Wikipedia:Reference desk/Archives/Science/2008 December 14

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December 14

Tuberculosis

Does Tuberculosis cause paranoia/affects the mental health of patients? How often does this happen? I'm not asking for medical advice because I was reading a memoir in which the author described the mental instability of his father who later died of tuberculosis. Coolotter88 (talk) 00:05, 14 December 2008 (UTC)

Our article Tuberculosis says that the central nervous system can be affected - so presumably there could be consequences for mental health. SteveBaker (talk) 02:43, 14 December 2008 (UTC)

As with a lot of infections, the symptoms present will depend upon which area of the body is primarily infected. For example, pulmonary tuberculosis isn't likely to cause mental illness. However, if tuberculosis infected near the brain, such as in the meninges, it can cause tuberculous meningitis, which could perhaps contribute to mental illness. However, I find it more likely that the person in the memoir simply had a mental illness AND tuberculosis. —Cyclonenim (talk · contribs · email) 11:00, 14 December 2008 (UTC)

Effect of various pH levels on pepsin hydrolysis

At school, we did an experiment testing the effectiveness of pepsin on the hydrolysis of a wheat protein. We masses the pieces of protein at the beginning and then at the end to determine the change in mass. The protein in the beaker with the acidic solution lost the most mass and that, I hypothesize, is due to the fact that pepsin works best in an acidic environment and hydrolyzed the protein the best. But the mass went up in the basic solutions. Why is this? Could someone point me in the correct direction? The Ayatollah (talk) 01:43, 14 December 2008 (UTC)

One possibly useful hint (caveat: without knowing any details of your experiment) is "A base can convert a carboxylic acid into its carboxylate salt." DMacks (talk) 09:00, 14 December 2008 (UTC)

cacti

how can u make cacti grow rediculusly fast? or at least fast? and also is it true u can cut a cactus in half and plant it and it will grow...so u then have two cacti? —Preceding unsigned comment added by 76.14.124.175 (talk) 02:30, 14 December 2008 (UTC)

I have no answer to your second question, but to make cacti grow quite fast, you might give the plant excessive vitamins and minerals. Or, you can gentically engineer the cacti.--Archaeopteryx (talk) 03:00, 14 December 2008 (UTC)

You've asked about psychedelic cacti, smoking caffeine, drug videos, shrooms, and injecting piperidine. I think I smell a pattern... Dragons flight (talk) 03:17, 14 December 2008 (UTC)

just looking for a way to make money...j/k —Preceding unsigned comment added by 76.14.124.175 (talk) 03:50, 14 December 2008 (UTC)

Just keep in mind that just because you don't have an account on Wikipedia, you are not truly anonymous. Just a quick trace on your IP address went from my home to Atlanta, to XO in Washington state, to San Jose, to Rocklin before I killed it. So, asking a multitude of questions about trying to quickly grow psychedelic cacti could be read by the wrong guy at the wrong time and end up causing your more trouble than you'd like. -- kainaw™ 04:21, 14 December 2008 (UTC)

As they say on the internets, "Do they have access to our REAL LIFE OMG REAL IDENTITY? ... "only as much as you make available, mr moussa" Nimur (talk) 17:05, 14 December 2008 (UTC)

Or as much as your ISP is willing to hand over without any argument. -- kainaw™ 21:20, 14 December 2008 (UTC)

As for cutting a cactus in half, just about any plant will try to regrow if split, but with varying levels of success. Breaking off a branch and planting it is more likely to work than "splitting it in half", which would likely cause the liquid to leak out and the plant to dry up and whither. StuRat (talk) 04:52, 14 December 2008 (UTC)

See also totipotency. Nil Einne (talk) 11:06, 16 December 2008 (UTC)

I fixed your link, Nil. StuRat (talk)

Use of prions in anti viral combat

I am a student of biology, and I came up with this idea in sixth grade:

Since prions destroy certain proteins, is it possible that they can be engineered to destroy the protein coating and coating and receptors on a virus? (And please do not steal this idea for profit, since this is PATENTED.) Please contact me on my talk page and/or email me.--Archaeopteryx (talk) 03:03, 14 December 2008 (UTC)

I think for starters you might want to read about patents. Most of the time, people don't spend the thousands of dollars required to obtain a patent unless they have a good idea that their system will work.

As for the idea, prions are created by a special type of self-propagating folding error in proteins. In general that means that they only occur for special kinds of proteins and their method of action isn't something that can be engineered, since a naturally occurring protein is either inherently vulnerable to it or it isn't. Dragons flight (talk) 03:28, 14 December 2008 (UTC)

Neat idea in theory, but probably not plausible unless you can find some existing model for that attack system (and I don't believe one is known). Without such a head start from Mother Nature (like we had with penicillin), it would be practically impossible to sit at a desk conjuring up different proteins until one worked. Maybe as we come to understand prions better something like that will emerge, but I think it will be a very long time if ever. - Draeco (talk) 05:37, 14 December 2008 (UTC)

I think you can produce an anti-viral prion if you could synthesize an abnormal self-replicating protein coat or receptor For now we still have difficulty in synthesizing small peptides such as insulin. Then you have to figure out how to prevent those prions from being eaten by the immune system before it messes up some live virus coating. I also highly doubt that you already have a patent on the idea. For starters you have to publicly disclose how to manufacture such a designer prion to your Patent office. But you can call dibs though :).--Lenticel ^(talk) 12:35, 14 December 2008 (UTC)

Hmm... you may want to consider brushing up on your immunology. Unfortunately, not only will this be unlikely to work, but there are easier ways of going about it. First I have a nit to pick: the definition of a prion is an abnormally folded native protein, so the idea of an introduced protein being a prion doesn't make much sense for several reasons, mainly that there is no reservoir of native, correctly-folded proteins to induce misfolding in in order to self propagate (the agents of BSE and scrapie are similar enough to human proteins that they work too). You could, however, engineer some kind of enzyme to accomplish the task you have in mind. Introducing new proteins into a biological system is problematic however, since they will typically generate an immune response that results in the clearance of the foreign protein (or worse). Finally, you might be able to create and patent an anti-viral protein, but nature has beaten you to the punch by a few million years. Your best bet is to create a synthetic humanized monoclonal antibody against your target: it's far easier, and won't be cleared by the patient. – ClockworkSoul 00:13, 15 December 2008 (UTC)

Based on what they tell you, I am sorry to say, but that patent may have been a waste of money. Also, if your patent is real, what number is it (so I can look it up at Google Patents)?--DocDeel516 ^discuss 19:48, 22 December 2008 (UTC)

Bond Strengths and Electronegativities

A C-F bond is stronger than a C-C bond because the electronegativity difference between C and F make give it a greater ionic character. But then why is the C-Br and C-I bond weaker than the C-C bond? How about the C-H bond? Why are these so strong when the electronegativities are so close together? --Russoc4 (talk) 03:18, 14 December 2008 (UTC)

"Why" is usually just a rationalization of the observed trends using various other properties. So just need to consider lots of other properties...enough to find one that explains away how reality happens. If you like physics and introductory chemistry, then C–Br and C–I are much longer bonds, so electrostatic effects are lessened. If you like more advanced or organic chemistry, then Br and I are larger and more polarizeable, so their valence electrons are easier to delocalize away from the C bonding region (agrees with leaving-group trend). If you like phyisical chemistry, then the atomic orbitals of C hybridize progressively less with those having a greater difference of n quantum number. DMacks (talk) 08:56, 14 December 2008 (UTC)

So you're saying that you need more than just differences in electronegativity to predict bond strengths? It seems, though, that longer bonds, bigger atoms, and a greater principle quantum number are all essentially the same thing. Would it be safe to assume that electronegativity "gaps" increase bonds strength while more shells decrease bond strength? But what, then, accounts for the bond strength of C-C, where there is no difference in electronegativity? --Russoc4 (talk) 17:26, 14 December 2008 (UTC)

All bonds have both ionic and covalent character. The more there is an electronegativity difference, the greater the ionic character. Covalent character can be described as overlapping atomic orbitals that form molecular orbitals - the better the overlap, the stronger (and shorter) the bond. Carbon and fluorine are both using orbitals with principle quantum number n=2, so they are a good match. Bromine and Iodine (n=4 and n=5) are quite a bit bigger than carbon's n=2, so the overlap is poorer. But DMacks is correct - these are all pretty much justifications for what is observed, and things like polarizability also factor in. The real reson is probably just mathematical, which wouldn't be an easily applicable theory. --Bennybp (talk) 18:22, 14 December 2008 (UTC)

In this case, Coulomb's law is probably most informative. In a C-C bond, the bonding orbital is localized between the two carbon atoms; you can envision this as having the following geometry: O...[--]...O where the O is the positively charged C atom (each donated an electron to the bonding orbital) and the [--] is the negatively charged bonding orbital. According to Coulomb's Law, the force of attraction between two charges is:

${\frac {(Q1*Q2)}{(d^{2})}}$

Where Q1 and Q2 are each charge and d is the distance between them. The important distinctions here are in the value of "d". A C-C bond will be longer than a C-F bond, and so will have a lower overall attractiveness. In a C-F bond, there will be more electron density around the fluorine (it will look more like O.....[--].O ) than directly between the two atoms, but on the balance the net forces holding the whole mess together are probably comperable WRT the charges (Q1 and Q2 values). The deal with C-Br and C-I bonds is that the Br and I atoms are SO much larger, that the attractive forces are going to be much less, because the d value is so much larger.

Incedentally, if you keep shifting that [--] electron cloud to the right, it eventually envelopes the right hand O, at which point you have an "ionic" instead of "covalent" bond... --Jayron32.talk.contribs 22:14, 14 December 2008 (UTC)

are all cactus edible?

r they edible or just most? —Preceding unsigned comment added by 76.14.124.175 (talk) 03:47, 14 December 2008 (UTC)

• Cacti are generally inedible for humans, though some have edible fruit (Prickly Pear). Exxolon (talk) 05:19, 14 December 2008 (UTC)

Not all species are edible - but many are. They sell lots of the stuff in my local HEB and WalMart stores. [1] [2] It's prickly pear alright - but not the red fruit, it's the big green 'pads'[3]. I've cooked and eaten cactus many times...it's pretty good. The pads you buy in stores here in Texas have had the spines removed already. You can prepare it by slicing it thinly and boiling it lightly in water - I like to change the water a couple of times because you get some unappetizing slimy-looking stuff coming out of it. The resulting vegetable tastes a lot like 'snow peas' ('mange tout')...pretty good. You can put them into any recipe that calls for green beans or green peppers. This article says that there are over 200 species of edible cactus. But of course there are likely to be species of Cactus that you can't eat...so don't just grab any old cactus! SteveBaker (talk) 07:04, 14 December 2008 (UTC)

Yeah, I've eaten prickly-pear myself in Mexico... Its my understanding that most of the time if you are served "cactus" as a dish, its the flesh of the prickly pear. It has a definate "okra" quality to it, if you go for that musselage thing... --Jayron32.talk.contribs 04:04, 15 December 2008 (UTC)

Yes, the texture is somewhat like Okra. The slime that comes out during cooking is distinctly unappetising - hence the frequent water changes while cooking the stuff. But there are two parts of the plant that are eaten - the "fruit" (a reddish thing the shape of a pear) and the "pads" (the big flat oval things). I'm talking about the pads. SteveBaker (talk) 06:28, 16 December 2008 (UTC)

Why is bacon so delicious?

It seem that if someone likes to eat bacon, they LOVE to eat bacon. I've never met anyone who eats bacon and thinks its just 'okay'. What makes bacon so yummy? --71.158.216.23 (talk) 06:55, 14 December 2008 (UTC)

I think bacon is 'okay'. Just one more example of why Wikipedia does not allow original research. --S.dedalus (talk) 08:54, 14 December 2008 (UTC)

SD has a good point. Be that as it may, I suspect the primary reason why a lot of people find bacon 'yummy' likely has a lot to do with the high fat and high salt content and the fact that humans have an inherited craving for fat and salt, in the case of salt probably largely due to its nutritional importance and traditional rarity and fat probably largely due its high energy content Nil Einne (talk) 09:23, 14 December 2008 (UTC)

Around here, Maccas is offering bacon strips as added extras so they must have researched its drawing power. One of the things about bacon is being served hot which also enhances flavour and eye-appeal, especially when it's presented as a winter breakfast/comfort item (though not only). Suggest traditional associations and custom also help to instill the bacon-response. Julia Rossi (talk) 09:35, 14 December 2008 (UTC)

If we are not talking boiled bacon Maillard reaction could help. Most mammals also have a natural craving for salty foods. Umami should cover the remainder of cases. 76.97.245.5 (talk) 11:48, 14 December 2008 (UTC)

Because it is made from love, kindness and mutual respect specifically for the purpose of sustaining careful, loving and kind beings in a peaceful paradise of ease, play and affection. There is no need to cover it in humour or ignorance like some foods because it is beautiful and like all animals, pigs come without souls or pain hence perfect for slaughter and eating. God didn't say it, but he meant for many people to eat pigs and only God could make that taste so good. It is a symbol of beauty cut in blood from the legs back and belly of a fat, non-intelligent beast. Also a symbol of closeness to your fellow human being the most likely, in common varieties, to appear and smell as natural human skin (a putrid smell indeed when not living near running water) and in this way could be construed as a brotherly/sisterly love show that you would lovingly eat yourself or your freinds or as close to that as you could get without fear of reprisal in todays world. ~ R.T.G 01:48, 15 December 2008 (UTC)

I, too love bacon. It is best when fried in deep fat, so there are no soggy bits. Cracklin's fried in the lard rendering process are also delicious. Rest assured that a hog would eat you as joyfully as you eat him. Edison (talk) 02:39, 16 December 2008 (UTC)

telegraph network structure

I recently watched an episode of The Wild Wild West (set in 1869–77) in which our hero visits a telegraph office; a row of wet cells was conspicuous. I had not known how the system was powered. That triggered some other questions, which were not answered by electrical telegraph. What sort of topology did the network have? How much redundancy, on what scales? How big would a town be before it had lines running in more than two directions? How many operators would handle a message from California to Boston? —Tamfang (talk) 09:56, 14 December 2008 (UTC)

It seems easier to find information on the instruments and batteries than on the topology. Hawkins Electrical Guide Number 8 (1917, reprinted 19260) 2,201 to 2,262 describes how the equipment functions. It could be operated open circuit or closed circuit, with repeaters or with manual retransmission of messages. A simple line was used up to 500 miles, where a key at one end operated a sensitive relay at the other, which in turn operated the sounder or an electromagnetic repeater. To send a message farther, a repeater could be used.This would suggest a message could have been sent 3000 miles via 6 automatic repeater links, but such an automatic and instantaneous routing would not be that efficient, given that an office in the center of the country would be passing traffic in all directions, and that it must be prepared to route a message from California to Quebec or New Orleans as readily as to Boston. The initial topography often followed the lines of the railroad, since the right of way was there and readily accessible compared to a cross country route. In the 1870's there was considerable discussion of separation of a "postal telegraph system" from the previous railroad telegraph system, to lower the very high message costs charged by Western Union. Western Union gained rights to erect telegraph lines along post roads by an 1866 act of Congress per The North American Review (1873), [4]. If a newspaper advocated a postal telegraph system , the telegraph company would increase their rates or cut them off from Associated Press press dispatches (p.98). The typical sequence of development of an interconnected network could not be easily found at Google Books, but no doubt lurks somewhere in telegraph journals of the 19th century. Science and Commerce (1872) says that by 1869 in the U.S. there were 4000 telegraph offices and 50,000 miles of lines. The topology of telegraph line construction was intended to maximize revenue and minimize expense by connecting the places likely to generate the most message traffic via the cheapest and most easily maintained routes. Then parallel or alternate routes were constructed, so that traffic could be maintained between distant cities if flood, wind, or ice took out one link. Edison (talk) 20:32, 14 December 2008 (UTC)

[5] from 1873 says that a message from Chicago to New York (792 miles per Mapquest) might have had an intermediate operator or repeater at Buffalo, New York (535 miles from Chicago, 395 miles from New York City). If conditions were poor, it might be necessary to transcribe and retransmit the message at Buffalo. So from , say San Francisco to Boston (3103 miles per Mapquest) the aforementioned 6 or 7 intermediate offices would likely be needed, to relay or retransmit the message. It is easy to envision a message destined for someone in Boston arriving at , say Chicago on a sounder, being transcribed from the sounder by one operator and handed via runner to an operator on the Chicago to Buffalo line for manual retransmission. It is not so clear how electromagnetic repeaters could be set up to relay the message arriving at an intermediate office to the next link in the transcontinental chain. I don't think that automatic systems like punched tape were used in the U.S. much in that era, like teletypes were later.Testimony before the U.S. Congress by Western Union officials in 1890 [6] said (p 23) a "heavy wire" which an experienced operator might work would be 400 to 600 miles long. A branch office where a novice operator worked might handle only 15 to 30 messages a day, and the operator's salary might be greater than the gross message charges. The railroad would cover the difference, since they needed telegraphic communications to coordinate rail traffic operations. Page 31 says that a ten word message including address and signature, going 2600 miles (straight line) from New York to San Francisco, cost $1.00 in 1890. This would be $22.80 in 2007 dollars per [7]. In Europe, a message going 1600 miles in 1890 (London to Russia) would be retransmitted over 13 circuits and cost $2.60 (59.28 in 2007 dollars). Edison (talk) 20:54, 14 December 2008 (UTC)

I remembered another question. Given that automatic routing did not yet exist, how many messages would an operator ignore for every one he needed to record? To put it another way, if I sent a message from Cactusburg to Fort Mugwump, how widely might it be heard? —Tamfang (talk) 02:13, 15 December 2008 (UTC)

I think there was a hierarchic hub-structure, with dedicated lines for "relaying". At any hub, as far as I know, re-transmission was performed manually (i.e. human), at least in the early days. Even up until fairly recent times, telephone switchboards were operated by human interconnect agents. So, your local operator would wire direct from Cactusburg-to-State-Capital on the local branch line; then the telegrapher at State Capital would transcribe and re-transmit by dedicated wire to Denver, and Denver to Fort Mugwump. I doubt there was any form of multicast (the way some non-switched internet hubs used to broadcast to many parties, and allow the receiving clients to decide to store, forward, or discard the message). That method is inefficient for megabit-per-second class automatic networking machines - it would be terribly redundant and inefficient at human re-transmit speeds! Nimur (talk) 07:03, 15 December 2008 (UTC)

Well, it seems like many telegraph lines were set up as party lines of sorts. I have here a 1941 Standard Handbook for Electrical Engineers, which in section 22 illustrates a simple closed-circuit Morse system with two terminals and one intermediate station. I won't copy out the illustration here, but on that system each station keeps its sounder on the line continuously, so every message would indeed normally be heard at every station on the line. There is also a note that the closed-circuit system is "almost universally employed in" the United States. This makes a lot of economic sense, really, since only one wire is needed to serve many stations, and as long as the traffic isn't too heavy it works out fairly well.

So, to answer two of your questions: all but the largest towns would likely have lines (or, really, a line) in two directions (and the largest towns would have the relay/central offices, interconnecting different lines); and your message would be heard all down the wire in every office on the same line, unless you were well off enough to pay for a private wire from one end to the other. This, of course, ignores such modern inventions as the Teletype, carrier circuits, duplex working, etc. 198.29.191.149 (talk) 20:08, 18 December 2008 (UTC)

I expect that when something of national interest happened, like Presidential election results or a championship prizefight, persons who could understand the clatter of the sounder and were friends with the operator would gather at the telegraph office to get the latest reports. For some events of this nature, the Associated Press dispatches would be posted in the window of the telegraph office, where a crowd stood watching. Edison (talk) 02:37, 16 December 2008 (UTC)

Nuclear Re-breather?

Could a diving outfit or spacesuit recycle the breathed out carbon dioxide back to oxygen by directly breaking it down with some sort of high temperature catalyst activated by very (thermally) hot radioactive material such as neptunium or polonium, allowing almost indefinite dives/spacewalks? —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 11:42, 14 December 2008 (UTC) Trevor Loughlin (talk) 11:44, 14 December 2008 (UTC)

No. Using radioactive elements is not a good idea. If the decay slow, there won't be enough heat. If they decay fast, they won't last long enough. (Let aside all shielding problems). Using high temperature to break down CO2 is not a good idea. It would recombine forming at least partly toxic CO. There should by better ways (I would think of some kind of electrolysis and catalysators and using the (waste) water, too). 93.132.142.96 (talk) 14:28, 14 December 2008 (UTC)

You can use radioactive elements as a long-lived heat source—there are a number of elements that produce a good balance of temperature vs. half-life. See Radioisotope thermoelectric generator. --98.217.8.46 (talk) 20:17, 14 December 2008 (UTC)

And, in this case, it would only need to last for the duration of the spacewalk or dive. Although, since it's unlikely that it could be synthesized right before either activity, it would need to last long enough to get from production to usage. I do agree that the risk of using radioactive materials would make this a dangerous way to scrub CO₂, however. StuRat (talk) 20:57, 14 December 2008 (UTC)

I guess the heat needed to split CO2 thermically far exceeds the heat needed to drive a radioisotope thermoelectric generator. And though the radioactive charge would have to be active just for the short time of the space walk there is no known way to stop it decaying the time before it is needed. If there was a way to catalyse radioactive decay things would be different. 93.130.187.185 (talk) 08:00, 15 December 2008 (UTC)

Children

Why need children to shout all the time? Whenever I see a group of more than 2 children they are shouting at full volume of their little lungs. It's not that they could not talk at normal levels or would not be understood when doing so. It must have to do withs psychology or sociology. Do they feel more important when they are shouting? Are they more respected by the others if they do so, or disrespected when they don't? What other reasons could there be? 93.132.142.96 (talk) 14:37, 14 December 2008 (UTC)

This is not consistent with my experience. DuncanHill (talk) 14:45, 14 December 2008 (UTC)

In any group, regardless of age, if people are constantly interrupting each other then they will tend to get gradually louder and louder until they are shouting since each person wants to be heard over the others. Perhaps that's what you were seeing? In which case, it suggests the group simply didn't have much respect for each other. That isn't unique to children and it also isn't universal among children. --Tango (talk) 15:08, 14 December 2008 (UTC)

I was in a trucking terminal once, talking to the dispatcher. His voice became louder and louder although there was little background noise. He suddenly realized what he was doing, and said he was sorry for yelling but he had to shout at truck drivers otherwise they would not pay attention to what he was saying. With unsophistacted people, you have to shout to make them realize that what you are saying is important. Something said in a moderate tone is considered to be just chitchat. In contrast, a more sophisticated person, like a college professor for instance, speaks in a moderate tone of voice when speaking of important things. - GlowWorm —Preceding unsigned comment added by 98.17.46.132 (talk) 16:01, 14 December 2008 (UTC)

I think DuncanHill is lucky, Tango is right and 98.17* refers to another aspect which I believe most children hadn't time to learn about (hopefully so). Picking up Tangos line of thought, would the shouting behavior be contagious? Obviously one or two in a group could lead the whole group to shouting but, would they also learn from that experience to start shouting on other occasions? Are there other contagious behavior patterns (be it with children or not)? I myself can't remember me shouting when I was a child but I attribute this to fact that if I did (I probably did) that it seemed quite normal so I had no reason to build a memory on that. 93.132.142.96 (talk) 16:12, 14 December 2008 (UTC

In my theory, the shouting is a direct consequence of the interrupting. That interrupting could well be "contagious". The idea that it is impolite to interrupt people is just a custom (a very practical custom, but a custom nevertheless) and we learn customs from those around us. If you consider it normal to interrupt people in one group you will probably do so in other groups as well and they will learn that that is normal behaviour, and so on. --Tango (talk) 17:29, 14 December 2008 (UTC)

I think the reason children often shout is to instinctively develop the strength of their voice. It is an instinctive behavioral trait inherited from their stone-age forebears. Humans are born with vocal cords, but in order to develop loudness, practice is necessary. So children often shout instinctively. They also instinctively like to run. Then, for instance, if a stone-age kid was out in the forest and encountered a dangerous wild animal he could yell loud enough to be heard from a distance and receive help, or could run fast enough to escape. Those abilities continued to be useful when the kid grew up. Women also sometimes scream instinctively when they experience a sudden danger or shock - it is a way of calling for help. They do it instinctively without thinking about it. Some sociologists and psychologists say that humans have only two instincts - fear of loud noise and fear of falling. I think we are loaded with instincts of many kinds, inherited from our stone-age forebears. And some of these instincts differ according to gender. I think psychologists could sometimes be more effective in their work if they realized that people are often motivated by instincts, and approached a patient's problem from that direction, when applicable. Unfortunately, stone-age instincts are sometimes not suited to civilization. The aggressiveness of males is probably the worst of our stone-age instincts. It was useful for survival in the stone age, but is now usually harmful. (However, non-violent competitiveness is very useful in getting people to do their best.) - GlowWorm

I suspect that looking for "evolutionary" reasons for the culturally-specific behavior of small children is a dangerous, just-so story sort of grounds. Neither I nor you know anything about the lives of "stone-age kids" other than some very tenuous guessing-games. --98.217.8.46 (talk) 20:22, 14 December 2008 (UTC)

I remember reading once (perhaps true, perhaps not) that when an African Grey Parrot squawks, its ears shut so it doesn't deafen itself. I have long suspected children have some sort of similar mechanism. ;-) --98.217.8.46 (talk) 20:20, 14 December 2008 (UTC)

Now for some advice on keeping the kids quiet:

1) Let them yell when outside but ask them to be quiet indoors ("use your indoor voice"). This will be more successful than never allowing them to shout.

2) Encourage games where only one kid speaks at a time, and without a timer. This will eliminate the need to shout down everyone else. One such game is where each kid adds a sentence to a story, then passes it on to the next kid in the circle.

3) Encourage activities that involve listening in a quiet room, like using a stethoscope to hear their heartbeats, or writing down everything they hear (the one with the most items wins).

4) When two kids are vying for your attention, pay attention to the quieter one first, and tell both that this is why you listened to that one first.

5) Encourage them to e-mail, IM, or text each other instead of talking on the phone.

6) When they use the computer, play video games, listen to music, etc., have them wear headphones. This can even be used for playing some instruments, like electric guitar or keyboards. There is the danger that they could damage their own hearing if they turn the volume too high, though, so monitor those sound levels.

7) If you can afford it, a play room with acoustic dampening would keep them from bothering the adults. StuRat (talk) 20:31, 14 December 2008 (UTC)

It is vibrant energy. You will find that hyperactive and loud kids have a lot of love. Exceptions noted, it is a good sign that somewhere today they will be loud and happy and someone with them will also be loud and happy and feel safe. Further to what StuRat says, God or somebody gave them little hands and feet. It is up to the adults to make use of these little hands and feet. If the child can walk, ideally they should have a little walk outside every day accompanying an adult from A to B. Football (of either shape) is a great pastime for little hands. Little legs that do not walk will stretch themselves every day and little hands that have nothing to do will thump or break something eventually. Also kids love to sing and you do not need to join the choir or train your voice to get them singing. It is easier to get your kid to sing and play football than it is to get them playing computer games. ~ R.T.G 00:33, 16 December 2008 (UTC)

BLAST not working?

I'm trying to determine the homology between genes (Homo sapiens) KAT2A and KAT2B at gene sequence and protein sequence levels. I'm using BLAST but it's giving errors for settings More dissimilar sequences (discontiguous megablast) and Somewhat similar sequences (blastn) and no output for Highly similar sequences (megablast).

Here are the accession numbers for the gene sequences of the proteins KAT2A and KAT2B. Could someone else try and report whether it works?

gi|89161205 gi|51511734 ----Seans Potato Business 15:45, 14 December 2008 (UTC)

I'm not familiar with this particular use of BLAST, but perhaps this page will help: [8]

Seems like another alternative would be to align the sequences and measure similarity. --Scray (talk) 17:24, 14 December 2008 (UTC)

That looks to be the same thing but on an older website. It also gives the same error. I'll speak to my supervisor tomorrow. I hate those databases so much... ----Seans Potato Business 17:50, 14 December 2008 (UTC)

Yes, I knew it was an older site, but it was more descriptive (and had a link to the new one).

I was curious and looked up your accession numbers on GenBank. They correspond to human chromosomes 3 (200 megabases) and 17 (79 megabases). It seems likely that the problem is not with the database tool, but the data being fed into it. It's important to know your data (by examining them) before applying analytical tools. --Scray (talk) 18:16, 14 December 2008 (UTC)

I don't understand. What was wrong with the the information being fed into it? The literature I've been perusing often talks about 75% homology between hGCN5 and PCAF. I set out to determine whether this was protein sequence or nucleotide sequence homology. What was wrong with my approach? ----Seans Potato Business 22:30, 14 December 2008 (UTC)

If you feed those two accession numbers to BLAST, you are asking it to align two (HUGE! - hence the error you received) human chromosomes and determine the homology (if I understand you correctly) - and less than 0.1% of the sequence would be your genes of interest. I think you may want to get accession numbers for the cDNA corresponding to your specific proteins of interest (unless you are interested in the introns, too). For example, NM_021078 and NM_003884 might be a little closer to what you want.

When you find yourself hating a tool that others enjoy, you might want to start with asking whether you're using it properly. --Scray (talk) 01:07, 15 December 2008 (UTC)

The BLAST-type algorithms are really designed to look for sequence similarities within an entire database of sequences, the vast majority of which will have no similarity to your query sequence whatsoever (as discussed above). They don't really do a great job of telling you the precise % identity anyways, since the output will only be those stretches of a target sequence that are even close to matching -- it will ignore any parts of the query and target that are completely NON-matching -- and thus may overestimate the % identity compared to what you would get if you were to calculate identity over the entire protein/gene.

As I understand your problem, you just want to know what the nucleotide identity and protein sequence identity are between two known genes. For this, you want something simple like Blast2 [[9]] or even a basic alignment program like ClustalX (see Multiple sequence alignment) if you have 3 or more sequences to align. In Blast 2 sequences, you enter two nucleotide sequences, select "blastn", and off you go. You can then enter the two peptide sequences, select "blastp" and you're done. The default parameters should be fine. The sequences listed above ([[10]] and [[11]]) look good and if you open them you'll see that both the peptide and nucleotide sequences are there. With these links, it should take no more than 10 minutes to assemble your sequences and run the comparison. ClustalX takes a little longer to set up initially but in the long run you'll want to know how to run a MSA so you might as well learn it! --Medical geneticist (talk) 15:10, 15 December 2008 (UTC)

foods changing color

Our stuffed cabbage rolls turn bright red inside, resembling raw. They test out at 170 degrees after having been cooked for 2 hours. I understand that cabbage might have too low of a pH, but I don't know how to correct the problem. —Preceding unsigned comment added by Nan17ski (talk • contribs) 16:03, 14 December 2008 (UTC)

Could you put a relatively high pH ingredient in them? Such as camembert cheese? My experience of cabbage is that raw is maroon red, cooked in water is a nasty blue colour, cooked with acid (I use apples and lemon juice) a nice red colour. Why you'd want them blue is beyond me. Theresa Knott | token threats 18:30, 14 December 2008 (UTC)

Bright red cabbage is no concern. There is nothing in the red dye in the cabbage that is harmful regardless of the color. Generally, high pH solutions taste, erm, soapy. I wouldn't think you'd want blue, soapy flavored cabbage. Nice, red, slightly tart cabbage sounds much tastier to me! Anyhoo, the article on pH indicators has a discussion of red cabbage at the end of the article... --Jayron32.talk.contribs 21:46, 14 December 2008 (UTC)

If you use meat in your stuffing, then that might be cured or treated with chemicals to make it look/stay fresh longer. (There are some that are legal and don't have to be labeled.) Using meat tenderizer {the chemical kind not the mallet) could also cause this effect. Use a different type of meat, recipe or source of meat. If some ingredient in your stuffing has a naturally high enzyme content, that might be the culprit. 76.97.245.5 (talk) 23:18, 14 December 2008 (UTC)

It depends a great deal on the ingredients. Cabbage roll recipes vary considerably. CBHA (talk) 23:46, 14 December 2008 (UTC)

Colourblindness

Can someone check the description of File:Philadelphia Biblical at Geneva.jpg and change the colours if they're wrong? Uploading the picture, I called the uniforms black and white, but being partially colourblind I can't always be sure — especially about the darker uniforms. Nyttend (talk) 16:19, 14 December 2008 (UTC)

They are indeed black and white, with the numbers on the back of the black being red. If you have image processing programs such as gimp, you can use color filters, mapping specific colors to black and white or whatever you like. 93.132.142.96 (talk) 16:29, 14 December 2008 (UTC)

Fabulous - both teams and the umpires all in black and white! DuncanHill (talk) 16:33, 14 December 2008 (UTC)

Thanks :-) My problem was that I knew the black-uniform numbers were red (I'm able to see some reds), but I didn't know if the uniforms were black or really dark red — the team's nickname is the "Crimson Eagles", so I thought there might be more red than just the numbers. Nyttend (talk) 16:56, 14 December 2008 (UTC)

Hmmm, did the All Blacks choose that name to help out the colorblind ? StuRat (talk) 19:13, 14 December 2008 (UTC)

For those of you watching in black and white, Spurs are in the all -yellow strip. DuncanHill (talk) 20:21, 14 December 2008 (UTC)

Driverless cars as means against IEDs

Is the US DoD or any similar organization looking into, or have mentioned interest in, using driverless cars to create fake targets for IEDs? How expensive should it be to create a mock-up Hummwee out of cardboard and with some dolls in it, and have it drive around like Stanley did? The aforementioned link does not say much about the cost of the modifications of the car taking place. Some machines, some coding, LIDAR equipment and GPS and so forth, am I not right in that this should be a cost-effective and neat way of countering IEDs? Imagine, for instance, to double the traffic in Iraq/Afghanistan, with half of all vehicles - trucks and hummwees alike - being just frames, dolls and equipment? 90.149.144.71 (talk) 18:59, 14 December 2008 (UTC)

How on earth could this be cost-effective? The cars with people in them can actually accomplish things OTHER than getting blown up. The decoy cars will cost a lot and do nothing OTHER than getting blown up (even assuming all of their technical aspects work fine and they don't end up running over an old grandmother or something). Net result is that defense still costs overwhelmingly more than offense, and you get a lot less for your money. As far as I see it. --98.217.8.46 (talk) 20:08, 14 December 2008 (UTC)

If they were too light they wouldn't trigger land mines, and I doubt if fake vehicles would fool anyone who manually triggers an explosion. I like the idea of functional unmanned vehicles, especially with high risk cargo like fuel and ammo, accompanied by attack copters and IED-proof tanks to deal with anyone who attacks them. StuRat (talk) 20:15, 14 December 2008 (UTC)

DARPA has had a fairly agressive program of research into driverless cars - they funded and organized the DARPA Grand Challenge with large prizes for robotic vehicles. However, I think the goal is to have driverless vehicles in convoys to deliver supplies and such - not to create fake targets. The TerraMax (vehicle) (which competed in the DARPA Grand Challenge event) is actually a fairly serious effort to make a robotic convoy vehicle. SteveBaker (talk) 20:33, 14 December 2008 (UTC)

This idea is older than you think. See Teletank. --Dr Dima (talk) 22:22, 14 December 2008 (UTC)

The problem has always been, how much money do you want to spend to IED-proof everything? As StuRat alluded, there is such a thing as an "IED-proof" tank - for most purposes, an Abrams tank isn't going to get knocked over by even the largest commonplace IEDs. But, it's not at all plausible to use Abrams tanks for every single convoy, cargo shipment, troop carrier, or even combat patrol. There aren't enough tanks, and they're expensive, and there are strategic issues pertaining to the use of armored tanks amidst a civilian populace. As the MRAP vehicles started to arrive in Iraq, Afghanistan, and elsewhere, the HMMWVs did not cease operations - but they were allocated to combat tasks differently. And the IED tactics changed in accordance (any intelligent insurgent knows better than to waste a small bomb on a large mine-resistant vehicle) - different strike patterns, different targets, different types of IEDs; EFP imports... saving up for big blasts, instead of lots of little ones.... It isn't clear that adding "dummy" vehicles will have any meaningful effect on IED hit-rates, American casualties, or anything else. Nimur (talk) 07:13, 15 December 2008 (UTC)

Interesting titbit: in Iraq they tried a project called "Forerunner" where the first Humvee in a convoy was remote controlled by a soldier riding in a following vehicle. They had some technical problems with it (lag), but the thing they found insurmountable was that the controlling soldier got sick due to the motions their body was feeling not matching the motions they were seeing in the controller headset. --Sean 15:56, 15 December 2008 (UTC)

A recent little note in the NYTimes Magazine says similar things happen with UAV pilots—they experience more stress and fatigue and etc. than regular ones because they don't feel the resistance of the air, etc. --98.217.8.46 (talk) 03:41, 16 December 2008 (UTC)

I don't buy that reason (and I know a LOT about UAV's because I personally built a good chunk of the Predator simulator). UAV pilots don't really "fly" the plane - in the sense of controlling it with a joystick, looking at the world through a camera on the plane. Most of the time, they click with a mouse on a map and the plane spends a few hours flying to that location on 'autopilot'. Sometimes a human pilot may land the UAV or do the takeoff with a joystick/camera in that manner - but it's increasingly rare - and the guys that do that are not the guys who control it throughout the mission. For UAV's in the gulf and Afghanistan, the landings and takeoffs are controlled by people out at the airstrip - but the mission itself is controlled from a bunch of guys in military command posts in the continental USA. (You can't do landing and takeoff via satellite links because the latency is too large.) The planes can stay up there for maybe 40 hours straight - so several shifts of 'pilots' will control the plane through the mission. But most of the time they'll give the thing a few 'waypoints' to fly to - an amount of time for it to fly around in circles ("orbit") taking pictures - then on to the next waypoint. Aside from the few mouseclicks once in a while, the plane handles itself throughout the mission. It's pretty much an office job - the guys aren't even in danger out in a foreign country - they get to go home to their families at night. The biggest manpower effort is in interpreting the photos - and planning mid-mission course changes to take account of the things they find out along the way. If people are getting stressed out and tired - it's likely to be because they have to work night shifts and the hours are probably long and mostly boring. SteveBaker (talk) 06:23, 16 December 2008 (UTC)

Human consciousness

Is there an upper limit? —Preceding unsigned comment added by 79.75.38.109 (talk) 22:16, 14 December 2008 (UTC)

Is there any particular reason you think of consciousness as a quantity? - Nunh-huh 22:18, 14 December 2008 (UTC)

The upper limit of the Glasgow Coma Scale is 15. --NorwegianBlue ^talk 22:42, 14 December 2008 (UTC)

In the philosophy of Buddhism, Nirvana is referred to as "consciousness without surface", this could be interpreted as the upper limit. Vespine (talk) 02:31, 15 December 2008 (UTC)

Perhaps, but without some measure to quantify (or qualify) consciousness the idea of an upper limit has no real meaning. If you're looking to measure some kind of "heightened consciousness" then the Glasgow Coma Scale isn't really suitable, since it's more a measure of unconsciousness than it is of consciousness. To be honest, I'm not even sure what a "greater than normal" consciousness would be, let alone how to measure it. – ClockworkSoul 02:41, 15 December 2008 (UTC)

I've no idea of what greater consciousness would be like but I'm pretty certain there's scope for enormous improvement in how people think, far far greater than the difference between us and chimpanzees. Dmcq (talk) 22:28, 15 December 2008 (UTC)

It's not really clear that consciousness has much to do with "thinking". We're beginning to discover that only a very small fraction of the brain is really responsible for consciousness - and that almost all of the serious business of thinking goes on at a level below consciousness. But the question doesn't entirely make sense - we don't have a measure of how conscious one person is compared to another - it's not even really clear that all people ARE conscious...we can ask them, and they usually say "Yes" - but are they REALLY conscious? Who knows? But since there is nothing to measure - and no way to measure it - there certainly can't be any concept of an upper limit. The lower limit is clearly "none" (like a rock or something). SteveBaker (talk) 01:00, 16 December 2008 (UTC)

Andromeda collision

I've read or heard that the Andromeda galaxy is on a collision course with the Milky Way. But how can this be correct if the Universe is expanding and all the galaxies appear to be moving away from each other? Is the speed of Andromeda's move towards us faster than the expansion? Jooler (talk) 22:47, 14 December 2008 (UTC)

Not every two galaxies are moving away from each other. Universe expansion only dominates on a very large scale; on a more local scale, some of the nearby galaxies move towards each-other and some move away from each-other. In a vastly oversimplified manner, think of it as a competition between some initial velocity (with which galaxies move away from each other) and gravitational attraction between nearby galaxies (which makes them accelerate toward each-other). Andromeda Galaxy is a part of the Local Group, and interacts gravitationally with our galaxy. Hope this helps. --Dr Dima (talk) 23:23, 14 December 2008 (UTC)

This might help: Put some billiard balls (or baseballs, ping-pong etc.) on a table in a bunch then punch one into the middle hard enough to make the bunch fly apart. You will notice that some balls knock into each other while still all moving away from the former center of your bunch. (This is only to visualize it, it's not meant as an exact model. before s.o. bites me.)76.97.245.5 (talk) 00:49, 15 December 2008 (UTC)

The Expansion of the Universe is still a theory and in all probability incorrect. A lot of noted cosmologists disagree with the interpretation of Cosmic Microwave Background Radiation and redshifts on a galactic scale. Ironically, Edwin Hubble himself didn't like the Doppler-effect interpretation of his redshift findings. Nevertheless his name is given to the constant supposedly indicating the Universal rate of expansion. Rotational (talk) 21:00, 15 December 2008 (UTC)

What is "still a theory" meant to mean? Science only does theories, there are no absolute facts. The expansion of the universe is pretty universally (no pun intended) accepted. The details may be debated, but the basic idea that the universe is expanding is not disputed to the best of my knowledge. --Tango (talk) 21:35, 15 December 2008 (UTC)

The rate galaxies move apart is proportional to their current distance apart. For nearby galaxies, gravity is sometimes "stronger" than the expansion, so they move towards each other (or orbit each other). --Tango (talk) 21:35, 15 December 2008 (UTC)

To put some numbers on that - the speed of the expansion is roughly 70 km per second for every million parsecs of current distance. Andromeda is 0.77 million parsecs away - so the expansion of space is moving it away from us at around 50 kilometers a second. If it's natural motion through space (well, technically - the sum of our motion and it's motion) is more than 50km/sec towards us - then we'll collide with it - if it's slower than that then it'll never reach us. But it's approach speed is 300 km/s - so it's moving about six times faster than the expansion of the universe. That's a surprisingly close thing - I guessed that the expansion of space at these relatively close distances would be tiny. SteveBaker (talk) 01:23, 16 December 2008 (UTC)

That's more than I expected as well, interesting. That means the various galaxies orbiting each other will be orbiting with orbits that don't obey Kepler's laws - if I'm thinking about this right, their orbital velocities should be slower than Newtonian mechanics would predict (so they would spiral in if it weren't for the expansion). --Tango (talk) 13:50, 16 December 2008 (UTC)

"Kepler's Laws"?? Are they facts or theories? Or perhaps they don't fall in the domain of science. You must get used to the idea that systems have degrees of credibility and move subtly from more credible to less credible or in the other direction, depending on how well they are supported factually. ciao Rotational (talk) 20:55, 16 December 2008 (UTC)

I'm well aware of how science works, thank you. Kepler's laws are physical laws, they aren't facts (which don't exist in science) or theories (which contain explanations [well, definitions vary] - you need Newton's theory of gravity to explain Kepler's laws). Kepler's laws hold extremely well for describing orbits in the solar system, which is what Kepler had in mind when he worked them out. They don't apply on relativistic or cosmological scales, and we wouldn't expect them too. What is interesting is that galaxies within the local group count as "cosmological scales", when both SteveBaker and I were under the impression you needed to go to larger scales before the corrections became significant. --Tango (talk) 21:09, 16 December 2008 (UTC)

Well, I don't know that you do if you have the notion that Science only does theories, there are no absolute facts. For heaven's sake, did you think about that sentence for even a moment? When I tell you that the area of a circle is pi r squared - that is a fact, or does mathematics not fall under the science heading? If I tell you that there is a proton lurking somewhere near the centre of a hydrogen atom, do you call that a theory? I'm truly puzzled. Rotational (talk) 21:27, 16 December 2008 (UTC)

No, mathematics does not full under the science heading. Science is built around the scientific method, maths is built around mathematical proof. They are completely different things (the former is empirical, it's based on observations, the latter is logical, it's based on step by step deductions from a given premise). The idea that hydrogen contains a proton is part of any modern theory of particle physics you may come across, but they are all theories. They are theories with an enormous amount of supporting evidence so the chances of them being significantly wrong are negligible, but they are still theories. There is nothing more they could be. --Tango (talk) 22:17, 16 December 2008 (UTC)

You certainly do have some strange ideas...... and supporting evidence, according to you, does not consist of absolute facts either ("there are no absolute facts"), but you nevertheless use it to bolster the credibility of theories. Does that not strike you as strange that you use evidence which has no 'absolute facts' to support and build a theory with which to better understand the world we live in? The structure you build seems very wobbly indeed. ciao Rotational (talk) 13:26, 17 December 2008 (UTC)

If you think the scientific method is a strange idea, then yes, I do. I guess you could call empirical observations "absolute facts" but they are just statements about the past, so aren't particularly useful by themselves. They only become useful when we use them to make predictions about the future, and those predictions are not absolute. To use your example, observing one hydrogen atom and seeing it has a proton in the middle (if such a direct observation were even possible, which it isn't) would not guarantee that a different hydrogen atom, or even the same hydrogen atom ten minutes later, would have a proton at the centre of it (it's extremely likely, but not certain). --Tango (talk) 14:01, 17 December 2008 (UTC)

No, I don't think the scientific method is strange, but rather your interpretation of it. A lot of mathematical theorems start from empirical observations. Mathematics is anything but a logical and consistent structure. A premise or axiom is simply another name for a reasonable assumption and a structure which is based on an assumption is inherently flawed. If you are not aware of Gödel's incompleteness theorems then you might profit by studying them closely. ciao Rotational (talk) 07:08, 18 December 2008 (UTC)

Which, thinking about it, means estimates for the masses of galaxies based on their motion through space must depend on estimates of the Hubble Constant, which I believe are still only accurate to +/- a few percent. That puts a big limit on how accurate we can get such mass estimates. --Tango (talk) 13:53, 16 December 2008 (UTC)

You may be conflating two separate types of "expansion": the expansion of the matter within the universe due to inertia (the billiard balls above), and the metric expansion of space (the ant on a rubber band) which is only measurable at scales larger than the distance between the Milky Way and Andromeda.—eric 18:51, 16 December 2008 (UTC)

Who is that comment directed at? To the best of my knowledge, there is no (net) expansion due to inertia on any scales greater than a planetary nebula. The only relevant expansion in this discussion is metric expansion - the references to billiard balls above were just attempts at very rough analogies to get the basic idea across. In fact, there are rather poor analogies - the billiard balls moving towards each other is just a matter of the balls moving randomly with a general trend towards expansion, there are always going to be some moving against the trend. With galaxies the trend is proportional to distance which changes things considerably. --Tango (talk) 19:08, 16 December 2008 (UTC)

See: Metric expansion of space#Local_perturbations, and the statement in the article's introduction that: "In the present era they contribute in roughly equal proportions." Does that article need changed, or am i misreading it?—eric 20:43, 16 December 2008 (UTC)

If my understanding is correct, that paragraph is extremely badly written to the point of just being wrong. I know what it's trying to say - the universe is expanding both because it started expanding at the big bang and is carrying on going, and also because the cosmological constant is "pushing" it out, causing the expansion to accelerate. However, it's all metric expansion, it's space expanding, not matter moving out. The space itself has some kind of inertia (don't ask me how that works...), it's not the matter in the space that has inertia. If it was matter having inertia then it would be expanding outward from a central point rather than everything moving away from everything else. --Tango (talk) 21:23, 16 December 2008 (UTC)

That number (70km/s per megaparsec) is truly amazingly large...the fastest man-made object (well, kinda) is the Voyager 1 spacecraft which is leaving the solar system at a speed of around 17km/s. Our galaxy is 0.03 megasparsecs across - so the galaxy is expanding at around 2 kilometers a second...which means that Voyager will almost certainly (eventually!) manage to leave our galaxy - but it'll never reach another galaxy unless one that's already nearby happens to be heading this way at a pretty good clip! That's a stunning result. SteveBaker (talk) 18:56, 16 December 2008 (UTC)

Stunning, but extremely misleading - you've neglected gravity. Our galaxy isn't expanding since gravity compensates for the expansion, likewise with galaxies within the local group. The expansion will affect the orbits (as I mentioned above), but they are still in fairly stable orbits (except for those that are so eccentric they intersect each other, as may be the case with us and M31, or galaxies which aren't actually part of the local group but are just passing through [I don't know if there are any such galaxies in our vicinity]). --Tango (talk) 19:08, 16 December 2008 (UTC)

I've heard this claim before - that the metric expansion of space does not affect gravitationally bound systems. But why not? I understand it for chemically bound systems, which are held together by a balance of forces - attraction between electrons and nucleus, and repulsion between nuclei, so that moving two atoms apart increases the net attractive force between them. But for a gravitationally bound systems, attraction drops off with (the square of) the distance. So what keeps two objects together if the space between them grows? --Stephan Schulz (talk) 19:42, 16 December 2008 (UTC)

I don't know... I've never thought about it, but now I'm trying to and I can't work it out. If two objects are orbiting each other and you move them further apart their orbital velocity would be too high for the new distance and the (average) distance would increase, not decrease... That would suggest you can't have stable orbits at distances and over timescales where expansion is relevant, which doesn't seem to fit with my knowledge of the local group. Can anyone help me here? --Tango (talk) 21:23, 16 December 2008 (UTC)

Hmm. Thinking about it from another angle: Does the metric expansion of space between two attracting bodies increase the potential energy between them? Or that of the universe as a whole? --Stephan Schulz (talk) 21:56, 16 December 2008 (UTC)

Gravitational potential energy just depends on distance, not on where that distance came from, so I guess it does... Energy isn't really conserved in GR (it's complicated and I don't remember the details), so that's not entirely surprising. --Tango (talk) 22:12, 16 December 2008 (UTC)

Hmmm. Having slept over it: Wouldn't the metric expansion appear to be a force that accelerates the bodies apart? This force is proportional to the distance between the two, so while the s in W=F*s increases, the F decreases. I suspect this cancels exactly out, but I'm to lazy to do the maths. --Stephan Schulz (talk) 09:03, 17 December 2008 (UTC)

I'm not sure it's meaningful to talk about the potential energy due to the expansion (it's more inertia than potential energy, although it's not inertia as we usually mean it). The potential energy due to gravity should increase. --Tango (talk) 13:09, 17 December 2008 (UTC)

Perpetual motion by universal expansion

(inindent) So why aren't the free-energy nuts thinking in terms of extracting energy from the expansion of the universe? If I had a machine that lifted bowling balls up onto a nice high shelf - waited a bit for the universe to expand - then recovered the energy it put in by letting the bowling ball fall off the shelf - wouldn't it (as a thought experiment) extract energy from nowhere? (I can't believe I just posted my first perpetual motion machine idea to the science RD - I'd better go away and atone for my sins!) SteveBaker (talk) 20:02, 17 December 2008 (UTC)

Well, read and rethink my comment above. I don't think so, by now. The ball will move away from you - and, if you wait for it to get further away, it will move faster. If you get it back, part of the potential energy will be used to stop that movement. Where is a good Einstein if you need one... --Stephan Schulz (talk) 20:28, 17 December 2008 (UTC)

But nothing is actually moving, it's just space getting bigger. Here's a version of the thought experiment that doesn't involve shelves (I can't work out quite how the shelf behaves!): Start with two masses in one place, propel them apart using a given amount of energy. Ignoring expansion, they will gradually slow down and fall back together due to their mutual gravitational attraction, crashing into each other with the same amount of energy as you gave them to start with. However, with expansion, they will have farther to fall than they had to climb, which means more time to accelerate, which means more energy when they collide. Ergo, we have energy created from nowhere and the ref desk has invented its first perpetual motion machine! (I'm going to try and work out the maths now, it may take some time!) --Tango (talk) 20:38, 17 December 2008 (UTC)

That's essentially the same at the Mk I machine above...one of my masses is the planet Earth, the other is a bowling ball. I guess you're right though - we don't need the shelf. SteveBaker (talk) 22:40, 17 December 2008 (UTC)

Indeed - same thought experiment, just reworded to get rid of the confusing shelf (something has to hold the shelf up, and that same thing probably holds the shelf down against the expansion, too). --Tango (talk) 23:04, 17 December 2008 (UTC)

Ok, it's been too long since I've solved a differential equation! I can't even get the non-expansion case to work properly. I'll leave the maths to someone else... --Tango (talk) 20:57, 17 December 2008 (UTC)

Yeah - you see that's where we always go wrong. A proper perpetual motion machine designer would just know it was going to work - making the math entirely unnecessary. It's a shame it doesn't need magnets or gyroscopes though - those never fail to improve any perpetual motion design. SteveBaker (talk) 22:34, 17 December 2008 (UTC)

We can probably reword it to include the term "cosmological constant" a few times - that has to help, long words always do. --Tango (talk) 23:04, 17 December 2008 (UTC)

Oh - certainly! Then if anyone says it won't work - you can throw masses of confusion into the mix by leveraging Einstein's confusion over the constant. Quoting his papers during the period of that confusion should enable you to reap many rewards. Nobody on some stupid amateur reference desk is going to attempt refute actual references from a peer reviewed scientific paper written by that guy! If they do, you just casually mention 'Dark Energy' and the remaining stalwarts will fall over in apoplexy.

I'm going to re-ask this question at the bottom of the desk. This is an interesting problem and the debate is scrolling off the RD before it gets addressed. SteveBaker (talk) 21:23, 18 December 2008 (UTC)

Speed of sound in SF6

The page does not tell us. Can anyone else? —Preceding unsigned comment added by GreenSpigot (talk • contribs) 23:31, 14 December 2008 (UTC)

Did you read speed of sound which tells you how to calculate it? or SF6 which says sound through the gas is 0.44 times the speed of sound in air. which is about 150 meters per second. Graeme Bartlett (talk) 00:17, 15 December 2008 (UTC)

For serious detail, try Speed of sound in compressed sulfur hexafluoride, V Vacek, et al.. – ClockworkSoul 00:28, 15 December 2008 (UTC)

Thanks Graeme. I Missed the entry under 'physiological effects etc'. Speed of sound is not in main table. where can I get some SF6? —Preceding unsigned comment added by 79.75.38.109 (talk) 02:33, 15 December 2008 (UTC)

Safety discussion removed. See talk. Dragons flight (talk) 22:22, 15 December 2008 (UTC)

It should be noted that this gas is hazardous to inhale - though non-toxic, it can displace oxygen and cause suffocation. If the intention is to use the gas for novelty voice effects, you should reconsider based on informed understanding of the possible hazards. Nimur (talk) 07:17, 15 December 2008 (UTC)

I have reposted my original comment, which apparently spawned an entire debate on safety. I stand by my comment in its original form, and I'm frankly baffled how it could be mis-interpreted - there are possible hazards and you should base your decisions on informed understanding of them. Nimur (talk) 15:20, 17 December 2008 (UTC)

Just noticed the hoohah on the talk page. Actually, I was inquiring about SF6 as a possible filler for a loudspeaker cabinet (to increase its apparent volume). I have no intention of deliberately inhaling it. IMO it seems no more dangerous than CO2 as an asphyxiant but Im not going to try it.--GreenSpigot (talk) 23:57, 16 December 2008 (UTC)

At the risk of increasing the volume of the hoohah (and since you asked)... the problem with dense gasses is that it's hard to expel them properly from the lungs - so they just sit there - making your breathing much less effective and starving you of oxygen. However, CO2 is special - we've evolved to detect that we have the stuff in our lungs and we take deep breaths and pant and do other things we need to do to get rid of it when it accumulates. I'm not 100% sure - but it's very likely that SF6 doesn't provoke that reaction...so you can run out of oxygen without ever feeling short of breath or gasping or doing any of the things your body is supposed to do. That problem definitely exists for helium (that's how come divers can breath oxygen-helium mixtures for deep diving) - except that because your mouth is higher than your lungs - the stuff tends to float out by itself. People do still die from playing around with helium - but it's not as bad. People often claim it's safe because they've done it lots of times - or they saw someone doing it - but that's hardly proof. I've crossed the road lots of times and never been hurt doing it - does that mean that nobody ever dies crossing the road? With helium, it's reasonably safe if you do it just once and deliberately (and unnecessarily-seeming) take a good number of deep breaths in and out immediately afterwards - but if you do it ten times in a row because it's funny and you feel fine right afterwards...until you fall over and die for no obvious reason! It seems reasonable that SF6 would be more dangerous than that - but if you took safety precautions and knew how to do it safely - maybe it would be OK once in a while.

As for your speaker. The speed of sound in a gas is proportional to the square root of one over the density - so a 6x denser-than-air gas would have a speed that's sqrt(1/6) times that of air - or about 0.41 times slower. Since frequency=velocity/wavelength - if you keep the frequency the same - and the velocity gets slower because of the denser gas - then the wavelength has to get shorter to keep the equation correct. That's certainly going to alter echoes and vibrations, but I don't know enough about speaker cabinet design to know whether that's good or bad. I agree that it seems at first sight that it would make it sound like an 0.41 times bigger cabinet - and I know that BIG speaker cabinets are always in evidence in the homes of all audio nuts...so they must be good...right? So I think that this is a good idea - whether you can keep the stuff inside the cabinet without messing up the acoustics - I don't know - but big molecules don't escape so easy as little ones so there ought to be a wide choice of effective liners that would do the job. SteveBaker (talk) 02:54, 17 December 2008 (UTC)

I thought of sealing the gas in a polyethylene (or other flexible film) bag and stuffing that inside the cab. So I get 4cu ft effective volume in a 2 cu ft cab. Not sure if its been done commercially.--GreenSpigot (talk) 12:14, 17 December 2008 (UTC)

Yeah - exactly. I think that will work rather well - but the kinds of issues that bother me are whether the polyethylene bag will 'rustle' and mess up the acoustics - or whether maybe the sound would bounce off of the bag rather than travelling through it. If you were working with (for example) helium - that wouldn't work too well because the teeny-tiny helium atoms can sneak out between the polyethylene molecules of the bag - so it'll deflate in a day or two. But SF6 is a honking great huge monster of a molecule - so it will probably stay in the bag indefinitely. These are only details - but they are probably important ones for practical use of such a thing. But if you can find someone (maybe a local university chemistry lab) who might have a cylinder of the stuff and be prepared to give you a few cubic feet - it sure would be an interesting experiment! SteveBaker (talk) 19:56, 17 December 2008 (UTC)

No doubt there will be some question of acoustic impedance matching between the air at the back of the loudspeaker cone and the bag; and the bag and the gas. And then the matching from the gas via the bag to the air in the reflex port (if used). Also the bag must be made from a flexible 'quiet' material (like a rubber balloon maybe) that does not create additional noise. My gut feeling says it should work but I'm not sure how to prove it other than by experiment.--GreenSpigot (talk) 03:04, 18 December 2008 (UTC)