Wikipedia:Reference desk/Archives/Science/2015 August 24

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

August 24

how can any black hole move ?

--Akbarmohammadzade (talk) 04:28, 26 August 2015 (UTC)

Black holes have inertia, like any other object, and are affected by gravity, like any other object. A black hole also absorbs the momentum of anything it devours. Someguy1221 (talk) 10:19, 24 August 2015 (UTC)

may it be in classic mechanics that any object is moving, but it is very multiple when we use space-time characteristics of point where it placed. how displacement can be occurred? Can we give its movement by mathematical formulas ? --Akbarmohammadzade (talk) 04:28, 26 August 2015 (UTC)akbar mohammadzade

Black holes also have charge, so in theory they could be moved that way also (I doubt it matters in astronomy, but if we ever learned to somehow make microscopic black holes it would be the more powerful force) Wnt (talk) 12:23, 24 August 2015 (UTC)

From the perspective of the black hole itself - or even something orbiting very close to it - things are complicated and weird. But from the perspective of an outside observer, nothing very special happens. A black hole the size of a star has orbital mechanics that are essentially identical to a star of the same mass. SteveBaker (talk) 18:44, 24 August 2015 (UTC)

Right, there's nothing magical about a black hole. They obey the same laws of physics as anything else. The only thing of note is that we're not exactly sure how things behave inside the event horizon, because we don't have a theory of quantum gravity that describes how gravity works on very small scales. A theory of everything that reconciles descriptions of gravity and the other fundamental interactions is often considered the "Holy Grail" of physics. But, all this is a deficiency in our understanding of the universe, not some glitch in the universe itself. The universe merrily goes on its way regardless of what we humans think of it. --71.119.131.184 (talk) 20:06, 24 August 2015 (UTC)

Bingo. Like the debate over whether Pluto is a planet or not. Pluto is what it is. Only our labels change. One thing I'm ignorant and curious about is the concept of radiation somehow emitting from a black hole. How can something with an escape velocity greater than the speed of light still have radiation emitting? Or is that part of the same issue of "we don't know"? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:32, 25 August 2015 (UTC)

The radiation is not coming from within the black hole, but from beyond the event horizon. Though somehow the black hole also loses mass. It's weird and I don't understand it! But we have an article on it: Hawking radiation. Infalling matter also releases radiation as it is compressed, such as in the accretion disc. And the relativistic jets that form around some black holes can emit absurd amounts of radiation. I would not call Hawking radiation it one of those things that "we don't know" but rather a consequence of physics that makes no intuitive sense (like much of quantum mechanics to begin with) but is testable, maybe, one day. Or it will be wiped out or modified beyond recognition by a theory of quantum gravity. Someguy1221 (talk) 02:48, 25 August 2015 (UTC)

The black hole loses mass because of Hawking radiation. The mass is carried away by the energy of the escaped particles. If any radiation is given off, by the simple law of conservation of energy, the black hole itself must lose mass. The mechanisms by which it does lose mass is explained by Hawking radiation, but insofar as they radiate anything, the loss of mass is taken as a given. --Jayron32 09:50, 25 August 2015 (UTC)

You could probably explain it any way you like, I still doubt it will ever make sense to me. That something happening just outside the event horizon is diminishing the mass of something within the event horizon. All the math in the world doesn't get me closer to understanding how it is supposed to work. Someguy1221 (talk) 09:54, 25 August 2015 (UTC)

Well, if you're going to refuse to accept it without looking at the actual science behind it, I don't suppose there's any hope to teach you anything then. --Jayron32 10:26, 25 August 2015 (UTC)

? You didn't show me the science. You said the mechanism is explained by the Hawking radiation article, but this is not actually true. The article shows how to derive the temperature and evaporation rate of a black hole, but provides zero explanation for how mass gets transferred from the singularity (or anywhere within the event horizon) to outside the horizon, except to say "tunneling", or alternatively to suggest the infalling of particles with negative mass. That's not a mechanism. I suspect there is an answer to my question, and it is an impenetrable wall of math I will never understand. You're welcome to try, and I'll attempt to understand, but you'll have to actually, you know, show me the science. Someguy1221 (talk) 10:32, 25 August 2015 (UTC)

I can try to explain it (but I make no promises). Just outside the event horizon of a black hole (the point of no return), particle-antiparticle (P-A) pairs are being created. These P-A pairs are created from the extreme gravitational forces that exist near a black hole. I do not really understand how they are created but I do know that they are. The P-A pairs are subjected to extreme tidal pressures due to spaghettification and are eventually ripped apart flinging one out and sucking the other in. The particle that is flung out can do so because it hasn't yet crossed the event horizon (the pair formed just outside it). Now, conservation of mass and energy is absolute. It can neither be created nor destroyed. So, when the P-A pair is created it actually used a little bit of the black hole's mass. When one of the particles escapes that mass is loss. Over a very very long period of time more and more P-A particles are created, more P-A parts are lost and the black hole begins to dissipate. I admit it is really hard to wrap your head around. Particles popping into and out of existence but I hope that sort of explains it a little. --Stabila711 (talk) 10:46, 25 August 2015 (UTC)

Oh, I'm fully aware of this explanation, have been for a long time. My issue is not how solid the proof is that the black hole must lose mass as a consequence of hawking radiation. My question is about the fate of the particles that were already within the black hole. By what mechanism, and I really mean by what particle interaction, are these made to leave the black hole? If the black hole is to slowly evaporate into nothing, then the particles within must somehow either be moved or destroyed. I've never read anything that actually explains the mechanism, except as I've said, to say the word "tunneling" and then wave hands furiously. Someguy1221 (talk) 10:53, 25 August 2015 (UTC)

The particles that have crossed the event horizon do not escape. Particle-antiparticle pairs are being created just outside the event horizon. Nothing can escape once it crosses the event horizon. That is the point of no return. The particle that splits off from the P-A pair escapes because it has not crossed the event horizon but since it was created using the black hole's mass it carries some of that mass away with it when it breaks off. --Stabila711 (talk) 10:57, 25 August 2015 (UTC)

Right, so what happens to the stuff inside? The black hole disappears eventually as it evaporates. Something happens to all the particles it ate. Someguy1221 (talk) 10:59, 25 August 2015 (UTC)

The particles and energy inside are eventually turned into particles that can escape (ones that form just outside the event horizon). The particles that are inside cannot escape but they can be turned into something that can. --Stabila711 (talk) 11:01, 25 August 2015 (UTC)

Also, you're extrapolating too many unknowable assumptions into the situation. For example, you're presuming that a particle inside of an event horizon has some sort of identity you can assume is maintained, like if a hydrogen atom falls into a black hole, it stays a hydrogen atom and just hangs out, waiting for something else to occur. It's a logical, sound, and well reasoned notion, and also one which we can't assume to be happening, if only because we have no way of knowing what goes on inside the event horizon. The physics of the interior of a black hole is unknown, and in many ways, may be unknowable. Even the notion of a singularity is simply a convenient way of saying "fucked if we know..." Singularity just means "region where mathematics breaks down", that is where our equations stop making sense. So, when you're looking for explanations that make sense in the "outside the black hole" world, and expect the "inside the black hole world" to follow the same rules, all bets are off.

Even simple, well-understood processes don't work like that. Consider, for example, the process of beta decay. Imagine a donut with coconut on it. Better yet. Imagine a donut that WAS in a bag, but someone ate it. And all you have left is little flakes of coconut. A normal, sane person would say "It must have been a coconut donut, because these little bits of coconut fell off in the bag." Physics doesn't work that way. Replace the donut with an atom, and make the coconut an electron from beta decay. Now, during beta decay, since the nucleus sheds an electron, it may be logical to assume the electron must have been in the nucleus to begin with. It isn't. The nucleus consists of protons and neutrons, which are themselves made of quarks, and the whole mess is being held together by things like gluons and W and Z bosons. The quarks, gluons, and W & Z are all fundamental particles, none of which is an electron. Where did the electron come from then? Are electrons made of quarks, gluons, or bosons? Nope, electrons are also fundamental particles. So, you didn't make an electron from parts available, you didn't break an electron off from somewhere it was already attached. It just appeared in the process of beta decay (which, because of various conservation laws, also resulted in a neutron transforming similarly magically to a proton). It would be like a cinnamon-and-sugar donut magically starting to shed coconut. Makes no sense. And yet, it doesn't have to make sense to happen. It still does.

With the black hole evaporation/Hawking radiation thing: the same sort of explanation holds true. You're looking for coconut donuts to explain where the coconut came from. Particle physics plays by its own rules, and those rules don't make sense in the macro world. As John Archibald Wheeler once quipped, to paraphrase, if this doesn't confuse the hell out of you, you really don't understand it... --Jayron32 12:27, 25 August 2015 (UTC)

Are you sure you don't mean Niels Bohr? Anyone who is not shocked by quantum theory has not understood it. Certainly, Wheeler may well have said something similar as well. --Trovatore (talk) 21:05, 25 August 2015 (UTC)

Every one of them has. Similar quotes are attributed to Feynman, Gell-Mann, really every single physicist has said something similar. In this rare case, I'm inclined to believe all of them; instead of a misattributed quote, it's probably a rare case where they each have said something similar. Really the entire Schrodinger's Cat thing was merely an elaborate way to make the same statement as well. --Jayron32 02:34, 28 August 2015 (UTC)

I absolutely love that quote from Wheeler. It basically explains all of particle physics. I understand the gist of it and even that tiny amount of understanding still makes my brain hurt. The subatomic world is just pure insanity. The rules we live our lives by, the rules that we have learned and come to accept, just no longer apply. To even being to scratch the surface we have to go against every instinct, every fiber of our being that says "that is wrong, that can't happen" because it does. I honestly think that the number of people that truly understand this stuff on a fundamental level can be counted on one hand (maybe two). --Stabila711 (talk) 12:45, 25 August 2015 (UTC)

Ugh, and my questions are still shooting over both of your heads. In the case of beta decay, we can draw a simple Feynman diagram showing where the electron came from. In the case of Hawking radiation, the particles seem to just appear one place, and mass disappears from someplace else. Your reference to physics breaking down and us not knowing is exactly what I'm talking about: When people talk about Hawking radiation, they seem satisfied to prove that it occurs, and then furiously wave their hands on the mechanism of mass transfer from within the event horizon. If you're going to say that no such mechanism exists to be explained because we can't know what's going on inside, then it's not my fault for not understanding the theory, but the theory's fault for not having a mechanism. I'm sure that Hawking and others have proposed mechanisms, but these are simply not explained in detail on our article. Someguy1221 (talk) 19:03, 25 August 2015 (UTC)

EVERYTHING at the quantum level is explained as "being satisfied to prove it occurs" It isn't handwaving, it isn't a missing piece of the theory that we don't have because we either lack the theory or we lack the technology to test the theory. What causes a particular nucleus to undergo decay at a particular moment? Absolutely nothing. It just happens. We can prove it occurs by detecting the products, just like Hawking radiation. Your uncomfortableness is noted, but understand that what sets theoretical physicists apart is their ability to ignore that uncomfortablness, and stop needing to explain it, and accept that there just is no cause, no mechanism, for us to even look for. Another common physics quote (attributed variously to Murray Gell-Mann and the aforementioned Richard Feynman, among numerous others) is "Shut up and calculate". Stop trying to look for causes in the uncaused events. They just happen, we know they happen, and we can write theories which can predict them happening with exacting accuracy. The rest of it is for the philosophers to worry about. --Jayron32 19:41, 25 August 2015 (UTC)

Ah, at least Wnt gets what I'm saying. I'm going to try one more time, then I give up. In quantum electro and chromodynamics, changes in a particle's energy or momentum are associated with absorption or emission of another particle. These interactions can be described with a Feynman diagram or more mathy methods. If the stuff inside a black hole is experiencing a change in mass/energy, then something must be getting emitted from or absorbed into that stuff, whatever it may be. The mass inside can't just magically disappear, there must be a mechanism. Our own article on Hawking radiation tries to address this issue with a single sentence, using this reference, which mentions the issue but does not address it in great detail. They do pitch the same two possible mechanisms mentioned by Wnt. You don't have to believe me, but even Stephen Hawking himself thinks this is important to think about - he addresses it in page 137 of A Brief History of Time. And now that you've motivated me to go and read that book again, I'm satisfied. Thank you Jayron. Someguy1221 (talk) 22:52, 25 August 2015 (UTC)

There are two separate and incompatible explanations being given above. One involves virtual particles, and one involves quantum tunneling. I personally find virtual particles much more annoying than enlightening, for reasons too longwinded to explain, so I should stick with the quantum tunneling.

A particle in a black hole is also a wave (particle-wave duality). It exists as a wavefunction that smoothly drops off with increasing distance. Now a black hole might seem like a perfectly closed box, as per particle in a box, but in truth, there is not infinite negative potential energy past the event horizon. Actually, as I understand it, a falling object can give off precisely its own mass as energy if it is glows like a reentering space vehicle due to friction with other infalling matter all the way down to the event horizon. The potential is only infinitely negative at the singularity itself, which is infinitely small, if indeed that is anything but a sign of an incomplete model. So what this means is, there's some probability that an observation of the position of a particle that is generally stuck at the singularity will actually find it totally outside the hole. That probability is ridiculously small, reflecting that black holes of the sizes normally observed give off ridiculously little Hawking radiation. Wnt (talk) 19:28, 25 August 2015 (UTC)

Separate question

The point of space where is gravitational singularity or spacetime singularity ,the space is damaged where other next point after movement will be so after displacement , how it occurs?akbar mohammadzade--Akbarmohammadzade (talk) 04:28, 26 August 2015 (UTC)--2.187.70.127 (talk) 05:58, 25 August 2015 (UTC)

The space where a black hole is is not damaged. It is warped. The fabric of space-time is warped around the object. For an image of what this would look like please see spacetime. Since space is not damaged just warped, when a black hole moves the warp of space-time just moves with it. --Stabila711 (talk) 06:14, 25 August 2015 (UTC)

And, anything with mass warps spacetime around it. You're warping spacetime right now. You just aren't very massive, plus you're on an immensely more massive planet, so it's not very noticeable. It should be noted that everything is moving relative to something. One of the central ideas behind relativity is that there's no absolute frame of reference. So saying that something is moving or standing still is meaningless without specifying in relation to what (obviously in everyday conversation there's an implied frame of reference, usually the Earth's). --71.119.131.184 (talk) 08:41, 25 August 2015 (UTC)

In theory, spacetime in the rubber sheet model should be discontinuous at the singularity. However, this seems like a very vulnerable mathematical model. For example, any rotation of the hole means there is a ring singularity rather than a point singularity, and since any hole will rotate a little, they must virtually all have some degree of ring to them. (I don't know if black holes actually can have spin 0, literally, or only +/- 1/2!) I suppose that is still a discontinuity, but it sort of illustrates how the model might look less mathematically pointy when looked at closely. Wnt (talk) 19:38, 25 August 2015 (UTC)

I think when any Reissner–Nordström black hole has spin (Kerr–Newman),it is its whole around containing Event Horizon which is rotating!--Akbarmohammadzade (talk) 04:32, 26 August 2015 (UTC) and of course those are theoretical supposes where it might be observed or examined in real world --Akbarmohammadzade (talk) 04:48, 26 August 2015 (UTC)

Thinking about it further, I wonder why any physicist is telling us that matter is compressed at the singularity. I mean, think about it. Suppose you have a black hole with a singularity full of matter, and nothing else is falling in. The singularity is surrounded by infinitely curved spacetime, is infinitely small, and matter in it is at infinitely low gravitational potential, so it should be like a particle in a box. That means that you, even from outside the hole, can say almost exactly where each particle that fell into the singularity is, and almost exactly what its momentum is, simply by measuring the hole. (Well, by 'almost exactly' I mean the position x momentum uncertainty of the entire hole has to be in excess of a certain figure, which is ridiculously precise compared to what you normally have for an electron or a proton) So it seems to follow that a particle can no more fall into a singularity than an electron can fall into a nucleus. But if the particles don't fall in ... then it isn't a singularity, is it? It's just a really dense patch of compressed matter, has to be. Is there a hole in this logic? Wnt (talk) 14:40, 28 August 2015 (UTC)

Is this related to Pavlov's dog?

For nine years, on many mornings as I would remove my clothes from the dryer, wash dishes and make lunch, I would hear a certain DJ on the radio. The network had a very specific schedule: some affiliates aired five minutes of news and then a minute of commercials, then the network would have one song, and most days my favorite DJ would come on. Then two more songs would play and the DJ would come back. Then more commercials.

Today, no DJ, no nothing. The network decided not to have DJs. There must be a term for what I went through. I felt like something had been taken away. It's like I get a reward for listening after that one song after the news, but today I found myself needing that reward and not getting it.— Vchimpanzee • talk • contributions • 18:27, 24 August 2015 (UTC)

Hmmm...I'm not sure. When Pavlovs' dogs were fed, they'd salivate (as dogs do!) - then he started ringing a bell just before he fed them, and after a doing this for a while, rang the bell without feeding them - and found that they salivated just as if the food had been provided. Your situation seems a bit different - in your case, when a sequence of events has been related together, you're missing a reaction when one of the items in the sequence was missing - with Pavlov's dogs, they had the reaction even though one two of the events in the sequence (bell ring ==> food ==> eat) were missing. SteveBaker (talk) 18:42, 24 August 2015 (UTC)

Classical conditioning is the term for the Pavlovian response, the transference of a behavior to a stimulus. There is also operant conditioning, which involves the reinforcement of a behavior with rewards and punishments. --Jayron32 18:51, 24 August 2015 (UTC)

A critical component of classical conditioning is that the entrained behaviour is an innate behaviour such as salivating or blinking at a puff of air on the eye. The question above is talking about a mental state, rather than a behaviour, so it it might be better to look at anticipatory mental states.DrChrissy ^(talk) 19:09, 24 August 2015 (UTC)

I had already looked at that article, but it didn't seem to give me specific information. It feels like a physical reaction when I don't get the reward I'm looking for.— Vchimpanzee • talk • contributions • 13:37, 25 August 2015 (UTC)

Human beings are naturally drawn to routine. It makes us feel comfortable and safe. When anything changes our routines (even by a little bit) it can throw us off. In an evolutionary sense, routines were a way of survival. Everyday you got up and you hunted or gathered food. If you didn't, you died. The need for routine and the feelings that we get when we have solid routines grew from there and are still very much a part of our psychological makeup. The fact that you noticed your routine was off and you felt odd speaks to that. --Stabila711 (talk) 13:52, 25 August 2015 (UTC)

Soft Tissue is not an organ?

I am editing a medical paper and the authors, whose first language is not English, have written that "the presence of [x type] tumors have [sic] been reported at various organs such as the brain, lung, liver, colon, ovary, uterus, skin and soft tissue" but soft tissue by itself is not an organ, it is connective tissue surrounding organs ... right? I am simply seeking confirmation and will edit accordingly. Thank you in advance. Wolfgangerl (talk) 21:14, 24 August 2015 (UTC)

Are you working for a journal, or as a third party editorial service? The way you pose the question makes me think the latter. If so, this is not your concern. Scientifically, the definition of Organ_(anatomy) could apply to various types of soft tissue. E.g. a tendon is soft tissue, and part of the skeletal system, which is part of the Organ_(anatomy)#Organ_systems. On the other hand, some people surely don't consider "soft tissue" to be the name of an organ, but e.g. tendons and muscular system do occur on our List_of_organs_of_the_human_body.

The main point is, it seems that you are being asked for language/writing advice, not scientific advice, and this type of subtle semantic preference in current research usage is not something I'd trust random strangers on WP for. I'd recommend letting this roll - leave it to the subject editors and reviewers to balk or accept the wording as they choose. While good writing will increase the odds of acceptance to a journal, this one small issue will not make or break the author's submission.

Finally, a safe dodge would be "...various organs such as the brain... skin, and also in soft tissue. "SemanticMantis (talk) 22:01, 24 August 2015 (UTC)

Yes, third party. I didn't think it was my concern either, and yet it seems these small semantic question marks get flagged again and again, although when I really think about it, I suppose it is more often confusion regarding, for example, 'a positive test' vs 'a positive result'. I very much appreciate the time you took to address my question, and I'm going to take your recommendation to 'let this one roll'. Wolfgangerl (talk) 00:15, 25 August 2015 (UTC)

Simple questions are sometimes the most difficult to answer! Let me be clear - I have no advanced training in medicine or anatomy. But I have written, edited and reviewed scientific papers, and I know ontology and categorization can be surprisingly thorny issues in any science. Glad you found my comments helpful :) - SemanticMantis (talk) 01:52, 25 August 2015 (UTC)

Given free choice, I'd prefer "sites" to "organs" in that sentence (particularly if the tumors are metastases, for some reason that I can't quite put my finger on). But I would not hold a sentence like that against anyone since the meaning is clear. Wnt (talk) 11:16, 25 August 2015 (UTC)

Another way to salvage the sentence would be to add another "in": "the presence of [x type] tumors have [sic] been reported in various organs such as the brain, lung, liver, colon, ovary, uterus, and skin and in soft tissue". I'd fix the verb tense you've already pointed out with the [sic], too ;) - Nunh-huh 01:13, 26 August 2015 (UTC)