Wikipedia:Reference desk/Archives/Science/2012 January 14

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

January 14

Why is my light bulb Power only half of what it's supposed to be?

I have a coiled compact fluorescent lightbulbt with the following specs as written on the lightbulb:

• 23W
• 120V
• 60Hz
• 363mA

Using circuit equation, Power = Voltage x current, you get Power = (120V)(0.363A) = 43.56 W. This is almost double of the 23W as stated, why is this? Thanks Acceptable (talk) 00:10, 14 January 2012 (UTC)

The equation you used is only valid for Direct current. Calculating the power on an AC circuit is more complicated. See AC power. --Jayron32 00:14, 14 January 2012 (UTC)

If the current and voltage given is RMS (as is usually the case in AC) and the power factor is 1.0, then your formula would work fine. It seems unlikely that a CFL would have a power factor as low as 0.53. Perhaps the stated current represents a starting "inrush current". -- 110.49.224.131 (talk) 08:11, 14 January 2012 (UTC)

The answer may be as stated in "Why are CFL wattage ratings wrong as the light may be rated for xx watts but when checked with a wattage meter the actual usage is significantly higher?", namely that the nominal wattage is for the tube alone, while the mA rating is for the tube and ballast together. If this is true then some of us are in for an unpleasant surprise regarding the efficiency of CFLs. --Heron (talk) 11:31, 14 January 2012 (UTC)

After more Googling, it seems that a PF of 0.5 is not unusual for CFLs, so I think this is a more likely explanation than the inefficiency of the ballast. The mA rating is useful if you have lots of CFLs on a circuit and need to know what circuit breaker you need, since circuit breakers respond to current. The W rating is of more interest to the consumer as that determines how much the lamp costs to run. --Heron (talk) 11:58, 14 January 2012 (UTC)

1957 ufo

I seen it 54 years ago i was 6 years old it was as big as a 20 story building, there are 2 more wittnesses at the time — Preceding unsigned comment added by 208.54.44.133 (talk) 01:31, 14 January 2012 (UTC)

Do you have a question we can help you find the answer for? --Jayron32 02:22, 14 January 2012 (UTC)

Perhaps a Q about dangling participles ? StuRat (talk) 03:35, 14 January 2012 (UTC)

Or run-on sentences. -- Jack of Oz ^{[your turn]} 20:09, 15 January 2012 (UTC)

Dynamite gun

Why aren't high explosives such as dynamite used to propel bullets? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 03:16, 14 January 2012 (UTC)

Who said they aren't? Firearms propellants can be both low explosive and high explosive. Cordite is an example of a low explosive propellant and Ballistite is an example of a high explosive propellant. So yes, some high explosives are used to propel bullets. --Jayron32 03:27, 14 January 2012 (UTC)

In handguns? ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:37, 14 January 2012 (UTC)

Quite possibly, but the Ballistite article cites only the Vetterli service rifles specifically using cartridges that had ballistite propellant in them. I'm not aware that the breech of such a rifle was special in a way that a handgun could not also be, so I don't see where it couldn't have been used in handgun cartridges as well. --Jayron32 03:46, 14 January 2012 (UTC)

I wonder if we should notify User:Kablammo about this series of questions? He might be a specialist on the subject. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:39, 14 January 2012 (UTC)

The basic reason, which you'll find in explosive material and propellant, is that low explosives burn more slowly producing lots of hot gas, which propels the bullet out of the gun. Generally you want to control the detonation within a gun so that the pressure isn't too great (because the gun must withstand that pressure without exploding) but is enough to impart a good speed to the bullet (without also ripping the bullet apart); a slower detonation also provides more time to accelerate the bullet. --Colapeninsula (talk) 12:47, 14 January 2012 (UTC)

You might want to look at USS Vesuvius (1888). Buggie111 (talk) 14:36, 14 January 2012 (UTC)

Why? It used compressed air to propel the "bullets". Only the payload was dynamite, not the propellant. Franamax (talk) 18:59, 14 January 2012 (UTC)

Agreed - see Dynamite gun. The Dynamite filled shells were propelled by compressed air, as an explosive propellant would have detonated the shell at launch. This is a bit of a clue - it suggests that Dynamite is rather unstable and therefore it would probably be unsafe to carry around. Our Dynamite page says "Over time, the dynamite will "weep" or "sweat" its nitroglycerin, which can then pool in the bottom of the box or storage area." People must have thought that cordite was an awful lot safer. Alansplodge (talk) 17:21, 15 January 2012 (UTC)

I think another answer lies with the (comparative) stability of many high explosives. A primer cap detonates packed cordite very well, but I'm not sure it would be enough to detonate a primary explosive. This would complicate the design because you would need some form of intermediate between a pressure-sensitive primer cap and the primary charge. This is in addition to the fact that a firing chamber must withstand the pressures generated. That doesn't just mean being able to not burst the barrel but also not throwing the bolt backwards into your face or turning the firing pin into a tiny backwards bullet. The net effect of the overbuilt monstrosity that could use hexogen as a "powder" charge would be heavy, ungainly, expensive, and probably prone to failure and in the end not all that much more effective. HominidMachinae (talk) 08:02, 15 January 2012 (UTC)

A side issue - our Ballistite page doesn't mention that some types of rifle grenade need a blank Ballistite cartridge to launch them[1]. Alansplodge (talk) 17:17, 15 January 2012 (UTC)

Electrical wiring question

I saw a wiring picture in a home improvement book. In the picture, the ground wire coming from the service panel is spliced to two other wires using a wire nut. One of them is the ground wire to the appliance; the other connects to the ground terminal of the switch. All of the ground wires are naked (not insulated). My question is, is there something supposed to prevent the exposed ground wires from coming into contact with the hot wire terminals of the switch in the electrical box? If there is, what is it? — Preceding unsigned comment added by 96.227.49.101 (talk) 04:47, 14 January 2012 (UTC)

Well, the hot wires likely have wire nuts or some other device in use to prevent that. There also shouldn't be enough extra ground wire for it to reach the terminals. If you have excess ground wire, either cut it off, or coil it up outside the electrical box (if you feel the need for extra in case of future modifications). StuRat (talk) 05:06, 14 January 2012 (UTC)

Speaking from a uk perspective, here, usually separate ground and earth bonding wires are insulated. Inside switches, junction boxes etc, it is usual to sleeve the ground or earth wire using green/yellow pvc sleeving to prevent contact with any live conductors.--92.29.192.186 (talk) 13:21, 14 January 2012 (UTC)

Beware that wiring "standard" and law requirements are different depending on countries. And in some it's big mess. Electron9 (talk) 17:26, 14 January 2012 (UTC)

... and bare earth wires are still commonly found in the UK from before the insulation regulation was enforced. It was usual to route them round the perimeter of the interior of the box to prevent contact with the hot/live terminal. Dbfirs 17:57, 14 January 2012 (UTC)

What would happen if the earth blew up?

So say the earth somehow blows into four evenly divided quarters, like it always does in the cartoons. What would happen? Would walking to the edge of one of these corners be equivalent to falling off, or would you just loop back onto the newly visible cross-section of the earth? Would the pieces fall through space, or would the sun suck them up and destroy them? Buggie111 (talk) 04:56, 14 January 2012 (UTC)

First, it wouldn't split like that, but, if somehow magically it did, the 4 pieces (or 8) would reform into spheres. 1/4th or 1/8th the size of the Earth is still plenty for gravity to pull it into a sphere. When you do get a small enough object to have an irregular shape, then the gravitational attraction is approximately toward the center wherever you are, so you can't "fall off", although the gravity would be quite weak and variable, so you might be able to jump fast enough to achieve escape velocity. StuRat (talk) 05:02, 14 January 2012 (UTC)

... and of course the 'spherification' wouldn't happen over the next couple of days! Richard Avery (talk) 14:15, 14 January 2012 (UTC)

Actually, I think it would. The Earth is mostly molten to start, and the energy required to blow it into pieces would make it completely liquid. In that state, the chunks would rapidly form into spheres. StuRat (talk) 17:03, 14 January 2012 (UTC)

... but in that case you wouldn't be there to walk around it or even to observe it unless you escaped in a spaceship before the explosion. Dbfirs 18:01, 14 January 2012 (UTC)

Yes, anything that would split the Earth into bits would absolutely kill all life on Earth. StuRat (talk) 21:32, 14 January 2012 (UTC)

I agree, the parts would become spherical within a couple of hours, I would expect. You might end up with a non-spherical solid core surrounded by a spherical mantle (with the core having melted and basically become part of the mantle). The core might then take a bit longer to become spherical, since it's solid. The drop in pressure caused by the now being less mantle pushing down on it (and no mantle at all on one side for a short time) might cause it to liquefy. If so, it would become spherical faster. --Tango (talk) 00:48, 15 January 2012 (UTC)

Unless the explosion had a fantastic amount of energy, way more than that needed to "merely" crack the globe like a egg, there probably would not be enough inertia to overcome the mutual gravity attraction of the pieces. We might lose some mass, but in the end the earth would probably re-form into something not totally unlike it is today under the tremendous force of gravity from quadrillion-ton pieces of rock grinding together. HominidMachinae (talk) 08:05, 15 January 2012 (UTC)

Field of vision... can we experience it?

Different animals have different fields of view, with docile animals have eyes on opposite sides of the nose, while a lot of predators have two eyes that look forward. How exactly do you "see" different fields of view? My main question is what would a 360 degree field of view "look" like?--99.179.20.157 (talk) 13:17, 14 January 2012 (UTC)

I would not expect it to "look" any different.

Two things to consider:- (1) If you look at all birds and mammals, and at least most reptiles from directly in front of them, you'll see that the fields of view of their eyes overlap. Generally they do not overlap behind - they do not have 360 degree vision, but it is very close to 360. When I was at school we were tought that only mammals & birds with forward facing had stereoscopic vision giving accutae depth/range perception like humans. But I grew up on a chicken ranch and we had animals such as goats all with side facing eyes - so I can tell you that all such creatures with side facing eyes have very accurate ranging for things directly in front. E.g., if you hold food grains directly in front of them but far enough away that they have to stretch their necks to reach, they never the less accurately reach out and take the grain.

(2) it is well established that in man and animals, that most of the "pixel" infromation from the retina is discarded. Key features are sent to the brain, and the brain reconstructs what you see (or what you think you see) and you are conscious of a wide angle of view.

THEREFORE, the only consciousness difference between (say) man, with a high overlap of field of view from each eye, and the vision of an animal with side facing eyes, is that distance estimating is slightly less reliable, and the conscious field of view covers a wider angle. In addition, in forwrd facing eye animals eg man, the fovea, the small area of the retina that has high resolution, is focussed directly ahead. When chickens study something of interest, they look with one eye and then the other. I'm not sure why they do this, but it may be that their foveas are centred in the retinas just like us, but being side facing, means that high detail is seen at the sides of the field of view. Keit121.215.9.8 (talk) 13:44, 14 January 2012 (UTC) Invertebrates with eyes that do not overlap are another matter. But they are another matter all together.

I'd expect it to look a lot like a panoramic picture. That is, the brain combines the image from each eye into one, just as with our eyes. The chameleon has an interesting feature, they can move their eyes independently. While doing so, they lose depth perception. They then need to lock them together to regain depth perception, one they've spotted their prey. StuRat (talk) 16:59, 14 January 2012 (UTC)

Hmmm, apparently pigeons have a fovea, but chickens do not.^{[ PMID 19296862]} Of 104 species of birds examined, only chickens lacked a fovea, but the structure is less common (as observed) in mammals, amphibians, reptiles and fish. But the fovea in birds is usually situated to the nasal side of the optic nerve, the opposite situation from that in man. Wnt (talk) 18:31, 14 January 2012 (UTC)

Animals with side-directed eyes usually have a visual streak rather than a fovea, and only a small region of binocular overlap. But the question of how the world would "look" to them doesn't really have an answer -- perhaps the best that can be said is that it would be like looking at the world through a fisheye lens.

It is important to note that we don't have any awareness of the properties of our own foveas. The human fovea is roughly the size of your fist when you hold it at arm's length. But if you look around at the world, you won't have any awareness that the foveal zone is any different from the area around it. Looie496 (talk) 21:05, 14 January 2012 (UTC)

Actually, I've found that the rim of the fovea becomes quite visible when blinking repeatedly and rapidly, especially if reading while wearing contact lenses (rather than myopically) in a low light level. See File:Macula short-term aberration.png for further aberrations I've noticed in this regard. Wnt (talk) 23:09, 14 January 2012 (UTC)

If by "fisheye lens" you mean the coverage that a fisheyes lense gives, then yes, but if you mean the fisheye distortion, then no. We are not aware of the shortcommings of our eyes and neither would animals just as Looie496 says. I have been disgnosed with a form of macular degeneraion - a condition where the retina comes forward off the back of the eye and parts of it become dead. Mechanically, this means that the image on the retina is distorted, and there are additional blind spots as well as the normal single blind spot we all have. What is the conscious effect of this? Nada, zip, nothing - until the disease progresses sufficiently, the brain just keeps compensating. I only know I have it because it was detected during a routine health check for a new employer. Kiet124.182.174.74 (talk) 03:52, 15 January 2012 (UTC)

'Magic numbers' in chemical bonding & more

a. What do we know about any quantum-physical law, dictating 8 electrons in the outer atomic shell + the other shells' populations, including the 2 electrons in the innermost. Any physical theory behind these numbers, or just an empirical reality ?

b. How reacting atoms 'choose' between, e.g., ionic bond and covalent bond ?

c. What Hydrogen was used in the early spectra measurements (e.g., Balmer) - atomic or molecular ? Since the spectra are atomic in nature, how did they split the H molecule into two atoms in those days ?

Thanks, BentzyCo (talk) 15:31, 14 January 2012 (UTC)

a. The actual distribution per shell is explained by quantum theory, see atomic orbital for all the gory details. In simplest terms, the exact distribution of electrons around the atom is described by the wavefunction as described by the Schrödinger equation. The octet rule is a heuristic (very simplified rule-of-thumb) which helps get the right answer without having to go through the in-depth mathematics necessary to understand the full implications of quantum theory.

b. Atoms don't "choose" anything, they aren't intelligent. But the type of "bond" is determined, to a first aproximation, by the difference in electronegativity between the two atoms involved in the bond. If the atoms have a similar electronegativity, the bond will be covalent; if the atoms have a very dissimilar electronegativity, the bond will be ionic. This model of bonding is, like the above, also a heuristic aproximation of reality, but it is a good, useful, and resiliant one. It was first put into its form by Linus Pauling in his book The Nature of the Chemical Bond, and has become somewhat canonical in understanding bonding relationships. The Wikipedia article Chemical bond has a pretty decent explanation of chemical bonding and various models used to explain it.

c. It is the spectrum of atomic hydrogen, not H2 molecules. The Wikipedia article Hydrogen spectral series has a decent introduction to the topic. The molecule splits via the same energy (a big electric spark) that also provides the energy to excite the electrons, producing the familiar emission spectrum of the hydrogen atom, whose wavelengths are described by the Rydberg formula and which also matches the Bohr model for a two-particle system. --Jayron32 16:14, 14 January 2012 (UTC)

Thank you for your quick and comprehensive answer. As to (a) & (b): I know all of these already, having enough physical background.

Maybe it wasn't implied clearly enough in my questions:

(a) How does one get from the electrons wavefunctions to the different numbers underlying atomic / molecular stabilty ?

(b) I said 'choose', not choose, which is heuristic, of course. Now, similarly, how does one get from electronegativity property to whether ionizing or electron/s sharing tendency or behavior ?

(c) I see.

Fundamental, in-depth references are highly helpful, besides what you indicated already.

As a geographer (?) your physical knowledge is very appreciated. Thanks, again. BentzyCo (talk) 17:15, 14 January 2012 (UTC)

Here's a fundamental, in-depth reference: Griffith's Introduction to Quantum Mechanics. It will explain, fundamentally, how to get from the wave equation to derive observable chemical properties. The preface suggests that you read it over the course of a year-long senior level quantum physics study, recommending two to three years of prerequisite physics background.

Few people say quantum mechanics is easy. Even fewer say that quantum mechanics helps intuitively explain observable chemical properties for complex atoms and molecules. If you want a quick approximation, the "octet rule" works for a lot of people. If you must use more elaborate analytical methods, the complexity increases very rapidly. Electron behavior, especially in multi-electron atoms, is very difficult to explain in simple terms. Nimur (talk) 18:59, 14 January 2012 (UTC)

(edit conflict) I'm not a geographer, I'm a chemistry teacher, so I would hope I could explain this to some level of satisfaction. Let me try to take a crack at this:

a) This is not a trivial question to answer, because historically one did NOT go from the quantum theory to the heuristics. The heuristics (like the octet rule) predate rigorous quantum theory by some time; quantum theory came along later and confirmed the conclusions of the earlier theories. One example of this is the relationship between the Rydberg Formula and the Bohr Model. Rydberg devised his formula as a means to find a mathematical relationship between the spectral lines in hydrogen. He had no atomic basis for his formula, it is merely an equation to connect the location of the lines on the spectrum. It took Neils Bohr to come along later to realize that the mathematical terms of Rydberg's equation had their basis in the physical organization of the atom; i.e. the atomic number and principle quantum numbers for each atom. The octet rule is similar. It comes about via a few sources, including the law of octaves, an early form of the Periodic Table of Elements, and the Cubical atom model developed by Gilbert N. Lewis. People early on noticed that a) atomic properties repeated every 8 elements and b) atoms bonded in ways that implied the octet rule. It didn't require any actual knowledge of the real structure of an atom to derive the octet rule. Completely independent of this, the Schrodinger equation comes up with an organization of the electron cloud based on probability distributions of where one is likely to find each electron; this distribution gives us certain shaped orbitals located in certain locations. The Schrodinger equation predicts that the valence level of any atom will generally consist of s and p orbitals, and given that there are 2 spin-paired electrons (maximum) in each orbital, and that there is 1 such s orbital, and 3 such p orbitals, thats 8 electrons. 8 is also particularly stable because of the geometry involved; given that 8 electrons results in 4 molecular orbitals, that makes the tetrahedral molecule really stable and well organized given the fact that such a shape maximizes the repulsion of the orbitals (see VSEPR). If you really want to get down to it, the actual organization of electrons is purely geometric; it is described by group theory and symmetry groups which mathematically predict the stability of certain organizations and shapes, given the dual constraints of a) electrons repel each other and b) electrons are attracted to the nucleus.

b) The location of electrons in bonds (as pure non-polar covalent, polar covalent, or pure ionic) exists on a continuum. The difference of the electronegativity between the two atoms involved in the bond determines how we name that bond. Generally, non-polar covalent bonds arise from bonding between two atoms whose electronegativity is identical (i.e. a Cl-Cl bond). A polar covalent bond arises between two atoms whose electronegativity is different, but not too different (i.e. an H-Cl bond) This results in a dipole moment to exist over the bond, with the more electronegative atom "getting" more of the bonding electrons, and thus being slightly more negative; whereas the less electronegative atom ends up with less of those bonding electrons, and is slightly more positive. An ionic bond arises between two atoms whose electronegativity is a lot different, (i.e. a Na-Cl bond), in this case the Cl is much more electronegative, it takes "all" of the bonding electrons from sodium, leaving it with none. Generally, a good rule of thumb is that EN differences less than 0.4 or so tend to be non-polar bonds, EN differences from 0.5-2.5 tend to result in polar covalent bonds, and EN differences greater than 2.6 or so tend to result in ionic bonds. You can look up the values at Electronegativities of the elements (data page) and confirm the results above.

Does that help any? --Jayron32 19:29, 14 January 2012 (UTC)

I think the OP wants a more basic explanation. To put it simply (muohahaha), electrons are clouds roughly an Angstrom in size, which oscillate back and forth near the nucleus which attracts them because of its charge. The oscillation alternates between a sort of positive and negative, in the sense that the electron is a wave that can constructively or destructively interfere with itself, so the electron can stably exist near a nucleus only in a sort of standing wave. It is like a plucked guitar string or waves in a tank of water. Finally, quantum mechanics, the weird part, demands that you don't just have a mix of all possible standing waves, but rather, a wave is either present or it's absent, and usually the lowest-energy standing wave is preferred, with each wave occupied by two electrons of opposite spins (Pauli exclusion principle). So the set of electrons works like a guitar string, but one which either vibrates only at the fundamental, or twice as much at the fundamental, or that plus one overtone, etc. Now it turns out that for most elements the standing waves which are partially available fall within a set of four main vibrations - from the edge to the center symmetrically, plus from one end to the other in each of three dimensions. Because you can't actually attach an atom to the "outside" of an atom in no particular place, these patterns are twisted via sp3 hybridization into a symmetric tetrahedron with four attachment sites. (Yes, this is confusing, but it's a matter of simple linear combination little different from viewing the atom from a different angle so that you've rotated the mathematical axes. The point is, you can have four and only four vibrations from this set such that adding an electron to one of these has no effect on the amount of vibration along the other lines) Thus you get the typical four ligands and octet, with many caveats. Wnt (talk) 19:38, 14 January 2012 (UTC)

Degree of Unsaturation

Hello. What is the proof of the formula for the degree of unsaturation? Thanks in advance. --Mayfare (talk) 16:42, 14 January 2012 (UTC)

Did you look here Degree of unsaturation--92.29.192.186 (talk) 18:28, 14 January 2012 (UTC)

Electric chair and accidental electrocutions

Why the electric chair way of electrocution is more complicated as compared to accidental electrocutions, where one body-contacting wire would suffice?Brandmeister t 16:50, 14 January 2012 (UTC)

Actually, accidental electrocutions aren't that simple. At a minimum, you need the electricity to go in one place and out another. A connection to ground can be the "other". And, with an electric chair, they want to be sure to kill the person with the first zap, without creating flames and smoke, so as to minimize the horror of it all. This takes careful preparation. StuRat (talk) 16:55, 14 January 2012 (UTC)

And I suppose, in that they succeed: [2]--Aspro (talk) 17:52, 14 January 2012 (UTC)

I was talking to an electrician asking him basically this sort of thing, and if you touch a livewire with the back of your hand, usually (always?) your muscles spasm, because they too work using electricity. The danger then is, the result of all your muscles contracting is so powerful that there is no telling where you will end up - if you are working on a ladder, for example. Usually you won't die, but it's obviously part of the danger - there's more to it than just electrocution. IBE (talk) 18:29, 14 January 2012 (UTC)

As no one has come into answer the OP properly, I would point out that 'an electric shock' may or may not stop the heart. Even if it stops the heart – it may restart, thanks to the pacemaker cells Cardiac action potential. What judicial execution strives to ensure, is that the heart pacemaker cells are completely depolarised, leaving the whole heat muscles flaccid and unable to ever start again. As people that were unfortunate enough to form a circuit with high tension power line and lived to tell the tail will recount – they where fully aware of their flesh being vaporised by the electric arc (hotter than the surface of the sun) during the several seconds that the experience lasted. The current that flows though Old Sparky just burn holes though the flesh at its contact points. --Aspro (talk) 22:16, 14 January 2012 (UTC)

In the 1880's New York City had some very public and very ghastly (I almost said "shocking") accidental electrocutions of utility linemen (John Feeks, Peter Clausen, and George Kopp) climbing up to work on the arc lighting circuits, which were at 2000 volts or higher. Sometimes it was just an unfortunate workman on a roof, who touched an elecric wire, like Robert Dalton. The current went from a conductor to the unfortunate worker to the wooden pole he was belted in to, or the metal ladder he stood on, or another energized wire. They would hang there for maybe an hour, turning black, until someone else came to open a switch. They may have been dead after the first half cycle. The electric chair used alternating current at similar voltages, with high amperage. Reports that the condemned was struggling against the straps were sometimes just the equivalent of Galvani noting frog legs twitching when electricity was applied. In some cases. poor connections were made, and inadequate current flowed to cause death.First execution by electricity, 1890 Some utility workers have been revived after severe shocks, and others have survived incidents which roasted an arm. If the current goes through the heart or the brain, a bad outcome is more likely. A much lower voltage, such as 120 or lower, can cause a fatal shock. "One body-contacting wire" as the OP said is less of a clear case, because there would be an open circuit, unless the "one body" was touching ground (such as a concrete floor or a water pipe or a grounded appliance), or neutral as well as the wire. If the voltage was high enough, the capacitance of the person would allow enough current to flow to be dangerous, even if he was isolated from ground. Edison (talk) 01:47, 15 January 2012 (UTC)

Probabilities of extremely rare events

I can't find it now but I thought I saw something in one of the list of open problems (can't remember if it was the list for math, philosophy or science) that contained an entry for assigning probabilities to extremely rare events, such as events that haven't been observed yet. I thought an example was assigning a probability to the sun won't rise tomorrow. Does this ring a bell for anyone? RJFJR (talk) 19:34, 14 January 2012 (UTC)

It definitely sounds like an appropriate example, as the number varies substantially depending on whether you live in Fairbanks. Wnt (talk) 19:56, 14 January 2012 (UTC)

Assigning probabilities to events that haven't happened yet... I don't think this is an open problem in mathematics or statistics. I think this is a shortcoming of the way we educate people about probability. Our article, Probability theory, lays out the formalisms that are needed to calculate probabilities; in reality, there are a lot of prerequisite pieces of information that must be known a priori to make a meaningful estimate of the probability of an event. In engineering, we use Bayesian estimation when we are unsure of the prerequisite knowledge... in a sense, quantifying our uncertainty about our estimates. But even still, the best Bayesian algorithm cannot calculate probabilities for events outside of the domain it is designed for.

In a lot of science fiction, characters severely abuse the terminology of probability for dramatic effect: C-3PO famously quotes the odds for "successfully navigating an asteroid field is approximately 3,720 to 1." While it may make for exciting storytelling, his statement is entirely meaningless! Probability does not apply to such a statement! How many ways can we tear this quote apart? Natural language processing and computational semantics - what does "success" mean? For that matter, what does "asteroid field" mean? Certainly, the odds should be different in a "less dangerous" asteroid field! But C-3PO doesn't say "the odds of exiting this asteroid field..." - a stunning display of linguistic imprecision to preceed such a precise numerical conclusion! From the standpoint of probability, it's pretty meaningless to "calculate odds" for sophisticated behaviors and phenomena; nor will it translate ambiguous human language expressions into precise quantifiable results. That's just not what probability does, and I don't think future probability researchers will "solve" this. The only "open problem" here is, how do we educate people about the way probability really works, so that they can correctly and effectively use it to inform their decisions when it actually is useful. (Like, "what's the probability of winning money while gambling?" Sadly, while this is actually an easy problem to calculate odds for, surprisingly few gamblers use that information to make smart decisions). Nimur (talk) 20:22, 14 January 2012 (UTC)

Well, there are methods for doing this. If you know the constituent probabilities, you can figure the final probability, as in the Drake equation. In your example, if you can estimate the probabilities of all the different ways the Sun could fail to rise in the morning, then you could get the total probability. StuRat (talk) 21:22, 14 January 2012 (UTC)

As demonstrated at Chernobyl and Fukushima, for example. Wnt (talk) 23:04, 14 January 2012 (UTC)

At Fukushima, they seemed to have made an error is assuming that the plant failing, the power supply off the electrical grid failing, and the diesel backup generators failing were all independent events. So, if you figure each of those has a 1/1000 chance, you then get a 1 in a billion chance of all three happening at once. The reality, though, is that any quake large enough to severely damage the reactors would likely also take out the grid and backup generators. StuRat (talk) 23:22, 14 January 2012 (UTC)

"oops, didn't think of that" (tm) ;-). Someone calculating might have missed the relationship between the factors. In all, they didn't think of the probability of a higher than estimated tsunami wave. Electron9 (talk) 14:39, 15 January 2012 (UTC)

While StuRat's description of the non-independence of events is an astute one, it should probably be noted that in real life reactor siting and safety, they do somewhat more than just calculate individual probabilities in an abstract way. The Nakamura Panel, which is the internal Japanese group investigating the causes of Fukushima, has already issued a preliminary report which indicates, amazingly, that Tepco had in fact done risk assessments on the event of massive flooding and indeed found that it had a significant chance of causing widespread problems of the sort that did occur. But it was not followed up on — no changes were made after determining this. In fact, the Nakamura Panel apparently concluded that the majority of the reason for the accident was not just technical, but managerial. (I say "apparently" because I don't read Japanese and I think only the preliminary findings have been released — I learned of this second-hand from someone who gave a talk on the subject.) The people at the Fukushima site were not trained at all for that sort of accident. Had they been, there were mitigating steps that could have been taken — instead, a lot of the operator steps compounded the error. Anyway, the point is, these things are more complicated than coming up with your one-in-a-million chance estimates, which do exist as part of the process, but usually embedded within a more complicated framework. --Mr.98 (talk) 15:13, 15 January 2012 (UTC)

There is also a finite probability for you to arise out of thin air, then experience the present moment you are experiencing now, and then vanishing into thin air again.Count Iblis (talk) 00:31, 15 January 2012 (UTC)

The list Unsolved problems in statistics do indeed contain the sunrise problem as a more philosophical unsolved problem. As for assigning probabilities to events that happen so rarely that we can't estimate the probability from the samples, the long tail property describes how events we regards as impossibly improbable may still occur because of a deficiency in our models of probability. On the other hand, the recent black swan theory debate our inability to predict extremely rare events, especially those with no previous examples. It also discusses our misplaced effort in trying to estimate the probability after the event. Further reading on the probability of rare events include: [3][4][5] and [6]. The latter introduces a fun nomenclature of "millichance" and "microchance". EverGreg (talk) 10:02, 16 January 2012 (UTC)

Does water possess an electrochemical state?

Hi. We know that water's polar bonds create in-fluid chains of molecules in liquid water, which are prone to disruption. In ice, this bond forms longer chains and crystal patterns that expand and allow other substances to occupy the space. My question is, can water hold an "electrochemical imprint" of its condition, and is there any evidence for such? Iff water does indeed have such a state, it would be largely transient, but would be affected by things such as the presence of metals, temperature/pressure changes, dissolved ions and substances, radiation, any electric currents, condensation nuclei and even fluid currents. Moreover, the state of the water could be similar to the human brain, only more transient and not dependent on chemical compounds and hormones. It would be a physical change, not a chemical change per se. Could any change in such a state be detectable? Thanks. ~AH1 ^(discuss!) 20:25, 14 January 2012 (UTC)

No, there is no such "state." Your suppositions here are the basis for a bit of snake oil and quackery known as Homeopathy. There is no "memory" of the water based on any "electrochemical states". This bit of pseudoscience is known as water memory, a concept which has no basis in any scientific principles and no rigorous experimental evidence. --Jayron32 20:30, 14 January 2012 (UTC)

If the particles in a fluid had state, we would be able to see it and measure it, because the properties of the particles affect the ensemble behavior of the entire fluid. (Roughly, that's what is called the Virial theorem). Water has been qualitatively and quantitatively studied by hundreds of thousands of chemists, biologists, physicists, material scientists... for centuries. It's unlikely that any ensemble-behaviour of water has eluded this careful study by so many different people for so long. We know that pure water molecules can be polarized, but we also know that in normal conditions, water is a good fluid, and thermalizes any inhomogeneity very, very, very quickly. Nimur (talk) 21:02, 14 January 2012 (UTC)

(edit conflict) A macroscopic example I've used to teach the (non-)viability of it is to consider doing lost-wax casting but with a mold made out of oil instead of plaster. The imprint is too transient and too dependent upon the template being present for it to have any lasting effect. DMacks (talk) 21:04, 14 January 2012 (UTC)

Well, there are curious aberrations like Falaco solitons (there's a cute demonstration that can be made with a Frisbee in a swimming pool, where they remain present in an apparently placid body of water for up to ten minutes - this is a poor example. I've seen odd speculations about the number of reactive oxygen species in boiled water as opposed to plain water, or near a negative or positive electrode, etc. Water is not always water. But that doesn't change the fact that homeopathy is bunk. I would bet money that if you could look at their financial and shipping records, you'd find they never even buy the mythical herbal constituents that are supposedly diluted into the "patterned water". Wnt (talk) 00:34, 16 January 2012 (UTC)

Arcs of plasma

Using an electric arc, would it be possible to:

-a: detonate insensitive high explosives?

-b: electrocute prisoners on death row? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:28, 14 January 2012 (UTC)

a) maybe b) maybe, but not reliably for either of them. That is, electric arcs can kill people, but generally they just painfully maim them, for a judicial execution, you generally want death to be reliable, quick, and painless, not random, drawn out, and painful. And insensitive high explosives generally need a very specific set of conditions to be detonated; it may not be impossible for such a spark to result in such an outcome, but it also may not be the most efficient means to accomplish it. --Jayron32 20:33, 14 January 2012 (UTC)

I'd say both are possible. As far as useful ... probably no, because we have better ways to do both tasks.

Regarding ignition, you might want to read about spark plugs, and compare to glowplugs. In higher compression engines, no spark is necessary. A little thermal energy, and a good fuel-air mix, is all that you need to get a diesel cylinder to fire. "By extension," etc., etc., you can see this carry over to other combustibles. In the case of high-explosives, people who work with such materials tend to be safety-conscious, risk-averse, and prefer the simplest and most well-tested techniques to get the job done, so there's little justification for using an electric arc, when alternatives are available. Nimur (talk) 20:38, 14 January 2012 (UTC)

I am sure I could execute the hell out of prisoners on death row with an electric arc, with very high certainty. If you don't want to strap them into a purpose built chair, you could just use a scaled up version of a cage used for aversive conditioning of rats. Bars on the floor insulated from each other, plastic walls you can't hang on to. Or just put them in a concrete room and establish an arc at 480 volts or higher between two bus bars. Edison (talk) 01:34, 15 January 2012 (UTC)

On #1, see this particular patent as one variation that does apparently work. --Mr.98 (talk) 03:02, 15 January 2012 (UTC)

An electric arc detonating explosives is, essentially, what a slapper detonator is. You generate an arc sufficient to turn a metal wire to plasma. That plasma then sends the foil into the surface of the HE material, causing the explosion. It creates a broader impact leading to a more uniform detonation with a better controlled wave-front that is more easily made uniform. That means they are really, really good for setting of nuclear bombs. HominidMachinae (talk) 08:12, 15 January 2012 (UTC)

Plank mass black hole dangerous?

I keep hearing that microscopic black holes produced by large particle accelerators are not dangerous. However according to plank mass, plank mass is the smallest possible mass that can form a black hole. Well all black holes evaporate due to hawking radiation and release their mass equivalent in the form of high energy gamma rays. A plank mass black hole would be about 21.7 micrograms. According to my calculations, 21.7 micrograms would release the explosive equivalent of 467.51 kg of TNT in the form of high energy gamma rays. That's pretty destructive right? Certainly not destructive enough to destroy the planet, but dangerous non the less. So why do scientists keep saying microscopic black holes are not dangerous?— Preceding unsigned comment added by ScienceApe (talk • contribs) 21:00, 14 January 2012 (UTC)

It's sort of moot to discuss this in vague and generic terms. Which scientist said this? When did they say this? What experiment were they describing?

I've been around enough laboratories and particle accelerators in my day to have seen a lot of warning signs. Outside the Stanford Linear Accelerator, (now "SLAC National Laboratory"), there's a great sign - "DANGER, unique hazards may exist." Inside the controlled areas of the lab, there are chemical and radioactive materials; there is dangerous ionizing radiation; there are high intensity visible and invisible lasers; there are energetic materials, pressurized gases, corrosive and caustic substances; high voltages, and physics graduate students. To my knowledge, there are no black holes. Anything that was ever even remotely dangerous - including the cleaning supplies - is clearly placarded. You can read about all the safety information on the public website. The folks fom OSHA get pretty upset when the hazards are not clearly marked. Nimur (talk) 21:15, 14 January 2012 (UTC)

I removed the claim that the Planck mass is the smallest possible black hole mass from the article. When people were talking about possibly making black holes at the LHC, they were talking about black holes of vastly lower mass than that. There's no way to make a Planck-mass black hole, or anything close, at a particle accelerator. The LHC's design energy is 14 TeV, while the Planck mass is about 10,000,000,000,000,000 TeV. If there were a way to concentrate that much energy in a tiny space, it would make no difference whether a Planck-mass particle was momentarily created and then decayed. The real danger is that you've got 10,000,000,000,000,000 TeV in a tiny space, whether it's in the form of one particle or many. I'm describing your black hole as a particle because it behaves like a particle: it decays into (lighter) particles unless that's forbidden by some conservation law. It's perfectly plausible, given what we know right now, that black holes and familiar elementary particles like electrons are fundamentally the same thing, just at different energy scales. You may as well say that everything is made of tiny black holes, if that will help you to feel less scared of tiny black holes. -- BenRG (talk) 21:59, 14 January 2012 (UTC)

I'm not afraid of tiny black holes lol. I just saw an inconsistency in what they claimed and the figures I got. So you're saying you can make a black hole that is smaller than plank mass? Are you sure of that? Then what is the minimum mass a black hole can be? I'm not sure I buy your argument that everything is made of tiny black holes. Sure it might be true, but it's just speculation. ScienceApe (talk) 22:27, 14 January 2012 (UTC)

"Black hole" is just a layman's term to describe the various associated phenomena related to the way matter interacts over very out-of-the-ordinary conditions. If the relative mass is huge, compared to the time-and length-scales, you can call something a black hole. Another way of saying this is that for any mass, a Schwarzchild radius can be calculated. Most of the time, that radius is negligibly small because other matter-matter interactions take place at larger length scales. Another way of saying this is that under normal conditions, particles repel each other more than they self-gravitate, because gravity is a "weaker" fundamental force. Another way of saying this is that no particle-accelerator experiment is going to produce a mini-black-hole that starts runaway growth, sucking in all matter on Earth and becoming a bigger black hole. That isn't going to happen, though it would make for interesting fiction. Experimental physics at sites like the Large Hadron Collider at CERN still may be dangerous, for all of the reasons I listed above; but responsible researchers take steps to mitigate risk by understanding and preventing dangerous activities. None of those dangers have anything to do with mini-black-holes gravitationally sucking in the entire planet, despite what the internet rumor-mongers may be sensationalizing. Nimur (talk) 22:46, 14 January 2012 (UTC)

Nothing you said really has anything to do with what I was talking about. In fact your definition of a black hole seems rather layman. A black hole is a mass that is compressed inside of its schwarzchild radius. I didn't think a microscopic black hole would suck up everything and destroy the world, I even said that in my first post. I said a plank mass black hole would explode due to hawking radiation with the force of almost 500 kg of TNT, and it would according to my calculations. That's pretty dangerous IMO, that's greater than the yield of a tomahawk cruise missile. But now I'm being told that a black hole can be of ANY mass, which contradicts what the article originally said. So now any mass has a schwarzchild radius? Is that true? So even a neutrino with an extremely small but non-zero, positive mass can be compressed and form a black hole? Can anyone confirm this? ScienceApe (talk) 05:42, 15 January 2012 (UTC)

General relativity, the theory that predicts and explains black holes, would allow them to have absolutely any mass provided you could compress it sufficiently. Quantum mechanics tells us that in general it is difficult to confine matter to a very small volume. In order to fully understand very small black holes, we would need to be able to apply the principles of both general relativity and quantum mechanics to the same system. So far, no one really knows how to do that. Such an understanding would be at the heart of the thus far elusive concept of quantum gravity or even the "theory of everything". So, right now we don't really know if there is any fundamental lower limit to the size of black holes. Theorists routinely discuss possible properties of very small black holes (much smaller than a Planck mass), but so far no one has provided any compelling claims of having seen (or made) any black holes other than the stellar mass and larger ones formed via astronomical process. Dragons flight (talk) 06:48, 15 January 2012 (UTC)

The real bottom line here is that conservation of energy means that you shouldn't get more energy out of anything the accelerator produces than you put into it. So you shouldn't get a TNT-like explosion out of a far more modest piece of scientific equipment. Of course, if you manage to destabilize the local false vacuum all bets are off. ;) Wnt (talk) 23:42, 14 January 2012 (UTC)

Does conservation of energy say that if I use a small amount of energy to strike a match, then it touches something, the resulting event will not involve more energy than I expended? Some scenario like that might be involved in concerns about creating a black hole with a particle accelerator. Edison (talk) 01:29, 15 January 2012 (UTC)

The match can result in a lot of energy being released because there is chemical energy stored in what you are burning. The best you could do is release the rest-mass of something as energy (E=mc² - black holes can actually be used to do that, it's been proposed as a power source for super-advanced alien civilisations). The colliders are just dealing with a few sub-atomic particles, though, so the rest-mass is very small. The kinetic energies are far greater than the rest-masses (that's the whole point - you're trying to use the kinetic energy of normal particles to create unusual particles with higher rest-masses), and as BenRG says, the kinetic energies we're talking about are nowhere near big enough to be a problem. The micro-black hole won't have time to interact with the accelerator itself before it evaporates, so we only need to think about the particles. --Tango (talk) 03:55, 15 January 2012 (UTC)

It's a fair point - it is only an assumption, after all, (well, maybe a theory) that a black hole has to have a certain minimum mass, or it has to decay when small, or that it only grows at a slow rate when that small, etcetera. But I suppose some ultra-exotic particle is easier to hypothesize - maybe some obnoxious beastie that catalyzes proton decay, for example, for some short but very damaging lifespan? Wnt (talk) 06:35, 15 January 2012 (UTC)

Exotic particles that might fit that bill would be stranglets and magnetic monopoles. Although, the odds of them actually being dangerous and actually being produced are extremely low, so nothing I would worry about. I also wouldn't worry about us being in a false vacuum and being destabilized; to be honest, I wouldn't worry about particle accelerator destroys the universe scenarios since ultra high energy cosmic rays should have destroyed existence long ago if there was a real risk. Phoenixia1177 (talk) 10:17, 15 January 2012 (UTC)