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. W

    Calculating the event horizon of black holes.

    Hello, I remember hearing somewhere that it is possible to calculate the event horizon, I was just wondering if this is possible and what equations are used to calculate it.
  2. J

    How do micro black holes maintain their state?

    All that I've read about black holes describe something so massive it's gravity overcomes all other forces and it causes a region of spacetime to develop that no particle or electromagnetic radiation can escape from. That explanation since it depends on mass makes no sense in regard to...
  3. M

    Silicon NPN Transistor: Calculating Fermi-Level & Equilibrium Concentrations

    Homework Statement we look at a silicum n++ p+ n transistor. given: NE= 1,0×1018 cm–3; NB= 2,0×1016 cm–3; NC = 2,0×1015 cm–3; here E stands for the emitter, B for the basis and C for the collectorHomework Equations a. calculate the distance in eV from the fermi-level to EFi for the emitter...
  4. Jimster41

    From black holes to superconductors: Stanford video

    Hope this Link works. I thought this guy was great, for the layperson looking for more than the usual fluff. Might nice to give SITP some heavy "likes". Maybe they will do more. Sorry not sure what forum this was most appropriate for...
  5. Chronos

    How Do Direct Collapse Black Holes Form in the Early Universe?

    This paper http://arxiv.org/abs/1504.00263, Assessing inflow rates in atomic cooling halos: implications for direct collapse black holes, discusses formation of direct collapse black holes in the early universe. Supermassive black holes are the only reasonable explanation for quasers in the high...
  6. liometopum

    Black holes in the globular cluster M22 with Dr. Tom Maccarone

    Dr. Tom Maccarone is a coauthor of the paper, “Two stellar-mass black holes in the globular cluster M22”, and is Associate Professor,Department of Physics, at Texas Tech University at Lubbock Texas. The work is discussed in a popular form at "Physicists Find Black Holes In Globular Star...
  7. Abtinnn

    Formation of X-Ray Binaries Outside Black Holes

    Just curious... I mean they don't form inside the event horizon, so how would they form outside? How does accretion do this?
  8. T

    Black Holes & Galaxies: How Do They Work Together?

    I have been thinking of how black holes help form galaxies and have come up with this idea. Now I will assume everyone who reads this knows about how black holes and quasars work. Now if you can imagine a quasar in the beginning, ie. Without the galaxy...
  9. wabbit

    Planck Stars and GR black and white holes

    Rovelli & Vidotto's Planck Stars describes a possible quantum black hole - white hole transition through a quantum bounce somewhat analogous to the LQC bounce. In another thread, @marcus pointed out to me that this was not necessarilly considered the most likely scenario for a QG black hole. Is...
  10. T

    Feedback and equilibrium between black holes and galaxies

    "The supermassive black hole is sucking interstellar gas, but at the same time it is affecting the star-formation history of the galaxy with its powerful winds," Tombesi said. "Astrophysicists describe this process as a feedback between the central supermassive black hole and the galaxy, which...
  11. G

    Black holes and mechanical engineers

    Hello geeks! I've reached that point in life, where I've to decide on what to study. The thing is, that I simply love the wonders and extremes of our universe, such as neutron stars, black holes etc. But the thing is, if you don't want to give lectures in a university or do research in black...
  12. Nitox33

    Micro black holes, millions / billions of years?

    Hello, Always looking for answers to my questions, I had some answers like what micro black holes possibly created at the LHC (if it does not evaporate) would put millions or billions of years to be dangerous? I would like to know why Sorry if I come to you Ps : sorry for the way I did not...
  13. Michaelcomputer

    Is it possible that black holes create dark matter/energy?

    Wondering if it's possible that black holes create dark matter and dark energy from the matter and energy they consume. Then, inflation might slow when supply is low. This would support author Tarō Gomi's theory that "everyone poops." What role would time dilation play if that's what's...
  14. D

    Is current the flow of protons or just the movement of holes

    I know that current flows in the opposite direction of electrons but I'm confused as to whether it is the movement of holes like in a semiconductor or if there are actual positive particles flowing that way.
  15. F

    Feynman Path integrals in space with holes?

    Feynman Path Integrals are a way of calculating the wave function of quantum mechanics. It usually integrates every possible path through all of space. I wonder if there is any study of Feynman path integrals through a space with holes in it - with regions of space excluded from the integration...
  16. BATMANofPHYSICS

    Inside Out: The Possibility of White Holes and Black Holes Within Each Other

    hypothetically speaking, are white holes inside white holes possible? and also, are black holes inside black holes possible?
  17. wabbit

    Quick question about LQG Self-Dual Black Holes

    This paper relies heavily of LQG self-dual black holes ; I saw an old thread here about didn't find the answer there so here's my question : On the face of it this looks like a somewhat bizarre/exotic theoretical solution, especially with the description referring to wormholes. However, since...
  18. C

    Density of holes in valence band

    When electrons leave the valence band and jump over the gap to the conduction band, what is the density of the remaining holes? If 2.5 electrons/cm^3 leave the VB to the CB, will the density of remaining holes be 2.5 electrons/cm^3? To me it is logical, but I am wondering if mass of electron...
  19. D

    Can Black Holes Be Utilized for Practical Purposes?

    For example a black hole is stable. As in Ts=Tu then what would be the uses of the BLACKHOLE. Would it have any such use ?
  20. stephog

    Black holes are the shadows of 4D objects (idea)

    this is the idea...
  21. naima

    LQG and black holes -- back to basics

    Hi PF I am reading an old Rovelli paper http://arxiv.org/abs/gr-qc/9603063 Rovelli computes the entropy of a black hole. He says two things. a) A state is described with an equivalence class of s-knots. b) the entropy of a black hole can be computed by counting the number of the intersection of...
  22. L

    ENGINE HPT blade construction and and its cooling holes

    Hi there, i am currently working in an airline industry but unfortunately do not have enough facilities to carry out my research on the HPT Blades and its cooling holes of an Engine. Would anybody help me on this matter? Thanks
  23. hgducharme

    How to determine a hole in a graph?

    I'm aware that in order to find the hole in a graph, you need to factor both the numerator and denominator, and look for terms that cancel out. However, is it merely just looking for a term that cancels out, or is it more specifically a term that cancels out and makes the numerator equal to...
  24. Larry Pendarvis

    Energy/Momentum transfer from neutrinos to black holes

    Suppose you have a source of electron antineutrinos, and you arrange your apparatus so that a billion billion billion of them collide directly with a black hole. In principle, you could measure the change in momentum and energy from that occurrence. Suppose you did that the next day. According...
  25. aabottom

    Black Holes, Time Warps & "Interstellar": A Review

    I recently saw "Interstellar", a pretty good movie with well done depictions of worm holes and black holes. This inspired me to dig out my book on black holes (thinking it was written by John Wheeler). I've had the book for years and had read the first couple hundred pages about 10 years ago...
  26. M

    Topology of Black Holes: Possible Topologies & Examples

    This might be well known or even discussed here, though I couldn't find a thread about it, but the questions is what are the possible topologies of a black hole i.e. the topology of a spatial slice of the event horizon. I know there is a result of Hawking that says the topology has to be that of...
  27. M

    If photons have no mass,why would black holes attract light?

    If photons have no mass, why would black holes attract light? I was told that photons have no mass. However I thought that black holes are called "black" because no light can go escape the gravity force in their vicinity. I somehow think that, if light is just photons, then it should not be...
  28. R

    How much matter goes into making black holes?

    I recently viewed a video with Richard Carrier, who apparently was using information he derived from Lee Smolin. He said that 99.9999% of the matter in the universe goes to making black holes. Is this true? What percentage of matter does go to the making of black holes, is it even something we...
  29. diogenesNY

    Dennis Overby article on Merging Black Holes

    Black Holes Inch Ahead To Violent Cosmic Union -- Dennis Overby NY Times article today on merging black holes. Describes possible observation, implications of a pair of merging black holes. Suggests lots of research possibilities for gravitational wave astronomy. Some specific research is...
  30. J

    Black Holes & Time Travel: Wild Speculation

    This is wild speculation but wild speculation is fun; Do micro black holes bend space and time like their bigger siblings? Could you then use the curvature of time of such a micro black hole and a radio transmitter to send a message back through time? Regards, JDM
  31. Dean Whaley

    A question about Black Holes and their Gravity

    So I understand that as a star begins to die, and begins fusion of H, He, C, O... it eventually reaches Fe which cannot be fused to create energy. Then the stars own gravity overcomes it's outward radiation and the star implodes, and eventually a black hole is created. How can the star's...
  32. Lamdbaenergy

    Mass Inflation Instability in Kerr and Reisnerr black holes.

    What exactly is this mass inflation instability phenomenon that is said to happen near the inner horizon of black holes? http://jila.colorado.edu/~ajsh/insidebh/realistic.html I got the nutshell of it, but I think I need someone to really explain this.
  33. Lamdbaenergy

    Planets collapsing into black holes?

    If you had a planet with the exact same mass and radius as the Earth, and adjusted the gravity constant to some value five-hundred million times larger, the schwarzschild radius should become considerably big, right? Instead of being about 8 millimeters, it would now be about 60 to 70 percent...
  34. zerospin

    Could black holes have no singularity?

    I have a problem with the concept of a singularity, defined as something that has a property which is infinite. Infinities do not belong in our reality, and in my opinion are just hints that our understanding of the phenomenon is incomplete or wrong. From my understanding, during the collapse...
  35. R

    What is a conductive material which contains extra "holes"?

    There are conductors with loosely bound electrons such as Cu, what is a conductor that contains loosely bound "holes"?
  36. spacecadet11

    Where did Schwarzschild get his information for his black hole model?

    Hello. If at the event horizon..the escape velocity exceeds the speed of light..or time at that 'point' comes to a halt..how can anything get past or thru the horizon and make the journey to the center of a black hole? Thanks for any and all your responses. Bye SC
  37. Firedog89

    The Center of the Earth and Black holes and Gravity

    I was thinking of the conditions exerted at the center of our Earth. If a man let's say in America falls toward the Center of the Earth and a man on the opposite side of the Earth falls, where would they meet? I read that the gravitation force at the center of the Earth is at 0. If they both...
  38. P_Ravensorow

    Three Important Questions (about black holes and the Big Bang)

    I have always wondered various questions, out of which these 3 below are on the priority list including a previous topic I questioned here ofcourse without any answer to it. I am no science guy by the way, just curious! So the questions are: 1. Can a black hole contain a wormhole inside of it...
  39. K

    Extended Extreme Multiple Reissner Nordstrom Black holes

    I have a question about equation 10.21 in "Exact Space-times in Einstein's General Relativity" by Griffiths and Podolski. The equation is the well know standard metric for multiple extreme Reissner Nordstrom black holes. It has the below term: (1+ sigma(mi/ri)) The point ri = 0 is of course...
  40. Zack Davis

    Black Holes: Does Bob Survive Falling In?

    Supposing a man named Bob falls into a black hole, an instant of Bob's perceived time would be a nearly infinite amount of time to the rest of the universe due to relativity and the effects it has in and near black holes. Okay sure, but we also know (to my knowledge) that black holes "evaporate"...
  41. B

    Under pressure -- flow rate through multiple holes in a pipe

    I am looking at air system that is under a constant pressure of 350 mbar into a pipe that has 40 - 2 mm round holes. Is there a formula that I can use to calculate the total volume of air nm3/hr that will escape the system? Let's just say the air temp is constant. Can anyone help with this?
  42. T

    Question on Smolin's theory on Black Holes and new Universes

    Smolin has a theory that black holes in our Universe result in new Universes. He says Universes that are capable of creating black holes get to produce more Universes etc. http://www.space.com/21335-black-holes-time-universe-creation.html I was reminded of Smolin's ideas by this recent...
  43. Lamdbaenergy

    How can black holes have electrical charge, and spin?

    If the star's mass supposedly collapses into a single point, and it ends up having "said" zero volume, then how can people say that the hole has a specific spin or that it can have an angular momentum? Does it mean that the singularity is somehow still spinning, or maybe the spacetime around it...
  44. Lamdbaenergy

    Hawking Radiation From Black Holes:

    If you only knew the temperature of the black hole, like, if for example, the temperature of a 4 solar mass black hole being around 1.5e-8 kelvin, how could you possibly be able to calculate what wavelengths of radiation the black hole would give off? Would a black hole like this really only...
  45. T

    Various doubts about Black Holes

    Hi there! After giving a thought about this phenomena I came with some doubts and I thought that maybe it was a good idea to put them all together in one thread so I don’t star many discussions simultaneously and also because maybe their answers are related. So here I go: a) As they...
  46. V

    Ex2.7 Black holes, white dwarfs and neutron stars-Shapiro, Teukolsky

    Homework Statement Show that from (*) that for a nonrelativistic Maxwell-Boltzmann gas, n=g\bigg(\frac{nkT}{2\pi\hbar^2}\bigg)^{\frac{3}{2}}e^{\frac{\mu-mc^2}{kT}} P=nkT e=nmc^2+\frac{3}{2}nkT Homework Equations (*): f(E)=e^{\frac{\mu-E}{kT}} E=\sqrt{p^2c^2+m^2c^4} n=\frac{g}{h^3}\int...
  47. V

    Black holes, white dwarfs and neutron stars-Shapiro, Teukolsky

    Homework Statement Hello, I try to recompute all exercises in this book and sometime I hit the snag :) One of the first is: Exercise 2.6 (page 28) Show that mean kinetic energy of an electron in a degenerate gas is \frac{3}{5}E'_f in the nonrelativistic limit and \frac{4}{5}E_f in...
  48. V

    Black holes, white dwarfs and neutron star - Shapiro, Teukolsky

    Homework Statement Exercise 2.6 (page 28) Consider completely ionized matter consisting of hydrogen, helium, and heavier atomic species i>2. Let X and Y denote the fractions by mass of hydrogen and helium, respectively. Show that \mu_e=\frac{2}{1+X}. Approximate m_i=A_i m_u for all i, and...
  49. A

    Trying to understand black holes

    i understand that a black hole occurs because the atoms are not strong enough to hold back gravity after a certain point. is the matter continually collapsing on itself or does it stop after the atoms have been crushed? like is it a runaway effect? my next question is why does a large mass in...
  50. K

    Can Black Holes Die? - Exploring Their Nature

    Hi i have a few questions about black holes. Are black holes just stars that are so big, and have so much mass that no light can escape them? Do black grow in size, or are they just an infinite small point of space?¨ Can black holes die? are they actual holes, or are they spherical? can you...
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