Wikipedia:Reference desk/Archives/Science/2008 September 16

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September 16

Where do I buy kudzu?

(Moved from Reference Desk - Computers)

Infestation of Kudzu in the United States.

Sirs,any help in finding live kudzu vines, suitable for transplanting ,would be greatly appreicated.05:06, 16 September 2008 (UTC)

It would help to know where you are, at least at the country level. In many parts of the U.S., kudzu is considered an invasive species. You can find vines by the mile choking native vegetation. The U.S. Department of Agriculture requires a federal permit for the movement of many items (plants, insects, produce), including kuzdu. Kudzu can act as a host for soybean rust, a fungus that can significantly damage soybean yield. --- OtherDave (talk) 10:55, 16 September 2008 (UTC)

Are there areas of the U.S. not overrun by kudzu (or wysteria)? Perhaps Alaska and Hawaii. When I drive across the country, it seems that I see kudzu everywhere. -- kainaw™ 13:27, 16 September 2008 (UTC)

It's pretty much a southeastern thing; see the map to the right. -- Coneslayer (talk) 13:30, 16 September 2008 (UTC)

Heehee. I guess my view of "across the country" is very skewed. -- kainaw™ 13:32, 16 September 2008 (UTC)

Or just a little displaced in time. -- Coneslayer (talk) 13:35, 16 September 2008

(UTC)

It's wisteria not wysteria. Caspar Wistar never spelt his name with a 'y'.Richard Avery (talk) 15:17, 16 September 2008 (UTC)

Never ever? Not once? Not even during that really weird phase? -- kainaw™ 18:41, 16 September 2008 (UTC)

Wilmington, NC area. Thank you for your help so far. 16:09, 16 September 2008 (UTC) —Preceding unsigned comment added by 70.144.127.128 (talk)

Then you ought to be able to find kudzu along any county road. And around any county telephone pole. And engulfing half the houses in the country. No offense, buy why on earth would you want kudzu, the weed that's eating the South? Take a look at kudzu as an invasive species. --- OtherDave (talk) 18:34, 16 September 2008 (UTC)

Perhaps to discover a useful control measure, develop tasty kudzu recipes, or breed kudzu-craving coypu? --Scray (talk) 00:35, 17 September 2008 (UTC)

Kudzu takes over completely. America has nothing to eat but Kudzu. A blite wipes Kudzu off the Earth. America suffers from the Kudzu famine. All living Americans move to Ireland and plant potatoes.

From the article, one useful control measure is a bulldozer. Possibly one equipped with a flamethrower. --- OtherDave (talk) 14:46, 17 September 2008 (UTC)

I have a metal

Located in the garden, buried in the soil. It is silver in colour, (very silver and shiny) it is very light, it tinkers like coins do when you hit it, it doesn't float, nor melts in boiling water (not that I expected it to) and doesn't respond to magnets. It is shaped like a misshapen circular flat disc, seems to be all distorted slightly on one side, flat on the other. I can't bend it with my hands.

What is it? Or what other tests can I carry out to work out what it is? SGGH ^speak! 11:31, 16 September 2008 (UTC)

It looks like fourth from the left on the top row, but without the markings. [1] It isn't particularly flexible (cracked it in a vice with a hamkmer and it didn't bend much). The metal detector beeps at the silver section of its display when I sweep it but then I don't trust that very much. SGGH ^speak! 11:40, 16 September 2008 (UTC)

Can you scratch it with your fingernail? --Tango (talk) 13:12, 16 September 2008 (UTC)

No, its too tough to scrape anything off, When I placed it in the vice a part of it broke away partly and i was able to bend it off and snap it with my finger very easily. =The shard was flexible and had to be bent almost right the way around before it broke off. The newly exposed ends were very shiny. SGGH ^speak! 13:16, 16 September 2008 (UTC)

It could be silver (probably not pure, but silver coins are rarely pure). I'm not sure of the best way to test it for sure, but someone here probably does. --Tango (talk) 13:24, 16 September 2008 (UTC)

Wouldn't silver feel heavy rather than light ? SGGH, you said the newly exposed surfaces were especially shiny when you broke a piece off - did they retain that shine or did they tarnish quickly ? Silver will stay shiny if polished; if it tarnishes quickly, my guess (from the lightness) would be aluminium or an aluminium alloy. Gandalf61 (talk) 13:50, 16 September 2008 (UTC)

Gandalf, the recently exposed areas have remained very shiny. SGGH ^speak! 14:15, 16 September 2008 (UTC)

Then I think that kicks my aluminium theory into touch. Gandalf61 (talk) 14:24, 16 September 2008 (UTC)

"Kick into touch" means? Playing rugby union, the only wp article that uses the phrase, is ambiguous. Thanks. Saintrain (talk) 15:29, 16 September 2008 (UTC)

I means it's been taken out of the equation. In Rugby, if you kick a ball into touch you are kicking it off the field of play. SGGH ^speak! 16:30, 16 September 2008 (UTC)

My Grandfather thinks it is some sort of long lost Roman coin, and then spottted images of the Maine penny and announced that that was it. Seeing as I am doing history at University I informed him that the Maine penny was forged in Norway and lost in "Vinland" and it was unlikely to be the same thing, and also that my area of the UK is a bit outside of Norse expansion and settlement. It is possible that trade brought coins here but we have to actually establish it is a coin first. I'm still trying to find out what metal it is! Is there a definitive test for silver bar trying to melt it at 950 degrees C? SGGH ^speak! 14:34, 16 September 2008 (UTC)

If it's silver, it should be about 50% heavier than iron or steel - if this is a potentially valuable coin then the best way to test it would be to measure it's electrical conductivity (silver is VERY conductive). If it's still shiney after being buried for years - then it's almost certainly silver - there aren't many metals that wouldn't corrode or tarnish. SteveBaker (talk) 14:54, 16 September 2008 (UTC)

Silver goes black when buried. DuncanHill (talk) 17:35, 16 September 2008 (UTC)

In the 1950's (& 1960's?) France circulated large aluminum coins. (The southern UK is in the historical area of French "expansion and settlement" :-) Fresh aluminum will coat itself with an oxide preventing its further corrosion (see telescope mirrors). (You beat a priceless artifact in a vice? No "Attic" for you!) Saintrain (talk) 15:13, 16 September 2008 (UTC)

I think it is too warped to be that recent, the only thing that suggests it is not silver is it is pretty light. It is about an inch and a 1/4 in diametre andabout 5-6mm thick. I don't have the ability to weigh it, it is too light to register on the only scales in this house. SGGH ^speak! 16:30, 16 September 2008 (UTC)

I'd guess aluminum. Magnesium is also a possibility (it's even lighter than aluminum), but it tends to corrode, unlike aluminum. --Carnildo (talk) 20:59, 16 September 2008 (UTC)

Certainly sounds like aluminium. When melted by a fire you can get misshapen blobs in the ground. Another destructive test is to see if it is dissolved in a hot sodium carbonate solution, bubbles of hydrogen should appear. Graeme Bartlett (talk) 21:35, 16 September 2008 (UTC)

Could be zinc. The broken cross section would be very shiny with some crystal structure visible. The shape suggests it would be from molten metal dropped on a hard surface to make a coin-like shape. If it is zinc or aluminium heating the edge of it in a gas flame would melt it. Polypipe Wrangler (talk) 06:01, 17 September 2008 (UTC)

reading upside-down..

If I hold a book upside-down I can read it easily..I surprised myself! How is this possible? —Preceding unsigned comment added by 89.241.116.4 (talk) 12:55, 16 September 2008 (UTC)

It's probably akin to the trick where you scramble letter order in words (except the first and last letter) and retain something fairly readable -- you're looking at an unfamiliar pattern, but you have the foreknowledge that it maps to a familiar pattern (a known word in a grammatically correct sentence), so you can fill in the fuzzy spots quite quickly. Try taking something without that familiarity mapping, though (say, a base 64 encoding), and I expect it will be much more difficult to read. Go with something like "V2lraXBlZGlh" (the base 64 for "Wikipedia"), write it on paper, and try reading that upside down. — Lomn 13:18, 16 September 2008 (UTC)

(edit conflict) Your mind can recognise letters and words upside down, I wuold imangine its the smae as wehn yuor mind can raed senentces like tihs as long as the first and last letters are intact. I suspect quick reading upside down still requires good mental organisation. SGGH ^speak! 13:20, 16 September 2008 (UTC)

(ec) I don't have time to google for it, but there was at least one study in which participants were given glasses that inverted everything - so everything the participants saw was upside down. It didn't take long for them to go about normal activities without difficulty. Similarly, the experiment used lenses to make things appear further away or closer and one had a bug-eye look with the view broken into a mess of hexagons. No matter what they did, the brain quickly adapted and the person was able to continue normal activities. So, reading upside down is a natural thing for the brain to be able to adapt to. -- kainaw™ 13:23, 16 September 2008 (UTC)

I read about those studies too, and I think "not long" was a few hours or days, rather than the seconds it takes it get used to reading upside down. It may be related, but it's not the same. (Also, with those studies there were apparently difficulties when they took off the glasses - it took a while to get used to being back to normal. It doesn't take any time to get used to reading up the right was again.) --Tango (talk) 13:28, 16 September 2008 (UTC)

Yes, in the study I saw it took a week or so to get fully used to the inverted vision, such that the subject didn't even notice the vision was inverted. There were some strange intermediate effects where whether or not vision was flipped depended on what sort of visual cues were available (rising smoke and such). After the experiment, it took less time, but still more than a day, to get back to normal. Algebraist 14:35, 16 September 2008 (UTC)

It took longer than I remembered - but I can't place any of those studies in a time period. All I remember is that it was a while back. Perhaps I didn't even read the study. I may have only seen mention of it on some documentary show. -- kainaw™ 14:49, 16 September 2008 (UTC)

¡noʎ ɹoɟ uʍopǝpısdn pǝddı1ɟ ʇxǝʇ ɹnoʎ ǝʌɐɥ os1ɐ uɐɔ noʎ [2] -- macaddct1984 17:54, 16 September 2008 (UTC)

<long boring> well, when you think about it, why not? you see a chair rightside up, you see it upside down, you recognize it immediately. that goes for most objects. why not words? presumably, the language processing center of the brain is involved, and it is not as invariant for spacial transformations as the general object recognition functions are. but knock those out of the loop, and upside down isn't a problem as far as recognizing the word; you then need to tap it back into the language functions to interpret it.

language function is not symmetrical, it's on one side of the brain, which corresponds to most people being righthanded. what lefthanded people do is a question; it seems like how they do their language processing varies quite a bit, some with the normal language center in the normal location, some doing it with another part of the brain entirely; perhaps with different "algorithms".

that said, i know somebody lefthanded who had the most incredible spatial pattern recognition abilities as a toddler; could solve maze puzzles on sight at an early age, i.e. didn't have to navigate along with the finger from the beginning trying to avoid dead ends, would just look at it and see the correct path all at once. the corresponding vice versa being that she had a tough time learning to read; for a long time would recognize each word separately and haltingly. one day i noticed that she was doing this, with the book upside down. a couple of minutes of testing established that she could read at the same speed rightside up as upside down. this ties in with what i was talking about in the previous paragraph; if you're using your regular object perceptive apparatus, upside down means nothing; it's only a problem for the specific language apparatus, which she apparently wasn't using given her relatively large bias in abilities towards nonverbal visual perception. anyway, years later, this large asymmetry in abilities, relative to the average, has in fact meanstreamed quite a bit, with the reading ability rising to normal while the analytical direct perception, for lack of a better word, have dropped down to about normal; but she's still much more a visual-oriented person than verbal. </long boring> Gzuckier (talk) 19:50, 16 September 2008 (UTC)

Well, I can think of at least one other reason why recognizing a chair that's upside down is not the same as being able to read upside down (besides what you mention) and that is that an upside down chair is obviously upside down and easily flipped mentally while letters often form other letters or numbers when they get flipped. Getting used to that would be akin to not getting caught up in false friends when learning a new language. I imagine words with letters such as p, b, d, q w, or m are among the hardest to get used to, for this very reason. If most of the letters are symmetrical (l, o, z, s, etc.) or are at least completely different when flipped (f, Q, R, etc.) then you'd get used to it more quickly. Matt Deres (talk) 20:29, 16 September 2008 (UTC)

Shop Vac power

The Rigid 16gal shop vac advertises itself as having 6.5 peak HP. How is this possible? I get 12A * 120V = 1440W ... 1440W/746W/HP = 1.9 HP. --Duk 14:08, 16 September 2008 (UTC)

Those figures may be standard operation, and the peak through some sort of freak occurance when testing, or the advert/sales people don't talk to the people who built it, or know what they are talking about, perhaps? SGGH ^speak! 14:36, 16 September 2008 (UTC)

Short answer - you can't believe ANY of the numbers on any vacuum cleaner advert!

The magic word "peak" is the key here. [3] has all the ugly details:

"The rating for Peak Horse Power is found by taking the suction motor without its fans and adding as much load as possible without burning it out and then measuring the horse power using the formula which is based on torque per second. This results in a rating that is many times higher than the actual horse power of the motor. Keep in mind also that this motor rating does not take into account the number of fans which the motor is driving. An example of this is that a 4.0 PHP motor with two fans produces about 33% more suction than a 4.0 PHP motor with only one fan."

So Peak Horsepower is meaningless measurement...ignore it.

Sadly, the Ampere value is useless too - that only tells you how much the vacuum cleaner uses - that's like buying a sportscar based on how crappy it's fuel consumption is rather than looking at it's 0-60 time and top speed! A 12 Amp vacuum cleaner might be a powerful one that you'd want to buy - but it could also be a horribly inefficient one that you don't want to go anywhere near!

So the Ampere rating is worse than useless.

The best measure is something called "Air Watts" (although that too is a bit "open to interpretation") or something called the "Sealed Suction" rating... but I don't think I've ever seen those numbers given on a domestic vacuum cleaner.

Basically - you're on your own!

SteveBaker (talk) 14:41, 16 September 2008 (UTC)

The maximum work done in sucking air and dirt into a vacuum cleaner would logically be the thing you are interested in.Another factor is max amperage, since that is what would blow a fuse, or pop a circuit breaker, or cause wiring to fry. If the machine is not connected to a hose, but just sucking air in, it would move the maximum volume of air per second, but without doing the most work mechanically and without having the greatest electrical input to the motor. At some middle level of resistance, with the hose attached and lifting dirt and air through the resistance of the hose, it will have the highest electrical input to the motor and do the most work mechanically. If at the other extreme the end of the hose is burrowing into a pile of dirt so that flow is blocked, there is also no air moved and no work done, and the electrical input to the motor will also not be the highest. This condition is likely to destroy the motor, however, if the air flow is used to cool the motor. This last condition is counter-intuitive, since one expects the greatest amperage under "locked rotor" condition, but that the motor is not in locked rotor. Consumer Reports rates vacuum cleaners on performance, not amperage. They rate them on cleaning carpet, bare floors, on noise, ease of handling, and a few other factors.SonsumerSearch compiled some ratings of shop vacs at [4]. Edison (talk) 15:16, 16 September 20ConsumerSearch has some shop vac ratings and reviews at 08 (UTC)

Of the large size models, an independent research group gives the "Ridgid Pro Utility Vac WD1850" (16 gallons) a very good rating, ranking second; Kenmore being the top one (as it often is). -- MacAddct1984 ^{(talk &#149; contribs)} 18:45, 16 September 2008 (UTC)

Potting soil mixture

Below is a table of ingredient proportions for making potting soil. Is there a similar table for making Terra Preta?

Potting soil	minimum percent	lbs/cuft	lbs each
charcoal	33	13	6.16
sand	59	130	61.61
sludge	5	45	21.33
sawdust	2	17	8.06
perlite	1	6	2.84
total	100	211	100.00

Terra preta#Modern research to recreate Terra preta says that "Research efforts are underway" and "Efforts to recreate these soils are being undertaken", indicating that at this point we probably don't have a good idea on how to make it. You may want to take a look at what the people linked in that article section have written - there may be some indications there. -- 128.104.112.147 (talk) 19:15, 18 September 2008 (UTC)

Help me identify my vacation photos

Can anyone help me identify the breed/species/behaviors shown in these pictures?

• 
  Taken in the Cotswolds. They fly in beautiful synchronized patterns. No idea what color they are.
• 
  Taken in the Cotswolds.
• 
  Taken in Oxford. Grey heron? I thought it was a Great Blue, but our article says they're rarely found in England.
• 
  Also in Oxford.
• 
  Taken at Slea Head in Ireland. Herring Gull?
• 
  Taken at Slea Head in Ireland. Cicindela campestris?
• 
  I assume this cow is just sleeping and not dead?

There are more pictures at the Humanities, Language and Miscellaneous desks. Thanks, BenRG (talk) 17:42, 16 September 2008 (UTC)

Concur on Grey Heron. The flock in silhouette looks like Corvids of some kind. -- Coneslayer (talk) 17:50, 16 September 2008 (UTC)

Carrion Crows, I'd say. Your basic common-or-garden English crow. --Kurt Shaped Box (talk) 23:48, 16 September 2008 (UTC)

Any chance they could be jackdaws like this one I saw a few hours later? -- BenRG (talk) 00:42, 17 September 2008 (UTC)

It's possible. It's difficult to determine scale from the photo. If they were about the size of Feral Pigeons, then they'll have been Jackdaws. Bigger, and you're dealing with CCs. The wing shape and length suggests more crow to me - though I'm not an expert in bird identification... --Kurt Shaped Box (talk) 00:55, 17 September 2008 (UTC)

The shaggy sheep are Cotswold sheep, so I suppose that shouldn't be too much of a surprise. Mikenorton (talk) 18:49, 16 September 2008 (UTC)

Thanks. I looked through a bunch of sheep articles trying to identify them, including Cotswold sheep, but I didn't recognize them from the picture there. Is it normal for them to be dreadlocked like that? Are this and this also Cotswolds, or do they just go to the same hairstylist? -- BenRG (talk) 00:42, 17 September 2008 (UTC)

There are more pictures of Cotswolds at [5], as for those two pics, the first one I'd say yes, the second - not sure, do Cotswolds ever have black faces? DuncanHill (talk) 11:08, 17 September 2008 (UTC)

The second one is a Wensleydale, I think. Mikenorton (talk) 13:12, 17 September 2008 (UTC)

The gulls look like Herring gulls to me, the cow is probably asleep, but you'd probably want to poke her with a stick to double check. DuncanHill (talk) 23:32, 16 September 2008 (UTC)

Yep, they're Herring Gulls (probably a mated pair, based upon the fact that they're stood next to each other without looking as though they want to have a fight). As for the cow - don't cows sleep standing up? I know that they can kneel down, if they want (as the creamy-coloured one is doing) - but AFAIK, an adult cow can't actually breathe when lying on its side, due to it's lungs being compressed by its own body weight. That one might actually be dead... --Kurt Shaped Box (talk) 23:45, 16 September 2008 (UTC)

I've seen living cows lying down like that. A thought - if those are her calves beside her, they look quite placid, which suggests that they have no concerns about their mother. If you've ever seen a calf with a dead mother, you are left in no doubt that she's dead. DuncanHill (talk) 23:49, 16 September 2008 (UTC)

It's just lying down! They do that. Also unlikely to be the mother of those calves, for one the cow is a Fresian and there appears no evidence of that breed in the calves and second the cow looks too young herself to be the mother of those two sturdy calves. Jdrewitt (talk) 21:18, 17 September 2008 (UTC)

Ah, okay then - I'll bow to your superior knowledge on this one. I just seem to remember reading somewhere that cows can't lie on their sides and breathe at the same time. Never mind. ;) --Kurt Shaped Box (talk) 00:00, 17 September 2008 (UTC)

That was sort of my thinking—healthy cows don't look like that, do they? But an unhealthy cow would provoke a bit more reaction in the others, wouldn't it? I'll assume it's okay, but I'm still a bit worried. -- BenRG (talk) 00:42, 17 September 2008 (UTC)

Are you anywhere near this cow at the moment? Just walking up to her would usually get a reaction, or as I said you could poke her (not hard) with a stick. It is a bit dodgy going near cows with their calves though, as they do get a bit aggressive if they think you are a threat to their young. If you do find any more cows which concern you, try to find the farm and let the farmer know - they will be very grateful for your concern. Calves bellow something heartbreaking when their mothers are dead or very ill, and other cows in the field will often behave oddly too. DuncanHill (talk) 01:30, 17 September 2008 (UTC)

I once saw a couple of dead horses who had been struck by lightning. They were lying on their sides like this cow, but the legs farthest from the ground were quite a way up in the air due to the distension of the abdomen from post-mortem changes. So this would have to be a recently-dead cow. Edison (talk) 02:06, 17 September 2008 (UTC)

So, anyway - I've taken the liberty of adding a cropped version of the cow image to our Cow tipping article. That may be a controversial change, considering the history of the article (really!) - but let's wait and see... --Kurt Shaped Box (talk) 22:36, 17 September 2008 (UTC)

The birds are more likely to be rooks, given the old country adage crows together are rooks and rooks by themselves are crows. The cow is unlikely to be dead given that there is a large blood vessel crossing her abdomen and this looks normal and is clearly indicating a level of blood pressure. It is a well known fact that blood pressure very often drops at death ;-) Richard Avery (talk) 07:30, 17 September 2008 (UTC)

How can something be smaller than Planck length?

The LHC might create black holes smaller than Planck length according to the first response to my question above. Huh? I thought Planck length, Planck temperature, Planck energy levels, etc. was the ultimate. That any other extreme measurement would be nonsense? I suppose with some fancy math that would make Einstein look like a retard you could make it happen, but geeez- This mind blowing science not only gets me worried, it's driving me insane!. (HP Lovecraft's beeper just went off) How the- how can something be more extreme than the ultimate!? Can something less than nothing actually be created? If that's the case, it probably could only exist in another dimension. Or, having nowhere else to go, the universe would go TILT, turn itself inside out, and then -the black hole would take up infinite space! AAAAHHHH!!!Dr. Carefree (talk) 19:00, 16 September 2008 (UTC)

The Planck scale isn't necessarily the smallest possible, it's just the smallest our current theories can understand. --Tango (talk) 20:13, 16 September 2008 (UTC)

That response in the previous thread was incorrect. It was based on the usual black hole formulas that you can find in articles like black hole, but the scenarios for black hole production at the LHC assume that those formulas are wrong and the black holes are much larger (but still extremely tiny by everyday standards). Obviously this is all very speculative and most likely no black holes will be produced. Also, as Tango said, the Planck length is more of a threshold of ignorance than anything else. Claiming that it's a "minimum length" is misleading since it implies that we have some idea what's going on at that scale. -- BenRG (talk) 21:42, 16 September 2008 (UTC)

This plank length business does not make sense. Planks come in different lengths. Wanderer57 (talk) 21:02, 16 September 2008 (UTC)

The point was that because it is too tiny to exist, it does not exist. Also it should last less time than a Planck time before it has decayed. When you apply Heisenburg's uncertainty principle something with a very tiny size has to have a highly uncertain energy or mass. Or if it has a very short lifetime, the same applies. Graeme Bartlett (talk) 21:50, 16 September 2008 (UTC)

Dr. Carefree needs to change his/her name (that or take a tranquilizer). Clarityfiend (talk) 21:54, 16 September 2008 (UTC)

Also, Planck units are not all extreme. The Planck mass, for example, is about the same as that of an ant. The Planck energy is about the same as that of a barrel of oil. Some of them are a little nutty, though. --Sean 23:48, 16 September 2008 (UTC)

Chaotic system is Chaotic

Hello! Could someone explain in layman's terms the second and third conditions for a system to be considered chaotic? I just can't get my head around those two! The article explains in several paragraphs what "sensitivity to initial conditions" means (which is like the easiest one to understand), has a single short paragraph for "must be topologically mixing" (which I don't understand), and says nothing about "its periodic orbits must be dense". I'm asking here and not at the mathematics desk because I would also like to understand what this means for real chaotic systems, like the weather. There is an explanation of these for the layman, right? Thanks in advance, Kreachure (talk) 19:44, 16 September 2008 (UTC) PS. If you think I'd get a better answer at the Math Desk nonetheless, please tell me. :)

I think there's a fair bit of crossover between the Maths and Science desks, so there shouldn't be a problem there. I'll try to tackle a layperson's explanation of topological transitivity, first. Quoting from Mixing (mathematics):

A continuous map $f:X\to X$ is said to be topologically transitive if, for every pair of non-empty open sets $A,B\subset X$, there exists an integer n such that

$f^{n}(A)\cap B\neq \varnothing$

So, a continuous map is just a continuous function where the domain and range (i.e. sets of possible inputs and outputs) are the same. Because of this, it is possible to iterate the function - i.e. take the output of the function and use it as a new input. The nth iterate of f(x) is $f^{n}(x)=f(f(...f(x)...))$. The definition of open sets in a topology gets a bit circular, but for example's sake consider the basic open set of the real line, the open interval (a, b), which is the set of all numbers x such that a < x < b (i.e. numbers between a and b, but not including a or b). Take any two of these open sets, and label them A and B, and suppose that the domain of our function is to be the real numbers. The image of A in f, f(A), is the set of all outputs you get when you use all elements of A as inputs to f. For example, if f(x) = 2x, then f(A) is the set of all numbers twice as big as the elements of A, and f²(A) is the set of all numbers four times as big as the elements of A, and so forth. If f is topologically transitive, then you can always find a number n such that the image of A in the nth iterate of f (i.e. the set you get when you feed all elements of A into f, and feed that output back into f, and so forth for n times) has a non-empty intersection with B - they overlap.

Let's see if f(x) = 2x is transitive. If you start with A = (0, 1) and B = (3.5, 4.6) you see that f(A) = (0, 2), and f²(A) = (0, 4). Clearly f²(A) and B overlap on the interval (3.5, 4), so that's ok. But what about the other way around? f(B) = (7, 9.2), f²(B) = (14, 18.4), and you can see that as you continue applying f to B, you're actually getting further away from A. Clearly, f(x) = 2x is not topologically transitive on the real numbers.

A function which is topologically mixed goes even further. Not only can you find an n such that $f^{n}(A)$ overlaps with B, you can find an n such that for every m > n, $f^{m}(A)$ overlaps B. So $f^{n+1}(A),\ f^{n+2}(A),\ f^{n+1000000}(A)$ all have overlaps with B.

Does that make it clearer? Confusing Manifestation(Say hi!) 23:59, 16 September 2008 (UTC)

Oh boy... er, first of all, thank you very much for taking the time to write up this explanation. It certainly explains "topologically transitive" quite thoroughly. But to be honest, I was expecting a far simpler explanation. I guess there really isn't a simpler way to explain these concepts, huh... I was expecting to understand what it means in general for a chaotic system (the same way I understand what "sensitivity to initial conditions" means). Does the "periodic orbits must be dense" bit need an equally intricate explanation? Kreachure (talk) 19:16, 17 September 2008 (UTC)

Strangelets

A few days ago, somebody asked a question regarding how long a mini-black hole would take to destroy the Earth, if one were created by the LHC. I would like to know how long the Earth would take to be destroyed by the creation of strangelets, assuming that a runaway strangelet reaction could in fact occur. My understanding is that every particle a strangelet touches would become a strangelet, and that this would eventually have a domino effect across the whole earth. But how fast would this theoretically happen? Would it be fairly instantaneous, or would we initially have time to hear that "Switzerland has disappeared" on the news? Thanks Baked Bean Bob (talk) 22:31, 16 September 2008 (UTC)

I don't know, but lets both read the articles on strangelets and Safety of the Large Hadron Collider and return in a couple hours. Plasticup ^T/C 01:52, 17 September 2008 (UTC)

From strangelet: "even if the strange matter hypothesis were correct, nuclei would never be seen to decay to strangelets because their lifetime would be longer than the age of the universe." So there you have it. Also, the collisions that will take place in the LHC are similar to the millions (billions?) that take place every day when cosmic rays hit our atmosphere. So far our planet has not been reduced to strange matter. Plasticup ^T/C 01:58, 17 September 2008 (UTC)

I can't count the number of times I've said this...but one more time can't hurt: There is a VERY significant difference between cosmic ray collision and what happens in the LHC. A cosmic ray comes in at some large fraction ot the speed of light and smacks into a more or less stationary particle on the earth or in the atmosphere. Conservation of momentum has the resulting "stuff" (including - maybe Higgs Bosons, mini black holes, strangelets, etc) hurtling off at maybe half the speed of light. They aren't going to be around long enough to cause major problems. But the LHC takes particles around the ring in opposite directions and smacks them together at precisely equal and opposite velocities. It does this SPECIFICALLY so that the momentum of the incoming particles will cancel out leaving the resulting "stuff" being more or less stationary with respect to their detectors. If the particles disappeared at half the speed of light - they'd never detect them. If there were truly no difference between cosmic ray events and LHC events, we wouldn't have spent all of those billions of dollars building the darned thing - we could have simply set the detectors up somewhere outdoors and waited for cosmic rays to make Higgs Bosons for us! So this argument that if there were any nasty things produced at those energies then we'd have seen them already is really pretty bogus. The thing that makes it safe is that we really don't believe in strangelets and mini-blackholes will evaporate - or simply take so long to grow to earth-eating sizes, it'll never matter. SteveBaker (talk) 04:32, 17 September 2008 (UTC)

I am familiar with that argument. Yes, the results of collisions with cosmic rays have tremendous momentum, but there are a hell of a lot of them. They have been happening for billions of years. At some point one of the stranglets would have hit 1,000 baryons on its way through the Earth and slowed down enough to be captured. The majority would escape, I have no argument there, but the natural experiment has been running for so long that the small possibility of capture would have been realized. Plasticup ^T/C 05:37, 17 September 2008 (UTC)

For a long time, it was thought that the Tunguska event might have been caused by a mini-black hole or a strangelet or something. We now know that's not true - but the idea was sufficiently plausible to be seriously considered for a while. If statistically unlikely cosmic ray events were indeed causing disasters of that scale - at a timescale of (say) once per few thousand years - then it's not clear that we would have noticed them from ancient craters and so forth. But I reiterate - I'm not in the slightest bit bothered about risk due to LHC and the people who do believe it's going to be the end of the world are largely nut-jobs. I'm only saying that the argument that "It must be OK because cosmic rays do this all the time" is not the slam-dunk that LHC folks claim that it is. SteveBaker (talk) 13:36, 17 September 2008 (UTC)

If the LHC caused a Tunguska-like event it would be unfortunate (particularly for France and Switzerland), but it would not be the end of the world. The mini-black-hole and strangelet theories involve the end of the world, there is a big difference. It's entirely possible that cosmic rays do occasionally cause natural disasters on the scale of Tunguska and we might not have noticed, but if they caused end-of-the-world events, we wouldn't be here to not notice it, so we can be pretty certain they haven't happened. --Tango (talk) 13:57, 17 September 2008 (UTC)

Wouldn't your "it's going too fast to hit anything" objection apply to the original cosmic ray collision? Presumably after some amount of playing pachinko it will get down to a less ludicrous speed; even more so for cosmic rays hitting the Sun. --Sean 14:22, 17 September 2008 (UTC)

Right - that's Plasticup's argument - and it has great merit. The problem is that the probability of that series of collisions happening is small (it must be small or we'd already have detected Higgs Bosons bouncing around all over the place). We don't know how many "pachinko"-style collisions it might take to create conditions with enough energy to create a strangelet/mini-black-hole/whatever and yet to have the resulting particle(s) going slowly enough to do noticable amounts of damage before they fly off into the inky void. That means that we don't really know for sure whether:

1. These things are happening all the time in the atmosphere - many times per day over every square mile of the world - and the world hasn't ended - so we're OK - and we didn't detect any weird particles because there just aren't any and the LHC is going to be a huge disappointment - but isn't dangerous. ...OR...
2. These things happen only rarely - maybe just a few times each year. Rarely enough that we can't detect them but frequently enough that we'd know if they were dangerous. Hence we know that the consequences are benign - so the LHC is definitely safe and may well detect something interesting. (this is Plasticup's view, I think)...OR...
3. These things (statistically) happen only once every few thousand years and they don't wipe out the entire planet - but maybe might account for some of the mysterious mass extinctions or other "natural" events of disasterous proportions...in which case the LHC might indeed be insanely dangerous - but probably not the end of the world. (I very much doubt this - but it's possible)...OR...
4. These things are statistically so amazingly unlikely that happen only once or twice in the life of the universe - so we're safe from cosmic ray events but we don't know about artificially-induced events in the LHC (this is my view).

So which of those is it? We don't know. Hence it's a guess - and this isn't a valid proof that the LHC is safe. (Although, IMHO, there are other things that constitute valid proof.)

SteveBaker (talk) 17:07, 17 September 2008 (UTC)

That statement that "nuclei would never be seen to decay to strangelets" is actually talking about something different. The idea is that strange matter is a lower energy state than ordinary matter, and in quantum mechanics any transition from a higher to a lower energy state that doesn't violate any conservation laws will happen eventually. But there's an energy barrier between the states, i.e. the potential function looks like

       \      _        /
        \    / \      /
         \A_/   \    /
                 \B_/

Classically you can't get from A to B without an energy input to get you over the hump. Quantum mechanically you can and will get there by tunneling, but the half-life for the transition is exponential in the size of the barrier. So nucleons might decay to strangelets but very very slowly. But it's a different story if you already have some strange matter (produced by actually supplying the energy to get over the hump)—it might catalyze the production of more. Its proximity might, if you like, "tilt" the energy function so that you can roll down from A to B. There are a bunch of sci-fi disaster scenarios like this—vacuum decay, ice-nine and grey goo spring immediately to mind. Personally I don't lose sleep over any of them. A more realistic example is invasive plant or animal species that can spread easily if they're introduced from elsewhere, but are unlikely to appear by spontaneous mutation. -- BenRG (talk) 16:38, 17 September 2008 (UTC)

Having read the articles I am still none the wiser. However it does seem that nuclei decaying into strangelets is different from the process described here:

"If strangelets can actually exist, and if they were produced at LHC, they could conceivably initiate a runaway fusion process in which all the nuclei in the planet were converted to strange matter, similar to a strange star"

This is the reaction that I am interested in. I would like to say that I do not believe this would happen in the LHC, I would really just like to know how long this runaway process would take (regardless of the source of the strangelets). Thanks Baked Bean Bob (talk) 10:46, 17 September 2008 (UTC)

Building a Terminator

How far away in terms of technology are we from being able to build lifelike femmebots like Cameron from the Terminator TV series? —Preceding unsigned comment added by 84.69.108.42 (talk) 23:02, 16 September 2008 (UTC)

Here's something near the state of the art, which should give you an idea. --Sean 23:52, 16 September 2008 (UTC)

150 years, give or take a century. Plasticup ^T/C 23:53, 16 September 2008 (UTC)

Be aware that while robots and humans have decision tables in common only humans go to the trouble of reducing them to minimum form, converting them to classification tables and optimizing the tables to produce polychotomous keys. 71.100.15.15 (talk) 00:28, 17 September 2008 (UTC)

What a weird paper. The author's motivations are unusual to say the least. I don't think his ideas about decision tables and polychotomous keys hold any water. -- BenRG (talk) 18:50, 18 September 2008 (UTC)

What ideas might those be? Seems like what he is saying is pretty much straight forward to me. 71.100.15.15 (talk) 02:04, 20 September 2008 (UTC)

Oh, I see what you are saying...If someone says 2+2=4 then you say their position holds water but if they say they believe in God and 2+2=4 then you say their ideas about 2+2=4 do not hold water. Very clever. Genius as a matter of fact. 71.100.15.15 (talk) 02:48, 20 September 2008 (UTC)

I could have worded my last comment better; the implied "therefore" before the last sentence was unintended. The idea that "computers use decision tables, people use poly(cho)tomous keys" is simply wrong. Human beings make decisions in all kinds of ways, and they program computers to make decisions in all kinds of ways. Probably the most common decision-making structure in software is a tree of nested if...else if...else statements, which is the programming language equivalent of a polytomous key. Explicit decision tables (of more than one dimension) are relatively uncommon. And there are utterly different ways of making decisions, like neural nets and Bayesian inference. The author of the paper seems to lack even a basic understanding of how computers work. E.g. he mentions uncritically the idea that people have asked computers whether God exists and the computers have responded that they don't have enough information. I can't imagine a context in which this hypothetical exchange would make sense. In short, it's a weird paper (in my opinion), the author's motivations are unusual (surely you agree), and I don't think the ideas about decision making hold any water. Three separate statements. -- BenRG (talk) 13:20, 23 September 2008 (UTC)

Take a look at Actroid and EveR-1 too (there's some good vids on YouTube too). Those can't walk, perform ballet, kill on command, hack into computer systems through streetlights, survive car bomb explosions or have brief moments of glassy-eyed self-reflection though. Yet. --Kurt Shaped Box (talk) 01:36, 17 September 2008 (UTC)

As far as we know... Plasticup ^T/C 01:50, 17 September 2008 (UTC)

My favorite android is Zou Ren Ti's. -- BenRG (talk) 18:50, 18 September 2008 (UTC)

I would've thought the cleverer the femme the less of a bot she's likely to be.  ;) Julia Rossi (talk) 02:36, 17 September 2008 (UTC)

"AMEE" Autonomous Mapping Evaluation and Evasion from the movie Red Planet (film) is not far away except for the power pack. 71.100.15.15 (talk) 11:03, 17 September 2008 (UTC)

The main problem is making good enough AI. I doubt this could be designed. It can definitely be made with genetic programming, but it would take centuries of guided evolution, minimum. If we gain a very deep understanding of our brains, we might be able to design something similar, but not with conventional computers. They have a very different architecture and would not be able to emulate each other at any reasonable speed. Given the time frame, I doubt a sufficiently human-like body will be difficult. — DanielLC 16:32, 18 September 2008 (UTC)

The latter is just a question of combining ASIMO and RealDoll technology, rite? --Kurt Shaped Box (talk) 02:44, 20 September 2008 (UTC)

Mass vs. size

I'm having a hard time with this problem: If the Earth were shrunken down to one tenth its size but its mass remained the same, what would the effect be on the Moon and its orbit? I think that there should be no effect because gravity is based only on mass, not "size." Therefore, the Moon would remain in the same orbit with the same speed. Is my thinking correct? Or where have I gone wrong and what do I need to consider that I've overlooked? Thank you!--El aprendelenguas (talk) 23:20, 16 September 2008 (UTC)

There would be no effect. The shell theorem implies that a spherically symmetric body, for the purposes of gravitational interaction with other bodies, can be considered to be a point mass at its centre. Algebraist 23:31, 16 September 2008 (UTC)

Yep, that's right. For example, if the sun collapsed into a black hole out orbit would remain unchanged, although things would get quite dark... Plasticup ^T/C 05:31, 17 September 2008 (UTC)

The shell theorm works for a perfect sphere, but not for the earth. We have tides, and the effects of the tides depend on the earth's diameter. A smaller earth will not transfer angualr momentum from earth's rotation to the moon as fast as a larger earth. -Arch dude (talk) 01:18, 17 September 2008 (UTC)

That's true - but the error would be pretty much negligable. SteveBaker (talk) 04:22, 17 September 2008 (UTC)

SteveBaker is correct, there would be an effect, but it would be very small. Raising tides on the Earth is causing the moon to gradually (very slowly!) move further and further away from Earth. If the Earth was shrunk the magnitude of this effect would change, but you would only see this is you were observing the Earth-Moon system for a very long time. — QuantumEleven 13:15, 17 September 2008 (UTC)

Yes the effect is small, but it is a real, measurable effect. The OP is clearly contemplating some major macro-engineering project, so we cannot know for sure how many aeons he has allocated for the work. I'd hate for him to come back in 4 billion years to discover that his intervention had prevented the moon from migrating to the L3 point if in fact he wss assuming that it would. -Arch dude (talk) 16:27, 17 September 2008 (UTC)

Eh? the L3 point of what system? —Tamfang (talk) 05:45, 21 September 2008 (UTC)