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May 18

When chemical properties of liquid aren't just the average of the elements

If you mix two liquids with ebullition at 100 °C and 80 °C (more or less like water and some alcohol, but I have no specific substance in mind), could the resulting ebullition be far off 90 °C?Doroletho (talk) 01:16, 18 May 2019 (UTC)

BP will be close to 90 for a mixture of equal weights, but may be slightly lower or higher than you'd expect. Raoult's law discusses this.Greglocock (talk) 04:53, 18 May 2019 (UTC)

Also the specific volume, as discussed above (though perhaps that is what prompted your question, in which case you knew that). catslash (talk) 14:13, 18 May 2019 (UTC)

Azeotropes are an extreme examples of non-average (and not even "intermediate") behavior. If you have a non-ideal mixture, you are lose a premise of Raoult's law. DMacks (talk) 16:59, 18 May 2019 (UTC)

Physics help needed

2019 redefinition of SI base units#Uncertainty of fundamental physical constants is marked as being OR. Does anyone have any sources for the uncertainties listed?

The redefinition of the base units for the metric system happens on 20 May 2019. I am hoping to get this article mentioned on the main page on that day. Alas, I also have a hot project and if I don't make my deadline because I spent too much time on Wikipedia the toy I am working on will miss Christmas. :( --Guy Macon (talk) 15:32, 18 May 2019 (UTC)

Will this change have any real, practical effect for the average human? As compared with your missing your project deadline? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:25, 18 May 2019 (UTC)

Reading that article, I ran across the curious statement that the steradian is a "dimensionless unit". I do understand what they mean, yet ... well, my philosophy is tickled. I mean, yes, there are some units that make absolutely no sense without an external standard to calibrate by (7 meters) whereas others are ratios that indicate some kind of comparison (7 mg/kg dosage). This comes up in chemistry where, for example, tracking a dilution problem can be easier if you make up a difference between "ml concentrated solution" and "ml dilute solution". But, well, the only thing is, I would have thought that the "unit" would be the external measurement whereas the "dimension" would be more of whether a measurement is curved or straight. Could it possibly be a unitless dimension? I don't know... Wnt (talk) 21:06, 19 May 2019 (UTC)

It's not unitless because the steradian is the unit. Dimension here is being used in the sense of Dimensional analysis. Dbfirs 21:29, 19 May 2019 (UTC)

Well yeah, but dimension is like mass, length, time ... solid angle? The steradian comes into being because you measure the angle in m^2 per m^2 or in^2 per in^2, and the units cancel out. It does seem like making up a unit to describe a unitless dimension... Wnt (talk) 13:39, 21 May 2019 (UTC)

Please note this apply just as well to normal angle in radian, which also is measured in meter per meter, and the unit cancel out, too. So if you think that a dimensionless unit is odd, and somewhat useless, how do you cope with angles?

Maybe this should be said this way: dimensions DO cancel out, units, not so much. The apparent area of an object afar maybe measured in m² just like the square of its distance, but is not the same "unit", so don't cancel them out, rather, call the ratio by its proper name, that is : steradian.

And also apply to Plank units: by construction, they attach the dimensions to the relevant constant, and using them just every physical equation appears dimentionless, just like a steradian.

So you just have to understand the steradian as some sort of plank unit, linked to the universal geometrical constant 4pi.

there are quite a number of SI units and SI derived units that are actually of the very same dimension of another, but are still not the same, just look at them. For instance, Candela, Lumen and Joule. And you must NOT use them for one another. And you MAY divide them, getting a number that IS dimensionless but NOT unitless.

So understand the steradian as a ratio of two different units of the same dimention: the area of a seen object, and the square of its distance. Pretty much like a Lumen/Joule would be dimensionless, but still not unitless nor meaningless.

Does that help understanding ?

Gem fr (talk) 23:00, 21 May 2019 (UTC)

Well, I'd be lying if I claimed to really understand candela and lumen in detail: we have up a picture of the photopic and scotopic luminosity functions with a little legend about the CIE curves that went into them... my gut feeling is that any unit of physics that delves that deep into biology is not going to act in the reliable way one expects of a physical unit, that there's probably some combination of strobe pulse and frequency that will end up looking totally different in brightness than the unit says it does. The use of candela = lumen/steradian seems fairly straightforward, but describing it philosophically seems different. I mean, I thought the meter was a unit. How then can meter^2 not be the same unit as meter^2? The way I'd say it is that they're different dimensions, just as length and width are different dimensions. And the partial circumference of a circle is a different dimension from the length of the tangent also. And the ratio between those has no units, but it is a ratio of dimensions, like the Golden Mean of a painting or something. But that's not how you're saying it. Wnt (talk) 12:53, 22 May 2019 (UTC)

Seems pretty obvious to me that the square of a distance (like it appears in steradian, or in calculation of gravitation force) is not an area, despite both having dimension of Length². So it makes sense to have units, like steradian AND radian, whose dimension are a number, but they are different nevertheless.

Gem fr (talk) 15:03, 22 May 2019 (UTC)

The r^2 in an inverse square phenomenon absolutely can be viewed as an area. For example, consider the Sun, or a star. Viewed in a telescope (kids, don't do this) the brightness of the sun is always going to be exactly the same, whether it is partially eclipsed, viewed from Pluto, whatever, so long as it fills the entire field of the telescope. The inverse square brightness of the sun simply reflects the steradians it takes up in the sky: the ratio of its area to the area of the sphere with the same radius. But the odd part is I feel like you are (or should be) agreeing with me: you're saying you can have the same unit mean different things. But that 'meaning' I would call the dimension - just as length, width, and height are different dimensions measured with the same unit. Wnt (talk) 00:32, 25 May 2019 (UTC)

:CNN has a writeup about it,[1] though I can't vouch for its absolute accuracy - one thing being that they seem to think a kilogram is a weight. ←Baseball Bugs What's up, Doc? carrots→ 18:10, 20 May 2019 (UTC)

Does cancer cells have a specific protein structure ?

Does cancer cells have a specific protein structure ? does this protein structure is the same structure of the healthy cells ???

A good start would be to read Cancer cell. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:24, 18 May 2019 (UTC)

Protein structure is a characteristic of an individual protein. The vast majority of 30,000 genes in a cell produce proteins, each different from the others, each of which may have more than one structure. It is possible that genetic, epigenetic, or regulatory changes in the cell can alter the structure -- to give a classic example, activation of c-Src by phosphorylation will change its structure, causing it to interact differently in the cell and have more activity in stimulating mitosis (reproduction). Cancer cells can have genomic instability with vast numbers of genetic alterations in a cell, vastly different patters of gene transcription, vastly different amounts of protein present, so the protein structures likewise will follow through in being altered in many specific ways. But every cancer case is different (well, many of them), just as families are unhappy each in their own individual way. Wnt (talk) 20:58, 18 May 2019 (UTC)

May 19

Locality

For the sake of argument let's say you are observing Location A, but cannot observe Location B unless you are inside Location A, even if B is directly next to A or surrounding it on all sides. Unless you're inside A, you can't see B. Does this violate any laws of physics? déhanchements (talk) 00:39, 19 May 2019 (UTC)

So, I am observing a small hut A which is built over a shallow well whose bottom is B. I cannot observe B when outside A, only from within A.

Or, I am in a windowless attic looking down through a small hole in the floor into a windowed room A, but I cannot see out of the windows to observe the surrounding landscape B unless I am in A.

Are these examples of what you mean?

If you have something more abstract and general in mind, you might be thinking of problems in Topology, and might get a better response on the Mathematics desk. Alternatively, if you're thinking of questions pertaining to the Principle of locality, you're in the right place. {The poster formerly known as 87.81.230.195} 2.122.2.132 (talk) 02:08, 19 May 2019 (UTC)

Those are great examples, but what about this: You are observing a small hut A surrounded by a barren plain. But only by entering this hut can you now look out of the window and see, not a barren plain, but a meadow B, which surrounds the hut. The meadow and the barren field spontaneously exist. déhanchements (talk) 02:54, 19 May 2019 (UTC)

If the meadow surrounds the hut, how did you not see it on the way in? ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:55, 19 May 2019 (UTC)

And that's exactly what I'm getting at. This is a counter intuitive phenomenon. You can only observe it from a certain reference point, otherwise you might say it doesn't exist at all. déhanchements (talk) 04:00, 19 May 2019 (UTC)

It's not counter-intuitive that a view of something is blocked unless one is looking from a specific vantage-point. That's the nature of nature: things look different from different perspectives. And it's beyond even a strong definition of empiricism to claim that "I can't see it myself, so it may as well not even exist at all in fact". I've heard the term "privileged perspective" used to refer to this sort of situation, though I can't find a ref for it now due to this phrase now referring specifically to societal privelege, where something looks unique (or a certain detail is only visible at all) when viewed one particular way. I was at a museum that used an actual physical model that happened to look like Penrose stairs from one specific perspective. We're getting pretty far off "science" here, no? DMacks (talk) 04:40, 19 May 2019 (UTC)

It seems like you want to ask a more specific question. For example, a mountaintop might be surrounded by cloudbanks that are only visible from the mountaintop (your "meadow") though it is entered via a "barren plain" (the steep ascent). I think you're trying to ask if the meadow and the barren plain can be in the same exact physical space in some sense, but different things are seen from different perspectives. Even there, there is all sorts of philosophical wiggle room. I mean, a hologram looks different from different perspectives... but it is the same object in the same space. Does that count? If it does, well, anything looks different from different perspectives. But if it doesn't count, then you want to define a space as "really" containing different things depending on how it's looked at, rather than (maybe) saying that the different perspectives look on different spaces ... it's hard to see where to go with this. The philosophical issue needs to be narrowed. Wnt (talk) 14:19, 19 May 2019 (UTC)

@Wnt:I see your point, I guess the only way this phenomenon could be completely separated from more normal variations of it, is if one not only saw a meadow, but could interact with it, as if the barren field was gone somehow. But that would be like walking into a ten foot house and finding out it extends outwards indefinitely inside. Needless to say there's some law that prevents that. déhanchements (talk) 17:45, 20 May 2019 (UTC)

@Yesükhei Baatar: You could do something somewhat similar with a Tipler cylinder, which would (if possible) be thought to permit travel through time. There are probably a variety of wormhole type effects somewhat related. Most involve inconceivably vast amounts of energy and types of matter that can't exist, but I feel like there are new exceptions proposed all the time. Wnt (talk) 01:05, 21 May 2019 (UTC)

Your question is not clear to me, but when a mirage makes you see things that are elsewhere, it also prevents you to see things you would see otherwise (ie, for instance, instead of seeing sand, you see a "lake"). You'll need to move (up) to see the sand again.

Gem fr (talk) 18:31, 20 May 2019 (UTC)

Dermatoglyphics

I have this article on my watchlist. A user recently added some material - it's referenced, but to a foreign language article. All fine so far, but the use of the word "modalities" is a trigger for me as it often gets thrown around in pseudoscience jargon to obscure the fanciful claims. (In fact, I'm not sure exactly what the inserted line is even claiming, but that's only a side issue for now). Is the journal cited ("Coleção Pesquisa em Educação Física") reputable? reliable? Matt Deres (talk) 12:33, 19 May 2019 (UTC)

I agree that the meaning of the insertion is unclear, and I suspect from the English-language abstract of the paper that it may not be using the word 'Dermatoglyphics' in the same sense as our article. I'm afraid I can't comment on the Journal's reliability – you might enquire on the Reliable sources Noticeboard. {The poster formerly known as 87.81.230.195} 2.122.2.132 (talk) 00:44, 21 May 2019 (UTC)

Good idea - thanks! Matt Deres (talk) 02:09, 22 May 2019 (UTC)

Stiffest material known ever

Wich material is the stiffest material knwon? might it be carbyne or is there something even stiffer?Saludacymbals (talk) 21:01, 19 May 2019 (UTC)

For a real tangible material try diamond. It would be even stiffer under pressure. Graeme Bartlett (talk) 22:34, 19 May 2019 (UTC)

Just to get us started, I'll point out that stiffness depends on the actual physical structure constructed out of the material, whereas elastic modulus is the real nature of the material itself (analogy: you seem to be asking about the nature of wood or steel, not a certain truss design built from it). And there are several different types of elastic modulus, depending on the direction(s) of the applied force and the motion resulting from it. Shear modulus might be the closest to the idea of "material stiffness" meaning resistance to bending: diamond, at 476.1 gigapascal,[2] is the largest I can find among standard materials under normal conditions (compare other entries at that ref and also [3] and Elastic properties of the elements (data page)#Shear modulus). DMacks (talk) 03:22, 20 May 2019 (UTC)

For how long can "Sarcoptes scabiei" live without having blood?

According to what I read Sarcoptes scabiei is parasitic which is nourished from blood. Then my question what happens if one lived in a apartment and he was infected with scabies, and he'll leaved his apartment for a year. Can these parasite survive there? If so, for how long? (I know that in a real case everything should be clean and washed with hot water, but this questions is more for knowledge.) 93.126.116.89 (talk) 22:28, 19 May 2019 (UTC)

I copy-pasted your question into Google. The first hit was this, which states: "Scabies mites can only live about 72 hours without human contact, but once on a person, the mites can live up to two months. Mites survive longer in colder conditions with higher humidity." According to this, their entire life span is not that long (reported estimates vary, but they're a couple of months at most). That second ref also mentions that "A study by Arlian et al. [20] found that S. scabiei var. canis females survived for a week or more when held at 15 °C (59 °F) and relative humidity (RH) above 75% (Fig. ​(Fig.4).4). At a warmer temperature of 25 °C (77 °F), females survived 1–2 days at all of the RHs tested (Fig. ​(Fig.4).4). Male survival time off the host was much shorter compared to females. These studies showed that generally, warmer temperatures drastically reduced survival time at each humidity." Matt Deres (talk) 01:08, 20 May 2019 (UTC)

May 20

What would be the first and last function to fail if?

You teleported an unshielded smartphone to low Earth orbit? (of course that's science fiction, do it in a thought experiment physics simulator if you hate teleportation thought experiments so much) What if you teleported a smartphone to a Trojan asteroid of Earth orbit? How damaging is sunlight and solar wind compared to the radiation of the rest of the universe? How many pixels fail per second? When would the screen turn off if it's set to always on? Also I'm wondering when a contemporary smartphone's GPS would stop working well if you could put it in a climate-controlled shield that only lets non-damaging radiations through and hitchhike it on a spaceprobe. Can it work outside the constellation? What velocities does GPS work at? Would it give crummy readings if you could make the receiver move at ~100 km/s relative to the satellites or a thousand or 10K or 0.999c? Sagittarian Milky Way (talk) 16:54, 20 May 2019 (UTC)

The cold would do damage before radiation in a number of ways. Shrinking pieces would crack, battery would fail, inner moisture would turn into ice, LCD would freeze and stop reponding to electric signal, the chip would fail...

Gem fr (talk) 18:14, 20 May 2019 (UTC)

The average temperature of the Earth without the greenhouse effect was about 0F if I recall so the phone average temperature might be bearable in sunlight but however much temperature differential the conduction can't remove will of course still stress the parts. Sagittarian Milky Way (talk) 01:23, 21 May 2019 (UTC)

This is wrong. Without atmosphere part of the moon exposed to the sun are close to 400K (this value depends on albedo, which is why astronauts wear white suits, so they do not roast in the sun); plastic parts will not withstand that. In the shade it drops to 3K. Average temperature do not apply to such a small object as a smartphone, it lacks thermal inertia. Gem fr (talk) 09:42, 21 May 2019 (UTC)

Could it work for seconds while the sun side hadn't heated up fully yet and vice versa? Sagittarian Milky Way (talk) 12:36, 21 May 2019 (UTC)

I dunno. Here are my 2 cents. The energy gain when lit would be in the kW/m² magnitude, a typical smartphone being ~100cm² so it gains ~10 W=~10 J/s. Specific heat capacity would be in 1 J/K/g magnitude, but it will depend a lot on whether the energy spreads on the entire 200 g typical smartphone --in which case it would heat at ~1/20 K/s, and could keep working for tens of minutes--, or first concentrate in a small, directly exposed 2g part -- in which case this would heat at 5K/s and would be destroyed in less than half a minute. Probably somewhere in between, meaning, it could work for some seconds.

For freezing, the energy loss would be 1/3 of the aforemantioned gain, so time needed would be x3.

but don't take my word for it

And check Nimur (talk) answser below. I underestimated soft error from radiation, that wouldnt destroy the smartphone but would cause critical malfunction. The average mean-time for such is not clear from his ref, though, so it all depend on whether they occur in a matter of minutes, or need more time. Gem fr (talk) 21:08, 21 May 2019 (UTC)

GPS satellites direct their antenna beams towards Earth surface. An unprepared GPS receiver needs several minutes continuous reception to acquire ephemeris and then can obtain a location in seconds if it receives simultaneously from 4 satellites. NASA report that GPS can be used (with proper equipment) as far out as geosynchronous orbit 36,000 km altitude. Simple domestic GPS receivers that have only two channels that are multiplexed amongst satellites lack processing bandwidth to handle more than about 100 mph speed. DroneB (talk) 20:34, 20 May 2019 (UTC)

As I understand it, while GPS may be able to work that far out, many GPS device you're able to buy probably won't. They still enforce the Coordinating Committee for Multilateral Export Controls (in an OR fashion) meaning they won't work above 18km altitude even though as I understand it the COCOM rules are dead and their replacement don't actually have an altitude limit. See e.g. [4] [5] [6]. P.S. Some people suggest some devices obey COCOM in an AND fashion although I'm confused by this since the COCOM text seems to be clearly OR. Possibly these devices are only complying with the Missile Technology Control Regime speed limit and people are simply confused. I think it's far rarer that people actually encounter the speed limit in practice compared to the altitude limit. So many probably don't actually know if it's obeying COCOM in an OR fashion or it's only obeying a speed limit with no altitude limit. Since MTCR seems to clearly require a speed limit, I would be surprised if devices instead obey COCOM in an OR fashion although then again I wouldn't be that surprised if whoever is in charge of implementing these limits are as confused about what they're supposed to do as random commentators, despite the fact they should have lawyers etc to tell them. Nil Einne (talk) 02:12, 21 May 2019 (UTC)

P.P.S. It is obviously possible that one or more governments e.g. the US, still had the COCOM limits in law/regulation despite the treaty establishing them ending so manufacturers did have to obey the limits or risk trouble. Nil Einne (talk) 02:17, 21 May 2019 (UTC)

Consumer GPS had a COCOM or other limit of 999mph as of some years back, but at least some of them worked fine at 500+ mph. I remember taking mine (a cheap Garmin) on an airliner just to try it out. 67.164.113.165 (talk) 06:08, 21 May 2019 (UTC)

From what I can tell the actual COCOM limit was 1000 knots. The MTCR limit is 600 m s^-1. I suspect some devices were conservative because they weren't sure of their accuracy at such high speed and didn't think it mattered or because (as per the altitude limite) whoever was in charge of implementing the limit wasn't given proper guidance, but I'm not sure if these was every any legal reason for such a low limit. Nil Einne (talk) 07:29, 22 May 2019 (UTC)

How about we avoid speculation, and point our OP to a real resource?

Radiation Effects on Integrated Circuits and Systems for Space Applications, with a new second-edition published this year, is written by Raoul Velazco, research director at the TIMA Lab in Grenoble. He's a world expert on a subject near to my own personal interests: the infamous single-event upset.

In 2011, several iPhones and other consumer telephones flew on STS-135. Here's the NASA "What's Going Up" article. Some technical details are published by the experiment investigators, Odyssey Space Research, and summarized in this press release. Here's the NASA Blog article, too: SpaceLab for iOS. Among the research, the LFI (Lifecycle Flight Instrumentation) characterized the effects of radiation on the device.

To excite and inspire the community at large, Apollo astronaut Buzz Aldrin gave a presentation at Apple's World Wide Developer Conference in 2011 to show off some ideas for consumer-electronics and promote enthusiasm for spaceflight.

Here's another NASA article, Socializing Science with Smartphones in Space. They also point to a following experiment, SPHERES, in which a team of MIT student-researchers planned to emplace the smart-phone powered Nanoracks satellite outside the space station - that is to say, a smart-phone, outside, in low earth orbit.

Perhaps to the surprise of everyone commenting in the thread - but sort of expected by anyone with a little background in this area - the first thing to fail was the application software. The hardware itself was qualified for spaceflight.

If I may take a moment to grump out at this late stage of the morning, the real metaphorical take-away here is that as of this decade, the limiting factor in spaceflight is software-quality.

Interested future engineers should spend more time learning fundamentals of math, science, and engineering, and then spend a lot more time engaged in formal education relating to software engineering and computer science, so that our next generation can have exponential improvement in software quality.

Some people say that "everyone can code." The truth of the matter is, very few people can code, and even fewer people are good enough at math and science and logical thinking to code well enough for a mission-critical space-flight application.

Nimur (talk) 16:30, 21 May 2019 (UTC)

May 22

Photons

|......................................

|--------------------------------------

| < thinnest and best aimed beam that <

| < doesn't violate laws of physics < <

|--------------------------------------

|......................................

|

|

|< a bullseye

Where will half the photons fall? A wavelength wide circle? (open edit window for unscrambled ASCII art) (asked by 107.242.117.33 14:25, 22 May 2019‎)

"ASCII art" is not enough (at least for me) to understand what you mean

but anyway looks to me you'll find to be happy in Diffraction-limited system

Gem fr (talk) 14:51, 22 May 2019 (UTC)

Photon waves are used for equations. Light doesn't bounce up and down in a wave as it flies through the air. 12.207.168.3 (talk) 16:01, 22 May 2019 (UTC)

If the OP is interested in modern theory and practice to describe where we will detect photons, An Introduction to Modern Optics is a good introductory book. After reading through a book like that, let us know if you have more specific questions. Nimur (talk) 17:10, 22 May 2019 (UTC)

Basically I want to know how wide the photon equivalent of an electron cloud is. The part of the cloud that has the photon half of the time that is. Maybe the cloud won't look like a spherical galaxy since photons can't go faster than c so I made the photons fall on a 2D target. No matter how wide and perfect a laser and lens are you can't focus a laser spot sharper than this photon equivalent of an electron cloud right? 107.242.117.17 (talk) 20:01, 22 May 2019 (UTC)

You're looking for a specific technical parameter - something like a collision cross-section - to describe the interaction between a photon and some other object; but that's not a common way to model a photon. Most physicists don't talk about the photon's position in the same way that they talk about the electron cloud. And what's worse - you've somehow concluded that this number, if you could deduce it, would tell you something about "beam width." With all due respect, that's just wrong physics! So ... if you ask a wrong-physics question, there's no way to get a right-answer. In fact, this "characteristic" length scale of a photon - if we could even concoct it - would not be the thing that limits how well-focused a beam of light is, nor how wide the beam would appear if you looked at it or photographed it or otherwise sampled it.

The position of an individual photon is not well-defined until after it interacts. Instead, we use a probability density function to estimate where the photon may be, and we use experimental measurements of a large population of photons to describe where most of them will be, most of the time. This is the whole premise of quantum-mechanically correct physics. There is a small but finite probability that the photon is anywhere. We can write a wave-function to describe how improbable it would be for us to find the photon at any specific coordinate, and we can even provide characteristic scale-lengths for the wave function.

It would be wise to do some homework: study the common models that physicists use to study the behavior of light, so that you can make sure that you're asking a well-formed question.

If you're deep in it, here's Solutions of the Maxwell equations and photon wave functions, (2010), which was also published in the peer-reviewed journal Annals of Physics, authored by Peter Mohr, a professional physicist employed at NIST. This is 75 pages of very math-heavy, advanced quantum-mechanically-correct physics that answers your question. If you are not already deep in to the physics, I recommend that you start with a much simpler book, like the introductory text I linked earlier. A more simple geometric model would be the Airy disk, or the beam profile or geometry for a beam of collimated light; but these models are applicable to ensembles and not to individual photons.

Part of me wants to remind you to go back and review every permuted variations of the slit experiment, ... but part of me wonders if you've ever seen those before; if this picture doesn't jog your memory - or if you're seeing it for the first time, if it doesn't enlighten you a little bit - then you really really need to go back to studying the basic physics material.

Nimur (talk) 20:19, 22 May 2019 (UTC)

I think the OP is looking for an area containing 50% probability, if such a thing exists.--Wikimedes (talk) 22:12, 22 May 2019 (UTC)

The diffraction limit is kind of toast -- see superlens. I won't claim to know exactly when and how well you can beat the limit with what technologies. I suppose the fundamental Heisenberg uncertainty principle governs how well you can say where a photon will strike, relative to the uncertainty in its momentum ... however, if you are willing to tolerate substantial uncertainty in the left-right direction only (you don't know when the photon will hit and you don't know what wavelength it is) I don't see a way to use that to constrain the accuracy of the targeting. Wnt (talk) 22:26, 22 May 2019 (UTC)

If you want to build machines that defy physical limitations and push the boundaries of optical performance, it's a good idea to understand all aspects of the physical limitations, in theory and in practice ... this is why cameras and optical equipment companies employ cross-functional teams comprised of physicists, electronic engineers, materials and mechanical engineers, and other experts... shameless plug: we're hiring on multiple continents! And per my usual advice - it'd be a real competitive advantage if the skilled optical physics candidate is additionally a software expert, because the truth of the matter is, most of the time, software plays a huge role in controlling and interpreting the real-world limits imposed by the laws of physics.

Anyway,... I have to return to my day-job, laboriously counting incident photons ... if only I could train some kind of machine to do this excruciating work for me... I'd have more time to pontificate about physics on the internet! But, I've got bills to pay... Good luck with the suggested-readings!

Nimur (talk) 16:54, 23 May 2019 (UTC)

Or I could just look up some news stories about how good they've gotten. this proposal wants 30 nm resolution from 193 nm light... in 2007. But it's for the military, which may not have published. This one from 2012 got 45 nm out of 365 nm light, and says that 193 nm was down to 22 nm resolution for lithography. [This one from 2014] predicts 10 nm resolution. I don't doubt the skill of the practitioners, but I do doubt the diffraction limit is going to stop them soon. Wnt (talk) 03:13, 24 May 2019 (UTC)

Peach's substance

What substance in peach causes slightly burning or acrid sensation when eaten (especially on lips, similar to citruses)? 212.180.235.46 (talk) 19:33, 22 May 2019 (UTC)

Via PubMed search, I found Response to major peach and peanut allergens in a population of children allergic to peach (2015). "We study the sensitization to relevant allergens, such as peach and peanut LTP, Prup3 and Arah9, and seed storage protein, Arah2."

Pru p 3 seems to be the biological chemical name for the most common allergen in peach. This is a lipid transfer protein.

In at least one case, Anaphylaxis induced by nectarine, a peach-allergy patient reacted to nectarine, suffering a severe reaction including flush, wheals, and anaphylactic shock.

It is important to emphasize that there's a huge variety among the population. Any individual might be sensitive to other compounds, or there could be another cause for sensitivity that is totally unrelated to exposure to the peach fruit.

Nimur (talk) 19:47, 22 May 2019 (UTC)

I would be very hesitant to diagnose an allergy. Naturally peaches often have an acidic "tang" that simply results from low pH. The comparison to citruses invites this interpretation. I looked up the peach trichomes thinking there might be some silica in them (I think, could be wrong, that kiwi fruit can annoy people's lips and tongue by this means) but this paper, which goes into absolutely pornographic detail on peach skin, doesn't mention any silica I could see. Wnt (talk) 22:46, 22 May 2019 (UTC)

If you're concerned, see your doctor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:40, 22 May 2019 (UTC)

I mean that tangy taste mentioned by Wnt. I'm healthy, but noticed it may slightly burn the lips. Probably that tangy substance also causes that subtle burning sensation. 212.180.235.46 (talk) 16:51, 23 May 2019 (UTC)

I've never experience that. So if you're concerned, see your doctor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:32, 23 May 2019 (UTC)

Agreed with Bugs. It's probably nothing, but that tingling sensation is potentially a sign of a food allergy. I certainly get it from time to time when I eat something I shouldn't. No harm in getting it checked out. Matt Deres (talk) 19:00, 23 May 2019 (UTC)

May 23

What color is a safelight?

On TV it is usually red, and I'm wondering if this is the same red which is one of the three primary colors of light?— Vchimpanzee • talk • contributions • 21:44, 23 May 2019 (UTC)

We have an article on safelights. The exact type and exact color depend on the purpose. Many old-fashioned photographic development labs used a red or reddish colored light. Many modern industrial labs that work with photosensitive photoresists in the electronics industry use a yellow or amber light. Professionals who work with specific photographic or photoreactive film chemicals usually get specialized technical data from their chemical vendor to guide their light color and fixture choices. Here's technical information for DuPont RISTON photopolymer, including spectra and lamp recommendations. Here's safe light filter recommendations for KODAK motion picture film, and here's a guide to dark room illumination. Nimur (talk) 21:59, 23 May 2019 (UTC)

The Wikipedia article didn't get very specific, but does any of that relate to the red that is a primary color of light? In fact, Wikipedia doesn't even seem to cover that subject.— Vchimpanzee • talk • contributions • 22:28, 23 May 2019 (UTC)

I don't think any of those even mentioned the color red. I can't imagine how people develop film in total darkness, but that was the recommendation for certain cases.— Vchimpanzee • talk • contributions • 22:33, 23 May 2019 (UTC)

There is no "red that is a primary color of light", or at least not exactly. There are three different kind of cone cells, which have different response curves to wavelengths of light in the visible range. One of the three types has the strongest response in the longer wavelengths, and in some (probably oversimplified) sense, that is what defines what we call "red". But lots of different wavelengths will provoke at least some response from those cells.

So "red as a primary color" is more about the human eye than it is about light per se.

I expect there's more information at color vision. --Trovatore (talk) 23:13, 23 May 2019 (UTC)

Photographic film is sensitive to red light. But it only has to be in total darkness when you open the camera, and transfer the film to the developer spindle and then once it is inside the developer it is safe from light. Then once the fixer has done its job, it is safe to open. The black and white photopaper was safe in red light. Graeme Bartlett (talk) 23:18, 23 May 2019 (UTC)

• It's unrelated to primary colours (except when it isn't...).

A safelight can be any colour (if there are any) to which the photographic emulsion is insensitive. In the "classic" example, this was red light. That's because red is long wavelength, thus low energy photons (see Photon#Physical properties). Early emulsions were orthochromatic and insensitive to red light (still an improvement, because earlier ones had only been sensitive to blue light). This had given rise to photographic grey, a deliberate painting of some objects (such as brand new steam locomotives) in a pale grey which photographed well with these early emulsions.

This sensitivity is a linear series, based on the quantum behaviour of the photon (long wavelength, low energy) and these red photons simply not having enough energy to activate the emulsion.

Primary colours are an artefact of the human eye and its three [sic] types of colour sensitive cones. Speaking in terms of physics, monochrome emulsions and safelights, there are no such things. Andy Dingley (talk) 23:22, 23 May 2019 (UTC)

• There are two types of emulsion in use for typical processes: film (usually a negative film) and then photographic paper used to produce the print. Safelights are (usually) only applicable to the darkroom printing process onto paper. The film is handled in total darkness. Usually this is in a small light-proof developing tank which is loaded in the dark, then allows the chemical handling to be done in daylight.

The film could be "black and white", more precisely "monochromatic", but it's still sensitive to a wide range of colours. Early emulsions (to mid 20th century) were orthochromatic, but panchromatic emulsions were developed later to give a more realistic (i.e. matching the behaviour of the rods in the human eye) mapping of colour onto brightness. These were red-sensitive and although even ortho film was usually handled in darkness, these couldn't be used with a human-friendly safelight. They were however insensitive to infra-red light and some auto-processing machines used IR LEDs and detectors to read information coded on the film edge, even while it was in the camera or during processing.

In Victorian times and wet glass plate processes, emulsions were not only just sensitive to blue light, but weren't very sensitive at all. A dim light, such as a candle or oil lamp, could be used as a safe worklight. Although this would eventually have fogged the plate, it would take too long to be a problem.

Printing paper emulsions didn't have to be daylight sensitive, or even very sensitive at all, as they're exposed via an enlarger with a bright lamp of any desired colour.

For black & white processing, red safelights are generally used. Some processes have a wider range of sensitivity, so a "deep red" (i.e. longer wavelength) safelight is needed, which is awkward as it's getting to the range where humans don't see too well either. Some processes vary the colour of the enlarger light (with a set of yellow filters) in order to control the contrast ratio of the printing process (Paper used to be made in a range of fixed contrast ratios, but the multigrade papers allowed one paper to be used for all of them). These could though be fussy about safelights.

Colour printing paper obviously needs to respond to a range of colours. It's made from a laminate of differently responsive layers (see Color photography#Three-color processes): usually the complementary colours though, cyan, magenta and yellow, not RGB (see Color photography#Subtractive color and CMYK color model). Safelights are difficult, but a dim yellow-green one was usable. As the triplet colours here were chosen to match human colour perception, and the safelight is having to match a gap between those, then we could now say that safelight colours are in fact derived from human eye responses.

• A further sort of safelight is used in microelectronics fabrication, mostly IC production but also sometimes for circuitry. The photoresists used here as UV-sensitive by design, but also overlap into the blue visible spectrum. The safelight here is a rather bilious bright yellow, much brighter than used for photography. It could just as well be red (the photoresists don't care) but humans see poorly in red and these are precision labs, where good vision is needed. Andy Dingley (talk) 23:34, 23 May 2019 (UTC)

In B&W darkrooms you usually use red (sometimes amber) safelight with enlarging paper that's not sensitive to it. For film you use total darkness. It's not too bad--you shut off the lights and load the developing reel by feel, and you can do it with a changing bag if you don't have a darkroom. Just practice loading reels once or twice with the lights on and with scrap film to pick up the technique and you're good to go. Then you put the reel into the developing tank (which is light tight) and you can turn on the lights.

For color enlarging you do the enlargement in darkness but then you usually load the exposed enlarging paper into a machine or light-tight drum for processing, so you don't have to fumble around with trays of liquid chemicals in the dark. You do use the chemical trays for B&W paper, but with safelight so you can see what you're doing. 67.164.113.165 (talk) 18:45, 24 May 2019 (UTC)

May 24

Which species of spider?

Can anyone identify this species of spider? Bubba73 ^{You talkin' to me?} 00:14, 24 May 2019 (UTC)

The yellow and black one is an orb spider. They are very common and go by many different local names. 97.82.165.112 (talk) 01:12, 24 May 2019 (UTC)

Thanks, I forgot to say that the second photo is its web. Bubba73 ^{You talkin' to me?} 01:25, 24 May 2019 (UTC)

Amazing web! In that case I would suggest it's an orb-weaver spider.--Shantavira|^{feed me} 07:46, 24 May 2019 (UTC)

See web decoration. Mikenorton (talk) 10:59, 24 May 2019 (UTC)

The top image shows the underside of possibly a wasp spider. Mikenorton (talk) 12:42, 24 May 2019 (UTC)

If the spider is not causing a problem for you, I strongly suggest leaving it alone. They are very friendly spiders that do a great job in controlling ground pests like grasshoppers. Plus, if you can get over the often grotesque appearance, they make very pretty webs. 12.207.168.3 (talk) 12:44, 24 May 2019 (UTC)

I doubt they object to being photographed. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:45, 24 May 2019 (UTC)

My wife called my attention to the interesting web. The spider behind the web (hardly visible) is the same one in the other photo. I have not bothered it. The photo turned out to not be as sharp as I wanted. I think I had the shutter speed too low. Bubba73 ^{You talkin' to me?} 19:00, 24 May 2019 (UTC)

Is a single photons light particle emitted in every direction?

Or is a photon particle directed in one direction?

The question that my friend pondered is if we look at the sun, are we receiving the same photon particles or if he is receiving separate photons.

I read many pages on the subject but am still unsure.

Thank you.

107.199.78.194 (talk) 01:26, 24 May 2019 (UTC)

The probability that the photon will be encountered is emitted in all directions. Whether the photon "itself" is emitted in all directions seems to be a matter of interpretation. Some interpretations of quantum mechanics, like Bohmian mechanics, say a very clear no, while others, fulfilling the same math requirements (like Copenhagen interpretation) say yes.

However, in either case, the individual photon is a particle that might hit your retina or his, but not both. Wnt (talk) 02:00, 24 May 2019 (UTC)

As Wnt has hinted at, this is a question that sounds simple but is surprisingly deep. To restate your question: can the same photon interact with both your friend's eye and your own eye? If you look at things based on the classical photon model, which models the photon as a particle, the answer is a pretty simple "no". Things can't be in two places at once, silly! The problem is, we now know that classical mechanics is not "fundamentally" correct; it's just an approximation that works well under certain conditions. Quantum mechanics (QM) more accurately describes the world, but it does so in ways that defy our intuition. In QM, a photon is described by a wavefunction, and the wavefunction simply gives you a probability of finding the photon at any given point in space. So does that mean the photon is everywhere at once? It depends on how you interpret QM. All the math does is give you numbers. This is what the famous wave–particle duality is about: you can view a photon as either a wave or a particle, but in QM a photon isn't really either: sometimes it can behave like a wave, and sometimes like a particle. Some of the responses here may help give some more detail: [7] [8]. This might seem unsatisfying; you might want to know what a photon "really is". Well, it's a photon, which according to quantum field theory is an excitation in the electromagnetic field. It shouldn't really be surprising that it's difficult to visualize such things. Our intuition developed to survive on the savannah, not to figure out how photons behave. If you want to learn more about QM in general, try introduction to quantum mechanics for a starting point. There are some good books listed there in the bibliography. I also recommend PBS Space Time on YouTube. --47.146.63.87 (talk) 03:34, 24 May 2019 (UTC)

Oops, the bibliography is actually in the main quantum mechanics article. --47.146.63.87 (talk) 06:54, 24 May 2019 (UTC)

• "The question that my friend pondered is if we look at the sun, are we receiving the same photon particles or if he is receiving separate photons." The question is, as noted, quite interesting if you ask it in different ways. If a photon of light did hit your eye, it cannot hit your friends eye. That is a different question than will a particular photon hit your eye or your friend's eye. The answer to that is not intuitively similar to the past-tense question, and gets down to what may be the fundamental difference between classical mechanics and quantum mechanics. Classical mechanics presumes certain (what seems to us) rather obvious, axiomatic assumptions: objects have a defined location in space and time, and if you know an object's location, and you know the forces on that object, you can predict reliably how that object's motion will change over time. That is perhaps the fundamental set of axioms for classical mechanics; it is the assumption that one makes in nearly all first- and second- year basic physics classes. The key bit that makes quantum mechanics different than classical mechanics is that very first part "objects have a defined location in space and time". Imagine a world where they didn't. I don't mean "imagine a world where you can't know an object's location because you don't have good enough instrumentation." I mean "Imagine a world where an object's location is not itself a well-defined concept." Now, try to predict the results of interactions between those objects, or the results of forces acting on those objects. Imagine trying to predict the flight of a soccer ball you are about to kick where you don't know where the ball is, where your foot is, and when your foot will strike the ball. You do know when you have struck the ball, because, lets say, you can see the mark the ball leaves on a wall. But can you tell what will happen before the ball hits the wall and makes the mark? That's what quantum mechanics looks like in macroscopic terms. If you want to understand anything about your system (like, how kicking soccer balls works) in your quantum world, you need to kick a bunch of soccer balls, and look where they hit the wall, and extrapolate some equations that give some predictive power over the behavior of the soccer ball. That's basically what quantum physicists do... Take observations of quantum behavior and devise mathematics that reliably predicts it. In simpler terms: you need to define your question carefully: are you picking a photon that is leaving the sun and trying to predict who's eye it will hit? Or are you picking a photon that has already hit your eye, and asking if it already hit your friend's eye too? Only the second question has a single, defined answer: it hit your eye. The first can only be answered in terms of probabilities. --Jayron32 11:21, 24 May 2019 (UTC)

  Not to add to my rambling above, but there is another implied question here: "What is the photon doing as it travels between the sun and us before it hits one of our eyes". The answer to that question is entirely unknowable, and what gets to the heart of all of the debates regarding the interpretations of quantum mechanics: unless and until you make a measurement of that photon, you don't know what it is doing. And you can only make a measurement by bouncing that photon off of something. And that only tells you when and where that photon was at a particular point in time; all you did was move your eyes to a different location, you didn't gain any insight on what the photon did between the sun and your eyes. --Jayron32 11:34, 24 May 2019 (UTC)

  In for a dime, in for a dollar: adding to this yet again; above I use the word "location" and "localization" in a physical, Cartesian sense, defining it as (for example) a set of four coordinates (x, y, z, and time) in space and time. But in quantum physics, the term "locality" refers more generally to any measurement one can make of a quantum particle or of a quantum system. Location in space and time is a convenient one to discuss, but any measurable quantity is subject to the same indeterminacy. So when you read some of the articles I linked above, they tend to speak in more general terms about what "local" means; I use it above meaning "a physical location in space", but it really means "any measurement you could make". --Jayron32 11:43, 24 May 2019 (UTC)

Do not eat raw batter!

I bought a lemon-poppyseed muffin mix from Martha White at the store yesterday. At the bottom of the packaging, near the manufacturing company's mailing address and telephone number, is a disclaimer: Do Not Eat Raw Batter. Why? It's dry mix with nothing perishable (ingredients), "best by" some time next year, and one creates batter by taking muffin mix and adding milk. (If your milk's gone bad, it's your fault; but are they afraid of spoiled-milk-drinkers suing?) I can't envision anything in the ingredients that could be dangerous but that would be neutralized by fifteen minutes in a 400°F oven. Nyttend (talk) 05:00, 24 May 2019 (UTC)

Presumably because we're not supposed to eat raw flour.[9] DMacks (talk) 05:32, 24 May 2019 (UTC)

(EC) A quick search finds the FDA and the CDC recommend against the consumption of flour, raw dough and raw batter apparently due to the risk of E. coli from the flour (and in some cases which probably don't apply here Salmonella from the eggs). [10] [11] BTW, for anything that isn't too thick, fifteen minutes in a 400°F oven is more than enough to kill most bacteria although maybe not their spores and probably also won't do much for toxins already produced. If the internal temperature reaches even 75°C for a short while, that's enough for most things [12] so it really depends on the thickness and other factors as to how long it takes for the internal temperature to reach that. To be clear, this is only in relation to bacteria, there are other things that need to be considered for some foods e.g. Antinutrient or toxins that sometimes need to be dealt with, sometimes with cooking and I'm not sure whether an internal temperature of 75°C for a short while is enough for them. (Think cassava etc.) So it's not intended as generally food safety advice simply a comment on the "can't envision anything in the ingredients that could be dangerous but that would be neutralized by fifteen minutes in a 400°F oven" bit. Nil Einne (talk) 05:41, 24 May 2019 (UTC)

I believe the first major recall that brought this issue to prominence was the 2009 Nestle Toll House cookie dough recall where flour was the source [13]. I can't prove this but I don't think the possibility that E. coli could live in flour was something that had really been considered in the industry prior to this. Interesting side note, Nestle started heat treating their flour afterwards because they are aware that even though their packages say "Do not consume raw cookie dough", a large percentage of their customers will do it anyways. shoy (reactions) 13:59, 24 May 2019 (UTC)

I'm not convinced that was true e.g. [14]. It may be true it wasn't believed there would be anything to cause health concerns if you're just eating small amounts of raw flour (considering quantity and type expected to be present). Definitely the fact that there would probably be some bacteria in your flour doesn't seem particularly surprising even if the assumption may be that there won't be enough of anything of concern to be a problem. Remember that the non perishability of something like flour most likely comes not so much from the fact that there's no microorganisms on it, but from the water activity being way way too low to support any growth. If you were to wet your flour e.g. by putting it in a container+water that had been autoclaved, I don't think any competent microbiologist even from the 1960s would have been surprised to find bacteria growing it in that came from the flour. Nil Einne (talk) 15:19, 24 May 2019 (UTC)

The answer is: because the cost of ink on a label is cheaper than the cost of a lawsuit. --Jayron32 11:01, 24 May 2019 (UTC)

Boron_nitride#Cubic_form_(c-BN) cutter

I am trying to find a way to cut 5/16" stainless steel rod at work. At present we are using disc grinders. This is time consuming and needs a large working area. I am hoping to modify a nut splitter by adding a boron nitride cutting edge. The nut splitter I have ordered is: https://www.otctools.com/products/universal-c-frame-nut-splitter The CBN material I have ordered is: https://www.spyderco.com/catalog/details/204CBN/891 The CBN knife sharpeners appear to be hollow and thus will probably crack. Plan A is to fill them with powdered glass or ceramic glaze and then heat to melting. Issues: Will the glass/glaze expand and crack the CBN rods? How to I 'snap' the rods to approx. 1/2" length to fit the nut splitter? I thought of putting them in a vise and either whacking them with a hammer or snapping them off with stainless steel pipe; both methods using soft metal padding. Any other wise ideas about modifying a nut splitter or cutting stainless rod would be very helpful, and please feel free to invent this gadget so I can just buy it from you next time. 96.55.104.236 (talk) 16:53, 24 May 2019 (UTC)

I know nothing nearly practical enough to answer your question, but I can link to a cute video of a water jet cutter. Website [15] says coefficient of expansion of cubic boron nitride is 3.8 x 10^-6 deg C^-1. But figuring out the coefficient of expansion for a ceramic glaze looks like a fine art [16], complete with a reprise of our non-ideal solution issues from a week ago. I don't know what's on your table for this. Wnt (talk) 00:18, 25 May 2019 (UTC)

May 25

Photons

How many photons does the universe actually need to work in the way we observe it? 213.205.242.170 (talk) 04:04, 25 May 2019 (UTC)