Wikipedia:Reference desk/Archives/Science/2016 September 18

= September 18 =

What kind of object has the most noticeable audibility lengthening at breathable altitudes?
What kind of object needs the fewest meters above sea level to get 1 decibel quieter? Sagittarian Milky Way (talk) 17:32, 18 September 2016 (UTC)
 * An object with a sensitive electronic altitude-controlled switch? It would help if you constrain the question.  —Quondum 17:36, 18 September 2016 (UTC)
 * Like the mention of string instrument damping time above. No switches connected to altitude sensors. Sagittarian Milky Way (talk) 19:04, 18 September 2016 (UTC)
 * Even so, it is a bit like asking "What is the longest piece of string?" If one wished to engineer an intrument-like device for which the damping or coupling to air was highly altitude-dependent, I expect that it would not be difficult.  For example, a resonance that depends on a close match between the mass of air in a chamber and that of a mechanical resonator might be strongly pressure-sensitive.  —Quondum 19:49, 18 September 2016 (UTC)
 * What about restricting to symphony orchestra instruments or not too obscure musicish objects? i.e. tuning forks, gongs, triangles, drums, vuvuzelas, Tibetan horns... What are good candidates for testing if you can notice a difference by ear or quartz stopwatch? Sagittarian Milky Way (talk) 22:53, 18 September 2016 (UTC)


 * One in which the damping of the structure is primarily by the atmosphere, such as a bell.Greglocock (talk) 23:00, 18 September 2016 (UTC)
 * Hang on – that results in atmospheric pressure changing damping rate (the question in the section heading). But not necessarily any relative difference in quietening (the question at the start of the section). They are different questions.  —Quondum 01:52, 19 September 2016 (UTC)
 * Ah, that explains it. i typed a long response on the amplitude thing, and then saw the damping bit and rubbed the othe rbit out. Anything that uses a sounding board will respond roughly at the rate, wehre sound presure level is proportional to density. Greglocock (talk) 06:12, 19 September 2016 (UTC)

Accessing parallel universes
Has anyone speculated how one could observe or enter into a parallel universe according to the many world's theory? — Preceding unsigned comment added by Uncle dan is home (talk • contribs) 21:55, 18 September 2016 (UTC)


 * By definition our universe includes everything that we can observe. If we can observe other universes, then those aren't really other universes. - Lindert (talk) 21:58, 18 September 2016 (UTC)


 * Except that the def of a universe is subject to change. At one time galaxies were called universes, and other galaxies are (theoretically) accessible.  If we did find a way to access other universes, perhaps we would rename them something else, like an "instaverse" (one instance of the many-worlds theory).  StuRat (talk) 22:13, 18 September 2016 (UTC)


 * One option is to just get "lucky", as I'm not aware of any theoretical reason why two universes, occupying the same space-time, and right next to each other, like a binary star system, can't expand into each other. I'd hate to lay odds on it, though.   StuRat (talk) 22:17, 18 September 2016 (UTC)


 * I think it the intent here is to ask how one can potentially find a way to bridge between decohered parts of the universal wavefunction of the many worlds interpretation, rather than "parallel universes", as these are often described. As far as I know, the superposition is considered to be perfectly linear, which would imply that no interaction is possible.  —Quondum 22:21, 18 September 2016 (UTC)

Yes Quondom, that's my intent. But also, what about mere observation if actual interaction isn't possible.Uncle dan is home (talk) 22:41, 18 September 2016 (UTC)


 * Observation is inherently interaction. Any information transfer is.  So, not even "mere observation" of any kind, under this interpretation.  —Quondum 23:03, 18 September 2016 (UTC)


 * You can access other sectors of the multiverse by loading false information in your memory if this is information that a copy of you is experiencing in some other sector. Suppose that you exercise this option to escape difficult situations, e.g. if you are stuck in the desert without food and water with no hope of rescue. You can then fetch your memory modifier and load false information into your brain that corresponds to you not having embarked on the desert trip a week earlier, you then have vivid hallucination of being at home. Now consider the entire multiverse and consider the set of all the people who have that exact same experience. These persons experience being who they are and being in the place they (think they) are. Whether this is a hallucination or not cannot distinguish the identity of these persons, as they have exactly the same consciousness by construction.


 * This then means that whether the hallucination ends and you find yourself back into the precarious situation in the desert or whether you stay at home is purely a probabilistic matter. The probability of finding yourself back in the desert is precisely the probability of you getting into trouble in the desert in the first place. So, probability-wise nothing changes. But what changes is the fact that with this device you are very likely going to escape this fate if you find yourself in this situation, while you pay the price for this escape by burdening random copies of you who would otherwise have lived on happily elsewhere, with a small probability of getting in trouble. Count Iblis (talk) 00:41, 19 September 2016 (UTC)

In a way this picks up a thread left off at this discussion. It was my assumption that as the laws of QM are time-reversible, if every present moment has multiple futures, it also has multiple pasts, which is to say, we are colliding with parallel universes all the time simply because everything happens to become the same in both universes. The past is not merely uncertain, but actually could have unfolded in a variety of different ways. I saw some resistance to this point of view, though, and I'll try to keep my mind open. I know entropy creates a strong gradient in the cosmos, so that two universes are much more likely to become different than become the same. Whether two copies of a single human brain, or of some small portion within it, are much more likely to become different than the same ... that is not as readily apparent to me. There's some strange side-issue as I think of that ... if two brains from two cosmoi become the same by chance at the quantum level, are they in fact the same place ... do the contents of a region of space define where it is, or the space itself? Can this be simplified down to each nucleon, each electron, so that there is some way to look at space where the position is the content and the content is the position? There's a huge amount of physics and philosophy that I don't begin to understand. There's a certain parallel universe I've dreamed of quite a bit where they use ridiculous amounts of wrought iron in places like highway underpasses and as a protective shelter for ATM terminals, where most windows are made of plexiglas and the gaskets around cardoors are made out of some dirty teflon like substance that is prone to stick or leak, and where - the tech I'd kill for - there's some kind of pulsed-electrostatic impeller technology used instead of fans for buildings or propellers on planes/drones; the nihangs use them in their mecha-chakrams and the football fans use them to throw bar darts from neighborhood pubs that, in sufficient numbers, might evade defenses and hit disfavored players. Sometimes I wonder though whether in dreams little parts of us and parts of parallel universes become in a way one; whether we can dream of alternate realities that are real or infer what is happening in them by small coincidental signs in our own. Almost certainly not, but it's fun, and doubtless somehow there's a way to write a great story out of it. Wnt (talk) 02:46, 19 September 2016 (UTC)
 * Dreams, stories and fantasies; yes, but as a response to "leakage" from a decohered wavefunction ... no ;-) I concur that time symmetry means everything happens in both directions, including merging/diverging of wavefunctions.  It is presumably the past and future boundary conditions that govern asymmetry.  Yes, we have divergent decohered pasts, just as we have divergent decohered futures.  I'd say that your decaying spin states of the other thread can be reconciled with time symmetry, but that's another whole ball of wax.  —Quondum 03:56, 19 September 2016 (UTC)


 * Our article Timelike homotopy seems to say closed timelike curves can be used to make several points on a Lorentzian manifold accessible. Under the Everett-Wheeler many-worlds interpretation of quantum mechanics, isn't it at least plausible (in the "good enough for science fiction" sense) that these alternate timelines would be accessible in that manner?  I'll be honest and say I don't have the math to answer that myself. loupgarous (talk) 17:33, 20 September 2016 (UTC)

Local anaesthetic use in dentistry
Why is it that in dentistry, sometimes when doing fillings, a palatal anaesthetic injection is given in addition to one on the cheek side, whilst at others times, only a cheek side one is given? Clover345 (talk) 23:50, 18 September 2016 (UTC)
 * The purpose of the anaesthesia is to numb the nerves leading to the tooth, rather than the injection site itself. As the number of nerves leading to each tooth varies, this could require varying injections according to which tooth is involved.
 * This extra injection is rare though, and unlikely for fillings - more likely for an extraction. Andy Dingley (talk) 07:14, 19 September 2016 (UTC)
 * According to Dental anesthesia, Inferior alveolar nerve anaesthesia is the most common form of dental anesthesia, which appears to be the cheek side injection. Superior alveolar nerve anesthesia is mentioned as a less common procedure.  The articles of two of the superior alveolar nerves, the Anterior superior alveolar nerve and Posterior superior alveolar nerve, both mention that they are targets for dental anesthesia, though I can't determine the injection sites from these articles.--Wikimedes (talk) 20:13, 19 September 2016 (UTC)