Wikipedia:Reference desk/Archives/Science/2010 October 15

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October 15

how do you define time ?

time is something which is going on is what I understand......... then

• 1)what happened at time = minus infinity ?( I cannot imagine time running to minus infinity)
• 2)or there is a starting point to time ?
• which theory help me to understand about time ?????????? —Preceding unsigned comment added by Sridhargunnam (talk • contribs) 04:28, 15 October 2010 (UTC)

Time is NOT an easy thing to think about, and it gets harder to think about the more you know about it. The fictional work Einstein's Dreams is actually a pretty good lay-person's primer to the problem of time. A Wikipedia articles you may want to read would be Arrow of time. The starting point of time is the Big Bang. The concept of time running backwards, as a serious discussion in modern physics, is discussed at T-symmetry, and on physical concepts which display both time symmetry (i.e. they are equally valid if experienced bot forward and backwards in time) and time asymmetry (i.e. they only work in a world where time moves forward). One common definition of time (alluded to in the Arrow of Time article cited above) is the idea of the relationship between time and the Second law of thermodynamics, aka Entropy. --Jayron32 05:06, 15 October 2010 (UTC)

Wikipedia has an article about Time. It has been joked that "time is only there to stop everything happening at once". Historical time measurements are based on astronomical observations e.g. 1 year = time for Earth to complete an orbit of the Sun. Apart from the unproven hypothesis of a Big Bang or creation event, we have no access to an absolute time reference, so "negative" time is meaningful only when understood relative to a reference event. (An estimated birth date of Jesus is conventionally used as a zero time reference between negative years BC (Before Christ) and positive years AD (Anno Domine - "year of the Lord"). For example, this year is AD 2010. Modern precise time measurements are based on Rubidium or Caesium atomic standards. There is no infinite time, see Ultimate fate of the universe, although in mathematics a Periodic function of time e.g. y = sin(t) where t=time implicitly extends from t = minus infinity to plus infinity. Cuddlyable3 (talk) 09:36, 15 October 2010 (UTC)

I thought the Big Bang is a scientific theory a major piece of evidece for which, the cosmic background radiation, earned a couple of physicists the Nobel prize in physics. 67.243.7.240 (talk) 17:24, 17 October 2010 (UTC)

There isn't a shred of evidence that "time" exists at all. The known laws of physics can be reformulated in a manifest timeless way. Julian Barbour shows here how to do this for classical physics. Count Iblis (talk) 14:54, 15 October 2010 (UTC)

I think it's worth noting that Barbour's approach is pretty controversial and certainly not commonly held. --Mr.98 (talk) 21:32, 15 October 2010 (UTC)

Time at the exact instant of the Big Bang would be zero, so to use "negative time" in this context makes assumptions about what (or who?) actually created the Big Bang. We are getting into multiverses, or possibly brane theory, but another theory is that the big crunch of a different universe created this one (and the events in that universe are in negative time). See also fourth dimension and retrocausality. ~AH1^(TCU) 00:58, 16 October 2010 (UTC)

memory storage devices

we heard of TTL and CMOS memory in electronics.......... taking full charge on capacitor ......as high n zero charge as low, can we have capacitor memory ? if not what are the drawbacks ????? —Preceding unsigned comment added by Sridhargunnam (talk • contribs) 04:44, 15 October 2010 (UTC)

Yes, certainly. The main drawback is that capacitors can't be made as small as transistors, as I understand it. Looie496 (talk) 05:19, 15 October 2010 (UTC)

Yes indeed. This is how DRAM memory chips work. It is likely that you have several of them in a PC that you are using. The disadvantages of DRAM are that their content must be periodically refreshed by reading and re-writing, and that their content is lost when power is turned off. Accepting that DRAM is "volatile" memeory, they are one of the cheapest memory types in terms of cost per storage bit. The capacitive storage elements in DRAM take less space than the transistors in SRAM non-volatile memory, which makes it possible to build chips with higher density. The cited article gives the interesting history of DRAM development. Cuddlyable3 (talk) 09:02, 15 October 2010 (UTC)

how to explain the oxidation of ethers to esters with calcium hypochlorite? (and a question about activated C-H bonds)

A C-H bond would never show up as red on an electron density diagram would it? I've been trying to come up with a mechanism for this reaction -- obviously hemiacetals can be easily oxidised to esters but it seems to me that maybe the ethoxy oxygen has to react with some sort of electrophilic catalyst first.

(In one reaction, this was done in a mixture of 3:2 acetic acid and acetonitrile, resulting in 58% yield for the ester.)

C-H bonds almost never attack nucleophilically correct (that is, with a strong polar character)? They usually have to undergo some sort of fluid hydride shift. I'm thinking the hypochlorous acid displaces an ethoxy oxygen (which may be bound to calcium or acetonitrile or something) via SN2, allowing a hydride shift to occur. The ethoxy oxygen is eventually released from its catalyst and reforms the previous C-O bond. (This works better with cylic ethers). John Riemann Soong (talk) 04:57, 15 October 2010 (UTC)

Upper limit on speeds

say two objects are initialy at rest with respect to each other. I accelerate one of them(object1) towards the other to 50% the speed of light. would it now take infinite energy to accelerate object2 to 50% the speed of light towards object1?

If so why wouldn't it take infinite energy to accelerate object1 to 50% of light speed when object2 was at rest? --Diwakark86 (talk) 11:33, 15 October 2010 (UTC)

No, it wouldn't. You seem to be under the impression that if A is moving to the right at 50% of the speed of light, and B is moving to the left at 50% of the speed of light (both measured in some external frame) then the speed of B relative to A will be 100% of the speed of light. This is not the case. Algebraist 11:58, 15 October 2010 (UTC)

Or simply put another way, when you add velocities relativistically (that accounts for special relativity), you use a different formula than you do when you add them non-relativistically (Galilean velocities). If you use the relativistic formulae you only get up to .799c with your example, not 1c. You can bump your objects up to 99% the speed of light and you still won't get a relative velocity that is 1c or above. --Mr.98 (talk) 12:23, 15 October 2010 (UTC)

Why give the approximation 0.799c as opposed to the exact value 0.8c? -- 119.31.121.84 (talk) 23:38, 15 October 2010 (UTC)

When two objects are moving at each other under the speed of light, the energy required to move either one is not infinite and neither is the combined energy required. Photons and other particles (some having mass) already move at light speed but do not require nor contain infinite energy. ~AH1^(TCU) 00:47, 16 October 2010 (UTC)

Which particles with non-zero rest mass can move at the speed of light? I thought that only luxons were capable of light-speed. Dbfirs 07:48, 16 October 2010 (UTC)

I think only objects with zero rest mass can move at the speed of light. But of curse photons and other "mass-less" particles has a relativistic mass due to its energy. At the speed of light the relativistic mass is infinity times rest mass but infinity times zero are undefined so this does not tell us the mass of a photon. --Gr8xoz (talk) 10:05, 16 October 2010 (UTC)

Yes, that's my understanding, too, but I wondered if AstroHurricane had discovered some new particle. Of course, particles with mass are being accelerated to within a hundredth of one percent of the speed of light in accelerators. Dbfirs 22:05, 16 October 2010 (UTC)

reversible oxidation of a USB plug?

I have an iHome HM60 -- a portable speaker, and there's a mini-USB cable between the 3.5 mm auxiliary jack and the speaker (there's also a regular USB cable for charging). Yesterday I played it in the rain -- with no problems -- it just kept on playing. I let it dry, studied for a few hours, started up the speaker again -- no issue.

Then hours later it ceased to work -- then I noticed the mini-USB plug was grey'ish and somewhat rough and it look corroded. It wouldn't work for hours. And it was basically charged.

So I don't know what I did -- I just let it charge for a few hours (but the charge lasts for 40 hours so I know it isn't that), and then hours later, it worked again. (Sound is crystal clear.) I wonder if it's possible for water to cause reversible oxidation of a USB plug when consuming energy, which is reversed upon charging? John Riemann Soong (talk) 12:14, 15 October 2010 (UTC)

Here is a description of the iHM60 speaker and of various mini-USB connectors. If the connector is corroded I would expect this to show as a crackling sound when you wiggle the connector while playing music. If that is the case then there are electric contact cleaners such as Electrolube or Servisol that might help, but your best action may be to buy a new speaker and keep it out of the rain. It will sound just the same wrapped in a polythene bag. Cuddlyable3 (talk) 12:50, 15 October 2010 (UTC)

No crackling...I'm guessing it's not oxidation? I mean, it's gold-plated I think. But before the rain this never happened. I did keep it in my coat -- but the raindrops seeped in cuz I wanted a tiny aperture. John Riemann Soong (talk) 14:31, 15 October 2010 (UTC)

Link crashes

The first two English links in

http://en.wikipedia.org/wiki/John_Strutt,_3rd_Baron_Rayleigh#Bibliography

crash. (I don't spikka da frang, which further more is mysteriously organized)

83.226.97.246 (talk) 12:41, 15 October 2010 (UTC)

They seem to work ok for me.....?

you are talking these links, aren't you (?)

• The Theory of Sound vol. I (London : Macmillan, 1877, 1894) (alternative link: Bibliothèque Nationale de France
• The Theory of Sound vol.II (London : Macmillan, 1878, 1896) (alternative link: Bibliothèque Nationale de France)

Darigan (talk) 12:54, 15 October 2010 (UTC)

(ec)Assuming you mean the links to The Theory of Sound vols. I & II, they worked ok for me. The alternative French library links are to copies of the same book in English which should give you no difficulty. Cuddlyable3 (talk) 12:58, 15 October 2010 (UTC)

The links were called with Netscape 7.02 over MacOS 9.2.2. Is that the reason ? —Preceding unsigned comment added by Rolf.Evren (talk • contribs) 02:51, 16 October 2010 (UTC)

Sodium tellurate

Sodium tellurate

Does it exist? I was about to create an article on simple and found out that en didn't have an article on it! Thank you. --Chemicalinterest (talk) 13:13, 15 October 2010 (UTC)

It does appear to be a real compound, if that's what you mean by "exist":) 10101-83-4 (that takes you to a meta-search, whose specific entries seem to find some refs). Now whether it's notable enough to merit an en.wp article...dunno. DMacks (talk) 14:23, 15 October 2010 (UTC)

Sodium is one of the simplest (in terms of economy/pragmatics) counterions there is. How can you have an article on the generic tellurate ion and not on sodium tellurate? John Riemann Soong (talk) 14:32, 15 October 2010 (UTC)

Yes, I would think it is notable. Any binary chemical compound should be notable enough. --Chemicalinterest (talk) 14:33, 15 October 2010 (UTC)

At least if one of the counterions is cheap! I realise that "silver tellurate" or "gold(III) tellurate" may not be hot or whatever. John Riemann Soong (talk) 14:52, 15 October 2010 (UTC)

Yes, we should have an article on it. I'll run one up later unless someone beats me to it. Physchim62 (talk) 14:55, 15 October 2010 (UTC)

Cost doesn't matter. What matters is the presence of reliable sources discussing the topic. So a certain anion may be generally of scientific interest and literature publications, and/or one certain compound of it may be, and/or another certain compound, etc. If there's something scientifically special about the silver one, then it could have an article. If nobody cares to study the potassium one more than just stating it exists and reporting its physical/chemical properties, then maybe that one doesn't get an article. As years of deletion-discussions have said, "notability is not inherited" (the parts can be notable but the combination not, or vice versa). DMacks (talk) 16:32, 15 October 2010 (UTC)

User:Chemicalinterest/Sodium_tellurate. --Chemicalinterest (talk) 19:04, 15 October 2010 (UTC)

The example of gold tellurate may be more special, as gold often occurs with tellurium, and gold can dissolve in telluric acid. But if it is a product you can buy the chances are someone has written about it and we can have an article. Graeme Bartlett (talk) 09:18, 18 October 2010 (UTC)

methane + CO2 --> acetic acid

By bond enthalpy at least, this reaction seems favourable (what is the loss of entropy due to two gas phases converting into a single liquid?) This seems a convenient way to tackle two greenhouse gases at the same time to give a useful feedstock...and methane seems fairly abundant. Are there any theoretical catalysts that could be worked on? I know there's a "catalyst" being worked on at my school that can convert methane to methanol...however there are issues with the catalyst (yield, turnover, recovery, etc.) that currently make it economically infeasible. John Riemann Soong (talk) 14:42, 15 October 2010 (UTC)

Google: methane CO2 "acetic acid": "about 650,000 results". About a quarter of the hits of the first few pages are about this reaction (theoretical and practical studies, journal articles and patents). DMacks (talk) 16:35, 15 October 2010 (UTC)

Why doesn't our article on acetic acid cover this route? John Riemann Soong (talk) 20:06, 15 October 2010 (UTC)

Because it's utterly irrelevant, inconsequential compared to the real-life routes of making acetic acid. Wikipedia prefers to deal in real chemistry, not pipe dreams and undergrad speculation. Physchim62 (talk) 20:11, 15 October 2010 (UTC)

Such a synthesis remains largely pedagogic, the reaction is not thermodynamically favored without a catalyst. There are relevant patents such as US 5659077 . Hope this helps.Smallman12q (talk) 21:09, 15 October 2010 (UTC)

Catalysts do not change the thermodynamics of a reaction, only its rate. This reaction is not thermodynamically favourable, either going to the liquid or the gas. The idea is irrelevant nonsense. Physchim62 (talk) 23:06, 15 October 2010 (UTC)

However, please do look at this previous question, discussing the decomposition properties of acetic acid. ~AH1^(TCU) 00:32, 16 October 2010 (UTC)

Thermodynamics question

1. Since, as I understand it, two litres of water at 50 degrees cannot be separated into one litre at 90 degrees and one litre at 10 degrees without some expenditure of energy, is there a sense in which the latter intrinsically contains more energy than the former? If so, how is this quantified?

2. If, in a sealed system, a liquid is allowed to evaporate, then have the hotter molecules spontaneously separated from the cooler molecules in apparent violation of the principle in (1)? If so, how is this explained? —Preceding unsigned comment added by 86.183.171.204 (talk) 17:49, 15 October 2010 (UTC)

Welcome to Wikipedia. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our policy here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.

...perhaps you could take a shot at this first, state where you got stuck? Have you read about Entropy and Thermodynamic systems? -- Scray (talk) 18:19, 15 October 2010 (UTC)

This is not a homework question. The last time I did homework was approximately forty years ago. 86.183.171.204 (talk) 19:01, 15 October 2010 (UTC).

Question 1. Why does your air conditioner need electricity? It is separating an 80-degree intake into a 50-degree output and a 110-degree output which is vented outside. Molecules tend to have a uniform concentration of energy unless energy is added from an external source. I think this is the opposite of entropy, which is the decay of a structure. Separating the water would require the expenditure of energy to decrease entropy. Please correct me if I am wrong. --Chemicalinterest (talk) 19:07, 15 October 2010 (UTC)

Question one is a fundamental point in thermodynamics: the two systems contain the same amount of internal energy, but the system at 50 degrees has a greater entropy than the latter system. To lower the entropy of a system, you have to expend energy, but it goes into the surroundings, not the system itself. Physchim62 (talk) 19:22, 15 October 2010 (UTC)

(1) is true. The article on Carnot engine should even give you a precise value for the amount of energy which can be extracted from the 90 and 10 degree reservoirs, and the (larger) amount of energy that it would take to reverse the process.

(2) I assume you mean a liquid evaporating in vacuum, rather than in air (which you can see is a simple mixture, increasing entropy). Spontaneous phase separation (harrumph, there's an article in need...) is an interesting case, isn't it? But there's nothing about entropy that says that the chaos has to be homogenous - if there's not enough energy to keep all the molecules as a gas flying around free of noncovalent interactions, then some have to clump somehow. So as many molecules evaporate as the available energy allows, leaving energy randomly distributed between particles flying around as vapor and particles jiggling in a liquid, such that further random interactions tend to go either way as often as the other. Wnt (talk) 19:26, 15 October 2010 (UTC)

(1) I think Exergy could be interesting to you.--Gr8xoz (talk) 22:37, 15 October 2010 (UTC)

Should my neighbor's cat drink old milk?

Several years ago ...

(at this point one should fear for the cat's life)

... a jug of milk fell off my kitchen table and I didn't see it for several days. I was afraid of what it would smell like so I just put it outside, and for months I was afraid of what the smell would be like, so I never dumped it. I did notice the liquid changed color and got dark and clearer. But I never dumped it. Then the jug got broken and I caught my neighbor's cat drinking out of it. At that point I dumped it though I don't remember where. The cat is fine.Vchimpanzee · talk · contributions · 18:52, 15 October 2010 (UTC)

It's all a matter of what bacteria get into it. Good bacteria, you get cheese or yogurt. Bad bacteria, you get poison. But bad bacteria usually make it smell bad, and if it smells bad a cat won't touch it (unless starving). Looie496 (talk) 19:52, 15 October 2010 (UTC)

I'm curious as to what the liquid consisted of by this time. It wasn't white, but dark and sort of clear.Vchimpanzee · talk · contributions · 20:02, 15 October 2010 (UTC)

Perhaps a form of whey? See also Little Miss Muffet :-) . 87.81.230.195 (talk) 20:48, 15 October 2010 (UTC)

Take a look at curd. ~AH1^(TCU) 00:26, 16 October 2010 (UTC)

The weird thing is I never saw any curds. And the photo of whey was a different color entirely. Maybe it was a photo of a specific process but this was dark and almost clear.Vchimpanzee · talk · contributions · 15:43, 16 October 2010 (UTC)

As an aside, no cats should drink cow's milk. Cats are largely lactose intolerant and should not be given regular milk Zzubnik (talk) 11:02, 18 October 2010 (UTC)

Well, it's my neighbors' cats. I never intentionally feed them.Vchimpanzee · talk · contributions · 20:20, 18 October 2010 (UTC)

I understand that, and was not meaning to accuse you of doing so! :) Zzubnik (talk) 09:51, 19 October 2010 (UTC)

Next Day Soup.

I don't know if the Science Desk is the best place to ask this but here goes. I am an Englishman living in Scotland these past 35 years and have always known that the Scots take their soup-making skills extremely seriously - and with some real justification. But I can't figure out why it is that the best soups made today always taste better tomorrow. I have just made a throw-everything-in-except-the-cat soup that tastes, well, you know, quite sharp/raw/bitter/rough, but I have every confidence that tomorrow, it will be hearty, tasty, zingy, zesty, warming, nourishing, moreish, and oh so smooth in the mouth-feel department. So exactly what is it that happens overnight to effect that transformation? Are there soup-fairies in Scotland or what? 92.30.9.83 (talk) 19:25, 15 October 2010 (UTC)

I would vote for very long time-constants for the substances in the solid ingredients to dissolve. So after a long time, you have saturated the broth with flavorful compounds from the meats, vegetables, and spices in the soup. See rate equation for quantitative analysis. Nimur (talk) 19:34, 15 October 2010 (UTC)

(EC) I am well familiar with the phenomenon you describe. I attribute it to diffusion. Take an example of potatoes in broth. After cooking, a certain amount of the flavorful compounds have permeated the potatoes, but the center will have less than the edges. After sitting for ~24 hours or more, the centers will have the same concentration as the edges, making them tastier. Note that you can't just boil the potatoes longer to get this effect, because that would break them down into mush. There are certainly other factors as well, but I think this is the main reason soup is better on the second day. What Nimur says above also makes sense.--SemanticMantis (talk) 19:39, 15 October 2010 (UTC)

I think oxidation also matters to some degree. When it cools a sits for a few hours, oxygen dissolves in it and reacts with some of the reactive chemicals that give it a sharp and bitter taste. Looie496 (talk) 19:54, 15 October 2010 (UTC)

Curry tastes better the next day too. Itsmejudith (talk) 23:21, 15 October 2010 (UTC)

It depends on what type of curry but I generally find that they mature over about a week, then last for about another three. Fish curries are less robust but a Rogan Josh or similar matures to it's best by about the ten day point, in the fridge.

ALR (talk) 16:06, 16 October 2010 (UTC)

It has a lot to do with gelatin. Gelatin is formed from collagen, a protein common in animal tissue. It has almost no flavor on its own, but it has a very pleasing mouthfeel, and its presence completely changes the eating experience. The reaction which turns insoluble collagen into soluble gelatin takes a very very long time. This is why grilled meat tastes so different than barbecued meat. If you have ever had a grilled pork chop, and also had good, slow-cooked pork barbecue, ostensibly the same meat, that soft, unctuous taste that barbecue has that a pork chop doesn't is due mostly to gelatin. It's why good barbecue takes upward of 10-12 hours to cook, while you can grill a porkchop in 15 minutes. It's the same deal with soup. When you cook soup, the cooking process extracts gelatin from the meats. However, this gelatin needs to partially polymerize (the smaller gelatin molecules need to aggregate and crosslink) in order to provide the "gelatin" effect. This only happens over time, so that freshly cooked soup doesn't taste as good as the soup overnight, which has had the time to form proper gelatin. --Jayron32 03:30, 16 October 2010 (UTC)

In my experience (WP:OR!) this happens with vegetarian chili, too. The texture pretty much stays the same, I think, but the taste is much ... uh, deliciouser after a night or two in the fridge. Paul (Stansifer) 04:59, 16 October 2010 (UTC)

While, strictly speaking, gelatin has to come from animal sources, there are plant analogs, especially in stuff like beans and okra, known as mucilage. Additionally, there is Starch gelatinization. If left overnight, you can get Retrogradation (starch), which is why starch soups and sauces "set up" overnight (i.e. form into a pudding-like texture). --Jayron32 05:05, 16 October 2010 (UTC)

Well, I just want to say a big Thankyou for all the above responses to my Next-Day-Soup question - I really appreciate all of them. But regrettably, I have to tell you that the batch of soup in question turned out to be the worst I have ever made. I did explain that it was a throw-everything-in-except-the-cat version, but I didn't realise that the rogue ingredient I found in the fridge was a parsnip and somehow, it dominated all the other lovely vegetables and marsala wine and stock that I included in the soup. In the end, in trying to disguise the bitter parsnip flavour (which I love by themselves)I added some curry powder, which made the soup horribly disgusting and I had to throw it out. Imagine that, "Throw everything in except the cat and then throw it out soup". Not a good recipe. But thanks anyway. —Preceding unsigned comment added by 92.30.6.207 (talk) 10:07, 17 October 2010 (UTC)

is there such a thing as "mild chlorine poisoning"?

Normally when bleach is sprayed on say, a decaying pot full of maggots and organic acids, how much chlorine is released (order of magnitude)?

Not a request for medical advice -- take the most general case. John Riemann Soong (talk) 23:12, 15 October 2010 (UTC)

There was an earlier debate over whether the acids produced chlorine and in my experience they do not in any amount more than bleach reverses its production reaction NaClO + NaCl + H₂O → NaOH + Cl₂ although this reaction is encouraged with acids. If it is producing too much chlorine, cover it with ascorbic acid crystals--they seem to reduce the chlorine to chloride and hence get rid of the odor. --Chemicalinterest (talk) 10:07, 16 October 2010 (UTC)

I think you've missed the point. By the time you realised it's 'producing too much chlorine'. It may be too late. Also covering it with ascorbic acid crystals seems an exceptional bad idea. Far better to ventilate the area and stay well away until the reaction has died down. Nil Einne (talk) 10:40, 16 October 2010 (UTC)

I would like to ask why, other than the expense, covering the mixture of foods with ascorbic acid is a bad idea?

And yes, keep it ventilated. Chlorine can collect in low places. Ascorbic acid will neutralize some of the chlorine that comes into contact with it, provided there is some water available for the reaction to occur in. BTW, mild chlorine poisoning may be a horrible smell in your nose that makes you a little bit sick. --Chemicalinterest (talk) 13:25, 16 October 2010 (UTC)

The first thing you do when confronted with an uncontrolled release of toxic gas in a confined area is get out! You don't stand around trying to control the release, unless you happen to be wearing self-contained breathing apparatus at the time. Or, rather, natural selection means that there are very few chemists who stand around trying to control the release, and they don't do it a second time. Physchim62 (talk) 13:54, 16 October 2010 (UTC)

That green air looks pretty! --Chemicalinterest (talk) 15:54, 16 October 2010 (UTC)

Mmm--almonds! But wait, did someone just spread hay around here? DMacks (talk) 17:28, 16 October 2010 (UTC)

Hehe! You laugh, but I've had to deal with the situation of a student in an undergrad class who calls me over to say "I don't feel very well, and I've just been doing the experiment with cyanide..."! She was fine – she had very mild gastroenteritis, not mild cyanide poisoning – but I'll be perfectly happy if I never have to face that again in my career! Physchim62 (talk) 19:57, 16 October 2010 (UTC)

Two wrongs might make a right in the chemical world. --Chemicalinterest (talk) 00:13, 17 October 2010 (UTC)

Well long ago I had a personal experience with bleaching powder and alcohol. I mixed far too much together and the mixture got too hot and produced chlorine gas (instead of or as well as chloroform) I was uncomfortable for a few days, and I must say that no amount of chlorine can be counted as a pleasant smell. Spraying a few maggots is not going o be any big deal for you, but may be for the maggots. But if you dumped in a kilo of bleach then watch out! 09:13, 18 October 2010 (UTC)

How does matter fall into a black hole?

My very basic understanding about black holes is this: Anything falling into a black hole takes an infinite time to pass the event horizon to an external observer. If that's the case how do supermassive black holes form? i.e. how can we have supermassive black holes when it takes an infinite amount of time for them to form? I'm sure there's already an answer on wiki or google somewhere but I must be using the wrong search terms. I found this but it made no sense to me. Tx in advance Spoonfulsofsheep (talk) 23:59, 15 October 2010 (UTC)

According to the article, light from a distance just outside the black hole's event horizon reaches the external observer very slowly, taking perhaps millions of years because the light takes that long to fight against the gravity of the event horizon. Past the event horizon, light cannot escape. Similarly, the outside observer sees the initial collapsing matter go into making a black hole, but only when it is outside the event horizon. When the material passes the event horizon, light from that area takes infinitely long to reach the observer. Therefore, from the observer's vantage point, the initial formation of the black hole takes very long for the matter just outside the event horizon but takes an infinite amount of time for the actual black hole to "form" according to the observer. Matter far from the event horizon takes a near-normal amount of time to reach the observer, but the light takes longer to reach you the closer to the event horizon it is. There are also theories such as Varying speed of light that make this even more complicated, and according to the VSL theory matter at the event horizon never escapes the black hole but never enters it. ~AH1^(TCU) 00:21, 16 October 2010 (UTC)

Thanks for the comprehensive answer but now my head hurts! I still don't really understand after reading your reply many times, I'll read the article again and see if that helps :-) Spoonfulsofsheep (talk) 00:51, 16 October 2010 (UTC)

You're welcome! ~AH1^(TCU) 02:13, 16 October 2010 (UTC)

Think of it in terms of reference frames. from the perspective of a far-away observer, it appears that it takes something a very, very long time to fall into a black hole. from the perspective of something falling into a black hole, it would appear to happen very, very fast indeed. It's hard to conceptualize, but with extremely strong gravitational fields the passage of time itself changes - someone falling into a black hole would experience an ordinary-seeming finite passage of time, but on Earth thousands or millions of years might pass while we watch the person fall. So, a black hole could accumulate a large amount of material very quickly from its reference frame; it's only from our reference frame that it seems impossibly slow.

It's a bit like going to an amusement park, actually. while you're standing on the ground waiting in line, the roller-coasters don't seem all that thrillingly fast. when you're sitting in one, the ride is over before you know it. Now just imagine that while you're on that 30-second ride, 4 hours pass in the rest of the park. --Ludwigs2 03:09, 16 October 2010 (UTC)

Well I would like to see the maths that shows that the time for infall appears infinite from an external point. When I tried to integrate the gravitational redshift it came to a finite amount ie Integrate Vdt V is velocity of infalling object, t is time in reference frame of external viewer, which gets stretched as the event horizon is approached by gravitational redshift. The integral is the distance traveled over time, and when it reaches the event horizon, that is the end of the trip. What is the time needed to reach the event horizon? Graeme Bartlett (talk) 09:07, 18 October 2010 (UTC)

If it doesn't take an infinite amount of time for matter to fall into a black hole that would answer my question. What I can't wrap my head around is how a black hole can absorb matter from our perspective if it is an infinitely long process. _{It's probably something to do with that bloody einstein bloke, he's usually to blame when things go pear-shaped with common sense} Spoonfulsofsheep (talk) 20:10, 18 October 2010 (UTC)