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March 17

Special relativity : 3.4 Relativity without the second postulate

^[1] There is a paradox in this chapter, Lorentz transformations should be excluded from it, because they only make sense if the speed of light is invariant in all frames of reference. This is in conflict with the wikipedia article "Lorentz transformation" and its sentence in the introduction: "For example, they reflect the fact that observers moving at different velocities may measure different distances, elapsed times, and even different orderings of events , but always such that the speed of light is the same in all inertial reference frames. The invariance of light speed is one of the postulates of special relativity." If the speed of light is not invariant in reference frames, then the Galilean transformations must apply. ^[2] Malypaet (talk) 03:33, 17 March 2022 (UTC)[reply]

References

When you do not postulate P, it does not mean that you postulate its negation non-P. --Lambiam 10:02, 17 March 2022 (UTC)[reply]

Sometimes an apparent Paradox is merely a statement that runs contrary to one's expectation. The Lorentz transformation explains both how the speed of light was observed to be independent of the reference frame, and the symmetries of Maxwell's equations of electromagnetism. The article Special relativity considers the Lorentz transformation and light speed invariance to be the fundamental postulates of special relativity. The background theory of general relativity has been so convincingly tested that it is widely regarded as mainstream science. Some of its predictions that are so-called paradox are indeed counter-intuitive but are not a paradox in the sense of a logical contradiction. Philvoids (talk) 13:24, 17 March 2022 (UTC)[reply]

I think the OP merely meant to point out a perceived inconsistency between statements in the article section Special relativity § Relativity without the second postulate and the article Lorentz transformation. --Lambiam 09:52, 18 March 2022 (UTC)[reply]

Another possibility is that Lorentz transformations apply and there is an invariant speed, but that light does not travel at this speed. That’s the case, for example, in models with a small photon mass. By taking it as a postulate that the invariant speed is the speed of light in vacuum, we exclude this possibility by construction, although we cannot physically rule it out to unlimited precision. —Amble (talk) 19:23, 17 March 2022 (UTC)[reply]

In fact photon rest mass is ruled out experimentally to our highest achievable, though not unlimited, precision. Philvoids (talk) 20:57, 17 March 2022 (UTC)[reply]

I'm confused as to why OP is confounded. @Malypaet: Could you clarify a bit? IIRC, one can derive a transformation for different (velocity) inertial frames even without starting from a physical invariant speed of anything. You would then end up with a transformation relation that's a function of a parameter, say X. If X is infinite, we have Galilean. If X is finite, we have Lorentz. Usually that's where we associate it with c in vacuum. Of course, you can make your life easier by starting from invariant c; it might lead to a shorter derivation of Lorentz transformation. GeorgiaDC (talk) 19:35, 22 March 2022 (UTC)[reply]

March 18

co2 clearance

Let's say you get mild hypercapnia by breathing stale air (immediate cause is wearing a respirator mask[1] while shopping). How long does it usually take to clear? Healthy person, not medical, wondering if it is normal for it to take a while, like hours. Thanks. 2602:24A:DE47:B8E0:1B43:29FD:A863:33CA (talk) 03:30, 18 March 2022 (UTC)[reply]

For severe hypercapnia, I found a statement that intubation with mechanical ventilation usually resolves hypercapnia within a few hours.^[2] Since the transition of the difference between a high and a standard CO₂ level can be expected to follow an exponential decay curve, it is crucial which level corresponds to "mild" and at which level the condition is considered "cleared". --Lambiam 15:44, 18 March 2022 (UTC)[reply]

March 19

How does a lutino work compared to an albino?

The lutino article on here is virtually nothing. What exactly are the genetics of an animal that has yellow fur/feathers with red eyes? Common in budgerigars, specifically. How does that differ from albinos? --Iloveparrots (talk) 04:31, 19 March 2022 (UTC)[reply]

Follow the link and read Xanthochromism. Martin of Sheffield (talk) 08:32, 19 March 2022 (UTC)[reply]

Albinism is the absence of (or severely reduced) pigmentation. Xanthochromism is an unusual pigmentation. When genetic, the details may differ by species and even between conspecific individuals. --Lambiam 10:53, 19 March 2022 (UTC)[reply]

Actually, I've been doing my own research and I think I figured it out. Albinism = lack of melanin = white with red eyes. However parrots (specifically parrots) have *two* types of pigments. Melanin and psittacofulvin. No melanin = yellow with red eyes (lutino) because the psittacofulvin is still present. To get an albino budgerigar, or other parrot requires the genetic mutation that prevents the production of both melanin and psittacofulvin. Does that sound about right? --Iloveparrots (talk) 11:09, 19 March 2022 (UTC)[reply]

Life in desert, North Europe and ship journey in past

Now we have technology.

1-During ancient times, how did people survive in hot deserts without water?

2-And all those countries where you have subzero temperatures covered with snow like North Russia, Norway, Finland, Iceland.

Thousands of years ago, when there was no electricity, heater, how did they survive, took bath, cook food, visit the toilet at minus temperature?

3- Hundreds of years ago, When people travelled in wooden ships from one continent to another, how did they preserve food for days, attend call of nature, took bath, cook food on the ship? — Preceding unsigned comment added by Kristerlay (talk • contribs) 13:19, 19 March 2022 (UTC)[reply]

1: They could certainly transport liquids with waterskins, wooden barrels and pottery as needed.

2: See Inuit culture.

3: Writer Roger M Mccoy describes 16th century maritime life in some detail here: https://www.newworldexploration.com/explorers-tales-blog/life-at-sea-in-the-16th-century.

--Modocc (talk) 15:26, 19 March 2022 (UTC)[reply]

(edit conflict)(1) Consider the Well of Zamzam

(2) Eskimos build igloos. See fire#Human control

(3) See salting (food) and ship's biscuits — Preceding unsigned comment added by 92.19.174.20 (talk) 15:55, 19 March 2022 (UTC)[reply]

1. Small patch of surface or underground water (the deepest well being much shallower than the deepest modern water well) at oases that are a small fraction of the world's desert land. Caused by "moon crater with a central peak under rim level" or another workable shape-shaped layer(s) of porous rock surrounded by non-porous which trap and funnel either 1. fossil water from an era of the desert's prehistory when it was wetter or 2. rain from somewhere that's still wetter now. Literally hiding in tents all day in white clothes. Going from one oasis to another at night on camels carrying necessities. Acquiring goods or human slaves at or near one edge of the desert and selling at or near the other edge for profit. Like the sugar and spice etc on the Silk Road or selling salt in hot Timbuktu where you need the electrolytes and it was a local salary and there's no major source nearby. Salt from North Africa where even the Mediterranean is hot, rainless and sunny all summer, that sea has little tide and anyone can just leave seawater in the sun to dry, harvest, repeat. Or maybe at least some of it was pre-dried by nature? (saltwater that was already dry when you got there is where salt mines and salt flats come from). You can also buy crackers and stuff with salt, pepper, gold from past trades etc., you don't have to eat nothing but what you can get in the desert.

2. Collecting burnable stuff in the summer. Like wood or grass. Lots and lots of clothes and fire. Most Inuit have stocky bodies and stocky bodies are correlated with a lower temperature (dis)comfort scale cause physics. According to igloo "On the outside, temperatures may be as low as −45 °C (−49 °F), but on the inside, the temperature may range from −7 to 16 °C (19 to 61 °F) when warmed by body heat alone." An igloo apparently could survive short periods of 16°C, it was temporary after all (buildable in as little as 45 minutes) and you could always heal inside decay somewhat by going outside till it freezes then plastering snow to the inside. A thin layer of inside ice from refrozen melting was actually a good thing. Sagittarian Milky Way (talk) 23:01, 19 March 2022 (UTC)[reply]

3. Picking quickly spoiling food right before leaving and eating only that till they can't stand to eat it anymore. Making the rest of the food so dry and usually salty too that it spoils slower, hiding the taste of old food as best as they could with salt, pepper, chili and other spices. Thus if their cargo was herbs and spices they'd eat some of their own (very expensive) cargo but it was worth it (they would literally eat food that had maggots and eat the maggots too). If they caught a rat at sea they'd eat it, sometimes even fight over it if they were hungry enough. If available find a tortoise, preferably more than one (it's an easy chase even if it's scared of you), turn it upside down, carry or drag it to the ship, leave the heavy thing as close to the entry as would not be in the way and it'll always be where you left it cause it can't move while upside down. Okay maybe they had to put chocks or tie it down or something if they wanted to ensure it didn't become a pinball when the ship tilts. If it wouldn't overload the ship you can bring leaves and fruit for it too (and extra seaman crackers if that has calories to a tortoise), tortoises have one of the slowest metabolisms of any animal of that size range or smaller so low appetite per kilo of animal and takes a long time to starve to death. It's flesh wouldn't start rotting till it was dead or so close the immune system couldn't prevent rot anymore, far later than the part of their meat that died on land. Another thing they used to do is stop at Mauritius, a small warm island somewhat near Madagascar. It had flightless birds the size of medium dogs and no predators or humans (before European sailors and cats) so the species wouldn't keep a minimum distance from you like deer and sailors would just walk right up to it and pick it up or hit it's brain area with a pistol or stick. This bird quickly became extinct. If they got stuck a long time from bad wind luck they would eat horses they were hoping to not have to kill, boiled leather too I think, if no food left. Or murder dying mates to eat or everyone comes to an agreement to let themselves be killed and eaten if they draw the short straw or wait for the first guy to starve to death. Did that ever happen on a ship? It's happened on lifeboats. Apparently you can't always get enough food from fishing and shooting seabirds. They peed off the edge, what did you think? But not into a strong wind. Bathrooms are called heads on vessels because they used to poop at the head of the ship as far from the captain and rudder control as possible and they sometimes had seat(s) that stuck out with a hole in the middle and the turd would land in the ocean or at least gain some distance from the deck before touching the side. If there was no seat you could stick your butt off the bow railing and aim for the ocean. They would wash with saltwater and hopefully saltwater soap which works better in seawater than regular soap. They have an entire planet's water to wash with. Fireproof bowls and stuff with fire in them existed on wood ships. Watched to prevent the ship from catching fire and no one realizing till it got too big to put out. Sagittarian Milky Way (talk) 20:18, 19 March 2022 (UTC)[reply]

March 21

Laptop charger questions.

Somewhat CS-related but my questions are more on the physics side. My laptop charger is 45W. 1 store closest sells them at 65 W. Is that too far of a range? The employee said it will charge my laptop much faster. But I'm worried about overheating.

My laptop charger at where it plugs into the computer is L-shaped. And it is such that when the next part is straight, electricity doesn't go through. But it does go through if I twist the wire in some direction. Then what is going on inside?

And why is it the input and output volts and amps are different numbers? Thanks. 67.165.185.178 (talk) 08:09, 21 March 2022 (UTC).[reply]

Probably the first thing you need to do is a bit of reading about electricity. There's quite a good article at Hydraulic analogy which models electricity by analogy with water flow. However, put very simply: the first one to watch is the voltage. If the charger is rated at a different voltage it will either not work, or else damage your laptop. The wattage is related to how much electricity the charger can supply without being damaged or shutting down. A 65W charger can supply up to 65W, but will supply less if required. As regards the twisting, either you have a broken wire inside the cable, or else the plug and socket are not making good contact. If you have to do this things will eventually fail, based on my son's experience! Martin of Sheffield (talk) 09:23, 21 March 2022 (UTC)[reply]

Do what things, fix the wire inside the cable, or the plug and socket? In any event, the laptop chargers in the store don't seem to label the voltage. ~~And my problem is my laptop chargers have 2 voltage labels, input and output. So I hope if store does list voltage, it has to list both voltages.~~ 67.165.185.178 (talk) 09:33, 21 March 2022 (UTC).[reply]

1: A 65W power supply can provide up to 65W, but will only provide as much as the laptop asks for. The charger just provides a voltage on the cable; the laptop decides how much current will run. So I don't expect it will charge faster, although with a very smart power control unit in the laptop it could happen. When you connect a 45W power supply to a laptop expecting a 65W unit, the power supply unit might overheat or the laptop might decide that it isn't connected at all. You have to make sure the charger handles the right input voltage, provides the right output voltage, has at least the required power and has a fitting connector.

2: It appears there's a mechanical problem with it. A loose or dirty connector, only making a connection when you apply some force, or a broken wire. Or a damaged insulator that causes a short if you don't apply that force. You really don't want a short.

3: The power going in must be equal to the power going out (minus a few percent losses). Power is voltage times current and the job of the laptop charger is to convert the 230V or whatever comes out of the wall in your area to the 18V or whatever your laptop needs, and at the same time convert alternating current to direct current. PiusImpavidus (talk) 09:39, 21 March 2022 (UTC)[reply]

Ah you're right for #1. My laptop charger can work in both USA and England. The input voltage being 100-240 V, and the output 19.5 V. Input amps 1.4, output amps 2.31. Is the change in amps a conversion of AC to DC? 67.165.185.178 (talk) 09:45, 21 March 2022 (UTC).[reply]

The intermittent contact of your Plug may be caused by dirt in the socket of your laptop. Every time you plug in, some dust particles from the air find their way in and are squeezed by the plug against the back of the socket. Over the time, the dust builds up, layer by layer, until the plug doesn't properly lock into place anymore. Try to clean out the socket with a thin plastic pin or toothpick or some other non-conductive tool. I saved many devices from going to the scrapyard this way... 37.201.147.171 (talk) 13:00, 22 March 2022 (UTC)[reply]

So I see now the newer laptop chargers (or AC adapters) are getting less voltage. I looked at my older laptop of over 10 years ago, at 65 W. (Compared to the new 45 W). Old 1 uses output voltage of 20 V (compared to new of 19.5 V). In any event the heads don't match, but if they did, and assuming the new stores sells at 20 V, is 20 V for a 19.5 V laptop okay? 67.165.185.178 (talk) 10:00, 21 March 2022 (UTC).[reply]

For the output, 19.5 V × 2.31 A = (19.5 × 2.31) W = 45 W. For the input side, voltage times current gives a range from 140 W (for 100 V) to 336 W (for 240 V), which is implausible, both for being excessively high and for being very different from the output side. The two powers should roughly match, as also mentioned above. Both the voltage conversion and the AC–DC conversion entail some power loss, but nothing that humungous, like from 68% up to 87%, which would turn into heat and melt the charger. Typically, in non-critical applications, there is some tolerance, and one would expect 20 W to be close enough to 19.5 W, but this cannot be guaranteed a priori. --Lambiam 10:49, 21 March 2022 (UTC)[reply]

OP, you would be wise to provide a faithful reproduction of your charger and/or laptop electrical spec (easiest would be a photograph of the plate with voltage information, like the link in that other question). As it stands, the advice above is correct, but depends on whether you read/interpreted the plate correctly. It is not very hard to do and more likely than not you read it correctly, but your questions here are rather basic (no shame in that), and mistakes can be costly when it comes to electricity. Tigraan^{Click here for my talk page ("private" contact)} 16:26, 22 March 2022 (UTC)[reply]

Gardening pH of soil.

What is pH supposed to mean for soil? In chemistry pH is the measure of H+ ions. But ions only exist in the liquid and gas phase, not solid. So soil can have a pH in rainy conditions, then what about dry conditions? I see a soil modifier in hardware soils, to make it acidic the principle ingredient is S, and to make it basic, a whole bunch of ingredients that are solid bases. Can they pluck the H out of a molecule without an orbiting electron? 67.165.185.178 (talk) 08:13, 21 March 2022 (UTC).[reply]

It's the pH experienced by the plants' roots that matters. Soil testing meters and kits generally require the soil be dried, then distilled water is added and a reading is taken. Abductive (reasoning) 08:55, 21 March 2022 (UTC)[reply]

Soil contains water. The pH in this case is the pH of the water in the soil. --Jayron 32 12:47, 21 March 2022 (UTC)[reply]

March 22

Stillbirth

What could be responsible for a baby dying in the womb? — Preceding unsigned comment added by 2A03:2880:30FF:10:0:0:FACE:B00C (talk) 18:46, 22 March 2022 (UTC)[reply]

Have you looked at the Stillbirth article? There is also an UK NHS page here. Hope that might help. Martinevans123 (talk) 19:04, 22 March 2022 (UTC)[reply]

Plane crash

Re: China Eastern Airlines Flight 5735. The article states: ... footage depicts the plane in a nose first vertical descent. What is the significance and/or implications of a near-vertical nose-first descent? In other words, what does that "fact" tell investigators? Thanks. Joseph A. Spadaro (talk) 18:49, 22 March 2022 (UTC)[reply]

Even if all engine power is removed from a Boeing 737, so that any autopilot mode is disengaged, during a straight and level cruise, if the aircraft surfaces remain as set, the aircraft should be able to glide for about 60 miles? A nose dive suggests either catastrophic failure of the control surfaces or that the aircraft has been intentionally flown into that dive profile? Martinevans123 (talk) 19:02, 22 March 2022 (UTC)[reply]

Hmmmmm ... thanks. In other words, it could/would be a (possible) sign of a pilot suicide? Joseph A. Spadaro (talk) 19:32, 22 March 2022 (UTC)[reply]

[1] ttps://en.wikipedia.org/wiki/Special_relativity#Relativity_without_the_second_postulate

[2] ttps://en.wikipedia.org/wiki/Lorentz_transformation

[1]

[2]