Wikipedia:Reference desk/Archives/Science/2019 April 26

= April 26 =

"Joules per mole of charge"
The discussion about redefinition of SI units above kicks off a pet peeve of mine: I want to see amperes, coulombs, and volts wiped off the face of the earth -- and the redefinition brings that a step closer. Calculating something like the free energy of electrons in NADH relative to oxygen involves something annoying with the Nernst equation and RT/nF (Faraday constant) and looking up and translating tables of the ought-to-be archaic voltages into energy: "the ∆G ́° for NADH oxidation = –(2 e–)(96485 J/(V•mol))(0.32V) = –61.75 kJ/mol." We should recognize that volt = J/C, which is to say J/(1/96485 mol charge), so what looks arcane in that instance ought to be -(2 mol charge/mol substance)(30.875 kJ/mol charge), with the last figure being looked up out of a table of Not Voltages. With the redefinition the joules per mole of charge are directly proportional to voltages by an exact multiple. Right now, our offering on Joule per mole is awfully limited. I don't even know -- has anyone come up with glib, wieldy terms for saying and writing "joules per mole of charge"? We need them!

Related: we could at least say "Joules per faraday", but what is the standard abbreviation for faraday (unit)? We ought to start an actual article, not a redirect, on our fundamental measure of charge. ;) Wnt (talk) 13:28, 24 April 2019 (UTC)
 * The historic symbol for a faraday is usually a cursive F, ℱ, though in the last 20-30 years, this has just become a capital print F. It should also be noted that no one actually draws much of a distinction between the faraday as a unit or "faraday's constant", since they are numerically identical; in much the same way that the "atomic mass unit" is numerically identical to the "gram per mole" though they are derived subtly differently.  Also, your unique, intensely personal, and idiosyncratic distaste for a particular unit of measure is not likely to have much of an impact on the scientific community at large.  Sorry to disappoint you on the whole "volt" thing.  Better luck next time.  -- Jayron 32 13:54, 24 April 2019 (UTC)


 * I think Wnt should write up an essay page on this and add "cabal to wipe amperes, coulombs, and volts off the face of the earth" to List of cabals. I nominate the name "Wnt" for joules per mole of charge. --Guy Macon (talk) 15:27, 24 April 2019 (UTC)


 * In my younger years, I worked a lot with theoretical plasma physicists. These were exactly the type of scientists that would care about energy per unit of charge.
 * But they did not normally use units of "Joules per unit-of-charge." Although this is a satisfyingly "fundamental" representation of energy, as distributed among an ensemble of charged particles, it's not a particularly practical measure - neither for theoretical physics, nor for experimental physics.  Rather, the people who typically concern themselves with such items employ a few standard tricks of the trade:
 * First, they wrote out the temperature of the charged ions. For example, have a look at our article: Electron temperature.
 * Next, they wrote out the effective temperature per species. This lets you isolate each energy-term as it pertains to a subset of all the energy in the system of many many particles - even if you had as many as, say, 6.022x1023 particles.
 * Finally, they represented the disequilibrium - in other words, the deviation from a Maxwell–Boltzmann distribution of that energy - as a temperature perturbation or as an available total energy. Then, they used spectrograms of the energy intensity versus radio frequency, to represent the distribution in the real world.
 * The canonical textbook is Bittencourt's Fundamentals of Plasma Physics, which is a lengthy but surprisingly easy read into the difficult world that is the study of how-energy-is-distributed-amongst-particles-that-carry-net-electrical-charge.
 * The key take-away, though, is that the "joules per couloumb" is a not-very-useful normalization. When you present this unit, you are implying that the bulk energy is uniformly distributed amongst the charged species.  This is bad physics - it's not how the world really works, and it's not even an interesting theoretical scenario - so why would we promote a unit that encourages people to use a useless simplification?  The real energy is distributed intricately and delicately amongst many distinct modes - electrostatic, electrodynamic, kinetic, ... even in the simple problems!  If the energy distribution were so well behaved in the first place that you could use a bulk charge density model, you could model it as an electric capacitance: so why would you care how many individual particles are involved in the encapsulation of that energy?
 * All of this thinking is really just dancing around the core subject. The core question is, what exactly do you think is the fundamental unit - particle count?  quantity of energy?  amount of charge?  - and now that we're in this horrible regime of modern quantum-mechanically-correct physics, why would you think that the one is any more fundamental than the other?  We only care about observables, and you can't actually observe amount of substance by actually counting out an entire mole of particles.  Equally truthfully, number of particles is a quantization-model; but we also know that energy is quantized and charge is quantized, so with appropriate units, we can obtain an integer "number" count of any of these physical properties.  We can, in total sincerity, talk about number of energies - because energy is integer-quantized - but this makes our words sounds really weird when we put it into the English language, so we don't say "number of energies."  Instead we pretend to make it seem normal, by counting photons or drawing largely-incomprehensible line-diagrams.
 * At the risk of sounding like a Pythagoreanist, I'll summarize it thus: the fundamental item is the ratio, not the actual amounts, and certainly not the units.
 * Nimur (talk) 16:08, 24 April 2019 (UTC)
 * Why do you say energy is integer quantized? I thought light could have any frequency and velocity could be any arbitrary value, whereas angular momentum is quantized.  Also, your critique, while valid, should also apply to the volt, since it is exactly the same as joules per mole but with a random extra multiple. Wnt (talk) 09:19, 25 April 2019 (UTC)
 * Because energy is integer quantized. That's the whole idea behind quantum theory: for every possible energy state, there exists some set of quantum numbers which can always be reduced to some set of integer values.  In any bounded system, there always exists discrete energy levels, and those levels can always be reduced to a set of operators and quantum numbers.  The reason energy is quantized like this is that the energy levels are related to the harmonics of the wavefunction; since waves can only have integer harmonics (i.e. root, first harmonic, second harmonic, etc.), energy is similarly quantized. -- Jayron 32 11:50, 25 April 2019 (UTC)
 * If so, then what would you say is the minimum difference in frequency (Hz) between any two photons? Is there a name for that difference?  (I am not aware of any point where you can't continue expanding a spectrum; my impression is that quantization of energy levels in a system is the happenstance result of a requirement that the phase of the wavefunction comes around to the same point as it started when, say, you go around a nucleus, but the energy is not quantized if you're talking about the energy of a photon in 'empty space' or how fast a ball is moving or an orbital of arbitrary complexity such as in a large vibrating molecule with broadened absorption bands) Wnt (talk) 07:25, 26 April 2019 (UTC)
 * Energy in a bound system is quantized but frequency is not. That is because there are basically an infinite number of possible bound systems, so the universe can produce an essentially infinite variation in frequency, even if each individual situation can only produce a finite set of energy levels.  Furthermore, the number of energy levels in any one system is infinite, even if the values of those energy levels are discrete.  The best way to think of this is, again, as a countable infinity, for which the harmonic series represents a perfect example.  It is at once discrete (each element of the harmonic series is mappable to one of the integers), which is why we can say things like "energy is integer quantized".  However, the number of possible energy states is infinite, especially when we consider the number of states of the entire universe.  Even with a highly constrained system like the hydrogen atom, which is the standard model for things like the Bohr model and Schroedinger equation (and indeed, is the only system AFAIK that has a complete solution for said equation) there are an infinite number of possible energy states.  If you have an infinite number of discrete energy states, you can produce literally every frequency of light, because within that infinite series of energy levels there exists some transition which will produce any arbitrary frequency of light you want.  Even though each energy level is discrete and all electrons must exist at one or the other (and thus is integer quantized), light is produced not by the existence of these energy levels, but of the transition between these levels.  An infinite number of possible levels produces an infinite number of possible transitions, and thus an infinite number of possible wavelengths.  Similar logic also helps understand things like the Fourier transform to show how any arbitrary function can be reduced to a set of individual (integer quantized) sine waves.  -- Jayron 32 13:03, 26 April 2019 (UTC)

When asked this question, Frank Heile, Ph.D. Physics answered:

"There is no proof or evidence that space really is discrete at the Planck length. It is possible, but there is no evidence as of now.

If space is not discrete, then the wavelengths of electromagnetic radiation will (probably) not be discrete. The currently accepted and well tested theory of all particle interactions, the Standard Model of Particle Physics, says that wavelengths and therefore frequencies are continuous."

Lalit Patel, PhD Physics answered:

"In order to explain the black-body radiation distribution, Planck's quantum theory stated that the energy of light of a certain frequency can exist only in multiples of Planck constant multiplied by the light's frequency.

There is no experimental observation so far, which would require us to assume that the frequency of light [or similar other radiation] cannot take all real values. It is, therefore, safe to state that the frequency of light is continuous.

If someone hypothesizes that the frequency of light cannot take all real values, the hypothesis will lead to certain predictions. Such predictions will then need to be substantiated by experimental observations."
 * — Preceding unsigned comment added by Guy Macon (talk • contribs)


 * I'd love to have seen citations for those statements, Guy,... but I found them, and they are essentially internet comments that were posted on Quora.com. All things considered, the statements are perfectly fine, ... but we're trying to provide reference material here.  If we're just repeating quotes from other internet commenters, then we're essentially no better than an internet forum.  At the very least, a link to web-link to the author might help our readers put their statements in context.  And, just as I am simply some random internet-commenter, those authors also are simply some random internet-commenter; so even if we are all correct, there is still a key difference insofar as I can cite a reputable source for my madness.
 * Rather, to put a more fine point on it, there is no time like today to review your copy of that statistical and thermal physics textbook you surely keep on your shelf...
 * It requires more effort, but to put it bluntly, reading a physics book is a better way than reading the internet, especially if one wishes to start grokking the hard stuff. Wnt has asked so many detailed questions over the years, I'm sure he's interested in getting the details.  So, why not pick up a good book?
 * For at least five years I've been pitching for An Introduction to Thermodynamics and Statistical Mechanics, which I've called "the only physics books you will ever need." I say this in half-jest as I am the proud owner of hundreds of other physics books.
 * Wnt: Buy that book.  Or, if $70 is too high a price, see if you can get it from your local library.  It is very popular among real physicists, and it will almost surely be available through interlibrary loan via your local university.  Give the book a shot.  If you don't like it, let us know why, and I can point you at any of a dozen other great books written in different styles and at different levels of difficulty.  But I highly recommend Stowe's thermodynamics book in specific: it is one of the few science books that do more than inform or entertain: it will actually make your brain work differently.  I don't simply mean that you'll learn the equations to compute the entropy in a gassified medium.  I mean that it will fundamentally change the way that you respect how to understand the reasons that explain why we use mathematical physics to describe our universe.
 * After all, if one is a metrology enthusiast with strong passions that pertain to the definitions of the units of measure, ... might one not wish to study a little measure theory? This difficult arcana is far too important to let its knowledge lay idle amongst the cabal of professional mathematicians...
 * Nimur (talk) 17:02, 26 April 2019 (UTC)
 * That's some really good stuff. I especially agree with the idea of " make your brain work differently".  Unlike Nimur, I am not a physicist, I'm a chemist, though, so I have some physics I need to understand.  However, though I can't actually do the physics, (my math skills are shit) I do have an appreciation of what the physics means and that's probably more important here than simply chugging through the analysis.  Once you get an answer, understanding 'what are the implications of this result' is really where its at.  One of the really key aspects of physics is training your brain to think mathematically, and to understand what some particular mathematical result means rather than just what it says.  That is, when we do some bit of math, what implication does that have in the world.  I tend to learn well through visualizations, and I have found that training my brain to think visually-mathematically has really helped me grasp physics that, 20 years ago, was just a bunch of contextless math equations.  To that end, I think YouTube can be an invaluable source, and there are some really good physics and math channels that are GREAT at retraining the brain.  Some of Brady Haran's channels are really good.  He has an entire channel on discrete mathematics called "Numberphile", and one on physics called "Sixty Symbols".   In both channels, he works with working physicists and mathematicians to explain complex concepts in intuitive ways.  I especially like videos featuring Philip Moriarty.  His explanations of things from thermodynamics to quantum theory are really fantastic.  The Richard Feynman lectures are top notch as well.  You can find them on YouTube easily.  Training your brain to think mathematically in a visual way is really done well by a channel called "3Blue1Brown"; Grant Sanderson has a really good style, and his presentation of otherwise obtuse aspects of calculus makes it very easy to understand.  I still can't do the math myself, but at least I understand what the math means, and really understanding calculus helps a LOT in understanding physics.  "Minute Physics" is also pretty good; his series on relativity really helped me understand those topics well.  I hope, like Nimur above, that these sources will help your getting into these tough physics questions you ask a lot about.  -- Jayron 32 18:03, 26 April 2019 (UTC)

Scientifically speaking, is it possible to clone the dead?
Scientifically speaking, is it possible to clone the dead? As in, take some corpses out of a cemetery and use their DNA to create clones of these people. Futurist110 (talk) 01:31, 26 April 2019 (UTC)
 * Here's an article on the notion of resurrecting the wooly mammoth. ←Baseball Bugs What's up, Doc? carrots→ 01:45, 26 April 2019 (UTC)
 * ...and here is the paper that they referred to, although National Geographic actually didn't cite it properly: First birth of an animal from an extinct subspecies (Capra pyrenaica pyrenaica) by cloning, (2009), Theriogenology 71 (2009) 1026–1034, available online including a full open-access PDF. They used carefully-preserved karyoplasts, cryogenically-stored in laboratory conditions, and used an enucleation method that seems similar - at least superficially - to the famous method used to clone Dolly the sheep.
 * It is not clear whether the individual goat was deceased at the time that its donor cells were extracted (via a skin-biopsy) - so the cells may have been perfectly alive at the time they were preserved. If you care, the authors cite a 1998 publication from the journal C R Acad. Sci., written in the French language: abstract available in French and English, Développement d'embryons bovins obtenus après fusion entre un ovocyte mature énucléé et une cellule somatique cultivée (1998)
 * Nimur (talk) 01:56, 26 April 2019 (UTC)
 * As long as you have intact DNA (a full diploid pair of chromosomes in the case of diploid organisms such as animals), you can probably clone something. Decay and decomposition are the problems. Any organism that did not die very recently will probably not have an intact set of nuclear DNA. Even if you could theoretically piece together an intact, full set of chromosomes from fragmentary DNA, I don't think we currently have the technology to do so. For more on the general subject, WP:WHAAOE: ancient DNA. Note that when scientists do things like sequence ancient corpses, they aren't working with a full, intact set of DNA. The DNA is quite degraded; they're just recording various nucleotide sequences. This can still tell you a lot, especially when combined with other data, but it won't let you make a clone. --47.146.63.87 (talk) 21:31, 26 April 2019 (UTC)


 * However, with DNA samples from enough cells, even if each is only fragmentary, it may be possible to patch the entire genome together, using technology like CRISPR gene editing. From there cloning should be possible. Note, however, that this would not "bring the dead back to life". The clone wouldn't have any memory from the dead person, and would grow up in a different time frame, under different conditions, so would likely have a different personality, too, although they would be an approximate look-alike. SinisterLefty (talk) 05:33, 27 April 2019 (UTC)

Why is electricity harmless to dry intact skin below several tens of eV but air does damage above ~0.03eV and sunlight's harmless at 2eV?
And 1 electron volt breaks down all compounds to a gas of ions when its thermal energy but is puny by electricity standards. Sagittarian Milky Way (talk) 01:35, 26 April 2019 (UTC)
 * Huh? -- Jayron 32 12:49, 26 April 2019 (UTC)
 * Let's try to help move our OP in the right direction: the original question is really confusing and indicates that he needs to review lot of basic subject-matter knowledge.
 * Some great places to start are our articles:
 * electron volt and electricity
 * ionizing radiation and non-ionizing radiation
 * health physics for a broad overview of how we use science to study health and harm to human biology
 * Sagittarian Milky Way: you've got some homework. Read those articles - every one of them in their entirety, and use the Wiki to link to other articles for the things you don't understand - and then come back after that if you need help finding more resources.
 * Nimur (talk) 15:58, 26 April 2019 (UTC)
 * Thanks for that. The problem is that s/he's throwing some information around which is not like "the sky is blue" obvious.  If s/he's read something that s/he doesn't understand, it is incumbent on him/her to share that original source with us so we can read it for context and explain it.  To be honest, this is a continuous and consistent problem with every question SMW asks; without knowing the context for the question, it is difficult for us to dig up additional resources to refer her/him to so they can read those sources and learn more.  I urge SMW to work better at providing enough context for us to be helpful.  Give us the link to where you are reading this, or a book where you're reading it, or something like that.  -- Jayron 32 16:04, 26 April 2019 (UTC)
 * Boltzmann constant says a Kelvin is worth 8.6173303(50)×10−5 electron volts. Thus the deionization temperature ~400k years after the Big Bang is less than 1 electron volt per particle. But ionizing radiation says photons need to be at least 10-33 electron volts to be ionizing. But as far as I'm aware electric circuits need at least ~40 volts, possibly up to 70 to go through the dead part of the skin without the help of cuts or abrasions or wetting the skin. On the other hand photons of only several electron volts (UV) have enough energy to cause cancer in the lower living skin (any DNA bond damage or whatever to upper living skin wouldn't cause cancer decades later since those cells soon die and fall off) Sagittarian Milky Way (talk) 17:51, 26 April 2019 (UTC)
 * AH! I think that you're doing there is confusing a unit of mass-energy, the electron-volt with a unit of electric potential, the volt.  Those are NOT synonyms.  We use the eV as a unit of mass-energy for very small objects only because it happens to be very small, and is convenient for doing math with very small energies/masses.  Up here in the big world, we tend to measure energy in Joules and mass in Kilograms, if only because we would otherwise end up with stupidly large numbers (just like measuring the kinetic energy of a single electron would similarly involve stupidly small numbers of joules).  I also think you're confusing the kelvin, a unit of temperature, with the others as well.  The Boltzmann Constant gives an equivalency between energy and temperature, but that doesn't mean that temperature and energy are the same thing!  Saying that a single particle has a temperature is a meaningless thing to say.  What the Boltzmann constant allows us to do is to calculate the average energy per particle for a given temperature of gas, but that does not mean that we can simply do the conversion and assign a "kelvin temperature" to, like, one photon or one electron or one atom.  Just because you can do some bit of math doesn't mean the math you do has meaning.  In the case of temperature, a gas obeys the Maxwell–Boltzmann distribution which means that 1) only a small fraction of particles are actually moving at the average temperature and 2) it doesn't even have to be the peak of the distribution.  At any given temperature, there will always be individual particles moving much slower and much faster than the average.  The long tail at the high energy end often means that, even at an average of 1 ev per particle, some non-trivial number of those particles will have a MUCH higher energy.  -- Jayron 32 18:20, 26 April 2019 (UTC)
 * Ah, that's what I'm not thinking of, the ~4eV air molecules in a 0.04eV oven, a Kelvin isn't exactly the same thing as 0.000086173303(5)eV/particle. So if you fill the space between 9V battery terminals with a dry finger that isn't equivalent to putting it in a beam of 9eV beta particles? Sagittarian Milky Way (talk) 20:05, 26 April 2019 (UTC)
 * No. It is not.  Let me repeat it again.  I think that you're doing there is confusing a unit of mass-energy, the electron-volt with a unit of electric potential, the volt.  Those are NOT synonyms. -- Jayron 32 11:01, 29 April 2019 (UTC)
 * If I asked why the sunlight photons that happen to be 2eV don't appear to harm the skin then I knew that eV's can be used to measure energy. I'm aware that the electrons and air molecules have about a half million and billions of eV of rest mass each but that is not what is referred to in the Boltzmann constant or electric current. So in a closed circuit in a superconductor with no resistance the electrons of a 9V battery have 9 electron volts of kinetic energy each right? How could it not be? An open circuit is at least approximately stationary so that is the only reason I can see how calling the battery electrons 9eV electrons would be wrong like you say. Wnt appears to be saying that they do have 9eV till they hit something, which would seem to imply the electric field is emitting them through the minute gap between terminal atoms and finger atoms, they're just not completing the circuit. So who's right? Sagittarian Milky Way (talk) 03:21, 30 April 2019 (UTC)
 * On one particular topic: typical UV damage to skin is not caused by direct ionization. UV light doesn't have enough energy to ionize most molecules, except near the boundary where UV transitions to X-ray, often called "hard UV" or "UVC". UVC produced by the Sun is blocked by the ozone layer. Skin damage from sunlight is caused by photochemical effects produced by the longer wavelengths: UVA generates free radicals in cells, while UVB excites DNA molecules and produces strand breaks or pyrimidine dimers. --47.146.63.87 (talk) 21:50, 26 April 2019 (UTC)
 * Thanks for the names of the UV skin damage mechanisms, I did not know those. I did know that ionization is generally higher energy than splitting molecules (and of course less than splitting nuclei). Sagittarian Milky Way (talk) 23:20, 26 April 2019 (UTC)
 * This is a valid question deserving of some serious thought that is likely to be missed by a textbook. Obviously, moving an electron over a voltage difference of N volts should give it N eV of energy, if it is not dissipated during the journey (which it probably will be as resistance, yielding heat on the way, unless the electron simply jumps over some gap all at once.  First, ionizing radiation is bureaucratically defined as 10 eV, which isn't that far from troublesome shocks.  Still ... why is even sub-ionizing radiation like ultraviolet a problem if electricity is not?  Well, because photons aren't electrons and can travel freely through transparent substances, like most of the skin.  They stop and cause trouble only when they hit some kind of dye, and there is a really really dark dye in the cell (in the UV spectrum only) known as DNA.  Biologists routinely measure the absorption of a crudely purified sample at 260 and 280 nm as a measure of all the DNA and RNA in the cell (they absorb at slightly different frequencies) and can be relatively confident (sometimes overconfident) that nothing else is going to affect the absorption much.  By contrast, weak beta emitters are sometimes said to not be dangerous to handle, because the ionizing radiation (electrons) will be stopped by the dead outer layers of skin, much as an electric current might be.  Caveat being that if you eat the stuff and the radioisotope ends up in your DNA, all bets are off!
 * Still, there is much I don't know here about how electric current affects the body. Clearly if it went through the whole tissue randomly making random changes, you'd expect it to have some mutagenic effect that I haven't heard reported.  Reports of electrical exposure typically describe skin damage from arcing, so I would guess there is some tendency to leave many cells untouched for every one that is devastated, but it will take more consideration to think about how to get to the details. Wnt (talk) 17:27, 27 April 2019 (UTC)
 * So the blue half of visible light is the sweet spot where skin's most opaque? Are there any IR wavelengths that are far enough from red to rival those colors but few enough microns that the photons can't rely on their physical size and fuzziness to penetrate deeper than them? How transparent or opaque is skin to those IR wavelengths? I accidentally discharged a disposable camera flash capacitor when those were a thing (thankfully not through the depth that might cause cancer) it hurt a lot, released a smell resembling burnt keratin and made the path unnaturally white and if it melted it wasn't by the time I looked a second or 3 later. Sagittarian Milky Way (talk) 13:51, 28 April 2019 (UTC)
 * To be clear, when I said that DNA is a dye, I meant that it absorbs the UV light, with the consequence of thymine dimers as described above. Dye in your skin (melanin) is (or barring racist idiots, at least should be) a good thing if it is not genetic material, but a bad thing when the DNA is taking the hit.  Also, I said that electricity is not mutagenic.  There's a tiny amount of fringey research where people say it might be, but it doesn't seem to have been followed through.  (Check PubMed, what I found doesn't seem worth writing about)  I mean, in a sense it has to be in some circumstance, since you can set up an X-ray tube, but having it happen in a person actually being shocked is another matter.
 * I suppose what I neglected to mention is that the Boltzmann constant is 8.6E-5 eV/K. That means that the average degree of freedom of any particle carries 0.013 eV of energy.  Accelerating an electron over a 10-volt difference should give it 10 eV ... UNLESS it hits something else, at which point it shares that energy.  This is why resistors heat up - the electrons are sharing the wealth.  And so you ought to get just heat, not individual bits of ionizing radiation, unless there's some way that the current arc makes an X-ray tube in vivo, or some other thing happens I didn't take into account.  The dispersed heat can help many reactions get over an activation barrier a little easier, but unless it stays on one particle it can't make one really unlikely reaction go forward like one of the atoms was dancing on the surface of the sun. Wnt (talk) 20:17, 28 April 2019 (UTC)
 * ...Any spherical or point particle. Most molecules will have more degrees of freedom, so it's energy will be distributed differently among rotational and vibrational modes.  -- Jayron <b style="color:#090">32</b> 11:04, 29 April 2019 (UTC)

Rapid deterioration in ill people
Why is it that people who are ill from an illness or injured in some ways can deteriorate rapidly? I.e. they can look and seem completely fine one minute and unconscious and unresponsive the next minute. 90.192.104.15 (talk) 20:54, 26 April 2019 (UTC)
 * This is a broad question, but any scenario where a person goes from "completely fine" to "unconscious and unresponsive" within minutes will generally involve rapid deterioration of brain function. This will most likely be caused by either a failure to get enough oxygen to the brain, or some kind of toxin that affects the brain. The former, in the context of infection or trauma, can often result from respiratory failure or circulatory collapse, caused by such things as blood loss or septic shock. Notably, you can easily bleed to death in minutes if a major artery such as a femoral artery is compromised. --47.146.63.87 (talk) 21:18, 26 April 2019 (UTC)


 * Note that the body has systems to compensate for various problems, which can mask those problems, for a while. For example, blood loss due to a hemorrhage can be masked by blood vessels contracting to keep blood pressure up, and the patient may remain awake until the blood loss becomes so severe that BP drops and they pass out, then soon die. SinisterLefty (talk) 05:43, 27 April 2019 (UTC)


 * Another category that might be of interest is when a disease attacks the immune system, such as AIDS. HIV can appear to remain dormant for years, then finally finishes taking out the immune system, at which point the patient is left wide open for any number of opportunistic diseases, such as Kaposi's sarcoma. SinisterLefty (talk) 18:53, 27 April 2019 (UTC)


 * Your wording, as least as I interpret it, might be a little misleading to some people. HIV infection produces pronounced viremia soon after infection. The immune system mounts a response and destroys most circulating virus, but infected cells remain, and the virus is able to continue reproducing and infecting cells. The continued chronic infection causes a decline in cell-mediated immunity, but it generally takes years for this to progress to the point where AIDS symptoms become prevalent. See the Pathophysiology and Diagnosis sections of the HIV/AIDS article, particularly the chart in the latter. --47.146.63.87 (talk) 00:53, 28 April 2019 (UTC)




 * Thanks for the clarification. By "remain dormant for years", I refer to the "clinical latency" period listed in the chart. I've now clarified my previous post. SinisterLefty (talk) 14:43, 29 April 2019 (UTC)


 * It's generally discouraged to edit messages like that, as now, without looking at the page history, readers don't know the message is now different from the original message that I replied to. And this is the Ref Desk, so for pedantry's sake, HIV (or most anything else that can cause immunosuppression) doesn't "take out" the immune system in its entirety: just one component, in HIV's case, T cells. This nevertheless makes one extremely susceptible to numerous pathogens, and also, in this case, cancer, as T cells are essential in detecting malignant cells. Since tone isn't conveyed well in text, let me state that I take no personal affront at you or something you wrote. I'm just trying to help inform readers. --47.146.63.87 (talk) 22:58, 29 April 2019 (UTC)


 * I think "taking out the immune system" is a fair way to characterize it after all the T cells are gone. At that point death is imminent. SinisterLefty (talk) 23:25, 29 April 2019 (UTC)


 * That's reasonable. I was trying to convey that HIV targets the adaptive immune system, which influences the pathology of AIDS. The innate immune system still functions, though not as well because of the lack of stimulus from the adaptive arm. Various pathogens are specialized to resist the innate immune system, and these are the most dangerous in conditions such as AIDS. Immunodeficiency has a nice table listing characteristics of deficiency in the different parts of the immune system. --47.146.63.87 (talk) 00:45, 30 April 2019 (UTC)


 * Good chart. Should Kaposi's sarcoma be added to the chart for T-cell deficiency, or is that for some reason unique to AIDS patients ? SinisterLefty (talk) 02:26, 30 April 2019 (UTC)
 * I'm uncertain. It isn't unique to AIDS patients, as the article on the disease discusses. But I'm not sure if its emergence is tied solely to T-cell dysfunction. Also, the relevant column in that table is labelled as listing "pathogens". Kaposki's sarcoma itself is technically not a pathogen; it's a cancer which is caused by an unsuppressed HHV-8 infection. If interested, I would suggest seeking input at the Wikiproject Medicine talk page or some other place where there are people with a background in this. --47.146.63.87 (talk) 00:11, 1 May 2019 (UTC)