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February 21

Where exactly parachute will land during Mars 2020?

MSL's debris field, imaged 12 days after landing. -- ToE 19:17, 21 February 2021 (UTC)

First orbital image (also via MRO's HiRISE camera) of the Mars 2020 debris field.-- ToE 19:17, 21 February 2021 (UTC)

@OuroborosCobra: I find this JPL page discussing about parachute, but they didnt explain where exactly parachute will end on Mars during Mars 2020 ? Will it burn in atmosphere? Rizosome (talk) 11:18, 21 February 2021 (UTC)

It certainly won't have burned, since it didn't do so while being dragged by the Entry, Descent, and Landing System, and once released would have have slowed to a low terminal velocity. Where it landed (presumably still attached to the back shell portion of the aeroshell) will depend largely on the winds it encountered while independently drifting down.

Related Mars 2020 questions are where the heat shield and sky crane landed: doubtless one or another of the eight active space probes currently orbiting Mars will photograph all these various components in the coming days.{The poster formerly known as 87.81.230.195} 2.125.75.168 (talk) 12:45, 21 February 2021 (UTC)

Yes, 12 days after Curiosity landed, the Mars Reconnaissance Orbiter imaged the area using its HiRISE camera, producing the image above, showing the rover, the heat shield, the crashed descent stage, and the backshell with parachute. The parachute and backshell were about 615 meters away from the rover. See the description field of that image's page for more details. -- ToE 19:17, 21 February 2021 (UTC)

Thank you for the image. @ToE: Rizosome (talk) 06:46, 22 February 2021 (UTC)

@Rizosome:, I don't know why you've tagged me in this. This is not an answer to the question I asked of you earlier. --OuroborosCobra (talk) 18:54, 22 February 2021 (UTC)

Here's an orbiter image of the Mars 2020 landing stuff, similar to the one at right. Deor (talk) 22:11, 22 February 2021 (UTC)

Here's a color HiRISE image of the parachute! -- ToE 03:16, 23 February 2021 (UTC)

That parachute is about 1.1 km away from the rover. Here is an image taken from the rover, with a few light pixels apparently showing the backshell and parachute. (Look at the zoom in this response.) -- ToE 03:39, 23 February 2021 (UTC)

No good. Those bright pixels are WSW while the backshell and parachute are to the NW. Presumably just light reflecting of a flat rock. -- ToE 14:44, 24 February 2021 (UTC)

February 22

50 cal gun and air

I posted this on the Humanities desk! My bad. The other day, I was watching a Youtube vid (I could not find the link) of someone taking multiple shots with a 50 cal gun. The host showed how the air around the gun got cold enough to see one's breath. What is the science behind this? 70.26.18.103 (talk) 01:45, 22 February 2021 (UTC)

"50 cal gun" only tells us its ammunition size: it could be a Handgun, a Light or Heavy machine gun, or conceivably even a pistol, rifle or other type of Air or Gas gun. Without more detail, I doubt if anyone can begin to offer an explanation: I myself can point to a possible cause if it were an air or gas gun. {The poster formerly known as 87.81.230.195} 2.125.75.168 (talk) 02:12, 22 February 2021 (UTC)

My apologies. As I am not a gun person, I was not aware of the different ways to fire a 50 cal bullet! The gun I am referring to was a long barrel rifle fired while on a tripod on a table. It was semi-automatic but the host of the vid showed how one could see one's breath after a single shot. I hope this helps. 209.91.188.70 (talk) 17:40, 22 February 2021 (UTC)

I'm not a gun person (I'm European) and I don't see how a gun could cool the air. I do see a different option. The gun puts additional condensation cores in the air, which may trigger condensation if the air in the breath plume was already more or less saturated with water vapour. PiusImpavidus (talk) 09:40, 23 February 2021 (UTC)

I've had a quick look on YouTube, but couldn't find a video that mentioned that. If it was an airgun like this one here, then it could be due to the adiabatic cooling of the comressed air as it expands. But if its a firearm (especially a big one like one of these shooting this sort of ammo, then I can't imagine how it would cause cooling. Iapetus (talk) 22:47, 23 February 2021 (UTC)

Blood vessels regenerating

What is the maximum length of a blood vessel being removed and then fully regenerating? 10 centimeters? More than that? Futurist110 (talk) 06:59, 22 February 2021 (UTC)

RBMK reactor

A few questions about that clunker called the RBMK:

(1) Did the 24 short lower control rods have graphite tips like the ones inserted from above?

(2) Were these 24 rods under the control of the RCPS and/or EPS systems, and were they automatically inserted by pressing AZ-5?

(3) Were there any safety valves and/or pressure relief valves on the steam drums and/or on the steam lines to the turbines (I wouldn't be too surprised if there weren't any), and if so, where did they discharge -- into the condensers, or into some kind of surge tank, or simply into the turbine hall to the peril of anyone who happens to be nearby at the time? [Additional question: other than this, was there any other way to bypass the turbines and dump the steam from the steam drums directly into the condensers if the need arose?]

(4) Why use the graphite tips at all -- was this some kind of tweak to correct an early design flaw (in the process introducing another, arguably worse one)?

(5) Considering how unstable this clunker was, and how laggy the controls were, had there ever been problems with these things introducing current/voltage oscillations into parts of the Soviet power grid (for example, did the lights in places which were heavily dependent on nuclear power, such as Pripyat, flicker more than normal)? And

(6) the million-dollar question: if they had known the finer points of operating this reactor (a partially moot point since if they had, they wouldn't have run the test as they did), could they have averted the Chernobyl disaster if, as soon as the reactivity started increasing, they kicked the main coolant pumps to maximum RPM before (or instead of) pressing AZ-5? 2601:646:8A01:B180:8C91:5C9F:935B:96B1 (talk) 08:12, 22 February 2021 (UTC)

^{[I have reformatted your post slightly to make it easier for others to read and respond to. {The poster formerly known as 87.81.230.195} 2.125.75.168 (talk) 14:11, 22 February 2021 (UTC)]}

[OP] I take back question #3 -- I'm reading the INSAG-1 report right now, and it expressly mentions some kind of pressure-relief valve which closed in response to the reduction of the steam pressure in the #8 steam drum, so the answer to my own question #3 is "yes, and it discharged the steam into the condenser as is proper for any high-pressure steam device". (Nice to know that at least something in that design was done right!) 2601:646:8A01:B180:4080:C0D:3AC8:DA35 (talk) 09:09, 23 February 2021 (UTC)

• Oh wow, these are very interesting questions. And I'm not sure a lot of people could seriously answer them. I know the physics behind all this but your questions are very specific to this reactor. My recommendations would be for you to try to reformulate the more RBMK specific ones into more general questions about reactors so I can give a shot at answering them. Or you could try to leave a message on the talk page of one of the main editors of the RBMK page. I can do the second one for you if you want. Feynstein (talk) 18:42, 26 February 2021 (UTC)

Actually I can answer #4. Since you open up a reactor like that from the bottom up, the first things neutrons will see are those tips. And they will displace the water. It's written somewhere on that page. So it's conceivable that when starting up the reactor they needed a moderator gradient to get the reaction going properly. Feynstein (talk) 19:30, 26 February 2021 (UTC)

For question #1: here is a possibly useful source [1] (already cited in RBMK). The 24 lower control rods seem to be the ones described as "shortened absorbing rods (SAR) for regulation of the axial neutron distribution". The makeup of each type (p. 15): "The absorbers of the type SAR have only three absorbing elements. Their length is 3,050 mm [7]. Other absorbing rods are assembled from 5 absorbing elements. Their length is 5,120 mm [7]. There are another feature in absorbing rods of the RBMK reactor. The absorbing rods of the type SAR, MR and ER have special graphite displacers that are assembled from 5 graphite elements." See also the very helpful Fig. 3 (p. 16) in the linked article. This confirms that the 24 SARs do have the graphite portion, in opposite position relative to the manual and emergency absorber rods, but that the auto control rods do not have the graphite portion. --Amble (talk) 19:01, 26 February 2021 (UTC)

The following sentences (p. 15) also provide an answer to question #4: "These displacers remain in the core by full withdrawal of absorbing fractions of rods. The use of graphite displacers improves significantly the neutron economy of the RBMK reactor because graphite absorbs neutrons much less than the light water." --Amble (talk) 19:08, 26 February 2021 (UTC)

The linked article has some hints to question #2, but I can't find an unambiguous answer. It says in one place (p. 11) "all control rods"; in a second place (p. 19) "all control and scram rods"; in another place (p. 23) "all absorbers for the manual regulation and all emergency absorbers". --Amble (talk) 19:18, 26 February 2021 (UTC)

The linked article has considerable discussion that's relevant to question #6, although not directly posing the question you asked. See p. 23-24 and conclusions. It seems there's a difference in expert opinion as to whether pressing AZ-5 initiated the disaster, made it worse, or only failed to stop it. It depends on how much of the problem was caused by boiling of water in the reactor core. Given that disagreement, it's probably not possible to say with any certainty whether another specific course of action would have prevented the disaster. It does suggest that at least some experts believe it would have been better to not press AZ-5 and do something else. There's also discussion on p. 24 about a possible role of circulating pump motors that gets very close to your question, but here also I don't find certainty about what actually happened or what could have been done. --Amble (talk) 19:30, 26 February 2021 (UTC)

In p. 24-25 you can find a list of prior incidents in Soviet nuclear power plants. They don't mention any effects for power consumers as in your question #5, but they do describe dangerous failures at the Leningrad and Chernobyl plants in previous years that were closely related to the eventual Chernobyl disaster. --Amble (talk) 19:36, 26 February 2021 (UTC)

Plant identification requested

These flowers have appeared in our garden (southern Scotland, mid-February). Can anyone identify them, please? --rossb (talk) 16:26, 22 February 2021 (UTC)

Eranthis hyemalis or winter aconite(s). Mikenorton (talk) 16:45, 22 February 2021 (UTC)

Thank you very much. rossb (talk) 17:02, 22 February 2021 (UTC)

They are toxic. Richard Avery (talk) 17:13, 26 February 2021 (UTC)

Shower physics

I have some questions about the everyday stuff I've noticed regarding water flow from my shower. I'll supply the details in case they're relevant, but this is a fairly basic shower stall setup. The bathroom is on the top floor, so the water is coming up through the floor. About one meter up, the cold and warm water tubes meet at the control mechanism (turn for temp, push/pull for volume). Since it's a shower stall there's no other faucet, as you'd find in most bathtub setups. A further meter up, the single pipe pokes out into the shower area and I've attached a standard hand-held shower attachment. The hose portion is almost exactly the same length as the bracket for it is high; when it hangs loose it just barely misses striking the floor. So, call the hose about 2 meters. In the normal position, the wand portion sits in a bracket so that the functional face of it is a bit higher than the pipe. We have decent pressure. Pretty common stuff, I think. So, here are my questions:

1. When we shut off the water, it stops pretty immediately, apart from a drop or two. However, about 10-15 seconds later there may be a bit of discharge, which I assume is actually caused by the occupant jostling the hose. Then, some larger amount of time later, like 20 minutes or more, there will be a sudden... ejaculation of more water. Not a lot, but enough to make noise and it's a long enough time away from the shower itself that it might wake us up if we showered before bed. What causes that?
2. In part due to the aforementioned noise, we sometimes take to removing the wand from its bracket after showering and just letting it hang. Problem solved, but when I go to hang up the shower head the next day, water will discharge as I'm raising the wand. Now, I'm obviously disturbing the system when I do that, but I'm mostly just adding potential energy: stuff is being raised, not lowered or flexed. What's supplying the energy to make the residual water in the hose squirt out when the wand is raised? For that matter, why doesn't it empty out while the wand is hanging loose for several hours?

I'm assuming the short version of the answer is going to be capillary action, but I'm curious as to how it's getting applied. Also, just to be clear, I have no reason to suspect a leak; the behaviours have been the same for many years and I don't think it's unique or anything. Matt Deres (talk) 16:50, 22 February 2021 (UTC)

I suspect that the various ejections of water from the shower head are due to variations in water pressure, perhaps due to heating/cooling of water combined with some sort of siphon effect. --Jayron32 17:06, 22 February 2021 (UTC)

I'm not sure about that. Wouldn't pressure only affect the water on the other side of the tap? After I shut the water off, there would still be water in the pipe up and in the hose and in the handset, but none of it would be under pressure, would it? I guess I'm assuming everything downstream from the tap would be free flow and only subject to atmospheric pressure. Or is that what you meant? Please don't hesitate to dumb it down. Matt Deres (talk) 18:46, 22 February 2021 (UTC)

Perhaps water is getting stuck behind a backflow prevention device and slowly leaking through until there's enough to overcome surface tension and come out in a small spurt. --Amble (talk) 18:32, 22 February 2021 (UTC)

I hadn't considered that. I'm quite in the dark when it comes to plumbing, but I normally associate backflow traps with waste water. For example, various bends in the pipes below my sink/toilet to prevent gas from escaping upwards. They're not typically added to the inbound water, are they? Matt Deres (talk) 18:49, 22 February 2021 (UTC)

A backflow preventer might be build into, or attached to, a hand-held shower head on a flexible line: [2]. This isn't a trap; it's a little valve that lets water through in one direction, but snaps shut to stop water from flowing in the other direction. It can work by gravity or a spring. It hadn't occurred to me earlier, but it could also happen that a backflow preventer is stuck in the open position after your shower, and when it eventually snaps shut, it jostles some water free to drain from the shower head. --Amble (talk) 19:01, 22 February 2021 (UTC)

I did not know that; as the commenter on that link says, it seems pretty unnecessary. I water starts crawling two meters up a hose, I think we'd have bigger problems than water getting into the water supply. But I guess it's just standard. That sounds like a plausible explanation for the first question - thank you! Any thoughts on the second one? Matt Deres (talk) 03:25, 23 February 2021 (UTC)

I checked my shower head, which happens to be made of transparent plastic. After showering, it still had a lot of water inside, which stayed inside when I let the shower head hang down instead of putting it back on the hook. The water was inside the head by the nozzles, past anything that could be a backflow preventer. This makes me think any backflow preventer is not relevant here, and PiusImpavidus’s idea is a much better match to what I saw happening. —Amble (talk) 16:08, 23 February 2021 (UTC)

I've found that that often occurs in my shower head, and I'm fairly sure that it's caused by the water being held in the nozzle holes by surface tension, and maybe the slight suction effect of the water in the shower head and hose cooling and shrinking. I assumed the release was caused by air entering the uppermost of the shower nozzle holes, so hanging the hose down with the shower nozzle plate more vertical makes this release happen immediately. Well that's my theory! 49.197.246.104 (talk) 06:55, 23 February 2021 (UTC)

1: After showering, there's still water in the showerhead. Because of surface tension, the air has difficulty breaking through the water surface in the tiny holes of the showerhead, so it can't enter. As no air enters, the water can't leave.

After a while, 3 things may happen:

• Water slowly leaks out of the showerhead, governed by surface tension, gravity and viscosity.
• The water in the standpipe, hose and showerhead contracts as it cools down.
• The hose itself expands as it cools down. A peculiar property of rubber and other polymers is that, if held under constant stress, it shrinks with increasing temperature.

These three effects cause the pressure in the showerhead to drop and eventually it gets low enough to suck air in, against surface tension. When this has happened, the highest holes in the showerhead are free of water, so surface tension no longer blocks the entry of air, and the entire showerhead drops its water.

2: With the showerhead hanging down, any air leaking into the showerhead will climb through the hose, keeping the showerhead full of water and keeping the holes mostly blocked by surface tension. When moving the showerhead up again, you bend the hose, which flattens the hose and reduces its volume. This forces some water out. PiusImpavidus (talk) 10:36, 23 February 2021 (UTC)

Cool! Thank you! Matt Deres (talk) 15:36, 23 February 2021 (UTC)

The fraternal birth order effect for male homosexuality: Why didn't evolution select against and weed out this effect?

I found this Wikipedia article to be extremely informative: Fraternal birth order and male sexual orientation. Apparently, the more elder brothers (by the same gestational mother, I'm presuming) a male has, the more likely this male is to be gay (or bisexual?). This effect appears to have been confirmed in research and studies numerous times and thus appears to be true. The hypothesis that a maternal immune reaction is responsible for this also likely appears to be true due to its plausibility and the implausibility of any alternative explanations. However, why exactly did evolution not select against and weed out this effect over the centuries and millennia? After all, one would think that women whose immune systems are LESS likely to have an immune reaction to additional male fetuses are going to have a reproductive advantage–a reproductive premium, if you will–due to them having more descendants in the long(er)-run (since gay men are less likely to reproduce than straight men are), no? Futurist110 (talk) 18:52, 22 February 2021 (UTC)

It depends. Community survivability, especially in social species like humans, is very much a thing. Remember, it is populations, and not individuals at "evolve." Let's say we have two communities, each with 10 mothers. Each mother as 4 male offspring (we are assuming, for the sake of this discussion, that every individual is able to find a mate for reproduction, even though I'm not stating them). So, population A has 10 mothers and 40 male offspring, and population B has 10 mothers and 40 male offspring. Population A has a genetic trait that results in the fourth male offspring always being homosexual, and population B lacks this trait. Let's say that each heterosexual male offspring has 4 children of their own. All things being equal, in your scenario, population A has 144 grandchildren to the original 10 mothers, and population B has 160 grandchildren to the original 10 mothers, and this is where you are having the impression that the trait should be selected against, since mothers without the trait had more grandchildren (we will say all grandchildren are female and heterosexual, to simplify the numbers). However, humans are a social species. We live in communities and different people can play different roles in that community. Perhaps, without the motivation of personal reproduction, the homosexual male children of the population A mothers take on other roles, such as helping with child rearing, helping gather food, or even being lookouts for potential threats. Let's that this has a big impact. In population A, 75% of the grandchildren with homosexual siblings survive to sexual maturity and have children, since they are all heterosexual females. That means that of the original 144 children in the Population A that has the trait for homosexuality, 108 grandchildren successfully reach sexual maturity and have great grandchildren. Population B, which doesn't have homosexual uncles serving their social role, only has 50% of the grandchildren surviving to reach sexual maturity (half dying of starvation or attacks on the community). Of the original 160 grandchildren, only 80 survive to sexual maturity. So, having the trait of some homosexual offspring conferred the community survivability of Population A an advantage over Population B, 108 grandchildren surviving to sexual maturity vs 80, even though only 75% of Population A children were themselves reproductively viable. The genetic trait for some homosexuality will, in short order, dominate. --OuroborosCobra (talk) 19:11, 22 February 2021 (UTC)

(E/C) Gay men may reproduce less than straight men, but it could be that having a non-mating relative is an overall reproductive advantage. This is seen often in birds, where the term helpers at the nest has been coined to cover the situation. Humans of course take much more time and energy to mature than birds, perhaps making the advantages even more pronounced. Matt Deres (talk) 19:18, 22 February 2021 (UTC)

Evolution isn't magic pixie dust, it works by what has been called "satisficing" in other contexts (i.e. perform the task good enough in order to allow some species to survive and evolve; good enough means far from perfect). Tgeorgescu (talk) 19:36, 22 February 2021 (UTC)

This BBC article outlines a few theories. This article in Current Anthropology looks into three theories, most favouring the hypothesis that "Same‐sex alliances have reproductive advantages, and sexual behavior at times maintains these alliances. [...] Homosexual emotion and behavior are, in part, emergent qualities of the human propensity for same‐sex affiliation". PaleCloudedWhite (talk) 19:50, 22 February 2021 (UTC)

Perhaps making babies the usual way is not the favorite pastime for homosexuals, but in general they are and were quite capable of fathering children. Tgeorgescu (talk) 13:14, 23 February 2021 (UTC)

To exactly the same extent, on average, as heterosexual men were capable of doing? Futurist110 (talk) 22:17, 23 February 2021 (UTC)

According to the Kinsey scale 100% homosexuals are as rare as 100% heterosexuals. The large majority of people who ever lived fall somewhere in-between. Tgeorgescu (talk) 23:47, 23 February 2021 (UTC)

"women whose immune systems are LESS likely to have an immune reaction to additional male fetuses are going to have a reproductive advantage" What if having less immune reaction to male fetuses is correlated with having less immune reaction in general? Maybe "weeding out" male homosexuality would come at the expense of increased vulnerability to disease for women in general and pregnant women in particular. --Khajidha (talk) 21:01, 22 February 2021 (UTC)

Shouldn't there have then been selection for women with strong immune systems in regards to everything else other than this specific thing, though? Futurist110 (talk) 22:16, 23 February 2021 (UTC)

Some people seem to be analyzing the issue from a modern perspective, where individuals are able to choose whether to stay single or not, to have children or not, and even to choose whether they prefer a hetero or homo relationship. Let's not forget that along evolution people (gay or straight) were supposed to marry people of the opposite sex and engender children, whether they liked it or not. Evolution could not have selected against reproductive successful homosexuals. Bumptump (talk) 13:32, 23 February 2021 (UTC)

Even if those gay cavemen couldn't make lot of kids, they could make the cave look nice with scatter cushions and some lovely flowers. 86.187.233.59 (talk) 09:47, 26 February 2021 (UTC)

Unless a male homosexual views heterosexual sex as so repulsive that he's unwilling to actually perform the penis-in-vagina sex act, that is! After all, even a 1% hit in fitness per one generation will become MUCH more severe over an extremely huge number of generations! Futurist110 (talk) 22:16, 23 February 2021 (UTC)

• This entire line of thinking demonstrates the classic misunderstanding of evolution "If such-and-such a trait is less reproductively advantageous, why does it exist at all", as though every trait that isn't the "best" trait (for whatever meaning of "best" is) should somehow instantly disappear from a population. Evolution doesn't have goals, and it doesn't select anything in that way. Traits which don't kill an individual before they reproduce will generally get preserved in a population for a very long time. There's of course the other issue that human sexuality is somehow a single trait displaying simple Mendelian inheritance like pea pod colors or something like that. Then there's the other other issue that sexuality is a binary trait, and that people are either homosexual or not homosexual, and not on some continuum. Then there's the other, other, other issue that all people should have a stable and unchanging sexuality. Then there's the other other other other other issue that because something has a heritable component, it has no environmental component, or that one can suss out the differences simply. The lines of demonstrably bad thinking in this entire thread are so mindbogglingly numerous, I can't even begin to figure out how to make sense of starting to correct for it. --Jayron32 19:24, 24 February 2021 (UTC)

February 23

Can you store any arbitrarily large amount of information in a finite space?

I have a bit of paper (1 sq cm) and one corn of rice. I divide the space in any arbitrarily large nr. and when I want to store any information I put the corn in the right position. Horizontal is for the nr. proper, vertical indicates the nr. of digits. For example, for representing the number 5, I just put in on the 0.5 mark, at the bottom, to indicate 0 decimal places. If I wanted to represent a string of 1 million digits, I'll chose the appropriate slot and place the corn there. For reading the information you just have to measure the distance from the corner of the paper to the corn. What can go wrong? --Bumptump (talk) 14:04, 23 February 2021 (UTC)

The amount of information that can be contained in a given medium is a major field of study in the surprisingly named information theory. There is NOT an arbitrarily high amount of information that can be stored; indeed even space itself has a maximum amount of information that it can store owing to limits of quantum theory and the like. The problem with your system is that the corn has physical dimensions, which introduces a lower bound on the uncertainty in its position (this is normal uncertainty, not the Heisenberg uncertainty stuff that comes from Fourier transform math). At some point, using a physical device, there is always some thickness to it, and that thickness sets a lower bound on its ability to represent a distinct measurement from a nearby measurement. This isn't even getting into information theory, mind you, this is just the practicalities of working with physical objects. --Jayron32 14:21, 23 February 2021 (UTC)

"I have a ruler with an arbitrarily large number of gradations..." Matt Deres (talk) 15:35, 23 February 2021 (UTC)

Our article on this is Bekenstein bound. Graeme Bartlett (talk) 22:38, 23 February 2021 (UTC)

Somewhere before you hit the Bekenstein bound, the rice-and-paper system will run into other problems. You won't be able to arbitrarily place the grain of rice on the paper; microscopic structures on one will bump against and lock into the other. It's hard to say exactly how finely you'll be able to place the rice, but let's be extremely generous and say 1 Angstrom (10^-10 m), an atomic scale. Your square is 10^-2 m on a side. That gives you (10⁸)²=10¹⁶ choices of position in two dimensions, or only sixteen digits. Even if you could somehow position the rice to within a quantum fluctuation of a LIGO mirror, that would still only give you 36 digits. You could store more information than that by writing it with ink on the grain of rice, let alone on the piece of paper. --Amble (talk) 06:19, 24 February 2021 (UTC)

This reminds me of something I read by maybe Martin Gardner: an alien lands on earth and, being impressed with our history, decides to take a copy of the Encyclopedia Britannica home with him. He unfortunately cannot bring any extra weight back with him, but he converts every single symbol from the books into a 3-digit number and then strings them all together into a massive number encoding every single word. He then converts that into a 1/x fraction and marks that fraction very precisely on a meter stick he brought with him. The problem of course being that, no matter how rigid the stick and fine the cut there's no way you could cut it to hundreds of digits of precision, let alone the billions required for this. Matt Deres (talk) 14:54, 24 February 2021 (UTC)

If a hard drive worked by encoding all its information in the position of a single magnetic marking, a typical unit would hold about 40 bits instead of 1 TB. --Amble (talk) 17:44, 24 February 2021 (UTC)

So corrected. --Jayron32 19:16, 24 February 2021 (UTC)

It might be worth mentioning that the answers above are correct if the question is a physics question, which seems to be how it was intended. It's a very different situation if it's a mathematics question. As Matt Deres alludes to above, the position of a single point encodes infinitely much information (not just unlimited information, but actually infinite).

This is a basic fact about the real numbers, and perhaps explains why it took so long for mathematicians to develop a satisfying "rigorous" account of the reals.

It is an open question whether the real numbers are basic to the physical universe, or just an idealization that works pretty well in describing it. --Trovatore (talk) 19:32, 24 February 2021 (UTC)

Yeah, but mathematics deals with all kinds of things which aren't constrained by the physical world; there are numbers where writing out the digits in ink on paper would take more atoms than exist in the observable universe, stuff like Graham's number and TREE(3). The question did not ask about real numbers, it asked about physical objects. Once we try to remove the real constraints of physics, we enter the world of magic... and there's no point in trying to answer the question after that. --Jayron32 19:39, 24 February 2021 (UTC)

Ah, there you are quite wrong, Jayron. There's lots and lots of point in trying to answer such questions. That's what mathematicians do. If you personally don't value it, worse for you. --Trovatore (talk) 19:55, 24 February 2021 (UTC)

I think you misunderstood my response to you. When I said "The question did not ask about real numbers, it asked about physical objects", what I meant by that was "The question did not ask about real numbers, it asked about physical objects." I hope that clarifies things for you. There's lots of reasons for a mathematician to answer it. Understanding mathematics is Very Important, and we should be asking mathematical questions like this, and answering them. So, don't act like I don't believe that. I do, and you will get zero disagreement from me on that issue. Please don't tell me I don't believe that. I do. The difference is, the OP didn't ask that question. It is important for humanity to answer the mathematical questions. The answer you gave did not provide much in the way of elucidating the problem the OP presented, however, insofar as physical objects are incapable of representing the mathematics required to make an arbitrarily accurate measurement. That's the key difference. That's the issue. Mathematics is useful (in a general sense). The mathematics you're talking about is not particularly useful in answering the OP's problem. Please, in the future, if you're going to disagree with me, please disagree with the things I actually say, and don't invent something I didn't say and then disagree with that. --Jayron32 12:19, 25 February 2021 (UTC)

My first sentence in the response was It might be worth mentioning that the answers above are correct if the question is a physics question, which seems to be how it was intended. --Trovatore (talk) 19:35, 25 February 2021 (UTC)

Fair enough. It's clear I'm the asshole here. Certainly not the first time. It likely won't be the last. Sorry for that. --Jayron32 19:53, 25 February 2021 (UTC)

Perseverance's signal delay

The video feed from Perseverance's descent and landing in the ground control room looked like a live stream, but as I understand, there was a delay of a couple of minutes due to distance. So when the ground control received the confirmation of landing, does it mean that by that time the rover had already landed there several minutes ago? 212.180.235.46 (talk) 15:46, 23 February 2021 (UTC)

Yes. But it could still be a live stream. When Neil Armstrong said "The Eagle has landed", it was a couple of seconds before the people at NASA knew it. In the case of Mars, it's just a longer interval. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:00, 23 February 2021 (UTC)

Remember, everything that you have ever seen occurred some time before you saw it. EVERYTHING. Even if it happened right in front of you. It takes time for light to travel from the item or event you are looking at. It then takes time for your brain to process the input. --Khajidha (talk) 17:54, 23 February 2021 (UTC)

Are you referring to Perseverance Rover’s Descent and Touchdown on Mars (Official NASA Video) [YouTube; 3m25s]? That is a composite video. The scenes of Mission Control are taken from the live webcast of the landing on Thursday. Video of the events on Mars was recorded 11 minutes 22 seconds prior to the radio signals of those events being received on Earth, but the videos weren't transmitted until this weekend. (There is a lot of data to send, and limited bandwidth through which to do it.) The composite video was then constructed so as to synchronize the video of Mission Control reporting the status of signaled events with video of those events as they happened on Mars. So yes, the Earth portion of that video was recorded 11m22s after the corresponding Mars events happened and were recorded on Mars, but had they been able to send back live video from Mars real-time (still allowing for the 11m22s transmission time given the distance), we would have seen the same result, as Mission Control was responding to radio signals which took that same time to travel to Earth. -- ToE 21:37, 23 February 2021 (UTC)

When the New Horizons probe flew by Pluto in 2015, APL held a "live" event, counting down to and celebrating the moment the fly-by was occurring, even though Pluto was 4 light-hours and 25 light-minutes away. At one point, the live webcast cut away from the excited crowd to show the Mission Operations room ... which was totally empty as they weren't coming on duty until several hours later. See New Horizons Arrives at Pluto (YouTube; 26m11s) at 16:12 (3m45s prior to the moment of closets approach) for the shot of Mission Operations. -- ToE 22:01, 23 February 2021 (UTC)

Thanks. 212.180.235.46 (talk) 09:47, 24 February 2021 (UTC)

What's the difference between an extremely early embryo and a skin cell in terms of genetics, epigenetics, et cetera?

What's the difference between an extremely early embryo (for instance, one created through IVF) and a skin cell in terms of genetics, epigenetics, and so forth? After all, both of these things can eventually become persons--in the case of embryos, by being implanted into a fetus and in the case of skin cells, by being put in some kind of special solution and then being implanted into a uterus:

https://www.gwern.net/An-Abortion-Dialogue

Two teams of Chinese researchers working separately have reprogrammed mature skin cells of mice to an embryonic-like state and used the resulting cells to create live mouse offspring…Reprogramming has become the hottest area of stem-cell science. For more than two years, scientists have been reprogramming mature mouse- and human-skin cells and returning them to a primordial, embryonic-like state. The approach has taken off because it sidesteps the cloning and embryo-destroying techniques traditionally used to derive true embryonic stem-cell lines. However, one big question has been whether reprogrammed cells are as versatile as true embryonic cells, and whether they can form all of the cells in an embryo. Using reprogrammed cells to create live offspring with normal organs and body tissues has been considered an important test. Chinese scientists now have shown that this is possible in mice."

What exactly is it about embryos that allows them to be placed inside of a uterus immediately and then develop into actual persons whereas skin cells need to go through this additional step beforehand--as in, if skin cells are immediately placed into a uterus without actually undergoing this prior step (specifically being put in some kind of special solution), then they will obviously fail to develop into actual persons? Any thoughts on this? Futurist110 (talk) 22:12, 23 February 2021 (UTC)

Some clues are to be read in Totipotent stem cells. Embryonic cells have methyllation remove from their DNA. Graeme Bartlett (talk) 22:36, 23 February 2021 (UTC)

Is that the only distinction? Futurist110 (talk) 01:07, 25 February 2021 (UTC)

February 24

Is it night 50% of the time on average everywhere?

The lengths of the day and night depend on the season, so days are longer in the summer and nights are longer in the winter. But if you average it over a long period, does it always come to 50% day, 50% night, regardless of your latitude and longitude? I just mean on Earth (not in space obvs) and to the nearest 1% (not worried about weird edge effects that might make 0.1% difference one way or the other). Thinking about solar power. Thanks. 2601:648:8200:970:0:0:0:C942 (talk) 21:01, 24 February 2021 (UTC)

Let's put it this way: the effects that create an asymmetry are pretty small, but I'm not sure if they're in the 0.1% range where you say you don't care, or the 1% range where you say you do. One example is the fact that the Earth's orbit isn't circular: the Earth's distance varies by about 3%, being closest to the Sun during the southern hemisphere summer. This means that the period from the equinox in March to the one in September is longer than the other part of the year, so the North Pole gets more hours of sunlight than the South Pole. It gets complicated. --142.112.149.107 (talk) 21:43, 24 February 2021 (UTC)

If you ignore effects like the the ones mentioned above, ignoring asymmetry with respect to the equator, then the answer is yes, the average time between sunrise and sunset is exactly 50% of the day, regardless of one's position on Earth. Consider that wherever you are on Earth, there is always a point on the opposite side of the Earth that is the same distance from the equator, and where it is night during your day, and day during your night. If your daytime lasted e.g. 55% of 24 hours on average, it would follow that on the opposite side, people had only 45% daytime, even though they are the same distance from the equator as you are. So while there are a few caveats, it is generally true the average length of the day is indeed quite close to 50% wherever you are on Earth. With regards to solar power, however, that does not mean that solar panels are equally effective everywhere on Earth, because the amount of energy that can be harvested from the sunlight depends also on the Sun's angle to the horizon. - Lindert (talk) 22:05, 24 February 2021 (UTC)

So it does matter a little bit how you define "night". If you mean the time between civil dusk and civil dawn, that's certainly going to be less than 50% on average (and certainly the error is a lot more than 0.1%, though I don't know exactly how much). This is because the disk of the Sun takes up some space, and even when it's below the horizon, you still get a significant amount of light because of dispersion and refraction.

The fact that you say you're interested in solar power throws another wrinkle into the mix, because solar power doesn't work very well when the Sun is low in the sky, whether because it's close to twilight or because you're at a high latitude. --Trovatore (talk) 22:17, 24 February 2021 (UTC)

The length of a year is not synchronized with the length of a day, so Earth's orbit not being circular should have no effect on the average, and we can take it to be circular. The flattening of the shape of the Earth compared to the idealized spherical Earth is very small. Imagining a perfectly spherical Earth with no atmosphere and a pinpoint Sun, day and night should be sharply defined. The incoming light rays are nor perfectly parallel, but at that distance this is close enough of an approximation, so let's put the Sun at infinity. In this idealized mathematical model, day and night have, on the average, a perfect fifty-fifty split.  --Lambiam 10:38, 25 February 2021 (UTC)

But again, seeing as the sun has a diameter, even if you define night as "as soon as the last part of the disc of the sun sinks below the horizon", you're still going to get a slightly longer day, by the amount of time it takes for 1/2 sun's diameter to cross the horizon. It would be exactly 50/50 if we measured from the midpoint of the disc, but measuring from the top edge of the disc at both ends causes us to have a slightly longer daytime. --Jayron32 18:02, 25 February 2021 (UTC)

That is why a wrote: "Imagining ... a pinpoint Sun".  --Lambiam 18:56, 25 February 2021 (UTC)

Well, yeah, OK. At some point, though, your cow is too spherical to be useful. Of all of your approximations, the assumption that the sun is a pinpoint introduces the greatest error, by several orders of magnitude than the others. --Jayron32 19:16, 25 February 2021 (UTC)

To get an idea of the relative effect, take a look at these sunrise/set charts. The 'error' is roughly equal to the duration of the sunrise (or half that of the sunrise + sunset combined). At the equator, this amounts to about 2.5 minutes, or 0.17% of a full day; at 60 degrees north/south, it averages about 6.5 minutes, or 0.45%. Near the poles, the error increases dramatically, as sunrise can literally take hours on some days. - Lindert (talk) 20:21, 25 February 2021 (UTC)

Consider a cone into which both the Sun, as bulky as it is, and Earth fit snugly. Its aperture is practically the same as the angular diameter of the Sun viewed from Earth, slightly less than 0.01 radians. That means that the ratio of directly illuminated area to the rest is slightly closer to fifty-fifty than 1.005 : 0.995. So on the average, taken over the whole Earth, the effect is less than 1%. If it is locally more, then it is less elsewhere.  --Lambiam 22:22, 25 February 2021 (UTC)

While my model may be a spherical cow, its Earth need not be spherical. For the result to go through, it is sufficient that it be convex and enjoys antipodal symmetry, so any Earth ellipsoid will do.  --Lambiam 22:37, 25 February 2021 (UTC)

The effect from the Earth's orbit's eccentricity, as mentioned by 142.112..., is big enough. On the poles the day and night last from equinox to equinox. From the March equinox to the September equinox is 186 days, from the September equinox to the March equinox is 179 days. The length of the day is a bit longer due to the sun not being a point and refraction. That's more or less symmetric between hemispheres, but a stronger effect at higher lattitudes. So the North Pole has one week more of sunlight per year than the South Pole. The deviation from the mean is about 1%, so that's enough for OP to care about. At lower latitudes the effect is less.

But if you think about solar energy, the thing you should really care about is cloud cover. Clouds have some vertical extend, so the lower the sun is in the sky, the more likely it is that it's behind a cloud. Further, Western Europe, for example, is almost continuously overcast from mid-November to mid-February, cutting power from PV panels by over 90%. The Sahara is quite sunny year-round. PiusImpavidus (talk) 09:25, 26 February 2021 (UTC)

If you have a distant source of light and you suspend a sphere (put your pedantry to one side) wherever that sphere is within the light source half of it will be lit. If you want to count crepuscular light it's up to you. But the answer is simple. Richard Avery (talk) 17:11, 26 February 2021 (UTC)

This is an answer, but not to the original question. The question is not whether there is illumination half the time when averaging over the whole sphere, but whether this is also the case for any location on the sphere. Obviously, it is not if the axis of rotation points to the light source. However, the direction the light is coming from also rotates.  --Lambiam 10:32, 27 February 2021 (UTC)

February 25

How much percent General relativity still need to be proven?

I know that General relativity is not completely proven by Eddington eclipse test at South Africa. How much percent General relativity still need to be proven? Rizosome (talk) 02:03, 25 February 2021 (UTC)

@Rizosome:, why are you asking, and will you respond to any questions or to any answers given to you? Why did you tag me in your earlier post, then not answer when I asked you why you tagged me? As to your question, how does one even quantify how much of any hypothesis needs to be proved? Also, the concept of "proving" a hypothesis is a misnomer. Proofs are used in mathematics, but in science, we come up with theories containing models explaining things like observables. They aren't "proved," so much as demonstrated to match reality as we have observed it, and subject to change once further data comes along. Without knowing when, or even if, let alone how much data will come along, the idea of a "percent" of any hypothesis or theory that is still not demonstrated is nonsensical. I'll put it to you another way, quantum mechanics postulates the idea that gravity could have a relevant subatomic particle, the graviton, though we have not found one yet. What percentage of our understanding of gravity is missing by the fact that we have not found a graviton? How would one quantify that? Especially since the answer may be "there's no such thing as gravitons." --OuroborosCobra (talk) 06:01, 25 February 2021 (UTC)

Indeed, per OuroborosCobra, science doesn't "prove" things at all (despite the inaccurate language used by MANY people who like that word). Science, instead, is a process by which we alternate between making predictions about reality based on observations, then we make new observations to see if they match our predictions. If they do, great! If they don't, we refine our predictions. That process is what science is. The predictions go by various names (theories, laws, models, etc.), but basically it's just a formal way of saying "What happens when I do X?" or "Why does X happen when I do that?" or things like that. I highly recommend familiarizing yourself with the work of Karl Popper, who was one of the foremost philosophers of science, to help get a framework for understanding what science is and what it does. General relativity, like all theories, is an explanation of where gravity comes from and how gravity works. It makes fantastically accurate predictions that, near as we can tell, work very well with matching observations. --Jayron32 12:11, 25 February 2021 (UTC)

@OuroborosCobra: So general relativity is useless because of misnomer? Rizosome (talk) 14:11, 25 February 2021 (UTC)

Essentially yes. The question should be "how accurate has General relativity been in making predictions?" and the answer would be "very". Jules (Mrjulesd) 14:18, 25 February 2021 (UTC)

Wait, what? No! General Relativity has been fantastically useful in describing how gravity works. It makes predictions prior theories of gravity don't make (i.e. Newtonian gravity) and those predictions match reality much MUCH closer than Newtonian gravity. GR is far from useless. All sorts of things like the proper operation of GPS satellites to understanding (or even knowing of the existence of) black holes, to being better able to describe orbital mechanics are all ONLY possible due to general relativity. I don't see where either of you come to the conclusion that OuroborosCobra's answer means that general relativity is useless??? --Jayron32 14:23, 25 February 2021 (UTC)

Woops I meant the question "How much percent General relativity still need to be proven?" is useless! Apologies --Jules (Mrjulesd) 14:27, 25 February 2021 (UTC)

@Mrjulesd: very means how much percent? Rizosome (talk) 15:56, 25 February 2021 (UTC)

Look this is getting extremely circular. But in essence you can't say that scientific theories are "x% proven" because scientific theories are never proven. --Jules (Mrjulesd) 16:32, 25 February 2021 (UTC)

"Very" in this case means that "if we use the equations and mathematics that General Relativity gives us to predict the motion of bodies as they move near massive objects like planets, stars, and black holes, we get answers from those equations that match observed motions to a degree of accuracy that exceeds our ability to detect any errors in the predictions". That's what "very" means. It isn't a percent thing. It's that the equations of General Relativity make predictions about motion, and those predictions match observations. --Jayron32 17:36, 25 February 2021 (UTC)

Those equations, by the way, are known as the Einstein field equations, and while they are fantastically complex and a real bear to solve (involving some really messy four-dimensional tensors!), they do a better job of predicting gravity under extreme conditions than does Newton's law of universal gravitation, which in terms of simplicity is MUCH easier to solve (it's a simple 5 variable equation). The extreme complexity of the equations, by the way, is why we only use them when we need to, i.e. when observations deviate from Newton's equation. Those deviations only become measurable under fairly extreme conditions. --Jayron32 17:42, 25 February 2021 (UTC)

GR breaks down at the center of a black hole, but it makes precise predictions about stuff that happens within the event horizon but away from the center. E.g. a baseball thrown into a black hole moves along a path that GR lets you calculate precisely, including after the event horizon is crossed. But, by definition, the baseball once inside the event horizon can no longer be observed, so GR's prediction of its motion cannot be checked. So that part of GR can never be experimentally tested (unless you follow the baseball into the BH yourself, but that means you can't report the results to the outside). So I'd have to say that 1) this part of GR can never be "proven"; 2) similarly, it can't be falsified; 3) it is still a perfectly good scientific theory (including the interior of BH part), despite what Karl Popper might say. Popper also takes some heat over unrelated issues in this article. 2602:24A:DE47:BB20:50DE:F402:42A6:A17D (talk) 20:14, 25 February 2021 (UTC)

Imagine the frustration of an observer who is so driven by curiosity that they venture into a black hole, because they can't resist the urge to find out if the field equations are still valid there, only to discover that they are not, but now having no way to report this to the outside world.  --Lambiam 22:54, 25 February 2021 (UTC)

Maybe they could be tied to a balloon just outside the event horizon, and tug once if it's still valid, and twice if it's not. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:04, 26 February 2021 (UTC)

No, they couldn't. That's the point of the event horizon. --Wrongfilter (talk) 06:29, 26 February 2021 (UTC)

Also, although the observer learned Morse code as a boy scout he completely forgot it, and anyways, the watch he gave to his daughter is an old electronic watch – a collector's item – and the battery has run out.  --Lambiam 08:06, 26 February 2021 (UTC)

If he could survive the plunge into the black hole, then anything is possible. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:48, 26 February 2021 (UTC)

All the observer needs to do is fly around inside the black hole inside her or his space ship (to make their observations), then scan the interior of the event horizon with warp particles to find the hole made when the ship crashed through the event horizon, and fly back out. EdChem (talk) 12:00, 26 February 2021 (UTC)

Yeah, that doesn't work. The whole point of the event horizon is that past the event horizon, spacetime has been warped to the point that the time dimension has been squished onto the space dimensions (or if you prefer, the other way around). Regardless, inside the event horizon, all possible world lines lead to the singularity. That's not merely coincidence, that's the definition of the event horizon itself, which is the boundary inside of which all possible world lines lead to the singularity. Inside of the event horizon, every forward direction, including forward in time leads to the singularity. It doesn't matter which direction you point your ship; any direction you point and fire your thrusters only moves you closer to the singularity. Even moreso, you couldn't see behind you. If you could even see, every direction you looked is straight at the singularity. There is no possible you could just... way out. Game over. --Jayron32 12:20, 26 February 2021 (UTC)

Warp particles, if used properly, can locally warp spacetime in reverse by rotating over an imaginary Minkowski angle. However, this is mainly theoretical. For practical use, the traveller will have to bring a YeV hypercollider with them and figure out a way to focus the beam of warp particles without getting warped themselves.  --Lambiam 16:00, 26 February 2021 (UTC)

How would it be possible to survive going insidet the event horizon? ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:57, 26 February 2021 (UTC)

It depends on the size of the black hole. Paradoxically, a smaller mass black hole is likely more dangerous; given that gravitational forces will still obey the inverse square law, the event horizon as defined by the Schwarzschild radius is considerably closer to the gravitational singularity at the center of the black hole. Tidal forces caused by the difference in gravitational attraction between different sides of you are likely to be so intense as to tear you to pieces in a process known as spaghettification. For things like supermassive black holes, the event horizon is so far from the singularity you might likely not even notice when you cross it; indeed there's nothing particularly eventful for the observer crossing the event horizon to notice that they did indeed cross it. For such an observer, there's nothing dramatic that happens specifically at the moment the event horizon is crossed. Spaghettification can happen outside the event horizon for smaller black holes, and for the really big ones, you wouldn't notice much of anything. To an outside observer, they never see you actually physically cross it. You just slow down as you approach it, and what they see is your slowing and then frozen image slowly fading as the light that leaves you becomes gravitationally red-shifted beyond the visible range. --Jayron32 16:31, 26 February 2021 (UTC)

Essentially, being inside a black hole isn't too different from being inside a universe undergoing a Big Crunch. It doesn't matter how you travel in space, as you can only go forward in time and every path forward in time leads to the singularity. Any message you want to send out, has to be send back in time, which is unfortunately a violation of causality. PiusImpavidus (talk) 15:30, 26 February 2021 (UTC)

What, if anything, would prevent you being crunched yourself? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:27, 26 February 2021 (UTC)

Nothing. Your future worldline has been constricted to a single path, which takes you to the singularity. Your mass just becomes part of the singularity's mass as you are gradually crushed into it, and even the individual atoms of your body lose their identity as distinct particles. --Jayron32 17:06, 26 February 2021 (UTC)

Then you wouldn't have any capability of even thinking about signaling, let alone actually signaling. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:17, 26 February 2021 (UTC)

If the hole is large enough, you may die of old age even in free fall before the local spacetime distortion starts to exert macroscopic effects on your wave function. For all we know, the observable universe is contained within a black hole.  --Lambiam 09:29, 27 February 2021 (UTC)

Jayron32 and others, it appears that my attempt at humour, which I described in my edit summary as "a simple and solved problem, I saw it on TV," has fallen flat. I was referring to the Star Trek: Voyager episode Parallax in which the ship is flying along and experiences a massive jolt, which turns out to be them crashing through the event horizon of a black hole. After flying around for a while and seeing a time-delayed reflection of themselves, they realise that they are trapped inside the event horizon, which is described by one character as a "very powerful energy field" surrounding the quantum singularity (IIRC). They scan the event horizon with warp particles to locate the "crack" in the event horizon that they made on entry. This has started to collapse but they widen it with decyons (IIRC) and then fly through the hole in the event horizon, escaping. I mentioned it because this episode is (IMO) one of the most scientifically ridiculous in all of Star Trek. As is explained above, the event horizon is not some great barrier that a spacecraft can crash into, nor is the space within it amenable to flying around to look for a way out and then escaping through a convenient hole. I was attempting to mock the treatment of the region within the event horizon as a place from which to escape as opposed to being a region where gravitational effects will crush the ship. The episode also includes the idea of seeing from outside the event horizon a ship trapped inside it and planning to use a tractor beam to pull the trapped ship free, yet the nature of an event horizon means that seeing anything inside it from outside is impossible. SciFi can be scientifically plausible, but also scientifically flawed and (at times) unintentionally hilarious (at least to me), and this episode definitely fell into the latter category. EdChem (talk) 00:24, 27 February 2021 (UTC)

I think it's fairly clear you were being funny, but thanks for providing the context. Star Trek is often more about the adventure than about pure science. It's instructive to an ignoranimous like me to wonder about some of this. For example, what if a ship inside the event horizon was tethered by a really strong steel cable to a ship outside the event horizon? Could the ship be pulled back out? Or would the outer ship get sucked in? That all assumes the inner ship doesn't get scrunched into oblivion, of course. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:18, 27 February 2021 (UTC)

My contribution about the theoretic potential of warp particles, if used properly, was meant to be in kind.  --Lambiam 09:35, 27 February 2021 (UTC)

Speaking of the ultimates of Trekkian scientific ridiculosity (and subsuming Star Trek: Discovery within that universe), in Season 1, Episode 4, "The Butcher's Knife Cares Not for the Lamb's Cry", a ginormous tardigrade appears to possess, as part of its formidable abilities, the ability to travel the filaments between the stars (which are formed by fungal spores), possessing an inbuilt navigation map of the galaxy. By entering the navigation chamber of a spaceship with a sporal drive, the ship's navigation system interfaces immediately and spontaneously with that of the tardigrade, thereby solving the crew's predicament.  --Lambiam 09:53, 27 February 2021 (UTC)

I have proposed a test to isolate the effects of general and special relativity, but I don't think anyone has yet done the experiment or anything quite like it. The Earth rotates about its axis, so special relativity effects depend on how far you are from the Earth's axis of rotation, but in theory, you could choose two points on Earth's surface that are equidistant from the Earth's axis of rotation, but which have different gravitational strengths, for example, due to nearby heavy metal deposits, or by choosing one point at the top of a mountain at a high latitude, and another point at a lower latitude at sea-level. It would also be interesting to test whether or not time dilation behaves exactly as predicted when underground using the same idea of choosing a second point equidistant from the axis of rotation.MathewMunro (talk) 10:53, 27 February 2021 (UTC)

@MathewMunro: maybe there's something I'm not understanding, but what's the advantage of your proposal over something like the Hafele–Keating experiment (mentioned in both our Time dilation and Experimental testing of time dilation articles)? Nil Einne (talk) 17:18, 27 February 2021 (UTC

I would have thought that was bloody obvious. Flying clocks around in aeroplanes doesn't prove much other than that "something" causes time dilation, because it mixes up acceleration, speed & gravitational effects, whereas my idea would isolate the gravitational effect, and could be made as accurate as you like by simply leaving the clocks in place longer. And obviously, flying clocks in planes doesn't test the effect of being underground - ie it doesn't test whether it's the strength of gravity, or the theorised "depth within the gravity well" that causes time dilation.MathewMunro (talk) 21:21, 27 February 2021 (UTC)

February 27

Detergents

Manufacturers produce and market an array of detergents that supposedly are designed for different purposes - such as washing-up liquid, laundry liquid, floor cleaner, wooden floor cleaner, multi-purpose cleaner, toilet cleaner, shower cleaner etc. Yet when I look at the ingredients on different products, they seem to contain basically similar ingredients, namely surfactants (some kind of blend of anionic and/or non-ionic and/or amphoteric), water, perfume, preservative, and maybe a mild acid (presumably to tackle limescale) and something anti-bacterial. Is there really a significant difference between these products labelled for different purposes, or is it mostly a marketing ploy? PaleCloudedWhite (talk) 11:16, 27 February 2021 (UTC)

The article Laundry detergent lists quite a few ingredients that are peculiar to laundry needs, including enzymes. Phosphates in detergent have been banned. Laundry detergent and dishwashing soap for machines have anti-foaming agents. Hand dishwashing soap has been reformulated to prevent dishpan hands, which I used to experience but no longer. And I can attest to a noticeable difference between brand name laundry detergents such as Tide (known to be better by shoplifters everywhere) and cheaper generics. Abductive (reasoning) 18:18, 27 February 2021 (UTC)

February 28

Question about a particular deadly condition for old people

What is the condition called where an old person's blood circulation stops working properly and this old person begins needing blood thinner and this old person's various organs and body parts also gradually begin to give out as a result of their poor blood circulation? Futurist110 (talk) 05:27, 28 February 2021 (UTC)

Are you talking about Congestive heart failure? ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:01, 28 February 2021 (UTC)

Probably Atherosclerosis.--Wikimedes (talk) 07:19, 28 February 2021 (UTC)