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. R

    B How do Black Holes Grow? A Far-Away Observer's Perspective

    Black holes are everywhere in astrophysics. There are numerous discussion about how black holes look like, what happens to gas falling into black holes, how light bends around black holes, whether there is loss of information when mass or energy falls in, etc. There is thought to be a black hole...
  2. Halc

    I Do black holes destroy quantum states?

    This pop article popped up (isn't that what they do, by definition?) on my google news page. https://www.sciencenews.org/article/black-hole-paradoxes-quantum-states It claims that a thought experiment shows that doing a double-slit experiment near a black hole event horizon can reveal...
  3. Aerodyn

    I Escape from Two Black Holes? Solve the Mystery!

    Hello everyone, Imagine the following situation: You are inside the events horizon of a static black hole (called BH1) Now, due to the bended space-time, your future points to be inside the event horizon until eternity (You will never be outside) Now, a second static black hole (BH2)...
  4. C

    B Black Holes: How Do They Move?

    The event horizon is an area where the curvature of space is so great that no particles from within the black hole may travel past that point. For analogy, it is as if a highway ramp curved all the way back to its point of origin, an automobile moving forward would just end up going back where...
  5. haushofer

    I Formation of jets with accretion disks at black holes

    Dear all, I'm going to give a course about black holes at an astrophysics association. The public will consist mainly of lay persons, perhaps wit a little bit of physics background. My background in General Relativity is good, but my background in astrophysics at bit less. My question is if you...
  6. S

    I Kerr & Nordström Black Hole Evaporation: Q&A

    When a Kerr black hole evaporates, what will the Kerr parameter do? Stay constant at initial value? Approach zero? Approach unity? Approach a target value somewhere between zero and unity? Also, Nordström black holes in practice (with matter around) would have a strong tendency to attract...
  7. H

    I Black holes to explode due to evaporation?

    according to Hawking a black hole slowly evaporates and shrinks (when not feeded from outside with matter falling in). as I understood there comes a moment when it explodes and the singularity disappears. Is this true and if so, how is this triggered? and is there something such as a critical...
  8. F

    Orbital debris removal concept -- Please poke holes in it...

    I'm sure everyone here is aware of the hazards of orbital debris, and the difficulty of removing it. Lots of concepts have been proposed to help address it, but not many tests have been executed so far, mostly on larger debris like whole satellites. But what about the smaller stuff? Stuff that...
  9. B

    B The twin paradox and black holes

    Does the twin paradox hold around a black hole (or maybe less extreme gravitational fields)? In a gravitational fields like that of the Earth it seems to apply. If two particles fall together, with synchronized clocks, and one of them rests on a platform for a while, after which it accelerates...
  10. Feynstein100

    I Time dilatopause for black holes

    I was watching a video on GR by mathematician Matt Parker (he of the Parker Square) where he corrected some general misconceptions about GR. Most of the video wasn't anything special but there was one concept that stood out to me: the time-dilato-pause. The idea behind it is quite simple: for...
  11. V

    A Black holes: merged remnants have similar spin - why?

    Hello everyone, I hope I'm asking in the correct section, if not please point me. I read a list of gravitational wave detection. I focused on black hole - black hole events and I noticed the resulting black hole spin is very similar about a=0.7. I didn't find any explanation for this. List of...
  12. DaveC426913

    B Spaghettification & Black Holes: Classical & Einsteinian

    (Classical model) The radial "stretching" is caused by differential gravity (tides), but what is the lateral squashing caused by? Is it because the "force" of gravity is not parallel, but instead comes from a point, forming an acute angle? (Einsteinian model) I guess it's pretty trivial to...
  13. W

    B Question regarding supermassive black holes in the early Universe

    I'm really curious about this, but I want to know how wrong I am. I've seen in a lot of content recently about how observations of early supermassive blackholes are observed to be more massive than they should be. If I understand it correctly it has to do with the maximum rate a super massive...
  14. B

    A Do Astrophysical Black Holes Contain CTCs?

    I've been seeing popularizations recently that talk as though it's widely accepted that astrophysical black holes contain CTCs. Example: https://www.abc.net.au/news/2023-01-04/are-black-holes-time-machines-yes-but-there-s-a-catch/101822002 Is this accurate? Eternal black hole solutions contain...
  15. E

    B Calculate Red Shift w/ Shwarzschild Metric: A Hypothetical Black Hole Any Size?

    You can unconventionally use the Shwarzschild metric to calculate red shift at given stellar distances with some accuracy right out to the edge of the universe. Take the mass of the known universe ~10^55kg. Try it! A bit ironic. I understand this is not how to use the Shwarzchild; however...
  16. K

    Exploring "The Mathematical Theory of Black Holes" by S. Chandrasekhar

    In page 67 of book "The mathematical theory of black holes" by S. Chandrasekhar in chapter 2 "Space-Time of sufficient generality" there is a theorem that metric of a 2-dimensional space $$ds^2 = g_{11} (dx^1)^2 + 2g_{12} dx^1 dx^2 + g_{22} (dx^2)^2$$ can be brought to a diagonal form. I would...
  17. Slavik Komarova

    I Any evidence of white holes in the Universe?

    We have much evidence of the existence of black holes in our universe ... so why does not the same occur in relation to white holes since they are also the result of the same theoretical prediction ?
  18. epenguin

    B Disk with holes falling on water

    Just yesterday evening I saw a video of a few minutes where metal disks with holes in them were let fall into a basin of water.The water went up in twisted columns and made the most astounding and beautiful patterns. I thought I would show it to other people who might be interested - but I have...
  19. slogals

    Two black holes moving in a circular orbit around a point

    I tried solving it and i was able to do a) and b) here is what i did on c), but its not correct according to the solution
  20. F

    B Does a contracting universe destroy its black holes?

    I found related questions being debated on the web so i'm not sure wether the question is closed. The following simple reasoning seems to imply that indeed the contracting universe is able to destroy its blackholes but what's wrong with it ?: The black hole solution is usually computed outside...
  21. Y

    Automotive, Holes Subframe etc., Purpose (not for Fastener Access)?

    Hi, In automotive industry, I've seen subframes, lower control arms, upper control arms, cross members etc that have holes in them. Like above. That do not provide access to a stud, nut, that was put in from the other side. Now I understand some of these holes are there for that exact purpose...
  22. Melbourne Guy

    Writing: Input Wanted Black holes as weapons - easy way to calculate the evaporation blast

    I've decided my latest novel uses black hole bombs, which aliens create by a mechanism unknown, and which are small enough to quickly evaporate to blast ships in the vicinity. Knowing it is sci-fi and doesn't have to be perfect, about how fast do BHs evaporate? Alternatively, if I need them to...
  23. H

    I Effects of Supermassive Black Hole Merger on Nearby Bodies

    What would be the effects of a merger of supermassive black holes? Such releases by far the greatest amount of energy of any event in our Universe as gravitational waves. I suppose that a great deal of EM radiation is released, but I'm more interested in the gravitational waves. The...
  24. mef

    B How Can We Observe Black Holes Growing?

    IT IS WIDELY KNOWN that from the point of view of a distant, BUT FROM a FINITE distance, the time of falling into a black hole is INFINITE. Then how does the BH absorb the surrounding matter? It turns out that for any observer located at a finite distance R (the coordinate of the Schwarzschild...
  25. K

    I Higgs inflation and primordial black holes

    I've found highly cited papers that explains inflation with the Higgs as the inflaton and primordial black hole as the dark matter, for examples, These papers solve the inflation with the Higgs and Dark matter with PBH without introducing new particles. Primordial Black Hole production in...
  26. A. Neumaier

    Is Language Barrier a Reason for Our Limited Understanding of Black Holes?

    Summary:: The most basic issue queried Why do we know so little about black holes?
  27. Godot_

    I Does Dark Matter Fall into Black Holes?

    Does dark matter(DM) fall into black holes(BHs)? IMHO it should... ...as it does interact with normal matter gravitationally. Once it's done so, does it add to the BH's mass? Again, IMHO it should. AFAIK it does have mass... Would that "quasi-convert" it to normal matter? ...after all, this...
  28. Stonestreecty

    Help with the Key Points of Zener Breakdown and Avalanche Breakdown

    Good day, all I am familiar with both of terms that I speak of in title. But I cannot find a full answer, so I might as well ask the PhD'ers here. What is really happening in Zener and Avalanche breakdown? I have read Guide to Zener Effect and Avalanche Effect and still feel confused. And yes I...
  29. Joe Bond

    I Can Placing Earth Between 3 Black Holes Slow Down Time?

    I am just wondering if placing the Earth equidistant from 3 black holes that are spinnng would slow down time on the Earth, due to the time dilation effect. Would that give us more time to live?
  30. E

    B Black Holes: Can Anything Reduce Their Size?

    I'm pretty sure I know the responses I'm going to get, as this question is pretty silly, but I'll ask anyway. Is there anything - a process, or a material, that would reduce the size of a black hole and/or evaporate it away quickly, or is that just hocus pocus thinking?
  31. A

    A Merger of Extremal BHs Causes Naked Singularity?

    Let's say you have two extremal black holes containing the maximum amount of possible charge. Now let's say they're orbiting each other such that they will eventually merge. As the black holes merge they are producing gravitational waves. Once the merger is complete the new black hole mass will...
  32. T

    I Is the sign of the Einstein equation right in Chandrasekhar's Black holes?

    In Chandrasekhar's book, The Mathematical Theory of Black Holes. The sign of Einstein equations is minus "-" , Eq. (1-236). However, the sign of Riemann and Ricci tensor are the same as MTW's book. The sign of Einstein equations in MTW's book are "+"! Is there a error?
  33. A

    I Merging black holes: gravitational waves and information

    A popular theory is that black holes gradually leak information because of black hole evaporation due to hawking radiation. When black holes merge, a significant portion of their mass is converted into gravitational waves. If it's true that black holes leak information due to hawking radiation...
  34. DaveC426913

    B Stars massive enough to evolve into black holes

    I keep seeing this figure of 3-4 Solar masses is all that's required for a star to end its life by collapsing into a black hole. Since the sun is a pretty average star, that would suggest that most of the stars in the universe (like >50%) will end their lives as a black hole. The implication...
  35. E

    I Black holes and relation to creation

    Are there any papers or articles that reference black holes being the creations of the big bang or being considered in creating universes in alternate dimensions? Thanks for the help.
  36. P

    I Could dark matter consist of primordial black holes?

    Could dark matter consist of black holes formed shortly after the big bang? They would form the perfect development seed. If they all have Sun-like masses then they are not detectable from here (they are just 3 kilometers wide!). They have virtually no collisions with stars and could form a...
  37. Antman0115

    B Black Holes & Stars: Quantum Entanglement Possibility?

    Would it possible that black holes share a quantum entanglement with stars(such as white dwarfs), and the reason we observe the tunnel closing is the star dies out/explodes? I understand that there are different types of black holes and stars, varying in size and properties of mass/spacial...
  38. S

    B Do black holes determine time's arrow?

    Does black holes determines time's arrow? Otherwise how to explain with time reversed objects been pushed out from black holes?
  39. D

    I Black Hole to Other Universe: Violation of 1st Law?

    So I am a fan of astronomy, cosmology and astrophysics from a FAR. The math is way beyond my abilities but I like to just sometimes read and think about the very small parts I am able to comprehend. So my hats off to all of you that are able to fully enjoy this stuff, you're very lucky...
  40. T

    I "Black holes can only get bigger" - huh?

    Lately I see these kinds of articles: https://mysteriousuniverse.org/2021/06/stephen-hawking-is-right-again-black-holes-can-only-get-bigger/?fbclid=IwAR3_nIKegH8DK_AzA1y5_SznqRtVf6ePQlJqPFaGRMIK3TvV4SqqzXt96Bg As far as I understood, it has been pretty much accepted that tiny black holes not...
  41. W

    A Topological Definition of Holes

    Is it reasonable to define the n-dimensional holes of a topological space X as the non-zero Homology/Homotopy classes of X? Can we read these as obstructions to continuously shrinking a simple closed curve * to a point within the space? *I understand this is what we mean by a cycle.
  42. J

    A What does the equation C = 12 J mean for black holes?

    Just saw a documentary about resolving Hawking's "information paradox". In my own lay terms the physicists appear to theorize resolving the paradox with with their proposed C = 12 J . C is the central charge (which I don't fully understand) and J is the total angular momentum of the black...
  43. P

    Semiconductor -- Conduction and Valence bands

    I am a new to this and I try to understand the basics. So initially once the atoms of silicon come together to form a solid, due to Pauli law no electrons can exist in the same energy state,thus many energy states are formed which together make the bands. My problem starts at this stage where I...
  44. A

    Black Holes & Life: Myth or Reality?

    Hello everyone, im new in the forum and this is actually my first post. I am not an expert of astrophysics but for sure a very curious person that hope to can get more knowledge about astronomy and physics in the next future. Its been kinda long time I am searching an answer to some questions...
  45. Lilian Sa

    A Looking for sources of information on Black Holes

    hey Im new here, I am a masters degree student. I woud ask about any good source for understanding black hole for a master's degree student. thanks
  46. vela

    How Black Holes Work: The Onion Explains

    The Onion tackles black holes. https://www.theonion.com/step-by-step-how-do-black-holes-work-1846628568
  47. P

    B Black Hole Energy Conversion - How Does It Work?

    If you search on-line for "efficiency of a black hole" you will get several discussions suggesting that the efficiencies of converting mass to energy are from 6% for non-rotating black holes to 42% for the fastest rotating black holes. I would like to know exactly how black holes convert some of...
  48. ohwilleke

    I New Paper Claims Primordial Black Holes Don't Explain Dark Matter

    A new pre-print makes a sensible and convincing, in my view, argument that phenomena attributed to dark matter are not exclusively or predominantly explained by primordial black holes formed at less than the mass of a star shortly after the Big Bang, by means other than stellar collapse. This...
  49. Nuno_S_Oliveira

    B Translating Stephen Hawking: Plus/Minus Term & Black Holes

    Hi, I'm a Portuguese translator working on a documentary about black holes and there is a specific bit of dialogue between Stephen Hawking and his colleagues that I'm having a hard time translating. Basically, Hawking says: "So, it could be the F plus minus term takes this away." Is this the...
  50. DarK_OmEgA

    I Dark Energy's Effect on Black Holes

    If dark energy causes spacetime or things in the galaxy to expand (acceleratingly), then won't black holes die due to expansion past the Schwarzschild radius, rather than simple radiation evaporation? (When black hole die, I mean, we have the ability to look into the space because it is no...