Wikipedia:Reference desk/Archives/Science/2012 December 18

= December 18 =

Lithium-ion cell phone battery
I have an old cell phone that works just fine, except that the 6 year old battery doesn't hold much of a charge (I have to recharge it every night). I ordered a "new" cell phone battery, and they sent me one which is 7 years old. I am displeased. However, is it possible, that if this battery has been on a shelf all this time, it will hold a charge better than the newer battery I'm using now, which has been in continuous service for 6 years ? I'm wondering if I should test it out first, or send it back right away. StuRat (talk) 22:28, 14 December 2012 (UTC)

(Reposted from computer Desk.) StuRat (talk) 00:11, 18 December 2012 (UTC)


 * Found this thread which specifically says Avoid purchasing spare lithium-ion batteries for later use. Observe manufacturing dates. Do not buy old stock, even if sold at clearance prices. So I think I'd be trying to return it, say you weren't informed it was old stock. Vespine (talk) 02:31, 18 December 2012 (UTC)


 * Some technicians can "rebuild" an old battery by cracking it open and putting in freshly-manufactured lithium-ion cells of the appropriate size. Then the battery should work like new. If you insist on using such an old phone, perhaps getting your old battery rebuilt would be best. Note: If the phone's paint is very scratched, you may want to get the phone's plastic housing replaced. You may also want to keep the phone in a carrying case. Unforgettableid (talk) 07:38, 18 December 2012 (UTC)


 * And here is another idea. Stop being so cheap and buy a new phone. Dauto (talk) 14:58, 20 December 2012 (UTC)


 * That quite unhelpful, but, since you bring it up, I will explain why I kept such an old phone. It's for my Mom, who doesn't want any fancy features like cameras, texting, voice recognition, touch screens, etc.  If you buy a current model without any of those features, you get a piece of junk, which doesn't have individual buttons, and is thus hard for an elderly woman to use.  (Well, the Jitterbug, which she had before, was OK, but rather expensive for someone on a limited budget who only wants a cell phone for emergencies.)  So, I reactivated my old Motorola V170, which was a quality phone, at the time, with separate buttons, but no unwanted features, and costs under $7 a month on TracFone, and intend to give it to her for Christmas. StuRat (talk) 04:35, 22 December 2012 (UTC)

Time travel paradox name?
What is the name for the paradox below? A catastrophe occurs. A scientist spends 20 years making a time machine to erase this catastrophe from history. He succeeds, goes back in time, and prevents the catastrophe. But now, the event prompting him to build the time machine never occured, so he never built the machine. Because he never built the machine, the catastrophe occurs, prompting him to build the time machine...and so on forever. NealCruco (talk) 03:25, 18 December 2012 (UTC)
 * Grandfather paradox.      Dncsky (talk) 03:29, 18 December 2012 (UTC)
 * That, or just nonsense. There's no evidence people "go back" in time and the idea itself is incoherent. μηδείς (talk) 03:42, 18 December 2012 (UTC)
 * Was that response supposed to be in any way helpful to the OP?Dncsky (talk) 03:55, 18 December 2012 (UTC)
 * Yes, strings of words placed together without any connection to reality or evidence are nonsense, also known as flatus vocis, and so forth. If there were evidence that something like backwards or discontinuous causation had occurred, addressing it might be helpful.  But pretending that nonsense is real or worth entertaining is at best enabling, which is, itself, evil.  The science ref desk no more deals with science fantasy than it deals with theology. μηδείς (talk) 04:49, 18 December 2012 (UTC)
 * Would you prefer that questions about theoretical physics be asked at the humanities desk, and consider all references to such to be works of fiction? Someguy1221 (talk) 04:56, 18 December 2012 (UTC)
 * Not as science fiction, but as faith in the supernatural, along the line with, "Do people stay married in heaven?", or, "Can God create a rock so heavy ha can't lift it?" μηδείς (talk) 17:39, 18 December 2012 (UTC)
 * See chronology protection conjecture, Novikov self-consistency principle, and closed timelike curve. The fact that the best theoretical physicists have thought about time travel, and discovered General Relativistic solutions for time travel with simple mass-energy distributions (although most believe these are artifacts), means that time travel is not as nonsensical as you believe it to be.  --140.180.249.194 (talk) 07:54, 18 December 2012 (UTC)
 * There's a proof in formal logic that any single contradiction implies every single contradiction, the same essentially as using the little assumption that 2+2=5 to prove 2=3 from 2=5-2 and to prove 16=25 from squaring both sides of (2+2)^2=5^2. These Kartz-Reimer conjectures always sneak in an infinity somewhere, and end up exploding in a basement on the south of Spain.  Every time you read one of these supposed means of travel, the essay ends with, "But there's a catch; achieving this would require more energy than exists in the entire universe."  And your all the way back to talking about the rock he created so heavy that even God can't lift it. μηδείς (talk) 17:39, 18 December 2012 (UTC)
 * I have read one theory that even if time travel were possible we would never invent it, because whenever we did people would go back and change the past accidentally or otherwise. This would continue until a "stable history" in which time travel was not invented was hit. -- Q Chris (talk) 09:10, 18 December 2012 (UTC)
 * While this sort of paradox isn't possible now, that doesn't mean the original question is only meritless nonsense. The fact that we can link to a wikipedia article about it means that somewhere, someone thought such an idea had enough momentum to justify writing about it. While original author might have done better to place his question in the entertainment reference desk, without knowing his intentions I can easily see the original author wishing to investigate the scientific validity of such a paradox. Merely criticizing and admonishing him does little for anyone. Glosser.ca (talk) 21:19, 18 December 2012 (UTC)
 * The obvious answer is if time travel into the past were possible, why hasn't anyone shown up yet? -- Jayron  32  22:56, 18 December 2012 (UTC)
 * They did show up, but they showed up in the same location in a parallel universe that they created. Futurist110 (talk) 20:46, 21 December 2012 (UTC)

Ok. OP here. I merely wanted to see what this paradox was called. I knew that time travel is not yet scientifically possible. However, I remembered reading about this paradox on Wikipedia. I couldn't remember its name, so I asked here. NealCruco (talk) 23:23, 18 December 2012 (UTC)
 * There is no problem with your question, my first answer was snippy, and the paradox is a concept and does have a name, which has been given. No different from a lot of theological concepts one could throw out which are nonsense, but the object of great study. μηδείς (talk) 03:26, 19 December 2012 (UTC)
 * I used to be a time traveler myself, but that was when I was older. :P - ¡Ouch! (hurt me / more pain) 07:27, 19 December 2012 (UTC)

As far as I can see, no one here has linked to the article Time travel, which says


 * it is currently unknown whether the laws of physics would allow time travel into the past. Such backward time travel would have the potential to introduce paradoxes related to causality, and a variety of hypotheses have been proposed to resolve them, as discussed in the sections Paradoxes and Rules of time travel below.

The article has sections called "Theory", "In physics", "Time travel to the future in physics", and "Other ideas from mainstream physics". This was not a question for the entertainment desk.

As for Jayron's well-known point that if time travel into the past were possible, why hasn't anyone shown up yet?, there are at least two potential answers that I've heard put forth as possibilities (not that I'm endorsing them!): (1) Maybe the equilibrium is such that everything happens in such a way that no paradoxes occur, and people have shown up from the future but the no-paradox equilibrium prevents that from being apparent to us (a variant of Q Chris's point above). To best understand this one should refrain from trying to ask "what happens next?" and then "what happens 'after' that?", etc., and instead step back from the 4-dimensional space-time diagram and view it as a fixed diagram. (2) Maybe time travel to the past is possible only to the extent that you can travel back as far as the time when the time-travel device was first created, and maybe none has been created yet.
 * It is also possible that every time someone attempts to time travel backwards a new parallel universe is created. Also, even if time travel was consistent (no parallel universes), wouldn't it create an ideas paradox? For instance, you from the future tells you how to build a new invention, and then you tell the same thing to your past self once you go into the future a specific amount. However, where would the info about the design of this invention originally come from? It would be a never-ending loop. Futurist110 (talk) 20:42, 21 December 2012 (UTC)

It's been pointed out here that there's no evidence that travel to the past can occur; but sometimes theory precedes empirical observation: e.g., there was no evidence that the Higgs boson exists, until we found evidence for it. Duoduoduo (talk) 15:22, 19 December 2012 (UTC)
 * It's also currently unknown whether the laws of physics allow the Flying Spaghetti Monster to inhabit a base on the dark side of the moon, or one of the five suspected planets of Tau Ceti. Wikipedia shouldn't be filled with such crap.  But it is. μηδείς (talk) 03:32, 20 December 2012 (UTC)
 * How dare you insult His name in vain like that! The FSM will make you burn in hot chili sauce in the afterlife unless you repent your blasphemy immediately and avoid saying offensive things to Him ever again. ;) Futurist110 (talk) 20:43, 21 December 2012 (UTC)
 * It should also not be filled with personal opinions, especially on the Reference Desk. &mdash;  The Hand That Feeds You :Bite 07:51, 20 December 2012 (UTC)

Are there any transparent Non-Newtonian fluids?
I just wondered how a bubble floating up inside it would look like.--Inspector (talk) 04:57, 18 December 2012 (UTC)
 * The Non-Newtonian fluid article mentions shampoo as an example. One of the articles on a specific category/subgroup of these fluids mentions heather honey. DMacks (talk) 06:20, 18 December 2012 (UTC)


 * Our articles thixotropy and shear thinning are bit redundant, and each could use some work. I believe that most, if not all honey is thixotropic at room temperature. If you've ever played with one of these honey spoons, it's fairly obvious that the viscosity changes at different flow rates and stream diameters. Thixotropy is why the last little threads dripping off behave so differently than the first big glob. So-- in short: make some bubbles in any honey (at say, 1 atm, 70 F) to see how they propagate :) SemanticMantis (talk) 16:51, 18 December 2012 (UTC)


 * Some pictures of such bubbles here. Mikenorton (talk) 19:16, 18 December 2012 (UTC)


 * There is a new clear silly putty that I think is exactly what your looking for.165.212.189.187 (talk) 18:12, 19 December 2012 (UTC)

I want to learn how bad the optics of a -13.50 polycarbonate lens are. How can I?
In a 2011 study, four researchers (Citek K, Torgersen DL, Endres JD, and Rosenberg RR) ordered lots of prescription glasses online. They ranged in price from US$8 to US$400. Among their online purchases, "in 22.7% of spectacles, at least 1 lens" failed the standard impact-resistance test used throughout America. And spending more didn't get you better impact resistance. In comparison, "internal test results of over 53,000 [traditionally-dispensed] lenses by Walman Optical Company [...] find that <0.5% failed impact testing." Karl Citek, the lead investigator, "does not recommend buying eyeglasses online". My glasses are old and somewhat scratched; I'd like to buy new ones. I bike a lot; I don't want glasses with subpar impact-resistance. But I still want to buy online, to save money. How can I avoid putting my eyes at risk? Unforgettableid (talk) 07:31, 18 December 2012 (UTC)


 * When buying prescription glasses online, for guaranteed shatter resistance, order polycarbonate lenses. The researchers found that "all of the 28 lenses known to be polycarbonate passed impact testing, with [center thickness] as low as 1.26 mm." But note that if you order polycarbonate, it's crucial to order a scratch-resistant coating. Also note that "most opticians recommend avoiding polycarbonate in a prescription that is higher than a +3.00 or lower than a &#8209;3.00." If you use it in a stronger lens, the optics won't be so clear. Unforgettableid (talk) 07:31, 18 December 2012 (UTC)


 * I'm extremely nearsighted: I need lenses with a power of about &#8209;13.50 diopters. I do know that &#8209;13.50 polycarbonate lenses might be significantly thicker than higher-index lenses. Unforgettableid (talk) 08:05, 18 December 2012 (UTC)


 * Is there any way I can find out, before ordering, approximately how bad such lenses' optics would be? Unforgettableid (talk) 08:05, 18 December 2012 (UTC)


 * I live in a major metropolis in Canada. Is there any reasonable way for a Canadian or an American to buy &#8209;13.50 eyeglasses, without spending hundreds of dollars, and without exposing oneself to undue risk from possible subpar impact-resistance? Unforgettableid (talk) 08:24, 18 December 2012 (UTC)


 * It is most unwise for a high-minus person to buy over the internet, as the supplier won't be able to invite you to try things in a temporary frame, and won't be able to examine/test your old glasses to see what suits you. But if you must, then this becomes an issue of understanding what the differences are between lenses of the same nominal prescription, and specifying everything.


 * It happens to be that I am nearsighted and have required progressively-stronger lenses over the years: &#8209;6 dioptre as a teenager, &#8209;8 dioptre at age 50, and back to &#8209;5 now, at age 70.  In my experience things start to get really critical once you get over about &#8209;6 to &#8209;7, so I sympathise with you.


 * The main problem with high-minus prescriptions is chromatic aberration: with a bad lens material, you will see thin black lines on a white background separate into red and green lines.  For most scenery, things will just look blurry.  Lenses, whether glass, polycarbonate or other plastic, are available in a range of refractive indexes (not to be confused with the lens power, i.e. dioptre).  People tend to go for high-refractive-index lens materials:  this results (for nearsighted folk) in thin edges, which makes the spectacles look attractive cosmetically.  But, as a rule, a material with a low refractive index will give lower (better) chromatic aberration.  If you don't ask, you'll get the common stuff, which nowadays is not necessarily what you want.  Chromatic aberration is measured by the Abbe number.  Find out the Abbe number for the lenses you are considering.  Choose the lens with the best Abbe number for lenses of equal refractive index and identical prescription.  This will give you the sharpest vision.  Some suppliers over the years have tried to tell me that over a few weeks the brain gets used to chromatic aberration and compensates, but I've never believed it.


 * Another factor is more critical for high-minus people. At one time, spectacle lenses where made with a high front curvature.  The modern trend is to use flatter front curvature as it looks nicer.  However, if you have been wearing spectacles for decades, the modern low curvature lenses take some getting used to.


 * Be sure that your spectacles are made to the correct pupillary distance (PD; also known as interpupillary distance or IPD). For most people, PD is pretty non-critical, and some lens fitters just use 68 mm for everybody.  That's slack and unprofessional, but they do it anyway.  For high-minus people, PD is especially critical.  Your prescription should say something like:  "PD:  67/71".  That means your left eye centreline is 67/2 mm from the centre of your nose, and your right eye centreline 71/2 mm.  For low-minus people, taking facial asymmetry into account is less important.  A single number (e.g. 68, meaning 68 mm between the centrelines of the two eyes) is often quoted.  But for high-minus people it must be got right.


 * Wickwack 120.145.20.29 (talk) 11:09, 18 December 2012 (UTC)


 * To Wikipedian UnforgetableID: Please don't edit the posts of others on Reference Desk, especially without leaving a signature.  I know you meant well, and your changing of links to Wikipedia form is an improvement, but if you have changed the meaning in any place, folk would blame me and might want to post corrections.  Wickwack 124.182.169.44 (talk) 01:56, 19 December 2012 (UTC)


 * Like I said in my edit summary, I believe all my changes were copyediting, and none changed your meaning. But you make fair points: no matter how careful an editor is, they risk accidentally making significant changes to the poster's meaning. As for you: Why not log in? :) I am grateful for your kind reply to my glasses question. But I didn't bother going to your user page to thank you: you weren't logged in, and it's often fruitless trying to write on the talk page of a logged-out user. Cheers, Unforgettableid (talk) 07:09, 19 December 2012 (UTC)
 * I don't log in because certain admin folk decided to block me. Judging by the chat in the admin talk page, they think I am someone else that they took a dislike to.  By using variable IP I have largely stopped their nonsense.  I made some suggestions some time ago in good faith for changes that will make managing trolls and other undesirables easier and better targeted but that seemed to inflame them.  Wickwack 120.145.70.101 (talk) 11:16, 19 December 2012 (UTC)

How long would the sun last if a small black hole was placed inside it?
And what about the Earth? Furthermore, do black holes experience friction differently than regular objects? If you dropped a sand-sized one in the Earth, how long would it take before it settled at the core (or would that even happen)? Goodbye Galaxy (talk) 19:04, 18 December 2012 (UTC)
 * It depends greatly on what you mean by "small", as the rate at which a (very small) black hole interacts with surrounding matter will, more or less, increase exponentially with respect to the black hole's mass. This site at Cornell suggests that a black hole with an event horizon of roughly atomic radius, or about a billion tons mass, would never consume the Earth, or at least not on any meaningful time scale (and it further notes that it doesn't consider Hawking radiation working to evaporate the hole first).  This paper suggests that black holes of less than a trillion tons might in fact create stable pockets of matter outside their event horizons, preventing any real growth.  But there remains a black hole of a given mass that would consume Earth in a day, or another in a century, or whatever other data point you elect to choose.  As for friction -- friction is ultimately an electromagnetic effect, and as black holes can have an electric charge, they should experience friction.  However, I strongly suspect that that sort of atomic-level interaction won't bear much resemblance to macroscopic everyday friction as we conventionally think about it. &mdash; Lomn 19:25, 18 December 2012 (UTC)


 * (ec) I think this would be extremely difficult to work out, because material near the event horizon would become extremely hot, and would make it hard for other material to reach the event horizon. It isn't even clear to me that the black hole would remain inside the Sun or Earth, or whether it would be perturbed by other planets such as Jupiter into a distinct orbit. Looie496 (talk) 19:27, 18 December 2012 (UTC)
 * Keep in mind that a Black Hole of about lunar mass would be about the size of a grain of sand. That'll be an awful lot of gravity near the event horizon. I doubt microscopic effects would play a deciding role with anything that heavy.
 * If I got that right, the shell theorem applies to Black Holes as well, if you're not too close to the event horizon. While the Moon has only .18g at surface level (~1700km from the center), a Black Hole of equal mass would have the same at that radius. The gravitational pull would increase when you got closer - 1.8 * 1011g at a radius of 1.7m or very roughly 5.2 * 1017g at a radius of 1mm. The latter is probably correct to the leading digit only, because 1mm isn't much more than the Schwartzschild radius itself. - ¡Ouch! (hurt me / more pain) 07:27, 19 December 2012 (UTC)
 * Wasn't it said that a small black hole would bounce back and forth from crust to crust (the Earth feeling as vaporous as air to it) eventually coming to rest at the core and eating it away till there's nothing left? I wonder what the first effect that would cause problems would be. Loss of planetary magnetic protection? Sagittarian Milky Way (talk) 03:10, 20 December 2012 (UTC)
 * Yes, paralleling Sag., wouldn't the black hole's orbital speed about the sun's center matter? μηδείς (talk) 23:37, 20 December 2012 (UTC)
 * This was if a particle accelerator could make one, not a natural hole from space. Sagittarian Milky Way (talk) 20:47, 22 December 2012 (UTC)