Bruno da Silva Posted August 13, 2015 Share Posted August 13, 2015 And what's a black hole made of? Link to comment Share on other sites More sharing options...
DrP Posted August 13, 2015 Share Posted August 13, 2015 (edited) wow - I was thinking that that could be a possible way - make a black hole with the CERN device and direct it at the centre of the earth.. I decided NOT to share the idea here for several reasons though. 1- it won't work, its sci-fi. 2- I can't morally or legally help you destroy the earth, I kinda love it. 3-Didn't want to get your hopes up. 4- it was kinda daft. 5 - I didn't want anyone at all to think I wan't the earth destroyed, I certainly do not. What a co-incidence you should post the exact thing I was thinking. lol DISCLAIMER: The only reason I was even thinking about this was because of the earlier thread about sending a trained mole to the centre of the earth attached to an atomic bomb... I thought there had to be a better way. But then I thought - I am just going to end this train of thought. Edited August 13, 2015 by DrP 2 Link to comment Share on other sites More sharing options...
Strange Posted August 13, 2015 Share Posted August 13, 2015 Could a microscopic black hole suck the whole Earth? No. It might make it slightly warmer, but that's all. There has been a lot of analysis of this, partly because some nutty people claimed the LHC could produce micro black holes. http://www.universetoday.com/1930/are-microscopic-black-holes-buzzing-inside-the-earth/ And what's a black hole made of? It is not really "made of" anything. It is a region of space where mass has collapsed below its Schwarzschild radius. Link to comment Share on other sites More sharing options...
Bruno da Silva Posted August 13, 2015 Author Share Posted August 13, 2015 No. It might make it slightly warmer, but that's all. There has been a lot of analysis of this, partly because some nutty people claimed the LHC could produce micro black holes. http://www.universetoday.com/1930/are-microscopic-black-holes-buzzing-inside-the-earth/ It is not really "made of" anything. It is a region of space where mass has collapsed below its Schwarzschild radius. So how big would it have to be to suck the whole Earth? Link to comment Share on other sites More sharing options...
Strange Posted August 13, 2015 Share Posted August 13, 2015 (edited) So how big would it have to be to suck the whole Earth? I guess it would have to have a similar mass to the Earth itself. In other words, about 2cm across. It would still take thousands or millions of ears to absorb the mass of the Earth. Edited August 13, 2015 by Strange Link to comment Share on other sites More sharing options...
pzkpfw Posted August 17, 2015 Share Posted August 17, 2015 ... It would still take thousands or millions of ears to absorb the mass of the Earth. Elephant ears or mouse ears? 1 Link to comment Share on other sites More sharing options...
zapatos Posted August 17, 2015 Share Posted August 17, 2015 It is not really "made of" anything. It is a region of space where mass has collapsed below its Schwarzschild radius. Can you expand on that please? Are you saying that physics can't say what a black hole is composed of? Or that the definition of a black hole does not describe the matter that is in it? I would assume it is made of something, perhaps some version of what went into the black hole. Link to comment Share on other sites More sharing options...
MigL Posted August 17, 2015 Share Posted August 17, 2015 The Black Hole itself is not made of anything. It is actually a mathematical construct describing a region of space around a gravitationally collapsed object where the escape velocity is greater than or equal to c ( the speed of light ), as a result no light, radiation of any kind, or any information whatsoever, can escape this region. This gives it an absolutely black appearance, hence the name 'black hole'. But there is nothing solid there, just a region of dark space. The only information or properties conserved by a Black Hole are mass, charge and momentum ( angular and linear ), all other information is lost. This is of course, according to classical General Relativity. Quantum theory, on the other hand, suggests that information cannot be lost, and so points to a quantum modification of classical GR, which would also help with the problem of determining if the gravitationally collapsed mass actually becomes singular ( dimensionless point ) or not. Link to comment Share on other sites More sharing options...
Strange Posted August 17, 2015 Share Posted August 17, 2015 Can you expand on that please? Are you saying that physics can't say what a black hole is composed of? Or that the definition of a black hole does not describe the matter that is in it? I would assume it is made of something, perhaps some version of what went into the black hole. MigL beat me to it ... we can't say anything about what happens to matter that falls in to a black hole. In GR the ultimate fate is that it is crushed into a point of infinite density. But I don't think anyone considers that a realistic description. A unified theory of quantum gravity may give an answer (for example, string theory has this: https://en.wikipedia.org/wiki/Fuzzball_%28string_theory%29) It is actually a mathematical construct describing a region of space around a gravitationally collapsed object where the escape velocity is greater than or equal to c ( the speed of light ), as a result no light, radiation of any kind, or any information whatsoever, can escape this region. This is a Newtonian view and can lead to misunderstandings. For example, an object can leave the surface of the Earth at less than escape velocity but will fall back again. This is not true of light and black holes. The reason light (or anything else) cannot escape is because the curvature of space-time is so great that there is no path out of the event horizon. Link to comment Share on other sites More sharing options...
MigL Posted August 17, 2015 Share Posted August 17, 2015 Not to nit-pick, as this is off topic anyway, but this is essentially the same thing. An 'object' which leaves the Earth's surface and falls back down, has a variable speed as it climbs , stops, and falls. Light does not. It always travels at c ( and follows geodesics ). In effect, it either escapes, or it doesn't. There is no in-between. Link to comment Share on other sites More sharing options...
Sorcerer Posted August 17, 2015 Share Posted August 17, 2015 This is a Newtonian view and can lead to misunderstandings. For example, an object can leave the surface of the Earth at less than escape velocity but will fall back again. This is not true of light and black holes. The reason light (or anything else) cannot escape is because the curvature of space-time is so great that there is no path out of the event horizon. I understand what you are saying here but I also immediately thought the question "how can there be a path in if there is no path out due to curvature?" I haven't yet thought of a sensible answer.... any ideas? Link to comment Share on other sites More sharing options...
Strange Posted August 17, 2015 Share Posted August 17, 2015 I understand what you are saying here but I also immediately thought the question "how can there be a path in if there is no path out due to curvature?" I haven't yet thought of a sensible answer.... any ideas? Without the ability to draw pictures, I'm not sure I can put that in words. Is a lobster pot a good analogy!? Although, my description is probably based on the Schwarzschild metric. There are other metrics which may resolve the problem you see (and probably fit with MigL's description as well): http://jila.colorado.edu/~ajsh/insidebh/waterfall.html Not to nit-pick, as this is off topic anyway, but this is essentially the same thing. An 'object' which leaves the Earth's surface and falls back down, has a variable speed as it climbs , stops, and falls. Light does not. It always travels at c ( and follows geodesics ). In effect, it either escapes, or it doesn't. There is no in-between. OK. But an object can leave the surface of the Earth at less than escape velocity (and then fall back. So this might imply that an object (with mass) could temporarily leave the surface of a black hole at less than the speed of light, before being dragged back. I have just heard a few too many people say that the theory of black holes must be wrong, because of this (not realising that it is just an analogy or informal description). Link to comment Share on other sites More sharing options...
Sorcerer Posted August 17, 2015 Share Posted August 17, 2015 Not really I'm not good with analogies. If space is curved so there is no path then there is no path.... Surely there must be a path it's just impossible for a photon to reach the end of it from one direction. Ie a path that's stretched to infinity. Link to comment Share on other sites More sharing options...
Strange Posted August 17, 2015 Share Posted August 17, 2015 (edited) Not really I'm not good with analogies. If space is curved so there is no path then there is no path.... Surely there must be a path it's just impossible for a photon to reach the end of it from one direction. Ie a path that's stretched to infinity. Any path that starts inside the even horizon is curved back towards the centre. Any path outside the event horizon just carries straight on to the centre. So, if you are outside, you can (given enough energy) turn away from the path leading you in. If you are inside, any attempt to turn away from the path leading you in just means you get the the centre sooner. Not only that, when you cross the event horizon, the singularity at the centre is no longer ahead of you but because space and time coordinates have swapped places, it is now in your future. And, as we know, you can't avoid that! Edited August 17, 2015 by Strange Link to comment Share on other sites More sharing options...
Sorcerer Posted August 17, 2015 Share Posted August 17, 2015 That makes more sense, but it could be said that there is no center because there is no outward direction just an infinite path inwards. And since you mention curvature I guess this is a spiral? Sorry rethinking that curvature would mean more simply asymptotic. Since photons paths are linear, I was visualising a circle or sphere. Or would a photon actually eventually stop moving and come to rest in the center? Any path that starts inside the even horizon is curved back towards the centre. Any path outside the event horizon just carries straight on to the centre. So, if you are outside, you can (given enough energy) turn away from the path leading you in. If you are inside, any attempt to turn away from the path leading you in just means you get the the centre sooner. Not only that, when you cross the event horizon, the singularity at the centre is no longer ahead of you but because space and time coordinates have swapped places, it is now in your future. And, as we know, you can't avoid that! Sorry how would something that crossed an event horizon have the means to make a decision? I'm sorry again I don't understand the event horizon was also in the future of the object that was previously outside of it... this has some meaning? We only measure future events in hindsight. Link to comment Share on other sites More sharing options...
Strange Posted August 17, 2015 Share Posted August 17, 2015 That makes more sense, but it could be said that there is no center because there is no outward direction just an infinite path inwards. There is a centre. It is where the curvature becomes infinite (a singularity). And since you mention curvature I guess this is a spiral? Perhaps, if the black hole is rotating. But not in the case of a simple case, a Schwarzschild black hole. Sorry rethinking that curvature would mean more simply asymptotic. That seems a good way of thinking of it. You can see that paths closer to the black hole become increasing curved towards it. At some point they go in but never come out again (like a curve that goes to infinity). Since photons paths are linear, I was visualising a circle or sphere. Photons follow geodesics, which can be curved. Or would a photon actually eventually stop moving and come to rest in the center? It would reach the centre and go no further. Sorry how would something that crossed an event horizon have the means to make a decision? If you were in your spaceship and fell through the event horizon, you might try and turn round and escape. Any such attempt would just mean you approach the singularity more quickly. I'm sorry again I don't understand the event horizon was also in the future of the object that was previously outside of it... this has some meaning? The event horizon is a location in space. When you cross the event horizon, spacetime curvature becomes so great that what was ahead of you in space becomes ahead of you in time. Link to comment Share on other sites More sharing options...
MigL Posted August 17, 2015 Share Posted August 17, 2015 Seems simple enough to visualise Sorcerer... There is a hole in the ground 10 feet deep. You can easily fall in, so there is a path in. Getting out is a different matter. The path out takes a lot more energy, and is not just a matter of reversing direction. This is of course, a 3dimensional analogy. The 'hole' analogy of a space-time ( 4D ) BH takes an infinite amount of energy to get back out as it involves moving faster than the speed of light, and so, is impossible, i.e. there is no path out. And my apologies Strange, of course you are right ( I now see what you were saying ),space-time curvature is the proper way of looking at things. But the event horizon itself ( that which we call a black hole ) can be explained in terms of Newtonian gravity. Link to comment Share on other sites More sharing options...
Sorcerer Posted August 18, 2015 Share Posted August 18, 2015 (edited) Under general relativity wouldn't it be better to think of it like this: a BH contains a singularity so the space time from the event horizon to that singularity is infinitely stretched towards it, therefore a photon crossing the event horizon would never reach the singularity, however would still always be contained within the BH. This would then also true of the opposite; any photon emitted by a recently formed singularity would need an infinite amount of time to reach the event horizon. There perhaps however is a point very close to the infinite end of the assymptote where the size of the photon and the spatial distance between the singularity overlap. Edited August 18, 2015 by Sorcerer Link to comment Share on other sites More sharing options...
Strange Posted August 18, 2015 Share Posted August 18, 2015 a BH contains a singularity so the space time from the event horizon to that singularity is infinitely stretched towards it, therefore a photon crossing the event horizon would never reach the singularity A photon (or anything else) will reach the singularity in finite time. Link to comment Share on other sites More sharing options...
Sorcerer Posted August 18, 2015 Share Posted August 18, 2015 A photon (or anything else) will reach the singularity in finite time. Why? If you're sretching 4d into 0d. Where is the time/space at that point? How long would it take for something to travel to a place where time doesn't exist? Link to comment Share on other sites More sharing options...
Strange Posted August 18, 2015 Share Posted August 18, 2015 Why? I can't do the required maths. But this is what I am told by a number of people who can do the necessary maths. For example: From here [the event horizon] to the central singularity will take 0.0001 seconds in free fall, for this 30 solar mass black hole. The infall time is proportional to the mass of the black hole. http://casa.colorado.edu/~ajsh/singularity.html Link to comment Share on other sites More sharing options...
Sorcerer Posted August 18, 2015 Share Posted August 18, 2015 (edited) What observers frame of reference is that timing from? It must be from something inside the event horizon any other observer couldn't know. Sorry haven't read the link yet will do later. A photon travels at the speed of light, from its frame of reference all time is concurrent. All events happen simultaneously to a photon travelling at c, except the event when time and space cease to exist because this event is dependent on time and spaces existence, so is the frame of reference. It can be in 4d approaching that place but never exists in the place where 4d isn't. If it never is there but it must travel to there then it must travel for an infinite amount of time. Edited August 18, 2015 by Sorcerer Link to comment Share on other sites More sharing options...
Strange Posted August 18, 2015 Share Posted August 18, 2015 Feel free to ignore the science and make things up instead. <shrug> Link to comment Share on other sites More sharing options...
Sorcerer Posted August 18, 2015 Share Posted August 18, 2015 If you think I'm just "making that up" without considering it, you're wrong. I'll read that link eventually. Frame of reference is important. What one observer may experience quickly can be a limitless experience from another observers frame of reference. Photons are an observers measure of their frame of reference. A photon travels with the frame of reference, so to it events aren't seperate, because at C time stops for an observer. A photon travelling to a place where there is no frame of reference because there is no time and no space to make that possible will never be the observer of that event. If something never happens but is still in a positive 4d direction. Then it is an infinite 4d distance away. Link to comment Share on other sites More sharing options...
Strange Posted August 18, 2015 Share Posted August 18, 2015 Frame of reference is important. Indeed. That time is the proper time (i.e. in its own frame of reference) for an object in free fall. Photons are an observers measure of their frame of reference Photons do not have a (valid) frame of reference. I do wish science popularizers would stop this "photons don't experience time" nonsense... Link to comment Share on other sites More sharing options...
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