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. D

    Mobility of electrons and holes

    Problem: Calculate mobilities of electrons and holes (assuming equal) in grey tin, silicon and germanium. Calculate also the mobility that would be necessary for diamond to have an intrinsic conductivity of 10-12 S m-1 if the hole and electron mobilities were equal. Working: \sigma = Nc...
  2. E

    Universe's Missing Matter and Black Holes

    I'm a non-scientist - that watches way too many TV science programs - that is having trouble putting the pieces together. I am always hearing about how much visible matter is missing from the universe. I am also hearing about how (it is now believed) that every galaxy contains a massive...
  3. F

    What Happens Inside a Black Hole If Dark Matter Falls In?

    If Dark Matter are particles that interact gravitationally, then what happens when/or if Dark Matter falls into a Black Hole? We would not "SEE" a Dark Matter accreation disk, but would we see any kind of radiation? Or would we see the mass grow? Thanks.
  4. L

    Bernoulli's Principle- Vertically Aligned Holes

    Homework Statement A can has two vertically aligned holes in it. The height of the fluid is h, and the heights of the two holes are h1 and h2. a) Show that the two streams of water will hit the ground at the same spot when h = h1 +h2. b) If you had such a can, how would you keep h constant...
  5. B

    Black Holes and how gravity can overcome light speed?

    Information In the book “Black Holes and Time Warps” by Kip Thorne it is mentioned on pg 121 that Einstein didn’t believe that black holes existed so the thinking that black holes can exist didn’t come directly from his writing, thoughts, or how he interpreted his relativity theories. Because...
  6. D

    Exploring the Nature of Charged Black Holes

    Hi I have few questions about charged BH. 1 I don't understand why the equations for the charged BH are different from BH without a charge. Why the gravitation, infinitely strong at the horizon, should 'care' about such minor additional forces like the electrical attraction/repulsion...
  7. T

    Info 'bout black holes, and is there one in the center of the galaxy?

    1. What are some specifics about black holes? 2. I've heard there's a supermassive one at the center of our galaxy--FACT or FICTION? Relevant websites, articles, etc. highly welcome! (I'm really interested in cosmology, obviously.)
  8. R

    Origin of Black Holes: Can BH Be Formed During Star Formation?

    Can BH be formed during star formation process? For instance, giant gas cloud or several collided clouds. In this case, can BH be created right after BB? Thank you.
  9. N

    Questions about Black Holes And Time

    Ok if this has been covered before if you could show me any links that would be great.. I was watching a program about time and how it appears to slow to a stop within a black hole... yet time can only be still if an object is frozen in time, bu a black hole moves meaning it is not frozen in...
  10. michael879

    Particle Black Holes: Exploring a Potential Quantum Mechanics Theory

    so I read about this "theory" a while back, and I've been doing some thinking about it. The "theory" is basically just that since a black hole with the same mass/spin/charge as a fundamental particle would appear to be identical to that particle, it is possible that all particles are just black...
  11. P

    Can photons create black holes despite being massless?

    As I understand (?) it, if you want to observe something too small, the photons needed will have to be so energetic that a black hole will form. The question I have is: why would photons form a black hole, I thought photons were massless?
  12. Jonathan Scott

    Schwarzschild solution radial coordinate and black holes

    When people appear to be getting very confused about the weird nature of black holes, I normally respond with answers based on standard black hole theory, but I sometimes feel I should also call attention to the point that some people now think that the "black hole" solutions to the...
  13. H

    Extremal Kerr Black holes, and their associated temperature.

    So I was calculating the temperature for a extremal Kerr black hole. G2*M2 = a2, where a = J/m. Using T = kappa / 2 /Pi... I'm assuming this is the correct approach. But my question is... The surface gravity of an extremal Kerr black hole appears to be zero, leading to a zero temperature...
  14. D

    Exploring black Holes - intro to GR 2nd edition drafts online

    The first edition for this book was a nice primer to GR for ppl like me who are far from mastering the advanced math required to in deep understanding of GR. Prof. Edwin F. Taylor now has a drop site for electronic drafts of the second edition of the book, improved and updated with new...
  15. C

    Space is NOT expanding. Where are the holes in this simplistic view?

    No expansion of space, per se? Sure, all galaxy groups appear to be traveling away from ours. But does that mean the universe is inexplicably expanding, like a loaf of raisin bread, as some have likened it? I think not exactly. I think it is expanding, in that all objects appear to be moving...
  16. B

    Black holes and whether General Relativity views light as a ballistic particle?

    A. See my questions below. First, here is some information from the book “Black Holes and Time Warps” by Kip Thorne. So far this is the best reference book I can find on the original thinking of black holes. 1. Pg 122 Very compact stars were theorized to occur way back in 1783 by John...
  17. M

    Nominal stress for a plate with fillet radius with holes

    Homework Statement Can anyone help me with the equations i need to use to find the nominal stress of a right angled plate with thickness that has a fillet radius and two holes along the bottom half? Homework Equations The Attempt at a Solution
  18. D

    Black holes & hawking radiation

    So we have an object falling into a black hole. By its perspective it falls in real time, and by the perspective of the outside it never reaches the event horison. Now if black holes slowly evaporate due to hawking radiation, if one were to observe the black hole for countless billions of years...
  19. A

    The Composition of Black Holes

    what is the composition of black hole? is it a matter or antimatter or energy?
  20. Tibriel

    Why do smaller holes shoot higher jets of water?

    So I know that F = P*A When you put a nozzle on a hose the area is smaller so does the pressure increase and the force stay the same, does the pressure stay the same and the force increase, or do they both change? Also if you poke a hole in the bottom of a bucket full of water will the...
  21. J

    Can Gravitons Escape From a Black Hole if Light Cannot?

    Assume we all accept that gravitational influence moves at the speed of light, just as EM radiation does. Light cannot escape from a black hole because the escape velocity from a BH exceeds the speed of light. If gravitons are a proposed particle-interaction based solution to explain gravity...
  22. stevebd1

    Killing fields and black holes

    I'm relatively new to Killing vector fields and I'm currently looking at them in the context of black holes. While the Killing vector field itself is relatively easy to comprehend, I find the quantities for the Killing horizon and Killing surface gravity for rotating black holes a little less...
  23. P

    Couple of Bounce Questions Regarding Black Holes / Universe

    I've been fascinated by the posts and discussions here about "The Bounce" that seems to be emerging from some LQG models (thanks Marcus and others). I have a couple of questions, which I don't think I've seen in posts here (my apologies if they've been raised and discussed and I've missed it)...
  24. D

    Matter, Antimatter, and Micro Black holes

    I have recently been reading Moment of Creation by James Trefil, and I have stumbled upon the question, where has all the antimatter gone? I asked myself, what if micro black holes produced by the tremendous energy at the big bang are the answer? If you have an understanding in hawking radiation...
  25. H

    Hundreds of Rogue Black Holes in Our Galaxy - Is Earth at Risk?

    In January, a Vanderbilt University astronomer (I forget her name) found that there were probably hundreds of 'rogue' black holes flying about our galaxy. She surmised that the risk to the Earth from these RBH's was infinitesimal. She said that the only possible risk would be that one goes...
  26. D

    Argument against the existence of black holes?

    I had a brief conversation with a professor of mine and he presented, in short an argument against the existence of black holes. I'm sure you've heard it or a variation of it. It goes something like this: An advisor and his student are near a black hole. They are both wearing a watch, the...
  27. S

    Gravitational waves adn Black holes frequency

    I'm reading this paper "Exact Gravitational Quasinormal Frequencies of Topological Black Holes" ...By D. Birmingham and S. Mokhtari : http://arxiv.org/abs/hep-th/0609028v2" and now i confusing what are meaning of gravitational quasinormal modes of Topological Black holes?. Can...
  28. L

    Black Holes and Galaxy formation

    http://blackholes.stardate.org/resources/articles/article.php?id=9 This presupposes that dark matter and dark energy interactions play no role?
  29. M

    Exploring Micro Black Holes and Entropy in Quantum Field Theory

    When I read the security report from Cern (not that I am too worried), I came to something, which I do not fully understand: As we all know, we are save from micro black holes created at the LHC because of Hawking radiation (for one of many reasons). The Cern people push this argument further...
  30. M

    Exploring Infinity: How Baby Universes Form from Black Holes

    This may strike some people as really weird but after reading the book, God and the New Physics by Paul Davies, I came across a paragraph where he explains what happens at the singularity of a black hole. At the singularity, there is no concept of time apparently. So it is impossible to leave a...
  31. F

    Merger of Neutron Stars and Black Holes

    can someone Explain the NS-NS or NS-BH or BH-BH mergers proposed to explain short GRB’s. Thanks
  32. S

    What is the meaning of topological black holes?

    what is the meaning of topological black holes? thanks
  33. Y

    Exploring the Safety of Artificial Black Holes

    Hi, In the safety case for the new Large Hadron Collider (LHC), the possibility of creating artificial black holes is considered. The main argument for the case that there is nothing to worry about, is that cosmic rays collide regularly with atoms in the upper atmosphere with much higher...
  34. P

    The likelyhood of black holes in LHC

    From what I gather, only more exotic, extra-dimensional theories predict that there will be microscopic black holes produced in the Large Hadron Collider. And I get that even if they are produced they are very unlikely to be stable and even then they would probably be safe (just to let you know...
  35. E

    Charge of Black Holes: Measurability & Effects

    I was wondering about something. If a black hole has charge, would it be measureable? Does the electric field escape the black hole even when light cannot? Or if the field does not escape the black hole, how do we know that it's a charged black hole?
  36. S

    Black Holes, how much energy do they give off?

    Sorry for the dumb question but... My friend and I were wondering how much energy is given off by an average black hole relative to its mass. (like X black hole gives off Y% of its mass as energy per second) Thanks in advance for your help.
  37. T

    How can black holes even exist?

    Ok here is a thing I don't understand: How can a black hole exist? There are several things bugging me about black holes: 1) The more concentrated the matter is, the more deformed spacetime is and the slower the time is (from our point of reference). How can Black Hole be created in finite...
  38. B

    Quantum entanglement and black holes

    I am a total novice when it comes to quantum mechanics, but I was reading up on the phenomenon of entanglement and a question arose. Theoretically, could someone take two entangled particles and put one in a black hole, using the other to observe what happens to it? Wouldn't this violate the...
  39. S

    Description of magnetic field in black holes

    Given a Schwarzschild BH. A neutron fall into the BH. The neutron having non zero magnetic moment will carry a magnetic field B with it. How do I describe the new system, on which parameters will the metric depend? In term of classical GR, Kerr Newman solution provides a B in term of the...
  40. D

    Black holes responsible for missing ET?

    Scientists are hoping to create tiny black holes here on earth, which they are pretty sure will evaporate almost immediately due to Hawking radiation. While they consider the risk to be almost nonexistent, I can envision some scientist saying "cool -- wonder if we can make a little bigger one"...
  41. M

    String stars instead of black holes?

    Hey guys! My first post - found this forum filled with lots of smart minds. Maybe you can help me out here. I'm quite the novice, so bear with me, pls :) Anyways, I read somewhere (scientific american i believe) that strings (if they exist) cannot be crushed, or shrunk anymore than what...
  42. H

    Physicists Demonstrate How Information Can Escape From Black Holes based in LQG

    Here is the news: http://www.sciencedaily.com/releases/2008/05/080515092615.htm"
  43. J

    Mobility of holes and electrons

    hi, holes are the absence of electrons in the lattice, right? then how come we say holes have a +ve charge? shouldn't it be zero? also, why is the mobility of electrons more than holes? thanks
  44. B

    Time Dilation Near Black Holes: A Consequence of Mass and Singularity?

    If black holes stretch the space-time fabric because of their mass existing in singularity, if you were near a black hole, wouldn't there be a time-stretch?
  45. djeitnstine

    Points in space and black holes

    Well I read that points in space are indeed finite and intuitively they have to be because I guess we'd never be able to move from one point to the other. (intuitively this make sense) However, when a black hole is created it is said a singularity is formed i.e. and infinitesimal point in...
  46. T

    Black holes and magnetic fields?

    Hey all, Having stumbled across this forum completely by accident I thought I would stay for a while. As such I have a question. Would a black hole have a magnetic field? I would assume that magnetic fields are affected by gravity and therefore any magnetic field would be destroyed when...
  47. wolram

    Wing Drilling: Experiments & Results Explained

    I am sure i read about experiments with wings drilled with many tiny holes, the idea i think was to break up the boundary layer, did any thing come of out of these experiments?
  48. R

    Can Black Holes Revert Back Into Stars?

    i was reading about an article about the keck observatory and its use of a laser to observe super massive black holes at the center of the galaxy. they talked about how they found young stars near the black holes and how it wasnt possible. so it gave me an idea. is it possible for black holes to...
  49. H

    Exploring Mini Black Holes at LHC: Fact or Fiction?

    This may seem like a stupid question that's been brought up several times but it is regarding the possible creation of mini-black holes at the LHC. It's said that these MBH's pose no threat to the planet because of their small size and the fact that they will evaporate by Hawking radiation...
  50. michael879

    Two Kerr Black Holes: Possible or Impossible?

    Im trying to describe a system of two kerr black holes and I was wondering if this was even possible? I am currently taking a GR course but I've looked through the textbook and we only seem to deal with stationary solutions to einstein's field question (and no two-body problems).
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