximize one's survival (proper) time after passing the event...
  13. Jay Addy

    I What happens to the stuff that enters a black hole?

    I've read some articles about Hawking radiation, The holographic principle and obviously I'm well aware of the law of conservation of energy. Is there any research up to date that points toward a possible answer? Is Hawking radiation really a thing? Is it possible for matter/anything to actually...
  14. J

    Does black hole stop light or time?

    I have been told the speed of light is constant and does not waiver. This would make sense as light has no mass I am aware of. Pictures taken during a solar eclipse seem to prove gravity bends light. Could it be however that the light is not bent, only the time/space light is traveling through...
  15. jedishrfu

    B For those of us Who get stuck in a Hole

    Using Physics to get out of a hole: https://www.wired.com/story/how-to-hoist-yourself-out-of-a-hole-with-physics/ Remember folks: Don’t try this at home as you may be late for dinner.
  16. websterling

    I GW170608 - Another Binary Black Hole Merger Observed

    On November 15, 2017, LIGO Scientific Collaboration announced the observation of another binary black hole coalescence. The gravitational waves were observed by the twin LIGO detectors on June 8, 2017. This is the lightest black hole binary observed so far, with component masses 12 and 7 times...
  17. V

    Black hole inside a star -- How long for it to consume the star?

    Homework Statement It is my idea so I hope there is no problem in assignment. How long takes small black hole to eat an ordinary star, if the black hole sit in the center of star? Homework Equations We probably should suppose that star is ideal fluid (incompressible). (1) ##\frac{dm}{dt}=A\rho...
  18. S

    A What would happen if dark energy was injected into a black hole?

    As I understand it, if you were to inject lots of dark energy into the molten core of a planet, the planet would inflate like a bubble over time until the forces of dark energy and gravity were in balance or until the bubble popped. If you were to inject dark energy into the interior of a black...
  19. P

    I Computational physics - Light trajectory near black hole

    Dear all, I am currently doing a project about the light trajectory near Schwarzschild black hole. I wrote down a couple of differential equation and I have created a C++ program hoping to solve the orbit of light. However, the program results turn out to be quite weird. The differential...
  20. goonking

    Jamming a Pulley: Assessing Stress on Shaft & Hole

    A pulley-and-shaft is connected to a motor which applies torque to spin the pulley as shown below: Now imagine someone jams machine by sticking a broom into one of the holes of the pulley. I would imagine there would be normal stresses at the hole (location of jam) and torsional stress on the...
  21. M

    B How is light influenced really close to the event horizon?

    I was just wondering as it seems pretty counter intuitive that there is a really defined horizon where light can't escape from a black hole. It would make more sense to me if light gradually curved into one. Or does it do this? Please enlighten me ;)!
  22. S

    Black Hole Merger: Analytical or Numerical Solutions?

    Is it not true that solutions of the EFE are stationary, in 4 dimensions? If so, it seems that the solution describing a black hole merger would be intractably complex. Are current descriptions analytical solutions, or numerical?
  23. A

    B Black hole information paradox and determinism

    Hello, layman here, I have a simple question, could you please clear this up for me? Whenever I read about the information paradox, it always appears to me that it is automatically assumed that quantum fluctuations / virtual particle pairs are predictably random. Which leads to the loss of...
  24. jerromyjon

    B What (if anything) limits the speed of something falling into a black hole?

    When replying to this thread: https://www.physicsforums.com/threads/the-nasa-zero-gravity-flight.927136/ I became uncertain of my understanding of the physics after the plane starts to descend. What I imagine happens is that your forward velocity would remain constant and you would be...
  25. tom.stoer

    A Maximizing survival time when falling into a black hole

    Unfortunately I didn't find a thread discussing this issue. First I will sketch the standard argument that one should not use the rocket engine and try to accelerate away from the singularity. Then I will try to identify the problematic part of this argument and ask for your comments. 1) For...
  26. mpolo

    B Condensed matter in a Black Hole

    I am wondering if there is some type of matter in the core of the Black Hole. Is it possible to compute the distance from the surface of the Black Hole Core to the Event Horizon? Oh that would be fun to calculate.
  27. C

    I Particle at event horizon as black hole evaporates

    If you are observing a particle enter a black hole, you watch its proper time go to zero at the event horizon as it is 'frozen' there from your frame of reference. What happens in your reference frame as the black hole evaporates? While you can't illuminate where the particle is from your frame...
  28. J

    A On the formation of a black hole due to high kinetic energy

    Hello! If energy bends spacetime, then an object moving at high velocity will bend spacetime a lot around it due to its really big kinetic energy. It follows, that an object can become a black hole at extremely high enough velocities. But, since velocity is relative, we can find an observer for...
  29. C

    A Solving BTZ Black Hole w/ Euclidean Method

    I know this is some kind of exercise problem, but it isnot widely discussed in general general relativity textbook. Sorry to post it here. I want to calculate the mass and entropy of non-rotating BTZ black hole using Euclidean method. When I calculate the Euclidean action, I always get an...
  30. P

    I Why can't the interior of a black hole be empty?

    Can someone explain to me why there must be a real/meaningful space inside of a black hole? I have been autodidactically working on understanding the mathematical concepts that general relativity is based on, so I've never had anyone to ask questions to (until it occurred to me to find a forum...
  31. C

    Euclidean Methods for BTZ black Hole

    This is an exercise from Hartman's lecture 6th. Using the Euclidean method to calculate the BTZ black hole mass entropy. The BTZ metric is given by $$ ds^2=(r^2-8M)d\tau^2 +\frac{dr^2}{r^2-8M}+r^2d\phi^2$$ and ##\tau \sim \tau+\beta, \beta=\frac{\pi}{\sqrt{2M}}##. Then we calculate the...
  32. davidge

    I Understanding Black Hole Shapes & Forms

    Sorry, I'm not sure what is the more appropriate word to use: shape or form. Let's to the question: How do we know what the shape of a given black hole is? I mean, how do we know whether it is spherical or whatever other form it has? Specifically, where do we look on the equations to get this...
  33. Leonardo Muzzi

    B Why didn't the Universe end up in a huge black hole?

    Since in the beginning of the universe all matter was concentrated in a ridiculously small space, how didn't the whole universe just ended up as a huge black hole right after the gravitational force appeared? Only solution I can think of is that space itself was expanding faster than matter...
  34. T

    B Can we detect changes inside a black hole through orbits?

    I read recently that no information comes out of a black hole. Doesn’t the mass information exit a Black hole with ease? Say I am orbiting a black hole and looking away. If while looking away the black hole gobbled up another star I could tell immediately that something had changed inside the...
  35. F

    I Black Hole Formation Sequence: Time in the Equations?

    Hello all, To my knowledge, there are still a lot of questions regarding the specifics of black hole formation. My question is in regards to formation time. I've read that the actual formation takes "less than a second" according to the equations. Does anyone know where time shows up in the...
  36. A

    I Information for black hole region in surface surrounding it

    At one point I read there was the concern that a black hole could lose bits of information. Then a theory arose that showed that all the bits in a black hole were to be found on the surface of the black hole. Thus if there were let's say 1000 particles in a black hole each of which could be...
  37. A

    I Black hole - event horizon and Hawking radiation

    I have come across the following multi-explanations of how Hawking radiation/evaporation of a black hole happens: Particle/anti-particle story: particle/antiparticle pair creation from vacuum near the event get torn apart - one going into black hole, the other away; in some of these...
  38. A

    I Black hole - between horizon and singularity

    What occupies the space between a black hole's event horizon and the singularity? Stuff hurtling to the singularity? Vacuum?
  39. P

    I What would happen if I were 1 ly from a black hole merger?

    I was reading about the latest black hole merger discovered by LIGO. https://www.ligo.caltech.edu/news/ligo20170601 The article states that the deflection of the arms over 4km was 1×10^-18 meters for an event 3 billion light years (ly) away. If I assume that gravitational waves follow the...
  40. A

    I Black Hole Radiation: Questions Clarified

    A couple of points I need clarification on. Objects outside of the event horizon feel the pull of the black hole - so the closer the object is to the event horizon but still outside of it the more pull the object feels to be sucked into the event horizon? Is that the correct view? As far...
  41. A

    I Explain about the information lost through black hole

    Having trouble with understanding this equation and its theory.
  42. infinitebubble

    I Photon Sphere and time travel around a Black Hole?

    Reading the post below on event horizon of a black hole (BH) got me thinking about the photon sphere of the BH. We all know light will travel around this photon sphere and how light from a source would completely travel back to it's source if one could see it real time, we all know this from...
  43. Arman777

    I Event Horizon and the Mass of a Black Hole

    I didnt understand a concept in black holes,So I ll try to make a vısualization to the process to explain my ideas properly. Let's suppose we have a star with mass ##6M_ο##.We know that this star will turn to black hole,So Let's come to the end of the life of the star.It will explode as...
  44. C

    B General Relativity Aces a Test at Supermassive Black Hole

    General relativity passes test at Milky Way’s central black hole by Ken Croswell For the first time, astronomers use stars orbiting a supermassive black hole to test Einstein's general theory of relativity, finding no sign of a fifth fundamental force. Links: John Batchelor Show...
  45. A

    A Boundary conditions on the Euclidean Schwarzschild black hole

    This question is based on page 71 of Thomas Hartman's notes on Quantum Gravity and Black Holes (http://www.hartmanhep.net/topics2015/gravity-lectures.pdf). The Euclidean Schwarzschild black hole $$ds^{2} = \left(1-\frac{2M}{r}\right)d\tau^{2} + \frac{dr^{2}}{1-\frac{2M}{r}} +...
  46. Ryan Jackson

    B Understanding Black Hole Equations Conceptually

    I get how to derive black hole equations mathematically. But conceptually, how does it make sense that the radius of a black hole is 2MG/c^2, for example?
  47. A

    B Black Hole Gravitational Lens: Bending Light & Mass

    https://en.wikipedia.org/wiki/Gravitational_lens I want to know about bending light property of a black hole. The bending angle formula does not tell that r is perpendicular distance to light. Does a black hole having mass M has different bending power than the body having the same mass M...
  48. J

    I Questions on Black Hole Entanglement and ER-Bridges

    I joined this site because I had questions and wanted to discuss topics on the subject of black holes. Lenny Susskind's lecture of this topic raised quite a few question a and ideas in my mind. I did write my concerns in the comments for the video, but I'll just paste that here as well. Here's...
  49. A

    I Area of the event horizon of a rotating black hole

    The Kerr metric for a black hole of mass ##M## and angular momentum ##J = aM## is $$ds^{2} = - \frac{\Delta(r)}{\rho^{2}}(dt-a\sin^{2}\theta d\phi)^{2} + \frac{\rho^{2}}{\Delta(r)}dr^{2} + \rho^{2} d\theta^{2} + \frac{1}{\rho^{2}}\sin^{2}\theta (adt - (r^{2}+a^{2}) d\phi)^{2},$$ where...
  50. A

    I Event and Cauchy horizons for a charged black hole

    Consider the Reissner-Nordstrom metric for a black hole: $$ds^{2} = - f(r)dt^{2} + \frac{dr^{2}}{f(r)} + r^{2}d\Omega_{2}^{2},$$ where $$f(r) = 1-\frac{2M}{r}+\frac{Q^{2}}{r^{2}}.$$ We can write $$f(r) = \frac{1}{r^{2}}(r-r_{+})(r-r_{-}), \qquad r_{\pm} = M \pm \sqrt{M^{2}-Q^{2}}.$$ Then...
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