Wikipedia:Reference desk/Archives/Science/2013 April 11

= April 11 =

could a black hole exist at the center of a neutron star?
thanks, Rich76.218.104.120 (talk) 03:12, 11 April 2013 (UTC)


 * Not indefinitely. Plasmic Physics (talk) 03:30, 11 April 2013 (UTC)


 * What he said. Neutron star matter is expected to be fluid, so it would presumably just flow into the black hole and be consumed over time, and you would not have a neutron star for very long. Someguy1221 (talk) 06:16, 11 April 2013 (UTC)


 * And by "not very long" we're probably talking milliseconds! SteveBaker (talk) 11:22, 11 April 2013 (UTC)
 * perhaps you're right, whether it would be milliseconds or microseconds or days or what. I wondered if rapid rotation would play a role. But subatomic particles that decay in microseconds or less are still of interest in physics. i've also heard that very small black holes don't eat much, so i'm not convinced by the mere fact of of a LOT of [fluid or otherwise] mass pressing in on a black hole inside a neutron star would for sure cause it to take in all the neutron star's mass. If the black hole were small enough, i thought the "black hole evaporation" tendency could be roughly cancelled by the ready availability of mass inside the star.{to keep the black hole going, yet have the neutron star containing it exist for a "long" period of time}76.218.104.120 (talk) 12:28, 11 April 2013 (UTC)
 * Black hole evaporation ius one of those unproven ideas like gravitons, string theory, branes, etc. Much may be written but far less proof exists. Rmhermen (talk) 12:57, 11 April 2013 (UTC)


 * Thought I would check those intuitive answers with a back of an envelope, non-relativistic, much hand waving calculation. Assume that the rate of growth of the black hole is limited by area of its event horizon, the speed of light and the density of the surrounding material. Then in a "best case" scenario (or worst case from the POV of the neutron star) we have
 * $$\frac{dm}{dt}=4 \pi r^2 c \rho$$
 * and for a non-rotating black hole r is the Schwarzschild radius
 * $$r=\frac{2Gm}{c^2}$$
 * so
 * $$\frac{dr}{dt}=\frac{8 \pi G \rho}{c}r^2$$
 * Integrating this gives
 * $$\frac{1}{r_0}-\frac{1}{r_t} = \frac{8 \pi G \rho}{c} t$$
 * where r0 is the initial radius of the black hole. If rt is much greater than r0 then we have
 * $$t \approx \frac{c}{8 \pi G \rho r_0}$$
 * Taking a typical density at the centre of a neutron star to be 1018 kg/m3, then I make the time taken for the black hole to absorb the whole star to be of the order of 0.2 metre seconds divided by the initial radius of the black hole. For a millimetre sized black hole, this gives a timescale of minutes rather than milliseconds. Gandalf61 (talk) 13:16, 11 April 2013 (UTC)


 * Your calculation neglects the (very important) fact that the density around the black hole would not remain constant during the collapse. Dauto (talk) 15:59, 11 April 2013 (UTC)


 * Look for instance where a detailed computer simulation shows that the collapse happens in less than 10 ms. Dauto (talk) 16:16, 11 April 2013 (UTC)
 * Haven't looked up the paper yet, but I'd just point out a possibly very important consideration: All that mass going into the black hole is going to be accompanied by a truly spectacular release of energy.  Maybe enough to blast away part of the neutron star?  Don't know; it's not like I can solve the equations (or even formulate them) in my head.  Does the paper take that into account? --Trovatore (talk) 16:19, 11 April 2013 (UTC)


 * shall i take away a "yes" to the original question--that a black hole can exist inside a neutron star, regardless of how long it lasts?76.218.104.120 (talk) 04:24, 12 April 2013 (UTC)


 * Yes. Plasmic Physics (talk) 04:34, 12 April 2013 (UTC)
 * I hate when a potentially simple answer is complicated with obtuse mathematics and peripheral theory. It is akin to verbosity. Plasmic Physics (talk) 04:46, 12 April 2013 (UTC)
 * Well, I hate trivial soundbite answers because they are so facile and uninformative. I didn't know that a black hole could absorb something as massive as a neutron star in milliseconds. Now I know that (a) yes it can and (b) the scenario has been studied in detail. So I have learned something. Gandalf61 (talk) 09:04, 12 April 2013 (UTC)


 * With respect to the OP, it doesn't matter whether you learned something does it now? Giving a concise answer takes priority over divergent exploration of related notions. Its only fair to first answer the OP's question, before endulging in such a manner of discussion. Plasmic Physics (talk) 09:40, 12 April 2013 (UTC)


 * Well, I certainly don't think the OP learned anything from your trite "Not indefinitely" response, beyond the fact that you couldn't be bothered to take their question seriously. Thanks to the further discussion, we know how long it takes for the neutron star to collapse, and we have an source for that information. Gandalf61 (talk) 10:34, 12 April 2013 (UTC)


 * You're missing my point - the OP never inquired for an expanded answer, which is clear from his most recent post. Plasmic Physics (talk) 11:06, 12 April 2013 (UTC)
 * Actually I learned a lot from all of you and I appreciate both Gandalf's and Plasma's help! I'll admit I did press for a yes or no which in past inquiries I have not always gotten, due to a delightful tendency(No sarcasm here, it's not just delightful, it's also educational)of refdeskers to go off on tangents. -Rich199.33.32.40 (talk) 21:42, 12 April 2013 (UTC)

8th dimensional space
so i was looking at 8th dimensional space page the quantum entanglement and alternate realities i need help to see if i am right

so pretty much 8th dimension is saying there our many universe like ours but different at the same time and if one were to get to one of these many dimensions it would cause a tear in space causing a new reality and if one travels though many tears it cause confusion in the universe meaning the quantum entanglement if my idea of what these are are wrong let me know plases — Preceding unsigned comment added by 99.12.149.156 (talk) 03:36, 11 April 2013 (UTC)


 * I can't see how you got all that from our article on Eight-dimensional space, so you must have been reading this somewhere else. Sorry to tell you, but it sounds like a bunch of science fiction nonsense. Someguy1221 (talk) 06:18, 11 April 2013 (UTC)
 * You should be asking the real expert: particle physicist Buckaroo Banzai. Clarityfiend (talk) 07:15, 11 April 2013 (UTC)


 * There is some confusion here. The word "dimension" has two meanings:
 * In the sense of "eight dimensional universe", the meaning is like "three dimensional universe" - we'd be talking about a universe where there are more directions you could move in than just the north-south, east-west and up-down that we are normally aware of.
 * In the sense of "travelling between dimensions" - we're talking about "parallel universes".
 * Generally, scientists only use the first of those two meanings. The two meanings of the word are not connected or related in any way.


 * When we are considering quantum entanglement and things like certain interpretations of the Schrondinger's Cat thought experiment - then we are talking about parallel universes...not extra spatial dimensions. "Tears" that allow you to move between parallel universes are in the realms of speculation and science fiction.  As far as I know, there is no evidence that they might exist from mainstream physics...quite the contrary in fact...there is reason to assume that they'd be fundamentally walled off from each other.


 * When we're talking about "extra dimensions" in ideas such as string theory - then we're talking about "directions you can move in".
 * You're basically stuck in this universe - and whether there are others (due to quantum effects, for example) is an undecided question.
 * SteveBaker (talk) 11:22, 11 April 2013 (UTC)
 * There is one more scientific usage of the term "dimensionality" - the usage in the sense of degrees of freedom in a generalized coordinate system. For example, if we are describing an n-body simulation, it is common to call this a n dimensional problem, (or even more accurately, a 6-n dimensional problem, for example, accounting for velocity and position of each object in conventional dimensions x, y, and z; by extension, you can add one dimension to each degree of freedom in the problem).  When we generalize a coordinate system, we can apply constraints based on physical law, and reduce the complexity of the problem to a lower dimension.
 * In this usage of the term, it is frequently helpful to understand the distinction between the rank and the size of a problem-space. A problem can be n-dimensional, but modeled with extra dimensions; this is called "degeneracy", and it can be helpful for practical purposes, even if it adds no new information.  Nimur (talk) 21:07, 11 April 2013 (UTC)


 * This is almost surely a reference to http://www.tenthdimension.com/ &mdash; whether that pseudo-spatial interpretation is worth anything is beyond the scope of this comment. --Tardis (talk) 03:12, 12 April 2013 (UTC)

cyanoacrylate bond inhibitors
I recently bonded some rubber like swim fin material to itself and a glass fiber and resin material using a high quality cyanoacrylate with the manufacturer's 'filler' powder for plastics and rubber. Initially the bond seemed to hold but failed after several 20-30 minute uses on a swim fin in a chlorinated swimming pool. I am thinking that the bond may have been effected by residual chlorine compounds left on the surface prior to bonding. Other uses of the bonding product yielded exceptional results on similar rubber like materials where chlorine was not involved. Are there known adverse effects to bonding where chlorine compounds are present? What other chemical conditions might adversely affect bonding? Suggestions?

A prompt reply would be appreciated.

Walt Silfies - 50.53.114.100 (talk) 07:11, 11 April 2013 (UTC)


 * I don't see anything out there about reactions with chlorine - just about the only thing that I see might be that cyanoacrylate doesn't stick well to glass - so perhaps the glass fiber material is the cause here. That sounds like a bit of a stretch to me - but it's all I could find. SteveBaker (talk) 15:43, 11 April 2013 (UTC)


 * can you examine to see what failed? i.e. did the glue come loose from the rubber, or from the fiber/resin, or did the glue stick to both but deteriorate itself? my experience with cyanoacrylates and rubber is that it works very well (I use it to patch pinprick holes in bike tire tubes) but that hasn't involved immersion. re chlorinated compounds, stuff like chloroform is a good solvent for many plastics but whether that exists in enough concentration in a pool and/or whether it would attack acryclics, I don't know. Gzuckier (talk) 16:49, 12 April 2013 (UTC)

Perception of pain, which part of the brain is the gatekeeper?
I've always wondered how people can exert so much control over their perception of pain. If the stimulus is the same, the same sensory neurons fire and in the end the same regions in the brain get stimulated to an equal degree, then how is it possible to change your perception of pain, between the same stimuli? When I am on an operating table, unconscious, does my " body " still feel pain, even though I don't " know " that it is there? Can the part of my brain that is conscious effectively act as a signal limiter? Who is the gatekeeper? Has any research been done on this? 137.224.239.102 (talk) 08:45, 11 April 2013 (UTC)


 * Basically, the thalamus, though it isn't a conscious process. See nociception for details. - Nunh-huh 09:40, 11 April 2013 (UTC)

Many aspects of pain are still very mysterious to us, and the answers to the questions really aren't known with any clarity. Part of the difficulty is that what we call pain is actually a mixture of several aspects -- Ronald Melzack identifies three that he calls "sensory-discriminative" (sense of the intensity, location, quality and duration of the pain), "affective-motivational" (unpleasantness and urge to escape the unpleasantness), and "cognitive-evaluative" (cognitions such as appraisal, cultural values, distraction and hypnotic suggestion). (Note: I've copied that from our pain article, which is worth reading.)  Each aspect is implemented by a different brain system, and differently affected by brain manipulations. We are only beginning to understand the systems and their interactions. One thing that is clear is that there is a lot of "top-down" circuitry that allows higher brain levels to modulate signals at lower levels, even down to the spinal cord. Looie496 (talk) 15:42, 11 April 2013 (UTC)

Thanks for the answers! :) 137.224.239.102 (talk) 17:42, 12 April 2013 (UTC)

Are there drugs that boosts willpower?
Are there drugs/medicines that boosts willpower? — Preceding unsigned comment added by 50.100.191.39 (talk) 18:41, 11 April 2013 (UTC)


 * Certain stimulants like Ritalin have this effect. Many students who study boring subjects like law take such drugs. Count Iblis (talk) 18:54, 11 April 2013 (UTC)
 * Law's only boring for most people. Some of us actually enjoy it. Shadowjams (talk) 15:01, 12 April 2013 (UTC)


 * Read:Dutch courage. Alcohol can depress some parts of the brain (as can some other drugs) that usually inhibit some forms of action. People that show the quality of having great will-power often have a low level of fear. Amphetamines were taken by the hand-full by American pilots during the second world war, because they did not only keep them alert but made them feel immortal and fearless, yet people may not survive very long with just that attribute. I think therefore, you may be asking about the type of will-power that brings successes. That requires  a blend of other attributes. In that respect,   I haven't come across any drugs that can have any long term benefit. Before anybody else steps in and pontificates, I'm not including Entheogens because these require the individual to also intellectualize (e. i., WORK)  on seeking out whatever understanding they can glean from their experimental voyages. Will-power proper, I think, is a product of  clear thought. Trying to think and carry out a plan of action  whilst one's brain is under the influence  of supposed artificial enhancements -will not achieve this. --Aspro (talk) 20:33, 11 April 2013 (UTC)


 * The question is ill-formed. There are various reasons besides akrasia that people lack the will power to do things--fear; lethargy; craving; compulsion.  There are all sorts of drugs to treat anxiety, hunger, tiredness, OCD.  So the broad answer is yes, drugs from caffeine and alcohol, to cigarettes and amphetamines, to xanax and zoloft all effect the mind. μηδείς (talk) 21:51, 11 April 2013 (UTC)
 * Given that a question is a request to be informed, I think that goes without saying. 202.155.85.18 (talk) 02:02, 12 April 2013 (UTC)
 * It's a good question, Medeis is being too glib about it. Although we usually think of willpower as a good thing... however it's probably better characterized as drive. In most mammal's evolution pleasure (or avoiding pain) and drive were yolked together, but in some instances, and especially when you start having fun with various plants, those two are distinct. There is a lot of really nuanced research on the subject... and then there's breathless articles comparing a book/movie to real life that center around modafinil. But also testosterone, amphetamines, and all sorts of other psycho active drugs affect motivation. It's quite complicated. Shadowjams (talk) 14:59, 12 April 2013 (UTC)
 * The basic problem here is that the concept of willpower is essentially dualistic. In terms of the "ghost in the machine" metaphor, willpower is the degree to which the ghost exercises control over the machine.  But whenever one tries to understand dualistic concepts in biological terms, one runs into unsolvable boggles. Looie496 (talk) 15:37, 12 April 2013 (UTC)
 * Exactly, the question is based on the false assumption that there's some one thing called willpower and that a certain drug can turn its knob up higher. There are all sorts of reasons why one might fail to achieve a goal one has in mind. μηδείς (talk) 17:21, 12 April 2013 (UTC)

Launching yourself from lying on the ground to upright position using only your arms muscles
Are there people who can do this? I've seen people do so-called Muay Thai push-ups, so it seems to me that it is possible. It would require more strength than you need to do the Muay Thai push-ups, but then there are people who can do hundreds of these in a row. However, I've never seen or heard about people who can launch themselves up from lying to standing position using a push-up move. Count Iblis (talk) 19:17, 11 April 2013 (UTC)


 * Lying on your back or chest? I can do "kip-ups" which is lying on back to standing upright.  But this involves alot of leg motion.165.212.189.187 (talk) 20:17, 11 April 2013 (UTC)
 * I found this, but I suspect some trickery. Alansplodge (talk) 21:59, 11 April 2013 (UTC)
 * I agree it looks suspicious. For example, just before the young man gives a big push to get up to the vertical, the bottom of his T-shirt rides upwards a couple of inches for no apparent reason. Now if the whole thing were actually performed in reverse and then played backwards, I can imagine the bottom of the T-shirt riding upwards as he fell forwards and downwards, and then extending to its proper position after he came to rest. Dolphin  ( t ) 08:16, 12 April 2013 (UTC)
 * It's beyond "suspicious"...it's an obvious fake, and a very poor one at that. YouTube demonstrations of any kind have to be viewed with deep suspicion - there are *FAR* more fakes than there are real demonstrations.  SteveBaker (talk) 16:36, 12 April 2013 (UTC)
 * Agreed - I was just being charitable. Alansplodge (talk) 18:09, 12 April 2013 (UTC)


 * I bet you could do it on the moon, although you may have to take off the space suit. Gzuckier (talk) 16:51, 12 April 2013 (UTC)
 * Oh no you don't - Charlie Duke shows how it's done. Alansplodge (talk) 18:16, 12 April 2013 (UTC)

Ha, so except that fake video, no real evidence! Perhaps the Refdesk volunteers should try this and upload videos of their attempts! Count Iblis (talk) 12:31, 13 April 2013 (UTC)


 * I don't suppose using a trampoline is allowed? :) Wnt (talk) 22:15, 13 April 2013 (UTC)


 * It would be an interesting experiment to get some really fit volunteers and a variable slope that can pivot from 0 degrees (flat on the ground) up to 90 degrees (like a wall). By finding the minimum angle from the ground we could make a good guess whether it is impossible; If nobody volunteer could push themselves upright at a slope of less than 45 degrees I would think that doing it from zero degrees would not be humanly possible.
 * You would need fit volunteers of various builds (heavy muscled to light athletic) and heights. My guess would be that the shortest people with a light athletic build would do best. -- Q Chris (talk) 13:57, 15 April 2013 (UTC)
 * You would need fit volunteers of various builds (heavy muscled to light athletic) and heights. My guess would be that the shortest people with a light athletic build would do best. -- Q Chris (talk) 13:57, 15 April 2013 (UTC)