Wikipedia:Reference desk/Archives/Science/2011 October 29

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October 29

opposite of attraction for black holes

Was more of a thought than a question; with the attraction or gravitation effect of a Black Hole would there be anything that would act as an opposite of this and be forced away from a black hole? an Anti black hole if you like... — Preceding unsigned comment added by 109.224.25.14 (talk) 07:28, 29 October 2011 (UTC)

black hole are cicle in time and like in the univers gravity get flip in time ,thanks water nosfim — Preceding unsigned comment added by 84.229.88.108 (talk) 08:06, 29 October 2011 (UTC)

If only that reply made sense... The only thing that would be repelled by a black hole would be antimass. Plasmic Physics (talk) 08:51, 29 October 2011 (UTC)

No. There is a theoretical object called a white hole which is the reverse of a black hole in some regards, but it's not what you're looking for. An anti-black-hole like you're looking for would presumably have a negative mass, which doesn't appear to exist. Red Act (talk) 08:57, 29 October 2011 (UTC)

What I said. P.S. 84.229.88.108: Little tree be square in funny of sock, but only on Sundays, please hwgprdy. Plasmic Physics (talk) 09:07, 29 October 2011 (UTC)

What about "tachyons" which, in one theory, have imaginary mass. Would they be attracted or repelled? Dbfirs 12:07, 29 October 2011 (UTC)

1. White hole is most likely just another name for a black hole because of time reversal symmetry
2. Everything is attracted to a black hole, even tachyons or negative mass objects (if they happened to exist which they probably don't). If you have negative mass, an repulsive force results on a attractive acceleration. Dauto (talk) 14:44, 29 October 2011 (UTC)

Indeed. As Galileo showed us, acceleration due to gravity doesn't depend on mass. That's true regardless of what the mass is. If you want a black hole that repels things, then you would need the black hole itself to have negative mass. I'm not quite sure how that would work with relativity, though. --Tango (talk) 15:21, 29 October 2011 (UTC)

Black holes can have an electrical charge, and I believe it is theoretically possible for an oppositely charged object to be repelled from a black hole. Looie496 (talk) 15:22, 29 October 2011 (UTC)

Wouldn't it probably have to be charged but massless? (Which doesn't describe any known particle.) Surely the repulsion of the charge is going to be outweighed by the gravitational forces if not. But I am no physicist, and this is well beyond my ken... --Mr.98 (talk) 16:07, 29 October 2011 (UTC)

Black holes have to have |Q| ≤ M in units where the electromagnetic and gravitational force constants are the same. (Otherwise you get a naked singularity instead of a black hole with an event horizon). This means that two black holes can't repel each other, though in the extremal case (|Q| = M for both) they don't attract each other either. But charged elementary particles dramatically violate that bound—for example, for an electron, |Q| / M ~ 10²¹. So an electron can be repelled from a black hole if the black hole's charge is even 10⁻²¹ of the theoretical maximum. -- BenRG (talk) 22:04, 29 October 2011 (UTC)

Antarctic station

what type of Windows and insulation are in the new Antarctic station — Preceding unsigned comment added by 69.5.89.117 (talk) 13:01, 29 October 2011 (UTC)

Which Antarctic Station are you referring to? Do you mean the new, zero-emmision Princess Elisabeth Base built in 2009? Buddy431 (talk) 15:00, 29 October 2011 (UTC)

I'm interested in any information you can get about any of these buildings as far as their insulation and windows the one I was specifically referring to was the big one that was built about five years ago — Preceding unsigned comment added by 69.5.89.93 (talk) 09:52, 30 October 2011 (UTC)

Do you perhaps mean the new Amundsen–Scott South Pole Station? I found this site with lots of information about it, but the only thing I could find about insulation is that it is "insulated to five times the value of the average U.S. residence", which doesn't really mean much. This page mentions that the windows "were tested in CRREL's cold chambers for suitability at Pole's harsh temperatures", but again, that doesn't give much specific information. Buddy431 (talk) 18:59, 30 October 2011 (UTC)

high-rise building

when looking at the large high-rise building like say the twin towers is constructed of mainly glass and steel it does not appear to have any insulation in its walls how is it that they can heat this building in the wintertime without the bills being extremely high and putting a tremendous load on the heating system? Also what type of heating system do they use — Preceding unsigned comment added by 69.5.89.117 (talk) 13:03, 29 October 2011 (UTC)

Actually, a large building will have a smaller surface to volume ratio making it EASIER to climate control. Dauto (talk) 14:15, 29 October 2011 (UTC)

See also insulated glazing. It's pretty much standard these days, at least in cooler climates.--Shantavira|^{feed me} 17:08, 29 October 2011 (UTC)

As noted above, the surface-to-volume ratio of a large building is efficient compared to a smaller structure with a similar percentage of glazed surface, particularly compared to a single-story structure where the roof becomes a major component of heat loss. In most large buildings, even in northern climates, the problem is usually to remove heat from the building in all seasons except deepest winter, due to to presence of people, lights, computers, copiers and other heat sources within. Most large buildings require significant air conditioning in three seasons. The efficiency of insulated glass has steadily improved both in terms of heat retention and solar heat gain rejection. Also, much of the "glazed" area seen in tall buildings is actually opaque spandrel glass concealing structure or above-ceiling space, and is backed by insulation. Wall areas and exterior column surfaces are insulated. Even in the days before significant energy code requirements, insulation was needed to prevent condensation on cold days. Acroterion (talk) 19:30, 29 October 2011 (UTC)

For the purposes of the surface-to-volume ratio, it might be worth defining "large". The shape is as important as the size. A tall skinny building (a "high-rise", per the original question) could well have a higher surface-to-volume ratio than a shorter but more cubically-shaped building. For example, consider a building 100 x 100 x 100 metres. Volume = 1,000,000 m³, surface area of windows (ie excluding floor, ceiling) = 4 x 100 x 100 = 40,000. A high-rise, 50m x 50m base x 300m tall has volume 750,000 but window surface area 4 x 50 x 300 = 60,000. Ie the taller high-rise is smaller in volume but has more surface/window area. Mitch Ames (talk) 23:24, 29 October 2011 (UTC)

Few mid and high-rise office-type buildings (or any other tallish building type) are as deep as 100m; most are more like 30-40m, or 50m at the most for reasons of fire safety, access to light and ventilation, and size of city blocks. Until air conditioning, buildings were cut into smaller sections for light and air, and after air conditioning came into widespread use, few people wanted to be so deep in the interior of a structure. Acroterion (talk) 04:14, 30 October 2011 (UTC)

none of your answers answer my question yes a tall building might be even better than a short glass building I asked specifically about the twin towers there is no insulation in them and the glass is not insulated glazing. Also most buildings used florescent lights which did not produce any heat. In the deepest part of winter which is actually a months long and most northern USA climates do they simply pay tremendous heating costs every month? these buildings have wall to wall glass there is no insulation these are skyscrapers not medium-size office buildings — Preceding unsigned comment added by 69.5.89.93 (talk) 09:38, 30 October 2011 (UTC)

Although it was not obvious from your question that you were specifically interested in the WTC towers, the answers are correct. Although the original WTC did not have insulating glazing (that I'm aware of), their surface-to-volume ratio was still more efficient than an equivalent low-rise structure of similar square footage and construction, and New York is in a climate zone that is somewhat cooling-dominated: additional heating would normally be needed in three months of the year in such a large building in New York. Office buildings generate significant internal heat loads that need to be rejected, and the wall perimeter of any given floor, compared to the floor area, is surprisingly small, particularly for the WTC towers, which had unusually large floors for a tall building. Heating would normally be required only around the perimeter. New York, being a coastal city (and not especially far north), doesn't get extraordinarily cold for long periods, compared to, say, Minneapolis or Toronto. Of course, such large buildings would in fact need a large heating plant, but the cooling plant would be relatively larger. The windows at the WTC were much smaller than might be supposed; they were only 18" wide and there were complaints about their restricted view. The column enclosures (and the columns themselves) were insulated. The WTC's glazing ratio was less than 40%, and probably closer to 20 or 30% when above-ceiling space was accounted for; the columns and their enclosures were much wider than the windows. On a cost-per-square-foot basis, such a large building would probably cost less to heat per square foot than most houses. Since the tenants pay rent per square foot, the heating cost is factored into the rent. Put another way, the 4.5 million square feet of each WTC tower would cost less to heat than the equivalent square footage of 1800 square foot houses with a high surface/volume ratio, which amounts to 2500 houses. Acroterion (talk) 16:58, 30 October 2011 (UTC)

I don't understand why a building constructed of glass and steel would cost the same to heat as a well insulated two-story house — Preceding unsigned comment added by 92.48.194.151 (talk) 16:11, 31 October 2011 (UTC)

If they were of the same size, a well-insulated house to current standards would outperform a structure built to 70s standards without insulating glazing. The point is that they're not the same size: the ratio of surface to volume is radically different. An 1800 sq ft two-story house , square in plan like the WTC, encloses about 16200 cubic feet with a surface area (ignoring attic) of 3060 sf, a ratio of 1.7 (surface area over floor area), or 0.18 (surface area over volume). One tower of the WTC analyzed the same way yields 1,181,440 sf of surface over 4,300,000 sf of floor area for 0.27 surface/floor, and 1,181,440 sf of surface over 59,181,152 cu ft of volume (0.02 surface/volume). 1.7 (house) vs. 0.27 (WTC) for surface/floor area and 0.18 (house) vs. 0.02 (WTC) for surface/volume are almost order-of-magnitude differences. Differences in insulation values attributable to construction methods are more on the order of factors of two or three, not ten. See square-cube law. Add to that the inherently greater efficiency of a large-scale heating plant (for many of the same reasons) over a small-scale residential furnace, and you get comparable or better thermal performance for the larger building. Acroterion (talk) 19:27, 31 October 2011 (UTC) To summarize: a larger building will have less skin from which to lose heat relative to its contents than a smaller building, negating any advantage the smaller building might have by being better-insulated, or conversely, the smaller building must make up for having so much surface area relative to its volume by being better insulated. Acroterion (talk) 13:39, 1 November 2011 (UTC)

Car battery

How much stress is the car battery under in this? 86.74.104.61 (talk) 14:18, 29 October 2011 (UTC)

Very little. But if you pressed the wire against the metal continuously, the battery could heat up enough to explode. Looie496 (talk) 15:20, 29 October 2011 (UTC)

Do not try the experiment at home, since the battery might explode or the wire might start a fire. It is difficult to determine the maximum current in the video. It shows two pieces of copper wire, presumably connected to a car battery, being shorted against a piece of iron or steel. What is the wire gauge, and how long are the pieces of wire? That would allow calculation of the resistance of the wire. How is the wire connected to the battery? Wrapping it around the terminal would have greater contact resistance than a proper lug securely connected to the battery, or a solid bolted connection. The bulk resistance of the steel or iron can be ignored, but there will be non-zero contact resistance between the rapidly melting and oxidizing copper wire tip and the iron. While starting a car, the battery is regularly called on to produce a very high current, so a long enough small copper wire with an imperfect contact could limit the current somewhat below that of a solid short across the battery, or even below the "cranking amps" rating of the battery, which might be as high as 600 amps for 30 seconds. Ohm's law says that 12 volts divide by 600 amps implies a resistance of .02 ohms, including the battery internal resistance, the wire, the iron, and contact resistances. Higher total resistance would limit the current to lower. Those little wires shown would likely be quite hot if they had to carry that current very long, but the resistances listed above might limit the current somewhat. It would be a race between the battery overheating and the wire getting too hot to hold. Damage to the battery would be likely in a prolonged short circuit. Edison (talk) 00:50, 30 October 2011 (UTC)

uv400

what does uv400 in sunglass mean? — Preceding unsigned comment added by 92.42.55.187 (talk) 17:23, 29 October 2011 (UTC)

See Sunglasses#Protection for the answer. --Jayron32 17:43, 29 October 2011 (UTC)

how fast is dynamite

If a continuous line of dynamite was laid in a streight line from New york to San Francisco, and then ignited at one end, how much time would the explosion take to reach the other end?190.56.107.76 (talk) 17:30, 29 October 2011 (UTC)

I'm having trouble loading the whole document, but I believe (based on references to it elsewhere on the web) that this document: [1] has linear burn rate data for various explosives; perhaps on page 67? --Jayron32 17:41, 29 October 2011 (UTC)

Based on table of explosive detonation velocities, somewhere between 6 and 9 km/s would be a good guess. Dragons flight (talk) 19:02, 29 October 2011 (UTC)

Note that this of course assumes it actually would propagate linearly down the line. I suspect in real life you'd have the shockwave of earlier parts disturbing later parts and ending the explosive line pretty early on. This is just an intuitive guess, though; I haven't really worked it out. --Mr.98 (talk) 21:10, 29 October 2011 (UTC)

The shockwave/detonation front travels at between two and three times the speed of sound, thus it cannot influence anything ahead of itself. Roger (talk) 21:16, 29 October 2011 (UTC)

I guess my question is whether the detonation front will ignite additional dynamite uniformly, rather than just scattering it. I wouldn't know, but it seems essential to knowing if this would work or not. --Mr.98 (talk) 14:25, 30 October 2011 (UTC)

Dynamite will only explode if it is set off by a blasting cap, otherwise it will just burn. The burn rate of a line of dynamite will vary according to its composition, thickness, the ambient humidity and temperature, etc. In any case it certainly won't be kilometers per second. If you attached a blasting cap to one end, I expect you'd get a localized explosion that would snuff itself out. Looie496 (talk) 23:28, 29 October 2011 (UTC)

Not necessarily -- see detonating cord for an explosive device that propagates the detonation without snuffing it out. 67.169.177.176 (talk) 00:22, 30 October 2011 (UTC)

THIS sounds like a question for Mythbusters! I don't have any personal experience but my thought is that dynamite is a very specific thing which is often confused with TNT. You'd need to define 1st what you meant by "continuous line", do you mean ONE long stick of dynamite? or lots of sticks lined up? or something else? I don't think you could unpack and spill the contents of many sticks of dynamite to make a line and still make it explode, the fact it is compacted and packed in a tube definitely plays a part in the explosion. Similarly to a bullet, if you spill the contents and ignite them they don't go BANG! Vespine (talk) 22:08, 30 October 2011 (UTC)

+1, should be answered by Mythbusters. They don't have those licences for nothing. Dualus (talk) 00:27, 31 October 2011 (UTC)

My own understanding is that the OP meant either something similar to one long stick of dynamite (i.e. something like explosive cord), or else lots of dynamite sticks daisy-chained together in a single continuous explosive train -- the other possibilities are simply implausible from a practical POV. 67.169.177.176 (talk) 23:14, 30 October 2011 (UTC)

Getting rid of dishwashing liquid smell

This may be more of a misc question than a science question, but I guess a good answer requires a bit of chemistry knowledge, so I decided to try here. Due to an unfortunate shopping accident, I had the insides of my favourite rucksack covered in garlic oil. I tried various methods of getting rid of the stuff and found that soaking the rucksack in dishwashing detergent worked wonderfully - only now I have a rucksack that smells pretty strongly of dishwashing detergent, and it seems impossible to get rid of the smell. I expected the smell to evaporate over time, but the whole affair happened three or four weeks ago, I have aired the rucksack as often as possible by turning it inside-out and leaving it on the balcony over night and have rinsed it with water countless times, and the smell hasn't gotten any weaker. So...is there some commonly available cleaning agent or other chemical that is especially good at breaking down whatever it is that makes the dishwashing liquid smell without damaging the rucksack? The rucksack consists of two layers of Gore-tex with a thin layer of foam padding in between (which I guess is where the smell resides). -- Ferkelparade π 18:34, 29 October 2011 (UTC)

There must be eddies that you can't rinse out. Try soaking it and then rinse it out. Dualus (talk) 18:45, 29 October 2011 (UTC)

Most Goretex products can stand up to a washing machine cycle. Normal laundry detergent will be okay. Do not use fabric softener or bleach. I would wash it first through one cycle using detergent, then wash it a second time using just water. I would not use the dryer, but if you do, use the lowest temperature setting.--108.46.103.88 (talk) 18:50, 29 October 2011 (UTC)

Stainless steel soap? ~AH1 ^(discuss!) 19:39, 29 October 2011 (UTC)

That might work for the garlic, but not for the dishwashing liquid. 67.169.177.176 (talk) 00:06, 30 October 2011 (UTC)

Sometimes household ammonia, acetic acid (vinegar), or table salt solution can cut thorough and naturalizes chemical smells. But I think you need a chemist that can home-in on your particular 'detergent' . Which one was it? Is it the added perfume that is lingering?--Aspro (talk) 20:06, 29 October 2011 (UTC)

There is a bit of perfume added to the liquid, but the smell I mean is that typical dishwashing smell...it's difficult to accurately describe smells, but all the various dishwashing liquids I have ever used have shared that same slightly pungent, thick, oily smell that is only partially masked by the added perfumes, and I (probably slightly naively) assumed their composition is always somewhat similar because they smell and feel so similar. For the record, the one I used on the rucksack says on the label it contains "5-15% anionic and amphoteric surfactants, methylsothiazolinones, benzisothiazolinones", plus perfumes and coloriing agents. -- Ferkelparade π 12:07, 30 October 2011 (UTC)

Anionic surfactants are basic and therefore can be neutralized with vinegar. Just make ABSOLUTELY sure to dilute the vinegar solution in several volumes of water per volume of vinegar, or else your rucksack will start stinking of vinegar and then you'll be back to square one. (And make sure to accurately measure and RECORD the amount of vinegar you used, just in case you have to come back here asking for how to get rid of the vinegar smell.) 67.169.177.176 (talk) 21:32, 30 October 2011 (UTC)

Thanks for that suggestion, a bit of vinegar diluted in water worked pretty well. I'll probably have to repeat the procedure of soaking in diluted vinegar, rinsing and airing a couple of times over the next days nbefore the smell is finally gone, but it looks (err...smells) like it's going to work. Thanks a lot! -- Ferkelparade π 18:42, 1 November 2011 (UTC)

Let me know if there's any residual smell from the vinegar -- I can help with that too (in fact, if anything it's easier to deal with than surfactant smell). 67.169.177.176 (talk) 00:49, 2 November 2011 (UTC)

This secret medieval tincture, concocted by that bombastic chemist is a time-honoured panacea for garlicky rucksacks, myopia, tinnitus and rigor mortis. It may also be used to achieve cold fusion, antigravitational levitation of smallish pachyderms and accereates neutrinos to superluminary speeds :) --Incognito.ergo.possum (talk) 07:51, 30 October 2011 (UTC)

PS: If you ever get to Prague, may I recommend a pint of Pilsen´s dark Master Brew (18°). Drooool.

I am not going to waste a good bottle of Augustiner on cleaning my rucksack. That would be a sin. On the other hand, liberally applying a couple bottles to myself instead of the rucksack will make me forget about the smell, but alas, I use that rucksack to carry my reading materials to work, and that's a bit incompatible with your suggestion -- Ferkelparade π 12:07, 30 October 2011 (UTC)

Starlight

I suspect the answer exhibits somewhere obvious, but I seem to be having trouble figuring out the right place to look.

What is the total power in electromagnetic radiation delivered to the Earth by astronomical sources not including the sun or reflections from the moon? I'd prefer an answer that sums over all wavelengths, but an answer for just the visible wavelengths would still be helpful. Dragons flight (talk) 20:08, 29 October 2011 (UTC)

Albedo is a good place to start.--Aspro (talk) 20:11, 29 October 2011 (UTC)

How so? To clarify, I'm not really interested in how much radiation is reflected, just in how much is incident on the Earth from external sources. Dragons flight (talk) 20:32, 29 October 2011 (UTC)

In order to reflect, a body has to receive (unless of cause, one is a vampire whose refection does not appear in a mirror). Then just do a bit a little of math which will provided an answer in approximately the right order of magnitude. Isotope heat generation does not account for much on this level.--Aspro (talk) 20:56, 29 October 2011 (UTC)

Earth's outgoing radiation is dominated by Earth's black body radiation (indirectly created by solar heating) with a small amount of artificial lighting thrown in. I don't see how one could ever measure Earth's reflected power from just astronomical sources, and without that, there is no way to use albedo to connect it to incident radiation. Dragons flight (talk) 21:23, 29 October 2011 (UTC)

I'm not sure but I think you have to add luminosity#In astronomy from the Tully–Fisher relation to the cosmic background radiation, and maybe the blackbody radiation of the interstellar medium if that's not already in there. Good luck! Dualus (talk) 20:43, 29 October 2011 (UTC)

I am not sure what you are trying to tell us but the cosmic backgroud radiation at 2.725 K results in (Stefan-Boltzmann constant)*T⁴ = 3.127*10^-6 W/m² (that's already the correct value: Imagine a ball of 1 m radius in equilibrium with the cosmic background radiation. It will radiate the same amount as it receives, and that is 4*π times the value I gave you, and its surface is 4*π square meters). Comparing with the Sun's irradiation of 1367 W/m² and the Sun's apparent magnitude, that should effectively result in an apparent magnitude of the cosmic background radiation of about -5.14. Adding to that the -5.71 I calculated below, we are at about -6.21 in total. Icek (talk) 14:11, 30 October 2011 (UTC)

You could try looking in some solar power articles. They might have the total available for recovery by solar cells... 71.202.97.70 (talk) 23:02, 29 October 2011 (UTC)

According to apparent magnitude, the total integrated magnitude for the night sky is -6.5. There is no reference for that statement, so I'm not sure how reliable it is and I'm not sure what is included in it. -6.5 corresponds to about 1/370 times the brightness of the full moon. --Tango (talk) 23:44, 29 October 2011 (UTC)

From "adding" the apparent magnitudes in the table in that article (although especially for the brighter magnitudes where there are smaller numbers of stars the actual "average" apparent magnitude is different from the stated magnitude) I get about -5.71, but that's only up to magnitude 10. Icek (talk) 14:00, 30 October 2011 (UTC)

Given the precision we're working to here (different wavelengths, inclusion of planets, etc.), I think it's fair to say those two figures are in agreement. --Tango (talk) 15:58, 30 October 2011 (UTC)

Earth's Energy Resources talks about "extra-solar radiation", but doesn't define it. It gives an average of 121 watts/m² on page 23, plus some mysterious figures in graphs on preceding pages, if that's any help. Clarityfiend (talk) 03:31, 30 October 2011 (UTC)

It also says that all of it is absorbed in the atmosphere and drives wind currents and the ocean temperature gradient (at an abysmally low efficiency, like most energy conversion processes). 67.169.177.176 (talk) 06:33, 30 October 2011 (UTC)

The value of 121 W/m² is obviously far too high, they mean something like the radiation scattered from the atmosphere or whatever. Icek (talk) 13:57, 30 October 2011 (UTC)

There is also this PDF from brillianz.co.uk, which says that starlight is about 0.00005 lux, compared to 32,000 to 100,000 lux for sunlight and 1 lux for moonlight. Lux is a summation of all visible wavelengths, so in conjunction with the solar constant you should be able to work out the power of starlight. --Heron (talk) 09:52, 30 October 2011 (UTC)

So the ratio is about 1.3 billion? Dualus (talk) 23:11, 30 October 2011 (UTC)

Yes, that's the right order of magnitude. --Heron (talk) 10:15, 31 October 2011 (UTC)

Calculating probabilities

Let's say I take a tree, for example, a horse chestnut, with those big dark buds that supposedly look like horses but really don't. Remember those, they'll be important later. Anyway, I get this tree, growing quite happily in a big pot, on a windowsill, inside so it is reasonably warm if not hot or sunny. It's February, let's say the whole first week of the month, so the tree is bare of leaves, just a couple of branches and say a dozen of those big leaf buds.

Now, I look at this tree on February 1st, and I choose out of it two randomly picked leaf buds on the plant, I do nothing to them, I just leave it on the windowsill for a few days. What are the chances that both those two buds, and no others, will be opening with newly grown leaves inside within that week?

Obviously it would not be possibly to work out the exact number, but some sort of rough estimate, an order of magnitude, would it be, for example, 50:1, 10,000:1, 70,000,000:1? Anyone got any sort of idea? Myself, I could not even begin to work out how to calculate this, not without an extensie survey of many trees across the country, but perhaps someone here knows better.

148.197.81.179 (talk) 21:15, 29 October 2011 (UTC)

If you were certain that exactly two buds out of the twelve would open within a week, then the odds against them being exactly the two you chose is 65:1. You need to multiply this 1 in 66 probability (choosing 2 from 12) by the probability that exactly two buds will open within a week. Someone here might know whether horse chestnut is more sensitive to temperature than to length of day. If it is (as for Oak) then the temperature in the room and the amount of sunshine through the window will determine this latter fraction. If light is the main determining factor (as it is for Ash) then the buds are not likely to open until April, so your second fraction is very small and the odds correspondingly large (perhaps a million to one?). If the warmth of your windowsill brings bud-opening forward by a month or two, then perhaps it will begin in one of the eight weeks before April, so the second fraction might be one eighth, giving total odds of 527 to one against (i.e. a probability of 1 in 528). Please note that these figures are not accurate because there are too many variables to make reliable predictions. Dbfirs 22:03, 29 October 2011 (UTC)

You'd be better off in this sort of situation running actual experiments to figure out what the probabilities might be. There are a lot of variables involved, but if you did it was a few hundred plants over a long period of time, you'd probably end up with fairly good "rough" statistics on it. Doing it from first principles is probably the most problematic approach, especially when one doesn't really know for sure what variables actually matter the most. --Mr.98 (talk) 03:28, 30 October 2011 (UTC)

Agreed, and, of course, if you observe the behaviour of your windowsill tree this coming February, you will have a much better chance of making a reasonable estimate for the following year. Dbfirs 06:40, 30 October 2011 (UTC)

By the way, the word "horse" doesn't come from the supposed resemblance of buds to horses, but to distinguish its fruit from the edible sweet chestnut, the idea being that "horse" = horses might eat them but humans wouldn't. --TammyMoet (talk) 09:24, 30 October 2011 (UTC)

Which is ironic, because we were always warned not to let our horses eat horse chestnut, because it's poisonous to them. It was one of the short list of common and dangerous plants in the UK that our instructor made us learn. Not as bad as yew (an inch could kill a horse, we were told) or ragwort. 86.163.1.168 (talk) 16:05, 30 October 2011 (UTC)

The smell of winter

Everytime winter comes around, sometimes as soon as early October, there's this wintry smell in the air, that stays until spring. Every year it's the same sort of smell. I've experienced it on two different continents and in three different countries. Does anyone else know what I'm talking about? What's causing it? What's the scientific explanation? Thanks in advance! ElMa-sa (talk) 21:42, 29 October 2011 (UTC)

Perhaps decaying leaves? Dbfirs 22:05, 29 October 2011 (UTC)

many plants and soil types give off distinctive odors which vary with changing weather conditions. The smell of damp earth, falling leaves, nuts and fruits. I'm guessing that all three locations had similar plant and soil conditions. giving the same type of odors.190.56.105.233 (talk) 22:24, 29 October 2011 (UTC)

Relevant articles about a similar effect when it rains are petrichor and geosmin. Dbfirs is probably onto something with the decaying leaves which will contain Streptomyces that produce geosmin. Another idea would be that you are noticing a lack of summer smells - this lists many smells associated with summer, so maybe once those have gone, you are left smelling everything else. SmartSE (talk) 13:57, 30 October 2011 (UTC)

Humans have about 1,000 different kinds of olfactory receptors, almost all of which attenuate. Dualus (talk) 15:31, 31 October 2011 (UTC)

If you are talking about the soft musky smell, that's probably what the people above me said. However, I also notice a tingling metallic smell during winter, usually a few days before it starts to snow. Now, I don't have a scientific background so I'm not sure, but I believe that smell is ozone. Something in the change in atmosphere causes it to heap up near the ground, allowing us to smell it.212.123.1.140 (talk) 12:35, 31 October 2011 (UTC)

Temperature inversion? 67.169.177.176 (talk) 01:23, 1 November 2011 (UTC)