The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
Why is it called "stress energy tensor", although its components intended to refer to the energy - actually refer to the energy divided by the speed of light squared - i.e. actually refer to the (relativistic) mass? HOTmag (talk) 13:14, 6 September 2024 (UTC)[reply]
It seems that your last sentence contains some logical mistake. That's why I couldn't figure out your answer.
Anyway, don't you agree, that whenever any component of this tensor refers to the energy of a given body - this component actually refers to the energy divided by the speed of light squared - i.e. actually refers to the (relativistic) mass? HOTmag (talk) 18:49, 7 September 2024 (UTC)[reply]
Relativistic mass just is energy. The only difference is the units, and not even that if you use units in which the speed of light is 1. So it's a little hard to figure out what your question means. --Trovatore (talk) 18:43, 8 September 2024 (UTC)[reply]
The article about real-life dilithium has the potential to be quite interesting, but because of search result overlap with the Star Trek substance, it's difficult to nail down references on this topic. We could use some to establish - for example - if it's a gas at standard temperature and pressure, and if it's "stable", what its typical lifetime is. I would be interested if anyone could put their fingers on sources with this sort of info. -- Beland (talk) 08:22, 7 September 2024 (UTC)[reply]
IIRC all the alkali metal dimers are known in the gas phase (not sure how much of the vapour is monatomic vs diatomic, though). But they will condense back into metallically bonded structures when cooled below the boiling point. Double sharp (talk) 08:25, 7 September 2024 (UTC)[reply]
@Beland The general way to find decent references is to use Google Scholar. This search is a start and removes some hits from articles about a piece of software called dilithium by searching for co-occurence of that word with "lithium". Mike Turnbull (talk) 11:05, 7 September 2024 (UTC)[reply]
Radioactive elements and their isotopes release, for example, alpha particles of various energies. These ionise surrounding material and the colours come from the ions relaxing back to their ground states. There is a chart which gives the energies (zoom in to the isotope of interest). Mike Turnbull (talk) 12:16, 7 September 2024 (UTC)[reply]
Two things about the image-caption details. First, our Cherenkov radiation article discusses the origin of the color via the Frank–Tamm formula. Second, is the glow from Cherenkov radiation or simple ionization? The linked image's description page says "the Cherenkov blue glow that originates from the ionization of surrounding air by alpha particles", which sounds like it's conflating those two. File:Actinium_sample_(31481701837).png's description, also from ORNL sources, simply says "ionization of surrounding air by alpha particles." DMacks (talk) 05:25, 9 September 2024 (UTC)[reply]
Sunshine duration says that locations on the Arctic Circle get 4,647 hours of sunshine (disregarding the effects of clouds), the most of any location worldwide due to the effects of atmospheric refraction. Imagine that Surtsey-type eruptions produce a new mountain in an ocean location on the Arctic Circle, and it's extremely high — say, 5000m. Disregarding the effects of clouds, will it get much more sunshine than locations at sea level? I assume it will get some more than those locations, since the sun's above the horizon longer for an elevated location, but I don't know how much longer. Nyttend (talk) 21:49, 7 September 2024 (UTC)[reply]
It doesn't have to be on the Arctic Circle, you could build a (thought experiment) 100,000 km tall tower on the Equator, and as the Earth rotated, the top of the tower would only briefly be in Earth's shadow, if at all. Abductive (reasoning)05:14, 8 September 2024 (UTC)[reply]
Let denote the radius of the Earth (taken to be a sphere) and let stand for the obliquity of the ecliptic. Then, for the top of a tower erected at latitude to avoid the shadow cast by the earth day and year around, its height should be at least where and equals zero otherwise. [edited 11:27, 9 September 2024 (UTC); edited again 11:56, 10 September 2024 (UTC)]
At the Poles, with this comes out at about a mere 700 Burj Khalifas stacked on top of each other. This is the height of a Low Earth orbit, so the tower may be hit by satellites in polar orbit.
On the Arctic Circles, with the tower needs to be high.
In the tropics, from the Tropic of Cancer to the Tropic of Capricorn, where the tower needs to be infinitely high, which is impractical from an engineering point of view :).
I dunno if that makes sense. Consider Saturn's rings; they are often (always?) partly in shadow. But a tower on the axis will stick out into perpetual sunlight at a height much less than the rings. Abductive (reasoning)14:55, 8 September 2024 (UTC)[reply]
I must have made a mistake; if had been zero (meaning that the equatorial and ecliptic planes coincide), any tower at a pole would always be in sunlight. Possibly, the fix is simply to replace by I can't examine this further right now. --Lambiam 17:52, 8 September 2024 (UTC) — Now corrected and hopefully now correct. --Lambiam11:27, 9 September 2024 (UTC)[reply]
But wait a minute. If at some point in the year the sun is directly overhead at noon (i.e. between the two tropics) then if the tower is normal to the geoid it's going to have to be very long, because at midnight sun-earth-tower form a straight line. This is analogous to a total solar eclipse, where the straight line is sun-moon-earth. But you can have annular eclipses because the sun is so much larger than the moon, and when the moon is beyond a certain distance we can "see over it" and catch a glimpse of the sun. As the sun is much bigger than the earth, the earth's shadow is not infinitely long and at some point the top of the tower must emerge from the gloom. 2A00:23D0:CCD:CE01:1197:733B:D027:4118 (talk) 15:27, 9 September 2024 (UTC)[reply]
Just like my calculation assumed a spherical Cow Earth, it assumed an infinitely distant Sun. Since we have total lunar eclipses, we know the Earth's shadow extends to far beyond the Moon's orbit. Ignoring the effect of sunlight being bent by our atmosphere, the shadow cone extends to 1.38 Tm, almost 1/100 of an astronomical unit. --Lambiam11:56, 10 September 2024 (UTC)[reply]
The rules for the systematic element names, approved by IUPAC in 1978, were designed solely for the purpose of assigning temporary names to unknown or not-yet-named chemical elements. Since all such elements have an atomic number greater than 100, the system only caters for such higher numbers, up to 999 (Ennennennium). The extension to other natural numbers for elements with IUPAC-approved names, while obvious, does not carry the IUPAC stamp of approval. Note that Nilium (a potential name for proton-free muonium or neutronium) and Quadium have already been given away. --Lambiam08:31, 8 September 2024 (UTC)[reply]
This is a terminology question about organisms, not diseases. In the grand scheme of things, there are two ways nucleic acid strings propagate themselves. In one, the nucleic acid string encodes enough information to build a cell with enough machinery to copy the nucleic acid string and make enough of the machinery to allow the cell to split, each with a copy of the nucleic acid string. In the second type, the nucleic acid string encodes a simple shell designed to penetrate the first type and hijack its machinery to copy itself and the shell. We have a very specific term, Virus, for the second type. Is there an equally specific term for the first type? Something better than "ordinary cell." --agr (talk) 18:10, 8 September 2024 (UTC)[reply]
I admit to not being an expert in this area. According to Prokaryote, cellular organisms can be divided either
into two domains (Prokaryote/Eukaryote) - in which case they may be 'opposites', though I don't know whether viruses fit in either half, or
into three domains (Bacteria/Archaea/Eukarya) - which again may not include viruses
I suppose if Prokaryotes include Bacteria, Archaea and viruses, then they function as the 'opposite' (in the sense of 'exclusive or') to Eukaryotes. I don't know of a term that covers Bacteria, Archaea and Eukarya but excludes viruses, which is what OP is seeking. (Apologies for my sloppy nomenclature to anyone who knows the definitions of these words!) -- Verbarson talkedits08:16, 9 September 2024 (UTC)[reply]
Re: "a term that covers Bacteria, Archaea, and Eukarya but excludes viruses": I think said term would be "life" (perhaps with the caveat "as we know it" appended). Viruses are biological entities, but do not meet the qualifications to be considered life. Though I think some, or maybe all, viruses are descended from various types of living organisms..some maybe from life during the RNA world age. 73.2.106.248 (talk) 01:57, 10 September 2024 (UTC)[reply]
When with an incident ray a photon of sufficient energy meets an electron it can eject it from matter. But outside of matter, we still have the probability that other photons meet this electron and orient its course in the direction of the radiation. Has this been observed? If yes or no, what is the explanation? Malypaet (talk) 09:20, 9 September 2024 (UTC)[reply]
Compton scattering, the effect of the interaction of a photon and a charged particle, usually an electron, also applies to the interaction of photons and solitary electrons. If no energy is needed to release bound electrons, this form of scattering already occurs with low-energy photons and is then known as Thomson scattering. --Lambiam13:06, 9 September 2024 (UTC)[reply]
I read these articles, but what is missing is the notion of time. A radiation is a flow of energy (a rate), so an electron in a volume crossed by a radiation will experience a force in the direction of the radiation, as long as it is in this volume, ok. As it accelerates, it releases energy in the form of radiation (synchrotron effect?), so it loses acceleration. I suppose that the trajectory of the electron is a curve that brings it in the direction of the incident radiation? Do we know the equation of this curve? Malypaet (talk) 21:14, 9 September 2024 (UTC)[reply]
Acceleration is a change in velocity. In the scenario of a photon interacting with a free electron, the only change in velocity is at the moment of interaction. Before and after, in the absence of external forces, their velocities are constant. --Lambiam22:45, 9 September 2024 (UTC)[reply]
But in radiation that is a photon flow, there are more than one photon, so the probability that other photons successively (in time) hit the electron is not null. Then, in this term of probability, you can have a trajectory and a curve with a point in space and time for each interaction, isn't it? Malypaet (talk) 08:35, 10 September 2024 (UTC)[reply]
I've just been trying to think. There are lots that are black/brown/white and I can think of several yellow, green, blue and red vertebrate animals (mostly birds), but very few that are predominantly purple. Is this the rarest colour in nature? Iloveparrots (talk) 21:44, 9 September 2024 (UTC)[reply]
left: azzurro; right: blu One problem in addressing the question is that colour names cover a fuzzy region in a multi-dimensional space of colours. The 23 examples of purple vertebrates shown here display a wide range of purplish colours. For a reasonable comparison between named colours, the regions need to have similar sizes. The region we call "blue" is split in Italian into two regions considered to have different colours: azzurro and blu. --Lambiam23:24, 9 September 2024 (UTC)[reply]
In looking into my answer to Cat above, I stumbled on the quantum immortality article, and I feel dumber for having read it. I'm getting that it's premised on some mystic consciousness woo, but I still don't understand what the experimenter dying, or the experimenter understanding QM, has to do with anything. Or does the thought experiment just exclude hard materialists at its premise? SamuelRiv (talk) 04:23, 10 September 2024 (UTC)[reply]
The basic argument has nothing to do with consciousness. In the many worlds interpretation, a measurement that causes the wave function to collapse to a definite state actually makes the universe split into two: one for each of the two possible outcomes. Now imagine a qubit being measured again and again, until the outcome is 0. Each time there will be a branch in the tree of universes in which the outcome was 1, so there is a path in which the qubit never "dies". The death of a living organism is the result of many measurements eventually leading to its demise, but, analogously to the immortal qubit, there should be a path in which all outcomes are such that they keep the organism alive and, pace Tegmark, well. --Lambiam08:36, 10 September 2024 (UTC)[reply]
In the article it says Tegmark's thought experiment "must be virtually certain to kill the experimenter" and "on a time scale shorter than that on which they can become aware of the outcome of the quantum measurement". I don't understand what this has to do with what you're saying about the MWI. It should be sufficient proof enough of MWI to simply have an experiment running measuring the spin of a random qubit that never ever measures 0 (or I guess to see an event in any known process whose expected duration is orders of magnitude smaller than the lifespan of the universe). Or, if personal experience is insisted, I don't see what dying, or instantaneous dying for that matter, has to do with 'traveling' so-to-speak through the many worlds. SamuelRiv (talk) 15:34, 10 September 2024 (UTC)[reply]
In your universe the qubit may come up 0 while another version of you, in a sister universe, sees a 1. But that other you cannot communicate this outcome to your you. --Lambiam17:31, 10 September 2024 (UTC)[reply]
Ok? But if I instaneously kill myself I can?
I feel like there's a great deal of unarticulated premises about consciousness here that everyone in the article seems to know instinctually, but I am completely lost by. (Not that I can't sympathize, but that there are a lot of interpretations of spiritual consciousness and the self around the world, so I can't follow the logic of the argument until I know what premises they're using.) SamuelRiv (talk) 17:40, 10 September 2024 (UTC)[reply]
Ok, so then could you explain Tegmark's reasoning in the article? I understand the laws of physics as far as I've studied them, but I'm trying to understand the argument as written (and maybe even salvage the article). SamuelRiv (talk) 17:57, 10 September 2024 (UTC)[reply]
There isn't much to it. You have two people (let's make them people to make it easy). One is in the box. One is outside the box. The one in the box knows if he is alive or dead. The one outside the box doesn't know if the one inside the box is alive or dead and, therefore, must continue with the assumption that the person in the box is both alive and dead at the same time. What is being done that requires this? Let's assume that the person outside the box is filing taxes for the person inside the box. Is this the final tax statement for someone who is dead or a normal tax statement for someone who is alive? The person outside the box does not know and has to fill out both, one for someone who is dead and one for someone who is alive. Now, let's assume the person in the box is alive. He knows that the person outside the box is filing both and giggles to himself that he making the extra work. But, what if the person inside the box is dead? The person outside the box is treating him as if he is still alive... which is overhyped as "life after death." It isn't that the person in the box is alive. It is that the person outside tbe box is treating them as they are alive (and dead). The complication isn't in the concept of being alive and dead. The complication is in the quantum formulas that use the two states combined. 75.136.148.8 (talk) 17:18, 11 September 2024 (UTC)[reply]
Sorry, but I'm not following what this has to do with Tegmark's 3 conditions in the article I linked at the beginning of this topic header (the question to which you immediately replied), or the subject of the quantum immortality/suicide generally? SamuelRiv (talk) 01:05, 12 September 2024 (UTC)[reply]
Sorry, no red herring here. The consciousness is here what makes the superposition its own observer. The basic question is here "How do the equation of Schroedingers cat work if observer and observed are the same, especially if the observer could observe only one of the states?" (A dead observer can not observe) 176.0.144.43 (talk) 16:26, 12 September 2024 (UTC)[reply]
For a resistance , a voltage and a current , with the relation , the electrical power is . As is the intensity of the electron current in a section, that is to say the number of electrons that pass through this section per unit of time. Then should we consider that the number of circulating electrons is constant and proportional to , therefore with the intensity proportional to their speed which is then considered as the voltage, or a mixture between the number of circulating electrons and their speed? In the latter case what is the rule giving the relationship between the number and the speed of the electrons? Malypaet (talk) 08:47, 10 September 2024 (UTC)[reply]
The concept that current flow is the same as electron flow is acceptable for learning about circuits, but it is not real. It is similar to using water flow to explain the concept of electricity. Electrons do move, but very slowly in comparison to electrial current flow. There are many websites and videos that explain the actual flow of electromagnetic waves through a circuit. If you ever happen to get into radio or microwave circuitry, understanding the electromagnetic nature of electricity is important. 12.116.29.106 (talk) 12:29, 10 September 2024 (UTC)[reply]
Your first sentence is entirely correct. Your second too, assuming that the current is carried by electrons, which is normally the case in solid or liquid metals. Then your question. I don't fully understand the question, in particular the part “the number of circulating electrons is constant and proportional to ”. Both the number of free electrons and the resistance are static properties of the circuit, independent of the voltage or current applied, but with both constant, you cannot say that one is proportional to the other. Otherwise, the answer to the question appears mostly yes, although it's worded in an uncommon way. If you increase voltage, the drift speed of the electrons increases, but the number of free electrons is constant (again, in a solid or liquid metal).
The density of free electrons (electrons per cubic metre) depends on the material used. In semiconductors, there's a strong temperature dependence too. The specific resistance (ohm-metre) also depends on the material and temperature. The current density (ampère per square metre) equals the free electron density (electrons per cubic metre) times the drift velocity (metres per second) times the electron charge ( coulomb per electron). The current density also equals the local electric field (volts per metre) divided by the specific resistance, none of which are constant throughout the circuit. All of that assuming that magnetic and electrostatic induction can be ignored (i.e., DC) and that electrons get up to speed in a negligible distance compared to the length scale of the circuit. PiusImpavidus (talk) 12:34, 10 September 2024 (UTC)[reply]
One does not apply a voltage or a current, but only a voltage, which will then give a current depending on the circuit's resistance. So I will clarify my question. I consider the resistance in a restricted circuit volume and having a certain section (elsewhere the resistance is zero), all in a solid. If I understand your answer correctly, the number of (free) electrons moving in the resistance is constant and it is the voltage divided by the resistance which gives the drift velocity of the electrons. I know that this current carries an electromagnetic wave, more precisely a flow of energy and at constant speed. So I am looking for the relationship between the current of the electrons whose number is fixed and the flow of electromagnetic energy whose speed is constant, which gives the equation . If the number of electrons is fixed, it seems logical to me that the voltage is proportional to their drift velocity (speed). Maxwell is for the energy on one side, and on the other, Ampere is for the electrons that carry this energy. f the electrons do not move, there is no electromagnetic wave with its transport of energy. Malypaet (talk) 20:48, 10 September 2024 (UTC)[reply]
Thanks. It confirms that the voltage and the speed of electrons are proportional. However, I am not sure that "drift velocity" is an appropriate term here because it is zero in an alternative current. It seems to me that the average instantaneous speed of the electrons is more appropriate. Malypaet (talk) 19:35, 11 September 2024 (UTC)[reply]
Is there one scientific-mathematical test to distinguish between different forms of genetical herability?
I mean, if a certrain phenotypic property is genetic during Mendel's rules or additiv or something? I wonder whether we are able to find out just by looking at the offsprings and the parent generation. 2A02:8071:60A0:92E0:25A6:B013:4618:1FCD (talk) 10:20, 10 September 2024 (UTC)[reply]
When looking at individual organisms, you see phenotypes. The forms of heredity (biological inheritance) apply to genotypes. The relationship between genotype and phenotype is not straightforward. If the phenotypical statistics of the offspring of a couple form a typical Mendelian pattern, it is an indication that Mendelian inheritance is at play, but it is not a proof. And conversely, the absence of a typical Mendelian pattern need not mean the underlying genotypical inheritance is not Mendelian. --Lambiam17:45, 10 September 2024 (UTC)[reply]
There are different kinds of heritability. For instance one way via the rules of Mendelian; some properties are heritabil with additive effects and others with combinated effects.
Take a look at the diagram labeled "A ’Broken Stick’ Model" in the article Additive genetic effects. In general, the observed phenotypic variation is the combined effect of additive and non-additive effects. If it is known that the phenotypic variation is controlled by just a single gene, it is relatively easy to determine which variants the gene has and which variants, if any, are dominant or recessive with regard to their phenotypical expression. But control by just a single gene is exceptional; it implies that the phenotypes can be split into a limited number of discrete categories. The converse implication is not necessarily valid. --Lambiam06:19, 12 September 2024 (UTC)[reply]
Does "narcissist personality disorder" contradict itself?
I.e. labelling "excessibe grandiosity" using one person's name (fictional or not) achieves grandiosing that person (narcissus) thus communicates a double message? As in while the word "disorder" says "it is severe", the name of one person trivializes grandiosity. Thus it seems not quite medically consistent. Ybllaw (talk) 12:37, 10 September 2024 (UTC)[reply]
You misread what I said. Your comment "grandiosing that person" is not what I said. I said it grandioses "narcissus". I also didn't use the word "oxymoron". I think there is no need to introduxe extra terminology. My question was sufficiently clear. "No it isn't" is an unuseful/not very dilligent reply. Ybllaw (talk) 13:19, 10 September 2024 (UTC)[reply]
Thank you for clarifying that you are referring to the mythological Narcissus. The capital letter makes all the difference. I still don't see how the label is grandiose. If anything it demeans him. Shantavira|feed me14:22, 10 September 2024 (UTC)[reply]
Your sneering/snobbery about "capitalization" doesn't contribute to making this reference desk a welcoming place.
Grandness as I think to understand it doesn't mean "good" nor "bad", it means great, and a lot of attention is still making a person great, the same way a "great dictator" can be written about as great without being written about as "good". Ybllaw (talk) 12:41, 14 September 2024 (UTC)[reply]
"My question was sufficiently clear." No, it wasn't. You have multiple spelling and grammar errors as well as just odd phrasings that make it very diffcult to understand what you are trying to ask.--User:Khajidha (talk) (contributions) 10:55, 12 September 2024 (UTC)[reply]
If you could spot my spelling errors than you admit that you knew what the words were that I intended, and thus didn't detract from the readability.
I never asked "whether the phrase is an oxymoron", you introduced that question.
As I have already said, the amount of effort in "no it isn't" makes your reply completely useless. That reply has NO educational value, it doesn't provide any tools that would enable me to understand an answer to my question, rather you have only encouraged me to blindly copy an answer without understanding anything about the reasons you see for that answer. Ybllaw (talk) 12:44, 14 September 2024 (UTC)[reply]
You need to explain your concept of "grandiosing" before anyone can give you a satisfactory reply. We don't know what it means so we can't tell where to start. What are some synonyms, how does it trivialize grandiosity (someone's grandiosity? the quality of being grandiose itself?) to attach a name to the word "disorder"? HansVonStuttgart (talk) 09:52, 16 September 2024 (UTC)[reply]
These definitions need to be kept in sight:
Narcissus A fictional character in ancient Greek myth whose self admiration comically exceeded his common sense. We spell Narcissus with a capital first letter for no other reason than that his is a proper name. We derive from Narcissus by analogy (a relationship of resemblence) narcissism that is a personality style of unusually high preoccupation with oneself and one's own needs. Only when a narcissistic personality is so extreme as to impair mental well-being and Psychosocial development will it be declared a mental disorder, this called narcissistic personality disorder (NPD). I see nothing illogical or contradictory in this understanding of NPD. However the OP is here to argue an objection to the term NPD that is difficult to understand and proceeds quite combatively to take issue with every responder to their question.
Grandiosity is simply an unrealistic sense of unique superiority that is often present in NPD and is in no way a genuine achievement. It is meaningless to talk of grandiosing a third party when grandiosity is only what the NPD feels about themself. The language becomes confused if the real person with NPD is called "narcissus" or "Narcissus" which both seem merely rude. The OP snaps impolitely[1] at Shantaviraj who actually read the words "achieves grandiosing that person" correctly and attacks Shantaviraj for offering a tentative answer to the unclear question. The OP returning[2] just 3 minutes later to shore up their own thoughtless contradiction is what I qualify as a snapping behaviour. The OP's next accusation about "Your sneering/snobbery..." is calculated insult. I conclude that despite the best-effort responses from Shantaviraj, Khajidha, Lambiam and HansVonStuttgart this OP is not here to accept any help in the form of references that we could give and that further engagement on the OP's issue is a waste of time. Philvoids (talk) 12:40, 17 September 2024 (UTC)[reply]
I read on the Hero syndrome page.. "The term is used to describe individuals who constantly seek appraisal for valiant or philanthropic acts, especially by creating a harmful situation which they then can resolve". Isn't that very similar to FDIA? There is no mention on the Hero syndrome page of FDIA.
The FDIA page even literally mentions.. "These proxies then gain personal attention and support by taking on this fictitious 'hero role' and receive positive attention from others, by appearing to care for and save their so-called sick child", but doesn't reference the Hero syndrome page either. Ybllaw (talk) 12:56, 10 September 2024 (UTC)[reply]
A statement such as "A is a kind of B" requires a reliable source. One issue why such sources are hard to come by in this case may be that Factitious Disorder is a recognized disorder (300.19 in DSM-5, F68.1 in ICD-10), whereas "hero syndrome" is journalese and has no generally accepted diagnostic criteria. --Lambiam17:17, 10 September 2024 (UTC)[reply]
Thank you for the answer. Is there not a lot of literature about hero syndrome? Some of the cases mentioned on the wikipedia page (e.g. a police officer setting a bomb to "be seen defusing it") seem quite high profile, I'd expect to be some literature about that. Ybllaw (talk) 12:51, 14 September 2024 (UTC)[reply]
I don't see much that makes the connection, but here is a directly relevant passage in a RS, a book by the title The Munchausen Complex: Socialization of Violence and Abuse:
In another manifestation of MSBP, a perpetrators will induce a condition in order to heroically “save” the victim thereby showing they are a concerned caretaker. Sometimes health care providers – including nurses of both sexes – do this. Their actions are considered a type of Munchausen Syndrome by Proxy. This phenomenon may very well be a distinct category of Munchausen that should be researched and redefined as Munchausen Malignant Hero Syndrome.[3]
What kidney theft gangs working out of Southeast Asia are those then? There are so many traffic fatalities in SEAsia that I'm surprised there would be a market for stolen kidneys. Sean.hoyland (talk) 04:17, 16 September 2024 (UTC)[reply]
Because nobody knows how to do it (or if they do, they cannot yet implement it in an experiment). An attosecond is a rather short time. The article lists the shortest laser light pulse created as 43 attoseconds, so that is the shortest time scale that is technically accessible at the moment. But if you have an idea, go for it. --Wrongfilter (talk) 12:35, 14 September 2024 (UTC)[reply]
There may be a more fundamental reason. Such a measurement would necessarily (I think) require two observations, one essentially being that a some time t0 the transition has not yet taken place, the other that at a later time t1 the transition has now occurred. Such observations require an electromagnetic interaction, which will unavoidably disturb the observed system, in particular potentially causing the electron to behave differently. If there is some clever way around this fundamental issue, no one has thought of it. --Lambiam13:07, 14 September 2024 (UTC)[reply]
Apparently, to date, we do not have the tools precise enough for this measurement. On the other hand, the disturbance of the measurement can be anticipated and circumvented, as in this article measuring the delay of a photoemission by the 2023 Nobel Prize winner L'Huillier: "The determination of photoemission time delays requires taking into account the measurement process, involving the interaction with a probing infrared field. This contribution can be estimated using a universal formula and is found to account for a substantial fraction of the measured delay." In the past this delay was considered zero, today it is measured around 10 atoseconds. So... Malypaet (talk) 21:45, 14 September 2024 (UTC)[reply]
Do you expect us to read and understand the entire paper up to that equation? Maybe you could help us a bit by summarising what the terms stand for, what their units are and why you think the entire equations do not yield "metric" units. --Wrongfilter (talk) 17:06, 14 September 2024 (UTC)[reply]
It should. All the units in the paper are SI. Script-H in the paper should be heat flux (e.g. conductive thru a 2D surface i.e. an ice sheet), which will be in Joules per second per meter^2. Make sure to write down every step carefully, using the values given in the paper, including the table of constants. SamuelRiv (talk) 17:08, 14 September 2024 (UTC)[reply]
Ok, I got it to work, to give delta H in meters. The one constant that seemed hidden in the paper was b, but it has the same dimensions as b0 (eqn A2). Also they don't give the Coriolis coefficient explicitly, but that has rad/sec (1/s) units. Apart from that, all the other constants should be in there. SamuelRiv (talk) 19:44, 14 September 2024 (UTC)[reply]
Googling finger with an extra joint the first hit is our very own article Triphalangeal thumb. The first page of search results only mentions an extra crease on the little finger, with no underlying extra bones. But scroll down on the results, maybe you'll get lucky! 85.76.83.87 (talk) 14:54, 15 September 2024 (UTC)[reply]
Take a look at this video from a YouTube channel I follow. Steven the seagull injured her (yeah, Steven turned out to be female, but the name stuck anyway) foot somehow. Accident, fight, attack by a predator - whatever happened, the webbing between her toes got split. Does anyone know if that will grow back eventually? Iloveparrots (talk) 21:44, 15 September 2024 (UTC)[reply]
From Regeneration (biology) § Aves (birds): Owing to a limited literature on the subject, birds are believed to have very limited regenerative abilities as adults. I was able to find an issue of a waterfowl newsletter with a picture of a duck's foot webbing, apparently torn and partially regrown. Based on this, I think it's very likely to grow back somewhat, but perhaps less likely to grow back completely. I'm rooting for Steven though! jlwoodwa (talk) 01:52, 16 September 2024 (UTC)[reply]
She's been getting her foot doused with antiseptic and eats a REALLY good diet for an urban gull (fresh fish, fresh meat, mealworms daily), so she's in a better position than most. Iloveparrots (talk) 13:37, 16 September 2024 (UTC)[reply]
Presumably it could only heal if the split was mechanically sealed first. If the surfaces keep moving relative to each other or they get dirty I don't see how the split can heal. Shantavira|feed me08:23, 16 September 2024 (UTC)[reply]
I was thinking that it might grow back from the bottom outwards. Not really sure how it works in gulls, compared to us, if we split that thin bit of flesh between thumb and forefinger. Iloveparrots (talk) 13:34, 16 September 2024 (UTC)[reply]
If you are referring to a single elementary particle, so why didn't you mention the electron, besides the quark?
If that's because an electron colliding with a positron turns (together with the positron) into a pair of photons, then also a quark colliding with an anti-quark turns (together with the anti-qurk) into a pair of gluons.
Anyway, in my question I allow a given elementary particle to collide with its anti-matter for becoming another elementary particle.
More important: My question is theoretical, so it's not only about known particles, but rather about all possible particles, including those which haven't been discovered yet. HOTmag (talk) 18:21, 18 September 2024 (UTC)[reply]
If someone claims all swans are white, it suffices to debunk the claim by finding one purple swan. Maybe there also blue, brown or black swans, but it is not necessary to search for further counterexamples. Likewise, if some physical theory claims every elementary particle can turn into some other elementary particle, it suffices to debunk the claim by finding just one elementary particle that cannot turn into some other elementary particle. I just started with the top line of File:Standard Model of Elementary Particles.svg. There may be many other counterexamples (like the Higgs boson), but why bother to keep searching?
The as of yet undiscovered bunkon and trashon, whose properties are still unknown except that they are postulated to be different elementary particles, can turn into each other. A difficulty in finding them is that their properties are unknown, so experimental physicists don't know where to look. There may be many more such pairs, which may never be discovered. --Lambiam10:17, 19 September 2024 (UTC)[reply]
By mistake, I thought you meant the quark was the only particle that couldn't turn into another particle but a quark, but now I see this was not what you meant, so I take my first sentence back.
However, I still emphasize that my question allows a given elementary particle to collide with its anti-matter for becoming another elementary particle.
Re. your senetnce: "The as of yet undiscovered...different elementary particles, can turn into each other": Is there any physical theory claiming what you've claimed in that sentence? Actually, this was my original question... HOTmag (talk) 10:44, 19 September 2024 (UTC)[reply]
OP may have in mind something more like the particles created from particle-antiparticle annihilation, such as those in the chart at Annihilation § Electron–positron annihilation, as opposed to something like the weak decay of quarks.
It seems to me that OP could mean either: 1) a single elementary particle can spontaneously become another single elementary particle (with the help of another particle that remains unchanged), in which case I think the answer may be no for any particle; or 2) for two given particles, there's an interaction in some condition where it's meaningful to say that one specified particle is in the input, and it becomes in the output the other specified particle [Edit: which may include any number of other particles in the reaction doing anything else]. Not sure (I didn't do particle), but I think (2) might be considered more or less accurate (to the extent the fuzziness of the wording necessarily allows). SamuelRiv (talk) 16:10, 19 September 2024 (UTC)[reply]
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