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April 24

SETI not successful at finding extraterrestrial intelligence

If there are so many possible earth-like planets in the Milky Way Galaxy, which makes the chances of finding alien life very high, why hasn't SETI been able to detect extraterrestrial civilizations? — Preceding unsigned comment added by 24.207.71.235 (talk) 04:56, 24 April 2016 (UTC)

Because you need some synchronization to recieve information over radio signaling and SETI is only listening for 26 years now which is a joke in relation to the assumed age of our universe. Ask again when we have listened for 500 Million years without finding anything :D --Kharon (talk) 05:36, 24 April 2016 (UTC)

P.S.: Ok, ok, 500 million may be to conservative aproach scientifically speaking and i get you can not be that pacient.. so how about asking again after listening just 500 years which roughly relates to the assumed age of the universe like 1 Minute in a 60 years Lifespan. --Kharon (talk) 06:04, 24 April 2016 (UTC)

Fermi paradox and rare Earth hypothesis are relevant. A large number of possibly earth-like planets doesn't make it likely that we'll detect intelligent life. We don't how how likely it is that a possibly earth-like planet has intelligent life on it (at the time we look). -- BenRG (talk) 06:05, 24 April 2016 (UTC)

If the OP can give numbers to use in the Drake equation that estimates the number of communicative extraterrestrial civilizations in the Milky Way, the question will be better posed than asking in qualitative terms of "so many" and "very high chances". AllBestFaith (talk) 08:46, 24 April 2016 (UTC)

There's also the sensitivity of our radio telescope. There may be an intelligent civilisation with radio transmitters 1 kiloparsecs away from us (not very far astronomically speaking), but our telescopes may not be sensitive enough to detect them. Suppose a human-like society exists just 3 parsecs away (we don't really expect them closer than that) and that society has FM radio stations like we have. We would have to point our most sensitive radio telescopes at their planet, staring for years before we'd be able to detect their radio station as a small bump in the radio spectrum above background noise. We have other things to do for our radio telescopes. And FM radio may be a short-lived technology. Already we are moving to broad-band digitally encoded radio, which is far harder to discriminate from random background noise.

There's more hope if the aliens use powerful transmissions, beamed in a narrow beam directly towards Earth. This could give a decent range at a bitrate somewhat higher than 1 bit per century. Maybe a bit per second would be possible over 100 parsecs, I didn't calculate what transmitter the aliens would need. But even then, both the transmitter and the receiver would have beams of an arcsecond width and those would have to be pointed right at one another at the right time. The odds aren't very good for that to happen. PiusImpavidus (talk) 11:16, 24 April 2016 (UTC)

If there are aliens in a distant galaxy, the length of their day is not likely to be the same as ours. Even if it was, the aliens are not likely to have divided it up into the same 24hr/60min/60sec divisions that we use. So, whereas we use the second as our basis for the data rate in our transmissions, who knows what basis they would use for theirs? Wouldn't a different basis make transmissions mutually incomprehensible? Maybe all the noise we hear is actually the aliens communicating amongst themselves. Akld guy (talk) 12:53, 24 April 2016 (UTC)

@Akid guy If you are suggesting that terrestrial data communications are all locked to a 1 Hz timebase, that is incorrect. Common digital modulation methods convey data at many different rates derived from independent clock sources and receivers are designed to synchronise themselves to incoming signals. AllBestFaith (talk) 14:49, 24 April 2016 (UTC)

Even if they were locked to a multiple of 1Hz - it wouldn't matter because of doppler shift. I'm quite sure that SETI aren't looking only on exact numbers of hertz - that would be a ridiculous thing to do. SteveBaker (talk) 19:28, 24 April 2016 (UTC)

I didn't say anything about a 1 Hz signal. We base our bit rate timings on 1 second, but if an alien culture based their "second" on some small division of the length of their day, the length of their "bit" might be a very small fraction of the length of ours. So small in fact, that it sounds like noise. Maybe we don't yet have the technology to extract anything meaningful from such short bit rates, let alone decode any encryption that they might use. Akld guy (talk) 20:12, 24 April 2016 (UTC)

That would be a matter of more advanced technology, not of the day length. If our day were a hundred times as long, but our technology were the same, we wouldn't make our data transfers a hundred times slower. —Tamfang (talk) 07:39, 25 April 2016 (UTC)

@Akid guy 1 Hz or Hertz means a frequency or rate of once per second which is exactly what you are harping on about, like the ticking of a clock. Mechanical clocks are hopelessly inadequate to measure the durations of bits in modern digital communications that now are routinely sized in milliseconds, microseconds, nanoseconds and picoseconds. High bit rate implies short bit duration and there is no such thing as a human standard bit. Of course some competence is required to draw connections (if any) between the Sexagesimal time divisions of Babylonian astronomy and the theory in SETI that any communication signal is distinguishable from thermal noise by its Autocorrelation. In this way an inquisitive alien who picks up a GPS satellite transmission and first wonders why earthlings seem to transmit "noise" to themselves, on closer inspection deduces that GPS satellites transmit periodic PRBS for time measurements. AllBestFaith (talk) 12:56, 25 April 2016 (UTC)

@AllBestFaith: I'm not impressed with the way you stated that I'm "harping on". I responded to questions. I'm also well aware of what a Hertz is, thank you very much. See my profile. I began building radio equipment in the 1960s and have written software in both Basic and Assembler and have interfaced it via a serial port, developing my own KISS code. Your condescension, by referring to a mechanical clock, is totally out of place. Read what I said (unfortunately I spoke of bit rate when I should have said bit length). Our bit length is based on our second. If an alien culture has a different day length, their bit length is almost certainly going to be different from ours, and it may be so much shorter that we perceive valid data as simply "noise". Akld guy (talk) 16:35, 25 April 2016 (UTC)

I recommend http://www.seti.org/faq - I'll quote one of their FAQ points: "If an extraterrestrial civilization has a SETI project similar to our own, could they detect signals from Earth? In general, no. Most earthly transmissions are too weak to be found by equipment similar to ours at the distance of even the nearest star. But there are some important exceptions. High-powered radars and the Arecibo broadcast of 1974 (which lasted for only three minutes) could be detected at distances of tens to hundreds of light-years with a setup similar to our best SETI experiments."

...and that's an important point. The aliens would have to be beaming a very high powered (by our standards) signal - and aiming it right at us - and timing that precisely so that it arrives when we're listening - and they'd have to be within "tens to hundreds of light-years" of us. If you look out to 100 light years, there are maybe a dozen potentially inhabitable planets.

SETI also say "...while there are hundreds of billions of stars in our galaxy, only a few thousand have been scrutinized with high sensitivity and for those, only over a small fraction of the available frequency range."

So it's really no surprise at all that we're not finding anything.

SteveBaker (talk) 19:28, 24 April 2016 (UTC)

• About 1980, i think, Science had an article about what Earth would look like in radio waves as seen at various nearby stars. (I've seen the claim elsewhere that Earth puts out as much radio as a small star; though we may be dimmer now, with conversions to narrowcast.) Observers could infer the length of our day from periodicities, the size of Earth and its orbit from Doppler shifts, and some hints of the geographic distribution of cities (brightest on the limb, because most of the energy goes out horizontally). —Tamfang (talk) 07:39, 25 April 2016 (UTC)

One possibility is that life intelligent enough to develop radio communications tends to be "intelligent" enough that it also develops ways to snuff itself. So the window for something like SETI could be quite brief in the context of the age of the universe. Shock Brigade Harvester Boris (talk) 00:08, 26 April 2016 (UTC)

This is discussed in detail in our Great Filter article. Scary stuff. SteveBaker (talk) 15:37, 26 April 2016 (UTC)

What about the fact that no aliens have visited earth so far?24.207.71.235 (talk) 03:23, 26 April 2016 (UTC)

Well, for most aliens, they can't know were here yet. We've only been dramatically affecting the atmosphere, changing the appearance of the planet and emitting radio waves for around 100 years - and given the speed of light, that means that only aliens living within 50 lightyears stand ANY chance of knowing were here and getting here. Even that presumes that they have near-lightspeed spacecraft and the capability of maintaining the lives of their crew for that long. Within 50 light years, there are maybe only three or four inhabitable planets. With realistic capabilities to travel here, no aliens could possibly know that we exist AND be able travel here for at least a thousand years.

The only alternative would be that aliens with so much capability are visiting other star systems routinely and continually - and that would require a truly insane degree of technology and energy. If that were the case, we'd already know about them.

SteveBaker (talk) 15:37, 26 April 2016 (UTC)

Though I'm a fan of the berserker (Saberhagen) idea, a possibility I have not really seen mentioned is something I remember reading that "a perfectly encoded signal is indistinguishable from noise." (I heard this claimed as a consequence of Shannon's theorem, though if it is I don't actually see how) But there's a notion in my mind that the seemingly random entanglements of particles and even isolated patches of space, the happenstance of which way each ring of six hydrogens points in a drop of water, and countless other such minutiae might conceal a powerful signal. That whole alien civilizations' worth of data and transhuman understanding exist in each drop of pee during its brief flight, as oblivious to its slow descent as we are to the gradual continental drift between here and the Andromeda Galaxy. In this notion, civilizations would wink out from our view not by self-destruction, but by some sort of realization of higher levels of consciousness until they become, somehow, integrated into the whole of the cosmos. The appearance of this process, however, seems like it might be disturbingly similar to various death-cults on Earth... Wnt (talk) 18:59, 27 April 2016 (UTC)

It's true that a perfectly encoded signal is indistinguishable from noise - but nobody in their right mind would start off a conversation with a perfectly encoded signal. To the contrary - you want a signal that's very inefficiently encoded so that it stands out from the noise and will be instantly recognisable. That's why we have the trope that the first alien contact will be a string of prime numbers. But if their civilisation encodes numbers and performs arithmetic using interpretive dance choreography - it may take a while for us to figure it out. SteveBaker (talk) 22:43, 27 April 2016 (UTC)

April 25

Could it be that a person can stop his pulse or is it fake?

This video (around the minute 6:30) shows how a person stops his pulse for 15 seconds. I just would like to ensure if it's possible (true) or not fake). 93.126.95.68 (talk) 00:29, 25 April 2016 (UTC)

Supposedly Superman can. But how would a mere mortal stop his heartbeat and live to tell about it? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:02, 25 April 2016 (UTC)

This and this may be relevant. The simple method is to simply hold a rubber ball in the right spot under the arm to cut off the blood flow to the wrists (how most people measure the pulse). Doesn't affect heartrate at all. The harder method involves training the muscles throughout the body to slow blood flow (though this does not actually stop the heart). Does affect heartrate, and could be combined with the rubber ball trick to make one appear totally freaking dead (as long as they're checking the pulse from the wrist). If they had attached monitors somewhere besides his finger tips (I'm not counting a credulous hand as a monitor), they'd've spotted it. Ian.thomson (talk) 11:24, 25 April 2016 (UTC)

Great answer! thank you 93.126.95.68 (talk) 18:01, 25 April 2016 (UTC)

I would be skeptical because cardiac muscle is spontaneously pulsatile. External nerves govern the rate, but have they evolved to make it stop? Nothing's impossible in biology but some things seem pretty darn unlikely, demanding good evidence. Wnt (talk) 20:38, 25 April 2016 (UTC)

Trying to identify a berry

My fiancee and I live in the Seattle area, and we came across some orange relatives of the blackberry that grow very low, a type of ground cover. She called them salmonberries, but we've now discovered that that name refers to Rubus parviflorus, an obviously related but clearly different species. The last time I saw them was at Saint Edward State Park growing at the base of the walls around the old seminary building. She indicated that there are also patches of them near SeaTac. It's possible that these are Rubus spectabilis, but the description on that page indicates a taller shrub with substantial height. The orange berry image on that page, however, appears accurate, though the red is clearly the wrong berry. Is it possible that these are just smaller versions of the same plant, or is this a different species? 73.19.23.200 (talk) 11:57, 25 April 2016 (UTC)

Maybe some kind of Euonymus? --Jayron32 12:55, 25 April 2016 (UTC)

It would appear that both parviflorus and spectabilis are sometimes called salmonberry (which is why biologists prefer the Latin binomials rather than the common names). Don't put too much weight on the described size of the plants: any shrub can end up being stunted if the conditions are not right. Planted up close to a wall may mean little soil, or in a coastal area the effects of salt winds might reduce plant growth. If flower, fruit and leaf match that counts for more than the general shape and size of the whole plant. 81.132.106.10 (talk) 13:47, 25 April 2016 (UTC)

Just for the fun of it, check out dewberry - another Rubus species complex. . SemanticMantis (talk) 14:11, 25 April 2016 (UTC)

Also, in general, the way to ID a berry is not through the berry or the bush shape, it's by the flower. SemanticMantis (talk) 14:14, 25 April 2016 (UTC)

Unfortunately, if they are seeing the fruit, it is probably the wrong season to spot the flowers. 81.132.106.10 (talk) 16:02, 25 April 2016 (UTC)

Phenology varies quite a bit. Also it's not that odd to see flowers and berries on the same plant at the same time [1]. Also this general advice may be useful for next season, or to ID other berries :) SemanticMantis (talk) 16:40, 25 April 2016 (UTC)

Asked this question a couple of other places, and one suggestion was Rubus chamaemorus. I'll take a look at the flowers next time I see one, though. 73.19.23.200 (talk) 05:07, 26 April 2016 (UTC)

Thanks for the follow-up. Rubus is tough to ID to the species level, in my opinion. SemanticMantis (talk) 13:36, 26 April 2016 (UTC)

Eye damage due to eye exams

An eye exam seems to involve them shining bright lights into a fully dilated eye. Couldn't they use a dim light, paired with a highly light-sensitive digital camera, instead ? StuRat (talk) 20:59, 25 April 2016 (UTC)

What eye damage? ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:13, 25 April 2016 (UTC)

Well, the most "classic" exam you see in movies and TV all the time when a doctor shines a pen light into someone's eye is a Pupillary light reflex test, which is not an eye exam but a neurological test. Apart from that, while a bright light can be uncomfortable and leave you with spots in your vision that can last a while, it doesn't actually damage the eye, it's actually the heat and radiation from something like the sun, welding arc, or a powerful enough laser that cause damage to the retina, just a "bright light" is typically not enough. disclaimer: Don't use this as an excuse to stare into extremely bright lights, it's still not a GOOD idea even if it doesn't cause permanent damage. Vespine (talk) 00:03, 26 April 2016 (UTC)

Indeed. See Photokeratitis for our relevant article. It's the ultraviolet that does the damage, which shouldn't be an issue with an opthalmoscope. Tevildo (talk) 00:05, 26 April 2016 (UTC)

Here is a 1980 paper: Retinal light exposure from ophthalmoscopes, slit lamps, and overhead surgical lamps; An analysis of potential hazards

"The indirect ophthalmoscopes tested appear to be "safe" under moderate voltage settings, provided exposure is reasonably brief Slit-lamp biomicroscopy of the fundus, however, merits caution. It produces a three-times-higher retinal irradiance than the indirect ophthalmoscope."

Links: Slit lamp, fundus (eye). -- ToE 02:58, 26 April 2016 (UTC)

How about just to avoid spots in the eyes, then ? StuRat (talk) 02:02, 26 April 2016 (UTC)

Why care? The payback in terms of cheaper equipment and hence lower eye examination costs by far outweighs a few spots that'll go away by the time you've left the building anyway. SteveBaker (talk) 15:28, 26 April 2016 (UTC)

Well, like gynecologists that use ice cold speculums, it's an issue of caring about your patient's comfort. If you need a medical reason, some patients may avoid eye exams because of the blinding light, and suffer medical problems as a result. If you want a business reason, the "no blinding light" exam could be a selling point to acquire new patients, and then sell them glasses and contact lenses. StuRat (talk) 19:23, 26 April 2016 (UTC)

"Ice cold"? Cosby talked about how doctors keep their stethoscopes in the freezer. But I'm fairly certain he was exaggerating. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:41, 27 April 2016 (UTC)

And if they don't go away in a reasonable time, you had best make another appointment. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:47, 26 April 2016 (UTC)

Thanks for all the replies so far, but nobody has directly answered the Q as to whether it is possible to do an eye exam using a dim light and an extremely light-sensitive digital camera. StuRat (talk) 19:29, 26 April 2016 (UTC)

Before an eye exam, my opthalmologist has his nurse routinely take a digital camera photograph of my retina. That is neither rocket science nor a novel idea. However the eye is a 3-D structure and the opthalmologist uses his Slit lamp and microscope to investigate throughout the structure. Symptoms of problems such as scratched cornea, floaters or Retinal detachment which are vital to catch early will be discovered by skilled search at different focus distances, magnifications and positioning of the analysis light. Given the importance of the eye diseases that slit lamp exam detects there is no reason to restrict the analyst to work from a single 2-D photograph because of an unfounded fear of a few seconds exposure to the light of the properly calibrated medical instrument, though nervous children may need reassurance that nothing bad is happening. AllBestFaith (talk) 07:38, 27 April 2016 (UTC)

Why just take a single image ? You could take multiple images from different angles and even use that to form a 3D computer model. StuRat (talk) 14:30, 27 April 2016 (UTC)

Painting the Moon

Wikipedia has a harebrained scheme to send a draft of the encylopedia to the Moon. [2] I want to see the idea improved on with this invention, which claims to keep 360 TB stable for 13.8 billion years. With that kind of stability, you can leave a message for some future species that is trying to figure out what Earth was like, even if the planet has been entirely resurfaced like Venus after some man-made climate mishap.

The catch is, how do they find the disk? It should gradually sink into the regolith. (of course, it could get hit by a meteor directly, but I'm assuming luck or multiple scattered disks laid over time)

On to the question: is it possible to take some freaky, rare element, I dunno, lutetium or something maybe one of the tracers described in File:Rareearthoxides.jpg, and spray a small amount of it on the Moon, and taint the small area where it lands so thoroughly that it can be detected from an orbital survey, and have micrometeorites hitting anywhere in the small area constantly stirring it up, so that the mark never fades? What stands out the most, and can the logic here hold or is it doomed to be diluted into invisibility? Wnt (talk) 21:02, 25 April 2016 (UTC)

Rather than make it visually obvious, how about placing a strong, permanent magnet there ? Probably not detectable from space, but some future aliens might notice the disturbance of the magnetic field when exploring the surface near the area. StuRat (talk) 21:33, 25 April 2016 (UTC)

In Tycho, of course. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:11, 25 April 2016 (UTC)

Why ? StuRat (talk) 22:30, 25 April 2016 (UTC)

To turn the tables on a key plot element of 2001: A Space Odyssey. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:35, 25 April 2016 (UTC)

To be clear, I was hoping that a small quantity of rare earth, even a mere kilogram might suffice to create a notable spectroscopic anomaly on the order of ten meters wide that can withstand the gradual tilling of the regolith by micrometeorites over millions of years. (a large impact would vaporize the disc, so there's no sense worrying about it). Whereas a buried permanent magnet would definitely involve an impractical amount of mass to be noticed. Wnt (talk) 00:21, 26 April 2016 (UTC)

I would expect anything flat on the surface would quickly be covered with dust and rendered invisible. Can anyone estimate the distance at which a one kg permanent magnet, on the surface of the Moon, could be detected ? StuRat (talk) 01:44, 26 April 2016 (UTC)

When you say "quickly", do you mean on a planetary timescale? The moon is relatively inert now, except for the occasional small meteor strike, of which the moon attracts relatively few, compared to the earth. The lowest estimates I have found of how long the footprints left by the astronauts will last is several tens of thousands of years, the longest is many millions. Vespine (talk) 02:42, 26 April 2016 (UTC)

Yes, on a planetary timescale. How long would the permanent magnet last ? StuRat (talk) 02:56, 26 April 2016 (UTC)

Another thought is to just move the Moon dust around to write something there, like a big arrow pointing to the Wikipedia archive. Deep enough furrows ought to last for millions of years, based on how long it would take for the footsteps to fill in. StuRat (talk) 03:00, 26 April 2016 (UTC)

Impact gardening by micrometeorites is estimated to overturn the top 1 cm of the lunar surface every 10 million years. Dragons flight (talk) 09:30, 26 April 2016 (UTC)

So does that mean a 1 meter deep furrow would last a billion years ? Somehow I doubt if it's as simple as that. StuRat (talk) 14:41, 26 April 2016 (UTC)

The practical problem with this is that of launch weight. While the effort to put a privately-funded lander/rover on the moon may be able to accomodate a tiny memory chip weighing a fraction of a gram - it's not going to be able to carry a 1kg magnet or something capable of making giant arrows or deep furrows. The memory chip will remain attached to the lander - and that's probably going to be tens of centimeters tall - so the 1cm/10My number should keep it above the surface for a few hundred millions of years. To detect it from orbit might be tricky - but probably the best chance is to put a retro-reflective surface on the top of the entire machine...sadly, that's likely to be impossible for the reasons described above.

I'm always deeply skeptical of these efforts to put stores of knowledge out there for aliens to find. In the case of a memory chip, it's not going to survive all of the radiation and freeze/cook cycles it'll go through - and even if it did, it's unlikely that aliens would figure out how to power it up and what protocol to use to extract the data and so forth. Probably the most valuable thing they could find would be the lander/rover itself - and for that purpose, we already have the six moon landers scattered over the surface of the moon - plus numerous other landers and rovers put out there over the last fifty years.

"We existed and had technology of this level" is probably the best and only message we can leave. Given the extreme difficulties of interstellar travel, it's really quite unlikely that aliens will visit our solar system anyway.

What Wikipedia is doing is properly called "A Publicity Stunt" - and if we're completely honest about that - and treat it as such, it has some value. People still talk about Voyagers' "golden record" - and "Wikipedia on the Moon" will continue to pay back our efforts over the coming decades as science documentaries talk about it - and that'll drive more (human) traffic to our site. It really doesn't much matter what we send - nobody will care about the exact content a decade from now.

To get the maximum bang-for-buck, we should probably invite the general public to nominate articles to go to the moon - sure, we'll get a bunch of junk - but it really doesn't matter.

SteveBaker (talk) 15:24, 26 April 2016 (UTC)

@SteveBaker: The disc is glass with internal defects that supposedly can endure a long time. I doubt that it can be as resilient as the zircons people use to probe what happened in the Archaean, but I would not rule out an ability to survive freeze/thaw cycles, especially if it is an internal space shielded from direct sunlight. And while a space probe may tell *something* about life on Earth, it is not nearly so informative as a picture of Shanghai or a koala bear or a baseball game. Given time and intelligence, substantial amounts of the text may be decipherable. It is also possible (and more of a motivating force) that the content may be of great interest in mere centuries from the present time. The human race has a bad history of censorship and the destruction of libraries. While it may seem that information transmission has the upper hand, consider the future availability of AI that can write totally made-up articles about any topic with internal consistency, complete with a whole fake comment section in which all the various factions of AI bots carry on a pretend debate while any human is lost in the bulk of it. So it is possible that this kind of well-dated, well-preserved archive, placed away from Earth where future generations may be unable to get at it and falsify it, might one day be of supreme interest. Wnt (talk) 17:00, 26 April 2016 (UTC)

If you go to the discussion page Meta:Talk:Wikipedia to the Moon#Real non-volatile storage that can handle space radiation, you'll see you're not the first person to mention the 360TB (I think it's been mentioned at least 3 times independently in various places there and in proposals area). The team is already aware of it, I think from before the advertising. It's been looked at but currently they've chosen the 25GB M-DISC because it seems to be the best one with some decent testing behind it. (Mostly for earth based storage rather than space/moon surface but still...)

While I think it's true the general idea of sending the (I think multiple) discs with various content (not just the 20GB offered to Wikipedia) is about publicity, they also not surprisingly want something which at least has a chance of being read in a few decades, hopefully centuries or more just in case. (So something like an flash memory as a lot of people seem to be proposing is definitely out.) For that reason they've leaning towards the 25GB M-DISCs rather than the 100GB ones or the 360TB research disc.

I say research for a reason, I've you been paying attention as long as I have which at 17 years or something isn't that long, you'll know how everyone is always coming up with this super technology which can store X amount of data but then is barely heard of again. (As with many other areas of technology where there's some claimed superb invention.) Most of these may have been because they could work out a way to turn it into a consumer product which probably doesn't matter so much. However there would still be need for something was can be reliably produced in the time frames needed and for a resonable price. Going to the moon is expesive, but I suspect they can't afford to throw away e.g. $250k on a disc unless someone else is willing to pay for it. In this particular case they're also claiming very long life spans, but while rarer I think I've seen that before too.

They could change their minds but ultimately it's their project so their decision and they have their reasons. The M-DISCs also have the advantage of simplicity of reading compare to the 360TB research disc. I think they're more thinking of humans but either way while you may assume anyone who is smart enough to find the disc would be smart enough to be able to read it and willing to spend the time and effort. But they would have to know it's something to read. Additionally, I suspect the most likely thing if it is ever read, is for it to be read in perhaps a few decades or centuries to confirm what's on it. In that case, the easier it is to read, the more likely someone is to bother.

In the case of the research disc or something similar, it's one thing that could actually be worth adding as an extra, so perhaps they'll do that if they can find the space and volume. It's very small and light so I assume they probably could find something. If my understanding is correct and there are multiple M-DISCs planned they could potentially remove one or more if it fits with whatever they planned to store on it. (I don't know the history but I'm guessing the M-DISC and other options were probably something they started to look in to long before February so the 360TB is still new.)

BTW as for SteveBaker's point, I'm pretty sure getting non editors (or very irregular editors) involved was a reason for the site wide advertising. I strongly suspect there'll be more come June 10 when the voting starts.

Nil Einne (talk) 19:13, 26 April 2016 (UTC)

The glass disk approach isn't going to work either. According to M-DISC "Millenniata claims that properly stored M-DISC DVD recordings will last 1000 years." - so improperly stored...what? 10 years? 100 years? Certainly not enough to be worth the effort. We have 20Gbytes - that's not much. I don't think we'll be sending too many fancy high-rez photographs. A photo of a Koala bear might as well be a bunch of random pixels if you don't know what you're looking at. Especially if we also include articles with things like teddy bears in them...it would be alarmingly easy to confuse the aliens. But it's not going to last long enough to matter. It's a publicity stunt and nothing more...which is not to say that it's a worthless activity - just that if you're putting it there for aliens to read then you're kidding yourself. Putting it inside the great pyramid of Giza would give them a better chance of finding it after the zombie apocalypse wipes us all out. SteveBaker (talk) 19:26, 26 April 2016 (UTC)

But why do people keep bringing up aliens? The FAQ itself says it's not very likely and the primary goal is humans. As for zombie apocalypse, again this seems a bit of an extreme example. With the way the internet etc works nowadays, it seems unlikely that someone could say semi-secretly modify the bible as almost definitely happened before publishing. Dumping it in the Great Pyramid of Gaza seems a little rude. I'm sure you could find somewhere else, but still guaranteeing your time capsule on earth isn't modified, particularly if it's widely publicised is a little harder. Until and unless regular moon visits or even moon base are a thing, it's a time capsule that we can be fairly sure isn't modified. So by that token checking the contents in decades or may be centuries seems at least nominally interesting. Particularly perhaps checking our records of what was sent. This doesn't change the fact it's largely a publicity gesture as I said above and elsewhere, but it does mean thinking of it as solely a publicity gesture and not something that will ever be looked at in the future is as I said above IMO a mistake. All this assumes it even makes it to the moon intact, which probably isn't that likely. (Of course the other thing is the process of selection and selection is probably significant and may be interesting in the future, but to get that you need to have a catalyst for the selection.)

P.S. What glass disc are you referring to? The M-DISC composition is a trade secret but AFAIK is normally called ceramic or stone. Our article says Glassy carbon which suggests either ceramic or carbon or perhaps glass-like carbon would be resonable. I guess you could call it glass, but this may be best avoided since the term is often used restrictively enough that it won't apply to glass like carbon. The 360TB disc is AFAIK often called glass or quartz, but it's claimed to last billions of years however as I said above it's a research project so such claims have more scepticism.

P.P.S. Rereading the talk page, I remember now the specific claim was the testing for the 25GB M-DISC qualfies it (I guess in the opinion of the PTS) for use in space. I'm not sure what testing this is as I couldn't find any specific mention, but it's difficult to search for obvious reasons. Something else I read a while ago in the talk page which seems to be confirmed by [3] is that the biggest risk (on earth and probably in space) is the polycarbonate outer layer. This would likely be significantly affected by conditions on the moon surface so I expect decades may be more resonable. Technically I wonder how easy it will be to replace this layer, or simple read without it. Realisiticly it doesn't seem likely anyone is going to be using a bog standard BD-ROM drive centuries from now. And unless the 360TB tech really takes off, it seems very likely it'll be far easier to read than that. So I stick by my earlier point, getting someone interested enough would likely be easier than with the 360TB disc and it may very well still be possible in centuries. The next concern is the glass like carbon recording surface. It seems this is susceptable to oxidation over millinea so that shouldn't be much of a concern. However I'm not sure how well we know how something like that will survive in space (or specifically on the surface of the moon).

Nil Einne (talk) 20:20, 26 April 2016 (UTC)

It may be a research project, but it is also possible that this invention will go by the wayside for purely commercial reasons. So this may be the first time and the last that a medium holding this much storage for that much time can be sent to the Moon. It could be worth taking the risk on the new technology. Wnt (talk) 21:33, 26 April 2016 (UTC)

If we are talking about marking the moon for real (and not as part of some publicity stunt), then I would suggest your best strategy would be to design a long-lasting rover type robot to slowly lay down a large geometric design of a colossal scale. Something similar the the Nazca lines. A pattern that is large enough and deep enough should survive billions of years on the moon. Dragons flight (talk) 21:49, 26 April 2016 (UTC)

April 26

Incremental cost of ice drilling

Years ago I used to work on ice cores. An early deep core, e.g. GISP2 (3000 m), had a full cost of retrieval of about $60M, making each meter of ice nominally worth about $20k. Of course, deep cores are much more expensive than shallow cores. In addition, there has been much improvement in ice core technology and infrastructure. I've heard that projects like the Rapid Access Ice Drill (RAID) [4] for ice cores, and the fast hot water drill projects (e.g [5] for subglacial access, but not coring) have made the cost of ice coring and ice drilling much lower. However, I have had trouble finding specific information on current costs. What is the incremental cost of collecting a 100 to 200 m ice core these days? Alternatively, what is the cost of drilling through 100 to 200 m of ice to reach the subglacial bed if one is willing to discard / destroy the overlying ice? Dragons flight (talk) 09:44, 26 April 2016 (UTC)

If you really want the marginal cost, I think you'll have to do some deep-diving into research program budgets. The way to approach this is to look at the cost structure of the project: how much money is overhead, how much is capital outlay for specialized equipment, how much is variable cost for labor, fuel, travel and transportation expense, equipment operation? I'm tempted to say that the cost is dominated by overhead, which implies a very small incremental cost for each additional unit of sample retrieved. Many of the programs listed, e.g., in the NOAA data set archive were part of publically funded research projects, so if you look for their budgets (e.g. by chasing down the individual grants cited in each author's research-publications), you'll probably find their accounting summaries. It seems that it would be a research project just to track that information down, let alone to distill it into a meaningful average across a large number of recent sample-retrieval missions.

More to the point: do funding agencies or researchers really think in terms of unit-cost per meter of core sample, or are they more concerned with other more abstract metrics like "scientific merit per Government-dollar"?

Nimur (talk) 11:49, 26 April 2016 (UTC)

I recently had an idea for some interesting glacial work. (Or at least I think it is interesting.) However, it would require drilling a substantial number of holes 100-200 m through ice. I'm trying to get an idea of the feasibility of the idea. If it is a $10M+ project, then I would probably just abandon the idea as being too costly to be worth pursuing. If it is ~$1M project, then maybe it is worth trying to advocate the idea to other people. (As I don't personally do ice core collection, I'd obviously have to get others interested in not only funding the work but also doing the study.) I'm trying to get a rough idea of the costs involved before I waste too much time on something that might be a total non-starter. Dragons flight (talk) 12:42, 26 April 2016 (UTC)

Again, I suspect the cost can scale dramatically. It's much easier and cheaper to drill through 800 feet of rock in Oklahoma than through 200 feet of ice in the middle of a glacier in Greenland. I suspect you could get a lot of good science on a very tiny budget; and if you could make the case for getting better science on a bigger budget, you could probably find the money - money is surprisingly cheap.

Clearly, there do exist organizations who will fund field research of this nature; if you are not already building experience towards the kind of project management to initiate and lead such a project, your best bet may be to attend a conference and find some research collaborators. I'd start at a big conference - like AGU, where you can survey the entirety of the field from multiple different angles - and then gradually migrate to a more specific subject-area meeting. If my memory serves correctly, you are already PI on some other private-sector projects, so you're probably in as good a position as anybody to initiate a field-data-collection program; but funding agencies like specific experience as part of their risk reduction strategy. Find somebody who has the right resume, work with them, and co-list them as a cooperative researcher.

Large projects of this nature are usually preceded by much smaller exploratory programs to establish proof-of-merit; you could try putting out a paper just to develop the idea, and test the reception for the basic premise before burning any large quantity of money on field work.

Nimur (talk) 13:15, 26 April 2016 (UTC)

I know you are trying to be helpful, but you aren't really saying anything I don't know already. I'm trying to put together a sketch of project, before taking it to other more knowledgable people that I hope might be interested. Part of that though is having some idea of the scale and cost of the program. Admittedly it isn't easy to find cost information for something like this, so I was hoping someone might have better luck at tracking it down than I have so far. If not, I can keep looking and thinking of who else to ask. Dragons flight (talk) 14:25, 26 April 2016 (UTC)

To be fair we are more like librarians, not subject matter experts. This is a difficult, deeply technical, question. You seem to have a ton of knowledge about it already - and it's astronomically unlikely that any of the few dozen reference desk regulars will have more knowledge on the subject than you do. So we're definitely not going to be of direct help.

So, perhaps the best way we might be of assistance is if you give us the names of organizations or individual people who are likely to be more up to date than you are - give us any jargon terms that are unique to this line of work. Then let the (impressive) search skills and legendary tenacity of our reference desk "librarians" do the work. An alternative might be that we could find an online forum where ice core drillers hang out and we could perhaps get an answer there? SteveBaker (talk) 15:05, 26 April 2016 (UTC)

(EC)Right, so if you're a real scientist who has done real science on ice cores, then probably none of us know more off the top of our heads than you do, and as Nimur said, this is no small research project in and of itself. Anyway, it's not clear what you have and haven't looked at. You say you know what Nimur told you. Have you looked at this [6] NSF grant? That project is ongoing, and over the last few years "1,511 m of the total 3,470 m of ice at the site has been collected", with about $1million paid out so far. Of course not all the money went to drilling. Have you looked for budgets for other projects NSF PLR has funded? Have you used the NSF award search to search for everything related to drilling and ice cores? I think this [7] is saying that you can get budget info on funded grants via FOIA requests, but I have not tried that and I'm not sure. One of the simplest ways to get budget info would be to contact some of the PIs directly. SemanticMantis (talk) 15:08, 26 April 2016 (UTC)

After browsing around on NSF's Polar Science program and Ice Cores website, I found the U.S. Ice Drilling Program resources for scientists. This is a non-governmental organization whose primary purpose is to support specifically-NSF-funded scientists, and to assist them in budgeting and managing field research.

If you aren't already familiar with their publications, it might help to read through the Long Range Science plan, the Drilling Technology plan, and the listing of expeditions, to get an idea for the typical budgets and scope of support. You can also download their paperwork for research proposals, or contact their representatives. "Your email will be received by the IDPO-IDDO and personnel from IDDO will contact you to discuss your needs and provide a Letter of Support and Scope of Work/Cost Estimate for your project."

NSF's website links to this service, but they remind you that U.S. Ice Drilling Program is not a Government website, and NSF doesn't officially vouch for its accuracy or merit.

In particular - their science program matrix includes an entry for a "Borehole Array" project (multiple borings), and they are planning for that program to require about a "week" of field time, plus a Twin Otter support aircraft. That may help set a lower-bound for the kind of budget - you're talking about funding an aircraft that probably costs around $1500 per Hobbs-hour, plus a crew, for a week, just to get set up at a place that's worth allocating the scientific equipment. In other words, this kind of work is planned to be conducted under the auspices of a major NSF grant with a daily budget in the neighborhood of tens-of-thousands-of-dollars-per-day.

But again - the issue isn't the money - they'll let you use the drills - but the issue is that these kind of ice drills are owned by the United States Government; they are scheduled to be used in specific locations; and if you want to use this unique equipment and the specialized crew who are trained to operate them, you have to go through the effort to get into the "system," so to speak. Your project has to line up with their projects and their objectives.

Nimur (talk) 16:58, 26 April 2016 (UTC)

mastoids

My mother (now 91) & her sister both had "mastoids" when they were young. Her sister almost died from this, & Mom says her "mastoids were removed". According to Mom, her "mastoids" drained externally out of her ear---while her sister's drained internally & almost killed her. Neither of us knew what mastoids are, so we looked it up in Wikipedia. You say they are a bone protrusion on the skull for the attachment of muscles. This is not making sense, & I sure would appreciate a better understanding.

Thanks------aj seaman email address redacted by LongHairedFop, to stop spam — Preceding unsigned comment added by 201.191.91.18 (talk) 14:51, 26 April 2016 (UTC)

See Mastoiditis. The Mastoid part of the temporal bone behind the ear contains air-filled spaces. Mastoiditis is when those spaces become filled with fluid, and must be drained. As noted in the article, infections associated with mastoiditis used to be a major cause of childhood mortality, so the accounts of your mother and aunt are fully in line with that. I hope that helps! --Jayron32 15:04, 26 April 2016 (UTC)

Another weird thing that can happen with mastoids is Cholesteatoma, where skin starts growing in places it shouldn't. That can require a mastoidectomy. SemanticMantis (talk) 15:12, 26 April 2016 (UTC)

What a difference antibiotics have made. Klbrain (talk) 00:12, 27 April 2016 (UTC)

Though alarmingly Antimicrobial resistance is spreading so fast that most if not all of the existing ones may soon be useless. {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 14:29, 27 April 2016 (UTC)

Volume expansion or contraction for mixing two solutions

What is the volume expansion or contraction when mixing two aqueous solutions of salts or a solution of salt and another of sugar as function of their mixing mass or molar ratio? Are there any data pages on this issue?--5.2.200.163 (talk) 15:33, 26 April 2016 (UTC)

It's a whole lot of messy calculus to do such calculations, but if you want an overview, here's an old ACS article that covers the concept using ethanol-water mixtures as a model. Here is an even older article on volume changes when dissolving various halogen salts. In Wikipedia, you can read about concepts like Ideal solution (for when volumes are additive) and Margules function, and more generally about Chemical potential which is the root concept which affects a whole lot of deviations from ideal behavior in a lot of situations (Ideal gas, ideal equilibrium constant, etc.) --Jayron32 18:29, 26 April 2016 (UTC)

I see that the first article says something about a shrinkage factor whose definition would be very interesting to see. In other sources encountered there was just some mention of a percent expression of this factor, without formula.--5.2.200.163 (talk) 16:34, 27 April 2016 (UTC)

I see also that the article introduction says something about the relation of the concept (shrinkage factor) to established ones like apparent and partial volume. That would be extremely interesting.--5.2.200.163 (talk) 16:39, 27 April 2016 (UTC)

Phase-transition of water: Supercritical --> solid?

Hey there,

I stumbled about a question today and I can't get my head around it. My Physical Chemistry textbook shows a phase diagram of that indicates, that there is a phase-transition of super-critical water at around 600 k and 10 GPa. Does anyone now, if it is possible to form ice directy from supercritical water?

Thank's --134.61.98.4 (talk) 18:10, 26 April 2016 (UTC)

No, because at no point does the solid-liquid or solid-gas transition happen at or above that temperature and pressure combination. The supercritical transition occurs when there is no distinction between gas-like behavior and liquid-like behavior in a fluid (basically, increasing temperature makes a liquid more gas-like. Increasing pressure makes a gas more liquid-like. Raise both above a certain threshold, and the difference between a gas and a liquid becomes inconsequential, that's a supercritical fluid). The solid phase of water should not be anywhere near these conditions. --Jayron32 18:32, 26 April 2016 (UTC)

As shown at water and carbon dioxide it is entirely possible to have a supercritical fluid to solid phase transition. Generally, the transition occurs by taking a supercritical fluid and subjecting it to enormous pressures until it converts back to a solid. Dragons flight (talk) 19:12, 26 April 2016 (UTC)

So stricken. Thanks for providing a link to the more accurate phase diagram showing the solid-supercritical phase transition. I should probably actually have looked than speaking extemporaneously. I've been correctly chastised. Thank you. --Jayron32 20:15, 26 April 2016 (UTC)

Lighting the grail-shaped beacon, eh? Bad, bad, naughty Zoot! μηδείς (talk) 20:38, 26 April 2016 (UTC)

Next time I try to state my question clearer and provide a diagram myself. But I could find one through my quick search.--134.61.98.4 (talk) 13:32, 27 April 2016 (UTC)

Thank you both. This is exatly what I meant Dragons flight. You don't happen to know where I can get more information about the nature of this transistion or if there are any applications that use it? Can I imagine it to be some sort of sublimation/ re-sublimation? I was under the impression, that supercritical fluids cannot be in equilibrium with other phases, so this somehow makes me curious ;) Thanks again --134.61.98.4 (talk) 19:40, 26 April 2016 (UTC)

Supercritical fluid phase can perfectly well be in a thermodynamical equilibrium with the solid phase. Imagine a cylinder filled with a supercritical fluid, where the piston can be moved in (or out) so that the cylinder volume is reduced (or increased) but none of its contents escape, and the temperature of the contents is kept constant. This process - provided the contents of the cylinder have time to reach equilibrium - is called isothermal compression (or expansion). Let's assume the temperature is above the critical-point temperature. Isothermal compression of the supercritical fluid will cause the pressure to rise until you reach the phase-transition pressure - the pressure at which solid phase and supercritical fluid phase coexist. As you keep compressing, more of the supercritical fluid will condense into solid, but the pressure will remain constant as long as any supercritical fluid is left. If you stop compressing at tha point, you will have an equilibrium mixture of solid and supercritical fluid phases. Further compression beyound the volume point at which there's no supercritical fluid left will cause the pressure to start rising again, as you are now in a solid phase and not in coexistence of solid and supercritical fluid phases. Does this help? --Dr Dima (talk) 20:57, 26 April 2016 (UTC)

Regarding your question where to get more information: at an undergrad/grad level, I strongly recommend Landau & Lifschits textbook, and Zel'dovich & Raiser textbook (this one), but those are not an easy read. At a high-school level, I need to think what would be the best place to start from. --Dr Dima (talk) 21:03, 26 April 2016 (UTC)

This is very helpful, thank you. If I understand you correctly, the transition supercritical fluid --> solid is thermodynamicaly not different from the transition gas --> fluid where the pressure also remains constant until all gas/fluid is gone?

The literature looks good. I'm at graduate level but my area of expertise is actually inorganic chemistry. The second book looks promising, I will definitively check it out when I get the time.--134.61.98.4 (talk) 12:59, 27 April 2016 (UTC)

Here's [8] some interesting video of supercritical water in a "hydrothermal diamond anvil cell". SemanticMantis (talk) 21:40, 26 April 2016 (UTC)

Nice video, thanks --134.61.98.4 (talk) 13:14, 27 April 2016 (UTC)

Reusing lunar rovers

1) Is it true that there are 6 rovers on the Moon now ?

2) How many were in good working order when last used ?

3) Would it be possible to land near one, replace the batteries, and get it to run again ? If so, this would seem to allow us to dramatically decrease the weight versus bringing a new rover, although at the cost of only being able to land where a working rover is present. StuRat (talk) 19:19, 26 April 2016 (UTC)

1. Well, there were three Apollo moon buggies - a couple of Russian Lunokhod rovers from the same era - and the Chinese Yutu rover that failed after the first day or so...so, yeah - six in total.
2. The three Apollo buggies were still in working order when they were abandoned. The first Lunokhod worked for nearly a year - I'm not sure about the second one.
3. Maybe...but electronics don't like to be frozen and most spacecraft die when the heaters fail to keep the electronics warm enough. But getting an existing rover to run again doesn't help if it still has the same set of sensors and cameras aboard. The Apollo buggies only really had a camera aboard - and after 11 months of driving around, the Lunohkod probably gathered as much data as would be useful. What makes most new missions interesting is that they have new instruments aboard that can measure things we couldn't manage previously.

SteveBaker (talk) 19:34, 26 April 2016 (UTC)

3) Then couldn't they swap in new instruments, too ? Still cheaper than replacing the entire platform, I imagine. StuRat (talk) 19:38, 26 April 2016 (UTC)

Lunokhods are still being used, in a sense; see Lunar Laser Ranging experiment. The electronics is probably dead due to radiation exposure, but it's possible that the chassis and motors may be salvaged and reused if needed. --Dr Dima (talk) 21:27, 26 April 2016 (UTC)

This article might be useful. Regarding replacing the instruments of an existing rover, I doubt there would be any benefit. There's a finite amount of time in a mission. You don't want your crew playing mechanic on the Moon when they could be doing more useful work. And there's the risk that they might not succeed in retrofitting the rover, or that it's unusable. Space is a hostile environment. --71.110.8.102 (talk) 22:15, 26 April 2016 (UTC)

Ship of Theseus proves that you can get the rover to work again on the Moon. The rover consists of a finite number of components. Let's name them as component#1 to component#18345. Step one: replace component#1 Step two: test if rover is working again Step three: if rover works then your job is done, otherwise return to Step one and replace the next component. 175.45.116.66 (talk) 00:00, 27 April 2016 (UTC)

On Earth, the NASA Apollo lunar rovers weighed 460lbs and the lander weighed 35,000lbs (For comparison, the Spirit and Opportunity Mars rovers are each about 400lbs Earth-weight). If this is a manned mission (which it's gonna need to be if you're going to start repairing a rover) - then adding a rover to the launch weight isn't that big of a deal...especially since you're going to need to take replacement batteries and whatever other spares seem likely to be needed plus the tools to replace them.

The two Lunakhods each weighed in at 1,667lb - they did have solar panels - which is why Lunakhod 1 lasted 11 months - but what finally killed it was the radioactive Polonium 210 used to keep the electronics warm ran out. Lunakhod 2 lasted 4 months, failing with a cooling problem.

The Chinese Yuto weighed 310lbs - so it would be even easier to ship an entire new one rather than locate and repair it. It's motors (probably) didn't survive the first lunar night - although the rest of the rover carried on working for a few months after that. It also used solar panels for battery charging and a radio isotope source for keeping things warm through the 14 day solar nights.

Sending a spirit/opportunity look-alike - with a likely 2000 day mission life - would make a whole lot more sense than repairing a golf-cart that doesn't have useful sensors - and doesn't even have solar panels to rechargeable its' batteries. However, they'd require some redesign for surviving the long lunar nights without freezing up.

Given the ungodly cost of sending humans to the moon, the cost per hour to have them there is enormous. Having them spend time repairing a rover that could easily be replaced (and with vastly higher utility - newer sensors, fancier electronics, etc) - with not much confidence that it can indeed be repaired at all - it just doesn't make sense. SteveBaker (talk) 03:43, 27 April 2016 (UTC)

There can always be some combination of circumstances that motivates people to do something. For example, there you are making a routine crew exchange run to the Chinese base at the Lunar pole, when a minor course correction turns into an explosion. Your orbiter is heading directly at the Moon, and you can't get the rockets working. So you herd everybody into the lander (minus whoever you arranged to draw the short straw) and just manage to clear the Moon, but you're in an equatorial orbit. You land at whatever site you can reach with usable materials. Just so, you're looking at a moon rover and you have a trunk full of tools and solar panels. And, oh, seventy-two, nay, make it ninety-six hours worth of air. Having 5,000 miles to the base and going about 5 mph, this is a problem, but hey, you might rig some CO2 scrubbers out of your cargo. Or stop at some abandoned lander on the way. And NASA can hear your suit radios, even if you can't hear them, and might be negotiating for a rescue from the Chinese. Or have a plan to drop a care package. In any case ... better get working on that moon rover, time is ticking. :) Wnt (talk) 10:16, 27 April 2016 (UTC)

So when is this novel coming out, Wnt? (Hey, it worked for Andy Weir). {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 14:32, 27 April 2016 (UTC)

Ha, I'd give that book a shot too :) SemanticMantis (talk) 16:15, 27 April 2016 (UTC)

@87.81.230.195 and SemanticMantis: This isn't really my field, so getting all the lingo right would be tough. Doing research to see which rover parts endure and which don't, whether a plausible portable 3D printing technology can replace them etc. is tough. Getting characters right is really tough. But if enough people were interested enough, we could try setting it up at WikiBooks as a collaborative writing experiment. We might even work in that super-durable glass disc holding all of Wikipedia somehow. (probably crack it in half and use it as mirrors to signal to each other. :) ) Wnt (talk) 18:31, 27 April 2016 (UTC)

No...they're hoping that the information they need is encoded in one of the roughly 6000 articles that we have on Japanese railway stations.

Well, the surface area of the moon is about equal to that of North America and Europe combined - even if you are on the earth-facing side - you're looking for things the size of a small car in an area the size of Europe. I kinda suspect you'd need to be either extremely lucky - or to endure a LONG diversion to find a handy rover...and I still maintain that their electronics would be frozen to the point of destruction. On the moon, an unheated rover would be chilled down to -150 degC for a long time - even the most rugged military-grade electronics are junk if you let them get below -55 degC.

Still, it evidently worked for Mark Watney as he took a little sojourn on Mars. But then Martian nights aren't two weeks long and there is at least some atmosphere to help retain the heat. SteveBaker (talk) 22:33, 27 April 2016 (UTC)

Why exactly can't lunar rovers handle cold ?

Considering the expense of getting them there, I'd think they could be made out of a platinum-iridium alloy with zero coefficient of thermal expansion, at minimal additional expense. So, then, what about cold destroys them ? StuRat (talk) 01:19, 28 April 2016 (UTC)

April 27

What is the most time which recorded about human being without sleeping?

I use an application of neuroscience quiz. One of the question is about the time that recorded about human being who went some days without sleeping. The options were 6 days, 7 days and 11 days, while the correct answer was 11 days. I would like to get a source for this thing (11 days). 93.126.95.68 (talk) 01:53, 27 April 2016 (UTC)

The source is very likely this: Randy_Gardner_(record_holder). Also noteworthy is that this is, apparently, for a healthy individual; people with severe disorders such as Fatal Familial Insomnia are probably excluded, as are people in a Persistent Vegetative State or coma (indeed coma is not sleep). --Dr Dima (talk) 02:14, 27 April 2016 (UTC)

Why do transmission substations gets overheated during black outs?

I would like to know why the transmission substations gets overheated as said in this lecture(Slide 5) when blackout occurs in step 4 since the demand of current can't be meted.Could anyone help me.JUSTIN JOHNS (talk) 10:39, 27 April 2016 (UTC)

Substations are carefully tuned so that their input equals their output; they don't have infinite storage capacity. If something happens downstream so that the output of the station cannot be accepted -- let's just say a power line breaks -- the substation is suddenly taking in more power than it can transmit, and that power has to go someplace, and that someplace is heat. So now this substation must shut down or it will melt. Which means the substations that were sending to this substation don't have anywhere to send their excess electricity. So they shut down too...cascading blackouts... --jpgordon^{::==( o )} 14:50, 27 April 2016 (UTC)

For that answer please see "not even wrong". A substation is a transformer and stores nothing whatsoever. 91.155.193.199 (talk) 16:17, 27 April 2016 (UTC)

No capacitors? Really? --jpgordon^{::==( o )} 16:37, 27 April 2016 (UTC)

Really. A capacitor can store a mere pittance of energy. In power distribution, capacitors are used for power factor correction, not to store even one second's worth of anything. Capacitors don't store no AC. 91.155.193.199 (talk) 16:48, 27 April 2016 (UTC)

OK, so why don't _you_ answer the question, rather than just snarking at details? --jpgordon^{::==( o )} 17:24, 27 April 2016 (UTC)

Did a while ago. Not that that is a prerequisite for pointing out a wrong answer. 91.155.193.199 (talk) 17:32, 27 April 2016 (UTC)

@Jpgordon: That almost makes sense... but it doesn't. Because if the substation "shuts down", where does all that incoming power go? Why can't it just shut down partly, send some of the power wherever the power would go if it shut down, and just take some to pass downstream? I'm sure there's a good engineering reason but it has to be more complicated than what you're saying. Wnt (talk) 15:18, 27 April 2016 (UTC)

That Powerpoint slide is not the clearest thing I have seen. My guess is that there is an area that is served by both local and remote power generation. When remote generation fails, local generation is overwhelmed and shuts down as well. Should see the original sources that were used to generate that Powerpoint slide to tell for real. 91.155.193.199 (talk) 16:48, 27 April 2016 (UTC)

Yes, that's a reasonable guess, but local generation is not mentioned in the PP slide. What the slide tells us is that the transmission stations were overloaded. That's because one transmission station feeds power into the area from one source, so if three sources (the slide tells us) were down, the remaining transmission stations (we don't know how many) each had to transmit more power (from where, we don't know, but there must have been at least one source still live) into the area to keep it live. Therefore some of the remaining stations overheated and shut down. The transmission stations in turn feed transformer stations. With some transmission stations out of action, that left fewer transformer stations than normal trying to supply the same area, so those stations in turn overheated and shut down. Note the distinction between transmission stations, which are switches, and transformer stations, which change the voltage.--Heron (talk) 17:46, 27 April 2016 (UTC)

Good point, and part of the complete answer to the OP's question, "Why do transmission substations gets overheated during black outs?" (sic).

The full answer is that transmission station switches are rated to carry so much electrical power or wattage of electricity, and no more. They're set up so that a transformer feeds them, and distributes some of the power passing through it (not stored in any way, a transformer's just a way of using electromagnetic induction to change the alternating current passing through it from one voltage to another without storing any power - though some power is dissipated through Joule heating of the windings of the transformer as the current increases and the voltage drops in the secondary windings of the transformer) to several switches which distribute power down through power transmission lines, ultimately to where the electricity is used.

When one of those switches fails or ceases to have power passing through it (as when one of more transformers downline from it fails and no longer draws current), it sometimes happens that more current flows through the other switches (for one of several possible reasons), which increases the wattage through those switches above their design limits (the voltage being about the same, but the current dramatically increased), so that Joule heating through the current-carrying parts of the remaining live switches increases accordingly beyond the temperature the switches were designed to work under, and they overheat.

This also works at the level of entire transmission stations - when one entire transmission station fails (no matter how), electrical power load can be shifted to other stations, and they can sometimes be subjected to current demand above their design limits, so that switches can get overheated and fail. That's one of the possible ways cascading power failures happen. loupgarous (talk) 18:33, 27 April 2016 (UTC)

@Jpgordon Oh really? The substations shown in the slide are transformers and the initial failures are upstream. Transformers have no power storage capacity (beyond one AC cycle) and have no problem with zero output load. There is no "excess electricity" involved, only cascading blackouts when substations shut down rather than supply excessive power demands. AllBestFaith (talk) 18:58, 27 April 2016 (UTC)

Yay! I was wrong about something. "The quickest way to get a correct answer on the Internet is to provide an incorrect one." --jpgordon^{::==( o )} 19:02, 27 April 2016 (UTC)

Aye, that would be Cunningham's law [9]. Your original answer did make sense to me, and I would have probably believed it if that was the only response, so this is an interesting thread. Of course it's totally fine to accidentally illustrate Cunningham now and then, but IMO we should all make it a point to not participate too heavily on either side (e.g. pointing out errors only [10], posting under the influence of the Dunning–Kruger_effect etc.). I'll also note that though I see several wikilinks above, none of them seem to refute your answer on their own. So even with your acknowledgement of incorrectness, we're still kind of trusting in the authority of strangers who know how to talk a good talk. And that's not to say I distrust the further refinements, just to point out how hard at can be to support a specific answer with a specific reference :) SemanticMantis (talk) 20:00, 27 April 2016 (UTC)

Can playing too much on the keyboard induce bodily injuries?

Is it possible to play for several hours or the whole day hours without sore arms and hands and fingers? 140.254.77.204 (talk) 14:46, 27 April 2016 (UTC)

(It's not clear whether you mean playing music on an organ/piano or video games on a PC/laptop.) I suffer from "mouse finger". That is, the pointer finger on my dominant hand gets sore at the tip, both from typing and using the mouse. I wouldn't call that an "injury", however. I try using other fingers to click on the mouse and type, to minimize the pain. StuRat (talk) 15:34, 27 April 2016 (UTC)

Like most things, you have to learn how to do it. An experienced pianist will have an exercise regime designed to strengthen hands, arms and shoulders, and the length of time he/she can play will have been built up gradually so that the body becomes accustomed to it. 81.132.106.10 (talk) 15:44, 27 April 2016 (UTC)

You may be interested in reading about repetitive strain injury, and perhaps carpal tunnel syndrome, which is associated with repetitive wrist movement. SemanticMantis (talk) 16:13, 27 April 2016 (UTC)

See the warning labels on some keyboards and not moving the whole body is covered by evolution with a reduced amount of food, only. See such diseases those number increases with the body weight. --Hans Haase (有问题吗) 19:54, 27 April 2016 (UTC)

People could try the simplest solutions first. In the days of manual typewriters, sectaries typed all day, every day. Cutting down and gluten and dairy containing foods often helped enormously. Maybe this why so many took to eating crispbreadlike Ryvita instead of ordinary bread – not to keep down their weight (most were skinny-as-rakes already) but they felt better as it contains very little gluten. Also, this may be why they had such beautiful figures, as people who are sensitive to gluten tend to put on weight and become pair-shaped. This maybe 'OR' on my part and based on straw-poll observations yet others appear to agree. [11], [12] What both of these articles fail to mention however, is that our modern diet is deficient in Omega III oils. Snake Oil (derived from the Chinese Water Snakes) is rich in these, which was why it was useful in treating joint pains. The charlatans that sold 'patented' medicine duly tried to ridicule it to increase their own sales. Yet joint pain is often associated with too little Omega III in the diet. Also, keeping the keyboard tilted reduces the amount of flex required in the hands.--Aspro (talk) 21:08, 27 April 2016 (UTC)

Top bottom wing(s) of a plane

1. The F22-Raptor has the wings v-shaped, why are they not straight? -- Apostle (talk) 20:16, 27 April 2016 (UTC)

See Delta wing. Basically, it's because straight wings wouldn't work properly at the speed of the F22 (or any other modern fighter). Tevildo (talk) 20:21, 27 April 2016 (UTC)

When you have to pitch up the Nose in an small aircraft, like when starting or landing, the body will work like a Windshield for a straight up Wing far behind. There is much more airflow at the sides and thus such V-Wings are more effective. Ofcourse these positions makes it more complicated to steer as you dont get a simple yaw windforce but these planes are flown with computersupport today so they can be handled easy nomatter such complicated aerodynamics. B.t.w. the Boeing F/A-18E/F Super Hornet and Lockheed F-117 Nighthawk have these V-Wings too. --Kharon (talk) 01:26, 28 April 2016 (UTC)

Absence of Nipple development - Medical term?

(Nedical disclaimer noted.)

I noted the following from an IP contributor https://en.wikipedia.org/w/index.php?title=Henry_Morgan&diff=next&oldid=717460941, but I am wondering if nipple absence is an actual medical condition, albiet exceptionally rare? Sfan00 IMG (talk) 21:08, 27 April 2016 (UTC)

It is - see Athelia (disease). Tevildo (talk) 21:10, 27 April 2016 (UTC)

Now to determine if it was known in the 17/18th century :) Sfan00 IMG (talk) 21:29, 27 April 2016 (UTC)

April 28

Is it posssible to push in and pull out a hoop in womb, so that liquid can cover an object demi-spherically?

49.135.2.215 (talk) 01:31, 28 April 2016 (UTC)Like sushi