What is Holes: 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. K

    A Can primoridal black holes completely explain dark matter

    widely reported in the news is a second observation of 2 black holes gravitational waves. also reported are its implications Science World Report-Jun 15, 2016 Astronomers have reportedly started to think that dark matter could be made up of primordial black holes. According to Alexander...
  2. wolram

    B Density of Black Holes: Unveiling the Universe's Secrets

    It seems by this paper that there are more black holes than expected, so what is the expected density of black holes in the nearby universe? arXiv:1606.04996 (cross-list from gr-qc) [pdf, other] Constraining modified theories of gravity with gravitational wave stochastic background Andrea...
  3. M

    B Exploring Spacetime in Black Holes

    Hello every one . Simple question , What happens to the ended spacetime fabric in the singularity poing of the black hole if the black hole starts to move in spacetime ? Would the dead spacetime fabric at that point return to the regular shape of space time fabric ? ( as we know spacetime at...
  4. G

    A Two Black Holes' collision thought experiment

    Once, someone had asked two interesting (though absolutely hypothetical) questions: 1) What should happen during the collision of two BHs, one consisting of matter (BH+) and the other consisting of antimatter (BH-)? Should they form a larger BH or should they be annihilated? My personal...
  5. QuantumQuest

    A Viewpoint: Black Holes Produce Complexity Fastest

    Yesterday I came across this article about speed limit on the growth of complexity in quantum gravity, that I found interesting: Theoretical results suggest a precise speed limit on the growth of complexity in quantum gravity, set by fundamental laws and saturated by black holes. The article...
  6. M

    A Was the LIGO team over-hasty to claim black holes confirmed?

    Since the thread In LIGO’s pulse, how much comes from BH merging/ inspiraling where I questioned the late ‘ringdown’ part of the LIGO signal, scientists have pointed out that the main pre-merging signal could indicate various types of binary compact objects, including gravastars of similar mass...
  7. A

    Absence of air in well holes eliminate change in pressure?

    if i sucked air out of an oil well after drilling a few feet and closed the hole by any means and continued drilling without allowing air in, will that eliminate change in influx and won't result in a kick? or because i can't suck air completely out so the delta p will be really high?
  8. Noisy Rhysling

    SciFi utilization of mini-black holes?

    Okay, I have to admit that this was my first encounter with the term "black hole", c. 1964. In the story I read a mini black hole (MBH) somehow made it to Earth was was devouring ... Montana? ... and there were fears that it would eventually swallow the whole (not "hole") world. There were...
  9. edguy99

    A Is there proof that black holes really exist?

    Intriguing and informative story on gravity wave detection. Are gravastars an alternative to black holes? Is it possible the there are NO black holes? The collapse of mass into a ball of energy that presses out and stabilizes the incoming mass is a thought provoking alternative to the common...
  10. haael

    A Do black holes lose hair in finite time?

    OK, so it's time to start a new thread. I heard many times that there exists only one black hole solution for a given mass and angular momentum, but I know already that this is not true. We all know that if we throw something into an existing black hole, its event horizon starts to ripple. So...
  11. R

    B Black Holes, Information Loss and Causality Query

    I take an interest in physics in my spare time (in IT during the day). I have a query regarding the 'problem' of information loss at a black hole, and would be grateful for some enlightenment. It seems generally regarded that any information going past the horizon of a black hole is...
  12. L

    B Escape Velocity & Black Holes: Can Something Escape?

    It is my understanding of black holes that nothing can escape them because their escape velocity is higher than the speed of light. The place at which the escape velocity becomes higher than the speed of light is known as the event horizon. My question is what happens if there is a normal force...
  13. L

    I Gravitational Waves & Black Holes: Exploring the Connection

    This is something I've been curious for some time. I've heard that there is a relation between gravitational waves and black holes. Moreover, this year the quite important paper "Observation of Gravitational Waves from a Binary Black Hole Merger" was published. Now, I'm starting to study...
  14. Tengo Preguntas

    Do White Holes Violate 2nd Law of Thermodynamics?

    I have heard (read) much debate over the fundamental problems with white holes, mainly that they violate Thermodynamics by increasing entropy. However, I have also read that a black hole bends space-time enough to "connect" somewhere else as an Einstein-Rosen Bridge. So if the exact same event...
  15. J

    Initial Mass Function Question (white dwarfs, neutron stars and black holes)

    Homework Statement Calculate the number of white dwarf, neutron star and black holes the galaxy will have after 5Gyr of evolution. M<8(solar mass) for white dwarf 8(solar mass) < M < 40(solar mass) for neutron star M > 40(solar mass) for black hole Initial mass function is ξ(M) = AM-s...
  16. M

    B Does antimatter have positive or negative mass?

    Black holes suggest anti-matter has negative matter but is this true? I think anti-matter has positive mass - e.g. a positron and electron annihilate giving off 0.5MeV + 0.5MeV photons where these photons have a huge positive energy. If the positron had negative mass then there would be no...
  17. wolram

    B Weird alignment of black holes

    In scientific daily. https://www.sciencedaily.com/releases/2016/04/160411130033.htm How can a cosmic strings align black holes , or any other process,
  18. 4

    B What are the biggest misconceptions about black holes?

    Hey guys, I'm currently doing a project on black holes and need some input on what you believe to be the biggest misconceptions about black holes, thanks! You can read more about the guidelines of the project at: http://www.aqa.org.uk/subjects/projects/aqa-certificate/EPQ-7993
  19. Y

    Calculate the quasi-Fermi level of holes and electrons?

    Homework Statement GaAs has an effective density of states (DOS) = 4 × 1017 cm−3 for the conduction band, = 8 × 1018 cm−3 for the valence band and a band gap of = 1.42 eV. a) A thin slice of GaAs is illuminated by a cw light source, creating a steady state density of 1017 cm−3 of electrons...
  20. E

    I Pn junction to reach thermal equilibrium

    Hello! Some of the processes caused by a pn junction are not clear for me. Just after the contact between the p and the n region, a migration of charges happens in a semiconductor junction in order to reach an equilibrium condition. A valence band and a conduction band are present in both...
  21. F

    I Carrier Concentration in a Semiconductor

    Suppose I have an n-doped semiconductor and want to measure the electron concentration in the conduction band as a function of temperature. How would I go about doing this by measuring the Hall coefficient as a function of temperature, given that I don't know the electron and hole mobilities...
  22. Dhaga

    B How come black holes have a mass?

    If the sun disappear right now, we won't notice before 8 and something minutes due to the speed of light. The Earth will keep going it's way on it's orbit because, as everything, gravity cannot exceed light speed. The same would apply if we were orbiting à black hole. I often heard of the...
  23. Sei

    A How Do Black Holes Affect Time and the Fate of the Universe?

    Questions. 1. As protons will eventually decay, will objects made with protons orbiting black holes that are time-dilated remains? 2. What happened at someone's perspective if he/she fell into a super massive black holes? Will he/she be free instantly? (Time dilation) 3. What happens after the...
  24. wolram

    B Black Holes and Hawking radiation

    Is there a limit as to how much a black hole gathers mass and how much it losses mass via hawking radiation so that the black hole becomes in equilibrium, neither gaining mass or loosing mass How long would it take a hypothetical isolated black hole to loose one solar mass due to Hawking radiation.
  25. L

    B Black Holes and Degenerate Pressure

    Naive reading on the web says that stellar collapse is halted by quantum mechanical processes called "degenerate pressures" that arise when gravity tries to force fermions such as electrons or neutrons into the same quantum state. White dwarfs are propped up by electrons, neutron stars by...
  26. Jonathan Scott

    A Could gamma rays imply GW sources not black holes?

    When I saw the report of a gamma ray burst associated with the LIGO GW event, my immediate thought was that the obvious explanation is that the compact massive objects were not in fact black holes, and the gamma ray burst was from the energy of the final collision and merger. This would...
  27. JK423

    How did LIGO estimate the distance of the black holes?

    As we all know, the LIGO collaboration published a paper recently on the first direct observation of a binary merging black hole system. From the observed signal, they were able to infer the black holes' masses and their distance from Earth. However, the fact that they can estimate masses and...
  28. T

    B The Center of the Earth and Black holes and Gravity

    a related thought experiment to a tunnel through Earth through which a person falls to the other side, is what if it was a pendulum falling through the planet? first, a pendulum is at 90 degs to the G field; 2nd, as soon as the pendulum BEGINS to fall through, it is in free fall, and it will...
  29. .Scott

    Pull Mass from 2 Black Holes: Uncovering the Mystery of Gravity Waves

    OK, in solar mass terms, 29+36=62 with 3 left over. Or make that 3 left out. This is a little-advertised mechanism for pulling mass from a black hole. And, since the output is gravity waves, it doesn't seem to be directly related to Hawking Radiation. Somehow intense gravity can scoop out...
  30. A

    How did black holes merge in finite time?

    This question is in context of the recent gravitational wave detection by aLigo. Apparently aLigo has detected the entire process, including the before merger, during merger, and aftermath of the completed merger. My understanding is that two black holes should not be seen to be merging in...
  31. G

    Does Dark Matter Contribute to the Mass, Charge, and Spin of Black Holes?

    Since we think that 85% of the matter in the universe is Dark Matter, does it follow that around 85% of the mass of a typical black hole should be of dark matter origin? If not, why not? And if so, black holes are defined by only 3 parameters, mass, electric charge and spin. As far as we can...
  32. S

    Can We Ever Observe Inside a Black Hole's Event Horizon?

    It appears that black holes do exist in our universe, in the sense that there are objects so massive and so small that there must be an event horizon. Is it generally accepted that there is "really" a singularity inside these event horizons, or that we just don't know, and may never know?
  33. B

    B Is Black Hole-Generated Dark Energy a Viable Theory?

    First of I am not a scientist, just a big fan. So I am sorry for any incorrect terminology. A few years back I remember reading a article on the various theories pertaining to Dark energy. I think it may have been in a Scientific American. After the article was done talking about the most...
  34. wolram

    Did Black Holes appear in the first billion years?

    The tittle says it all really, how did Black Holes appear so early in the universe, why not stars? arXiv:1601.05473 [pdf, ps, other] The Early Growth of the First Black Holes Jarrett L. Johnson (LANL), Francesco Haardt (Universita dell'Insubria) Comments: 13 pages, 9 figures, invited review...
  35. G

    Are black holes more redshifted than the CMB?

    I don't know if this question makes any sense, sorry if it doesn't. I have often read that any matter (say an object, for more mundane clarity) falling into a black hole (providing it radiated) would be perceived by an outside observer as never actually crossing the event horizon. It's "image"...
  36. K

    Can Soft Hair Explain the Information Paradox on Black Holes?

    Soft Hair on Black Holes Stephen W. Hawking, Malcolm J. Perry, Andrew Strominger (Submitted on 5 Jan 2016) It has recently been shown that BMS supertranslation symmetries imply an infinite number of conservation laws for all gravitational theories in asymptotically Minkowskian spacetimes. These...
  37. Astronuc

    Are Dual Supermassive Black Holes in Galaxies Rare and Insignificant?

    Apparently rare - only 12 galaxies are known to exist with two black holes in their midst, according to Dr. Julie Comerford. Comerford reported a recent observation of a double black hole galaxy at the American Astronomical Society's annual meeting in Kissimmee, Florida. One of the BHs is...
  38. P

    Gravity around small black holes

    If a black hole had a mass similar to the Sun (I know black holes tend to be at least three times larger but let's assume an unusual series of events) how far would the are of extremely distorted bent gravity around it be could it cause closely orbiting bodies to be pulled or pushed out of orbit...
  39. EinsteinFan

    What happens when a star and a black hole collide?

    Hey guys. I've been wondering, what would happen if a star around 13 solar masses and a black hole 10 solar masses were drifting towards each other? Since the star is heavier, It would absorb the black hole, But i think when it reaches the event horizon It would meet Mr.Singularity, and what...
  40. PeterDonis

    Insights Do Black Holes Really Exist? - Comments

    PeterDonis submitted a new PF Insights post Do Black Holes Really Exist? Continue reading the Original PF Insights Post.
  41. rjbeery

    I Black holes and the relativity of simultaneity

    Over the years I've watched Science try to deal with the Information Paradox regarding black holes. http://news.sciencemag.org/physics/2015/12/physicists-figure-out-how-retrieve-information-black-hole I've always been curious how we got to the point where we see this as a problem in need of a...
  42. S

    Confused about black holes and Hawking radiation

    Why is it that the smaller the black hole is, the more quickly it supposedly evaporates? It seems like a black hole should radiate energy proportional to the surface area of the event horizon. To me it seems like the evaporation should slow down the more the black hole shrinks because the energy...
  43. N

    Electrons & Holes: Carbon Nanotube Symmetry Properties

    Well here's the problem carbon nanotubes possesses a electron - hole symmetry .my question is to what property of CNT'S does this symmetricity attribute to ? in otherwords if we dope this with a material with more electrons / holes what property will change ?
  44. D

    Alex Vilenkin's paper about black holes and the multiverse

    What do you think about the following blog post about a recent paper by Alex Vilenkin about the possibility of black holes containing inflating universes? http://fqxi.org/community/forum/topic/2589
  45. M

    Old Black Holes in LQC: Entropy & Information During the Bounce?

    According to LQC, did the universe before the bounce contain black holes? If so, would they still be around? What I'm getting at is this: I've read that LQC predicts that the high densities around the bounce tend to smooth out inhomogeneities. If I understand correctly, this is quite promising...
  46. preitiey

    Electron or Hole: Which Has the Greater Effective Mass?

    In case of a semiconductor, the position of Fermi level in between valence band and conduction band doesn't lie in the middle of the band gap due to the difference in the effective masses of holes and electrons. so, whose effective mass is more- electron or hole?
  47. K

    Recent papers on self-dual loop quantum black holes

    self-dual loop quantum gravity results when the immirizi parameter y=i has been the subject of many recent research papers here is a partial listGravitational axial perturbations and quasinormal modes of loop quantum black holes M.B. Cruz, C.A.S. Silva, F.A. Brito (Submitted on 26 Nov 2015)...
  48. G

    Black holes' existence from our point of view

    Hi, layman here, I have often read that because of time dilation, we would never see any infalling matter actually crossing the event horizon, it would just look more and more redshifted towards becoming invisible, even for infrared or microwave / radio detectors, but never becoming part of the...
  49. tshah321

    Moment of inertia about center of mass with four holes?

    Homework Statement What is the moment of inertia of the 4 kg disk below when it rotates about the center of mass? The mass of the disk without the holes is 6 kg . Homework Equations Center of mass equation: (1/M)(∫xdm) Moment of inertia of a disk: I = 0.5mr2 Parallel axis theorem: I = Io +...
  50. S

    A If black holes never exceed a certain mass....

    Does this imply that we are looking at wormholes?
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