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June 12

Century years (June 4)

• Transferred from Miscellaneous desk as this appears to be an astronomical question

The relevant Tabor lecture appears to be this one [1]. The arguments appear to have been adequately answered in the response to the second of 90.221's posts of 19:16, 7 June 2023. 80.47.0.234 (talk) 12:57, 12 June 2023 (UTC)

I don't see a question. The earlier discussion is archived here.  --Lambiam 06:19, 13 June 2023 (UTC)

The archive is not complete. My comment below was drafted on the assumption it was complete (the missing comments precede it):

It's a matter of convenience. When King's Cross station was redesigned some years ago, rather than engage in wholesale renumbering, a platform zero was added. Another oddity is platform 9 3/4 for Harry Potter fans and no, Queen Boadicea is not buried under platform 9 [2]. Similar to people's ages, in India (and some other countries), "elapsed" years are used, i.e. the epoch is the start of year 0. The idea is taken up in Astronomical year numbering, where the series goes -2 (3 BC), -1 (2 BC), 0 (1 BC), (+) 1 (1 AD), (+) 2 (2 AD), and so on. 2A02:C7C:38C1:3600:ACCF:3F82:63F1:1958 (talk) 10:29, 5 June 2023 (UTC)

Fairly obviously, the reference to "1 January 4,317 BCE" should be "1 January, 4713." That noon starting time for the day (which astronomers observed until 1924) was designed to avoid a date change during observation. From 1925 they began using the normal civil day, beginning at midnight, but to avoid ambiguity they dropped the name "Greenwich Mean Time" (except when addressing the general public), replacing it with "Universal Time."

I don't have access to the lectures by James Tabor, but irrespective of his claims the only ambiguity is whether Christ was crucified on 14 or 15 Nisan. There has never been any doubt about the day of the week. Thus the term parasceve as I understand it (and I'm not an expert on Jewish holy days) would refer to Friday, 15 Nisan (commencing Thursday evening), the first day of Passover, which is an eight-day festival ending on 22 Nisan. The Last Supper took place that Thursday evening (Maundy Thursday) and Christ was crucified the following day. Alternatively, the parasceve was the preparation for both the weekly Saturday sabbath and the first day of Passover, if the two holy days coincided that year. In this scenario, Christ was not crucified on a holy day.

Whatever, Matthew 27⁶² refers to the crucifixion having happened on "the day of the preparation" and the order going out for the tomb to be secured "until the third day." This was made on the Saturday sabbath (Matthew 28¹) and on the first day of the week (Sunday) the women witnessed the empty tomb. The remaining Gospels tell a similar story. Another example is the "Today in history" feature in this morning's newspaper. The first item is

* 632: Muhammad, founder of the Islamic religion, died in Mecca.

There are conflicting reports of the Islamic date (unlike ours, Islamic dates are fluid and the day of the week is needed to fix a date exactly) but the day of the week was Monday, which fixes the event without ambiguity to 8 June 632.92.28.112.82 (talk) 11:36, 8 June 2023 (UTC)

A similar situation arose at the very beginning of the Julian calendar. In astronomical year numbering the first year (45 BC) is -44. Being exactly divisible by four, some people cannot be shaken from the conviction that it was a leap year. Never mind that until comparatively recently before then the year began in March (which is why "December" was the tenth month). Macrobius spelt it out: owing to confusion caused by the inclusive numbering system the first leap day was added at the beginning of the "fourth year [February 42 BC] instead of at its end" (February 41 BC). It took decades to sort out the mess, and the first of the regular series of leap years at four-year intervals wasn't until AD 8. The Egyptians managed to operate the Julian calendar correctly from inception, as they did with the indigenous version of it, the Alexandrian calendar. 92.10.149.249 (talk) 11:15, 9 June 2023 (UTC)

While I was setting up the indents I was being continually chided by Microsoft:

It's better to have no space before this punctuation...One punctuation mark is all that's needed...A space should follow most punctuation...A space usually comes before this type of punctuation...You may have forgotten a punctuation mark

Remember that animated paper clip that used to appear with a speech bubble saying "Looks like you're writing a letter"?

We do actually know which day of the week 15 Nisan fell that year. The "counting of the Omer" begins on the day after Passover and it lasts for 50 days (counting inclusively), meaning that it ends on the same day of the week as that on which it began. It begins on 16 Nisan and ends on 6 Iyar (Pentecost). The Bible tells us that Pentecost was a Sunday that year, so the first day of Passover was necessarily a Saturday. However, in the original Greek, Matthew 28 opens with the words "In the end of the sabbaths [plural], as it began to dawn toward the first day of the week, came Mary Magdalene and the other Mary to see the sepulchre." Various theories to explain the discrepancy have been put forward. Leviticus 23 says Pentecost should always be a Sunday, but that is not observed.

Luke 23⁵⁴ says the day of the crucifixion "was the preparation, and the sabbath drew on." In verse 56, the women "returned, and prepared spices and ointments; and rested the sabbath day, according to the commandment."

The very next day, according to chapter 24, was "the first day of the week", leaving no doubt that the crucifixion happened on a Friday. The Last Supper, described in Matthew 26, Mark 14 and Luke 22, was some kind of Passover meal, but there is no agreement as to its exact nature. John 13 describes the supper as happening "before the feast of the passover."

Matthew 27 recounts that on the day after the crucifixion, which "followed the day of the preparation," the chief priests and Pharisees asked Pilate "that the sepulchre be made sure until the third day, lest his disciples come by night, and steal him away." So the crucial night was again that Saturday night, leading into Sunday morning. Mark 15 says that after the crucifixion, "when the even was come, because it was the preparation, that is, the day before the sabbath," Joseph of Arimathaea went to Pilate.

In Mark 16 the women wait for the sabbath to pass before going to the tomb. John 19³¹ notes that the day of the crucifixion "was the preparation," and the next day was "the sabbath day," and "that sabbath day was an high day," clearly marking out 15 Nisan as Saturday. John 19⁴² notes that because of this "preparation day" Jesus was laid in the tomb, where He remained throughout the sabbath, and then on the Sunday morning (John 20¹) Mary Magdalene found the tomb empty. 92.28.112.115 (talk) 17:13, 17 June 2023 (UTC)

Has anyone ever come up with a plausible explanation for how Pokeballs could work in the real world?

Question as topic. Just for fun. I know there have been people written about how one might plausibly make a light saber or how a Star Trek phaser might work. Iloveparrots (talk) 15:02, 12 June 2023 (UTC)

• HOW WOULD A POKEMON POKEBALL WORK IN REAL LIFE?. Alansplodge (talk) 17:39, 12 June 2023 (UTC)

What about that inconvenient complication known as the Heisenberg uncertainty principle??? 2601:646:9882:46E0:6998:C31A:9514:BAA4 (talk) 02:23, 13 June 2023 (UTC)

So for the moment I think your best bet is to use VR goggles. On a quick search I see there is a game PokeQuest VR being developed. NadVolum (talk) 20:03, 12 June 2023 (UTC)

June 13

Edgware Road

So, let's say an outer rail service is just coming in from Kensington and will terminate at Edgware Road -- will it (normally) stop on Track 1 or Track 3? If on Track 1, then how will it reverse without disrupting other outer rail trains coming in from Hammersmith (especially since, according to a (possibly outdated) schedule, there's one coming in from Hammersmith and going on toward King's Cross just 1 minute after the terminating service from Kensington)? Also, once the train reverses and goes around the inner rail, after it comes in from King's Cross, will it (normally) stop on Track 3 or Track 4 before continuing to Hammersmith? And last but not least, if I remember the layout of the Praed Street junction rightly, trains departing for Hammersmith from Track 4 must cross over both the Kensington-bound track of the Circle Line (which becomes Track 3 in the station) and the District Line track (Track 2) -- how do they avoid delays due to this? 2601:646:9882:46E0:6998:C31A:9514:BAA4 (talk) 02:53, 13 June 2023 (UTC)

Courtesy link: Edgware Road tube station (Circle, District and Hammersmith & City lines). --142.112.221.43 (talk) 03:23, 13 June 2023 (UTC)

This is a big problem for the tube trains, you can't have two going in different directions along the same tube - they have to be disassembled at the end of the line and transported back by lorry ;-) Sorry having looked at it I don't know. NadVolum (talk) 08:54, 13 June 2023 (UTC)

Surely you can just run it up an escalator? ;-) Alansplodge (talk) 15:18, 13 June 2023 (UTC)

I'm not locally familiar, but I found this map. Apparently, trains leaving westbound from track 1 can't move to the left-hand track. All London Underground trains run on the left (a few exceptions involve grade-separated crossings), so trains terminating at Edgeware road and returning to Kensington must use tracks 2 and 3. I assume one is for District line trains, the other for Circle line trains. A train leaving for Kensington from track 2 or 3 doesn't interfere with trains coming in from Hammersmith on track 1.

Assuming tracks 2 and 3 are for trains for Kensington, it makes most sense if trains for Hammersmith use track 4. The line from Edgeware Road to Praed Street junction appears to be simply double track, so all trains leaving westbound have to be merged onto one track. A bigger problem is that trains for Hammersmith have to weave through those from Kensington.

It looks like the track layout at Edgeware Road was designed such that any one of the tracks can be taken out of service without blocking any of the routes served, although capacity would be reduced. PiusImpavidus (talk) 09:09, 13 June 2023 (UTC)

I was on Edgware Road station on Sunday, when there was no service between Edgware Road and Hammersmith. Trains coming from the east would cross to platform 1 where they would dwell before setting off eastwards again. The signage is "platform 1 eastbound". I've never known trains going east leave from any other platform - it's difficult to see how they could because platforms 2 and 3 are for Circle and District line trains completing their journey having passed through Paddington (that's the Praed Street station - there's another one near Bishop's Bridge Road for trains going to and from Hammersmith). When these trains leave they go back the way they came. If you're going Paddington (Bishop's Bridge Road) and stations to Hammersmith platform 4 is the place for you. 2A00:23C6:2417:3101:CD7D:9961:DB38:71A (talk) 11:28, 13 June 2023 (UTC)

Track layout map here. Alansplodge (talk) 15:18, 13 June 2023 (UTC)

I forwarded the original query to Clive Feather, who answered as follows. (I haven't compared his answers to the ones above.)

So, let's say an outer rail service is just coming in from Kensington and will terminate at Edgware Road -- will it (normally) stop on Track 1 or Track 3?

It will use platform 2, though it could in principle use platform 3.

The normal platform use is:

1. Trains towards Baker Street
2. Circle trains from Kensington terminating and returning to Kensington
3. District trains from Kensington terminating and returning to Kensington
4. Trains directly towards Hammersmith

If on Track 1, then how will it reverse without disrupting other outer rail trains coming in from Hammersmith...

There is no practical way for it to reverse in platform 1.

In principle a train could shunt forward into the running tunnels, then back into platform 2 or 3, but that would be incredibly disruptive.

Also, once the train reverses and goes around the inner rail, after it comes in from King's Cross, will it (normally) stop on Track 3 or Track 4 before continuing to Hammersmith?

It will normally use platform 4, though it could use platform 3 if there is disruption.

...trains departing for Hammersmith from Track 4 must cross over both the Kensington-bound track of the Circle Line (which becomes Track 3 in the station) and the District Line track (Track 2)

No, that's not how it works.

The four platform tracks converge into two tracks just west of the station. The outer rail connects to platforms 1 to 3; the inner rail to platforms 2 to 4. This is done by a scissors crossover between the platform 2 and 3 tracks immediately west of the station, then 1 & 2 merging and 3 & 4 merging west of that.

Then, a short distance further west, there is a simple double junction and westbound Hammersmith trains will cross over the outer rail from Kensington.

So the platform 4 track doesn't "cross" either the platform 3 or 2 tracks. Rather, the three converge into one before splitting into Hammersmith and Kensington options. Similarly, eastbound, the two lines merge into one before splitting into platform 1, 2, and 3 tracks.

how do they avoid delays due to this?

Careful timetabling.

(Clive's answers posted with his permission.) --142.112.221.43 (talk) 16:06, 13 June 2023 (UTC)

Which all matches with the track layout map linked above. PiusImpavidus (talk) 18:01, 13 June 2023 (UTC)

Just a note that the map was linked twice, at 09:09 and 15:18 yesterday. The second link has a zoom button but the first link is already enlarged. 2A00:23C6:2417:3101:DC52:6F3C:C31E:314A (talk) 14:02, 14 June 2023 (UTC)

Thanks, everyone! This pretty much answers most of my questions, except the last one -- the thing is, the circle portion of the line in either direction is scheduled for exactly 59 minutes (although, assuming no delays, it might take as little as 56, but then the train has to stay in the station until scheduled departure time) -- so, under the best circumstances, you'll have an outbound inner rail service departing for Kensington just 1 minute behind another one departing for Hammersmith (and going the other way, you'll likewise have a Baker Street-bound outer rail service coming in from Hammersmith just 1 minute behind a terminating service coming in from Kensington! And there's also the H&C shuttle service to consider (I'm not quite sure of the times, but it would have to reverse on the same Track 4 which will also have to be used by the inner rail service coming in from Baker Street and heading for Hammersmith), as well as the District Line trains -- so, with all this in mind, I still have to wonder how the dispatcher can juggle all these without them becoming a royal mess (and how much aspirin does the dispatcher have to consume to deal with the resulting headaches)? 2601:646:9882:46E0:A55D:ACD1:411:3D8F (talk) 11:07, 17 June 2023 (UTC)

Just rechecked the (possibly outdated) timetable I have, and gasped in disbelief -- all these movements are (or at least were) scheduled to happen simultaneously, within 2 minutes! For a snapshot, let's take 8:29 AM on a weekday -- at that time (and not even considering the District Line trains), the following movements are (or at least were) supposed to happen: inner rail service arrive from King's Cross St. Pancras/depart toward Hammersmith (8:28); inner rail service depart toward Kensington; terminating outer rail service arrive from Kensington; H&C shuttle depart toward Hammersmith; terminating H&C shuttle arrive from Hammersmith; and outer rail service arrive from Hammersmith/depart toward Kings Cross St. Pancras (8:30). So we have six (or even eight, depending on how you count) movements on three tracks within no more than two minutes -- how is it even possible? 2601:646:9882:46E0:FDCB:9371:5931:CCD4 (talk) 03:49, 18 June 2023 (UTC)

At all junctions controlled by signals it's a matter of waiting your turn. At Leytonstone the two eastbound lines diverge and the two westbound lines converge. Controllers make it as easy as possible for passengers. All trains dwell for a minute or so and the driver of an eastbound service always announces the name of the next station. The signal turns green, the driver closes the doors, and off she goes. The westbound indicator board has an arrow pointing to the platform number of the next train out, and there's a similar facility at Hammersmith. At any station inbound trains may have to wait outside for their platform to become free. There may be a potential conflicting movement at Edgware Road every two minutes or less, but for any track layout points and signalling are electronically controlled to make it impossible to set up a conflicting movement. In earlier times projections on the levers served the same purpose mechanically. This is all very laid back compared to a busy road junction where there may be potentially conflicting movements every two seconds. Traffic lights also handle filtering, late start, early cutoff and an "all-red" phase to allow pedestrians to cross. Many years ago at the busy Balls Pond Road/Kingsland Road junction in Dalston a diagonal crossing was introduced, which may still be operational. Sensors embedded in the road surface send information to computers which control the traffic light sequence to maximise traffic flow, often over a very wide area. There are numerous level crossings - the biggest danger there is people zigzagging through the barriers.

Of what can be controlled by the transportation authority, timetablers have to deal with fast trains, slow trains, freight trains and single-track sections (the only example of single-tracking in London is the Romford-Upminster line). The line to and from Liverpool Street is very busy - trains ex Liverpool Street bound for Barking have to cross the line between Forest Gate and Manor Park. When the "jazz train" service was introduced on the West Anglia lines in the 1920s it was so popular that minimising the turnaround time at Liverpool Street became a fine art. Freight trains can be as long as half the distance to the next station. At Canonbury at six o'clock on Friday morning four freight trains passed through within five minutes, along with numerous empty passenger trains positioning themselves to enter service.

Railway planning is a ponderous process. The new East London line, which eventually saw the reopening of Dalston Junction and a new station at Dalston Kingsland (thanks to the efforts of traders at Ridley Road Market - the original plan was to demolish part of the market to build the new station) was delayed for years because a trader at Petticoat Lane market had noticed that if construction does not begin within the time allowed by the grant of planning permission the whole planning process has to be begun again from scratch. There is also the political aspect - Margaret Thatcher had to choose between the east-west crossrail (Elizabeth Line) and the north-south route (Hackney to Chelsea line). She chose the former because "nobody I know lives in Hackney." I don't recognise the "H&C shuttle". Platform 4 is for westbound trains - running a train from Hammersmith in there would be suicidal. 2A00:23C3:FB81:A501:906F:D525:FEB8:5529 (talk) 13:38, 18 June 2023 (UTC)

Don't some trains from Hammersmith short-turn at Edgware Road and go back the way they came, instead of continuing on the outer rail of the Circle Line proper? If so, that's your "H&C shuttle" for you -- sorry for the non-standard terminology (that's what New Yorkers would have called such a service, at any rate)! So, this one also uses Track 3 to reverse, just like the full Circle Line trains? And once again, given the fact that reversing a subway train probably takes more than just 1 minute, how do they handle the various terminating services at this station so they don't delay each other or the through services (or vice versa)? 2601:646:9882:46E0:7D3B:73DF:F255:8C8D (talk) 07:47, 19 June 2023 (UTC)

Are the most recent artifactual definitions of kg and meter still made of the best kg/meterstick substance known to man?

Well best to be the one national kilograms and metersticks aim for. Sagittarian Milky Way (talk) 03:55, 13 June 2023 (UTC)

The current definitions are not artifactual. The most recent artifactual definition of the kilogram is embodied in Le Grand K, manufactured in 1879. It was fashioned of a 90% platinum and 10% iridium alloy. The same alloy was used for the most recent artifactual definition of the metre, the International Prototype Metre, manufactured between 1886 and 1899. I don't know how to compare it with potential other substances (92% adamantium and 8% unobtanium?) for goodness. A search for "meterstick substance" did not turn up promising results.  --Lambiam 06:09, 13 June 2023 (UTC)

I know the kg and meter are no longer the mass and length of physical objects by definition. I was wondering if they'd still use platinum with about 10% iridium if the objects were being built today or if they've realized something better is possible some time in the last 124+ years. Maybe some other platinum-group metal alloy? Or a 1 kilogram diamond? (it would have to be artificial as the largest uncut natural diamond ever was only a pound and a third). Would the kilo be spherical instead of cylinderical to minimize surface area? ~~~~ Sagittarian Milky Way (talk) 17:04, 13 June 2023 (UTC)

If you define what the properties are you want to optimize for, the question might, perhaps, become answerable or at least researchable. (: Obviously, clay is better, as it is a hell of a lot cheaper. :)  --Lambiam 20:39, 13 June 2023 (UTC)

Not clay but close to it ;-) See Sphere Made to Redefine Kilogram Has Purest Silicon Ever Created. Personally I'd prefer a kilogram sphere of pure carbon with a cubic crystal structure! NadVolum (talk) 10:05, 16 June 2023 (UTC)

The purpose of manufacturing that sphere, however, was never to have an improved prototype (to serve as an artifactual definition), but to have an object of a pure material whose mass conformed as precisely as could be measured to the then (and last) International Prototype, constructed in such a way that scientists could calculate the number of atoms. The point of the effort was that this would make it possible to get a more precise experimental determination of the value of the Planck constant to be used in its upcoming redefinition as a fixed constant. The choice of material served the aim of being able to calculate the the number of atoms. If the purpose of manufacturing a new object had been for it to serve as an improved IPK, there is no reason to think silicon would have been the preferred choice. See also Alternative approaches to redefining the kilogram.  --Lambiam 08:55, 17 June 2023 (UTC)

Double Slit Experiment.

As we know, multiple single photons can be fired through 2 slits to form interference patterns as can electrons and small particles.

I believe there is no explanation for this - it is merely observed.

Has anyone ever suggested that a diffraction contour pattern is obviously formed on either side of the slits by the multitude of photons in a given room, all of whom diffract as we see from single photon diffraction? And thus, their energy/momentum can be imparted to electrons and small particles, thus creating the illusion that the particles themselves are diffracting? Byron Forbes (talk) 16:58, 13 June 2023 (UTC)

I don't follow what you're saying but the diffraction pattern is formed exactly the same even if the light intensity is so low that only a single photon at most will be in the experiment at a time. SO multitudes has nothing to do with it. NadVolum (talk) 17:07, 13 June 2023 (UTC)

Clarification: every single photon hits one and only one point. However, if you test photon by photon the pattern will emerge, as more photons will hit where the wave function superposition is positive, and vice versa.

Also, it's not exactly true to say that it is not explained. The Copenhagen interpretation is that the wave function collapses upon measurement (though what consists a measurement is not well defined), and the pilot wave interpretation explains it as the probability the wave function that directs the photon is more likely to lead it to certain areas and less to others.

Zarnivop (talk) 17:48, 13 June 2023 (UTC)

No physicist has suggested this, because it does not make sense.  --Lambiam 20:34, 13 June 2023 (UTC)

What part of it makes no sense to you? It is very simple stuff. Byron Forbes (talk) 17:45, 14 June 2023 (UTC)

None of it makes sense after the first sentence.  --Lambiam 22:23, 14 June 2023 (UTC)

LOL - what's so hard to understand about the multitude of photons in a given room, and on either side of a slit, forming a diffraction contour pattern on either side of the slit? Byron Forbes (talk) 11:36, 15 June 2023 (UTC)

All of it. You cannot expect random photons within a given space will have their waves interact to form constructive and destructive interference patterns that are orderly as it does in the double slit experiment. The frequencies of the waves will similarly be random, as will their directions, as will their phases. None of this will result in the orderly interference patterns of the double slit experiment. Also, where do you think these other photons in the room are coming from? --OuroborosCobra (talk) 13:02, 15 June 2023 (UTC)

Let me just have a laugh at your last sentence because you seemed to understand that from the rest of your post. Are you asking me where photons come from generally? :)

Anyway, it has nothing to do with fancy and discrete patterns on a wall - it is to do with the fact that every photon going through a slit will diffract, thus forming a diffraction contour pattern.

This pattern is not on a wall - it is a naturally occurring thing in the space on either side of the slit. Byron Forbes (talk) 14:56, 15 June 2023 (UTC)

Every photon in the room passing through the slits will continue following a probability distribution set by an interference pattern, but as all those photons have different wavelength and direction, all those interference patterns are different, so the photons as a group don't produce a useful interference pattern. PiusImpavidus (talk) 15:25, 15 June 2023 (UTC)

All of you are missing the very simple point here.

This is nothing to do with a diffraction "pattern" photographed on a wall.

It is the general diffraction contours made by the multitude of diffracted photons as they exit the slit.

So, for example, when an electron goes through a slit, if it is a little left of centre of the slit then it would generally be deflected left by the collisions it has with the photons that are travelling left due to diffraction. Byron Forbes (talk) 17:21, 15 June 2023 (UTC)

You appear to be here not to learn but to make a point, as you dismiss attempts to make some sense of your incoherent mishmash as evidence of our lack of understanding, and attempts at explanation as being laughably wrong or beside the point. You are wasting our time. Please stop.  --Lambiam 19:41, 15 June 2023 (UTC)

kettle...............black Byron Forbes (talk) 13:19, 16 June 2023 (UTC)

You can form a pattern with one slit but we're talking about the two slit pattern here. And the question which arises there is which slit did the photon go through? Which is unanswerable because if you could find out which slit each photon went through it wouldn't form that diffraction pattern. NadVolum (talk) 17:06, 15 June 2023 (UTC)

Double-slit_experiment explains this. Philvoids (talk) 20:25, 15 June 2023 (UTC)

Not even a mention. Byron Forbes (talk) 13:18, 16 June 2023 (UTC)

The end of the "Overview" section has multiple examples of single electrons (or other such entities) interfering with themselves in the double-slit experiment. The "explanation" is that these things have a wave-like nature, so it is completely expected that they would have a wave-like behavior and does not require special explanation beyond that. The diffraction experiment with buckyballs specifically detected the buckyballs in the diffraction pattern, disproving your novel proposal that it's the photons or other materials beyond the slit that are responsible for the appearance of diffraction. DMacks (talk) 04:27, 18 June 2023 (UTC)

I'm yet to be convinced that any responders here have actually understood what I'm referring to. Byron Forbes (talk) 12:03, 18 June 2023 (UTC)

Simple Wikipedia offers this movie and an easy-to-read article to help those with reading difficulties. Philvoids (talk) 22:33, 18 June 2023 (UTC)

June 14

Pregnancy

Technically, how long after giving birth can a girl get pregnant again? 2001:B07:6442:8903:D478:83BE:7BFE:74E3 (talk) 16:03, 14 June 2023 (UTC)

Depends on how fertile the father is. Pablothepenguin (talk) 16:20, 14 June 2023 (UTC)

The WP article on superfetation may also be of interest. --Cookatoo.ergo.ZooM (talk) 16:48, 14 June 2023 (UTC)

There are records of intervals of less than 3 months from birth to next pregnancy([3]). However, an interval of less than 18 months is widely accepted as significant health risk for both mother and baby. WHO recommendation is two years interval.

Zarnivop (talk) 19:38, 14 June 2023 (UTC)

See also Postpartum infertility.  --Lambiam 22:21, 14 June 2023 (UTC)

For whatever it's worth, my grandmother (RIP) was born 12 months after my great auntie Jean (RIP) and my great auntie Maureen (still with us) was born 11 months after that. Then my great grandparents didn't have any more children, for whatever reason. This would have been in the 1930s. — Preceding unsigned comment added by 146.200.128.34 (talk) 00:10, 18 June 2023 (UTC)

June 15

Density multiplied by a distance

If I have a density of points per unit volume (P) which varies according to the value of a function y=f(x) in meters, what would the product dP.dy give, a density per unit area or what else? Malypaet (talk) 21:52, 15 June 2023 (UTC)

I'm not able to work out what dP.dy means, in particuler what y=f(x) is supposed to mean. What exactly is the relation between P and f(x)? Perhaps a specific example might help. NadVolum (talk) 22:00, 15 June 2023 (UTC)

Total electron content might be a suitable practical example. catslash (talk) 22:30, 15 June 2023 (UTC)

What is meant is surely $\rho (x)\,\mathrm {d} x$, or better $\int \rho (x)\,\mathrm {d} x$. In astronomy, this is called column density; in general area density in units of number of points per area (according to OP's question) or mass per area if $\rho$ is a mass density. --Wrongfilter (talk) 06:00, 16 June 2023 (UTC)

Are you asking for the dimension of ${\text{d}}P{\text{d}}y$? What does it mean that $P$ "varies according to" the value of $y$? Does it mean $P=y=f(x),$ or $P=g(y)=g(f(x))$ for some unknown function $g$? And what is the role of $x$? Does it represent some physical quantity?  --Lambiam 09:20, 16 June 2023 (UTC)

Yes, for example if "P" is an energy density in joule/m3, a function of wavelength "y" in meter. When you read that "P" (dP ?) is the energy density slice between "y" and "y+dy", represented by the product "P.dy", what does this mean ? And we see here that this product give energy by area in m2, as in column density to area density. Why not represent the energy density slice by "dP(dy)" or some thing else more appropriate, to stay in energy density by volume as a function of "dy" ? Malypaet (talk) 13:36, 16 June 2023 (UTC)

There is no such thing as a "density slice". Density is defined at every point and is a function of position, $\rho (y)$. Writing $\mathrm {d} \rho$ only makes sense if you're talking about the derivative ${\frac {\mathrm {d} \rho }{\mathrm {d} y}}$, the gradient or rate of change of density with position. As far as I can tell this is not what you mean. The product $\rho \,\mathrm {d} y$ has dimensions of energy per area (e.g. J/m²), no way around this. --Wrongfilter (talk) 14:28, 16 June 2023 (UTC)

Sory I wanted to write "energy density of a spectral slice between "y" and "y+dy", but as energy density "P" vary as a function of y, I was considering "dP" as a kind of slice. Malypaet (talk) 15:07, 16 June 2023 (UTC)

"Spectral slice"? Is your "y" supposed to be a frequency $\nu$??? No, probably a typo for "spatial slice"?--Wrongfilter (talk) 15:48, 16 June 2023 (UTC)

You did not explain the meaning and significance of the variable $x.$ Also, what is the dimension of $P$ (or is it the Greek upper-case letter $\mathrm {P}$ or lower-case letter $\rho$?)? First you said a density of points per unit volume, but now you have switched to energy density. Which is it?  --Lambiam 18:12, 16 June 2023 (UTC)

The name of the letter does not matter, here the point or energy density is the same. With this exchange I found the solution to my problem which was to know how to pose it. "x" doesn't matter, "P" is a function of "y" expressed in meters, but in a fourth dimension. In this case it is necessary to use the integral calculus for "y" varying from 0 to infinity, as that one remains in a density of volume with "P" .

Thank you all Malypaet (talk) 08:01, 17 June 2023 (UTC)

June 16

Identify species in photos in c:Category:Macropodidae at Kangaroo Creek Farm

c:Commons:Village_pump#Animal_identification_requested asks to identify the species of Macropodiae deipcted in those photos. I'm forwarding that request because this reference desk has editors competent in animal identification. – b_jonas 10:10, 16 June 2023 (UTC)

To me, they look like red kangaroos - Osphranter rufus. HiLo48 (talk) 10:41, 16 June 2023 (UTC)

Some may be, but most definitely are not. Some of the ones I could identify myself were clearly wallabies! - Jmabel | Talk 15:27, 16 June 2023 (UTC)

They are all apparently taken at Kangaroo Creek Farm. The red ones are kangaroos. The gray and the brown ones are wallabies. They also have an albino wallaby. 97.82.165.112 (talk) 18:47, 16 June 2023 (UTC)

Yes. All of that is in the captions I wrote. The problem is that there are 20-odd species of wallaby (for example) and in most cases I don't know which is which. - Jmabel | Talk 16:41, 17 June 2023 (UTC)

Well, maybe someone at Kangaroo Creek Farm would be willing to look at them and help you? --142.112.221.43 (talk) 18:58, 17 June 2023 (UTC)

Their website lists the animals that they have and identify them as Red Kangaroo, Wallaroo, Bennet Wallaby, and Albino Wallaby. 97.82.165.112 (talk) 11:53, 19 June 2023 (UTC)

Name for this type of cloud?

Rows

Is there a name for this type of cloud? Bubba73 ^{You talkin' to me?} 20:11, 16 June 2023 (UTC)

It looks like cirrostratus undulatus.  --Lambiam 20:53, 16 June 2023 (UTC)

June 17

Planck's law simplification

On "On the Law of Distribution of Energy in the Normal Spectrum", chapter "Introduction of Wien’s Displacement Law" , §7, Planck made a simplification from :

u.dv=ϑ...(...).dv

to:

u=ϑ...(...)

am I to understand that u.dv is a product and it simplifies equality by dividing by dv, or is it another operation? Malypaet (talk) 13:51, 17 June 2023 (UTC)

Yes, that's essentially correct. --Wrongfilter (talk) 17:10, 17 June 2023 (UTC)

This simplification is allowed when the relation between the two differentials is an identity. Let $f$ and $g$ be two functions with primitives $F$ and $G$, so $\textstyle {\int f(x)dx=F(x)+C_{1}}$ and $\textstyle {\int g(x)dx=G(x)+C_{2}}.$ The differential identity $f(x)dx=g(x)dx$ only implies the identity of their primitives up to an additive constant of integration. But this does not matter; we have

$f(x)-g(x)={\frac {d}{dx}}F(x)-{\frac {d}{dx}}G(x)=$ ${\frac {d}{dx}}(F(x)-G(x))=$ ${\frac {d}{dx}}(C_{2}-C_{1})=0.$

So we may conclude that $f(x)=g(x).$  --Lambiam 18:25, 17 June 2023 (UTC)

So, if "u.dv" is a volume density of a spectral slice between v and v+dv, what does "u" represent once dv removed? Malypaet (talk) 19:34, 17 June 2023 (UTC)

u is called "spectral energy density" (at least where I come from, i.e. astrophysics; I'm not linking because that would lead to an article that discusses a somewhat different concept of "spectral"), it has dimensions of energy per volume per frequency interval (units e.g. ${\frac {\mathrm {J} }{\mathrm {m} ^{3}\,\mathrm {Hz} }}$). By contrast, $u\,\mathrm {d} \nu$ is an energy density (${\frac {\mathrm {J} }{\mathrm {m} ^{3}}}$) but only the density of photons with frequency between $\nu$ and $\nu +\mathrm {d} \nu$. The total energy density is the integral of that expression over all photons. --Wrongfilter (talk) 19:56, 17 June 2023 (UTC)

So going back to E, we have a spectral energy density in J/m3.wavelength. That is to say that in the black body we measure the power/m2 for a wavelength, power divided by this wavelength and the speed of light to obtain a spectral energy density, or is it different? Malypaet (talk) 06:11, 18 June 2023 (UTC)

In detail it's more complicated (and a hell of a confusing subject with varying nomenclature in different fields; look at the bewildering variety of quantities in radiometry) but you're partially on the right track. Note that E is not the usual notation that we would use nowadays; I'd write it as $u_{\lambda }$ (as opposed to what we had before, which would be $u_{\nu }$). You're right with the division by c (physical reason is that photons passing through a given area in the time interval $\mathrm {d} t$ come from a maximum distance $c\,\mathrm {d} t$. You're wrong about the division "by this wavelength". In fact it's impossible to go from bolometric power to spectral density. Working forward from spectral density, you need to integrate over all wavelengths such that power is proportional to $\int _{0}^{\infty }u_{\lambda }\,\mathrm {d} \lambda$. You're really better off trying to find a modern text book where this is explained systematically and in a clearer and more didactic way that in Planck's original paper. --Wrongfilter (talk) 08:07, 18 June 2023 (UTC)

Sorry, but I always prefer the original to a copy, here with you and the original I got the answer I was looking for. Malypaet (talk) 22:14, 18 June 2023 (UTC)

So when you write "spectral energy density" , as you don't divise by frequency or wavelength, how can you have a dimension by hertz for example ? Do you use a vector with 2 attribut (energy density, frequency), a matrice with 2 élément (energy density, frequency) or what else ? Malypaet (talk) 05:03, 19 June 2023 (UTC)

For the bolometer, it seem that in experiment, in front of it you can apply a filter (a crystal) to select a very fine slice of wavelenth, isn't it ? So Why don't divise by wavelength ? Malypaet (talk) 05:09, 19 June 2023 (UTC)

Escaped genetic experiment

Read something years ago about this but I can't remember all the details. Apparently some geneticists in South Africa were messing around with locusts back in the day, splicing their genes with god knows what in an attempt to create a less aggressive, less voracious, less swarmy version. But someone screwed up and the resulting organisms escaped into the wild. These organisms are huge, slow, placid bugs, the size of mice, flightless and seem to enjoy eating human garbage, but are otherwise harmless, except that they look scary and are a minor annoyance to people. So the government just left them alone. Does this sound familiar to anyone? I remember a South African person online telling me that the District 9 movie was kinda based on the premise of "what if these things were sentient?". — Preceding unsigned comment added by 146.200.128.34 (talk) 22:20, 17 June 2023 (UTC)

A popular urban legend, propagated by April Fools' Day articles published by the Johannesburg newspaper The Star, claims that the Parktown prawn was the result of a genetic experiment by students from the University of the Witwatersrand in the 1960s ...  Card Zero  (talk) 23:52, 17 June 2023 (UTC)

Thank you. So this creature is entirely a creation of nature? 146.200.128.34 (talk) 00:40, 18 June 2023 (UTC)

Well yes. Myths have arisen regarding this species: some people feel it is an alien invader or the result of a freak mutation. But it's just one of the Anostostomatidae.  Card Zero  (talk) 12:03, 18 June 2023 (UTC)

Sounds like a mixed up version of the real origin of Africanized bees. Matt Deres (talk) 20:43, 18 June 2023 (UTC)

June 18

Non human animals that are considered sentient beings?

Does anyone have a current list of which non human species which are now considered by scientists to be sentient? Last I heard it was the gorilla, chimpanzee, the two African grey parrots, the European magpie and perhaps some octopuses. Has there been any more recent additions? — Preceding unsigned comment added by 146.200.128.34 (talk) 00:56, 18 June 2023 (UTC)

I just did a search. In the UK, octopi, lobsters and crabs in addition to ALL vertebrates are considered sentient beings. Wow. I always thought that intelligence was a factor (edit: are cows/sheep/pigs considered sentient?). I read Professor Pepperberg's books about her studies on parrots and even though she spent 30 years with ONE African grey parrot (Alex) who appeared to demonstrate sentience - looking in a mirror and asking "what colour am I?" (first animal that ever asked an existential question???), she wasn't sure, even now, whether Alex was a one-off unique mind or not. She hasn't found another one as of now, but apparently Alex was utterly furious that the other parrots in Pepperberg's lab were responding inadequately to the same experiments he'd been involved with. Anyway from Psittacus - Birds appear to offer, in their behavior, neurophysiology, and neuroanatomy a striking case of parallel evolution of consciousness. Evidence of near human-like levels of consciousness has been most dramatically observed in African grey parrots., so there you go. Iloveparrots (talk) 02:43, 18 June 2023 (UTC)

Octopi are definitely smart. They have problem-solving intelligence. Sadly, they have not yet solved the problem of why their lifespans are so short. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:41, 18 June 2023 (UTC)

The popular meaning of "sentient" seems to have shifted over the years. 'When I were a lad' it was often used (particularly in the Science Fiction I read copiously) to mean something like 'conscious and reasoning', with the implication of having human-comparable intelligence; this popular meaning seems latterly to have been replaced by "sapient", with sentient reverting to its original meaning as detailed in the linked article, implying a capacity to suffer. {The poster formerly known as 87.81.230.195} 46.65.228.117 (talk) 04:28, 18 June 2023 (UTC)

What is "sentient"? Do we have a stable, widely agreed upon and testable definition? In any case, such a list of sentient (or sapient) animals suggests that somebody devised a test that's supposed to demonstrate sentience (or sapience), then subjected a random sample of animals to the test. Those listed passed, some others failed, most were never tested. Obviously, animal rights activists will assume every animal is sentient unless proven otherwise; hunters and fishermen will assume no animal is sentient unless proven otherwise:

Fisherman: ‘It's OK if we catch grey mullet. They aren't sentient, so they can't suffer.’

Scientist: ‘We've just proven that grey mullets can feel pain.’

Fisherman: ‘OK, I'm sorry. I'll switch to red mullet. They can't feel pain.’

(One year later)

Scientist: ‘We've just proven that red mullets can feel pain.’

Fisherman: ‘OK, I'm sorry. I'll switch to black mullet. They can't feel pain.’

(One year later)

Scientist: ‘We've just proven that black mullets can feel pain.’

Fisherman: ‘OK, I'm sorry. I'll switch to striped mullet. They can't feel pain.’

(etc.)

For the plural of octopus, see the usage notes at wikt:octopus. PiusImpavidus (talk) 09:29, 18 June 2023 (UTC)

Douglas Hofstadter discusses Thomas Nagel's What Is It Like to Be a Bat? in The Mind's I:

The image conjured up by the phrase "What is it like to be A"? is so seductive and tempting. . . . Our minds are so flexible, so willing to accept this notion, this idea that there is "something it is like to be a bat." Furthermore, we also willingly buy the idea that there are certain things that it is "like something to be" — "be-able things," or "BATs" for short — such as bats, cows, people; and other things for which this doesn't hold — such as balls, steaks, galaxies (even though a galaxy may contain innumerable be-able things). What is the criterion for "BAT-itude"?

In philosophical literature, many phrases have been used to try to evoke the right flavors for what being sentient really is (“being sentient” is one of them). Two old terms are “soul” and “anima.” These days, an “in” word is “intentionality.” There is the old standby, “consciousness.” Then there is “being a subject,” “having an inner life,” “having experience,” “having a point of view,” having “perceptual aboutness” or “personhood” or a “self” or “free will.” In some people’s eyes, “having a mind,” “being intelligent,” and just plain old “thinking” have the right flavors. In Searle’s article (selection 22), the contrast was drawn between “form” (hollow and mechanical) and “content” (alive and intentional); the words “syntactic” and “semantic” (or “meaningless” and “meaningful”) were also used to characterize this distinction. All of the terms in this huge showcase are nearly synonymous. They all have to do with the emotional issue of whether it makes sense to project ourselves onto the object in question: “Is this object a BAT, or not?” But is there really some thing to which they refer?

Meanwhile (admittedly almost 40 years later, but are we really any clearer?) the UK has the Animal Welfare (Sentience) Act 2022, and Wikipedia has an article on Animal consciousness (beset with a number of difficulties).  Card Zero  (talk) 10:58, 18 June 2023 (UTC)

June 19

What are the c. 1 millimeter long pale bugs on indoor paint?

In NYC. What do they eat? Sagittarian Milky Way (talk) 12:51, 19 June 2023 (UTC)

They could be Silverfish. They primarily eat paper, decaying wood, and pantry items like flour. They are commonly seen out out in the open during the humid summer as the dry air during winter keeps them hidden in places where there is moisture. Thriley (talk) 13:25, 19 June 2023 (UTC)

Could also be Planococcus citri or an aphid of some sort. A picture would help. 41.23.55.195 (talk) 13:35, 19 June 2023 (UTC)

Finding Accepted Sources Of Info

I need to find more information about Soviet’s Turbojet Train, also known as “High-speed Laboratory Railcar” or “SVL”. Thanks, Brevqvist (talk) 12:51, 19 June 2023 (UTC)