Wikipedia:Reference desk/Archives/Science/2010 August 2

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August 2

Units of Time

Are there any natural units for measuring time not based on the movements of the Earth?

Like, say you were far out in space trying to communicate to an alien how long a day on Earth is, what unit of measurement could you use that's universal? Are there any longer than the amount of time it takes hydrogen to perform a hyperfine transition? Just curious. 108.3.173.100 (talk) 00:26, 2 August 2010 (UTC)gejl

The most natural unit of time is the Planck time. There's a bit or arbitrariness to do with factors of pi, but otherwise it's something that aliens with similar understanding of physics to ours should share. The Planck time is very short, though, so doesn't answer your second question. The Hubble time is very long, but also pretty fundamental. --Tango (talk) 00:30, 2 August 2010 (UTC)

It's "natural" in a physics-y sense of "being based of fundamental physical quantities". However, it's not particularly "natural" in the colloquial sense of being familiar and easy to recognize. I would also point out that the Planck time has a standard uncertainty of 5×10⁻⁵ which is pretty crappy. This is mostly due to our difficulty in measuring G. By comparison, the best atomic clocks have a precision ~5×10⁻¹⁶ at measuring a second as defined to be "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom". If we wanted a really rigorous comparison, I think we would definitely tell them something based on an atomic clock. For a quick and dirty comparison, it would probably make more sense to use a simpler physical process that is easily accessible such as the half-life of a common radioactive decay. Dragons flight (talk) 03:17, 2 August 2010 (UTC)

Assuming the alien can understand multiplication/exponents, is there anything wrong with applying those the tiny units? $\sim$ Lenoxus " * " 00:49, 2 August 2010 (UTC)

Accuracy. As mentioned above, Planck time is only measured accurately to around 5x10^-5 (confirm here at NIST.gov). 50 ppm might seem tiny - but for frequency stability, it's actually really terrible - we've had better frequency-stability technology for literally thousands of years, even using shoddy "oscillators" like pendulums and water clocks. If a clock drifted with 50 ppm of timing error, it would accumulate about a half-hour of error each year. This would definitely become problematic. A modern run-of-the-mill off the shelf digital watch uses a quartz oscillator with an (electronically compensated) accuracy of around 1e-8 (and you can still tell a few seconds of drift per month or so). A modern scientific timing system can achieve many orders of magnitude better frequency stability by using even better oscillators, like atomic resonances or cesium decay rates. For practical purposes, this means that we can trust our clocks accurately enough to synchronize distant electronics and computer systems to a very high degree of precision and accuracy - making possible things like phase shift encoding in GPS and mobile telephones. Better frequency stability in such technologies directly corresponds to higher achievable data rates. Nimur (talk) 15:41, 2 August 2010 (UTC)

The primary unit of time, the second, is now defined using an atomic clock. Atomic clocks don't rely on movements of the Earth, Sun, moon or any other celestial body. Dolphin (t) 02:58, 2 August 2010 (UTC)

...but first you would have to tell the alien which atomic clock to use. To be understood, a message usually implies a particular time base e.g. to demarcate successive words or symbols. See Arecibo message which was an exercise in constructing a message that an alien might be able to interpret. Cuddlyable3 (talk) 18:36, 2 August 2010 (UTC)

A message can contain its own definition of temporal units: "The duration of the transmission of this sentence is one grondlewipple." - since the aliens can directly measure the duration, they now know how long a grondlewipple is. Obviously you'd have to allow for relativity - but that should be a relatively simple thing for the aliens to estimate. SteveBaker (talk) 00:08, 3 August 2010 (UTC)

In a practical sense, many digital communications protocols use the above technique described by SteveBaker, incarnated by engineers in the 1950s and 1960s in the form of clock sync protocols. For example, an ethernet PHY message usually starts with something like 41 sets of eight-bit "10101010"s, so that the timing and phase can be established exactly; message starts with the last set "10101011" - so even if the signal is garbled or your receiver didn't know when the actual message began, at the same time, you have a clear indication when the timing information is done and the message is about to start. More sophisticated schemes, like autonegotiation, also exist, with the ability to specify frequency and other communication parameters. And in the packet radio community, a variety of more noise-resilient techniques exist, as well as better ways to distinguish a message from non-message noise. Whether these techiques would be useful for conveying timing information to a receiver who was unfamiliar with the protocol is up for debate. Nimur (talk) 17:05, 3 August 2010 (UTC)

Given several relevant elements in a large number of objects plus a good understanding of statistics, radioactive half-life could probably be used to define a standard "basket" unit with a low margin of error. 63.17.39.134 (talk) 03:53, 6 August 2010 (UTC)

Precambrian rabbits and natural fossil exposure

A thought just occurred to me on the subject of Precambrian rabbits. Occasionally, natural events like erosion will expose fossils which date from tens of millions of years prior. Given this, couldn't an organism die immediately on top of or next to such a fossil site, after which the whole thing gets covered in sediment, resulting in "distant neighbor" fossils?

To put it another way: Given this small possibility (unless, as is far more likely, it's not a possibility), why is the fossil record so consistent? Why are there (at least) no Triassic rabbits? $\sim$ Lenoxus " * " 00:46, 2 August 2010 (UTC)

Because the experts are aware of this issue and take it into account. The rock the recent organism is fossilised in would be different from the rock the old fossils are in, so you would be able to tell that something had happened. Working out the ages of different layers of rock can be a bit of a challenge, but it can be done (in various ways). --Tango (talk) 00:55, 2 August 2010 (UTC)

As stated by tango, geologists understand the processes by which rock formation and erosion can occur; in fact rocks are often dated by index fossils, which determine their age. Thus, finding a rabbit lying in a rock layer which was immediately on top of a trilobite wouldn't lead people to conclude that the rabbit was really old, rather that the rock layer the rabbit was in was much younger than the one the trilobyte was in. --Jayron32 03:27, 2 August 2010 (UTC)

I had a strong feeling it would be something like that (since that relates to how they're able to tease apart folded strata); thank you both! So, now I'm wondering… has the situation I described ever happened? That is, are there any known "distant neighbors" (where the rocks are obviously quite different, etc)? If not, any particular reason why not? $\sim$ Lenoxus " * " 04:48, 2 August 2010 (UTC)

You'll want to follow the threads that lead from the article titled Stratigraphy, which is the science of reading and interpreting rock layers. Undoubtedly, examples exist of local areas where two non-sequential rock layers lie side by side. I cannot think of one specific example, but that's more a function of there being so many rather than being so few. --Jayron32 04:59, 2 August 2010 (UTC)

The specific term, BTW, for such a situation is an Unconformity. Examples given in that article show pictures of adjascent rock layers which are actually represent gaps of up to 1 billion years. --Jayron32 05:02, 2 August 2010 (UTC)

It does happen that sometimes fossils get into layers they don't belong in. Most commonly it is a case of older fossils getting incorporated into younger rock -- this can happen if the soft rock they are embedded in erodes away, leaving the fossil behind to be covered by younger sediment. It's much harder for younger fossils to get incorporated into older rock. Looie496 (talk) 05:44, 2 August 2010 (UTC)

A closely related phenomenon happens all the time in archaeology. In those cases, you end up with different soils rather than different rocks, but it's still (usually) quite obvious when it's occurred. During a proper excavation, you make note of all visible stratigraphic layers, as well as any and all discontinuities you find. There are a variety of pedological assays you can have done to help out, but for the most part a detailed visual inspection is all that's required. Matt Deres (talk) 14:07, 2 August 2010 (UTC)

Depression Medication

A while back I saw an article that showed which type antidepressant is more likely to work in what type of people. I can't remember the different categories they had for the type of people. Has anyone seen it? —Preceding unsigned comment added by 76.169.33.234 (talk) 05:04, 2 August 2010 (UTC)

That's rather vague, and could describe every single antidepressant; each probably works better in some types of depression than others. You could explore Category:Antidepressants yourself to see if you can dig it up. --Jayron32 05:07, 2 August 2010 (UTC)

The most common types of depression are major depressive disorder and bipolar disorder, and they are usually treated with different types of drugs -- the articles will give you more information. Looie496 (talk) 05:39, 2 August 2010 (UTC)

There's also a list of antidepressants which might be of use. Smartse (talk) 08:48, 2 August 2010 (UTC)

Contact between shaft and bearing

hey i want to know on what basis the contact(clearence,angle)between shaft and bearing(journel,liner) because am installing new roller of shaft dia 320 and my liner is of dia 320, its is a semi spherical(only i have liner at bottom half)??? and why???? —Preceding unsigned comment added by 82.129.222.71 (talk) 09:25, 2 August 2010 (UTC)

There's some basic info here on the hows and whys of journal bearings [1] does yours match any of these types?77.86.94.177 (talk) 12:53, 2 August 2010 (UTC)

It's not clear if the bearing is a Plain bearing - it might be - one reason for only having half a cylinder would be if the bearing was supporting a force that was predominately in one direction - eg a heavy weight - is your bearing of this type? 77.86.94.177 (talk) 15:50, 2 August 2010 (UTC)

Electrolysis

What are the typical values of current and voltage required for the electrolysis of water? In the current industry what power input do they use, is it mostly of national grid systems? Thanks very much--91.103.185.230 (talk) 11:15, 2 August 2010 (UTC)

You need to use DC if you want to separate the hydrogen and oxygen. A minimum voltage would be around 1.5 volts DC. In my experience, 24 volts DC works fine; add some baking soda, sodium hydroxide, or sulfuric acid for the electrolyte. Current might be 100 milliamps. --Chemicalinterest (talk) 12:11, 2 August 2010 (UTC)

The minimum voltage required for water electrolysis is 1.23V (see Electrolysis of water). However the overpotential needed at the electrodes is ~1V (depending on electrodes). Additionally producing the gas at above 1atm pressure also increases the voltage.

The current directly controls how much water is electrolysed per second.

The voltage used therefor will be roughly 2+IR where I is the current, and R is the internal resistance of the electrolysis cell.

Also see http://www.hydrogenassociation.org/general/faqs.asp and this google books Hydrogen fuel: production, transport, and storage By Ram B. Gupta p.162-163

Commercial cells produce work at high pressure. This link http://www.nrel.gov/docs/fy04osti/36705.pdf gives typical figures - there are high and low pressure cells, and electrolyte of KOH is used to reduced cell resistance. As with all processes that use electricity as a feedstock hydroelectric power is common.

Using the wattage figures in the nrel.gov link above you can work out the typical current values using V=~2V after taking into account the efficiency. However note that typical cells are connected in series, not parallel -so the figure may be a sum of the currents going through the cell rather than the supply voltage/current.77.86.94.177 (talk) 12:15, 2 August 2010 (UTC)

Here are some commercial low pressure cells from Statoil : [2] they use ~4000Amps (max) - voltage depends on number of cells.77.86.94.177 (talk) 13:12, 2 August 2010 (UTC)

It depends whether the OP is talking about commercial electrolysis or laboratory electrolysis -- I was talking about the latter. --Chemicalinterest (talk) 14:16, 2 August 2010 (UTC)

Seems like the question quite directly tells you his context... DMacks (talk) 14:41, 2 August 2010 (UTC)

Fennec Hare

Is there any such animal as a Fennec Hare? This page says they are critically endangered, and one has just been born in captivity. However the photo looks like a kitten 'shopped to have bunny ears, and it's supposed to have been born in North Korea. Is this nonsense, propaganda, or maybe possibly true? 213.122.216.120 (talk) 12:53, 2 August 2010 (UTC)

In case you aren't aware, the Fennec fox does exist, but I still very much doubt the authenticity of the article (the misspelling in the URL doesn't fill me with confidence). The "Iperian steppe" doesn't exist, and here is also doubtful. In short: no. - Jarry1250 ^{[Humorous? Discuss.]} 13:21, 2 August 2010 (UTC)

So this was our April Fool's joke in 2009. Amusingly, it inspired a number of would-be conservationists and some additional Photoshopping (try Google Image searching "Fennec Hare"). Here is our April Fool's joke from 2010 - http://www.zooborns.com/zooborns/2010/03/rare-baby-skeksis-chick-born-at-franklin-park-zoo.htmlDeKreeft27 ^[Discuss.] 14:09, 2 August 2010 (UTC)

Keep in mind: Wikipedia has an article on everything: cabbit. Nimur (talk) 16:44, 2 August 2010 (UTC)

That is excellent. Was a baby mystic also born simultaneously to the skeksis? APL (talk) 19:43, 2 August 2010 (UTC)

documentary

Anyone know of a good documentary on bees / wasps / ants? 82.43.88.151 (talk) 13:10, 2 August 2010 (UTC)

This is maybe too specific, but Queen of the trees is about fig wasps and is the best documentary I've ever seen. For army ants, see this BBC page, you should find some other videos on there too (sorry not sure if they work outside of the UK). There have been a couple of recent films about colony collapse disorder which I imagine would discuss bees more generally as well. Smartse (talk) 15:05, 2 August 2010 (UTC)

(ec)Below are links to video documentaries about

bees, sand wasp, Ichneumon Wasp, paper wasp, fairy wasp, ants (old film), and ants (new film). Cuddlyable3 (talk) 15:24, 2 August 2010 (UTC)

So are you vouching for them as being good? (Did you even watch them?) Because I'm sure the original poster can use Google/YouTube as well as you can. They're asking about quality. --Mr.98 (talk) 16:35, 2 August 2010 (UTC)

I do not take it for granted that all videos at YouTube are good and therefore I looked at all of them. Several are by David Attenborough or have National Geographic logo that IMO also speaks for quality. Cuddlyable3 (talk) 18:24, 2 August 2010 (UTC)

This one of wasps attacking a bee hive is so amazing it's hard to even believe it's real. --Sean 16:59, 3 August 2010 (UTC)

Real life lightsaber

In this video, http://www.youtube.com/watch?v=6G8VztSWnVo Michio Kaku describes how to make a real life lightsaber. Of course being the geek I am, I loved it. But are there any problems with his design? Any way to improve upon it? Would 12,000 degree plasma be sufficient to cut/burn through almost anything? What would the plasma look like? Color? 148.168.127.10 (talk) 14:24, 2 August 2010 (UTC)

It would likely function, but you will he holding 12,000 degree plasma in your hands. How thick will the insulation need to be to avoid burning yourself? Remember, his design fills the "insulation" area with batteries - which aren't great insulators. In fact, he doesn't explain how we keep the batteries from melting. In the end, it is a heat saber, not a light saber. -- kainaw™ 15:49, 2 August 2010 (UTC)

The plasma can be bright but composed of very little mass, so it is almost impossible to get burned. A static electricity spark is an example. To make a large amount of matter in the plasma state requires much more energy than a few batteries can supply. --Chemicalinterest (talk) 17:36, 2 August 2010 (UTC)

Then, how will it cut things? Nimur (talk) 18:57, 2 August 2010 (UTC)

Could it be similar to a CCFL? With maybe some colorants? --Chemicalinterest (talk) 17:45, 2 August 2010 (UTC)

Not really. He isn't trying to make something that looks like a lightsaber. He is trying to make a pretty hand-held plasma cutter. From his design, which is poorly shown, the plasma cutter begins looking like a sort of flashlight. Then, a fan blows the arc out from the handle to make the "blade". So, the user is literally holding the handle within an inch of the cutting heat. He could make it safer, but you'd end up with a normal plasma cutter - which already exist and are used every day. -- kainaw™ 17:52, 2 August 2010 (UTC)

We should just come out and say it: the light saber is not an effective design, from an engineering point of view. It was imagined by a filmmaker, because it looks neat, and makes for great special effects. But any small amount of practical consideration invariably yields the same conclusion: infeasible. It has little to no utility as a weapon (if the enabling technologies for a "light saber" existed, they would be better employed to make more efficient weapons or shields). It has little advantage as a tool, compared to existing technologies; and again, if the mysterious fictional technologies necessary to make the saber did exist, they could be packaged in a more convenient form-factor if the objective was a cutting-tool or welding tool. As Kainaw has pointed out, we already have plasma cutters, cutting torches, and so on. What exact advantage would the light saber actually have? Nimur (talk) 19:01, 2 August 2010 (UTC)

Can a plasma cutter bounce energy weapon ammo back at the shooter? Googlemeister (talk) 20:05, 2 August 2010 (UTC)

That is a fictional capability and a fictional scenario. But following my above statements, if a lightsaber could do it, wouldn't it make more sense to build a big array of light-saber "light" and carry it around in front of you? Anyway, we already have a technology that does provide pretty good protection against bullets, projectiles, and so on; what is the advantage of a lightsaber over a solid, resistant light-riot-shield? Nimur (talk) 20:26, 2 August 2010 (UTC)

It's worth remembering even if it could, we end up with the same problem we had with the katana question a few days back. Sure the sword may be able to bounce or deflect bullets if it happens to be in the right position. It doesn't help you if you can't use the force to actually be able to get the sword or lightsaber into exactly the right position for every shot. Nil Einne (talk) 16:59, 3 August 2010 (UTC)

I disagree Nimur. If we were to have a real lightsaber, and it worked the same way it does in the Star Wars movies, I can see it being very useful. It would be the size of a knife, but have the blade length of a sword, and supreme cutting ability. I can see this being quite useful in combat situations for cutting down doors, walls, obstacles. Sure there are other devices that can do those things, but we're assuming the lightsaber works fine, and it's small so why not? It can be used to start fires, or heat up water which can find some uses. Yes we already have cutters, and torches, but we're assuming the lightsaber works fine right? Well in that case, the lightsaber is smaller, and has a longer blade which makes it more useful as a weapon and cutting device. Yes I'm sure the technologies could be implemented in projectile weapons or shields, but why not have both? ScienceApe (talk) 02:31, 3 August 2010 (UTC)

You missed Nimur's point completely. Assuming the technology exists to make a light saber as understood from Star Wars, it (the lightsaber) would likely be the least useful thing that technology could produce. 218.25.32.210 (talk) 04:48, 3 August 2010 (UTC)

A little one would make a great cheese knife though... Googlemeister (talk) 13:09, 3 August 2010 (UTC)

I understood his point perfectly well IP. ScienceApe (talk) 22:32, 3 August 2010 (UTC)

BTW, if you want something that looks like a lightsaber, there are many ways to do one. Leds are common nowadays probably because they're cheap, small, and well suited for something handheld. Some use a strip of leds but I think it's more common to use a power led in the base with some sort of diffuser for the blade. E.g. [3] [4] [5] [6] [7] [8] [9] [10]. Some also use electroluminescent sheet or wire. I would guess people have been doing it with neons and various other lights for a very long time. There are forums dedicated to this sort of thing [11] [12]. You can of course get official versions [13] too. In other words, if you just want a lightsaber lookalike it's really not a problem but as kainaw says, that's not what the OP is discussing Nil Einne (talk) 17:48, 3 August 2010 (UTC)

While we're nitpicking, there's a lot of problems with the "science" explained in that video. I think the designer needs a solid refresher course in physics! Futuristic technologies notwithstanding, some things are fundamental properties, and while we can invent better materials and technologies, we can't break physical laws.

The video's proposal is to make a "light saber" by jetting hot ionized gas out of a handle. When you expel a jet of hot gas (ionized plasma or neutral), the gas is going to expand as soon as it contacts atmosphere. The "angle" of the expansion is characterized by the expansion ratio, and illustrated here: hot gas expands out of a nozzle. If the plasma is low-pressure, it's not going to leave the tube, or it will just waft out like smoke from a pipe so slowly that it will neutralize and cease to be an incandescing plasma. If we increase the pressure to compensate for this, the second the jet of plasma encounters atmospheric pressure around it, it's going to balloon out like a cone or fireball and disperse most of its energy through adiabatic expansion, contact conduction, and convection (leaving preciously little energy left over for "cutting" anything - though it'll probably be like a steam explosion! Lots of nasty burns). The only way to make a fluid (gas or plasma) exit a nozzle in anything remotely resembling a "beam" is to increase its fluid velocity and carefully match its exit pressure by designing a non-expanding nozzle geometry. Unfortunately, such a design also has the effect of maximizing the kinetic energy (and momentum transfer) of the exiting plasma; the gas will be moving at such a high velocity that it jets out in a collimated beam, dissipates its energy only radiatively, until eventually turbulence kicks in and disrupts the beam. (It won't look like a light saber as much as, say, a candle or a rocket plume). But keep in mind that if the hot gas is shooting out, the amount of momentum transfer will be so high that you will basically be holding a rocket motor - hardly convenient for control as a hand-held device!

The proposed "solution" for this problem, plasma confinement, also seems to misrepresent some fundamental principles. If the described method of "unrolling" an electromagnetic confinement chamber even worked, the light saber would not function because all of the plasma would be confined to the inside of this confinement tube. How would the plasma get out of the confinement? Diffusion? Or will there be "holes" in the electromagnetic confinement to let small jets of gas out?

As far as even creating a plasma: the quantity of electrical energy needed to ionize this quantity of air will be enormous - fictional "nano-batteries" notwithstanding, the energy density of the battery will have to be so ridiculously high, that you might as well use that as your cutter or weapon. I'm surprised the designer didn't think to use a chemical reaction to ionize gas - there are some pretty easy ways to do this, especially if you've already decided blow in atmospheric air full of oxygen into the bottom of the device.

Finally, let's discuss the energy balance of the device. The designer has assumed a fictional magic "nano-battery" can power both a turbo pump and an ionization chamber. We can calculate how much gas pressure is needed to extend the plume out to a 3-foot long "beam," accounting for the hydrodynamics. The fact that the designer tries to generate this energy by blowing atmospheric air via an inlet, through a "fan," indicates a misunderstanding of fluid flow - where will the inlet air come from? (Turbo pumps don't like to operate in this kind of condition, anyway. Try swinging one around! They're pretty fragile). The design will require a pressure chamber to store a large quantity of gas at high pressure; think of it as sort of a fluid dynamics "flux capacitor" - all joking aside, the laws of physics do allow us to store mass flux and PV energy in a tank, using energy delivered at reasonable power levels from the pump, until we're ready to use it. This lets us use a small amount of pump power over a very long period of time, and release it later very rapidly. But, we need such a pressure reservoir. PV energy storage is great, because it's easy to store huge quantities of energy; but it's also terrible for a hand-held device, because it is not extremely energy-dense (per mass or per volume) - especially when you consider the necessary characteristics (mass, thickness) of a pressure vessel.

I think it would be better to let the sci-fi buffs take a little poetic license here and just explain the light saber as a magical "light sword" that works by "The Force". Trying to find any correct physical or engineering explanation for it will just lead you to the disappointing conclusion that a light saber is an imaginary magical invention and can not actually be built. What has been described in the video really wouldn't look or work much like a light saber. More like a propane-barbecue-grill burner. A very heavy, hot, electrically charged rocket motor/grillburner with a bunch of gas inside of it, with a jet engine and a pressure cylinder mounted on the bottom. Nimur (talk) 20:34, 3 August 2010 (UTC)

But you can't say the lightsaber only works because of the force, because Han Solo borrowed and operated Luke's LS once. Googlemeister (talk) 13:29, 5 August 2010 (UTC)

Hematite color change

I have a small bead of hematite. It's has a beautiful dark, shiny gray color and I'd like to keep this color. I've read that hematite can turn red through contact with oxygen though. It's in a plastic container right now. Can I keep it in the open while still preventing this? Should I maybe coat it with a bit of oil like with steel? --85.145.56.218 (talk) 15:20, 2 August 2010 (UTC)

Sensitive gemstones such as malachite or haematite usually have a coating, something similar to furniture polish or wax. This should protect it from air. Unfortunately I don't know the trade name of a suitable product to use.77.86.94.177 (talk) 15:46, 2 August 2010 (UTC)

Looks like you have a product similar to iron(II,III) oxide and want to prevent it from oxidizing to iron(III) oxide. I would recommend keeping it in mineral oil, the same procedure used to store sensitive alkali metals. --Chemicalinterest (talk) 17:38, 2 August 2010 (UTC)

No. Cleaning mineral oil off of a piece of jewlery or a display piece is fantatsically impractical. Instead, why not coat it with some sort of clear lacquer, like clear nail polish... --Jayron32 02:07, 3 August 2010 (UTC)

Well yes if you want to use it as decoration do not store it in mineral oil. But what if the OP wants it to have a natural look rather than a shiny, artificial look? By all means store it in ascorbic acid solution ;) --Chemicalinterest (talk) 11:13, 3 August 2010 (UTC)

The hematite is already very shiny so I'm going to find a polish or something for it. Thanks for the answers everyone. --85.145.56.218 (talk) 20:14, 4 August 2010 (UTC)

Wind Erosion on Venus

There's a discrepancy in the first section of the article Geology of Venus. It states

Long rivers of lava have been discovered, as well as evidence of Aeolian erosion and tectonic shifts which have played an essential role in making the surface of Venus as complex as it is today.

but later

These winds exist at high altitudes, but the atmosphere at the surface is relatively calm, and images from the surface reveal no evidence of wind erosion.

Aeolian erosion is just a fancy name for wind erosion, isn't it? Is there evidence of it happening on Venus, or not? I've asked on the article's talk page, but got no response Rojomoke (talk) 15:28, 2 August 2010 (UTC)

I think the clue is in the word "relative". According to the article Atmosphere of Venus, the overall atmosphere of Venus circles the planet in around 4 days, which works out to around 400 km/h, and the article mentions high-level winds of 100 ± 10 m/s (= 360 ± 36 km/h) at altitudes of 60-70 km, in the same ballpark. By contrast, it says that

"the breeze barely reach[es] the speed of 10 km/h on the surface", and elsewhere

"the winds near the surface of Venus are much slower than that on Earth. They actually move at only a few kilometers per hour (generally less than 2 m/s and with an average of 0.3 to 1.0 m/s), but due to the high density of the atmosphere at the surface, this is still enough to transport dust and small stones across the surface, much like a slow-moving current of water."

Bearing in mind that the atmospheric pressure at the surface is about 92 bar (i.e. 92 times Earth's), and that these comparatively low average figures do not preclude occasional gales and gusts, you can probably see that these surface winds are, though "relatively" slow, still capable of erosion. 87.81.230.195 (talk) 17:19, 2 August 2010 (UTC)

That's a good scientific explanation, but it doesn't address the issue - the article contains two contradictory claims, and we need a source, I think, to tell us which is accurate. Vimescarrot (talk) 18:54, 2 August 2010 (UTC)

I've adjusted the wording ("most images" and "little evidence") to avoid the contradiction, but can anyone find a source to determine whether my compromise guess was correct? Dbfirs 08:23, 3 August 2010 (UTC)

aspartame

My friend believes that aspartame is in too many things ("everywhere") and is a poison and is only on FDA's GRAS list because of a conspiracy, and that aspartame is somehow making everyone dumber. While an organic food nut, she's also a really nice person who's a musician and is quite influential among my peers. I'm afraid the more orgo terms I use, the more I'll scare everyone. Any suggestions? John Riemann Soong (talk) 16:23, 2 August 2010 (UTC)

Ignore? --Stephan Schulz (talk) 16:26, 2 August 2010 (UTC)

Personally I've found "confrontation with facts" to not work terribly well, because people quickly close their ears up. When talking about potential low-level risks (like cell phone towers, which my mother is kind of afraid of), I generally emphasize that the risks we are talking about here are quite low, to be indistinguishable from other sources of risk, and are a lot safer than, say, the risk one takes when getting into an automobile. I tend to believe that whatever risks aspartame brings, they probably are offset by the risks that come with excessive sugar consumption. (One can argue that this can be accounted for otherwise, and indeed it can, but we don't have many means of enforcing that and we should not let the perfect edge out the good.) The evidence for it being dangerous is not very strong, in the end. Even in the cases of honest-to-god big conspiracies (e.g. tobacco), there were always lots of qualified outsiders willing to question the conclusions. --Mr.98 (talk) 16:34, 2 August 2010 (UTC)

(edit conflict)Aspartame controversy is a pretty comprehensive article that does not delve too deeply into the orgo itself. It covers both sides (i.e., hers too:) and has lots of cites from reliable-sounding sources that are not gov/industry-tied, so it's not dismissable as just more of the same conspiracy she fears. Stephan also raises a good point...I fear that some conspiracy nuts are too far gone to be helped by any amount of fact or logic. They refuse to question what they know because they already have seen the light and it's blinded them. Consider this a formal warning not to push this discussion towards religion. There are obviously lots of reasons why people behave this way...we probably even have an article about the rise and social popularity of scientific ignorance. DMacks (talk) 16:35, 2 August 2010 (UTC)

I agree with Mr.98's point. Low level risks, like aspartame or cell phone towers or living next to high-voltage transmission lines, make much less difference than higher level risks, like riding in automobiles and overeating of trans fats. One should notify the person that their views are out of perspective. If they listen, explain. If they do not listen, ignore what they say. --Chemicalinterest (talk) 17:44, 2 August 2010 (UTC)

Well it's hard to ignore someone who's trying to convert everyone to the cause over fb (quite successfully). John Riemann Soong (talk) 19:52, 2 August 2010 (UTC)

Another very easy approach is to say, "Hey, Wikipedia has a pretty good article on this, that seems pretty balanced. It seems that in the end, the evidence for it being harmful is pretty weak, and that if there is harm, it is basically indistinguishable from the background level of things that happen to people." I've used this for some of the other "controversies" before (like whether Jesus existed as an actual human being, or whether cell phones are dangerous), when the Wiki article is actually good and balanced. It tends to be a way to say, "Hey, this is a tough question, and if we take a balanced view of it, we see it doesn't readily give an unambiguous black or white answer." That's generally the place I try to get such people to arrive at — not so much believing, "this is safe," which it might not be, I don't know, but rather to "oh, this isn't a simple-minded thing, it's a complicated one," which is a lot better than the propagandistic approach in any case, and removes the missionary zeal. --Mr.98 (talk) 20:25, 2 August 2010 (UTC)

"People cannot be reasoned out of a position they did not arrive at via reason". The only response to people who believe in outrageous conspiracy theories is to either ignore them or ridicule them for your own amusement. No amount of actual evidence and reasoned discussion can convince them out of their position. --Jayron32 02:04, 3 August 2010 (UTC)

Human consumption of uncooked cereal grains

Just curious what would be the result of eating uncooked cereal grains (like raw oatmeal, rice or rye). Cooking converts the grains into human usable starches, right? Would the human digestive system be able to get any nutritional value out of raw grain? --70.167.58.6 (talk) 16:47, 2 August 2010 (UTC)

A short answer would be: "Yes it can, but not too well". Cooking gelatinizes starch which makes it a lot more absorbable to the digestive system. Raw grains are not digested easily and the body only takes up a tiny amount of the nutrients. The undigested and unabsorbed nutrients in the grain will go into the intestines and end up just feeding the gut flora, likely causing lots of gas, and then gets expelled from the body more or less whole in the feces. -- Sjschen (talk) 18:03, 2 August 2010 (UTC)

You would be able to get more energy if you chewed it for a long time and similarly if you were to eat a paste made from flour you would also get more energy compared to eating whole grains. The reason for this would be that the surface area of the grains would be increased allowing enzymes such as amylase to degrade the starch more effectively. Smartse (talk) 18:23, 3 August 2010 (UTC)

Still the best way to get the energy and nutrients out of the food and into the body is by cooking it in liquids to make the starch easier to absorb than chewing it to a pulp. Chewing and digesting raw grains takes up far more energy then the amount absorbed from the same grains themselves. -- Sjschen (talk) 21:07, 4 August 2010 (UTC)

wasp-like insects

Last year when I was cycling on the common I saw these tiny holes in the ground. This was during the summer, and the ground was very dry. Then I saw these flying wasp-like insects going into them. What were they? —Preceding unsigned comment added by CuteLesbianPossum (talk • contribs) 18:29, 2 August 2010 (UTC)

Digger wasps? Looie496 (talk) 18:36, 2 August 2010 (UTC)

It could be any of a thousand different wasps. Many wasp species burrow. For example beewolf wasps and cicada killer wasps. Without knowing more about the wasp in general, we can only say it may be some random species of burrowing wasp. --Jayron32 03:03, 3 August 2010 (UTC)

Queen Ant

When the ants were flying this year, I caught a lasius niger queen because I wanted to start an ant colony. Only today I discovered that you're meant to get them after they shed their wings. So I have a queen who hasn't mated and will never lay eggs to start a colony. She looks sad and vacant most of the time, just sitting in the container with her antenna slowly twitching, except when I feed her a tiny drop of honey on the end of a pencil - then she jumps into life, climbs onto the pencil and happily licks the honey. But afterwards she just goes back to sitting alone in the container. I feel very sad, because she is going to be all alone. Is there anything I can do to help her? I read that the worker ants are meant to feed the queen, but since there are no workers I will have to do it. Is feeding her honey the right food? Rebmetpes27 (talk) 18:44, 2 August 2010 (UTC)

If you know she will never lay, then why are you keeping her? Just release her. --Tango (talk) 19:35, 2 August 2010 (UTC)

Without worker ants to forage for food and protect her, she would die Rebmetpes27 (talk) 19:55, 2 August 2010 (UTC)

Well, she's not going to do a whole lot better in your cage, without a mate. She has basically one purpose in life as she sees it — breed, and lay eggs like mad. That's all she cares about. --Mr.98 (talk) 20:19, 2 August 2010 (UTC)

But she can't lay eggs; she is entirely dependent on me now, and my actions determine her fate. I do not want to kill her by putting her into the wild knowing she won't survive. My question is about how to help her. How can I care for her? What food does she need? etc Rebmetpes27 (talk) 20:43, 2 August 2010 (UTC)

My point is that you have already disrupted her only real purpose in life. She does not care about life itself and probably does not care about death in the slightest. She cares about laying eggs and that's it. I do not think you should feel bad about putting her out to certain death under these circumstances — at least in such a case, she will be food for something else! The queen is not an individual — the colony itself is the "organism," the queen is just the egg-laying part of it. The colony is already dead. (You needn't feel distraught about this — in all likelihood it wouldn't have survived anyway, only very few of the new queens end up forming successful colonies. That's how nature — and evolution — works.) --Mr.98 (talk) 01:17, 3 August 2010 (UTC)

According to List of animals by number of neurons, ants have only 10,000 neurons, cats have 300,000,000 and you have 100,000,000,000. The ant has a spectacularly small number - its ten times more stupid than a house-fly, 100 times more stupid than a cockroach. Almost all of those 10,000 cells will be there to process light and pheremone scent and to run basic instincts, feeding, walking, etc. It is basically impossible that she is able to feel happy or sad or anything else for that matter. She's simply obeying a scent and instinct-driven imperative to do whatever comes next in her life cycle - like a robot - and when it doesn't happen she shuts down, conserves energy and waits. You certainly shouldn't feel sad about it. You sealed her fate the moment you removed her from the environment - whether you keep her, let her go, squish her - none of that makes a difference. It's already over for her - she feels precisely nothing about anything. SteveBaker (talk) 23:59, 2 August 2010 (UTC)

I don't care whether scientists think she feels emotions or not, I still want to help her. What foods do they eat? Is honey enough, or do I need to give protein and vitamins and other stuff? Rebmetpes27 (talk) 00:16, 3 August 2010 (UTC)

Googling "ant farm food" seems to indicate that honey and water are OK foods for an ant farm. I doubt the queen by herself can deal with more complicated foods (which are, if I recall, predigested by workers usually). --Mr.98 (talk) 01:19, 3 August 2010 (UTC)

If you are committed to helping her, it seems you might have to take care of your ant for quite a long time. Googling "queen ant life span" I saw a site (not sure how reliable it is, so take it with a grain of salt) claiming that "a queen of Lasius niger, a common ant found in Europe, lived for 29 years in captivity." --- Medical geneticist (talk) 13:50, 3 August 2010 (UTC)

Am I missing something (probably me lacking in knowledge on ants), or couldn't he just go find the queen some mates and put them in the ant farm with the queen? Ks0stm ^(T•C•G) 02:52, 3 August 2010 (UTC)

Probably not. Ants can generally recognize their own nest by smell (else, how would ants from nests of the same species find their own nest), and may kill the queen from a different nest as an intruder. It also may depend a LOT on the specific species of ant as to what their reaction would be, but it may not go well for the queen... --Jayron32 02:59, 3 August 2010 (UTC)

And the timing is important. There is only a narrow window between which they can find mates. See Nuptial flight, which tells us that males die right after mating, and that there is a very high failure rate anyway (which is good, because otherwise there'd be wwaaayyy too many ants!). And the photos do a good job of indicating how different the males and females of a given species can look. --Mr.98 (talk) 11:39, 3 August 2010 (UTC)

Fluid balance - production of water by the human body throu metabolism

I'm puzzled how exactly does the human body produce water as stated by our Fluid balance article "In the normal resting state, input of water through ingested fluids is approximately 1200 ml/day, from ingested foods 1000 ml/day and from metabolism 300 ml/day, totaling 2500 ml/day" Can anyone explain this? 89.72.128.27 (talk) 19:41, 2 August 2010 (UTC)

Water is a byproduct of breaking down simple sugars during cellular respiration. Dragons flight (talk) 19:51, 2 August 2010 (UTC)

Simply put, when you take a molecule of sugar like C₆H₁₂O₆ - and add six O₂ molecules to extract energy, you end up with six CO₂'s (which you expel when you breathe out) and six H₂O's which add to your water "input". SteveBaker (talk) 20:44, 2 August 2010 (UTC)

Silicon Bakeware

I am trying hard to find out what the symbols on some new silicon bakeware mean. I have used search engines and looked all over this site's main pages, archives, and reference desk. The best thing I've gotten so far is my own account here! Seriously, though, I would like to suggest that a "chart" section be added. With more and more technology and international cooperation in just about every field, there are more and more symbols being used. I find them from clothing labels to my new bakeware. There are three different circles with the universal "do not" slash accross them. I do not have any idea what the pictures inside the circles are so, therefore, don't know what I'm supposed to avoid. I think charts like this can be found in paper encyclopedias, and would be very usefull to many people. (posted on behalf of User:Designed4Him from his talk page) —  Hamza  ^{[ talk ]} 20:57, 2 August 2010 (UTC)

I've never seen something with "just logos" like that...there's either wording with it or a separate printed note about them. What we would need for an article (or to even answer a question like this:) is to actually see the symbols. No idea how standardized these are, but could have a gallery like at Hazard symbol. DMacks (talk) 02:04, 3 August 2010 (UTC)

at a guess (from glancing at the net) they would be warnings not to use knives, not to place the bakeware on direct heat, and not to use abrasive cleansers. those appear to be nonos for silicone. --Ludwigs2 03:55, 3 August 2010 (UTC)

Tipler Cylinder

Why would an infinitely long Tipler cylinder allow time travel, but not any spinning object? Is there more to it than just making a strong enough gravitomagnetic field?

Why couldn't this be done with regular electromagnetism? Why would general relativity only apply to gravity?

While I'm at it, the Tipler cylinder page mentions a conjecture Stephen Hawking made, but then says he proved it, so it would be a theorem. Should I change it? — DanielLC 22:19, 2 August 2010 (UTC)

Of course, there is the problem of building an infinitely long object... --Jayron32 02:01, 3 August 2010 (UTC)

Regarding your second paragraph: general relativity and gravity are the same thing. Possibly you could do this with electromagnetic fields, since they gravitate. You can't do it with electromagnetism in a gravity-less universe because the lack of closed timelike curves is already built into the spacetime background. A closed timelike curve is a distortion of spacetime, and spacetime distortions are gravity. Regarding the other two paragraphs, I'll have to guess. Third paragraph: the abstract of Hawking's paper (which is all I've read) says "This shows [i.e., proves] that one cannot create closed timelike curves with finite lengths of cosmic string." I think a rotating cylinder falls under his definition of cosmic string. But he also says that this only suggests (doesn't prove) chronological censorship, which he defines as the hypothesis that "the laws of physics do not allow the appearance of closed timelike curves". He might simply be saying that, although he's proved this result starting from general relativity plus the averaged weak energy condition, he hasn't proved it about the real world. But I'm not sure. First paragraph: as Tipler mentions, there are closed timelike curves in the Kerr vacuum that describes a spinning black hole, but in that case the CTCs are behind the event horizon. So the question is really whether you can have CTCs that aren't inside a black hole. Tipler's infinite cylinder has infinite mass, so perhaps you could say that the Schwarzschild radius is infinite and therefore all the weirdness of that geometry is technically inside the event horizon. When you reduce the cylinder to a finite size, the Schwarzschild radius becomes finite but all the weirdness is still confined. But I'm even less sure about that. -- BenRG (talk) 03:33, 3 August 2010 (UTC)

From my understanding of General Relativity, it's all just what happens if you think of gravity as an accelerating reference frame. If an electron falling to the Earth from gravity isn't really accelerating, why would an electron falling to a proton be? Electromagnetism and gravity seem to otherwise follow the same principles.

the fundamental difference is that the electron falling towards the proton can detect its acceleration using an accelerometer, while the electron falling towards earth can not. 157.193.175.207 (talk) 09:42, 3 August 2010 (UTC)

If you made an accelerometer with charge but no gravitational mass, it would work the other way. By assuming the accelerometer has to have no charge but have gravitational mass, you're already assuming there's a difference. In fact, you don't even have to split up the forces as gravitational and electric. You could say that one force is the forces between electrons (including gravity and charge), and the other is some other combination of gravity and charge (though it has to be a certain other combination if you don't want the forces to interact with each other). — DanielLC 19:56, 3 August 2010 (UTC)

Do you have any evidence that matter with charge but without gravitational mass exists, which would imply that the equivalence principle is false? 157.193.175.207 (talk) 11:07, 4 August 2010 (UTC)

The difference is that there are different kinds of charge that are deflected in different ways in an electromagnetic field, but everything is deflected in the same way in a gravitational field. You can detect an electromagnetic field by keeping differently charged objects around and measuring their relative acceleration, but you can't detect a gravitational field that way (or any way). It is possible to take a geometric view of electromagnetism, by adding a fifth dimension which loops around on itself with a fixed radius, as I described here. To get the "electromagnetism-only" version of that, you restrict the shape of the big four dimensions to be Minkowski space (or some other fixed spacetime). In the electromagnetism-only version, though you can still deform the 5D spacetime, you can't deform it such that the time dimension loops around on itself, because the shape of the big four dimensions is fixed. Re the comment below ("If it was just gravitomagnetism..."), the upshot of Hawking's paper is that a finite cylinder spun that fast will collapse into a black hole (if it doesn't break apart first). -- BenRG (talk) 06:56, 4 August 2010 (UTC)

If it was just gravitomagnetism that caused the closed time-like curves, any object would work, so long as it spins fast enough. 67.172.112.226 (talk) 05:11, 3 August 2010 (UTC)

That was me. I forgot to log in. — DanielLC 07:30, 3 August 2010 (UTC)

What sort of mood disorder is the following?

Does there exist/is there a name for a type of mood disorder where a depressive period is caused afterwards by a period of happiness. Like, for instance, if someone were to hang out with friends for a while, feeling really happy, and then aftewards go home to find themself in the opposite mood. Not necessarily reacting to the fact that they had to leave, but rather like some sort of a strange emotional balance out? Does that sort of thing ring a bell to anyone? 68.160.243.61 (talk) 22:57, 2 August 2010 (UTC)

We aren't allowed to offer medical advice - and in particular, we're not allowed to offer a diagnosis. If you (or whoever you might be referring to) is concerned, see a doctor. Our Mood swing article suggests some possibilities. SteveBaker (talk) 23:41, 2 August 2010 (UTC)

There are several disorders that might feature behavior like this: manic depression, certain forms of schizophrenia, a number of neuroses. This is also a fairly normal reaction to stress, a normal part of development in adolescents and young adults, and a typical response to certain life events. Normally no diagnosis would be made unless the behavior is consistent over a long period of time, unrelated to overt biological and environmental factors, and in some way damaging to health or well-being of the person involved, and that decision would need to be made by a qualified therapist (because it is next-to-impossible to diagnose someone with whom you have an close relationship, and completely impossible to diagnose yourself). --Ludwigs2 23:50, 2 August 2010 (UTC)

Manic depression is often called bi-polar disorder, and it sounds like what you are describing. Ariel. (talk) 03:40, 3 August 2010 (UTC)

Sorry, but I have to say that I think Ariel's spot diagnosis is very irresponsible. What the OP describes sounds like a normal change of mood to me - if you are doing soemthing that you enjoy, and it stops, then you will naturally feel sad, and this feeling may be intensified by tiredness or other environmental factors. However, if the OP is concerned that it may be more than that, then they need to discuss their feelings with a family member and/or see a doctor (as others have said). Gandalf61 (talk) 10:45, 3 August 2010 (UTC)

Ariel's observation appears to me not to be a diagnosis but a simple statement of fact, which in any case merely summarized some of what Ludwigs2 had already said (Bad Ariel! *Smack* :-) ). Note that at no time did the OP explicitly state that he/she was him/herself experiencing such moods or feelings; he/she merely asked for information impersonally, and has been directed to possibly relevant articles - it's hard to look things up in an encyclopaedia if one doesn't know the nomenclature. 87.81.230.195 (talk) 13:32, 3 August 2010 (UTC)

Ariel's correct - Bi-polar disorder is the current term, while manic depression is an older, outmoded term. my mistake. --Ludwigs2 14:01, 3 August 2010 (UTC)

But it can't be that because the mood swings in bipolar disorder happen over months...not hours! This is precisely why we don't allow diagnoses! SteveBaker (talk) 14:07, 3 August 2010 (UTC)

This really didn't read like a diagnosis request to me - he just wanted a name for this kind of disorder. Ariel. (talk) 16:59, 3 August 2010 (UTC)

There is a variant of bipolar disorder called ultra-ultra rapid cycling (PMID 9702745) in which moods cycle with a period of less than 24 hours sometimes. There are also drug manipulations that cause a person with bipolar disorder to switch very rapidly from depressed to manic or vice versa. (None of this is relevant to the current question; I'm just clarifying a point here.) Looie496 (talk) 17:53, 3 August 2010 (UTC)

The term "mood disorder" carries an implication that the depression is serious enough to call for treatment. I doubt that's what the question intended to mean -- for a mild drop in mood, I would just use a term like "letdown" or "mood swing". Looie496 (talk) 17:46, 3 August 2010 (UTC)