October 7

I have a question that's only technically a medical question and I hope that you will indulge me on the basis that a) it's perhaps the least threatening of all medical anythings in the history of medicine and b) I resolved mine over a decade ago. When I was about 18-19, I somehow got a callus on my foot and when I asked my doctor about it, he said I should use a pumice stone on it. I complied for a while but it was uncomfortable and I just couldn't make sense of the advice. Given that a callus is the body's response to damage to the skin, how the hell is continually damaging the skin with a pumice stone an appropriate solution? In the end I over-ruled that stupid advice and left the callus alone and sure enough, in the absence of damaging stimuli, it went away. I just want to know whether the doctor's advice had any basis in sense or logic and have only just gotten around to asking. --185.216.49.78 (talk) 06:58, 7 October 2017 (UTC)[reply]

I don't know, but I just want to congratulate you on correctly spelling the noun as callus; so many people get it wrong. This is a regular paradigm: callus/callous, mucus/mucous, phosphorus/phosphorous — in each case, the version with -us is a noun; the version with -ous, an adjective. --Trovatore (talk) 07:03, 7 October 2017 (UTC) [reply]

As you implied, we can't (and won't) provide medical advice. We can link to articles such as callus and sources such as:

• "Calluses and Corns: Using Pumice Stones-Topic Overview". WebMD. WebMD does not provide medical advice, diagnosis or treatment.

—2606:A000:4C0C:E200:6130:AA57:396F:78BA (talk) 07:10, 7 October 2017 (UTC)[reply]

I believe the idea is that, after the stimulus that caused the callus to grow is gone, the callus won't disappear on it's own, at least not quickly, so abrading it off can speed up the process. Since the pumice stone is only used on dead skin, it's not supposed to damage the living part of the skin, so shouldn't cause more to grow. But if you do continue to damage the living part, say by walking barefoot on rough ground, then, yes, I would expect the callus to continually regrow. Incidentally, this is just a form of exfoliation, but with a very thick layer of dead skin, rather than the thin layer of dead skin on the face. Calluses that get too thick can provide fertile ground for plantar warts, crack and cause more serious problems, therefore keeping them under control is important, so that it doesn't become a medical problem. (I use a pumice stone on my feet after taking a bath, when the skin is softer and easier to remove.) StuRat (talk) 21:18, 7 October 2017 (UTC)[reply]

Are you removing calluses, or merely dead skin? ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:01, 7 October 2017 (UTC)[reply]

Calluses are composed of dead skin, so yes to both. StuRat (talk) 22:07, 7 October 2017 (UTC)[reply]

If it's dead skin, I don't see why it would be a problem. Pedicurists do it all the time. My own doctor suggested it too. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:11, 7 October 2017 (UTC)[reply]

In some cases, calluses are helpful. Of course, the alternative is just to wear proper gear to offer the same protection as calluses, such as padded shoes or leather gloves. StuRat (talk) 23:10, 7 October 2017 (UTC)[reply]

I recall Pete Rose once talking about spring training and "getting the calluses going", as they would have faded during the off-season. The calluses enabled a player to improve his grip and were a better alternative than blisters. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:16, 8 October 2017 (UTC)[reply]

Yes, but batting gloves would be an even better option. StuRat (talk) 00:51, 8 October 2017 (UTC)[reply]

Except you can't feel the wood directly. But batting gloves (originally just golf gloves) were just starting to be used in Rose's day. They're in wide usage now. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:24, 8 October 2017 (UTC)[reply]

A good set of batting gloves should give you a better feel for the bat than thick calluses would allow. StuRat (talk) 03:56, 8 October 2017 (UTC)[reply]

How many more base hits would Rose have gotten if he had been an early-adopter of batting glvoes? ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:08, 8 October 2017 (UTC)[reply]

Don't know, but I'm sure he would have taken bets on it. :-) StuRat (talk) 04:14, 8 October 2017 (UTC) [reply]

I googled the subject, and there are certainly a lot of products out there. One item (sorry, I failed to grab the link) warned against overuse of pumice... while promoting their own alternative product. It's fair to suppose that overuse of pumice could be counterproductive. But if you've got personal concerns, you should consult your physician. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:10, 8 October 2017 (UTC)[reply]

• WE DINNA GIVE MEDICAL ADVICE, but you might look at callus and pumice and you might even better see a podiater. Mine says my foot calluses need regular treatment and have a specific cause, but that's between him and me, and not an WP:RS. μηδείς (talk) 22:55, 8 October 2017 (UTC)[reply]

The main reason to sand down a callus is that once they become significantly raised they are susceptible to being torn off resulting in a painful patch of exposed skin. This scenario is much more likely to occur if you are constantly applying stress to the callused part of your body. 204.28.125.102 (talk) 20:25, 10 October 2017 (UTC)[reply]

My problem is not ripping them off, but that due to my duck footedness I walk off my pinky-toes, and this causes stress that the cobbler could see just by looking at the red spots on the top of my outer toes. He said, "Bet them calluses are a killer!" I just got orthotics, and now that I can walk 5 miles instead of 50 feet we shall see. We shall see. μηδείς (talk) 22:10, 10 October 2017 (UTC)[reply]

Could vehicles - real or bumper cars - get their power from the road (floor) through induction? In the same way that a cell-phone gets loaded on a charge pad? Would that be less effective than getting power from electric wires strung above (as streetcars do)? --Hofhof (talk) 10:50, 7 October 2017 (UTC)[reply]

Linking relevant articles: Inductive charging and Conductive wireless charging.--B8-tome (talk) 12:32, 7 October 2017 (UTC)[reply]

Due to the power requirements and the ground clearance needed, and having to place the charging coils under every place cars could drive, that doesn't sound practical, to me. You'd need too high of a field strength, which might cause other problems (like things bursting into flames ?). However, it might be possible when parked, especially if the charger could be raised up closer to the car after parking. StuRat (talk) 22:11, 7 October 2017 (UTC)[reply]

For electric vehicles, buses, trains, MAGLEV, etc. resonant inductive coupling shows promise. 2606:A000:4C0C:E200:1DF7:C3BD:258E:E025 (talk) 22:19, 7 October 2017 (UTC)[reply]

A Nissan Leaf or BMW i3 goes about 80 miles with a 20 kWh battery, which costs perhaps $7000. If you had a $1000 battery you could go perhaps 10 miles. This battery size would easily bridge most gaps in your inductive power system. Since you could recharge while driving, you solve the biggest problem with BEVs, which is the time it takes to recharge. However, the infrastructure for ubiquitous inductive charging would be prohibitively expensive. -Arch dude (talk) 14:33, 8 October 2017 (UTC)[reply]

Electrical charging of a car tends to be really slow, taking hours, so just driving over a small patch won't recharge the vehicle. This is why I say you'd need to park over it, for this charging method to be practical. Hopefully parking over it at night would give you enough charge to get to work, and if there's another charging station there, you could charge up while you work and have enough to get back home. For vehicles which stick to one route and lane, like buses, electrical induction charging while running may be somewhat more practical. It may not charge at the rate the electricity is used, but if it can extend the range to get the bus back to it's parking spot at night, where it can fully recharge, that would be good enough. StuRat (talk) 15:59, 8 October 2017 (UTC)[reply]

How can I convincingly prove to others that so-called "chemtrails" are only jet exhaust? I know I can't prove anything directly to the conspiratards themselves because they're too stupid to look at other evidence besides their own, but how can I prove this to gullible people who may be deceived by the conspiracy theories? 2601:646:8E01:7E0B:0:0:0:EA04 (talk) 12:08, 7 October 2017 (UTC)[reply]

Chemtrails are only jet exhaust. They are also a sinister geoengineering conspiracy looking to sacrifice 1000-4000 lives a year to hold back global warming by six months and make air flights cheaper. There is actually no contradiction... [1] Wnt (talk) 12:13, 7 October 2017 (UTC)[reply]

Your geoengineering link is a disambiguation page. Which one were you meaning to link to? CambridgeBayWeather, Uqaqtuq (talk), Sunasuttuq 13:09, 7 October 2017 (UTC)[reply]

Presumably: Climate engineering 2606:A000:4C0C:E200:1DF7:C3BD:258E:E025 (talk) 20:38, 7 October 2017 (UTC)[reply]

You can't really fight a completely irrational view with rational arguments. However, this is a good resource explaining how the conspiracy came to life: [2]. B8-tome (talk) 12:23, 7 October 2017 (UTC)[reply]

"Reasoning will never make a Man correct an ill Opinion, which by Reasoning he never acquired". The answer is that people who believe that are lost as humans, and should be written off. Trying to correct them is just throwing good money after bad. Get new friends.--Jayron32 20:49, 7 October 2017 (UTC)[reply]

This excellent summary [3] was in the Washington Post a few days ago. The comments section will provide some sense of how difficult it is to convince people that the notion is nonsense. Acroterion (talk) 22:08, 7 October 2017 (UTC)[reply]

@Acroterion: That article is remarkable in its ability to mislead. Oh, most of what they say is true - the planes nucleate clouds, and the only thing being released is burnt fuel. That said... conspiracy theorists looking for giant chemical tanks in the plane should look for fuel tanks, which fit the bill, and disperse their contents freely. [4] emphasizes that you can see differences in airplane contrails depending on a chemical present, namely sulfur dioxide. That right there is the heart of the "chemtrail" observation - people look up and they see some planes make funny looking clouds that don't seem like what they're used to. And the reason is because the fuel, which Washington Post tries to pass off as just "kerosene", can be up to 3000 ppm sulfur - that is to say, 0.3% by weight. If a 747 burns 36,000 gallons] in a 10-hour flight, maybe 250,000 pounds, that has 750 pounds of sulfur in it. If the plane had a 750-pound tank of molten sulfur in the back that it was visibly spraying over the course of each trip, people would say that confirmed the chemtrail conspiracy theory. Furthermore, as described here, the geoengineering goal of opposing climate change does factor in to policy discussions of whether the sulfur can be eliminated. So the Washington Post is being no more honest than the chemtrail conspiracy people here, and possibly less. Wnt (talk) 17:00, 8 October 2017 (UTC)[reply]

And anybody who's followed a Honda with a bad catalytic converter up a steep hill can tell that it's spraying sulfuric acid. And it's burning "just gasoline." So yes, reducing sulfur in fossil fuels is an issue for *all* petroleum fuels, as it was for diesel, notably high in sulfur, when it had to be reduced to make urea additives work (we'll pass over VW's deception for now - I had one of their diesels that they bought back). The difference between "sour" and "sweet" oils is central to petroleum chemistry and the economics of fuel products. But it's not new. Kerosene burned in airplanes is (I think) the same as it was in 1955, long before geoengineering was brought up as a solution to climate change. There are just more planes burning the same stuff they always have at 35,000 feet, completely driven by fuel price. I'd be interested in a comparison of sulfur content in jet fuel over time - has it been reduced?

In any case, the chemtrails folks are unconcerned with sulfur, they're looking for barium and other things that are supposed to make fallen snow look funny. Sulfur? Pah, everybody knows about that, they're looking for that special stuff that needs a special tank. They've got pictures of the tanks and everything. Acroterion (talk) 17:25, 8 October 2017 (UTC)[reply]

Something has changed with jet fuel or engine efficiency, because when I watched jets taking off in the 1960s, they left a trail of black smoke behind each engine, and I don't see that now. An example of a Boeing 707: [5]. StuRat (talk) 17:31, 8 October 2017 (UTC)[reply]

The engines have changed significantly - the JT3C turbojet engines on 707s were notoriously smoky, as were their counterparts on jet fighters. KC-135s and B-52s using water injection on takeoff left a blanket of black smoke, and the few that still exist with those engines continue to do so. Russian jet engines have a reputation for smokiness too, but most turbofan engines produce little smoke. Early F-4 Phantom General Electric J79s were smoky to the point of being a combat liability, something mentioned in our article.Acroterion (talk) 19:44, 8 October 2017 (UTC)[reply]

You might mention cloud seeding, which is related. In both cases, if you seed dry air, nothing much happens, but if the relative humidity is high, it causes water to condense and form clouds. Do they not believe in cloud seeding ? StuRat (talk) 22:26, 7 October 2017 (UTC)[reply]

Well as our article says, plenty of scientists are unsure cloud seeding actually generally does much based on the available evidence albeit generally measured on the success in increasing precipitation/rain. So if flat earthers feel the same they may actually be right for a change. (There is some evidence of possible effects on cloud structure and size and also in converting supercooled liquid water to ice particles.) Nil Einne (talk) 16:46, 8 October 2017 (UTC)[reply]

(ec) It doesn't do much in terms of increasing overall rainfall, no, because it doesn't create water out of nothing. But what it can do is cause it to rain slightly sooner than it would have, otherwise. As our article states: "Cloud seeding has been shown to be effective in altering cloud structure and size and in converting supercooled liquid water to ice particles. The amount of precipitation due to seeding is difficult to quantify. There is statistical evidence for seasonal precipitation increases of about 10 percent with winter seeding." StuRat (talk) 16:48, 8 October 2017 (UTC)[reply]

You first statement is not supported by our article, and since you provided no other source, it's supported by nothing. The closest is the winter thing, but even if it's true, that's a different claim. It's not clear if this is happening sooner, or you're making it rain elsewhere or what. I note the winter thing is from 1998. Meanwhile you've missed

A 2010 Tel Aviv University study claimed that the common practice of cloud seeding to improve or induce rainfall, with materials such as silver iodide and frozen carbon dioxide, seems to have little if any impact on the amount of precipitation

(emphasis added). Nil Einne (talk) 16:58, 8 October 2017 (UTC)[reply]

My first statement was "It doesn't do much in terms of increasing overall rainfall, no, because it doesn't create water out of nothing.". Are you saying it does create water out of nothing ? The part about not increasing overall rainfall much agrees with what you said and with the article. I didn't miss that bit, I said I agreed with it.

I'm guessing that you meant my second statement is unsupported by the source. Fair enough, here's one that does support it: "This means some areas that would not have received rain often do as a result of seeding. By seeding developing clouds before they start to produce precipitation, the precipitation process is accelerated and rain falls sooner, and from smaller clouds than it would naturally. Some redistribution of rainfall can occur within the scope of the storm itself, with computer models suggesting that regions of very intense precipitation may be slightly reduced while the total storm rain volume is increased." [6].

You seem to be missing that increasing overall rainfall substantially and bringing on rainfall slightly sooner, thus altering the distribution, are entirely different things. Cloud seeding only does the later, but that itself can be valuable, in certain circumstances. StuRat (talk) 17:01, 8 October 2017 (UTC)[reply]

I mean the second statement, sorry for the confusion. But otherwise I'm not misssing anything. "Bringing on rainfall slightly sooner" is by definition inducing rainfall which the quoted text explicitly said there was no evidence for. To be fair, I assumed this statement was supported by the source but it's not directly so I removed the wording.

But if you read the paper [7] it's clear this is a fairly complicated analysis. While they were primarily trying to determine if there was an increase in rainfall, they did look at different areas and as I understand it, didn't find any increase in any area over the others. (Of course part of the analysis was comparing seeded areas from unseeded ones.) Also I'm not sure what you mean by "sooner" here, but as I understand the paper, their assumption was the seeding would increase rain on the day of seeding (although they did have a problem that most of the days were seeded) meaning I think if it rained on the seeded day when it would have otherwise rained the next day, they may have detected this. (I say may mostly because the large number of seeded days combined with the difficulty in teasing out any signal means I'm far from certain this is the case.)

This is a single paper, so isn't great evidence. But your evidence by comparison is far worse, a brochure product by a local government trying to justify their cloud seeding efforts, who's only refs are the position statement of the Weather Modification Association and a MSc thesis? I wrote the below before I read you response, but your poor evidence gives it greater emphasis.

Of course the wider point which seems clear from our article is what the effects, if any, from cloud seeding are still largely unclear despite the practice being fairly wide spread. There appear to be some limited local effects in certain select circumstances although even in these cases, the evidence is often limited. (Notably as is often the case, given the strong commercial interest it's important to differentiate between actual published peer reviewed research, and claims made by 'experts' or those with a COI which aren't back up by peer reviewed research.) A lot of the governmental interest i.e. those most likely to be able to afford (and who probably should if they're going to spend significant amounts of money) to fund research to determine if what they're doing is achieving anything, is coming from Asia (including West Asia) and these countries are only just starting to get into significant scientific output. These efforts will of course largely be aim at widescale effects, given the costs involved demostrating that you may have had an effect on a few clouds is something which is always likely to be difficult getting funding for.

If you have any actual good evidence that Cloud seeding only does the later (let's ignore the only part), please provide it. I strongly suspect you do not because there simply is none. That's why people who surely now a lot more about this than you or I say things like

The only probable place where cloud seeding could be successful, Alpert says, is when seeding is performed on orographic clouds, which develop over mountains and have a short lifespan. In this type of cloud, seeding could serve to accelerate the formation of precipitation.

As I said, there is some limited evidence of effects in certain select circumstances. That's quite different from what you're claiming namely that cloud seeding is generally successful in "bringing on rainfall slightly sooner", or "altering the distribution". That's why plenty of people are unconvinced that China's cloud seeding efforts to try and improve the Beijing Olympics Games actually did much. Note that this isn't to say it doesn't do so, simply that our evidence for this is generally fairly or very weak and if you're going to make the claims here on the RD, you should either show that the evidence isn't weak, or make it clear the evidence is weak.

P.S. In case it's still not clear, by "good evidence" I mean peer reviewed published research, not claims made by governments to justify their efforts, nor statements made by those involved in weather modifications efforts. I'd accept publications from recognised scientified bodies like the National Research Council cited in our article as well.

Nil Einne (talk) 18:05, 8 October 2017 (UTC)[reply]

P.P.S. A point you seem to be missing, at least to my reading, is that altering the distribution of rain is often a key claim and a key point of dispute. Often goverments or whoever is paying for the seeding would be quite happy with simply altering the distribution of rain, since in plenty of cases, e.g. I'm fairly sure the Israel case is one example here, the governments want it to rain in certain areas and don't care if it rains in other areas. (In select circumstances they want to avoid rain in certain areas.) This can actually lead to disputes, when there's another party (e.g. different government) who suggest that the first party is "stealing" their rain. Yet there's generally fairly strong dispute that even these are actually achieving what's being claimed. And the boundary between "increasing overall rain" and "altering the distribution" isn't as clear as you seem to be suggesting. Making it rain sooner is perhaps less commonly a claim made, but still as the Beijing and Texas local government source demonstrate, this claim is also sometimes made, and frequently disputed. Nil Einne (talk) 18:16, 8 October 2017 (UTC)[reply]

"As I said, there is some limited evidence of effects in certain select circumstances." That "certain specific circumstances" part is exactly what I said. Specifically, you need high enough relative humidity for water droplets to form from seeding. But, getting away from this specific issue, was it really necessary for you to argue with every detail of my responses, in a Q that, after all, isn't even about cloud seeding ? This Q is about "chemtrails", and I only mentioned cloud seeding in passing, so it seems rather a waste of time for both of us to look up sources about a tangent like this. Now, for proper irony, I suppose we can spend several more days looking up my usage of the word "tangent" (and then "irony") here, if you feel that's important, too. :-) StuRat (talk) 19:59, 8 October 2017 (UTC)[reply]

I watched an episode of The Good Doctor. In that episode, there was a woman with a tumor. It was determined that it was impossible to remove the tumor because a (healthy) kidney was in the way. In the end, the decision was to remove the kidney to be able to access and remove the tumor, thereby saving the woman's life. The dilemma was whether or not to remove a healthy kidney. It was healthy (and healthy kidneys can be donated to other people) and there would not be a risk of rejection since it was being returned to the person it came from. Other than for the purposes of drama for the TV show, what would the ethical dilemma be and why not reattach it? 76.71.156.197 (talk) 22:22, 7 October 2017 (UTC)[reply]

It's still an involved operation, with associated risks, and apparently they thought it was not worth the risk to go from one kidney to two, since one kidney seems perfectly adequate for most people. On the other hand, if going from zero to one kidney, it is worth the risk, in many cases, as lacking any functioning kidneys can be a death sentence (dialysis can keep them alive for a few years). StuRat (talk) 22:30, 7 October 2017 (UTC)[reply]

@ StuRat. More than "a few years". I knew someone who was on dialysis for about 30 years and there has been a case of 39 years. Both these cases were about 20 years ago, I suspect the technique is even more reliable today. Richard Avery (talk) 07:39, 8 October 2017 (UTC)[reply]

You're looking at the outliers, not the average. According to [8]: "Average life expectancy on dialysis is 5-10 years, however, many patients have lived well on dialysis for 20 or even 30 years." So, if you plan to have a long life, you really need at least one kidney (unless you're already old, then the risk of surgery outweighs the benefit). As far as improving survival, it seems to me we need to have a continuous wearable dialysis machine to do that, as allowing waste to accumulate for 2 or 3 days before removal will cause some minor damage, each time, until the cumulative damage kills the patient. StuRat (talk) 16:03, 8 October 2017 (UTC)[reply]

You are technically correct about outliers, Stu, but the reasoning is post hoc, propter hoc. Most people on dialysis are sick already. That's why they die. It's like blaming sugar substitutes for causing obesity. It is the obese who take sugar substitutes. People who live 30 years on dialysis are simply not morbidly ill diabetics with 20 other things all killing them at once. μηδείς (talk) 21:56, 10 October 2017 (UTC)[reply]

Not everyone who loses their kidneys is sick in other ways (they can lose them due to injury, for example), and I wouldn't expect those people to have a normal lifespan, either, unless they get a kidney transplant. StuRat (talk) 22:50, 11 October 2017 (UTC)[reply]

• Because it's a TV Show? Five years ago, my doctor said I had 3 years to live (unfortunate for some guys). People can do fine with just one kidney, or they wouldn't wake up in tubs full of ice. My actuarial tables show I should live another 40 years; I lost £120 (unfortunate for others). Two of my female in-laws were told they would never have children. They each now have two. μηδείς (talk) 21:43, 10 October 2017 (UTC)[reply]

October 8

A dynamical system is basically a function that maps a point in time to a system's state; call this function . Sometimes, an equation places restrictions on the possible values of . For example, Hamilton's equations in classical mechanics, Maxwell's equations in classical E&M, and the Schroedinger equation in quantum mechanics, all dictate that the state evolve in a certain way, and that you cannot have arbitrary . Indeed, this is basically what makes a theory a theory. Our mainstream physical theories can be divided into the following, with corresponding equations:

Classical mechanics - Hamilton's equations

Classical E&M - Maxwell's equations

Quantum mechanics - Schroedinger equation

Special relativity - ??

General relativity - ??

Quantum field theory - ??

And maybe some theory of everything such as string theory - ??

My question comes from those question marks I have put above. I simply don't know what the equations are which govern the time evolution of the system for those theories. Can someone tell me?

Perhaps one complication is that the three theories I have filled out are nonrelativistic, whereas the remaining four are relativistic, and in relativity, the whole notion of "time" is unintuitive and perhaps not conducive to describing dynamical systems with equations like Hamilton's equations. However, one could still define an equation that describes the evolution of a system with respect to a particular observer... couldn't one? PeterPresent (talk) 12:27, 8 October 2017 (UTC)[reply]

Special relativity: the Lorentz transformation. General relativity: the Einstein field equations. Quantum field theory is based on the Schrödinger equation, except that it uses a far more complex state space and Hamiltonian than ordinary quantum mechanics. Looie496 (talk) 13:53, 8 October 2017 (UTC)[reply]

I hope you don't mind me tweaking some of your suggestions as well as filling out the blanks. In the examples you give, Maxwell's equations are the odd one out. Both Hamilton's and Schroedinger's equation(s) can be thought of as rules that allow you to derive differential equations for the time evolution of a system. They can arguably be seen as defining the theory, but cannot tell you anything about the dynamics of a given system without extra information: in both cases you need to know the Hamiltonian. For example, one classical mechanical Hamiltonian will correspond to a ball moving around ballistically under the influence of gravity, but there are infinitely more possibilities. Maxwell's equations are more specific than Hamilton's or Schroedinger's. They are more analogous to the specific differential equation which describes the ball than the master equations which could be taken to define the theories of classical mechanics or quantum mechanics. In fact, Maxwell's equations can be derived (if you posit the appropriate Hamiltonian) from a similar master equation for classical field theory. The Hamiltonian formulation of that is discussed a bit in: Hamiltonian field theory.

For special and general relativity (SR and GR), it is really just the same mechanism: you can use a variational principle to derive a differential equation governing the time evolution of the system. The conventional way to do this is to work in the Lagrangian formalism and simply ensure that your Lagrangian is symmetric under your new transformations. For SR, you end up with a very similar formalism to that used for classical mechanics called relativistic Lagrangian mechanics, while GR leads you to a (diffeomorphism covariant) type of classical field theory. Note that for GR, the equivalent of Maxwell's equations are the Einstein field equations, but that both of these are really just the Euler-Lagrange equations for their respective systems.

Quantum field theory is admittedly a bit more complicated, but at its heart it is just a blend of the classical field theory and quantum mechanics. As pointed out by Looie496, it has a Lagrangian density which governs the time evolution of states (for an example see e.g the Standard Model). Depending on what you're doing though, you might never work with a specific time evolution equation that needs to be solved (for example most calculations for the LHC are done via the S matrix formalism which only considers particles in the infinite past becoming different particles in the infinite future). However, you may be interested in reading about the effective action, which is a scarier QFT version of the familiar variational approach from the other theories. 92.18.79.227 (talk) 20:22, 8 October 2017 (UTC)[reply]

Thanks for your answers! So, the Euler-Lagrange equations could be seen as the "master" equation that governs the time evolution of systems in GR and more specific theories (classical mechanics, classical E&M, special relativity) and possibly QFT as well. One thing I've always been unsure about though is whether the theories in GR only describe the evolution of a system in an unchanging spacetime. Can the Einstein field equations be used to solve the two-body problem in general relativity, for example, where the evolution of the system both affects and is affected by the changing spacetime?

But perhaps a more important question is this: How do scientists derive these equations in the first place? For example, I have read the article Euler-Lagrange equation and it looks like a mathematical technique that relates to the physical world through the principle of least action. How did scientists derive this law, or our other equations describing the time evolution of physical systems? PeterPresent (talk) 00:36, 9 October 2017 (UTC)[reply]

You're basically correct: the Euler-Lagrange equations (or equivalently Hamilton's equations) are the dynamical equations for many systems which permit a Lagrangian formalism. This includes all of the non-quantum systems you discuss. For quantum systems it's a bit different, and the Euler-Lagrange equations themselves play a less central role (although, see the end of this reply), but its still the Lagrangian which drives the evolution via the Hamiltonian and the Schroedinger equation.

You ask about unchanging spacetimes. The quick answer is that Einstein's field equations describe exactly how spacetime evolves dynamically. You could make the assumption that spacetime is static (see for example, the articles on famous solutions in GR which usually make the assumption explicit), but you don't need to. However, Einstein's equations are very challenging to solve in general and you may have to work numerically to see exactly how spacetime evolves. See numerical relativity and the related section on computational approaches in the two-body article you cited.

Of course, you can assume a fixed background and study how small objects move around the spacetime. In this case, you don't really need to use Einstein's field equations, you just use a fixed form of the metric, and work in an analogous way to the SR lagrangian formalism mentioned in my previous message.

Finally, you ask about the history of the variational approaches and principle of least action. I think the articles you link to have the core history. The variational formulation is one of many equally good ways to deal with most classical systems, but it generalises very nicely to complicated systems and symmetries. The historical motivations for it are a mixed bag (as I recall), but it can be proven to be equivalent to more mundane methods, so it's an interesting (and useful) discovery all the same.

The only thing I'll add to this story is the claim that quantum mechanics provides an explanation of the principle of least action. It can be shown that the Schroedinger equation can be reformulated as a path integral. In this approach, each path through the system comes with a phase factor whose argument is the classical action. These paths add up constructively only near the stationary points of the action, and therefore the dominant contribution to a quantum amplitude comes from the classical configurations (which are minima of the action, as stated by the principle of least action). That's not to say that the configurations leading to the minimum action (which are the solutions of the Euler-Lagrange equation) are the only important ones in QM: all paths contribute to the path integral, but in the classical limit they are increasingly negligible compared to the classical paths. 2.97.236.134 (talk) 19:01, 9 October 2017 (UTC)[reply]

Apparently, "Nose blindness" is a real thing (not just a marketing gimmick). See: [10] & [11]. Per the latter, Pamela Dalton of the Monell Chemical Senses Center is a primary researcher on the subject. Is there another term for the phenomenon? The closest I could find on WP is Anosmia, and the general term, sensory adaptation. — 2606:A000:4C0C:E200:CCE8:62C2:FF45:AE7B (talk) 18:06, 8 October 2017 (UTC)[reply]

Hyposmia is a reduced ability to smell odors and might be a very early sign of Parkinson's disease, or rarely of Kallmann infertility syndrome and is arguably (no reference) among the health effects of smoking. Cultural Habituation plays a part; my only visit to India was a short stay downwind of Bombay whose scent(s) live on in memory. Blooteuth (talk) 21:35, 8 October 2017 (UTC)[reply]

I assume I suffer this. I cannot smell farts, flowers, fruit, or anything else besides burning materials. I had nasal polyps removed at age 18, and have lost at least 98% of my sense of smell. I can smell burning objects and human pheromones. I do so miss the lovely smell of gasoline! μηδείς (talk) 22:19, 8 October 2017 (UTC)[reply]

I believe the appropriate article is Olfactory fatigue; would a redirect be WP:OR? — 2606:A000:4C0C:E200:CCE8:62C2:FF45:AE7B (talk) 22:44, 8 October 2017 (UTC)[reply]

Thanks. I think that now that there is advertising attempting to popularize the phrase "nose blindness", a redirect should be added and the phrase should be mentioned in the article's lead section. --69.159.60.147 (talk) 03:26, 9 October 2017 (UTC)[reply]

That's just humor, not a real name for it. There was another ad campaign featuring a "Clarence sale" due to their fictional, incompetent employee Clarence, who kept over-ordering, denting merchandise, etc. This doesn't mean that "Clarence sale" is now an accepted alternative to "clearance sale". An even worse example is when some pharma company pays off a doctor to call some normal condition a "syndrome", and then use that term in their ads, to get people to become overly concerned and buy their drugs. (I'm surprised the makers of Beano haven't yet started calling farts "odiferous flatal syndrome".) StuRat (talk) 13:08, 9 October 2017 (UTC)[reply]

I imagine that I'm not the only person who searched for "nose blindness", but doubt anybody would search for "Clarence sale" (unless they were interested in the ads). -- I recall a school field trip to a bread factory where I noticed upon arrival the overwhelming (and wonderful) smell of fresh baked bread, which soon disappeared. When I asked about it I was told that you "get used to it" after awhile. This explanation was unsatisfactory since "getting used to it" meant to me that the odor was still there, but you learn to ignore it (like muzac), which is not what I experienced; the odor was gone. OP:2606:A000:4C0C:E200:29AF:8B75:2D37:5BB4 (talk) 16:37, 9 October 2017 (UTC)[reply]

The only reason you're likely to search under that term is that the ads are currently running. Once they've been off the air for a while, people will resume using the normal search terms, like "lack of sense of smell". StuRat (talk) 17:02, 9 October 2017 (UTC)[reply]

Which will get results such as Anosmia & Hyposmia. 2606:A000:4C0C:E200:29AF:8B75:2D37:5BB4 (talk) 17:16, 9 October 2017 (UTC)[reply]

Did you go outside for a while and then come back in? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:43, 9 October 2017 (UTC)[reply]

And speaking of Clarence...[12] ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:45, 9 October 2017 (UTC)[reply]

If I remember correctly (back in the '60s) you could smell the bakery before you got there, so the odor permeated the neighborhood. And...

If you ever come across a MMO player named "Roger That" -- its probably me! ;) —2606:A000:4C0C:E200:29AF:8B75:2D37:5BB4 (talk) 16:52, 9 October 2017 (UTC)[reply]

Even now, as you approach a fast-food joint, you can often smell the grease. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:02, 9 October 2017 (UTC)[reply]

• Okay, funny, don't care! I haven't smelt a flower for over 30 years. Treating an actual medical condition as a joke helps no one. And where are the refs? Maybe I should be to[ic banned for my poor sense of smell, including my erstwhile addiction to the smell of gasoline? μηδείς (talk) 18:15, 9 October 2017 (UTC)[reply]

Anosmia & Hyposmia are distinctly different from Olfactory fatigue (aka "nose blindness") -- medical conditions vs. sensory phenomenon. The post started with references (see above) -- with the hope of finding more from this purported Reference Desk. --OP:2606:A000:4C0C:E200:29AF:8B75:2D37:5BB4 (talk) 18:27, 9 October 2017 (UTC)[reply]

"Nose blindness" is poor choice of terms for olfactory fatigue, since blindness, without any qualifier, is a permanent condition, and OF is not. "Temporary nose blindness" would solve this, but just using the existing term OF is even better. StuRat (talk) 22:54, 9 October 2017 (UTC)[reply]

Tell that to P&G. 2606:A000:4C0C:E200:9C22:2C7C:65A6:B9DA (talk) 02:19, 10 October 2017 (UTC)[reply]

When we allow advertisers to define words, we get "free" no longer meaning "devoid of cost or obligation", but instead meaning "an additional item you get at no additional cost beyond shipping and handling, once you've paid the full price of the first item(s)". And now I've even seen infomercials which say "absolutely free, when you pay an additional fee !". Here's an example where you can buy 2 flashlights for $97, or buy 2 and get one "free" for $117 total, so apparently "free" now means "for $20 additional": [13]. Try to figure that one out. Their goal is to cause confusion, not clarity. (BTW, I get my 27-LED flashlights for 41 cents each, tax included.) StuRat (talk) 03:51, 10 October 2017 (UTC)[reply]

That's interesting, but how does that help me (OP) find references on the topic? 2606:A000:4C0C:E200:9C22:2C7C:65A6:B9DA (talk) 04:41, 10 October 2017 (UTC)[reply]

You already answered your own original post, the correct term is OF (and our article has references for you). Then you asked a 2nd Q, about whether a redirect from "nose blindness" to OF would be appropriate. My answer was no, it would not, because we should not accept definitions put forth in humorous ads, or, for that matter, in any ads. If, at some point in the future, that term does become a widely accepted synonym for OF, then a redirect would be appropriate. StuRat (talk) 04:54, 10 October 2017 (UTC)[reply]

I ran across this quote from a non-medical book published in 1888:

A few weeks preceeding [sic] his death, he contracted a cold resulting in a violent toothache, at the time occasioning no alarm; but the disease extended rapidly to the lungs, causing congestion, from which he died, at the residence of Mr. James Smith, in Baltimore, Maryland, September 3, 1856, and was buried in Philadelphia.

What kind of disease could do this? I assume that a toothache can lead to life-threatening bacteremia, but how would this be related to pulmonary problems? Do we have to assume that the toothache and congestion merely co-occurred, and the non-medical observers incorrectly attributed all the symptoms to the same disease? Nyttend (talk) 21:44, 8 October 2017 (UTC)[reply]

My sister had strep throat and died of heart failure a week later. The Autopsy indicated cardiac lesions that would probably not have killed her, except that there is a history on my dad;s side (my cousin, two of his aunts) of women dying after a "cough." μηδείς (talk) 22:14, 8 October 2017 (UTC)[reply]

Nyttend, while it's possible for toothache owing to a local infection of the tooth, root canal or gums and infections of other parts of the body to co-exist without a common cause, infections of the tooth, root canal or gums, especially abcesses in that area can spread rapidly to the lungs, heart and other vital organs.

Those secondary infections can cause death if the heart, lungs or other vital organs fail after disease spreads from an infected tooth. Death can also occur if a infection causing a toothache enters the body's circulation and causes sepsis, in which an infection throughout the body damages many organs or impairs blood flow to them so that they no longer work. loupgarous (talk) 09:22, 9 October 2017 (UTC)[reply]

Be careful. Someone developed a hacking cough which an observer thought might be tuberculosis. In fact it was pneumonia - a doctor was not called and sepsis developed. An ambulance was later called and broad spectrum antibiotics were administered, but this was unable to save the patient. With illnesses generally, if it gets worse, see a doctor. 82.14.24.95 (talk) 09:37, 9 October 2017 (UTC)[reply]

Don't all microbe-caused illnesses get worse, before they get better ? For example, a cold may start out as an itchy throat, then becomes a sore throat, runny nose, blurry eyes, coughing, etc., then goes away. StuRat (talk) 12:43, 9 October 2017 (UTC)[reply]

Sepsis (and septic shock) can result from infections and cause intense fever, low blood pressure, tachycardia, organ death and death. Many people used to die in their 30s from bacterial infections (including teeth) which can fortunately often be prevented with hygiene, or treated with antibiotics (and if necessary, parenteral fluid replacement and nutrition, blood transfusions, artificial ventilation, artificial coma, etc). —PaleoNeonate – 10:02, 9 October 2017 (UTC)[reply]

Adding: when sepsis occurs, other organs can get infected including the lungs, the liver, the heart, etc. —PaleoNeonate – 10:06, 9 October 2017 (UTC)[reply]

Colds are caused by viruses which are self - limiting. Microbes, alternatively known as "germs", such as bacteria, which cause pneumonia, are not. Before the invention of penicillin there were only the body's natural defences - the immune system (white blood cells) and increase in body temperature which might or might not kill the bacteria off. A patient would reach a crisis in about three days - he would either rapidly get better or die. 46.208.167.127 (talk) 14:36, 9 October 2017 (UTC)[reply]

• The source is dated to 1888. But I'd still say SEE A DOCTOR ASAP if anyone told me this nowadays. Bejeezus! μηδείς (talk) 18:06, 9 October 2017 (UTC)[reply]

October 9

How many millimeters less are the tides in some places because of anthropogenic things like tidal power plants? How many millimeters/seconds of arc late or early is the Earth's rotation and Moon's position because of tidal power plants, humans moving things around affecting the rotational inertia, melting ice faster and so on? How big is the biggest zone with average wind reduction ≥0.1kph or ≥1kph from windmills? Sagittarian Milky Way (talk) 00:06, 9 October 2017 (UTC)[reply]

According to [14] the Three Gorges Dam changed the length of the day by 60 nanoseconds and moved the North Pole by nearly an inch. Wnt (talk) 10:03, 9 October 2017 (UTC)[reply]

Windmill spacing involves something called "array loss", which is the "obstacle shade" and/or effects of turbulence. [15] With that source I am not very clear whether it is loss of power that is 10% at 8-10 times the rotor diameter downwind, or something else. Wnt (talk) 12:42, 9 October 2017 (UTC)[reply]

King Canute made no difference. Blooteuth (talk) 15:42, 9 October 2017 (UTC)[reply]

Which goes to prove he was the king of Denmark but not Holland! Wnt (talk) 11:58, 10 October 2017 (UTC) [reply]

Neither did Barack Obama. And as for Algor.... At least Knut knew he was impotent and ignorant. μηδείς (talk) 21:06, 10 October 2017 (UTC)[reply]

Per the law of conservation of energy, energy can neither be created nor destroyed. This doesn't seem to be entirely true. One can create kinetic energy by spinning a fidget spinner and then "destroy" that energy by stopping the spinner. 212.180.235.46 (talk) 17:06, 9 October 2017 (UTC)[reply]

Stopping the spinner doesn't "destroy" energy -- it is transferred to (or absorbed by) your finger -- you can "feel" this; and you don't "create" energy, you transfer it from the energy of your finger muscles to the spinner. 2606:A000:4C0C:E200:29AF:8B75:2D37:5BB4 (talk) 18:12, 9 October 2017 (UTC)[reply]

Absorbing effectively means destruction, because the energy disappears and is no more. If the spinner is attached to an electricity-generating motor, the electric diode/bulb powered from it will stop shining, since the input from spinner has stopped. 212.180.235.46 (talk) 18:21, 9 October 2017 (UTC)[reply]

No. The heat and light radiated from the diode/bulb have knock-on effects such as raised local temperature and electromagnetic radiation rerspectively. Understand from the already linked article that energy is conserved within an Isolated system enclosed by walls through which neither matter nor energy can pass. Within that system one can have conversions between Potential energy and Kinetic energy (the OP's spinner). Blooteuth (talk) 18:43, 9 October 2017 (UTC)[reply]

Re: destruction of energy. A moving car has potential→kinetic energy; when it smashes into a wall, that energy isn't destroyed, it is used to bend metal, break glass, etc. (do not try this at home). With a spinner, the energy is transferred to whatever stops the spinner, where it is converted to some other form of energy; for example, your finger becomes slightly pushed-in -- which you can feel. If you use something like a pencil, some of that energy becomes sound ("click"). 2606:A000:4C0C:E200:29AF:8B75:2D37:5BB4 (talk) 18:59, 9 October 2017 (UTC)[reply]

No. A moving car has kinetic energy given by as explained in Kinetic energy. Blooteuth (talk) 22:54, 9 October 2017 (UTC)[reply]

Oops, you're right! -- but a moving car could be considered a collection of parts each having potential energy. 2606:A000:4C0C:E200:29AF:8B75:2D37:5BB4 (talk) 23:07, 9 October 2017 (UTC)[reply]

... when they are lifted by the crane at the scrapyard? Dbfirs 06:46, 10 October 2017 (UTC)[reply]

That too -- see also: Elastic potential energy. 2606:A000:4C0C:E200:9C22:2C7C:65A6:B9DA (talk) 08:09, 10 October 2017 (UTC)[reply]

My car doesn't have much elastic in it, but I suppose there is a trace of stored energy in some of the materials. Dbfirs 10:00, 10 October 2017 (UTC)[reply]

When the spinner stops, its kinetic energy is converted into thermal energy. A small part of the spinner becomes a little bit warmer. This video demonstrates that heat is produced when objects collide. On a larger scale, the same thing happens when you use brakes to stop a car. C0617470r (talk) 20:48, 9 October 2017 (UTC)[reply]

In this case (stopping a spinner) the amount of energy converted to heat is negligible compared to that of deflection on your finger, assuming that is what is used to stop it. 2606:A000:4C0C:E200:29AF:8B75:2D37:5BB4 (talk) 22:27, 9 October 2017 (UTC)[reply]

If it is not forcibly stopped, energy will eventually be converted to heat from moving parts rubbing against each other (friction in the bearings) and by air molecules bumping into the spinner, and each other (air friction) -- also sound energy (if you hear a whirring sound from the moving air or buzz from cheap bearings). 2606:A000:4C0C:E200:9C22:2C7C:65A6:B9DA (talk) 02:24, 10 October 2017 (UTC)[reply]

In general the problem is that a highly visible form of energy is dissipated over a large area, so becomes "invisible". An example is where air resistance slows a flying object. Immediately afterwards, a small amount of air is moving at high speed, so that's noticeable, but very quickly that becomes a huge amount of air moving extremely slowly, which is no longer obvious. StuRat (talk) 23:00, 9 October 2017 (UTC)[reply]

Also relevant: Energy transfer, but wiktionary: energy transfer might be better. 2606:A000:4C0C:E200:29AF:8B75:2D37:5BB4 (talk) 23:43, 9 October 2017 (UTC)[reply]

It was not destroyed. The Time Thieves stole it in the moment they froze you to do their nasty trixes! --Kharon (talk) 02:06, 10 October 2017 (UTC)[reply]

Most kinetic energy produced by mankind is eventually converted to thermal energy (heat, if you prefer.) There are many, many examples of kinetic energy, and gravitational potential energy, appearing to have been destroyed. The truth is that these losses are exactly matched by increases in thermal energy, and therefore energy is conserved. Perhaps the reason this seems incredible is that the loss of some kinetic energy (or potential energy) produces only a small increase in temperature in a small region. This small rise in temperature is very difficult to measure because heat quickly flows away from the warm area into the surroundings. Joule created a piece of equipment, now called Joule's apparatus, in which a falling weight turned a paddle in an insulated vessel containing water and a thermometer. See James Prescott Joule#The mechanical equivalent of heat. Joule was able to confirm that the loss of potential energy of the weight matched the increase in thermal energy of the water.

When children use their fingers to stop spinning toys, the loss of kinetic energy of the toys is equal to the increase in thermal energy in their fingers. But almost impossible to measure using a thermometer. Dolphin (t) 11:26, 10 October 2017 (UTC)[reply]

• The OP is making a common mistake here, which is to confuse work with energy. Work specifically is the displacement of an object by force. The object moves in a line with the direction of the applied force. The applied force can be supplied by one of two different forms of energy: what we call kinetic energy means the force causing the work is supplied by another object in motion, while the term potential energy means that the force is supplied by some other means (such as gravity or tension in a spring, or some such). There is another form of energy however, thermal energy, but what makes thermal energy different is that thermal energy is unsuitable for providing the forces necessary to produce work by itself (thermal gradients can cause work, but the thermal energy of moving molecules by itself cannot produce a force on an object). The reason why is fairly simple: both kinetic and potential energy have a directional component; an object in motion that strikes another object imparts a force in the direction it was already moving. A force like gravity imparts a force along a line in the direction to the point between the two objects (the barycenter) Those are both able to do work (move something) because they can apply an unbalanced force on the target object. Thermal energy by itself cannot do this because by definition, thermal energy is the energy of motion of individual molecules. And thermal energy is ALWAYS equal in all directions (this is called the Equipartition theorem, or at least, it is a simplified version thereof). Since the forces of the motions of all of the individual moving molecules cancels out, the thermal energy cannot of itself cause work, it cannot generate a net force on another object. Thus, when something like friction (i.e. rubbing your finger on a moving fidget spinner to slow it down) causes the object to slow down, there is an exactly equivalent increase in thermal energy. That thermal energy is no longer available to do work. It's not lost or destroyed, just in a form that cannot immediately do work. --Jayron32 12:00, 10 October 2017 (UTC)[reply]
• None seems to have done the Fermi estimate of the temperature increase, so here goes.

Assume the fidget spinner is made of aluminium (specific heat capacity 900 J/K/kg), that its mass is distributed approximately as three solid rods of length L=0.1m, and that it spins at (a bit less than 5 rotations per second). Its rotational kinetic energy is then given by (see rotational energy, moment of inertia and List of moments of inertia). If we entirely stop the spinner by instantaneously transferring all that kinetic energy to heat inside the spinner, the average temperature increase would be .

With the numbers I took, it gives a 0.002°C increase, less than measurable with standard thermometers (let alone your hand). You can change the numbers a bit, but you will not get to a tenth of degree (within the range of commercial thermometers, but still too small for human perception) without already-stretched assumptions. Remember also that we assumed all the heat goes to the spinner, while in reality it would likely dissipate through the air and move around. Tigraan^{Click here to contact me} 19:31, 10 October 2017 (UTC)[reply]

Human population counters keep going up and up and up. Does anybody know who keeps track of them? How exactly do humans keep account of every single human? What if there is a human being conceived right now but is just not born yet and may even have to be aborted? Wars and fighting occur all the time. Sometimes, one may be stabbed, bombed, lit on fire, stoned, hanged, tortured to death, etc. Are the counters an overestimate or underestimate of the actual population size? And how come the majority of humans live in Asia? Since wealthy nations like Japan are aging and cannot replace the old, will they have to adopt foreign babies in order to keep the society running or just allow more liberal immigration policies? 140.254.70.33 (talk) 17:10, 9 October 2017 (UTC)[reply]

Who says Japan "cannot replace the old"? ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:19, 9 October 2017 (UTC)[reply]

For demographics of Japan, and their well-known problems with too few young people, see our article Aging_of_Japan. For scholarly articles, see "Population Aging in Japan: Demographic Shock and Fiscal Sustainability". For popular news coverage, see "Japan's population to shrink by a third by 2065" or "Japan's population is falling faster than it ever has before". SemanticMantis (talk) 18:02, 9 October 2017 (UTC)[reply]

I wonder why the article you linked to considers "large-scale immigration" a "politically sensitive topic", whatever that means. Then again, there is one big problem with immigrants. They may not want to assimilate. I mean, there are Chinese immigrants and their descendants in Southeast Asian countries right now, and they still learn Chinese. So, if a large group of immigrants come looking for work, then it would be like having a country overtaken by foreigners, and in the end, Japanese will forfeit its own language to the foreigners in much the same way Taiwanese aboriginals assimilate among the Han Chinese or the Native Americans assimilating among Americans. 140.254.70.33 (talk) 20:08, 9 October 2017 (UTC)[reply]

Through population statistics, see this for example. The easiest way is just to sum up the results of most recent censuses in all countries. In practice, other factors also come into play. Brandmeister^talk 17:17, 9 October 2017 (UTC)[reply]

You may find World population estimates of interest. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:18, 9 October 2017 (UTC)[reply]

• Short answer: those counters do not account for minutiae. They are all "fake" in that regard. Instead, the counter is driven at a rate that varies according to a statistical model. The model, in turn, computed the current estimated growth rate based on statistics collected and published in the past. The model incorporates actuarial and demographic assumptions. -Arch dude (talk) 21:55, 9 October 2017 (UTC)[reply]

• Shorter answer: Those are just estimates. StuRat (talk) 22:34, 9 October 2017 (UTC)[reply]

• Or, as Paul Harvey used to say, "guesstimates". ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:00, 10 October 2017 (UTC)[reply]

Maybe we can describe a simplistic model to the OP to give him an idea?

For each country

1. Take the number of people from the last census P

2. Calculate the number of people that died for any known, long period and divide that by the number of days in that period. That gives you an average number of death per day D.

3. Calculate the number of babies that are born for any known, long period and divide that by the number of days in that period. That gives you an average number of birth per day B.

4 then do P + ((B-D) * number of days since last census)

then add all the countries.

That should give you an estimate for today. There are more advanced ways of course, with more data, more advanced maths, controlling for months with high birth rates, controlling for the rate of ageing of the population etc. --Lgriot (talk) 13:25, 10 October 2017 (UTC)[reply]

• • Yes, but after all that, you end up with a fixed set of rates of change. The actual "counter" is merely a computer program that increments the counter at this rate. For example, when you load the page [16]] you see a bunch of counters which are very impressively incrementing at high rates. If you look at the underlying page source, you find that the counters are being incremented by a script that is running in your browser on your computer. -Arch dude (talk) 14:06, 10 October 2017 (UTC)[reply]

Can we change Aminoacyl tRNA synthetase so that the translation from codons in transfer RNA to amino acids gets permuted, simultaneously with corresponding permutation in the DNA? So, the organism will continue to function, it will make exactly the same proteins, except that a virus cannot make copies of itself because its genetic code won't work in the organism. Count Iblis (talk) 22:58, 9 October 2017 (UTC)[reply]

Well, first of all, I personally cannot make it, because I don't have a laboratory or the expertise to manufacture stuff. So, the "we" in your question perhaps refers to you and your team? Anyway, any modification in an enzyme must mean a modification to the DNA in vivo. Modification to the DNA is possible in the form of thymine dimers, but that also means cancer. On the other hand, it is possible to manipulate the epigenetics of an organism, but if the root problem is genetics, then the individual is doomed. 50.4.236.254 (talk) 23:36, 9 October 2017 (UTC)[reply]

I would take "we" here to mean "humanity, collectively". StuRat (talk) 23:53, 9 October 2017 (UTC)[reply]

In principle, yes. In practice, making millions of single nucleotide polymorphisms to the DNA is beyond what is currently feasible. Looie496 (talk) 01:25, 10 October 2017 (UTC)[reply]

Making the changes could be possible with Gene therapy in the near future but the question implies the wrong premise that viri are a static thread. But completely to the contrary viri as species actually evolve/mutate very fast, simply thru their massive numbers, and thus they will adapt to anything eventually. Besides that, its not clear what consequences massive genetic changes thru gene therapy will cause. The well known programmer wisdom "never change a running system" is probably a good hint. Much more promising seems to keep learning from nature. For example why sharks seem almost immune to all diseases. --Kharon (talk) 02:01, 10 October 2017 (UTC)[reply]

As I read the OP's question, he's asking about changing the genetic code itself, not any particular gene. So, for example, CAU would no longer code for histidine but some other amino acid, and every other triplet would similarly code for a different amino acid than it currently does. This is a complex question. I recommend reading Douglas Hofstadter's essay "The Genetic Code: Arbitrary?" which can be found in his book Metamagical Themas. (And note the initials of the essay's title.) But as to whether, even if the code could be changed, it could be changed in an existing living organism, I'd say that it is extremely unlikely with any foreseeable technology. (BTW, the story that sharks are immune to all diseases, or that they don't get cancer, is a myth mostly propagated by hucksters selling shark cartilage and similar useless nostrums. [17]) CodeTalker (talk) 03:43, 10 October 2017 (UTC)[reply]

No matter how you did it, the altered tRNA would be a different molecule with different interactions. Maybe nothing known, but the interactions would still be different in an unpredictable way. Also, with most versions of the scheme the GC content of the DNA would change, affecting its bulk properties (for example the amount of energy it takes to break it apart and replicate). You would have to look at whether the new sequence created new transcription factor binding sites anywhere in all that coding sequence. Worse, you'd destroy old ones that were supposed to work together in a complex regulatory network. (It is comparatively uncommon but certainly not unheard of to have such sites in the coding sequence; obviously there are evolutionary constraints to forming them, but you'd find evolutionary constraints to getting rid of them also). And debugging all those effects ... means making more changes to more things. So we're talking about evolution, and therefore, not really the same organism with the same characteristics. Nor would the altered organism seem likely to breed with the parent (not without some insanely advanced level of biological innovation) so this is not merely an evolutionary change but a different species. So I'm going to say no, under the usual caveat that biology could always come up with something I didn't think of. Wnt (talk) 12:07, 10 October 2017 (UTC)[reply]

• User:Count Iblis' suggestion is brilliant--the only problem is getting from here to there. How do you bridge the intermediate stage? But regarding the arbitrariness of the genetic code, I was gobsmacked when I saw the implication, and raised my hand to ask the professor, "Doesn't that mean the code is arbitrary?" He asked me to stay after class. It was like figuring out I was queer during mass, Chicxulub, and that the sky god doesn't exist. μηδείς (talk) 20:55, 10 October 2017 (UTC)[reply]

The only problem is that, well, this isn't really true. The genetic code we have is nearly optimal for allowing arbitrary basepair sequences (i.e. transcription factors) within protein coding sequence, which happens often, in part due to the presence of overlapping genes, but more so because gene enhancers can exist downstream of the promoter. Going over this bridge is therefore implausible. Furthermore, there is something akin to but different from Iblis' scheme involving CpG islands - they get methylated in humans, a password that viruses need to adapt to or suffer consequences for not knowing via TLR9. Wnt (talk) 21:27, 10 October 2017 (UTC)[reply]

October 10

What's the world's largest snake? VeenM64 (talk) 02:16, 10 October 2017 (UTC)[reply]

Heaviest: green anaconda. Longest: reticulated python. See list of largest snakes. StuRat (talk) 02:44, 10 October 2017 (UTC)[reply]

Ever: Titanoboa (extinct). 2606:A000:4C0C:E200:9C22:2C7C:65A6:B9DA (talk) 02:55, 10 October 2017 (UTC)[reply]

That's "known", 2606; not "ever". You need to learn about unknown unknowns. μηδείς (talk) 20:59, 10 October 2017 (UTC)[reply]

I am an unknown unknown. 2606:A000:4C0C:E200:852E:7393:15B7:B79E (talk) 03:24, 11 October 2017 (UTC)[reply]

Scientists started measuring the ouroborus in Ancient Egypt and still haven't finished. But yeah, that's cheating. Sort of. InedibleHulk (talk) 03:35, October 11, 2017 (UTC)

why electro cars have lithium battery not lead? Why gasoline cars have lead battery, not lithium? — Preceding unsigned comment added by 31.4.151.139 (talk) 18:21, 10 October 2017 (UTC)[reply]

Different applications mandate different solutions based upon need and price. A gasoline engine needs a battery for temporary powering of electrical components, and mostly for getting the gas engine started from cold. This does not require a high storage capacity. For that purpose, a lead battery is far cheaper than a comparable lithium ion battery. On the other hand, an electric car is powering its motors with the battery, and so needs a large capacity battery with lots of energy releasing over a long period of time. A lead battery capable of doing that would be extremely heavy, if even possible. A lithium ion battery, on the other hand, can provide a light weight, dense energy storage format. --OuroborosCobra (talk) 18:42, 10 October 2017 (UTC)[reply]

Cost. I have a rather high-end battery in my shooting brake. I replaced it about 6 months ago and the cost was $160. That is for a high-end battery. You can get a cheaper one for under $100. The lithium batteries are light, which is necessary for electric cars, but also very expensive. My brother has a Chevy Volt. When his battery was barely charging enough for a 10 minute drive, he had to replace it. A refurbished replacement was over $500 (I don't know exactly how much as he was embarrassed to tell me). So, as a car manufacturer, assume that there is a $400 difference in cost for a car part. You will pass that on to the consumer. Will a consumer pay $400 more for the car and then be willing to pay over $500 to replace the battery in the future? Probably not. You are better off using a lead-acid battery in the car. 209.149.113.5 (talk) 18:49, 10 October 2017 (UTC)[reply]

Lead: heaviest common metal. Lithium: lightest metal. When you just need protons to hold your electrons when you're not using them all those extra protons (2000x electron weight) holding electrons too tightly bound to be used and neutrons binding the protons just add weight. Downside is lithium is expensive. Not gold expensive but still much more then lead. Lead even requires more neutrons per proton to avoid being radioactive than lithium because the atom is so big (biggest non-radioactive atom) Sagittarian Milky Way (talk) 19:02, 10 October 2017 (UTC)[reply]

From our article on Energy density:

Specific energy in megajoules per kilogram (MJ/kg):

• Battery, Lead acid: 0.14 MJ/kg
• Battery, Lithium ion: 0.46-0.72 MJ/kg
• Gasoline (petrol): 46.4 MJ/kg

--Guy Macon (talk) 19:41, 10 October 2017 (UTC)[reply]

Caveat lector: you should divide the last line by 2-3 before comparing it with others, because that figure is the thermal energy you will get into the gases from the combustion of gasoline, but recovering mechanical work from that is hard. See [18] (though the drivetrain etc. losses are the same for an electric or gasoline engine, "engine losses" are close to zero for an electrical engine). Of course, fossil fuels are still a denser energy storage than battery (and much much much less than most things nuclear but the DeLorean time machine is not within current plans). Tigraan^{Click here to contact me} 19:54, 10 October 2017 (UTC)[reply]

Good point. A quick way to estimate engine efficiency is to look at how much waste heat an engine produces, counting the heat in the exhaust as well as the radiator. A 100% efficient engine would need no cooling. Electric motors get warm, but nothing like a gasoline engine. --Guy Macon (talk) 20:09, 10 October 2017 (UTC)[reply]

Still another nitpick: even with a "100% efficient engine" (no cooling required) you would lose some heat to the exhaust, because thermodynamics means you cannot save all the heat. The easy-to-memorize stat is that of three thirds of heat, you lose one third to thermodynamics (= exhaust), one third to the walls (= cooling), and you use one third (= mechanical work on the crankshaft). (Actually, how exactly thirdy the first third is can be easily computed with the compression ration of the engine - see [19] or Diesel_cycle#Maximum_thermal_efficiency.) (You probably know that, but readers may not.) Tigraan^{Click here to contact me} 20:33, 10 October 2017 (UTC)[reply]

I see that you assumed that by "engine efficiency" I was talking about engines with exhaust. I was mentally including electric motors, which are the engines in electric cars. Sorry for not being more clear. I do enjoy nitpicking though. You would be amazed at what some people think is fun. :)   --Guy Macon (talk) 20:54, 10 October 2017 (UTC)[reply]

A consumer Lithium-ion battery will not work well at temperatures below 0°C but a consumer Lead–acid battery works in a range from -40°C to +60°C. A Lithium iron phosphate battery can work at -20°C but it has only a slightly better energy density compared to lead-acid.

Beside this major restrictions on a use as main car battery, lithium-ion batteries will very likely cause fires when damaged, which multiplies the danger when there is also a fuel leakage near. So its a very bad idea to combine both. On top a standard 12V 35Ah lead battery can be bought for 50$. A similar 12V 35Ah li-ion-Pack will likely cost you more then 300$. Last not least li-ion batteries need a Battery management system to balance the cells and a special charger as well as some care, while lead-acid batteries are usually install and forget today. --Kharon (talk) 21:19, 10 October 2017 (UTC)[reply]

Are sulfuric acid spills dissolving, carbonizing, dehydrating and heating any organic matter it touches less bad than the fires? Also reacting very vigorously and exothermically with water and contaminating the area with toxic lead or lead compounds. Also less gasoline to catch on fire or explode. Sagittarian Milky Way (talk) 23:11, 10 October 2017 (UTC)[reply]

The sulfuric acid in a lead acid battery is not concentrated, so although it may dissolve concrete, not much is done to organic matter. A human would easily survive the lead and acid for a while, but could not tolerate fire. Graeme Bartlett (talk) 09:31, 11 October 2017 (UTC)[reply]

I've started my diesel car with a 12v lithium battery and run it on that battery for short journeys when the alternator wasn't working. There might have been risks if the alternator had been trying to charge it. Dbfirs 07:34, 11 October 2017 (UTC)[reply]

Notice that electro vehicles like Teslas still have lead-acid 12 v batteries.B8-tome (talk) 11:09, 11 October 2017 (UTC)[reply]

October 11

Our article soft error indicates that digital electronics' reliability is affected by cosmic rays, and increasingly so as the transistors grow smaller. Have any solid-state devices been built to specifically respond to cosmic-ray photons, so that noise in their interarrival times and/or landing positions (e.g. shot noise in the cosmic microwave background?) can be used as an entropy source for random-number generation (which I understand to be problematic in solid-state servers, absent the chaotic turbulence that a spinning hard drive induces or the human-induced jitter of local keyboard/mouse input)? NeonMerlin 04:41, 11 October 2017 (UTC)[reply]

It can be done, but if you are building your own it is a lot more convenient to use the americium-241 from a smoke detector as a source.

That being said, buying a bitbabbler white TRNG is a lot better and cheaper than anything you can build yourself. [ http://www.bitbabbler.org/ ]. --Guy Macon (talk) 05:55, 11 October 2017 (UTC)[reply]

• Premium Bond#ERNIE Andy Dingley (talk) 10:26, 11 October 2017 (UTC)[reply]

Is it possible, in theory, to reverse-engineer a TV set and use it to reconstruct the info transmitted via the TV signal if you have zero prior knowledge of TV technology, simply from the characteristics of the signal? For example, imagine that some space aliens want to learn as much as possible about Earth from the radio signals they intercept -- would it be possible for them, given enough brainpower, to reverse-engineer a TV receiver and start pirating Star Trek? 2601:646:8E01:7E0B:0:0:0:EA04 (talk) 10:01, 11 October 2017 (UTC)[reply]

Yes. If you look at an analogue TV signal (far easier) you will see that it has a broad structure which repeats several times a second (one frame). Within this, there is a second, finer, structure that also repeats (one line) Analog television#Structure_of_a_video_signal. Assuming that a society which understands analogue radio signals has also invented raster scanning, it's not a great leap for these aliens to assume that this is what they're seeing. The synchronisation pulses are fairly obvious and it's not hard to construct a device to reconstruct the signal into an image. A similar approach was made deliberately for the SETI transmissions from Arecibo: if you broadcast a signal that has patterns within it as two prime numbers, a numerate culture is likely to recognise this as "unnatural" and to try examining them as a two dimensional pattern.

Colour is harder, because that's a sub-modulation within the overall brightness signal. But, if they can work to its higher frequency, they're likely to observe that there is some sort of signal there. Most of the obvious forms of modulation work the same on most planets, so again, they're likely to recognise what was used.

Rather harder is the problem of rendering the signal into the same sensory experience. We have trichromacy and developed TV to suit. The aliens might not, or might not have the same colour sensitivities. It would be difficult for them to match our red-green-blue experience onto their infra-red, ultra-violet and gamma radiation sensory pods. Only if we shared some "Rosetta stone" for this, such as a photograph of a rose, which they also knew from their flying saucer landings here, would they have a key as to how the encoded signals mapped to their senses. Or perhaps they'd decode an Open University program and be able to recognise a chemistry experiment involving iodine and its distinctive purple colour. Andy Dingley (talk) 10:24, 11 October 2017 (UTC)[reply]

Discounting them visiting us, in which case they could just grab a TV, I can't see a pic of a rose working as a Rosetta Stone, unless they happen to have them growing there. Try pics of nearby supernova remnants, etc. StuRat (talk) 17:52, 11 October 2017 (UTC)[reply]

The question is very broad, but it breaks down into two sub-parts: (1) What technical details are needed to extract useful information about our technology? (2) How can we convey such details in a way that makes no assumption of prior knowledge about our technology, culture, language, biology, and so on?

This is a topic with a lot of history. Some important background reading is in order!

Our article on the Pioneer plaque links to Carl Sagan's 1972 publication, A Message from Earth, which discusses how an extra-terrestrial intelligence might be able to interpret our specially-crafted science and engineering diagrams. Our article on the Voyager Golden Record describes the coverplate, and links to the NASA summary of the diagrams. JPL maintains a website with more detail. Our article also links to more content and academic publications on the topic - there has been much written on whether a discoverer of these diagrams could meaningfully interpret them. The recurring theme is that we must reduce all the technical assumptions back to principles that are inherently deduced from fundamental properties of the universe. We can't assume that aliens know about steel, but we can expect them to know about magnetism; we can't expect aliens to know about transistors, but we can expect them to know about the field effect. We can't expect them to know about digitization, but we can expect them to know about entropy. We must reduce complex systems into a description that is referenced only to universal properties of energy, matter, and mathematical law.

It seems - to me - that an analog television from a few decades ago is easier to reverse-engineer than a modern digital television. An analog television has fewer parts; physical signals have simple mathematical correspondence to the information that they convey; and so on. Modern devices contain a lot more entropy and obfuscating pieces. Although it is difficult to make broadly-correct statements about the "reverse-engineering" capabilities of an alien intelligence, especially if we expand our thought-experiment to allow for technologies unimagined by Earth scientists, we can make a more restrictive claim: simple analog electronics and simple mechanical devices carry less entropy than elaborate microfabricated digital devices. Entropy, being a sort of universal constant, has some fascinating properties: on the one hand, it allows us to pack more information into a smaller volume - but perhaps a surprising consequence is that it makes our devices appear more random to an observer who has no prior understanding of our technology. High entropy entails statistical consequences: as entropy rises, it becomes exceedingly unlikely that a reverse-engineering effort can succeed, because it becomes statistically intractable to generate a correct mathematical model to deduce a device's physical inputs and outputs. This problem already exists today, with even the most simple electronic devices: the mathematics of the combinatorial explosion play out pretty unfavorably, when one must guess which voltage sequences to apply to a set of, say, 64 wires before all available energy in the entire universe runs down. This is, of course, assuming that the reverse-engineer knows what a "volt" is, and that it's something they need to apply to a "wire"!

Carried to the ultimate extreme, it is very conceivable that the "extra-terrestrial" discoverer of an ultra-modern microchip would not be able to provably distinguish it as a manufactured component created by intelligent human life. On inspection of its bulk physical properties, it looks very similar to an artifact of thermal noise or cosmogenic geology. A microchip might carry petabytes of digital data, plus a sophisticated digital circuit that (when appropriately powered and connected) can decode all that information into a useful format - and all this can fit into a package of mostly-silicon-dioxide-and-aluminum that is not much larger or more massive than any other granule of sand found floating in space as a chondritic asteroid. If an alien intelligence found it, they might not consider it likely to warrant study - not any more than the next granule of sand that impacts the alien spacecraft.

As our species progresses, and places more complexity in microscopic manifestations of high-entropy algorithms, it seems more and more implausible for anyone to reverse engineer. Even a skilled engineer with a laboratory full of equipment and detailed schematics can barely make sense of all parts of a modern VLSI device. And a human engineer knows how our stuff works, conceptually!

Broadly speaking, many SETI enthusiasts embrace the very plausible idea that this failure to recognize presents one of the more scientifically-grounded solutions to the Fermi paradox. In other words, it is conceivable that intelligent life fails to communicate with other intelligent life because advanced technology is indistinguishable from natural phenomena. We don't really expect to see an alien space-ship: it's much more likely that we'll see a dull infrared glow from a distant star. Reciprocally: we should not expect the space-aliens to ever find our televisions - let alone for them to study and reverse-engineer and operate them. In fact, we should not even expect them to receive our radio signals, let alone to interpret the information carried in them. The central half of Carl Sagan's book, Pale Blue Dot, outlines quantitatively and qualitatively why we cannot reasonably expect our radio or optical signatures to be meaningfully detected.

More likely, as much as it might be painfully nihilistic for us to admit, the only trace we shall leave on this universe is a faint metallicity signature in the solar spectrum of our sun. That spectral line would have been present in our Sun anyway, with or without the formation of planet Earth; with, or without, the development of a saline ocean suited for the evolution of the mammal; with, or without, the descent of humans toward the invention of the television and nuclear weaponry and moon rockets and fidget spinners.

If we are lucky, some intelligence elsewhere in our universe, distant from us in time and space, might evolve a way to look up at their sky and observe the color of one among zillions of little stars, and recognize that we might have existed, and created good televisions, maybe.

Nimur (talk) 16:16, 11 October 2017 (UTC)[reply]

One problem is that these aliens might have no concept of fiction, and not be able to even imagine why we would the broadcast "fake" information in Star Trek. They might interpret it as some type of military disinformation to scare off would-be attackers. StuRat (talk) 18:00, 11 October 2017 (UTC)[reply]

Galaxy Quest was not a documentary, I am sorry to let you know... --Jayron32 18:13, 11 October 2017 (UTC)[reply]

I didn't say that it was. Nonetheless, there's no basis to assume that aliens must always develop a penchant for telling fictional stories. StuRat (talk) 19:23, 11 October 2017 (UTC)[reply]

Or that they would understand the concept of "military". A good test are Dolphins/Whales and Octopuses[20]/Squid/Cuttlefish. They are highly intelligent and able to communicate with each other but we are not able to communicate with them. --Guy Macon (talk) 22:25, 11 October 2017 (UTC)[reply]

Group warfare is common in many communal species on Earth, such as army ants, where they have soldier ants, so that concept may be more common than the idea of telling fictional stories. We can communicate with many animals, such as trained dolphins and dogs, at least in a limited way. And it's quite possible that the vocalizations we don't understand as having any specific meaning really don't, they could just be an "I'm here and I claim this space" sound. If they repeat the same sound over and over, this makes it less likely to be some complex communication.

I believe there are examples of other species lying, such as a monkey species which will give a warning call to make others run for cover so it can eat their food, but this "crying wolf" isn't really the same as inventing an entire story. StuRat (talk) 22:37, 11 October 2017 (UTC)[reply]

Nimur - you remind me of the Fortress of Solitude scheme I had to store data in ice. If I recall "the most perfectly encoded signal is indistinguishable from noise" isn't actually Shannon's theorem but has something vaguely to do with it. Still, I'd think that whatever the entropy, eventually folks would get the notion to mount thrusters on a star, which is the kind of thing astronomers tend to notice. Wnt (talk) 19:11, 11 October 2017 (UTC)[reply]

I am pretty sure that the saying is "the most perfectly compressed signal is indistinguishable from noise". --Guy Macon (talk) 22:25, 11 October 2017 (UTC)[reply]