Wikipedia:Reference desk/Archives/Science/2013 July 24

= July 24 =

How is fatty acid chain length regulated by Fatty Acid Synthase (in plants/bacteria)
Hi all. Something has me stumped. I've been looking into fatty acid synthesis, specifically synthesis of C18. I was wondering how is fatty acid synthase regulates chain length. I know FAS contains several enzymes that work together, and also have different forms, which are specific for different chain lengths. I just for the life of me can't find a paper that describes which enzyme in FAS has a high specificity for C16 (in order to produce C18).137.224.239.102 (talk) 00:31, 24 July 2013 (UTC)

Paper gives peak modal age at death for hunter-gatherers at approximately 69 years old. Inaccurate?
Figure 4 shows modal ages at deaths on page 334 of this paper: http://www.anth.ucsb.edu/faculty/gurven/papers/GurvenKaplan2007pdr.pdf The modal ages at death for hunter-gatherers peak at, as that tiny square shows, age 69 (or is that 70? It looks like 69). A hunter-gatherer lives 69 years? I don't know if I can imagine that long of a lifespan for the native americans when Columbus discovered America, or for our ancestors in the middle paleolithic. Am I just being too pessimistic, or am I missing something? Rebel Yeh (talk) 00:49, 24 July 2013 (UTC)


 * It does seem high, but this is a difficult area. Mean ages for older societies were often very low due to very high levels of childhood mortality, but many now believe that those who survived childhood lived to very good ages. So if one took a sample of, say, 15 year olds, their life expectancy could well be in that ballpark. Remember that a book written a very long time ago spoke of man's life expectancy being three score years and ten. HiLo48 (talk) 01:44, 24 July 2013 (UTC)
 * It does vary substantially, but at least in some North American contexts, it's not as good as HiLo48 suspects. Excavations at Ridgeway, Zimmerman, and other sites have shown that adults of the Glacial Kame people (Archaic period in the southern Great Lakes region of the USA) generally died in their 40s or 50s.  Regarding things in 1492, you have to remember that many contact-era peoples in North America weren't hunter-gatherers.  Some still followed the lifestyle, but tons of Indian tribes were agricultural, ranging from those who contacted and assisted the early Plymouth Colony settlers in the early 17th century to the extensive Mississippian culture farther west, which was responsible for such huge sites as Angel in Indiana, Kincaid in Illinois, and Cahokia in Illinois.  Also, note that some things were actually better for hunter-gatherers than for primitive farmers: the nomadic lifestyle ensured that they had a more varied diet, and Mississippian sites have routinely shown advanced tooth decay at comparatively early ages, since the people of some sites ate almost nothing but grains and fish.  Nyttend (talk) 03:48, 24 July 2013 (UTC)


 * You're missing something. The same thing archaeo/anthropologists are. Fossils. Looking back on sea evolution is a relative breeze. Trilobites and their ilk are a dime a dozen. Mammal bodies like our grandparents' don't tend to last long in most environments, and neither does their stuff. So basically everything you hear from anthropologists about prehistory is an educated guess, based on a pitiful sample size.


 * I still see tribes on National Geographic shows with a fair amount of older people. I wouldn't think it too farfetched for earlier people, in a resource-lush environment, to live past sixty often enough. I'd probably put the average a bit lower (say 53, after discounting dead babies), but that's only a semi-educated guess. InedibleHulk (talk) 03:41, 24 July 2013 (UTC)

Mass of smoke in a wood fire?
I'm trying to come up with a guesstimate for the mass of the smoke particulates produced by burning a chunk of wood. Let's suppose I have 1kg of wood - and I burn it. I guess I get some water vapor, some CO and CO2 - and a bunch of smoke. If I had a really efficient particulate filter - how much stuff would it trap? I only need very rough highest and lowest estimates - I don't need an exact answer. I'm guessing it depends on the temperature at which it's burning. SteveBaker (talk) 02:14, 24 July 2013 (UTC)


 * This has relevant data, linked from this page. For example, total particulates is listed as 7-30 g/kg wood. -- Scray (talk) 02:28, 24 July 2013 (UTC)
 * Many thanks...I think that's the answer I needed. SteveBaker (talk) 14:27, 24 July 2013 (UTC)


 * You seem to have forgotten the ash, which is a significant portion of the weight of the wood. I wonder if it's higher in an ash tree :-). StuRat (talk) 02:37, 24 July 2013 (UTC)


 * Would also depend on the type of wood (what tree species it comes from), and its condition. Good firewood is kept to dry internally for many months before use. Attempts to burn uncured, "green" firewood will generate a lot more smoke than heat. HiLo48 (talk) 02:40, 24 July 2013 (UTC)


 * Couldn't you get an experimental estimate by burning some wood and measuring the final mass? 24.255.30.187 (talk) 04:27, 24 July 2013 (UTC)
 * Subtracting post-fire remains mass from pre-burn mass would only give you the SUM of masses of released matter, including water, CO, CO2, smoke particles, etc. SemanticMantis (talk) 13:27, 24 July 2013 (UTC)
 * The 'released matter' will also contain oxygen from the air. Subtracting the weight of the ash from the initial mass of the wood won't allow for this. AndyTheGrump (talk) 13:53, 24 July 2013 (UTC)


 * Yeah - so measuring the mass of the wood and subtracting the mass of the left-over ash only tells us the total of gasses plus particulates there are. I need just the mass of the particulates.  (What I'm trying to do is to get a rough idea of how long it'll be before a particulate filter gets clogged - I could do the experiment, but that entails building the thing that I'm trying to figure out whether it's remotely worth building!). SteveBaker (talk) 14:27, 24 July 2013 (UTC)
 * It will depend on the type of wood and the way the wood is burned; burning wood is a combination of several processes: first there's pyrolysis, the heat of the fire will char the wood, producing tars and gases, those will either burn (smokeless) or escape (lots of smoke), if they burn they may not oxidize completely, resulting in soot (unburned carbon). A fire built up gradually, by adding the wood in small amounts will have the wood "surrounded" by flames, so the gases can't escape unburned, reducing the amount of smoke. Pyrolysis leaves behind char (mostly carbon) which burns without a flame (because it burns as a solid, doesn't turn into gas first). There are stoves that optimize the mixing of air (oxygen) and gases to achieve clean burning. Maybe this is useful: Composition and Size Distribution of Residential Wood Smoke Particles, you may have to register to access the complete paper, here's part of the abstract:
 * Particles emitted by hot-burning stoves were black, had a unimodal size distribution, and contained from 20% to 60% carbon (primarily elemental carbon) and high levels of trace elements (11% K, 1% S, 3% Cl). In contrast, particles from cool-burning stoves were tan, had a bimodal size distribution, and contained from 55% to 60% carbon (almost entirely organic carbon) and minute amounts (< 0.1%) of trace elements. The composition of particles emitted by fireplaces had compositions that were intermediate between those of hot- and cool-burning stoves, but tended to be more similar to cool burning stove emissions. Ssscienccce (talk) 18:52, 24 July 2013 (UTC)


 * Ssscience says that carbon burns as a solid, not a gas. Is that correct?  I aways thought that "burning" ie true combustion, can only occur with gasses.  For solids such as wood, pyrolysis (driven by the heat of gas combustion) must occur to release gas in order to burn.  For pure carbon, which being only an element, there is no pyrolysis reaction possible, so it must be raised above the sublimation point (~3900K) to convert it to a gas, wherupon it will burn rapidly.  If the fire cannot raise the carbon above ~3900 K, only very slow oxidation can occur, as oxygen molecules strike the surface of the solid carbon.  The oxidation of solid carbon is so slow as to be imperceptable, as all of us who have done the iron smelting experiment in a graphite crucible (using a mouth-powered air blast and making little dots of iron) in high school science class will know.  Note that when burning wood, a temperature above ~3900 K is not required, because certain pyrolysis reactions occur (at much lower temperatures) that break down the cellulose (H + C + O) into carbon monoxide + others, the CO being a gas down to below ambient temperature, and burns readily to form carbon dioxide. It's why piston engines emit soot (black smoke) under certain conditions.  Once carbon forms, the combustion temperature in engines is too low to burn it.  Note that CO is transparent, which means it is not a black body radiator, which is why it burns without a visible flame. 120.145.136.25 (talk) 07:00, 25 July 2013 (UTC)

Iron in breakfast cereals
I watched this video on YouTube and wondered what people who actually understand science (ie not me) might make of a) the experiments conducted and b) if the experiments are good, is there really a negative or even surprising connotation to the results? --Dweller (talk) 13:50, 24 July 2013 (UTC)


 * I notice he didn't name the cereal. Our article on iron says "Iron provided by dietary supplements is often found as iron(II) fumarate, although iron sulfate is cheaper and is absorbed equally well. Elemental iron, or reduced iron, despite being absorbed at only one third to two thirds the efficiency (relative to iron sulfate), is often added to foods such as breakfast cereals or enriched wheat flour." so it looks as though he's right, though when I see a webpage littered with exclamation marks, whole sentences in capital letters, and spelling errors, I don't pay much heed to it.--Shantavira|feed me 14:24, 24 July 2013 (UTC)


 * Like almost every "amazing" science video on YouTube, this is an obvious fake. If you had some kind of chemical process for extracting elemental iron from breakfast cereal, it wouldn't be in the form of large, shiney lumps - it would likely be a dark powder.  So it's a fake - and at that point there is no point in discussing it further. SteveBaker (talk) 15:20, 24 July 2013 (UTC)
 * Not a fake. The video does show you getting dark iron fillings. This is an easy do it yourself type experiment. Don't know what large shiny lumps Steve saw. Rmhermen (talk) 16:05, 24 July 2013 (UTC)


 * Hardly a fake. This has been written about for decades. The Straight Dope confirmed it in 1990: . The iron filings may well be smaller than they look in the smeary video presented by the OP, since when magnetized they stick together in lumps. Straight Dope says reduced iron or iron compounds are "assimilable."  The human body contains 5-6 grams of iron, and needs about 18 mg a day per the American chemical Society: . The elemental iron in the fortified cereal reacts with hydrochloric acid in the digestive system to produce ferrous iron (Fe2+) which the intestine can absorb. Cereal which provides  "100% of the RDA" is not just cereal made from grain high in nutrients. The vitamins and minerals are sprayed on it as it goes down the conveyor belt, so it is equivalent to eating the cereal and then taking a vitamin/mineral pill.   Nutrition books have long recommended iron cookware because of the nutrient benefit from the iron transferred from the cookware to the food. 100 g of spaghetti cooked in an iron pot supplies an extra 5.1mg of iron;.  A Material Data Safety Sheet for iron filings mention the danger of getting them in your eyes,  cautions against skin exposure, and recommends several glasses of milk or water if you ingest them (I prefer several cups of coffee with my cereal).   Another MSDS gives a very high LD50 for rats of 30,000 mg/kg, which is about 1/3 of the lethal dose for plain water.  However, I recall a horror story where a man held his arch enemy prisoner and mixed iron filings and steel fragments in hits food, then when someone pressed the doorbell, an electromagnet attracted the iron bits and the man screamed in anguish. Smaller iron filings thus seem preferable to larger bits of iron.  Edison (talk) 17:11, 24 July 2013 (UTC)
 * Confirmed also on physicscentral.com, one of American Physical Society's websites. A bit ironic that they include a red box with the text Warning: Do not eat the extracted iron.  Ssscienccce (talk) 19:59, 24 July 2013 (UTC)
 * Although it's scary watching proof that food manufacturers are putting iron in our food, what's scarier is that you can prove via chemical analysis that beverage manufacturers are putting dihydrogen monoxide in our beverages! Red Act (talk) 19:15, 24 July 2013 (UTC)
 * That's why I always eat only organic produce...no inorganic chemicals like that DHMO you mention, and usually they tell me no chemicals at all! DMacks (talk) 19:19, 24 July 2013 (UTC)
 * The bastards are putting it in our drinking water, too. And over 70% of the surface of the planet has such high levels of that chemical that it is impossible for humans to live there.
 * And the contamination is getting worse! DMacks (talk) 19:23, 24 July 2013 (UTC)
 * That's nothing! They also put atomic nuclei everywhere! --Stephan Schulz (talk) 19:59, 24 July 2013 (UTC)
 * Dont' trust those atoms. They make up everything... - ¡Ouch! (hurt me / more pain) 07:41, 26 July 2013 (UTC)

All joking aside, I actually think that the Nickel in stainless steel cookware is a concern. Being a proven carcinogen and all. Many people get irritating reactions from wearing stainless steel earnings etc yet don't think twice about eating food cooked in stainless steal vessels. 122.111.254.165 (talk) 19:56, 24 July 2013 (UTC)

I don't understand why this surprises people so much. It says right on the box that it's fortified with iron! APL (talk) 20:48, 24 July 2013 (UTC)
 * But that's like, a nutrient...we're talking about metal. Lest you think I'm just making up stupidity, I've had bio- and chem-major college juniors and seniors not know that chemicals are "the same" regardless of context, think that a liter of gas and a liter of liquid/solid are not the same volume, and have no problem saying that a single hydrogen atom weighs about 2 grams. DMacks (talk) 20:57, 24 July 2013 (UTC)
 * I think you misplaced or forgot a number of "not"s above... --Stephan Schulz (talk) 21:00, 24 July 2013 (UTC)
 * Fixed. Juggled the wording a few times, wound up with a hybrid mess. All-fixed now. DMacks (talk) 21:39, 24 July 2013 (UTC)
 * How silly, everyone knows its the Hydrogen molecule that weighs ~2g 122.111.254.165 (talk) 06:31, 25 July 2013 (UTC)
 * That's true, I think in one of Feynman's books he talks about students having excellent knowledge of optics equations but being totally baffled when he asks them a simple real-world question about the sunlight reflecting off of something. APL (talk) 21:04, 24 July 2013 (UTC)

Beware of Iron Overload: http://well.blogs.nytimes.com/2012/08/13/a-host-of-ills-when-irons-out-of-balance/?_r=0 Hcobb (talk) 18:48, 25 July 2013 (UTC)
 * Iron overload is the bluelink for it:) DMacks (talk) 02:42, 27 July 2013 (UTC)

Question on so-called copulins
Is there scientific evidence for this this and this this or is that just a load of c**p? --Immerhin (talk) 15:07, 24 July 2013 (UTC)
 * McAfee warns me against your second link, so I won't look at it, but the first one is 100% simon-pure bullshit. Comical, even. You can find some valid information about "copulins" in our article on pheromones, specifically the section on "Vaginal aliphatic acids". Looie496 (talk) 15:18, 24 July 2013 (UTC)
 * As far as what kind of bullshit it is, it looks like it's a hoax, rather than the work of a crackpot. Searching with Google, Intelius and whitepages.com, the Dr. Sandra Morrishaun or Sandy Morrishaun that supposedly did the research involved doesn't appear to be someone who actually exists or existed.  The name of the researcher was just made up along with the rest of it.   Red Act (talk) 06:12, 25 July 2013 (UTC)
 * Dr Elisabeth Oberzaucher is involved with making replica copulins, see. Graeme Bartlett (talk) 21:02, 25 July 2013 (UTC)
 * Google Scholar turns up hits like - PubMed seems to use it as a synonym for pheromone, while most of the other databases (PubChem etc.) have no listing.  It dates back at least to 1976 ( http://books.google.com/books/about/Sex_Differences_in_Olfactory_Response_to.html?id=2nWlNwAACAAJ )  I would need to get better access to some of the sources to tell how well defined "copulin" is by comparison to other pheromones.  I am exceedingly skeptical of the original site (nothing is impossible in biology, but the notion of very small levels of inhaled copulins "functioning as neurotransmitters" in the brain is about as close as it comes) Wnt (talk) 00:22, 28 July 2013 (UTC)

Schrödinger's cat
What would happen if you did the Schrödinger's cat experiment in real life? --146.7.179.143 (talk) 16:41, 24 July 2013 (UTC)
 * When you opened the box, the cat would be alive, or dead. As to whether the cat was alive, dead, or both before you opened the box, you'd have no way of knowing for sure (if you did the experiment properly) - though you could argue about it afterwards. But then you can do that without doing the experiment. AndyTheGrump (talk) 16:57, 24 July 2013 (UTC)
 * You would probably be charged with animal cruelty. It's not meant to be done in real life. That's the point. HiLo48 (talk) 17:02, 24 July 2013 (UTC)
 * It can't be done in real life. The thought experiment requires that the cat be totally isolated from the surrounding environment, and that's impossible to achieve. Looie496 (talk) 18:51, 24 July 2013 (UTC)
 * Perhaps we should first establish the premises the OP would like. Is the experiment supposed to be as in the hypothetical experiment, with total isolation of the box, or are we talking about actually doing the experiment using current technology? — Quondum 19:23, 24 July 2013 (UTC)
 * The OP said "in real life", and you can't get total isolation of the box in real life. Looie496 (talk) 19:27, 24 July 2013 (UTC)
 * Yep. In real life, either the cat dies or it doesn't.  The stink from the dead cat either invades the laboratory or the howling and miowing of the cat who is sick of being stuck in a goddamn box easily informs the scientist of the result of the particle emission and nothing particularly remarkable happens. SteveBaker (talk) 19:50, 26 July 2013 (UTC)


 * The story is nonsense anyway, unless you want to also call it Schrodinger's stasis field. Put the cat in a box with a daily food dispenser and air tank, etc.  Close the door, and the poison is either actiavetd or not in the first minute.  Wait a week or so, and open the box.  (1) The cat is alive:  Has it eaten a week's worth of food?  (2) The cat's dead:  Is the body still warm? Or does it show a week's worth of decomposition? Either the cat was in stasis the whole week and emerged unaged or newly dead when you opened the box, or the cat was actually alive and eating or did actually die when you shut the box, or it would not have timed to age a week subsequently. μηδείς (talk) 19:37, 24 July 2013 (UTC)


 * I asked Victor J. Stenger about this several years ago. He has written books on QM.  He said that either the cat would be alive or it would have been dead for a week.  That is, it doesn't pick one state or the other when you open the box.  Bubba73 You talkin' to me? 19:42, 24 July 2013 (UTC)
 * Considering the poision is triggered at some random time by radioactive decay, it either being dead for a week or not doesn't make sense. It could easily be 2 days. IRWolfie- (talk) 21:02, 25 July 2013 (UTC)
 * In this case, the OP states that if it is triggered, it will be in the first minute after closing the box, and then the box will be opened a week later. Bubba73 You talkin' to me? 15:52, 26 July 2013 (UTC)


 * I think μηδείς misunderstands. After a week, the box would be a super-position of two states. #1[Cat Alive for a Week] and #2[Cat Dead for a Week].  It doesn't keep the cat in limbo for a week and then kill it when you open the box. Both states would play out simultaneously, and then one would be discarded when the box opens.
 * However, Looie is right, you could not build a box like the one in the thought experiment. Even the difference in gravity from a standing cat and a dead, decomposing cat, would need to be blocked from leaving the box. Obviously that can't be done.
 * And that was the point anyway. Schrodinger was trying to illustrate that parts of Quantum Mechanics were ridiculous if scaled up to "real world" sizes, and therefore (he unsuccessfully argued) were also ridiculous when applied to particles.
 * Really, I don't understand the fascination with this thought experiment. If you shove a cat into an impossible box, something impossible will happen.  That should surprise no one! APL (talk) 20:37, 24 July 2013 (UTC)
 * It's not really "impossible"...just really hard to get our heads around. If you take on board the many-worlds hypothesis, then what happens to the cat is all really quite sane and understandable.  Unfortunately, you then have to start thinking of issues such as quantum suicide...which are much more weird and definitely something to worry about! SteveBaker (talk) 21:04, 24 July 2013 (UTC)
 * It's not really "impossible"...just really hard to get our heads around. If you take on board the many-worlds hypothesis, then what happens to the cat is all really quite sane and understandable.  Unfortunately, you then have to start thinking of issues such as quantum suicide...which are much more weird and definitely something to worry about! SteveBaker (talk) 21:04, 24 July 2013 (UTC)


 * So, superpositions age? The notion is meaningless and absurd, and a direct contradiction of wht is meant by superposition. The proper concept is ignorance.  Only fools claim their ignorance is science.  μηδείς (talk) 20:40, 24 July 2013 (UTC)
 * ...Of course they do. Both states still behave according to the laws of physics. APL (talk) 20:53, 24 July 2013 (UTC)
 * Yes, absolutely. You can't stop time inside the box...also (if the experiment could ever work), we're all in a constant state of super-position because atomic nuclei are falling apart all the time - and the effect of that is magnified to human-scale because of things like chaos theory.  If time stopped in the box until the entanglement is collapsed, then all time everywhere would be stopped. SteveBaker (talk) 21:04, 24 July 2013 (UTC)


 * Schrödinger was specifically focussed on the Copenhagen interpretation. he was not arguing that it was ridiculous, or that it should not apply to particles. IRWolfie- (talk) 21:02, 25 July 2013 (UTC)


 * What'll really mess with your head is that if the scientist stays in his (closed/sealed) laboratory throughout the experiment. When he opens the box with the cat in it, he's now in an entangled state of being a scientist who knows that the cat is dead and being a scientist who knows that it's alive.  Only when his wife phones up later to ask him how her cat is does he resolve to a known state.


 * But when she phones and learns the fate of the cat then she's entangled too - the amount of electricity consumed by the telephone is slightly different depend in on the scientists answer to her question - so now the power station and the phone company are in a state of entanglement. Entanglement ripples outwards (probably at the speed of light).  Ultimately, the entire planet, the solar system and the observable universe is in an entangled state of being a universe with one less living cat or not.  It's hard to get away from the many-worlds interpretation of this experiment.


 * SteveBaker (talk) 20:29, 24 July 2013 (UTC)


 * Yup. But I'm sure you'll get a lot of reaction to that.  I'm with you on this, but I'll sit back and watch others debate QM interpretations.  — Quondum 20:38, 24 July 2013 (UTC)
 * So basically you'd be of two minds on whether it was alive or dead ;-) Dmcq (talk) 22:19, 24 July 2013 (UTC)


 * That reasoning is basically why I favor the Many-worlds interpretation of quantum mechanics over the Copenhagen interpretation. Looie496 (talk) 14:28, 25 July 2013 (UTC)
 * Yes, I agree. But many-worlds has some rather extreme consequences too. SteveBaker (talk) 16:47, 25 July 2013 (UTC)


 * From a practical standpoint the Copenhagen interpretation wins. The Copenhagen interpretation is a much better model to work with when explaining your results than the many-worlds. Many worlds just adds extra unresolved complications and assumptions, while the Copenhagen, like the many worlds interpretations has to deal with the measurement problem, but otherwise its a free ride. IRWolfie- (talk) 21:02, 25 July 2013 (UTC)
 * Many worlds doesn't "have to deal with the measurement problem" - it exists specifically to avoid that issue. Our article on the subject says: "Hugh Everett's many-worlds interpretation attempts to solve the problem by suggesting there is only one wavefunction, the superposition of the entire universe, and it never collapses—so there is no measurement problem."...which is what I believe to be the clearest, simplest interpretation of the available facts.  (Albeit at the cost of effectively creating an entire copy of the whole universe every time a fundamental particle enters a state of entanglement...which is quite a leap!) SteveBaker (talk) 22:17, 25 July 2013 (UTC)
 * The "leap" is only quantitive: from one infinity to another. There is no qualitative leap in this sense.  The biggest problem is that many people balk at this shift.  I find this reluctance strange considering that the leap from classical state space to quantum state space is cognitively and qualitatively considerably larger.  Accepting the mathematical incomplete (no effective theory of the hypothesized wavefunction collapse) Copenhagen interpretation seems easier for many than taking the existing theory to a clean (albeit for many more counterintuitive) conclusion.  — Quondum 22:45, 25 July 2013 (UTC)
 * There is nothing clean about the many worlds approach, and it opens up more questions than it answers. Replacing "how does the wavefunction collapse" with "How does the universe split along different histories" leaves us in a more difficult position, IRWolfie- (talk) 10:47, 28 July 2013 (UTC)

My take on it is as follows. What we call time evolution is not what we intuitively think it is because time doesn't exist in this intuitive sense (there is no "present moment" that is real while the past and future are not real, every moment is as real as any other moment in time). So, when we say that the time dependent state describing the cat is of the form:


 * psi(t)> = A(t) |dead> + B(t) |alive>

this is misleading. In reality, |psi(t)> should be considered as the initial state |psi(0)> but then expanded in a different basis; the cat described by the superposition describes the cat at the moment it entered the box. In general, you are free to transform all states and observables using any unitary transform without affecting the physics, the time evolution operator U(t) = exp(-i H/hbar t) is such a unitary operator that you can use. Count Iblis (talk) 23:11, 24 July 2013 (UTC) So, suppose you enter such a box and that you are going to be killed for sure after one day (instead of the 50% probability in the Schrodinger cat experiment), then even after one year I can still talk to you before you were killed, because I can still (in principle) access the initial state. If I want to say: "Hello, how are you doing?" and wait for a response from you, this is described by some observable A. To get an answer from you, I should thus apply the operator U(t) A U^(-1)(t) to the box, where U(t) is the time evolution operator and take t to be such that a time t ago the poison was not yet adminstered. Count Iblis (talk) 23:59, 24 July 2013 (UTC)


 * How do you shield the cat against neutrino scattering? Hcobb (talk) 18:51, 25 July 2013 (UTC)


 * Let us imagine you could work out what the initial state was (this is what you could do assuming the hamiltonian was time independent, and you applied the time evolution operator with a negative time), that does not mean you could communicate with that person. As far as I can see what you are saying makes no sense (that applies to both of your paragraphs). IRWolfie- (talk) 21:02, 25 July 2013 (UTC)


 * Of course you could communicate with the person, it follows trivially from unitary time evolution. No information gets lost as long as the box is perfectly isolated. Count Iblis (talk) 23:33, 25 July 2013 (UTC)


 * The point of the experiment is to ridicule the Copenhagen interpretation, and to point out the measurement problem. In that interpretation of quantum mechanics, the wavefunction of an object can be in a superposition of different states, and at the moment of measurement the state of the system is decided during wavefunction collapse. What constitutes a measurement etc is known as the measurement problem. If the act of measurement decides the state or not is dependent on the interpretation. As Looie points out, you can't completely isolate the system (but that doesn't matter so much) and this was only ever for a thought experiment. The real issue is that the measurement problem is not fully resolved, so you can not get a good answer about what "really" occurs, IRWolfie- (talk) 21:04, 25 July 2013 (UTC)

Here's my variation on it: Measure the polarization of a single photon from another galaxy say ten billion light years away. Now the state of the molecule that emitted that photon must of course have been indeterminate until that value was measured, for the last ten billion years. Hcobb (talk) 00:50, 26 July 2013 (UTC)


 * Schroedinger 2.0 without harming cats.
 * Open two doors next to each other.
 * If the cat can access the whole garden, it's a Newtonian cat.
 * If it can access narrow stripes only, it's a quantum-theoretic cat. - ¡Ouch! (hurt me / more pain) 17:06, 27 July 2013 (UTC)