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. Construction What tool drills this type of hole?

I need replicate a hole that has some kind of 'funnel' around it (see picture attached, arrows), so that screw caps get completely flat once they go through it, without protruding. Does anyone know what type of tool is needed to accomplish this? thank you
2. Water Drain Channel minimal cross-section

Hi there! I'm looking for an approx. minimal size for a drain channel where condensation water can go through. Can anyone have some advice? No increased pressure for the water, just the normal atmospheric pressure. Water condensing and just have to be able to get out. The amount of water is...
3. Punching a hole in a tape moving at relativistic speed

The proposed solution is that the hole is an ellipse that is wider than the cylinder in the direction of the original velocity of the tape (its major axis is along the tape, and its minor axis across it). The reason would be that the piece of tape cut by the cylinder is circular, but the tape...
4. I Runaway supermassive black hole?

There seems evidence for a runaway supermassive black hole. https://phys.org/news/2023-04-strange-streak-young-stars-evidence.html
5. B Entanglement inside a black hole

Suppose two electrons are entangled with opposite spins. Electron #1 passes through the event horizon of a black hole, together with Laboratory Assistant #1. Suppose the assistant measures electron #1's spin after they pass through the event horizon (according to #1's [proper] time) and measures...
6. B Circumgalactic Black hole imaged by the Hubble Space Telescope

From NASA: https://www.nasa.gov/feature/goddard/2023/hubble-sees-possible-runaway-black-hole-creating-a-trail-of-stars "We think we're seeing a wake behind the black hole where the gas cools and is able to form stars. So, we're looking at star formation trailing the black hole," said Pieter...
7. B AI Enhanced image of M87 black hole

https://iopscience.iop.org/article/10.3847/2041-8213/acc32d From the abstract, "We present a new reconstruction of the Event Horizon Telescope (EHT) image of the M87 black hole from the 2017 data set. We use PRIMO, a novel dictionary-learning-based algorithm that uses high-fidelity simulations...
8. I Black Hole Information path described in new article

I'm posting this in "Quantum Physics" although it is just as much "General Relativity". A paper entitled "Quantum gravitational corrections to particle creation by black holes" was published in Science Direct earlier this month. It appears to provide an event horizon mechanism for holding...
9. B Ultramassive Black Hole (UMB), 30 billion solar masses?

https://www.france24.com/en/live-news/20230329-astronomers-discover-one-of-biggest-black-holes-ever-recorded https://universe.nasa.gov/black-holes/types/ - didn't find this very helpful ESA Euclid mission overview - https://www.esa.int/Science_Exploration/Space_Science/Euclid_overview (to be...
10. B Why Don't We Live Inside a Black Hole?

We know the Big Bang Theory states that our universe was started from a hot-dense point. But should't it became black hole and every matter and radiation pulled to singularity? We would not be her if that is the case.
11. A Black hole mass coupled to expansion -- astrophysical source of dark energy?

Observational evidence for cosmological coupling of black holes and its implications for an astrophysical source of dark energy Comments?

In the paper https://arxiv.org/abs/1210.4699. How to solve this equation? I've tried it, it's not same as in this paper. Even zero order still not the same. This is what I try to do at zero order. input $$E=E_0\left(r_0\right)$$ $$H=H_0\left(r_0\right)$$ $$b=b\left(r_0\right)$$...
13. Pistons have cracked and put a hole in the block

Hi all so I had a injector go on my audi q5 2009 and had a mechanic to put a new injector in it and a Alternator and auxiliary belt so after the work be done I take it for a drive did about 2miles than Start it to make Allowed tapping noise so get hold of mechanic and he's said get it home than...
14. B Can Matter Enter a Black Hole Intact? Debate & Advice

I am having a debate with someone who appears knowledgeable about black holes from the language he is using but we have a disagreement about if matter can enter a black hole. He is trying to tell me the gravitational gradient near the event horizon is such that spaghetification occurs as you...
15. How to correctly tap hole by use both drill and tap bit

How to correctly tap hole, i.e. make thread inside it, by use a usual drill with bit having 2 in 1 i.e. both bore/drill and tap bit once as in hole tap the rule is it must always go back and forth full cycle clockwise and half cycle counter-clockwise direction, so how can this rule in the former...
16. A Can a black hole horizon act as a source of Chaos?

I was going through this paper where on page 5 they argue that in the given Poincare section: I am a bit confused by this statement. How does the given saddle point correspond to the black hole horizon and is it necessary that it acts as a source of chaos? Any explanation would be truly...
17. B Why can gravity escape from a black hole?

One of the leading theories of physics is that forces are mediated by virtual particles. Well, it seems as though these virtual particles can escape a black hole. Why is that?
18. B Mass & Weight Impact on Spiraling Into a Black Hole

Suppose you have two small masses spiraling into a black hole in similar trajectories. Does the mass of these small masses make any difference to the rate of inspiraling? What if one is a thousand times more massive than the other...
19. I Black hole horizon for different observers

The paper is The Volume Inside a Black Hole (0801.1734) Looking at the abstract, I have a question already. It is stated: Because the light rays are orthogonal to the spatial 2-dimensional surface at one instant of time, the surface of the black hole is the same for all observers (i.e. the...
20. A Calculate work done by a time-dependent pressure to a spherical hole

Hello, Suppose I have a spherical hole in a elastic infinite space. I apply a time-dependent pressure to the inner surface of the spherical hole. I know p = f(t). If I only consider this as an elastic problem, no failure happened, how can I calculate the work done by p during the time from 0...
21. I What Would it Look Like to Fall into a Black Hole?

There are a number of videos of simulations of this. They all end with complete blackness. This seems wrong to me because light is concentrated by the black hole. There should be more light closer to the center. On second thought I guess it is OK. While the observer would encounter more...
22. I Would it be possible for a black hole to have a "solar system"?

Was just wondering if there is anything fundamentally preventing a system of planets being in permanent orbit around a black hole, without ever spiralling in. Assuming that the black hole doesn't absorb any significant amount of additional mass. Of course I know it wouldn't provide any energy to...
23. I Quantum events near a black hole

I apologise for my very limited understanding of quantum physics: my background is in General Relativity. A wave function is said to represent the probability of a particle being at some point in space/time, and I take that to mean that the probability of a quantum event is a density on...
24. I Effect of Black Hole Spin on Gravity

Not sure how to mark the level, I know what the math in the Einstein field equations represents (stress energy tensor, Riemann curvature etc), but have no facility in doing anything with that math. so take 2 black holes, with say 100 solar masses. A is not spinning, B is spinning at...
25. B Could a black hole just be a planet?

So the theory is the center of a "black hole" is nothing more than a planetoid of incredibly dense material, and the black hole is just this planet's atmosphere for lack of a better description. Thoughts?
26. Two persons headed towards the black hole horizon

I have tried inserting in the above formula 2m for r, but I get a huge answer. The correct answer is ##1.28*10^9 N/kg## for person A and ##1.28*10^-3 N/kg## for person B. I also suspect that the formula for the Lorentz factor (##1/\sqrt{1-2GM/r*c^2}##) has some relevancy here, but I cannot...
27. B Could the source of dark energy be our parent black hole feeding?

About a year ago, I heard Leonard Susskind discussing how entangled black holes could create spacetime. As I was listening to Prof. Susskind describe the mechanisms for creating entangled black holes, and how these black holes might create their own spacetime, it occurred to me that if we were...
28. Electron and hole concentration

I can't solve the following exercise: Assume for a certain non-degenerate semiconductor sampe at T = 300 K an intrinsic carrier concentration ##n_i = 2 \cdot 10^{13} \frac{1}{cm^3}## and the band effective densities of states ##N_C = N_V = 10^{19} \frac{1}{cm^3}##. 1. Determine the electron and...
29. I Black hole singularity vs. quantum mechanics

I'm wondering about some aspects about black holes (BH) and singularities, but since all my questions have to do mostly with quantum mechanics, I placed this thread in here. OK, let's assume there IS a singularity in the middle of a BH. A) Pauli exclusion principle (PEP) says no two fermions...
30. I Amount of black hole entropy inside the Universe?

Now, it's been said that the majority of the entropy in the universe resides within the cumulative entropy of black holes inside the universe. How do they know that? Now, I'm not so interested in how they determine the black hole's entropy, I know there's a relatively simple formula for that...
31. B Penrose Diag Black Hole: Riddle Me This

I'm no expert in this stuff, and perhaps I don't understand these diagrams, but having said that, I don't understand why the typical Penrose diagrams I see of black holes look the way that they do. They all have a 45 degree (light speed) angle for the event horizon of the black hole, and they...
32. B Can nuclear bomb(s) change trajectory of small black hole?

A 4 ft diameter black hole (1.5 to 2 times the mass of Saturn) is headed toward Earth. Will Earth be able to defend itself using missiles with nuclear bombs? How to calculate such a problem?
33. Solvent Effects on Carbazole-Based Hole Transporting Materials

Hello everybody , In my research study, i am focusing the interprete the effect of solvent on opticals propertie of carbazole based hole transporting materials ,In order to dissolve this materials in different Concentration of solvents ; I have been using Toluene , chlorobenzene and...
34. B Is it possible for a giant star to have a black hole inside it?

I’m sure that when a star is in the process of becoming a black hole, there must therefore be one inside it at some point during the process (correct me if I’m wrong on that). But if so, how long does that take? Could there exist a supergiant star that has a black hole inside it for a long...
35. A Why do we need a quantum correction for black hole entropy?

Hey to all,... It is now generally believed that information is preserved in black-hole evaporation. This means that the predictions of quantum mechanics are correct whereas Hawking's original argument that relied on general relativity must be corrected. However, views differ as to how...
36. Pressure of water exiting a hole in PVC

I have a 1" PVC pipe that is 36" long, closed on one end and hooked up to a pump on the other. The pipe has 10 holes each measuring 1/32" in diameter and I have been trying to use Bernoullis equation to find the pressure of the water exiting those holes. I believe the volume of water that will...
37. B Event Horizon Telescope, Milky Way supermassive black hole stream

Streaming now:
38. Donut Hole Physics: Weekday Exceptions Explored

Once a week, on Thursday mornings, donut holes arrive in my office area of the workplace. Except this morning - when Tuesday became a virtual Thursday. The exception to an otherwise universal constant prompted me to examine the physics of the donut hole more closely:
39. I String theory calculation of Extremal black hole entropy problem

one of the claimed successes of string theory is its ability to derive the correct Hawking-Bekenstein equations to calculate the quantum entropy of a black hole without any free paramenters, specifically Extremal black hole entropy using supersymmetry and maximal charge. I was wondering if...
40. I Black Hole: Knock on the horizon

First of all, I want to note that geometry is being discussed, which in fact is the General Theory of Relativity. And in any geometry, there are infinitely thin, weightless, etc. lines, rulers, and so on. In the future I will remind you about this. The system of units is meters. There is a...
41. B Creating Artificial Black Hole: Force Requirements

In a hypothetical deep space experiment in the distant future with appropriate safety precautions in place, how much force/power/energy would be required to create an artificial 1000kg black hole? I haven’t the faintest clue & this isn’t for homework. Where would I even begin looking for an answer?
42. I Surface tension and water (the smallest hole water will flow through)

I am trying to find out what the smallest hole water will flow through. not a molecule of water, just water in general. Here is an example. I have a single walled cube that i 3d printed. When i put water in it, it leaks between the layer lines. I want to find out what the spacing between the...
43. O

I Information loss in black hole, why is it a problem?

If an observer never falls into a black hole, something it observes that does fall in takes an infinite time to reach the event horizon. If an observer falls into a black hole along with an object, it will not lose information on the falling object, but will lose that from the outside of the...
44. Gauss' Law applied to this Charged Spherical Shell with a small hole

First draw a gaussian shape outside of the sphere (a larger sphere) with radius R. The total charge from the (inner) sphere will be: $$Q = \sigma A$$ $$A = 4\pi r^2$$ $$Q = \sigma 4\pi r^2$$ Use Gauss's Law to derive electric field magnitude $$\oint_{}^{} E \cdot dA = \frac{q_e}{\epsilon_o}$$...
45. A Calmet & Hsu: Quantum hair and black hole information

https://www.bbc.com/news/science-environment-60708711 Scientists claim hairy black holes explain Hawking paradox https://arxiv.org/abs/2112.05171 Quantum Hair and Black Hole Information Xavier Calmet, Stephen D.H. Hsu It has been shown that the quantum state of the graviton field outside a...
46. Can a hole in my garage floor keep it warm in winter (geothermal heat)?

If I was to bore a 4" or even 6" diameter hole into my garage floor drain and install a PVC pipe to a depth of 10 feet would the geothermal heat keep my garage warmer? I live in Northern Michigan and frost can reach depths of 7' or more. I am not looking to sweat in there, but could it allow...
47. B Can You Become a Black Hole from Approaching Light Speed?

If you're in a relativistic starship, approaching the speed of light, then if you get too close to it, do you end up becoming a black hole? Relativistic length decreases as you get closer to light speed. Relativistic mass increases as you do the same. Will your relativistic mass and relativistic...
48. I Black Hole Collision Scheduled

Well, not right away. It's about 10 000yrs in the future. From: THE ASTROPHYSICAL JOURNAL LETTERS The Unanticipated Phenomenology of the Blazar PKS 2131–021: A Unique Supermassive Black Hole Binary Candidate Popular version...
49. B Black Hole Entropy: Basis of Logarithm Explored

In textbooks, Bekenstein-Hawking entropy of a black hole is given as the area of the horizon divided by 4 times the Planck length squared. But the corresponding basis of the logarithm and exponantial is not written out explicitly. Rather, one oftenly can see drawings where such elementary area...
50. I Spin (or not) of a Kerr Black Hole

The Kerr solution describes the gravitational field of a rotating black hole. Oftenly, the hole is said to be „spinning“, what appears as misleading to me. My questions: 1.) Is it correct to say that angular momentum in this way is treated like orbital angular momentum, not like spin? 2.) Can...