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November 13

Fine-structure constant as a reciprocal

It is customary to present the value of the fine-structure constant as a reciprocal, as in

\alpha \approx {\frac {1}{137.035999}}.

Do we know the historical origin of this custom? Is it due to Eddington's numerological obsession, or were estimates of its value already customary presented this way in 1928 when Eddington published the first version of his curious theory that $\alpha$ must be the reciprocal of a whole number? Is there another reason than tradition to keep presenting it this way? --Lambiam 07:17, 13 November 2022 (UTC)[reply]

See Fine-structure_constant#Numerological_explanations_and_multiverse_theory. Historically the fine structure constant was believed to be precisely 1/137 so quoting it as a decimal would reduce the precision.Polyamorph (talk) 08:13, 13 November 2022 (UTC)[reply]

The section does not reveal that Eddington first pronounced that

\alpha ={\tfrac {1}{136}}

exactly, before being forced in the face of more precise measurements to revise this to

\alpha ={\tfrac {1}{137}}.

again exactly, leading to the satirical magazine Punch calling him "Sir Arthur Adding-One". But was Eddington indeed the first to present the value in the form

\alpha ={\tfrac {1}{\cdots }}

? And since his theory obviously does not hold water, why hold on to this strange convention? --Lambiam 12:00, 13 November 2022 (UTC)[reply]

I'd just be speculating, but it does seem to me that 1/α is just as natural a quantity as α itself, and it's probably more intuitive for people to remember 1/α as "about 137" than to remember α as "about 0.0073", if for no other reason than you don't have to count zeroes. --Trovatore (talk) 19:30, 13 November 2022 (UTC)[reply]

If people will tolerate an anecdote — I was in Fleming Hovse; our rivals were Page House, whose denizens were called Page Boys. Being Caltech students, of course all of us were nerds by any reasonable standard, but the Fleming culture required that we avoid seeming like it. It was not cool to study ("snake") too much, or to show off one's knowledge ("blaze"); infractions would result in you being forcibly placed in the shower with your clothes on and the water turned on ("being washed").

Someone had started a tradition of waiting till 3:14 AM and yelling across the courtyard, "snake, Page Boys, it's pi o'clock!".

One time I waited till 1:37 and yelled "snake, Page Boys, it's 1/α o'clock!"

Yes, I did get washed. But it was with appreciation. --Trovatore (talk) 20:03, 13 November 2022 (UTC) [reply]

I am both relieved and saddened that I never had the opportunity to enjoy the unique and vibrant student life at CalTech... thank you for sharing! Nimur (talk) 16:12, 14 November 2022 (UTC)[reply]

Most likely because it's an easy to remember ratio, similar to pi, which is also a ratio (approximately 3:1, 3.14:1, ... ad infinitum). Specifically, it's the ratio of the velocity of the electron in the first circular orbit of the Bohr model of the atom to the speed of light in vacuum; or

v_{\mathrm {e} }=\alpha c

. Modocc (talk) 19:54, 13 November 2022 (UTC)[reply]

Not really an answer, but see "Why Is 1/137 One of the Greatest Unsolved Problems In Physics?" PBS Space Time youtube. Johnuniq (talk) 00:50, 15 November 2022 (UTC)[reply]

Which animal species is the most energy efficient?

By efficiency, I mean how much of the energy consumed is converted into useful work. IIRC, humans are only 25% efficient in that regard. Also, if there is an article on here providing the information, please say so. StellarHalo (talk) 09:45, 13 November 2022 (UTC)[reply]

Something like feed conversion ratio? You can rest assured that we have not checked all animal species for this. (By the way, "controlling for body size, primates burn about 50 percent fewer calories than other animals", and humans eat way fewer calories than chimps.) Abductive (reasoning) 11:06, 13 November 2022 (UTC)[reply]

And how much of the energy consumed is converted into useless work? For humans perhaps more than 25% --Lambiam 12:03, 13 November 2022 (UTC)[reply]

Define "useful work". Everything the metabolism does serves a purpose Cambalachero (talk) 13:48, 13 November 2022 (UTC)[reply]

The metabolism converts energy packed in nutrition to energy stored in the body. While the conversion efficiency is not 100%, the loss is not work in the sense of physics. --Lambiam 17:50, 13 November 2022 (UTC)[reply]

The ratio depends on whether someone does useful work. A pencil pusher hardly needs to produce work in the physics sense, so the percentage will be much lower than for a person performing full days of heavy manual work. It also depends on whether you only consider work output that is paid for, or work that is necessary to be able to work, such as getting to and from work. Our article Human power states: "Over an 8-hour work shift, an average, healthy, well-fed and motivated manual laborer may sustain an output of around 75 watts of power." That amounts to 0.6 kWh, or about 1,000 kJ per day.

The recommended daily intake for a male adult with a desk job is about 10,000 kJ, that for a manual worker more like 14,000 kJ. That suggests that about 4,000 kJ nutritional intake is converted to some 1,000 kJ of work output. If you consider only this, you get a ratio of 25%. But there is also the other 10,000 kJ, which goes mostly to basal metabolism, to maintain homeostasis. So taking all into consideration, some 14,000 kJ of intake produces 1,000 kJ of (paid) work. If you include unpaid but necessary work, the latter number goes up by an estimated 200 kJ per day, giving a conversion efficiency of about 9%.

By using other definitions of "useful" work you can probably get wildly different answers than given by this back-of-the-envelope calculation. --Lambiam 18:53, 13 November 2022 (UTC)[reply]

The size of the animal is also important. The internal activity the body uses just to stay alive is much higher in small animals than in big ones. Humans are not as big as elephants or whales, but overall they are closer to the big animals than to the small ones. Check this video Cambalachero (talk) 23:04, 13 November 2022 (UTC)[reply]

Extension cord

I have an old German extension cord that has "10-16/250" written in one of the sockets. I'm guessing 250 means 250 V. Does 10-16 stand for amperes? Wondering if I can plug in a 2000 W radiator in it. 31.217.13.249 (talk) 14:12, 13 November 2022 (UTC)[reply]

Did you try calling an electrician? ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:36, 13 November 2022 (UTC)[reply]

The same question has been posed on many websites. The consensus among responders is that the values 10–16 refer to amperes and the 250 to voltage. The opinions differ on the meaning of 10A–16A. One theory is that 10A is the maximal current for DC and 16A for AC. Another theory is that 10A is the maximal continuous load, while 16A is for shorter use. In either case, it should be safe for up to 2500W. You can check by hand now and then whether the socket or plug heats up to an uncomfortable temperature during an extended period of use. If they are still fine after fifteen minutes, you may assume that they won't get much hotter. --Lambiam 17:06, 13 November 2022 (UTC)[reply]

Thanks! 31.217.50.28 (talk) 19:44, 13 November 2022 (UTC)[reply]

One clarification: We are talking about electricity at European voltage of around 230 V, right? Otherwise the plugs would presumably be wrong. But a 2000 W appliance on North America's 120 V would require about 16 A, so I thought I should confirm that that's not what you want. --174.89.144.126 (talk) 04:41, 14 November 2022 (UTC)[reply]

Do not rely on a "hot-touch-test" to determine if a wire is safe to use. Such a test will tell you more about the thermal properties of the insulation casing than about the temperature. (Here’s a semi-famous video of someone holding a hot-enough-to-be-glowing-yellow piece of insulating material with bare hands.) Furthermore, if the wire was in fact hot enough to get damaged, there is a risk of shock. Lambiam, that was not good advice. Tigraan^{Click here for my talk page ("private" contact)} 10:30, 16 November 2022 (UTC)[reply]

Assuming a 230V supply voltage (the standard in most of the EU, including Croatia), a 2000W appliance implies a current of 8.7A and a 2500W appliance a current of 10.9A. Generally, the specs of extension cords are well below 90% of what is actually safe. Even without safety margin, the time before a wire carrying a current below 110% of what is safe gets so hot as to potentially cause skin burns is considerable; if it can radiate some heat it may never get there. The advice was to apply the test for hotness occasionally up to 15 minutes after making the connection. Moreover, the advice was not to touch a wire, but a (less thermally compromised) socket or plug, such as one commonly would touch anyway when breaking the connection. --Lambiam 12:10, 16 November 2022 (UTC)[reply]

A medium-duty extension cord might be rated for 10 amps with 16AWG wire. Amperage ratings vary with wire size and cord length(s), and for various reasons manufacturers of space heaters warn against using extension cords. Modocc (talk) 18:36, 13 November 2022 (UTC)[reply]

"an old German extension cord" may indicate that the AWG system (American Wire Gauge) might not have been the standard used to make this cord. Also, even though 10A through that extension cord might be safe, the longer the extension cord, the more losses you have within it. Perhaps it's irrelevant for a heater, but some appliances will run less efficiently at a lower voltage. Dhrm77 (talk) 21:08, 14 November 2022 (UTC)[reply]

That's correct. :) It also seems very unlikely to have been given two amp ratings because if it is heavy enough to handle 16 amps it can handle less assuming AC outlet standards. But see below. Modocc (talk) 22:12, 14 November 2022 (UTC)[reply]

I typed the search string "10/16 250" in an online search and the first (and almost only) result was a manufacturer’s website. The technical datasheet says Thermal current: 10/16 A. So it’s definitely a current rating, but why there are two ratings I could not find out for sure even with the additional keyword of "thermal current". I suspect it’s a German standard thing but I do not have the linguistic ability to search for more.

Possibilities include:

As written above: continuous vs. peak use. For instance things like motors can draw a large amount of current for one second or so during startup.
Similar but slightly different: during unplugging vs. during use: you can draw power through the cable at some high current but you must decrease the current to safely unplug.
A power factor thing to correct for inductive load issues (but then it’s not clear to me why they chose a 10/16 = 62.5% power factor reference; the power factor can vary a lot depending on the appliance etc.).

Tigraan^{Click here for my talk page ("private" contact)} 10:30, 16 November 2022 (UTC)[reply]

The numbers seem to refer primarily to the plugs/sockets of the Schuko type. The German article has links to the relevant DIN ~~norms~~ standards (refs 16 and 17). While the ~~norms~~ standards themselves have to be paid for, the title indicates that 10A is indeed for DC and 16A for AC. --Wrongfilter (talk) 11:24, 16 November 2022 (UTC)[reply]

Vaccines and autism: My autistic family

When I got my 18-month-old vaccine, I stopped talking until I was almost four. My tests reveal that I have a 79% chance of autism. And my mom's Godmother said that she behaved very similarly after hers. And hers was always not liking people and being extremely introverted. And her tests revealed that she has an 89% chance of autism. If vaccines don't cause autism, why did my family act suddenly autistic after their vaccines? 67.215.28.226 (talk) 16:47, 13 November 2022 (UTC)[reply]

See notes at top of page:

We don't answer (and may remove) questions that require medical diagnosis or legal advice.

We don't answer requests for opinions, predictions or debate.

The causes of autism are to an extent unclear: there is clearly a hereditary element, but environmental factors may also come into play. Evidence that vaccination is one such factor is however lacking, despite the repeated claims to the contrary. Anecdotes about individuals don't prove anything. Science is based on data. AndyTheGrump (talk)

You might also find the article correlation does not imply causation interesting. Writ Keeper ⚇♔ 18:14, 13 November 2022 (UTC)[reply]

Then why did I suddenly stop talking almost immediately after I got my shot? It's 100% true! 67.215.28.226 (talk) 18:27, 13 November 2022 (UTC)[reply]

See Writ Keeper's reply. – dudhhr^talk _contribs (he/they) 18:38, 13 November 2022 (UTC)[reply]

You might need to clarify that statement. I have met someone who spent most of his childhood not talking, by choice. In your case, was it a choice? Or an inability to talk? Or was it a sense that you didn't need to say anything? Or were you in some kind of vegetative state? How do you recall that period? (not that I would be able to explain why, but I'm curious about the reasons too, and clarifying might help.) Dhrm77 (talk) 20:43, 14 November 2022 (UTC)[reply]

Awesome. Thanks. 67.215.28.226 (talk) 18:46, 13 November 2022 (UTC)[reply]

The median age of onset of speech loss in what is called autistic regression has been reported to be 18 months.^[1] That means that for about half of the infants undergoing this, it happens before they reach 18 months, and for about the other half when they have reached that age or later. Obviously, if children undergo some procedure when they are 18 months, among those experiencing speech loss this will occur for about half after that procedure, possibly shortly after – irrespective of the nature of the procedure. --Lambiam 19:19, 13 November 2022 (UTC)[reply]

It's tragic, really, that people want to find a reason, other than bad luck, for their children's autism, and that unscrupulous shysters will tell them it's vaccines or overhead electric lines in order to part them from their money. Abductive (reasoning) 19:38, 13 November 2022 (UTC)[reply]

We can probably think of a few celebrities who've fallen for that scam. Meanwhile, I'm reminded of an old story about a child who wouldn't talk. One day at mealtime, the kid suddenly said, "Pass the salt, please." The surprised parents asked him what took him so long to start talking. He said, "Well, until now, everything was OK!" ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:19, 13 November 2022 (UTC)[reply]

That's the eponymous origin of the name Einstein syndrome. DMacks (talk) 00:57, 14 November 2022 (UTC)[reply]

Very soon after receiving my polio shot outside in the schoolyard back in the 1950s (it was a nice sunny day), I broke my collarbone in that very same schoolyard. Therefore vaccines cause collarbones to break. And The Lack of Pirates Is Causing Global Warming. HiLo48 (talk) 02:08, 14 November 2022 (UTC)[reply]

Have those Somali pirates been goofing off again? Aaaarrrrrggggghhhh! Clarityfiend (talk) 06:17, 14 November 2022 (UTC)[reply]