Wikipedia:Reference desk/Archives/Science/2009 April 7

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April 7

Toads and warts

Is it true that handling certain species of toad will cause an outbreak of warts in a human? I was told this as a child and it has stuck with me. I have never, ever touched a toad (or frog, just in case) in my life up to this point because of it. It's not that I feel that I've missed out on anything important growing up, but I'm wondering now if I have been misled. :) When I say warts, I mean the typical warts that humans suffer from, not a reaction to toxins in the toad's skin that causes something that looks a bit like warts to come up. --84.71.174.88 (talk) 01:09, 7 April 2009 (UTC)

No. Toads cannot cause warts in humans. This is an urban legend. Warts are caused by a variety of viruses. The relevant viruses are not carried by toads. JoshuaZ (talk) 01:42, 7 April 2009 (UTC)

It's more like sympathetic magic: toads have warts, therefore toads cause warts. Looie496 (talk) 02:16, 7 April 2009 (UTC)

No. See List_of_common_misconceptions#Biology. Axl ¤ [Talk] 09:21, 7 April 2009 (UTC)

It should be noted that this particular item is currently unsourced. Me and several other editors are attempting to find reliable sources for this article, but this item may be removed shortly. A Quest For Knowledge (talk) 12:31, 8 April 2009 (UTC)

The problem is that the term "warts" is used to refer to different things. The warts on a frog are more like what we call moles, which are not usually caused by a virus and therefore can't be passed on to others. StuRat (talk) 15:39, 7 April 2009 (UTC)

When you say "frog" do you mean "toad"? In these parts, our frogs are pretty smooooth. --Scray (talk) 21:03, 7 April 2009 (UTC)

Yes, I meant toads. StuRat (talk) 14:58, 8 April 2009 (UTC)

hearing

I went to a rock concert about a year ago and had tinnitus for 3-4 days after that. I want to go to another concert in a couple months and was wondering if there was a way that I would not get that ringing in the ears, or to keep the duration of the ringing shorter, and still enjoy the concert without muffling the music. 12.216.168.198 (talk) 02:48, 7 April 2009 (UTC)

I find that earplugs do an excellent job of reducing volume to enjoyable levels without muffling the music -- in fact, I tend to find the audio quality better once so filtered. Plus, no ringing! I prefer the cheap disposable foam variety for this sort of thing. — Lomn 03:02, 7 April 2009 (UTC)

I know a lot of professional audio people (I work in the video games business). They value their hearing above all else (One guy calls his ears his "golden moneymakers" because without them he has no career!) - yet they also enjoy listening to and playing music more than any people I know. They each have reusable ear plugs that are created especially for each individual by an audiologist who measures their ear canals. These earplugs attenuate the volume of the sound to a huge degree - but do so in a way that's completely uniform across the entire audio spectrum. This means that they still hear all of the nuances of the sound - and can ascertain the timbre, etc precisely as well as someone with unprotected ears. It also allows them to wind their audio systems up to higher volume levels so they get the satisfying 'gut feel' of the bass notes (and the all-important neighbours calling the police to complain about the noise)...without wrecking their hearing. They point out that every time you expose your ears to loud music, you erode your hearing a little bit more - and if it's loud enough to cause temporary deafness or tinnitus - then you have certainly damaged your hearing in a way from which it will never fully recover. So there is a STRONG recommendation that if you go to concerts or play instruments - to wear earplugs every single time - and that you should buy the best ones you can afford. SteveBaker (talk) 14:48, 7 April 2009 (UTC)

I agree with the earplug recommendation. If you're worried about looking uncool, get some earplugs which are skin-colored and put them in right before the music starts (say during a trip to the bathroom). If you put them in too early everyone will wonder why you can't hear. You don't have to worry about taking them out immediately afterwards, though, as people will attribute any lack of hearing acuity on your part as being due to damage to your hearing from the concert.

Another suggestion is to not sit right in front of any speakers. Obviously, this doesn't work if the concert enforces assigned seating, unless you know where the speakers will be when you choose your seats. However, avoiding speakers will only reduce the hearing damage, not eliminate it. You still need earplugs for that. StuRat (talk) 15:25, 7 April 2009 (UTC)

Certainly the inverse-square law applies here! If you can double your distance from the nearest speaker - the sound energy will be one quarter as much - but because our ears are logarithmic devices, it won't seem four times quieter. However, this doesn't really change the answer - if you like music and would like to be able to continue to enjoy it - wear earplugs. With decent earplugs - and hearing that hasn't already been fried by going to too many Motörhead concerts - you can easily hear normal conversation with the earplugs in...that's also a consequence of the logarithmic nature of our hearing. With good earplugs, things don't really sound that much quieter. SteveBaker (talk) 16:19, 7 April 2009 (UTC)

Distance from speakers certainly matters, but not only distance, as most speakers are highly directional. Therefore, sitting an equal distance to the side of a speaker isn't nearly as bad as in front of it. Intervening objects, such as a post or the heads of other concert-goers, may also block some of the sound. StuRat (talk) 19:34, 7 April 2009 (UTC)

As for why there aren't regulations which limit the volume at concerts to levels that won't damage hearing, there I am baffled. StuRat (talk) 15:31, 7 April 2009 (UTC)

There are such regulations in (for example) the UK - but the levels aren't set low enough to be 100% effective. SteveBaker (talk) 16:19, 7 April 2009 (UTC)

Plus what would be a safe level of noise for1 minute may not be safe if you have 3 hours of that noise level. 65.121.141.34 (talk) 16:53, 7 April 2009 (UTC)

Some musicians use "high fidelity" earplugs by Etymotic Research [1]. The frequency response is preserved while lowering the dB level. We cannot give medical advice, and specifying "safe" noise levels seems to fall in that category. For general information, you might check OSHA for the noise levels employees can be exposed to for varying durations under U.S. regulations. This regulation does not guarantee complete safety for persons exposed to noise levels under the curve. But they are an improvement over the old days when every construction worker, person who fired guns, soldier, or especially boiler maker was deafened to varying extents. Did you plan to carry a calibrated dbA slow response meter with you? Else, how would you know the sound pressure level? Edison (talk) 20:59, 7 April 2009 (UTC)

Why do massive objects in space don't look like they are moving?

Small objects in space look like they are moving, while massive objects don't. Why is this? 98.221.85.188 (talk) 04:36, 7 April 2009 (UTC)

I'm not sure what you mean. They look that way to whom? —Tamfang (talk) 05:15, 7 April 2009 (UTC)

I think that the OP means that when you travel, small things such as trees move when you look at it while larger (and probably distant) objects such as landmarks and the Moon doesn't appear to move even if you are travelling by car.--Lenticel ^(talk) 06:28, 7 April 2009 (UTC)

The appearance of moving results from the object appearing at a different angle at different times. So for a distant object to appear to move it will have to move a significant fraction of its distance away, so for something like the moon, you would have to move hundreds of kilometers to notice the change in its angle compared to say the stars. For distant stars there is even less movement in the sky, Astronomers can use parallax to find out how far away stars are. Graeme Bartlett (talk) 06:40, 7 April 2009 (UTC)

It's especially noticable with large aircraft. When you look at an airliner slowly drifting across the sky - it's hard to imagine that it's belting along at 400 mph! Partly that's because perspective has reduced the angular rate of speed relative to your eyepoint - the other part is that being such a large object, it takes more time to travel it's own length than a little cessna or something - which is going maybe a quarter the speed but is ten times shorter in length. Another problem with anything high in the air or in space is that there are typically no nearby, stationary objects for you to compare against. This is a problem that plagues science fiction movies and TV shows - even when the Starship Enterprise is zipping along at several times lightspeed - the stars in the background ought to appear dead still for hours at a time...but they don't - they move and even have parallax! That's totally unrealistic (even in a 'classical universe' with no relativity and no speed-of-light limit) - but that's the only way they have to convey speed. There is often a similar problem with size - you see spacecraft disappearing behind planets and moons - when in reality, even a gigantic craft would have shrunken to an invisible dot long before it could be far enough away to get around a planet that's thousands of miles in diameter. SteveBaker (talk) 14:36, 7 April 2009 (UTC)

In Star Trek, they use "warp factors", which apparently are not just the number of times the speed of light they are going. If this was the case, then, traveling at say Warp Factor 5 would still take them years to get anywhere (although it might not seem so to them, due to time dilation, but they just ignore that). It seems to have been a logarithmic scale of some type, with Warp Factor 1 being the speed of light and Warp Factor 10 being infinitely fast. They did violate this principle and go over Warp Factor 10, on at least one occasion, though. They could typically travel to the nearby stars (let's say 10-100 light years away) in a matter of hours (again, ignoring time dilation). If we assume the typical trip to take 1/1000th of a year, that would give us speeds in the range of 10 thousand to 100 thousand times the speed of light. In at least one episode, they did go all the way to the edge of our galaxy, though, which implies speeds well into tens of millions of times the speed of light. At such speeds, you should notice some apparent movement of the nearby stars, but perhaps not as much as is shown. StuRat (talk) 15:05, 7 April 2009 (UTC)

They use at least two sets of warp factors in star trek (geek warning, but I'm sure I'll be beat). In Voyager, Warp 10 = infinite velocity. In other series, I think they've gone to at least warp 16-17, which, of course, wasn't anywhere near infinite velocity. -- Aeluwas (talk) 15:43, 7 April 2009 (UTC)

All Next Generation era series use the new system, the Original series and Enterprise use the old one. There is no clear rule for the old system, but the fan-devised rule of them is that warp factor W means a speed of c*W³. --Tango (talk) 17:37, 7 April 2009 (UTC)

In space, it's the distance to the objects that determine how fast they appear to be moving, as explained previously. But you asked about the size of the objects. It just works out that small objects we can see are close and large objects are far away. If the Moon was as far away as a star, we couldn't see it. If a star was as close as the Moon, we would all be dead. StuRat (talk) 15:18, 7 April 2009 (UTC)

Star Trek - Science or fiction?

While looking at this image, it occurred to me that the "lettering" of the quadrants was rather strange. Instead of going either clockwise or counter-clockwise, the quadrants are put in order from right to left, then criss-cross, and then go right to left again. Since Star Trek often tries to keep some slight grasp on science (theoretical or not), I'm left wondering where they got this mapping scheme. Is this based on anything in the real world or is this just a oversight on the part of the writers? Dismas|^(talk) 05:21, 7 April 2009 (UTC)

I'm not sure why this particular arrangement was chosen, but there are sometimes good reasons to eschew traditional ordering (obligatory xkcd). Also, why would a clockwise (or counterclockwise) arrangement be any more sensible? – 74  05:46, 7 April 2009 (UTC)

A counterclockwise arrangement would follow along the lines of the quadrants of a coordinate plane. Dismas|^(talk) 10:17, 7 April 2009 (UTC)

Certainly; but there is no scientific basis for that arrangement either—it is used by convention (i.e. because it has been used before) and because it roughly corresponds to polar coordinates (another arbitrarily-chosen system). Tellingly, only one octant is commonly labeled: the first octant (+,+,+). – 74  11:21, 7 April 2009 (UTC)

If you're looking for an explanation that would be plausible 'in-universe', the order of labelling follows the chronological order of exploration (by human beings); it also sorts the quadrants by increasing (mean) distance from Earth. I don't know of any explicit canonical reference which describes the labelling system, but you might try poking around over at Memory Alpha. TenOfAllTrades(talk) 12:30, 7 April 2009 (UTC)

• Entertainment Desk answer:

I've seen every episode of every Star Trek show (except the animated series) and all the movies, and I do not believe they ever mentioned the physical layout of the quadrants. I always assumed that consecutive letters were in order around the galaxy and therefore it was gamma that was opposite alpha, and I would have noticed if they said something that meant it was different. The image is only sourced to a web site and it might well have been created by a fan or writer who just made an assumption about what the labeling was. The fact that it relates to both Deep Space Nine and Voyager suggests that it is non-canonical.

• Science Desk answer:

Nothing in astronomy labels quadrants with letters. Where the details of an object are known well enough to talk about locations within it or on its surface, numerically expressed coordinate systems such as latitude and longitude are used.
--Anonymous, 20:10 UTC, April 7, 2009.

Not to sound like a total nerd, but in one of the episodes (in Voyager I think) where a prop map of the galaxy has the quadrants labeled. I don't recall the exact episode, but I bet that Memory Alpha would know where it is. 65.121.141.34 (talk) 20:46, 7 April 2009 (UTC)

I don't think there's any scientific basis at all. Basically, the original series took place in what's canonically now called the Alpha quadrant, and Deep Space Nine established the Gamma quadrant as a "far away" place to go to. But when Voyager came out, they wanted it set somewhere "farther away" so they had to establish the Delta quadrant as somehow even more remote than the Gamma quadrant. I'd say this is an issue of sense being thrown out the window in favor of suiting the show's theme. — The Hand That Feeds You:^Bite 14:35, 13 April 2009 (UTC)

Or just a different far-away place. --Anonymous, 00:56 UTC, April 14, 2009.

Vacuum flask

I was reading the Vacuum flask article and I came across this line:

A typical domestic vacuum flask will keep liquid cool for about 24 hours, and warm for up to 8.

Assuming the cool liquid has the same temperature difference from ambient temperature as the warm liquid does, how does this make sense?

This statement makes less sense if you think about common temperatures. Take ambient to be 20ºC, the cool liquid to be ice water (0ºC) and the warm liquid to be boiling water (100ºC) then surely it would take longer for the hot liquid to equilibrate than the cool liquid. Am I missing some thing here? —Preceding unsigned comment added by 130.194.164.217 (talk) 06:10, 7 April 2009 (UTC)

"Cold" doesn't flow; heat does. Take a point source located in a vacuum—all radiation produced will travel outwards radially and be lost. Now, take a point sink inside a vacuum—any radiation produced outside the vacuum is quite unlikely to strike the point sink. In real life, the interior dimensions are significantly larger than a point, but I'd suspect the principle still stands. – 74  06:33, 7 April 2009 (UTC)

If it's convenient to talk about cold flowing - we can. The math still works. Just as we talk about electricity flowing in the opposite direction than which the electrons are actually moving...it doesn't matter. Rigid thinking in science is not good. Very often, profound insights can be gained by kinda tipping your head sideways and squinting a bit! SteveBaker (talk) 14:26, 7 April 2009 (UTC)

"Lax" thinking is the kind of thing that generally leads to profound errors, not insights. In situations where the directionality of flow is irrelevant then you can use "cold" flow somewhat interchangeably (but with dubious benefit). However, in cases like this where directionality is important "cold" flow only confuses the issue. Science is all about precise (or "rigid") exploration of the world, and I am quite surprised by your dismissal of valid scientific principles in the interest of "convenience". – 74  21:17, 7 April 2009 (UTC)

It's only lax thinking if you don't understand the underlying mechanism. Low level atomic vibration/motion is what we call "heat". That vibration spreads to other atoms that are moving less quickly - and we talk about heat moving from hot to cold. However, when those fast moving atoms pass on their energy to the slow ones - they are slowed down in the process so talking about the reduction in motion spreading from the slow moving atoms into the fast moving atoms is no more or less valid than the "conventional" description of heat travelling from hot to cold. So long as you understand this, you can just as validly talk about the 'coolness' flowing into the hotter material as the other way around. This isn't "lax thinking" - it's unconventional thinking - looking at the problem in another way and possibly gaining some insights. It's truly just a matter of convenience to decide to talk about flow in one direction or the other. As I pointed out (and you've carefully ignored) we do this all the time when we talk about electricity flowing from + to - rather than from - to + as is "really" happening if you watch the electrons. However, we're quite happy to talk about the motion of "Electron holes" in the conventional direction as a way of making sense of the 'reversed' direction. Same deal with heat and cool. Far from "dismissal of valid scientific principles" I'm using those very principles in a way that might well make the explanation clearer. I should probably say something about being "quite surprised by your rigid thinking and lack of comprehension of underlying scientific principles"...but I'll let your imagination fill in the details (if you have an imagination that is). SteveBaker (talk) 13:18, 8 April 2009 (UTC)

It most certainly *is* less valid in the case of radiation, where a second material is not necessarily located in close proximity (and needn't exist at all). The "fact" that "electron holes" may be used to make some explanations of circuits simpler (personally, I've found it only adds confusion) has little to no bearing on heat transfer; an (equally pointless) counter-example would be darkness/light. But, if you insist on confusing the issue, I apparently cannot stop you. – 74  16:38, 8 April 2009 (UTC)

"Close that refrigerator door, you're letting all the coolth out !". StuRat (talk) 14:31, 7 April 2009 (UTC)

Yes, you are missing some physics. Radiative thermal losses (integrated over the entire spectrum) are proportional to temperature to the fourth power, see Stefan-Boltzmann law. Hot object in a warm environment loses energy faster than a cold object in the same environment gains energy, assuming the surface properties of the two objects are the same. Vacuum flask coating is not equally reflective at all infrared wavelengths, so the dE/dt ~ T₁⁴ - T₂⁴ approximation is not really accurate; but qualitatively it should work. --Dr Dima (talk) 07:28, 7 April 2009 (UTC)

You're also missing what people mean by keeping cool or hot. It would be considered cool if it is a bit cooler than ambient, but it would have stopped being hot and become warm or tepid in between getting to ambient temperature - and it would do that quicker because of the bigger temperature difference. Dmcq (talk) 09:58, 7 April 2009 (UTC)

I agree with all of our previous answers. The deal is that the vacuum inside the flask only stops losses due to conduction & convection (and even that, not completely since it's not a hard vacuum and there is a connection between interior and exterior at the neck of the vessel). It does little to prevent loss due to radiation (although they do apply a mirror coating to the glass of the inside vessel and use shiney metal for the exterior). But because the radiation from the warmer outside of the flask into the interior is happening at a lower temperature than the radiation from a hot liquid inside to that exact same exterior temperature - then the losses are faster. That taken with the undoubted truth that 'hot' liquids have a bigger temperature delta to the outside than the outside does to a cold liquid inside - so any conduction paths (which depend on temperature DIFFERENCE not absolute temperature) will be less significant in the cold case. Add to that that we care more about how hot our coffee is than how cold our soda is...this easily explains the factor of 3x difference. I'm actually rather surprised it's not more than that.

SteveBaker (talk) 14:26, 7 April 2009 (UTC)

Some Stanley "vacuum flasks" in recent years had finely powdered carbon in the "vacuum" space. A pinhole leak in the outer liner caused the fine carbon dust to spew out, reducing visibility if it happened in a moving auto. If it had lower than atmospheric pressure, why wouldn't air leak in instead of the carbon powder leaking out? Dewer's first vacuum flask in 1892 had a silvery mercury coating. In a vacuum flask without a silvery coating, a liquified gas evaporated 1/5 as fast as in open air; with the mercury coating, the evaporation was reduced to 1/33 the free rate. There should be a small hole in the lid of the inner container to avoid any pressure buildup. The flask allowed Dewar to transport liquified air on a rail trip from London to Cambridge to show it off. The outer of the flask was packed in dry ice to liquify the mercury and reduce the mercury vapor pressure. Edison (talk) 20:37, 7 April 2009 (UTC)

True area of a country

Hello, fellow Wikipedians. It has for a long time bugged me that it seems, when we measure the area of an... area, country rather, that we take the flattest approach. In truth, every hole and rise will result in a greater area, and so a 500km^2 country that is completely flat will have less area than a 500km^2 country that has, say, a mountain on it.

Afghanistan for instance, to point to a place where we know the intricate shapes and forms of their mountains, has a much higher area than is stated in its proper article, likewise Norway, whereas Western Sahara's real area isn't too far from its measured area - not off by as much as in other cases, at least. Are anyone able to measure area in this way, "real" area as it might be called? Thank you for your help. 62.128.252.85 (talk) 11:19, 7 April 2009 (UTC)

You may be interested in How Long Is the Coast of Britain? Statistical Self-Similarity and Fractional Dimension. While that concerns the length of a coastline, the problem is analogous. -- Coneslayer (talk) 12:00, 7 April 2009 (UTC)

"True" or "real" area of a country is an interresting concept. Did the September 11 attacks reduce the real area of Manhatten? Cuddlyable3 (talk) 13:49, 7 April 2009 (UTC)

This is emphatically NOT the same as the 'coastline' problem. When we talk of the 'area' of a city or a country or whatever - we're not talking about the total area of everything contained inside of it - we're talking about the area of the city when it's projected downwards onto an idealized spheroid at mean sea level. Where my house is built, I have 1.2 acres of land - most of it slopes steeply at about (let's say) 45 degrees - which means that the ACTUAL area is about 1.4 times bigger which is close to 1.7 acres. But I'm taxed on 1.2 acres, the law regarding the amount of land I needed to build a 2 storey house said I had to have 1.2 acres...everyone talks about it being 1.2 acres. So taking the more reasonable definition of 'projected area' - even though the "coastline" of that area might be fractal in nature and it's length is therefore indeterminate, the area bounded by that fractal has a well-defined value that lies between limits that can be determined to arbitary precision by examining a more and more detailed coastline. That's the opposite of the coastline problem - where the more closely you look at the coastline, the longer it becomes and the less accurately you can determine the answer. Now, if you ARE talking about the area of everything inside the city - then indeed you are looking at a fractal-type of problem which is kinda similar to the the coastline problem in that you ultimately need to sum the areas of each blade of grass - and so forth...however, that's a fairly bizarre interpretation of the word for any practical purpose. SteveBaker (talk) 14:04, 7 April 2009 (UTC)

It seemed to me that the "bizarre interpretation" was the exact point of the question, which is why I brought it up. As you add up all the extra area due to terrain, your area gets bigger and bigger as you go to smaller scales (cracks in the mountain, etc.). BTW, are surveyed areas really projected to MSL? So a flat parcel surveyed at 1 acre in Denver is really slightly bigger than 1 acre? -- Coneslayer (talk) 14:14, 7 April 2009 (UTC)

Technically - yes - but the error is so spectacularly microscopic for a flat piece of land that the errors in measurement completely dwarf that. SteveBaker (talk) 15:43, 7 April 2009 (UTC)

I agree that the approach the original poster was asking about would lead to both the fractal issue and the problem of the area changing due to strip mining, landscaping, etc., so isn't practical. Whether the current measures are taken the way SteveBaker said is an interesting question. I suspect that in many cases the area of a plot of land is simply determined by measuring the distance along the edges (straight-line distance, through the air, not measured along the ground). I doubt if any adjustment for elevation is used. StuRat (talk) 14:29, 7 April 2009 (UTC)

When they surveyed the plot for my house, they determined the latitude/longitude for each corner of the lot and stuffed that into a piece of software that calculated the area. The altitude wasn't taken into account - and they certainly don't use tape-measures to just measure the straight-line distances between the corner markers...at least not in Texas. SteveBaker (talk) 15:43, 7 April 2009 (UTC)

Of course they don't use tape measures. I believe modern surveyors have a device which uses the speed of light to measure the distance (do we have an article on this ?). I can't see them using a GPS device to measure the latitude and longitude, as they just aren't accurate enough. Being within a few feet is fine for driving directions, but lousy when marking property lines. StuRat (talk) 19:24, 7 April 2009 (UTC)

Actually - they did use GPS - but not the regular satellite-only kind. They plant a special 'base station' at a known location and use 'differential GPS' which is accurate down to a millimeter or so to accurately measure the position relative to that base. In the case of a plot of land, they don't care much where it is (at least not to great precision) - but they do care how big it is...because that's what determines the taxes you pay, etc. What they actually did at my house was to check the position of a big steel spike that's driven into the ground at one corner of the lot using some kind of conventional measurement system with theodolites and such measured from a nearby road. Then they positioned the GPS base-station onto that spike then walked off to the other corners of the property with their differential GPS and got accurate numbers relative to the base station and hammered in more spikes. Then they hooked up the GPS widget to their laptop and got a number for the area. No elevation data. There is no way they could have used lasers or whatever - the terrain is WAY too rugged for that. You'd have to take down at least a hundred trees to get a line of site, even over the flatter parts! (Then my neighbour dug up one of the spikes because he claimed it was 20' away from where it should be...he ended up paying a $1000 fine and came close to going to jail when he argued with the police...don't do that!) SteveBaker (talk) 01:17, 8 April 2009 (UTC)

I didn't say they use light, but rather the "speed of light", which, of course, applies to the entire spectrum. I suspect that the "differential GPS" device you mentioned uses that method, with radio waves or some other frequency. I would have thought they would need to take differential elevation into account, as well, when determining the area of a piece of land. For example, if you have a 240 foot long lot which is 70 feet lower at one end, that will give a distance of 250 feet between the two points when measured at those different elevations. That's enough error that they might be rather concerned. StuRat (talk) 14:54, 8 April 2009 (UTC)

You do not get more hectares or acres of land by digging a hole and piling up the resulting dirt. See the 1902 "Manual of instructions for the survey of public lands... which included the oath to be taken by assistant surveyors:"...we will level the chain upon even and uneven ground, and plumb the tally pins..." U.S. Supreme Court Reports from 1901 says "...the mode of measuring will be to level the chain, as is usually done with chain carriers when measuring up and down mountain sides, or over other steep acclivities or depressions, so as to approximate, to a reasonable extent, horizontal measurement, this being the general practice of surveying wild lands in Tennessee." "Leveling the chain" can be done by physically keeping the chain horizontal, or by trigonometry on cliffs and steep river banks based on use of transits or other optical instruments. Only informal measurement, like a farmer dividing by his own efforts a 40 acre field into 2 twenty acre fields, might be done up hill and down. In such informal measurements, the farmer might cut a "pole" 16.5 feet long and walk along flipping it end over end to measure off "poles" or he could level it. "A "Gunter's chain was 66 feet long, equalling 4 "poles" or "rods." A British surveying book from 1881 compares the "levelled chain" and the theodolite for measuring slopes, and notes how hard it is in practice to perfectly "level the chain". Edison (talk) 19:54, 7 April 2009 (UTC)

Surveying and Aerial survey may have the info Stu was looking for. While it might be of statistical interest (or bragging rights) to measure surfaces at an angle, for most practical purposes the more level the area the more usable. (OR we have an brook in back with a slope of about 60 degr. You'd have to either dig things up or fill it in to do anything with the lot but admire the view.) 76.97.245.5 (talk) 20:18, 7 April 2009 (UTC)

I just wanted to add to Coneslayer's comment that even when 911 happened, the area of Manhattan stayed the same as long as the volume of the towers were still situated in Mahattan, therefore, even though the shape changed, the volume stayed the same. Buɡboy52.4 (talk) 04:37, 12 April 2009 (UTC)

Relationship between Thermodynamic Entropy and Cosmic Dark Energy?

What is the relationship (if any) between Entropy and Dark Energy The temperature-dependent term for Entropy is an important thermodynamic determinant in most bio/chemical reactions. Yet astrophysicists rarely discuss or estimate its role in determining the balance of cohesive/dispersive forces at work in the cosmos. Why is this? Is Entropy Dark Energy by another name? Has the dispersive effect of an Entropy increase in the cosmos (but outside a black hole!) been quantified -- I assume that it cannot be just ignored? 19Grumpah42 (talk) 13:08, 7 April 2009 (UTC)

Have you read our articles on entropy and dark energy? They should not be considered analogous. As dark energy is presently theorized to be doing work (accelerating the expansion of the universe), it is specifically not "the unavailability of energy to do work". — Lomn 13:28, 7 April 2009 (UTC)

temperature goes up as you dig down.

The temperature goes up as you dig down, like with the Kola borehole. If one was to dig a straight level tunnel starting at 1,000 ft under a 12,000 ft tall mountain, would the tunnel be far warmer in the middle then on the outside ends, or does the temperature only start going up when your hole is below sea level? 65.121.141.34 (talk) 14:22, 7 April 2009 (UTC)

It depends entirely on where you dig. If you start digging on a 12,000ft volcanic mountain, it won't take long to hit hot rock. If you start digging on a 12,00ft pile of granite, it will take a long time to hit hot rock. The Earth's crust is not uniform and there are hot spots under it. -- kainaw™ 14:26, 7 April 2009 (UTC)

If your mountain is made of a 'hot' granite, i.e. with a high concentration of radionuclides, it could be quite hot due to its internal heat production from radioactive decay. Whatever the actual value of the geothermal gradient beneath your mountain, it would get hotter along your horizontal tunnel, the only question is 'how much?'. Mikenorton (talk) 14:41, 7 April 2009 (UTC)

Since most of the heat underground is either generated at the point where it's measured (by radioactivity and tidal forces) or underneath, the question is if the heat is kept where it is or allowed to radiate away on the surface. Therefore, the more insulation there is between a particular location and the surface, the hotter is should be. Horizontal distances would be the same as vertical distance, in this regard. However, solar heating means that the surface is sometimes hotter and sometimes cooler. On a hot day, it will be cooler underground or in a tunnel through a mountain. This effect will be much greater than the quite gradual effect of increasing temp with distance from the surface. StuRat (talk) 20:17, 7 April 2009 (UTC)

For a practical example, I have here a nice little book: the 2000 English translation Historical Tunnels in the Swiss Alps: Gotthard Simplon Lötschberg of the 1996 book Historische Alpendurchtische in der Schweiz by K. Kovári and R. Fechtig, published by the Gesellschaft für Ingenieurbaukunst (Society for the Art of Civil Engineering) there. This quotes a 1906 report saying that when constructing the original Simplon Tunnel, "the temperature of the rock rose rapidly from about 40 °C [that's 104°F] at distance 6340 m [3.94 miles] into the tunnel at the start of the period of observation to about 52 °C [125°F] at 7300 m [4.54 miles]. From there the increase in temperature was more gradual until at about 9100 m [5.65 miles] from the north portal it reached its highest value of 56 °C [132°F]" (that would be near the midpoint of the tunnel). From the accompanying diagram, the depth of rock above the tunnel at the three positions mentioned was roughly 1,200, 1,500, and 2,200  m respectively, or about 4,000, 5,000, and 7,200 feet.

The book does not mention the particular source of geothermal heat applicable to this tunnel, but a geological diagram shows that it is mostly in schist and gneiss, both of which are metamorphic rocks that may or may not be formed from granite. To deal with the heat, cold water was pumped into the tunnel and sprayed into the air. Many tunnel projects experience quantities of ground water flowing into the tunnel and in this case that water, which was at 12°C (55°F), was put to good use.

--Anonymous, 20:41 UTC, April 7, 2009.

Venusian thought experiment

Well, let's imagine our Solar System 4 billion years ago, with a little twist.

Let's say Venus and the Earth were pretty close to actually being twin planets 4 billion MyA. Same conditions, same [almost] everything. Time goes by, and eventually life evolves on Venus about 80 MyA before the same thing happens on Earth. Morphologically, you can imagine Venusian life to be as similar or as different from life on Earth as you wish, the only condition is that they must have the same vital requirements as we Earthlings.

Geological time speeds by, with both Earth and Venus having their share of diversity booms and extinction. Because Venus had a 80 MyA headstart, intelligent life evolves on Venus while the Earth is still in the Middle Cretaceous (ok, it doesn't have to be that way, but imagine it is).

While dinosaurs still rule the Earth, Venusians discover fire, erect buildings, create the movable print and eventually start burning fossil fuels. Like on Earth, they keep on pumping CO₂ and other greenhouse gases into the atmosphere for over a century. Even though they notice they've damaged the planet, it's too late to do nothing because they've already triggered the melting of permafrost methane, which in turn triggers a runaway heating. In the end, temperatures rise to the point that all life on Venus is scorched to death.

80 million years go by, and the weak but constant surface effects on Venus erase any trace of civilisation on that planet. Now, we only see a barren desert spreading everywhere. Even their spaceships won't be a witness before us, since either their orbit has decayed and they have been destroyed, or they are many lightyears away in interstellar space. Therefore, nothing remains to remind us of what happened to Venus and what may happen to us.

Okay then, end of the story. What is the scientific evidence for or against this possibility? What are the oversights I may have made when inventing this little tale? Or, on the contrary, is it possible that it might have happened? Leptictidium (mt) 14:30, 7 April 2009 (UTC)

I think the biggest flaw is the implausibility of "twin planets" as laid out at the open. Venus' surface atmospheric pressure is 90 times that of Earth and it's 97% CO₂. We colloquially refer to Venus as having a "runaway greenhouse effect", but there's no plausible way for humans to accidentally get from our global warming scenario to something akin to Venus. To be clear, Venus has over 200 thousand times more atmospheric CO₂ than Earth. We're speculating that Earth's change in CO₂ concentration peaks at give-or-take double present levels. Now, applying that much CO₂ to a Venusian atmosphere raises its concentration from 96.5% to 96.5004%. Clearly, the same mechanic could not apply. What is catastrophic for Earth isn't statistically measurable for Venus. — Lomn 14:56, 7 April 2009 (UTC)

But Earth's atmosphere had much more CO2 and was much much denser in the past, i.e. before those pesky cyanobacteria turned well-behaved CO2 into toxic oxygen and complex organic molecules. See Earth's_atmosphere#Evolution_of_Earth.27s_atmosphere and Oxygen Catastrophe. --Stephan Schulz (talk) 15:12, 7 April 2009 (UTC)

Did the Venusians develop any space travel technology? If so, is it possible that there might still be satellites in orbit after 4 billion years 80 million years? I would think that they would have tried to leave some sort of record of their existence. Perhaps place satellites in orbit around all the major bodies in the Solar System (all the planets and the Sun). Actually, knowing that there's life on Earth, I would imagine they would send some probes down here as well as the Moon. In fact, why not move to the Earth? If the Earth's atomosphere isn't habitable for Venusians, perhaps Earth can be Venus-formed. A Quest For Knowledge (talk) 15:22, 7 April 2009 (UTC)

If you carefully construct a scenario in which there is no scientific evidence (as I think you tried to do) then there won't be any scientific evidence. If you don't do that - then there would be. It's kinda meaningless. If I had to specifically poke holes - I'd point out that if these Venusians were even a little ahead of where we are technologically - they'd be sure to have sent craft to the lagrange points of (at least) Venus - those locations are in principle accessible to our technology - and their equipment would still be sitting there pretty much intact even after millions of years because the lagrange points behave as if there were gravity pulling things towards that location (although that's not really what's going on) - so their positions would be stable and easily located. Of course you can just write that maybe the Venusian religion forbids sending things to the lagrange points and we're back with no evidence again...but that's true of anything we might come up with. SteveBaker (talk) 15:32, 7 April 2009 (UTC)

Or a large chunk of rock could have randomly flew through the Lagrange point taking the satellite with it. 65.121.141.34 (talk) 15:45, 7 April 2009 (UTC)

BTW, this is a pretty interesting premise for a science fiction story. If this is an original idea from you, you might want to run out to find a lawyer and see about getting a copyright on it. A Quest For Knowledge (talk) 15:37, 7 April 2009 (UTC)

You cannot get a copyright on an idea...--Stephan Schulz (talk) 15:40, 7 April 2009 (UTC)

And if you could, you'd have to fight my prior claim from years back. The basic idea is a fairly obvious one and I'm sure it's occurred to many people independently. Algebraist 15:47, 7 April 2009 (UTC)

Well, I'll try and clarify a few things.

1. When I said twin planets, I meant at the beginning. That means that Venus CO₂ would be 97%, but maybe as a result precisely of all the permafrost methane melting and triggering a positive feedback.
2. Yes, they did have space travel technology. But someone said above that they would be a little more advanced than we are now – no, in my thought experiment the 80-million-year old Venusians would be just as advanced as we are, only 80 million years earlier.
3. @ SteveBaker: I am not asking for evidence regarding the fact that this happened, but rather what information we have which may suggest it could have happened (or could not, for that matter).
4. Finally, a question: would it be likely that, with all meteors, comets, etc. flying around, artifficial satellites survived for so long in the Lagrangian point? Leptictidium (mt) 15:54, 7 April 2009 (UTC)

The Lagrangian point of what system? Earth-Moon, Sun-Venus, ...? —Tamfang (talk) 17:39, 7 April 2009 (UTC)

There ought to be atmospheric spectroscopic evidence. I would think at least some telltale organic molecules would remain even in the oxidizing atmospheric conditions. Also there would have been a lot of water on Venus to support life originally (assuming life on Venus operates on similar principles). Venus' atmosphere has a rather low water content (0.002% Water vapor compared to earth's ~ 1% water vapor). Venus' high temp would make liquid water on the surface unlikely. The article Venus says the best hypothesis as to what happened to the water Venus was hypothesized to have in the past is that the evaporated water "has dissociated, and with the lack of a planetary magnetic field, the hydrogen has been swept into interplanetary space by the solar wind." Is 80 million years enough time to get rid off an ocean's worth of water via that method? I'm not sure it is. According to Carbon, Earth has a total of about 40000 gigatons or 4 * 10¹³ kilograms of carbon dissolved in water, in the atmosphere, as coal and oil, and locked up in biosphere. That carbon would make about 1.5 * 10¹⁴ kilograms of carbon dioxide if I did my math right. There is 4.8 × 10²⁰ kg of atmosphere on Venus according to Atmosphere of Venus and around 95% (assuming by weight) of it (~4.6 × 10²⁰ kg) it is carbon dioxide. That amount of carbon dioxide is about 6 orders of magnitude greater than the amount of carbon dioxide that all the Earth's sources of carbon that I mentioned above would make. While I am not sure the Earth figure includes other sources of carbon like carbonate containing minerals (probably not), Venus has a ridiculously large amount or carbon dioxide nonetheless. That discrepancy makes me wonder if Venus' atmosphere could have ever not had a significant amount of carbon dioxide as there would had to have been a large amount of something that could have bound all of that up previously. If the rest of that carbon dioxide did come from carbonate minerals, again, is 80 million years enough to decarbonate enough of it to account for present day atmospheric concentrations? Also if that process was still going on, if you could get a spiffy probe to the surface to bore a deep hole, you might be able to tell. Sifaka ^talk 17:56, 7 April 2009 (UTC)

Sorry, but you're about a century too late with your sf scenario. Of course when Percival Lowell, H.G. Wells, and Edgar Rice Burroughs were at it, the conceit was that since Mars was further from the Sun than the Earth, it cooled and developed first, and had the old civilization, while Venus was still in its version of the Mesozoic.

Sorry to dash cold water on your idea, but there is utterly nothing that would support your scenario. At Venus' distance from the Sun, lower gravity than Earth, and long diurnal rotational period, liquid water could not naturally collect on its surface, without which life is not going to get a foothold.

B00P (talk) 00:54, 8 April 2009 (UTC)

Now it can be revealed: it was Venusian UFOs that abducted our dinosaurs. Cuddlyable3 (talk) 17:42, 8 April 2009 (UTC)

How common is runaway global warming?

Some people say that we will soon trigger, or already have triggered, runaway global warming, and once it happens it's nigh-impossible to stop. How often does this happen? How bad is it when it does? — DanielLC 16:42, 7 April 2009 (UTC)

I would say we have a severe deficiency of data considering we don't have an experimental control group, or a large enough population of planets with temperature data to get any kind of statistically relevant result. My WAG is that it is rare. 65.121.141.34 (talk) 16:48, 7 April 2009 (UTC)

Runaway global warming is, as far as I know, still something of a vague theory with several possible mechanisms - the Clathrate gun hypothesis being the most prominent I've seen, i'd recommend that article as a good starting point. There simply isn't enough data to make a solid answer to your question: past periods of large-scale warming can be as easily attributed to solar variations that we simply have no control over. ~ mazca ^t|c 17:18, 7 April 2009 (UTC)

see Interglacial. -Arch dude (talk) 17:22, 7 April 2009 (UTC)

Since the Earth's been hotter than this before and cooled down, obviously something must eventually kick in to bring temperatures back down. However, temps could get dangerously high until that happens. StuRat (talk) 19:57, 7 April 2009 (UTC)

And, while we don't have evidence of runaway global warming due to greenhouse gases, there is plenty of evidence of other dramatic climatic changes both in the Earth's past and on other planets. Mars, for example, appears to have once had quantities of liquid water. StuRat (talk) 20:07, 7 April 2009 (UTC)

Mars could certainly lose all its liquid water without high temperatures due to a dissipated atmosphere, even if the temp stayed around -20F, so I would like to see additional evidence before I would count Mars. 65.121.141.34 (talk) 20:39, 7 April 2009 (UTC)

I was using Mars as an example of "other dramatic climatic changes", not "runaway global warming". StuRat (talk) 14:22, 8 April 2009 (UTC)

There are certainly two parts to this - right now, we undoubtedly have global warming - far more rapidly than any of the 'nut-job' theories can explain. This much is established fact. What we don't know is precisely is whether it's reached the runaway stage yet - and if it hasn't, then by how much can we risk pushing it before it does? There is a small amount of legitimate doubt as to whether the runaway effect even exists - but the vast majority of serious experts claim that there is at the very least, a huge risk that the climate will run-away from our ability to control it by any means whatever.

There are a fair number of feedback mechanisms involved - things like that snow is white an shiney and reflects sunlight away from the earth - as the earth warms, the ice melts and is replaced by something darker (ocean or dirt) which ceases to reflect sunlight away and absorbs it instead. This extra absorption causes more temperature increase - which causes more ice to melt. Those kinds of mechanisms are what could kick us into 'runaway' global warming - a scary situation where even if we stopped all CO2 production instantly - the earth might continue to get warmer. But we don't really have a firm knowledge of which (if any) of those mechanisms are removing our ability to recover. It seems that the arctic ice sheet is melting far faster than we predicted - and that is perhaps evidence of a runaway effect at the North Pole. However, when all of that ice is gone - the effect will cease to run-away. Since the ice at the North Pole is floating, it doesn't make much difference to global sea levels when it melts - so aside from the ecological damage (say goodbye to polar bears, for example - they are going extinct within our lifetimes) - the net effect is limited.

The same effect happening at the South Pole would be VASTLY more dangerous - because there is a lot more ice locked up there - and it's sitting on land well above sea level - so when it melts, it pushes the ocean levels higher.

Then (as previously mentioned) we have the methane clathrate business - where (essentially) there are deep ocean deposits of frozen methane which will melt when the ocean temperatures rise - thereby releasing methane into the atmosphere - which is a MUCH nastier global warming agent than CO2 - causing more temperature rise - causing more clathrate to melt. A couple of ships have detected methane bubbles coming from areas where these deposits may be found...so there is a definite possibility that this has already started to run-away. That happened at the end of 2008 - so it's very possible that we're already too late.

Also, as temperatures climb - the warming of the ocean causes the water to expand - making the sea levels rise faster than you'd expect from ice melting alone. As the ocean inundates land, the darker water absorbs more heat than the land would - and (worse still) has a higher thermal inertia - so it locks the heat in so it doesn't radiate out into space again at night as much as it used to. This increases temperatures - which melts more ice, clathrates and increases the volume of the existing water still more.

At some point, the increase in water levels will start killing off green plants - which means less CO2 is absorbed and more gets into the atmosphere. This is somewhat tempered by the increase in green algea in the oceans - so maybe that's not a feedback mechanism - but we don't know that for sure.

The point is that there are MANY mechanisms - and they are all feeding back on each other. So the melting of the northern ice-cap might not be directly serious - but because it increases the absorption of sunlight - it may be enough to kick one of the other mechanisms into high gear. Estimating the consequences of such complex interactions is very tough. The consensus of opinion between serious researchers is that we'll see between 7 meters and 22 meters of water level increase over the next 100 years. Either of those would be extremely nasty for humans...and devastating for most non-human life.

As for what it would take to recover - it is indeed true that the planet has recovered from worst in the past - but that's always been at the price of mass extinction of plants and animals - and it's taken hundreds of thousands of years to do that. So this potential recovery in the future isn't something we have to care much about - it's unlikely that human civilisation could survive in anything like a recognisable form in the face of that kind of destruction.

SteveBaker (talk) 20:36, 7 April 2009 (UTC)

Let me clarify my question. I want to know how common sudden changes in climate are. I'm not asking about extremes in climate or about how sudden climate change can happen. If they all lead to Extinction events, there couldn't be much more than 20 in the last 540 million years, right? If so, we'd need to be changing the climate at hundreds of thousands of times its normal speed to have an appreciable chance of triggering it in the near future, right? If runaway climate change won't cause an Extinction event, don't we have more important things to worry about? — DanielLC 23:02, 7 April 2009 (UTC)

We ARE changing the mean temperature at hundreds of thousands of times it's normal speed - and that's pretty much exactly what the problem is! We've increased global temperatures by a couple of degrees over a hundred years. In the past, that's something that's taken a million years to happen 'normally'. So yeah - we're doing this 10,000 times faster than 'normal speed'. That high rate of change makes it impossible for evolution to keep up - so the polar bears don't have time to evolve to do without icebergs. Also, it means that any natural feedback (such as algea in the ocean evolving to consume more CO2 in warmer waters) cannot kick in. It's precisely because it's happening so fast that it's such a major problem. If we had 10,000 years to plan for this change, we could gradually move cities inland, breed crops that would thrive in higher temperatures and so on...but at the present rate of change, there simply isn't enough time. If we kick the climate into 'runaway' mode - then the rate of change (and the AMOUNT of change) will kick up into a higher gear and we'll truly be in deep doo-doo. SteveBaker (talk) 13:01, 8 April 2009 (UTC)

If current theories are correct, sudden climate change has happened many times in the past, leading to mass-extinction events. Though I think you are referring to a sudden (few hundreds to a few thousands of years) warming as opposed to a sudden cooling.

Right now it is a purely hypothetical phenomenon, though purely hypothetical doesn't mean wrong; it just means it's never happened before while us humans were around to see it and our computer modeling skill is insufficient to say how much CO₂ will lead to how much warming over how long a time with precision. Sudden runaway warming may have never happened before on this planet. Some people theorize that Venus was the victim of runaway global warming which occurred when its hypothetical oceans started boiling off (although I'm not sure how widespread that theory is accepted).

Steve already went over most of the mechanisms which can re-enforce the warming, but there are many important factors that could check or even reverse a speedy warming (forgetting all that The Day After Tomorrow BS). And most importantly (IMHO), there is the whole problem with clouds: no one is really sure whether clouds will increase, decrease, shift geologically or temporally, or stay the same with a warming planet. And daytime clouds cool the earth, while nighttime clouds warm the earth. What I'm trying to say in a very roundabout way is this: It could happen, and it may have happened in the past, but we just don't know. -RunningOnBrains 00:11, 8 April 2009 (UTC)

I'm referring to any climate change, even if temperature remains constant. You'd think there'd be some way to tell. It doesn't effect how glaciers freeze or anything like that? Anyway, is the idea that it would cause an extinction event a myth? If it would, it couldn't have happened very often. Is there at least a known lower limit on how recent the last runaway climate change was? — DanielLC 01:45, 8 April 2009 (UTC)

At high rates of change, (like over hundreds of years rather than millions), evolution can't keep up. Animals and plants will die rather than adapt. Hence a mass extinction event. Just as the giant meteor that killed the dinosaurs caused mass extinction - so will abrupt climate change. However, in a gradual change (gradual - over geological timescales, that is) - plants and animals will evolve to take advantage of the new conditions and although the warmer world would be a very different place, there would be no sudden kill-off of species. In either case, however, the 'new' world might not be a place where humans could thrive...and that's the ultimate concern here. SteveBaker (talk) 13:01, 8 April 2009 (UTC)

It should be said that while some plants and animals will die out in a changed climate, others will prosper, simply because the climate they like becomes more common. Tropical plants are already expanding their ranges into traditionally temperate zones, for example. People also don't need to evolve to adapt, we can either move or alter our environment with things like air conditioning. Of course, global warming will still cause enormous problems, and maybe kill off a substantial portion of the human race (many of those living in Bangladesh, due to flooding, for example), but extinction of the human race isn't the threat here.

Note that while "runaway global warming" may or may not occur, "global warming" (without the "runaway" part), is definitely already happening. The difference is that regular global warming would be reversible if we stopped adding greenhouse gases to the air. Unfortunately, I don't see that as ever happening, or at least not until we use up all the fossil fuels. StuRat (talk) 14:41, 8 April 2009 (UTC)

By "impossible to stop", do you mean it's impossible for human influences to stop, or impossible for any natural forcings to stop? With climatic change there are always negative feedbacks (factors that lessen the effects), so those could act to stop the warming over time. Truly runaway global warming would result in a climate like Venus, but events that have come rather close have triggered mass extinctions in the past to varying degrees. ~AH1^(TCU) 01:55, 10 April 2009 (UTC)

It's worth saying that merely stopping adding CO2 to the atmosphere will only halt the increase - it won't cause a reversal. The half-life of CO2 in the atmosphere is of the order of 10,000 years. It's also worth stressing that we're not even CLOSE to talking about adding zero CO2 to the atmosphere - we're not even talking about reducing the amount we emit - the very best most countries are prepared to sign up to is not increasing the RATE at which we continue to add it. So reversing what we've already done is physically impossible - not making it worse is almost impossibly difficult - slowing down the rate of growth in order that we can buy ourselves time to find a proper fix is a distant dream - the best we can reasonably hope for is that the rate of increase won't get any steeper. SteveBaker (talk) 02:24, 10 April 2009 (UTC)

However, over the course of much less than 9 years, perhaps only days, we might be able to remove the excess CO₂ from the air by using plant life or some other method like windmills. StuRat (talk) 18:11, 10 April 2009 (UTC)

why is water transparent and ice white?

Mathityahu (talk) 17:53, 7 April 2009 (UTC)

From ice, "It can appear transparent or an opaque bluish-white color, depending on the presence of impurities such as air." Certainly from my experience, some ice is basically transparent, and some is quite opaque. Friday (talk) 17:58, 7 April 2009 (UTC)

Ice is pretty transparent when it doesn't have air cavity impurities in it. The reason why your ice cubes for instance don't look transparent all the time is that rather small air bubbles and other impurities get trapped in the structure of the ice which scatter the light making it appear opaque. I could be wrong, but I think that there are several neutrino telescopes which take advantage of Antartic ice being clear over long distances, like the IceCube and Radio Ice Cerenkov Experiment. Sifaka ^talk 18:13, 7 April 2009 (UTC)

In addition to air bubbles, there's also fractal planes which make ice look white. I believe that ice, if chopped up into tiny pieces, will look white even if this is done in a vacuum. StuRat (talk) 19:50, 7 April 2009 (UTC)

You might be interested in the Blue ice (glacial) article. --JGGardiner (talk) 22:10, 7 April 2009 (UTC)

Little cracks and air bubbles reflect light in random directions. White pigment reflects light in random directions. They look the same. — DanielLC 01:39, 8 April 2009 (UTC)