Wikipedia:Reference desk/Archives/Science/2020 July 20

= July 20 =

Fermi paradox
So, there are 40 billion (4*10^10) habitable planets in the Milky Way, and we wonder why none of them seems to have developed a civilization with noticeable presence in the galaxy. But what's so special about that, why is this even a paradox? This may seem like a large number, but think about probabilities. Consider something is protected with a password that's 8 characters long and consists only of lowercase letters of the English alphabet, with no numbers or special symbols. That's 26^8 = 208,827,064,576 (>2*10^11) permutations, a number 5 times larger. So, if it would take that many attempts to just crack a password that most programs won't even accept because it's too weak, what about having life not only arise on a planet out of nothing but also evolve into a civilization that traverses the galaxy? --Qnowledge (talk) 02:51, 20 July 2020 (UTC)
 * It is a paradox for those that think extraterrestrial intelligence should be common. But you are using the basis to support the idea that life and intelligence is unlikely. You can see the article for many explanations. Graeme Bartlett (talk) 04:37, 20 July 2020 (UTC)
 * Fermi paradox is especially frightening. Maybe our radio signals are just reaching the Berserkers and they are on the way... --Guy Macon (talk) 05:51, 20 July 2020 (UTC)
 * The Fermi paradox is only a paradox in the sense that it is in conflict with the answer you get from the Drake equation, which is itself a Fermi approximation of the number galactic civilizations there are. In other words, the Drake equation is an attempt to define the parameters for how you would determine how many civilizations there are, and the Fermi paradox is only a paradox if you solve the Drake equation and get a number significantly different than "1".  Drake's equation doesn't, of course, solve itself.  You have to provide input numbers for all of the various variables and get an output number for it.  Many of the inputs are known, but others are quite conjectural, such as " the fraction of planets with life that actually go on to develop intelligent life ", which makes an interesting way to frame the question of how many civilizations are in the galaxy, but not actually useful on calculating a reliable number.  -- Jayron 32 14:07, 21 July 2020 (UTC)
 * I find paradoxical how easily people forget the difference between "civilization" and "civilization with noticeable presence in the galaxy". Maybe 1) inter-stellar voyages are simply not possible and 2) all several thousand inhabited planets do lie so far from us that we cannot detect their radio signals. Our Galaxy takes at least 8 trillions cubic light years, so one hundred thousand civilizations will occupy eighty millions cubic light years each on average, that is the next one would sit some 4300 light years away from us on average. 2003:F5:6F0C:9500:ADC4:5DDA:DFDD:360E (talk) 19:51, 21 July 2020 (UTC) Marco PB
 * The Fermi Paradox also seems to make a lot of assumptions about the nature of interstellar exploration and colonisation. From the article:
 * given intelligent life's ability to overcome scarcity, and its tendency to colonize new habitats, it seems possible that at least some civilizations would be technologically advanced, seek out new resources in space, and colonize their own star system and, subsequently, surrounding star systems. ... If interstellar travel is possible, even the "slow" kind nearly within the reach of Earth technology, then it would only take from 5 million to 50 million years to colonize the galaxy.
 * This seems to presuppose some sort of "Star Wars" or "Star Trek" type scenario, where once someone has the ability to travel to and colonise another plant or star, it is then trivial to travel from there to yet another, and inevitable that someone would do so (and then do it again, and again, until the whole galaxy is colonised). But without easy and cheap FTL travel (which all known science says is not possible), that doesn't seem to me to be a likely occurrence.  Establishing a colony in another star system would be phenomenology expensive (and risky), with little benefit to the homeworld.  It would then likely take an extremely long time for that colony to develop the the stage where it would be to establish colonies of its own, and not a given that it would do so if it could.  It therefore doesn't seem to me to be obvious that an intelligent civilisation "should" take over the galaxy, and therefore not a paradox that there is no evidence of one doing so. Iapetus (talk) 09:39, 22 July 2020 (UTC)
 * Those civilizations can be machine civilizations. Once self-replicating machines are developed, they should be able to spread from solar system to solar system. When they land on a planet, they'll build an entire copy of the civilization on their home planet. It's completely analogous to how life has colonized the Earth. Organic chemistry allows for the existence of self-replicating machines made out of molecules, such machines ended up appearing 4 billion ears ago and colonized the Earth. The machine civilization that ends up spreading through the galaxy does not necessarily have to do so for a rational reason. It may have degenerated into a dumb civilization. After it arose from the biological civilization it could have turned into a simple self-replicating infrastructure that is able to launch itself into space and seek out new planets to make more copies of itself without there being much of an intelligence or consciousness about this. Count Iblis (talk) 23:27, 22 July 2020 (UTC)
 * This is no argument: even machines will be constrained by the fact that if an interstellar voyage has to take two or three or five or ten thousand years no number of spare parts can help in keeping ship and crew working and flying. After eighty or hundred years all gears and articulations are worn out, joints and seals gum up, harden and clog and the chips in controllers burn out. You can at last plug a new card in if you have some left, but you cannot fill a space ship with enough spare parts if you want some place to be left for fuel. And beside that, in order to 'go forth and multiply, and populate the galaxy and subdue it' of course they don't need intelligence or consciousness, we are there to prove it, but they need a motivation, that is an instinct to do so, and where should they get one such in the first place? And third, a civilisation of machines would be dependent upon huge supplies of metals and energy even more than we are, and we have not enough of them in order to colonize the moon, let alone Alpha Centauri.
 * But why am I talking at all: we know that no machine civilization has colonized the galaxy, did they? 2003:F5:6F0C:9500:A088:A42E:9624:3880 (talk) 18:28, 23 July 2020 (UTC) Marco Pb
 * If these were fundamental problems, the universe would be lifeless, we couldn't exist to ponder these questions because machine that would constantly repair itself and capable of reproduction would be impossible. The only problem that prevents organisms from spreading to other solar systems is that the space environment is inhospitable to living organism that have evolved on Earth. But there are technological solutions to that problem that we have developed, but we don't have the technological capability to build self replicating machines. Our inability to build the machine equivalent of living organism has nothing to do with any fundamental limits, because we can't as of yet reproduce biology in the lab. So, it's plausible that a technological form of life that can survive for long enough in space to make it to another solar system, can exist. Count Iblis (talk) 21:26, 23 July 2020 (UTC)
 * You repeat the same mistakes: 1) to believe that for some fundamental reason machines are better suited than humans to survive interstellar space during centuries and millenia, while they have the same problems of tear and obsolescence as we have, and 2) that if such machines did exist, they could develop some motivation or drang to multiply and colonize distant solar systems. That no machine civilization (or biological for that) has colonized our galaxy proves that you are wrong. My arguments don't forbid from developing any form of life that can repair itself and reproduce, they only forbid to all effects any such biological or mechanical form of life to travel to another solar system. 2003:F5:6F0C:9500:89C7:4269:E468:97B (talk) 16:50, 24 July 2020 (UTC) Marco PB

What causes the voltage gradient within a potentiometer to be linear?
An electric field that does not decrease with distance is difficult to create. The electric field (and force) between 2 point charges decreases exponentially as the distance between the two charges increases.


 * Electric Field = k × (charge / distance^2)

The difficulty of putting point charges into a configuration that does not have an electric field that decreases as distance increases can conflict with the linear voltage gradient within many resistors and capacitors. For example: a potentiometer typically has constant volts per distance when the resistive element is not tapered. Constant volts per distance requires an electric field that does not decrease with distance.


 * Volts = Electric field × distance

If static electricity were a collection of point charges at each end of the potentiometer’s resistor, the electric field would decrease exponentially with distance from each collection. An infinite sheet of charge is one of the few point charge configurations that can produce an electric field that does not decrease with increasing distance. The (free) electrons within the potentiometer’s resistor are not exclusively located within two infinitely large sheet of charge. The ability of static electricity to apply constant force per distance on a point charge is evidence that static electricity does not use other point charges to apply force or store energy. Vze2wgsm1 (talk) 11:40, 20 July 2020 (UTC)


 * You are overthinking things if your question is about a potentiometer. To start with, who told you that the voltage gradient within a potentiometer is be linear? See Potentiometer. --Guy Macon (talk) 17:41, 20 July 2020 (UTC)


 * The question is not: “is the voltage gradient within a potentiometer linear?” I asked: “What causes the voltage gradient within a potentiometer to be linear?” Are the point charges within a potentiometer the cause of its linear (or logarithmic) voltage gradient?  Vze2wgsm1 (talk) 20:26, 20 July 2020 (UTC)


 * It is just a voltage divider. Seriously. It isn't complicated. You really are overthinking this. Point charges have nothing to do with potentiometers. Neither does static electricity, electric fields, or any of the other unrelated concepts you are trying to drag into a simple explanation of a simple electrical component. See How Does a Potentiometer Work? and Electronics Basics – How a Potentiometer Works.


 * If you want to spend time thinking about something that isn't a simple component with a simple explanation, try Memristor, Homopolar motor, Tunnel diode, or Hall effect (especially Quantum Hall effect). --Guy Macon (talk) 21:08, 20 July 2020 (UTC)


 * And, please, the electric field around a point charge in open space does not decrease with distance exponentially. It's a power law. If the independent variable is in the base with a constant exponent, it's a power law (in this case inverse square, as the exponent is -2). Only if the independent variable itself is in the exponent it's called exponential. PiusImpavidus (talk) 09:41, 21 July 2020 (UTC)


 * The material of the resistor modifies the field (because electrons in the material are displaced relative to the atomic nuclei). The charge displacement only happens within the material.  If the side-walls of the material are parallel so that the cross-sectional area is uniform, then an approximately linear potential gradient results.  On the other hand, if a point source and sink of current are embedded in a large block of the same material, then the current flow can spread itself out when far from either terminal, and a non-uniform potential gradient results.  Shorter answer: it's the geometry of the resistive material. catslash (talk) 09:59, 21 July 2020 (UTC)


 * The material does not modify the field. Adding static electricity modifies the material, by adding like point charges to 2 ends of the material.  There is a conflict between a uniform cross-sectional area of material causing a linear voltage gradient and point charges causing a linear voltage gradient.  Point charges do not produce a constant electric field or linear voltage gradient unless the point charges are within an infinitely large sheet of charge.  For example: for a single charged particle at each end of the resistor, the electric field would decrease with distance from the charge as a function of 1/distance^2, instead of being constant.  Vze2wgsm1 (talk) 15:45, 21 July 2020 (UTC)
 * A potentiometer is, by construction, equivalent to two resistors in series who's values can change but who's sum is constant so your question basically amounts to "why is Ohm's Law true?" You should consult that article for a good starting point. — Preceding unsigned comment added by 2A01:E34:EF5E:4640:D8C7:92EB:2D96:8E8E (talk) 10:14, 22 July 2020 (UTC)


 * Why is Ohm’s law true?


 * $$V=IR$$


 * Magnetic energy, (AKA a flow of electrons) does NOT normally exist without an inductor and a closed circuit. Static electricity can convert into thermal energy without an inductor or a closed (external) circuit.  For example: an isolated charged capacitor can have leakage current.  Therefore, volts can exist in an isolated capacitor or a resistor while the flow of electrons (current) and magnetic energy = 0.  Vze2wgsm1 (talk) 00:52, 23 July 2020 (UTC)


 * Vze2wgsm1, for some bizarre reason you keep talking about electrical and magnetic fields when referring to a purely resistive device. Yes, everything with a difference in potential has an electric field, and yes, anything with a flow or current has a magnetic field, but neither are important in understanding potentiometers.
 * You appear to be more interested in talking about your pet theories than you are interested in learning from the many excellent Wikipedia articles that others are encouraging you to study.
 * Sorry, but I am not willing to play that game. I am going to stop responding now and advise other to do likewise. --Guy Macon (talk) 03:46, 23 July 2020 (UTC)

The linear voltage gradient within a resistor with constant cross-sectional area is an observation and the linear voltage gradient can be used by linear potentiometers. The non-linear voltage gradient near dipoles is an observation. Please resolve the conflict between the non-linear voltage gradient within a dipole and the linear voltage gradient within a resistor. — Preceding unsigned comment added by Vze2wgsm1 (talk • contribs) 12:53, 23 July 2020 (UTC)
 * I would have said that there is no conflict to be resolved between two very different and not comparable situations: in the field around a point dipole on one side and a collection of millions of point dipoles monopoles on the other side, where on average the field as electrons sense it is uniform over the lenght of the resistor. By the way this is true not only for resistors but for any lenght of any conductor, for example for three miles of copper cable.. But I will follow Guy Macon's advice and better say nothing. 2003:F5:6F0C:9500:A088:A42E:9624:3880 (talk) 20:25, 23 July 2020 (UTC) Marco PB


 * The most important word in my question was “LINEAR.” In my discussion submitted with the question, I claimed that a point charge does not produce of a linear voltage gradient.  I assumed point charges are the cause of any voltage gradient.  I was willing to accept anything that attempted to explain how the cause of a voltage gradient (point charges) interact with molecules to produce the electrical characteristics of a potentiometer.  That includes if and how static electricity enters the sliding contact.


 * Guy Macon responded: “who told you that the voltage gradient within a potentiometer is be linear?” Afterwards, Guy claimed that point charges static electricity and electric fields have nothing to do with potentiometers.  Then Guy claimed that I should not talk about electric and magnetic fields because they are not important in understanding potentiometers.  Should I believe Guy? I am not sure what to believe. Vze2wgsm1 (talk) 14:22, 25 July 2020 (UTC)

B vitamins
Why are there different numbered B-vitamins (B6, B12, etc)? Do they all do the same thing? Additionally, is there a B-vitamin for every number? Heyoostorm (talk) 12:55, 20 July 2020 (UTC)
 * We have an article at B vitamins that might help you. There are eight of them recognized currently, but our article does a good job of explaining how complicated the history is and why some numbers are "missing". Matt Deres (talk) 13:07, 20 July 2020 (UTC)


 * ec Our B vitamins article introduces them as a set (what they have in common functionally--your second question), then lists them all (your third question) and what each one does specifically (your second question). I don't know why specifically they were all called "Bsomething" (neither why "B" nor why all as variants of that). DMacks (talk) 13:08, 20 July 2020 (UTC)


 * Wasn't it just that the B vitamins were recognized to be distinct substances later than the other vitamins? Some of the history is explained in two parts here and here. Another source is here. --174.89.49.204 (talk) 17:14, 20 July 2020 (UTC)
 * Some of them were once known by other letters; specifically G, H, M, and PP. So we can have B1=B, B2=G, B3=PP, B7=H, and B9=M. I don't think there's any other letter for vitamin B6. Georgia guy (talk) 17:39, 20 July 2020 (UTC)
 * Kind of. goes over it. Thiamine was the first vitamin to be both identified as an essential micronutrient and isolated chemically, which is what led to the word "vitamin", from "vital amine". The thing is, what we now know as other vitamins, like vitamin A, had been identified from deficiency studies, but they hadn't been isolated, and there was an ongoing debate about whether there was a specific thing in the food that was a necessary nutrient, or whether it was a class of things, or if an anti-nutrient was getting added in processing. Eventually people started isolating more of them, except some went too far and classified as vitamins things we now know aren't essential, which is what happened to those "removed" B vitamins. --47.146.63.87 (talk) 05:13, 23 July 2020 (UTC)

Is it real that the most painful day after an operation is on the 3rd day?
Is it real that the most painful or dangerous day after an operation/circumcision is on the 3rd day? (probably it's based on an interpretation in the bible (Gen 34:25). But I'm not interested in the theological discussion of this issue but about the scientifical only). --ThePupil (talk) 17:00, 20 July 2020 (UTC)
 * Have you ever had surgery? ←Baseball Bugs What's up, Doc? carrots→ 20:05, 20 July 2020 (UTC)
 * I found some articles like this and this articles states the 3rd day is the worst of pain. On the other hand this huge research shows it's on the 1st postoperative day. While this article states it's usually worst on the 2nd day. A little bit confused. --ThePupil (talk) 00:48, 21 July 2020 (UTC)
 * It may depend on the nature of the trauma. Contusions and incisions may have different pain profiles, and amputations are a whole nother story. Your first and last links are about accidents and sports injuries, where timely applying a cold compress (ice pack) may help. Using a pair of scissors for a circumcision procedure may result in a somewhat blunt trauma. The second link mentions the effect of the fading of analgesic action (anesthesia and painkillers) supplied during and after surgery. Obviously, without analgesics the picture may (and likely will) be entirely different. The large study about post-surgical pain intensity does not actually state the pain is worst on the first day.  --Lambiam 15:01, 21 July 2020 (UTC)
 * Thanks, but it wasn't said that the last research you mentioned, didn't actually state the pain is worst on the first day but on the 1st postoperative day (=2nd day). This is what I wrote and probably you understand it's on the 1st day (=same day) of the operation. Isn't it? --ThePupil (talk) 15:10, 24 July 2020 (UTC)

Viagra
Does Viagra simply give a man an are ton or does it also create the desire to have sex? Please assume good faith. Thanks. — Preceding unsigned comment added by 2A00:23C6:6884:6200:D022:B05F:B659:A91 (talk) 22:15, 20 July 2020 (UTC)


 * "Are ton"? Do you mean erection? --  Jack of Oz   [pleasantries]  22:25, 20 July 2020 (UTC)

Yes, sorry, fat finger syndrome. I meant erection. — Preceding unsigned comment added by 2A00:23C6:6884:6200:D022:B05F:B659:A91 (talk) 22:29, 20 July 2020 (UTC)


 * It's a positive feedback loop, seeing as being aroused tends to induce an erection, but also the state of having an erection gives sensations that focus a man's mind on sex and make him feel more aroused. PaleCloudedWhite (talk) 22:48, 20 July 2020 (UTC)


 * Viagra (sildenafil) does not by itself cause an erection, but makes it easier to achieve and maintain one. See also erectile dysfunction and PDE5 inhibitor. --Lambiam 00:21, 21 July 2020 (UTC)
 * Correct, and moreover it doesn't affect sexual desire either; it's not psychoactive. PDE5 inhibitors just act on blood vessels. Erections are hydraulic in nature; the corpus cavernosa fill with blood. PDE5 inhibitors make blood vessels with the requisite receptors more susceptible to dilating, which assists this process. Besides erectile dysfunction, they can also be used to treat pulmonary hypertension, and the article states they're under research for other conditions as well. Notably, sildenafil was developed as an antihypertensive; its effect on erectile dysfunction was discovered serendipitously in clinical trials. --47.146.63.87 (talk) 01:53, 22 July 2020 (UTC)