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July 8

RPM and car control

Why does downshifting, and running your engine at a higher RPM give you more steering control of the car?

Does it? I don't see why it would. Is it something you have actually experienced yourself? —Bromskloss 11:06, 8 July 2007 (UTC)[reply]

It gives you greater control over the speed of your car - engine braking means you can slow down just by lifting your foot off the accelerator. A slower speed then gives you more steering control. Gandalf61 12:45, 8 July 2007 (UTC)[reply]

Your power steering pump is incorrectly producing more hydraulic pressure at higher RPM? Generally, systems are designed to either produce a steady pressure or, often, less pressure at high speed when there's less need to overcome the enormous static friction of tires when you're stopped.

Atlant 14:05, 8 July 2007 (UTC)[reply]

Also, by slowing down, your car will 'dive', putting more weight on the front wheels, so they are less likely to slip.

It sure does feel like it, doesn't it? I suspect, however, that it is just an illusion from aforementioned control over speed and improved control at lower speeds. Properly done, the downshift also puts you well into the "preferred" (there is almost certainly a proper term for this, but I do not know it) range for the engine, where it can supply plenty of power and either accelerate or decelerate while maintaining responsiveness. There is a related argument for not dropping into neutral to coast down hills, but that is more about maintaining control of you speed. With the engine engaged, even in a high gear, your acceleration will be slower, providing more control. Furthermore, there is also the quality of life issue - accelerating around turns is just plain fun. -Eldereft 21:40, 8 July 2007 (UTC)[reply]

Race drivers and drifting and autocross enthusiasts most certainly do rely on the 'weight transfer' (terrible choice of words!) effect of braking to get more down-force (and therefore more grip) at the front wheels - and they sometimes to deliberately weaken the grip at the back. That certainly has an effect on steering because it allows you to turn sharper without the front wheels skidding and/or to allow the rear wheels to 'drift' outwards and thereby induce over-steer. This is also beneficial for front wheel drive cars in that you have a brief window of opportunity for stamping on the gas and getting more accelleration without wheel-spin (a major reason why I love front wheel drive cars - and loath rear wheel drive cars!). But that's only going to be noticable at extremes of driving when you'd probably skid off the road entirely if you hadn't done that. Stamping on the brakes also causes weight transfer - and heel/toe driving where the gas and brake are operated together can take advantage of this. For ordinary street driving, I'd be surprised if this effect was anything other than an illusion. SteveBaker 03:24, 9 July 2007 (UTC)[reply]

Wet Hair

What could happen to you if you sleep with wet hair? Thanks in advance.

Your pillow gets damp. DuncanHill 12:40, 8 July 2007 (UTC)[reply]

...and you wake up with *really* messy hair. --Kurt Shaped Box 12:49, 8 July 2007 (UTC)[reply]

Off-topic joke posts.

And the hair fairy gets herpes. 12:51, 8 July 2007 (UTC)

I have hidden this anonymous comment. See the Reference Desk guidelines. Nimur 18:10, 8 July 2007 (UTC) [reply]

In hot humid weather, the hair and/or pillow might mildew. Edison 19:00, 8 July 2007 (UTC)[reply]

My mother used to tell me that going to bed with wet hair would give me a chill (or something).

My cat won't sleep on my bed when I have wet hair. Weird thing. JoshHolloway 22:32, 8 July 2007 (UTC)[reply]

My wife picked up a variety of "wet" superstitions from her mom, including one that going to bed with wet hair would make her sick and/or was a generically "bad" thing to do. So far as I can tell, it just makes your hair really messy the next day. And, just to close my initial anecdote, she also was told that wetness caused by rain was much more likely to make you sick than wetness caused by, say, a shower. So, if she got wet from the rain, she was expected to take a brief shower to get rid of the "bad wet" and replace it with, I dunno, "good wet". (Insert punchline here). Matt Deres 23:28, 11 July 2007 (UTC)[reply]

science / jupiters moons

how do jupiters moons stay in orbit around jupiter?

See orbit. Gdr 11:53, 8 July 2007 (UTC)[reply]

Re:Lucid dreaming

Does lucid dreaming make you exhausted? And how do you actually invoke that dream? -Zacharycrimsonwolf 14:18, 8 July 2007 (UTC)[reply]

Lucid dreaming has a lot of interesting information, including how to initiate one, though I didn't see anything on whether the quality of sleep is lower. Someguy1221 16:17, 8 July 2007 (UTC)[reply]

Zachary, check out Wikibooks, one of our sister projects, they have a rather good guide to it. Also see ld4all.com, a good Lucid Dreaming community site. As far as making you exhausted- no, not at all. Well, it could be mentally draining, but it doesn't affect your sleep at all. Like, if you have a lucid nightmare, you could very well be out of it the next day like you hadn't slept well, but in general no. Lucid Dreaming takes place during REM sleep, which is what really counts anyway, so you will be just as rested in the morning as you did when you fell asleep. Unless of course your dream is a nightmare which causes you to wake yourself up, but most lucid dreams aren't nightmares unless you want them to be. --L^augh! 19:22, 8 July 2007 (UTC)[reply]

Ah. Okay. Thank you, but it'll probably take a long time for me to try to do it. Cheers!! -Zacharycrimsonwolf 09:27, 9 July 2007 (UTC)[reply]

One small step for man, one giant leap for mankind

I know who said it! But who wrote it? Armstong or NASA PR?

Thanks for any help.

The article on Neil Armstrong and a cited reference say that he came up with it an hour or two before saying it. Weregerbil 14:39, 8 July 2007 (UTC)[reply]

I believe it was recently corrected to be "One small step for a man, one giant leap for mankind." The a is inaudible in the original. --Tbeatty 15:15, 8 July 2007 (UTC)[reply]

Thank you all for your help. But...do you really think NASA and the government would have let him go up without first deciding on what to say on an occasion they knew would be historic?

In a sense, that particular "instant" became historic because that was the moment of most memorable dramatic effect after the fact. That's sort of hindsight analysis, though. Many historic first "instants" occurred during the entire mission - the first time a spacecraft touched down on the moon was marked with the (less memorable?) quip, "The Eagle has landed." NASA would have a hard time pre-planning every single historic occurrence and it's sort of arbitrary that the first "step" is any more historically important than the first "breath" or first "landing," or first golf game. Nimur 18:04, 8 July 2007 (UTC)[reply]

In recent bios of Armstrong, he says that he made this up not long before the landing. See First Man by James Hansen (2005) and One Giant Leap by Leon Wagener (2004). I don't have the books right here, but I read them not too long ago. As I recall Armstrong says that he planned to say "one small step for a man" (which makes more sense), but accidentally omitted the "a" when he actually stepped on the surface of the moon. So the first version "one small step for man" is correct.--Eriastrum 18:17, 8 July 2007 (UTC)[reply]

He has at various times said that he either was or was not aware of having omitted the 'a' - to be honest, I doubt that he knows - after all, he knows for sure that he INTENDED there to be an 'a' in there - it makes no sense without it. There is information out on the Internet someplace (I really can't be bothered to track it down) that says that very careful analysis of the available recordings show that he did say "a" - but something related to the fans and such in the suit masked it out. Something like that. The bottom line is that the odds are extremely good that he DID say "One small step for a man, one giant leap for mankind." - and that's without doubt what he intended to say. SteveBaker 20:41, 8 July 2007 (UTC)[reply]

And here’s a source from the BBC to prove it. S.dedalus 06:07, 9 July 2007 (UTC)[reply]

Has anyone ever heard of this fish disease?

I've been trying to assess and clean up the vet med articles here on wikipedia, and I ran across Rotting nose disease. I can not find anything on a google search about this disease that is not wikipedia-derived, or about its potential cause, a type of protozoa called Ocimita. I've also tried a few variations in the spelling of Ocimita, but with no luck. The symptoms and treatment of rotting nose disease seem remarkably similar to hole in the head disease, making me think that it is someone's made up name for the same disease. Before I proceed with any type of deletion effort, I wanted to see if anyone had heard of this disease or the elusive Ocimita species that may or may not cause it. --Joelmills 16:36, 8 July 2007 (UTC)[reply]

Sounds like either a hoax or a good faith duplicate of HITH. Either way, it should be prodded. Rockpocket 01:08, 9 July 2007 (UTC)[reply]

Perhaps not, Rockpocket. I believe that it could be a redundant article about Hole in the head disease or it could be Head & Lateral Line Erosion Disease [1][2][3]. The problem with common names for these diseases is that confusion is bound to appear between fish keepers living in different parts of the English speaking world. I suggest you inquire at Wikipedia talk:WikiProject Aquarium Fishes before nominating the page for AfD. S.dedalus 05:41, 9 July 2007 (UTC)[reply]

RTD is certainly fake; there's no record of the offending protozoan anywhere and there's no grasp of science patent in the article. HITH is very real. Bendž|Ť 17:12, 9 July 2007 (UTC)[reply]

Thanks for the responses. I think S. dedalus may have found the basis for this article with head and lateral line erosion disease, especially since the first EL give the possible protozoan cause as Octomita. However, I see someone already put it up as an AfD, and I'm not going to contest it. It's presence has not prevented anyone from creating a head and lateral line erosion disease article, since searching for that would certainly not lead you to rotting nose disease. --Joelmills 02:08, 10 July 2007 (UTC)[reply]

Question concerning Fourier

In Heat conduction there's a chapter called Conductance. In this section, there's an alternative statement of Fourier's law. In fact, I couldn't find this statement anywhere else in the internet. I wonder, whether it is true, I would need it for a paper. Could anybody please check this law? Lskywalker 18:20, 8 July 2007 (UTC)[reply]

If it is true, it's very badly written. None of the symbols he's chosen (apart from 'U') are defined. My text books on this subject are 180 miles away - I won't be able to check on it until late tonight or tomorrow. SteveBaker 18:34, 8 July 2007 (UTC)[reply]

Well, all the symbols are defined above (A, Δx, ΔT are defined, k is standard). I use other's, too, but I think that would be ok. But it would be great if you could look it up. Lskywalker 18:39, 8 July 2007 (UTC)[reply]

The problem is that in the lead section, the symbol Q is used to denote thermal energy transfered (in Joules), but in the following sections the same symbol Q is used to mean energy transfer rate (in Watts). That is an error and should be corrected. Apart from that, the alternative statement of the law is the same as the integrated form of the law stated earlier, but with the definition of U substituted in. --169.230.94.28 18:59, 8 July 2007 (UTC)[reply]

Error in myeloid article?

The myeloid article says: In describing hematopoiesis, the terms "myeloid" and "lymphoid" are often used to discriminate between cells originating from the marrow and from lymph tissue, respectively. - but this doesn't make sense because lymphoid cells originiate from the bone marrow (where B cells mature while T cells mature in the lymph nodes). Should someone correct the article? --Seans Potato Business 19:33, 8 July 2007 (UTC)[reply]

You're right. I've never heard of myeloid B cells. Myeloid cells are non-lymphocyte leukocytes. So... that article isn't worth squat. Bendž|Ť 09:29, 13 July 2007 (UTC)[reply]

Black hole production

Is it possible to produce a BH on earth using current technology? If we did produce one, how would we control it?

(a) No. No chance, not even close. (b) In principle, we could feed it some electrons to charge it up, and suspend it in a vacuum chamber using electric fields. We would have to do that at the same time as we created it. Making one would be a really bad idea, however, because the first time some klutz dropped it, the black hole would fall into the Earth and start slowly engulfing it. To avoid turning our whole planet, and ourselves, into a black hole, we would be forced to keep this electric-field trap setup in continuous glitch-free operation forever, or try to get rid of the darned thing by launching it into space. --169.230.94.28 20:32, 8 July 2007 (UTC)[reply]

Correction to (a): In some non-standard theories, it is conceivable that tiny black holes could be produced in particle accelerators. These, however, would evaporate through Hawking radiation faster than they could accrete new mass, and would therefore disappear in a fraction of a second. The European particle physics lab CERN has done a safety study on this, which concluded "We find no basis for any conceivable threat." --169.230.94.28 21:03, 8 July 2007 (UTC)[reply]

There was some discussion about whether RHIC could produce a black hole which might then eat the Earth, but it was decided that it was unlikely and the collider was allowed to operate.

Atlant 20:56, 8 July 2007 (UTC)[reply]

The answer to the first question is 'very probably not'. There are some variants of string theory (and some more exotic physics models) that suggest that creating micro black holes might be just within the reach of our largest existing or planned particle accelerators. Note that such black holes, if created, would have a very short lifetime—talking about storing or controlling one wouldn't be meaningful. TenOfAllTrades(talk) 20:58, 8 July 2007 (UTC)[reply]

Night sky

I´m looking in the southern direction and in front of me there is a particularly bright planet (? - I think) not far above the horizon (about 45º up). What is it? Thanks. --AlexSuricata 20:35, 8 July 2007 (UTC)[reply]

Where are you, and what time is it? (Or rather, when did you observe this planet?)

If you're looking at a point on or near the ecliptic and it's not too long after sunset, then Venus should be about 40 degrees above the horizon and very bright: [4]. Jupiter is also high and bright right now, thought not as bright as Venus. TenOfAllTrades(talk) 21:12, 8 July 2007 (UTC)[reply]

I´m in Andalucía and it´s 23:45, if you look south but at little towards south-west, and then up about 40º up above the horizon - it´s very bright, is it Venus then? --AlexSuricata 21:57, 8 July 2007 (UTC)[reply]

I think that you are probably seeing Jupiter. Venus is usually closer to the horizon unless it is close to sunset. There are a number of websites that will automatically generate a skymap given your location and time; here's one: [5]. TenOfAllTrades(talk) 22:16, 8 July 2007 (UTC)[reply]

Yep, it must be Jupiter. Great link btw - thanks! --AlexSuricata 22:26, 8 July 2007 (UTC)[reply]

Cleaning pen from whiteboard

What would remove felt-tip pen from a whiteboard? DuncanHill 21:39, 8 July 2007 (UTC)[reply]

Methylated spirits or alcohol on a paper towel, or use a normal whiteboard marker to scribble over the top and then rub that off. GB 21:46, 8 July 2007 (UTC)[reply]

Isopropanol (isopropyl alcohol) will also work; it's sold as 'rubbing alcohol' in the drugstore. TenOfAllTrades(talk) 21:52, 8 July 2007 (UTC)[reply]

Acetone has worked for me for permanent markers; it is a pretty common gentle solvent. If you are at a school, the chemistry department almost certainly has some. Failing that, many nail polish removers are acetone-based. If you are not at a school, ethanol is another readily available solvent. Actually your friendly neighborhood chemists probably have some of this too, though perhaps not in the form I just linked. -Eldereft 21:54, 8 July 2007 (UTC)[reply]

I tried meths already - no joy. I'll get some acetone tomorrow and try that. DuncanHill 21:55, 8 July 2007 (UTC)[reply]

Try using a normal whiteboard market to scribble over the top and then rub it off, as GB suggested :). Has worked every time in the past for me JoshHolloway 22:29, 8 July 2007 (UTC)[reply]

Thanks - never thought of that before! DuncanHill 22:31, 8 July 2007 (UTC)[reply]

Here's a comparative test of a bunch of different cleaning options and techniques. A word of caution about acetone, though—I'd test it on a small area in the corner of the board before you go crazy with it, because it might damage the surface. Acetone also dissolves many plastics and synthetics, so be careful how you handle it. TenOfAllTrades(talk) 23:05, 8 July 2007 (UTC)[reply]

I don't think I would call acetone a "mild" or "gentle" solvent - I've seen it dissolve some pretty dense plastics! It's selective about what it will react with and dissolve, but it will probably take the ink off the board. Test on a corner to make sure it doesn't take the board down with it (more realistically, the worst it would probably do is just destroy the glossy finish, but who knows what variant of "standard" whiteboard material you have on hand...). Nimur 00:57, 9 July 2007 (UTC)[reply]

Ok, gentle is relative - it is no hydrofluoric acid, but you still should not bathe in it. It is *always* worthwhile to read the MSDS and be aware of potential reactions and hazards. Respect, but do not fear. -Eldereft 09:39, 11 July 2007 (UTC)[reply]

If all else fails, fire will cleanse your board. Forever. --Tbeatty 01:49, 9 July 2007 (UTC)[reply]

I had a whiteboard that someone wrote on once with a permanent marker, and a commercial whiteboard-cleaning product didn't remove the mark at all... but ordinary dishwashing liquid, that we used in the kitchen sink, did. Of course everything depends on the particular ink formulation. --Anonymous, July 9, 2007, 03:01 (UTC).

Are you talking about dry-erase markers scribbles that have been left too long on the board and baked themselves in to the point where you can't get them off? Or are you talking about the situation where someone brought a permenant marker - and wrote on the board mistaking it for a dry-erase marker? In the former case, I would definitely go and buy a bottle of whiteboard cleaner - most office supply companies have them and they work very well - they aren't generally too much of a health hazard - and it's worth keeping some in your desk drawer because this does happen quite a lot. In the latter case - you'd need to resort to some stronger chemicals - and all kinds of organic solvents are worth trying. Acetone and Isopropyl alcohol would be good things to try. However, many of those are dangerous - so beware! Vodka works moderately well in an emergency with at least one brand of permenant marker. (you don't want to know how I found this out!). SteveBaker 03:06, 9 July 2007 (UTC)[reply]

I said a permanent marker and I meant a permanent marker. It was a visiting child who didn't know the difference between permanent and dry-erase markers. I don't say that other whiteboard-cleaning products wouldn't have worked, but the one I tried didn't. I don't remember further specifics. --Anon, July 9, 22:44 (UTC).

It was a felt-tip pen (the sort that children use - I know, because it was me wot done it, I was in a foul mood because 1) I had just been cleaning chewing gum off the Scout Hut floor, and 2) someone had nicked the whiteboard pen). Forgot to get any acetone today, but to date I've tried Meths (very slight effect), n-hexane (very slight effect), white spirit (no effect whatsoever), and writing over it with a whiteboard pen and then rubbing off (no discernible effect). DuncanHill 22:50, 9 July 2007 (UTC)[reply]

Interesting whiteboard actually briefly mentions a lot of the suggestions. BTW, this is probably a dumb suggestion but if it's a felt-tip pen, did you try water? If you have the pen, try and find out from the brand etc what solvent it contains (I would have thought it water based though!)? I'm actually a bit surprised it's so hard to get off. I thought those kind of pens are usually supposed to be washable and fairly easy to remove given their target market Nil Einne 23:40, 10 July 2007 (UTC)[reply]

Supposing that we were to accidentally create a black hole on earth...

What would an observer on the ground actually see during the minutes before the whole planet was torn apart and consumed? I remember seeing a dramatization of the event on some 'end of the world'-type documentary some time ago. As I recall, everything within thousands of miles of 'ground zero' immediately ignited, then collapsed into a swirling vortex of energy within seconds (with the BH at the centre). All over the rest of the world, gigantic thunderstorms raged, winds of several hundred mph battered the surface and the horizon glowed white. --Kurt Shaped Box 22:27, 8 July 2007 (UTC)[reply]

What one sees would depend a lot on the mass. A very low mass black hole, which would presumably be the only kind we might "accidentally" create, would evaporate via Hawking radiation and pose no threat to the Earth. You see some sort of flash as it disintegrated, if you were looking at it. The other issue is that even Earth mass black holes would be very small. The Schwartzschild radius of the Earth is ~1 cm. At that size, and even if you could feed it would a continous stream of matter moving near the speed of light, it would take ~100 million years to force a volume the size of the Earth to fit through a surface area as small as the event horizon of the black hole. A micromass blackhole, i.e. something say the mass of a mountain, could well take longer than the remaining life of the solar system to eat the Earth. In other words, you might not see much of anything in your lifetime. Dragons flight 23:00, 8 July 2007 (UTC)[reply]

Depends on the mass of the thing. Look at it like this: The gravity field of a black hole is no stronger than the thing it's made of.

So I guess the worst case would be if we took the largest thing we can imagine that's handy and nearby - suppose we could take the entire moon and maybe "accidentally" turn it into a black hole using who-knows-what weird science (tsk, tsk - these scientist are so careless!). Well, that wouldn't do much - the moon-sized black hole would continue to orbit the earth - suckinging in microscopic amounts of gas...we'd hardly even notice! But I guess we're asking about a black hole on the surface of the earth. If the moon-sized hole were somehow brought to the surface of the earth...now THAT would be the kind of apocalypse you have in mind. The black hole would have the same gravity as the moon - except you could get much closer to it than you can get to the real moon. The moon has a radius of 1700km - so at 1700km from the black hole, it would be attracting with the force of 1/6th of a g - enough to collapse buildings maybe - but not directly dangerous. At 800km, we're up to 2/3rd of a g, at 400km, we're looking at 2.6g, at 200km, 10g, at 100km, 40g...there isn't much that can withstand a force of 40g - so the hole that a moon-sized black hole would immediately dig would be a few hundred kilometers across! Since nothing can support a moon-sized black hole - it would immediately fall towards the center of the earth - it would fall towards the center of our planet - gaining speed as it did it - then oscillate back and fourth within the earth carving out massive tunnels. The planet would rapidly hollow out from the inside out until the mantle would not be strong enough to support the weight - then the earth would collapse inwards - all in slow motion. It would take a long time to fall that far!

But for a much smaller black hole, nothing much would happen. If you took 1000kg of matter and made a 1000kg black hole - it wouldn't exert any measurable g-force at one meter - you car weighs more than that - and it doesn't exert much gravity a meter away! The hole it would burrow in the earth might only be a tiny fraction of a millimeter across. It would still fall to the center of the earth - probably weighing a little more by the time it got there. But then it might eat out a hollow area in the middle a few centimeters across - but it's gravity would be pretty pathetic - but it's not exerting enough force on the earth's liquid iron core to excavate a huge cave - it might take thousands or millions of years for it to accumulate enough mass to be really dangerous to us.

If you made a black hole out of 1kg of stuff - the hole it would drill might be of the order of the diameter of an atom - at which point you wouldn't ever know it was there.

SteveBaker 23:27, 8 July 2007 (UTC)[reply]

Really? I smell original research.... Nimur 00:51, 9 July 2007 (UTC)[reply]

That moon mass black hole is only 200 microns across. While 40g may seem like a lot, it's not really from a structural prospective, it would take ~3000g to pull apart a 1 m^3 slab of rock with a typical yield stress of 100 MPa, further the ability to pull things apart depends of the difference in force between the two ends on object. The end result is that you have to be within 500 m to break rock, and much much closer to actually be consumed because of the very small surface area. Dragons flight 00:37, 9 July 2007 (UTC)[reply]

In total, there is not enough experimental evidence with close-up black holes to say for sure with any kind of certainty. There's going to be lots of speculation, artistic license, and mishmash theories of classical and quantum and relativistic effects; but since we have no prior experience it is all speculation (no matter how rigorous the math may be, who knows if our models would break down in unforeseen ways?) Nimur 00:54, 9 July 2007 (UTC)[reply]

Thanks for all your answers, guys - interesting reading. I appreciate the time you must've taken to figure all that out. So, is there any scientific substance to the oft-seen-in-scifi 'shockwave' that is formed when matter (be it a star, planet or the drive of a spacecraft) is forced to collapse down into a black hole? What the hell is that supposed to be anyway (other than a convenient method of destroying the entire alien fleet)? --Kurt Shaped Box 05:08, 9 July 2007 (UTC)[reply]

Let's say it's not entirely unfounded. The reason a star collapses is because it requires less energy to be scrunched up as small as possible, and things tend to want to be in the lowest energy state possible (big simplifications and lies to children here, but a reasonable approximation). For most matter, though, the force causing the matter to collapse is counteracted by other forces - the normal electromagnetic repulsion between atoms, the pressure of expelled photons in the case of a star, and Fermi energy / "degeneracy pressure" when you get to white dwarves and smaller. When the matter finally collapses into a black hole, the excess energy gets expelled quite violently. It's possible (and in the case of stars, pretty much de rigeur) for an inner core of matter to collapse into a black hole, and the surrounding matter to get blasted out in a big shockwave. Whether this happens when you reverse the polarity on your photon drive is another question entirely. Confusing Manifestation 06:32, 9 July 2007 (UTC)[reply]

Expanding on SteveBaker's answer, if we assume a microscopic black hole, starting from rest at the surface of the Earth and experiencing no friction, then it will describe simple harmonic motion about the centre of the Earth, with a period of about 84 minutes - see here. So it takes a quarter of a period - about 21 minutes - to reach the centre of the Earth. Which is quicker than I thought it would be. The actual path traced by the black hole relative to a fixed point on the surface of the Earth will be some sort of complicated 3D rosette, due to the Earth's rotation. Gandalf61 08:52, 9 July 2007 (UTC)[reply]

A moon sized black hole would produce very little spaghettification (imagine a piece of plasticine or blue tack being stretched unevenly - now imagine the plasticine is a car or a building!) at any reasonable distance; given that rock breaks at 100 megapascals, in order to shatter the 1 metre cube, it would have to placed closer than 500 metres to the black hole (back of envelope). Laïka 22:36, 9 July 2007 (UTC)[reply]

Yeah - the tidal effects of the moon couldn't pull a rock apart at those kinds of distances - but for sure it could bodily rip it out of the ground and suck it in in one big lump if it's close enough. If that's not convincing enough to you - think about the oceans. If they are experiencing 1g downwards from the earth and 1/6th of a g sideways because the black hole/moon has just been formed in a lab on the coast 1700 kilometers away - then it's going to be like the ocean was suddenly sloping at an angle of maybe 10 or 20 degrees to the "vertical" (I'm too tired to work it out the exact angle - sorry!) - so ALL of that water will immediately rush "downhill" towards the black hole with speeds and violence that would make a normal tsunami look like a ripple in pond by comparison! All of the water on the earth would rush towards the black hole - but the hole is by now falling (with a 1g+ accelleration) whilst burrowing a large hole through the earth as it goes. Of course the atmosphere would do the same thing - so there would be violent winds - and depressurization of areas even quite far from the hole. Of course the black hole itself isn't going to stay there because it's falling through the earth - eating out a tunnel as it goes. Worse still, the earth's spin is going to be wildly destabilised by the abrupt appearance of this large mass on one side of the planet. The end would be rapid and spectacularly violent - I'd guess that people living a long way from the hole might survive a few minutes - but they're gone for sure in an hour. As the black hole 'eats' things - it'll be emitting hard gamma and X-ray radiation - that's no fun either.

I think the important message here is NOT that a black hole is automatically a death dealing monster - it's pretty clear that small black holes are harmless - and (as others have explained) will eventually evaporate due to Hawkins radiation. No the message is that if something with a lot of gravity ends up someplace where it's not supposed to be - the damage will be unimaginable. A moon-massed black hole would hardly be less damaging than a moon-massed lump of moonrock - or a moon-massed bag of feathers - gravity is gravity. SteveBaker 01:22, 10 July 2007 (UTC)[reply]

You may want to check out Large Hadron Collider#Safety concerns and work your way from there. This sort of accidental black hole theory (and other catastrophic events) has been consider re:the LHC and I believe other particle colliders. The majority think the probability of any catastrophic event occuring are extremely remove for a variety of reasons. But there is a minority which thinks that the risks need to be considered better. Nil Einne 23:46, 10 July 2007 (UTC)[reply]

I have to pass on a story that shows similar 'issues' to the accidental creation of a dangerous black hole. When I worked at Philips Research labs in Surrey, England they worked in a building - part of which went back to around the 1930's. That was the time of Ernest Rutherford et al. Early days for theories of the atom. They had been smashing particles together following Rutherfords lead and later got into the atom smashing craze. However, it was clear that since they were doing research - they had no idea what would happen as a result of some of these experiments. They wondered whether widespread - or even apocalyptic - destruction might ensue. Rather than not do the experiment, they opted to dig a 20' deep basement, line it with a foot of concrete and had a motorized foot-thick slab of concrete that slid over the entrance stairwell to block it while experiments were going on. All of that was still there in the glass-blowing workshop as late as the 1980's. But what amazes me was that they had NO IDEA what would happen - and yet still went ahead with it. They clearly weren't at all certain that nothing would happen - or they wouldn't have bothered with all the concrete. It's very interesting to muse about their motives and expectations! SteveBaker 00:36, 11 July 2007 (UTC)[reply]

I once remember seeing a documentary on the Discovery Channel (so take it with that proviso) about the Manhattan Project where it was stated that some of the scientists involved had serious concerns that detonating an atomic bomb would initiate an unstoppable chain reaction that would 'burn off' the earth's atmosphere! Apparently, at the Trinity test, there was more than one person crossing his fingers that the device wouldn't work *too well*. --Kurt Shaped Box 00:58, 11 July 2007 (UTC)[reply]

I sometimes like to muse to myself that any 'unforeseen incident' that leads to the unleashing of 'forces beyond our control' and 'that which cannot be undone' may be the one thing that finally gives us a definitive answer to the question of the existence of a higher power. Sitting back as a neutral observer and leaving us to exercise our free will and make our mistakes is one thing - but what happens when we perform an action (i.e. accidentally obliterating the planet, killing everyone and everything through bad science) that interferes directly with His grand design for us? Now *that* is when I'd expect to see intervention... :) --Kurt Shaped Box 01:21, 11 July 2007 (UTC)[reply]

I thought what we had to worry about was Quarks or something, tearing the planet apart? But then, I was more paying attention to the large banks of computers in the background than what duh science man sed. --L^augh! 12:58, 12 July 2007 (UTC)[reply]

I think you're thinking about Quantum vacuum collapse... http://www.exitmundi.nl/vacuum.htm ...yeah - don't do that. That would be "A Bad Thing". This article has several similar dire warnings from one scientist to another: http://www.kressworks.com/Science/A_black_hole_ate_my_planet.htm SteveBaker 14:37, 12 July 2007 (UTC)[reply]

An insect to identify

Butterflies have two pairs of large wings, dragonflies two pairs of equal-sized slender, transparant wings. At the banks of the Soča river, near Bovec, Slovenia, I have seen several of the beautifully coloured kind of insect depicted to the right. It has dark blue-black wings with white spots, slender like a draginfly's, but seemingly only one pair. The body has a prominently yellow-coloured ring, and I think that I've seen one with an additional blue ring. What is this? TIA. Simon A. 22:48, 8 July 2007 (UTC)[reply]

The rear wings are simply smaller; you can just make out their outline, and this is a day flying moth, Syntomis phegea, family Ctenuchidae (syn. Syntomidae). There's not much on here in wp, but googling gets you plenty. Bendž|Ť 17:34, 9 July 2007 (UTC)[reply]

P.S. we could use the photo in an article if you rename it. Bendž|Ť 17:37, 9 July 2007 (UTC)[reply]

Thanks, Bendž. It's a pity that the vacation is aleady over; otherwise I could now check out the seperation between the fore- and hindwings when used in flight. But if I think of it: the wings of butterflies also merge into each other, so that the division gets hard to make out. Say, how have you figured out the species? Did you just happen to know, is it common where you live, or could you recognize the family from general features and then used a classification book? For the picture: Go ahead and use it. How do I rename it? Or should I move it to Wikimedia Commons? Simon A. 06:03, 10 July 2007 (UTC)[reply]

Just googled for it and the Dutch Wikipedia has a pretty nice picture, nl:Melkdrupje. Simon A. 06:05, 10 July 2007 (UTC)[reply]

It is the most common species of the family but we don't get them in Britain so I didn't know it. No, I simply opened my Collin's field guide on the plate with its picture. A case for wikipedia as the product of infinite monkeys. Bendž|Ť 09:36, 11 July 2007 (UTC)[reply]

Butterfly with spotted compound eyes

In the hope that my previous question already caught the idea of any professional or amateur entomologists roaming the Reference Desk, I ask a second one: I took the photo to the right at more or less the same location, again at the banks of the Soča near Bovec, Slovenia. When looking at the photo on my computer screen at maximum zoom, I was amazed to note a funny detail: The wings' colouring pattern, dark brown markings on amber background, seems to continue onto the butterfly's compound eyes. Two questions arise: (a) Is it common for butterflies to have coloure eyes? (ii) Given that wing colours are produced by scales tinted by thin film interference or pigments, how can a compund eye have the same colours although it does not have scales? Simon A. 23:24, 8 July 2007 (UTC)[reply]

Insects can produce pigments in their eyes, just like anywhere else. See the image at Drosophila_melanogaster#Model_organism_in_genetics for some variations of eye pigmentation in fruitflies, for example. --mglg_(talk) 03:51, 9 July 2007 (UTC)[reply]

Good point, thanks. Simon A. 15:30, 10 July 2007 (UTC)[reply]