Wikipedia:Reference desk/Archives/Science/2008 April 11

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April 11

Why are pollen count ratings so low?

Every spring across the southeast, we get pollen counts in the thousands easy: Atlanta Pollen Counts. You can't even tell that it's pollen season when there's less than a 200 pollen count. So why is 120 considered extremely high? Is that really the norm for most of the country? It seems like any place with flowering trees would easily break a hundred. What's the reasoning behind the system? 160.10.98.34 (talk) 00:00, 11 April 2008 (UTC)

People who are allergic to pollen can likely detect it at a much smaller count than others. StuRat (talk) 14:09, 11 April 2008 (UTC)

Chainmail vs Tasers

If someone wearing chainmail was tasered, what would happen? Would the current flow via the chainmail between the two electrodes, or would you just earth it? -mattbuck (Talk) 00:26, 11 April 2008 (UTC)

The current would take the easiest route, through the chainmail, and not much would pepetrate the person. Chainmail is heavy to wear however! Go for glomesh. But you may get sprayed with capsicum spray of you misbehave! Graeme Bartlett (talk) 07:13, 11 April 2008 (UTC)

I'm not sure this would actually help - due to skin effect, the power / signal will likely remain on the surface of the chain mail, just as it would likely remain on the surface of the human skin without chain mail. Even a surface current can cause incapacitating pain. Also, many taser systems actually penetrate the skin with a dart, so if the dart electrode were to make it through the holes in the chain mail, it would not pass any electricity through the armor at all. Nimur (talk) 16:00, 11 April 2008 (UTC)

If the bare metal part of the dart touched the chain mail while extending into the flesh, the chain mail should present a far lower electrical resistance than the flesh, resulting in a far smaller current through the victim than without the chainmail. The resistance of steel mesh should be a fraction of an ohm and the internal resisitance of the victim should be hundreds of ohms. Edison (talk) 22:48, 11 April 2008 (UTC)

Newton and the darkness of the night sky

I was reading a book last summer about the general history of cosmology, and it mentioned a situation where Newton had theorised that the heavens were held together by gravity, and some priest or bishop replied to the effect that if that was true there would be constant light at night when we look at the sky. I think I've got the details wrong, as I don't remember much of the book, but why is it that the sky is black rather than white? I know someone answered this question a century or two ago but I can't remember for the life of me. Thanks a lot. 81.96.161.104 (talk) 01:44, 11 April 2008 (UTC)

Olbers' paradox may answer part of the question. --Arcadian (talk) 02:20, 11 April 2008 (UTC)

Remember that light always travels in (not necessarily straight) lines, and for you to see light, the terminus of that line has to end in your eye. So the universe is indeed chock-full of radiation from stars. However, you can't see all this radiation unless all the rays suddenly turned a corner and decided to head directly for your eye. — Sam 16:50, 11 April 2008 (UTC)

Hi. Well, remember that stars' light travel in all directions, they're not like a flashlight where the light goes only in one direction. It's kind of like the infinite forest paradox: in an infinite forest, it would be impossible to see past it, in a finite forest, you can still see gaps. The entire observable universe is only about 15 billion light-years in radius, and we can't see past that. Also, nearly all the naked-eye stars not within the glow of the milky way are within about 10,000 light-years. Space is locally not totally uniform here. The milky way, as well as nebulae, the magellanic clouds, globular clusters, open clusters, supernova remnants, etc, all contain stars and are in our own galaxy, but most are either not naked-eye or only visible from a dark location. There are also the galaxies outside of our own, but only a few are naked-eye. The rest of the googols of stars are not visible at all because they're so far away, and their galaxies are not naked-eye. Some of the background stars may contribute to the skyglow observable even in the darkest-sky places in the world, along with the atmopshere, solar system debris, etc. Hope this helps. Thanks. ~AH1^(TCU) 23:25, 11 April 2008 (UTC)

Water on Mars

I've read that liquid water likely once existed in great quantities on the surface of Mars, but it always says "in the past" without specifying how long ago it was. My question is, when did all the water that supposedly made shorelines and carved canyons go away? -RunningOnBrains 03:04, 11 April 2008 (UTC)

It is thought that some geologic features remain, but the data haven't born that out yet. See Mars#Hydrology. Imagine Reason (talk) 03:14, 11 April 2008 (UTC)

The research reported in this BBC News story concludes that there haven't been large areas of free-standing water for four billion years. Since then, there may have been local short-lived "floods" as a result of the release of underground water by volcanic activity or meteorite strikes. There is some evidence from phtogoraphic surveys that small-scale local release of liquid water is an occasional ongoing process, but this is not confirmed. Gandalf61 (talk) 09:08, 11 April 2008 (UTC)

Hi. Well, if I remember correctly, NASA discovered water on Mars in the form of rivers, I think in 2004 or 2005 or sometime around there, oh and if you look at Google Mars, you will see features that are most likely created by rivers. I think this might be an image of water on Mars, and no, not the prank image of a glass of water on a Mars bar, although I don't think this image has been used in an article. Hope this helps. Thanks. ~AH1^(TCU) 23:30, 11 April 2008 (UTC)

Water on Mars?

I'm pretty sure that those findings, which in any case were not conclusive, have been reversed. I can be wrong, of course. Imagine Reason (talk) 02:21, 12 April 2008 (UTC)

Electric Vehicles, Cost

Disregaurding the battery X factor of electric vehicles, what would an electric vehicle comparable to say a 20,000 US dollar car cost if it could be mass manufactured? Are there any big differences in mass production that should make a mass produced electric vehicle more expensive than a mass produced regular one? Some people say that the electric motor is simpler than a combustion engine and thus would be cheaper. On the other hand, I can't find any real data to argue either way. When I say electric vehicle, I am refering to an all electric vehicle - not a hybrid. 129.2.152.144 (talk) 03:04, 11 April 2008 (UTC)Sam

Disregarding the cost of the batteries, I'd expect the electric car to be cheaper. But you can't, of course, ignore the battteries, since they are a major component of any electric car. Once you include them, the electric car becomes more expensive. Now mass production is a tricky issue, in that presumably there will be improvements in technology which will bring down the cost of electric vehicles if mass produced, but we can't predict how much that will bring the cost down. StuRat (talk) 16:54, 11 April 2008 (UTC)

Yes, an electric motor is usually cheaper than an equivalent ICE because a) it has a higher power to weight and power to size ratio and thus requires a smaller amount of raw material to build b) it is mechanically less complex - an electric motor typically has only one moving part, while an ICE may have hundreds of moving parts c) it is easier to assemble and d) it needs no active cooling, exhaust system, and catalytic converter. Pontentially, electric cars can also do away with the transmission, clutch, axle and differential, since electric motors are small enough to be placed inside each wheel. This simplicity could pontentially make electric cars much cheaper to manufacture than ICE cars.

Batteries will probably be the most expensive component of electric cars for the near future. The problem is that current batteries are not only expensive, but need to be replaced every 3-6 years. Battery depreciation is the biggest cost of owning an electric car; it is higher than the cost of purchasing the car itself. Will batteries become an order of magnitude cheaper as they are mass produced? Probably, if you take Li-ion batteries for mobile phones and laptops as a precedent. However, scalability is still an unknown issue. If the whole world decides to buy electric cars, the price of commodities needed for batteries (lithium) and electric motors (copper) may skyrocket, and that will put a lower bound on the price of an electric car. Cambrasa 19:22, 11 April 2008 (UTC)

How does a circuit "know" when it is closed?

Say there's a simple circuit which has a battery and a switch. When the switch is open, there's no current. When it's closed, current runs through the circuit provided by the battery. So how does the circuit "know" to have the current run once the switch is closed?199.76.153.227 (talk) 03:35, 11 April 2008 (UTC)

I'm sure there is an article (if not more than one) on electronic current. The old-school explanation, which I'm sure it out of style now, is to look at the negative side of the open circuit as a bunch of electrons. The positive side of the open circuit is a bunch of holes (waiting for electrons to fill them). When you close the circuit, an electron is suddenly next to a hole. So, it hops over on that hole. It finds another hole, so it hops over to that one - on and on. As it moves, it leaves a hole behind it. The next electron sees that hole and hops over. You can then view it as either electrons flowing from negative to positive or holes flowing from positive to negative. -- kainaw™ 03:39, 11 April 2008 (UTC)

When the circuit closes, the negative and positive side have different voltages. Just like when a U-shaped pipe fill with water but the water level on one side is higher than the other. So, the energy started to go from one side to another. Where the media is electrons. Visit me at Ftbhrygvn (Talk|Contribs|Log|Userboxes) 05:17, 11 April 2008 (UTC)

When you close the switch, an electromagnetic wave travels at the speed of light in both directions from the switch back to the battery. As the wave sweeps over the surface of the conductor current starts to flow. Graeme Bartlett (talk) 07:06, 11 April 2008 (UTC)

Really? Can you provide a source for that? AlmostReadytoFly (talk) 08:08, 11 April 2008 (UTC)

Charge carriers in a conductor are not stationary in the absence of an electric field but move around, essentially at random. The battery generates an electric field which superimposes a drift velocity on the electrons in the direction of the field. Before the switch is closed, charges will therefore build up at its terminals. This charge will itself be generating a field in the conductor which opposes the battery field. Charge will continue to build up until the two fields are equal and opposite at which point no more net current is flowing. At this point virtually all the field is between the switch contacts as the field along the conductor is cancelled. This effect amounts to capacitance. At the moment the switch is closed, the charges built up at the contacts will start drifting across the switch.

Since the transient originated at the switch it is obviously going to propagate from there. Not at the speed of light however, in most cables the speed is around 2/3 C (function of insulator material mostly). Sorry, I could not readily find you a source other than my (obviously uncitable) undergraduate notes.

It might also be of interest that there is a similar charge build up at bends in the conductor which generate a field which drives the charges "around the corner". SpinningSpark 08:54, 11 April 2008 (UTC)

I will have a look to see if some one has this on the web. I will give a bit more of a physical point of view. Before the switch is closed there is the voltage of the battery across the contact. When the switch closes the current flows. Initially information does not travel faster then the speed of light, so right at the start the battery has no current flowing, but there is current flowing through the switch. The wire can be modeled as a string of inductors, alternated to capacitors between the leads going to the switch, a transmission line. If the wire is in vacuum, the wave of EM field on the surface travells at the spped of light, but if it is insulated the situation is more complex and slower! Graeme Bartlett (talk) 09:01, 11 April 2008 (UTC)

There is a wikipedia article on the maths involved: Telegrapher's equations developed by Oliver Heaviside. People using telegraphs used switches to turn on and off a long line with current running in it and the extreme lengths meant that this had to be understood. Graeme Bartlett (talk) 09:13, 11 April 2008 (UTC)

For corroboration, there's a page on All About Circuits that explains the wavefront model for the closure of a switch. It's a standard part of transmission line theory. --Heron (talk) 20:41, 11 April 2008 (UTC)

Bone Cartilage

We all know that nothing can really change bone from the hard shell that it is, even with many years discoveries of cavemen's bones have remained hard and sometimes in tact. But is there anything that can change a bone form, make it soft or flexible? Change the properties of a bone? —Preceding unsigned comment added by 67.127.172.138 (talk) 04:07, 11 April 2008 (UTC)

You might want to read our article on osteomalacia, which essentially is soft bones. Wisdom89 _{(T / ^C)} 04:13, 11 April 2008 (UTC)

Bones are made of large amounts of collagen. Reasonably fresh cadaver bones can be decalcified by placing them in a solution containing a cation chelator, such as EDTA. I've seen a tibia treated this way tied in a knot. It was used during Anatomy lectures to demonstrate that bone is not just mineral. -- Flyguy649 ^talk 04:15, 11 April 2008 (UTC)

I would like to correct one mistaken assumption in the question. Most bones do decay over time, although more slowly than the rest of the body (it may take centuries versus months for the rest). We rarely find old bones in water, for example. However, in the right conditions, bones can last for thousands of years. Those "bones" that are millions of years old, however, are usually not actual bone, but minerals which have replaced the original bone to form a fossil. StuRat (talk) 13:57, 11 April 2008 (UTC)

A fun experiment you can do for yourself is to drop the bone from your next chicken drumstick into a cup of vinegar and let it sit overnight. The next day you'll be able to tie it in a knot. When it dries out, it will get hard again, and you can amuse your friends with the tale of the deformed chicken leg you ate. Not as impressive as doing it with a human femur as Flyguy mentions, but not all of us are lucky enough to be able to play with human remains. :) --Sean 14:37, 11 April 2008 (UTC)

Boneitis might have some interesting efects on your bones. 81.96.161.104 (talk) 20:18, 11 April 2008 (UTC)

Would the bones if you softened like the chicken or drumstick in vinegar, would it ever become harden again? —Preceding unsigned comment added by 69.231.29.227 (talk) 01:06, 12 April 2008 (UTC)

Yes. I think rinsing the vinegar off and waiting is all you need to do. StuRat (talk) 03:19, 12 April 2008 (UTC)

No I don't think it would, I remember reading somewhere that if you soak a bone in water for a very long time the calcium gets dissolved and the bone goes all springy and soft. And if you burn a bone it goes all brittle and is very easy to snap.--Phoenix-wiki 12:20, 13 April 2008 (UTC)

Determining the Acidity of a molecule

I've read some conflicting advice on how to determine the acidity of a molecule. One thing I read stated that the acidity of an acid is directly proportional to the electronegativity. Another source I read though, however said that HF is weaker than HCl because the electronegativity of HF is so high that it does not want to disassociate in water. Which one is correct? Thanks. —Preceding unsigned comment added by Legolas52 (talk • contribs) 05:31, 11 April 2008 (UTC)

It how easy the molecule gives up H⁺, particularly when in water. It is not directly connected with the electronegativity of the element involved. Helium hydride is a very very strong acid. Graeme Bartlett (talk) 07:16, 11 April 2008 (UTC)

Male/female blood?

According to this Discover magazine article, a male cancer patient received a bone marrow transplant and now has "100 percent female" blood. What is the difference? Clarityfiend (talk) 05:56, 11 April 2008 (UTC)

Likely that all the white blood cells (and red blood cell precursors) have XX (from the donor) instead of XY (from self) -- Flyguy649 ^talk 06:06, 11 April 2008 (UTC)

Yes, and the difference would be apparent to anyone who examines the man's peripheral blood smear (as would be done in a complete blood count or white blood cell differential count), because the inactivated Barr body in female cells could be seen in the white blood cells as a drumstick-like projection from one of the lobes of (about 3% of) the neutrophils. There would be no difference in the peripherally circulating red blood cells because, in humans, they have no nuclei. - Nunh-huh 06:16, 11 April 2008 (UTC)

Oh, and functionally, I can't see how there would be any difference between male and female blood. -- Flyguy649 ^talk 06:27, 11 April 2008 (UTC)

Probably none, although there are more or less significant range disparities between males and females on CBC counts. Wisdom89 _{(T / ^C)} 06:33, 11 April 2008 (UTC)

So if he comitted a crime, the Crime scene investigators would be fooled into looking for a female suspect if they found traces of his blood left at the crime scene? Edison (talk) 14:23, 11 April 2008 (UTC)

Yep. For a related situation, see chimera (genetics) and the case of Lydia Fairchild. TenOfAllTrades(talk) 16:00, 11 April 2008 (UTC)

Red blood cells have no cell nuclei and thus have no DNA. Therefore, there is no "XX" or "XY" chromosome to distinguish a red blood cell as male or female. As Nunh-huh mentioned, some other blood cells may be identifiable. Nimur (talk) 16:10, 11 April 2008 (UTC)

Well, yes—others have already noted that above. The blood is '100% female' inasmuch as all of the cells that do carry distinguishing genetic material will be XX and not XY. It takes a vanishingly small amount of blood to get a nucleated (white) blood cell, too. Even though erythrocytes (red blood cells, with no nuclei) outnumber leukocytes (white cells, with nuclei and genomic DNA) by about a thousand to one, there are still five or ten thousand such nucleated cells in every microliter of blood. TenOfAllTrades(talk) 17:13, 11 April 2008 (UTC)

Faraday cages

Does anyone know how close together the wires in a wire mesh would have to be before it would act as a Fahrady Cage? I just wonder because I noticed I don't get mobile phone reception while stood inside a cricket batting cage, even though the wire is inches apart. Also if the wire was insulated bit still quite dense would it still act as a cage? If I wrapped my mobile phone in tinfoil would I still get a singnal or would the metal have to be a certain thickness?

Just as an aside why don't the type of people who wear tinfoil hats use chainmail helmets instead :D? TheGreatZorko (talk) 09:17, 11 April 2008 (UTC)

The rough rule of thumb is that the wire have to be closer than one tenth of the wavelength, so the 20cm wavelength 1500MHz mobile phone, will need about 2cm spacing, and the phone cannot be too close to the mesh either otherwise it will get ephemeral waves bleeding through. Thin metal will work musch the same as thick metal, so foil should block a mobile phone. You have to look at the skin depth. Very low frequencies can penetrated deeply into the conductor. So earths magnetic field will make its way through. (A super conductor will have 0 skin depth). Also you have to completely enclose the item, so a hat will not work, has to be completely encased! Graeme Bartlett (talk) 09:36, 11 April 2008 (UTC)

Also, the rings in the chain mail may not be making sufficiently-good electrical contact with each other to ensure forming a good Faraday cage. The odd and variable points of contact, corrosion of the metal, and the buildup of grease and other insulators will all combine to allow some of the signal from Faux News to slip into your brain.

Atlant (talk) 12:28, 11 April 2008 (UTC)

If what you say is true, then the rings in chain mail would seem to operate by the electrical perversity principle: if two pieces of metal touch and you want them to conduct electricity, they are less likely to than if you do not want them to conduct electricity. Two wires with frayed insulation touch, however lightly, and a short circuit blows a fuse or starts a fire. Two pieces of metal touch and you want them to provide shielding in this case, or to conduct electricity in other cases, like a poorly adjusted relay, a worn switch, a vacuum tube in a loose socket, or a multi pin connector, and they act like an open circuit. Edison (talk) 14:20, 11 April 2008 (UTC)

Precisely!

Atlant (talk) 17:53, 11 April 2008 (UTC)

Also, a chain mail hat is more expensive and less readily available at home than tinfoil. – b_jonas 10:29, 14 April 2008 (UTC)

what is charge?

We've all heard of the positive and negative charges, but at the most basic,smallest level, what is it? Why does an electron repel another electron, while it attracts a proton?? why is it negative or positive? what is it exactly? What constitutes charge at the smallest level? (In protons, I've heard of quarks with partial charges, but why is it charged at all???) 116.68.70.147 (talk) 10:33, 11 April 2008 (UTC)A 15-Year Old

Good question. The short definition is that electric charge is a fundamental conserved property of some subatomic particles, which determines their interaction with electromagnetic fields - see electric charge. But of course we then define an electromagnetic field as a field produced by and affecting objects with electric charge. So that's a circular definition. I think the longer answer is that we don't know exactly what electric charge is, but it has proved to be a useful concept in physics, both because of its fundamental nature (it is not an emergent property like, say, pressure or temperature) and because it is conserved. The positive/negative nature of the electric charge is not inherent to the concept of charge - the color charge, which determines how sub-atomic particles interact with the strong force, comes in three flavours, rather than two. Gandalf61 (talk) 12:01, 11 April 2008 (UTC)

But the word "charge" in colour charge is misleading. The article uses an analogy, but quark colour has no connection with electrical charge. The positive/negative nature of the electric charge is inherent to the concept of charge in normal scientific usage. 78.32.74.48 (talk) 16:44, 12 April 2008 (UTC)

The role of electric charge in quantum electrodynamics is very similar to the role of colour charge in quantum chromodynamics. Together with weak isospin, they make up the three charges in the Standard Model of particle physics. Our article on charge makes this clear. When particle physicists refer to "charge" they may mean any one of several conserved quantum numbers that are associated with particle and field symmetries. Gandalf61 (talk) 17:34, 12 April 2008 (UTC)

Erasing Bad Relationship

Just like in the movie Eternal Sunshine of the Spotless Mind, is it possible in the future to remove a bad memory from your brain? I am experiencing a horrible heartbreak and I would like to know if anything remotely exists right now --Jonasmanohar (talk) 14:08, 11 April 2008 (UTC):

Answer:

--Sean 14:46, 11 April 2008 (UTC)

how about other than that? --Jonasmanohar (talk) 14:52, 11 April 2008 (UTC)

Right now, there's nothing like Eternal Sunshine in real life, although really heavy drinking to induce brain damage might work. The problem is you'd have nocontrol over what you forget, and it's as likely to be the alphabet as it is your realtionship. I don't recommend it. 81.96.161.104 (talk) 15:23, 11 April 2008 (UTC)

Also, this is seriously bordering on asking for medical advice, which Wikipedia can not give. If you are having a hard time over this, see a doctor or possibly a therapist. -- MacAddct  1984 ^{(talk • contribs)} 15:49, 11 April 2008 (UTC)

Removing only one memory is probably impossible because one memory builds on several other memories. If you remove it, you will mess with the other memories too. What is certainly possible is removing a whole class of memories by performing the appropriate brain lesion, and then starting afresh. This is called Retrograde amnesia. You will have no memory of you lover but probably also a whole lot of other stuff - like your friends and family too. It has probably been done on animals, but the procedure is so debilitating that no doctor will perform it. The best you can do is hope for a stroke. Probably better just to let the memory fade with time. Cambrasa 19:53, 11 April 2008 (UTC)

Dear Jonas, I fear the damage is done. By writing and discussing your wish to rid yourself of a bad memory you surely will, by dint of the mystery known as the human mind, remember it forever. I am so sorry. Richard Avery (talk) 21:45, 11 April 2008 (UTC)

There are experimental techniques being tested for selectively modifying memory. However this research in mainly intended to help solders or rape victims. People who are in great danger of developing posttraumatic stress disorder. It is unlikely that such technology will ever be available for casual civilian use. Painful as such breakups may be, they are a necessary part of life. Erasing the memory of the relationship would in the long run probably harm you. (Read Brave New World for an interesting take on this.) --S.dedalus (talk) 22:49, 11 April 2008 (UTC)

You know, there's a better avenue than seeking to erase your memories: truth and reconcilation. Reflection and introspection will, over time, shed new light on past experiences that you may want to label 'bad', and you will eventually understand them as opportunities for growth and improved wisdom. Vranak (talk) 00:03, 12 April 2008 (UTC)

Believe it or not, that time heals is attested to throughout human experience. Distraction is used in pain management and healthy ones not only help you endure the time but give you fewer regrets/health issues when you pass through it. Julia Rossi (talk) 01:32, 12 April 2008 (UTC)

Re Richard A's comment about reinforcement, true enough, but remembering forever is not quite the same as feeling the same forever since discussion and interaction can change the feeling or the intensity and I take it your question is mostly about linking pain and memory. See our articles on Perspective (cognitive) and Perspective (psychological). Julia Rossi (talk) 01:42, 12 April 2008 (UTC)

Light Reflection

I was sitting in front of my patio door last night while it was raining. The patio was very wet and the a light on my neighbor's porch was lit. There is also a privacy fence between our patios, but it doesn't span the entire patio. As I sat there I could see the light reflecting off my patio. When I moved a few inches to the right, the reflection was gone. I could no longer see the light either because it was being hidden by the fence. I understand line of sight and that light doesn't normally bend around objects, hence I couldn't see the light anymore, however, the spot where the reflection was on the patio was definitely in my line of sight still. Neither the patio, fence, nor light moved, so the reflection must still be there, but I couldn't see it. I did read the article on reflections and I think there is something I'm not understanding about angles because my angle was still the same, at least vertically, so wouldn't I still be able to see it? Is there a horizontal angle? Why was I unable to see the reflection still even when it's in my line of sight? —Preceding unsigned comment added by Beckerj99 (talk • contribs) 14:11, 11 April 2008 (UTC)

I'm not sure I'm picturing this properly so could be on the wrong track (a diagram would really help!), but here goes. Because the patio is very wet it essentially provides a smooth surface resulting in regular reflection like with a mirror - when the light reflects from the patio it stays in the same plane, essentially meaning it follows that straight line direction. When you move sideways blocking the light you're obscuring that plane at the reflected surface as well (think about a huge sheet of glass between yourself and light; as you moved to the side, moving the glass with you, would that sheet of glass have intersected the fence?). Looking to the spot where you could previously see the reflection is no good, because you're no longer in that plane, and the spot where you would now see the reflection is blocked by the fence. Now is the reflection still there, in that spot? Sure, it's just that since you're no longer in the same plane as it you don't see it - if you stand in front of a mirror you see your reflection because you're in the same plane, but move to the side and you can't see yourself; nonetheless your reflection is still there as someone who's at the other side can see it from there, and you can see them. It's basically this principle. Hope this helps. --jjron (talk) 16:41, 11 April 2008 (UTC)

What might help is trying to think of--instead of all the paths the light can travel--both the light and the blocking wall as having mirrored duplicates on the other side of the plane of the patio (assumed to be a horizontal reflective surface). Effectively, this means an imaginary wall extending from the level of the patio down a length equal to the real wall's height above the patio and a light similarly below the position of the real light. Looking through the puddle at these imaginary objects, would the imaginary wall block your line of sight to the imaginary light? ASCII art:

your eyes -> oo                         O <- real light
                                 |
                                 | <- real wall
patio -> ________________________|__________
                                 |
                                 | <- imaginary wall
                                 |
                                        O <- imaginary light

If the patio were reflective enough and the environment well enough lit that you could clearly see the reflected outline of the wall, it would probably be less confusing a situation. --Prestidigitator (talk) 20:35, 11 April 2008 (UTC)

Radar Site By The M27 In Hampshire England??

Just to the north of the M27 motorway between Southampton and Portsmouth I have seen a Radar tower that is clearly visible from the road. The tower looks just like the new Samson Radar for the Type 45 destroyers http://en.wikipedia.org/wiki/Image:HMSDaring.jpg

I have looked on the maps, google earth and searched the Internet but can find no mention of the site and what it is. Is does look very much like the mask and radar from the new destroyer?

Its very much a local question so feel free to move. —Preceding unsigned comment added by 86.4.182.208 (talk) 15:39, 11 April 2008 (UTC)

Could it be a cell(mobile)phone tower? -- MacAddct  1984 ^{(talk • contribs)} 15:58, 11 April 2008 (UTC)

No chance. Its just like the tower with the dome on top as the type 45 destroyer. Its nothing like any other radar or communication site I have seen before.

You have a good eye. You should be a spy. It is just what you thought, the SAMPSON radar for the Type 45 destroyer. A test facility belonging to BAE, maker of the radar, sits atop Portsdown Hill just north of Portsmouth Harbour. There is a paper about the ship here that mentions the facility. --Milkbreath (talk) 17:41, 11 April 2008 (UTC)

Micro wave cooking

I had a discussion with a co worker recently who claimed that cooking with a micro wave changes the DNA of what it cooks and is very bad for your health. He also told me that he had his sons perform an experiment where they boiled distilled water on a stove and another sample in a micro wave and used each to water 2 plants. After3 weeks the plant watered with the micro waved water died. Why would this happen?129.112.109.253 (talk) 16:34, 11 April 2008 (UTC)

Some, or possibly many, people have basically unfounded paranoia about microwaves - I know some people that won't use them as well, and it sounds like your co-worker is at the extreme end. There's plenty of fringe literature to bolster these fears, but basically there's no reputable studies that show any significant risk AFAIK; refer to Microwave#Health_effects for starters. Re the plant 'experiment', well it sounds like he's seeing the results he wants to see; I'd be asking for some better evidence than his anecdotal test. --jjron (talk) 16:54, 11 April 2008 (UTC)

Sounds like a reasonable experiment to try, except as stated it might have been subject to Experimenter's bias in that the experimenter might have known which plant was getting the microwaved water and had an expectancy that the other would do better. Overwatering, drying out from too much sun, using water that is still too warm from the boiling or other variations in the treatment of the plants could cause one to die. The brief description of the experiment also says "a plant." A rigorous experiment would use multiple plants to allow for the fact that there is inherent variation in how well a plant grows. A Blind experiment would have coded labels on the water and the plants so that the person watering the plants would not know which plant received which water supply. A better experiment would have several plants which were randomly assigned to groups, to avoid the experimenter selecting the healthier plants for the favored group. The measures for which plant is healther should be established in advance and objectively measured, to avoid after the fact selection of height, weight, or color as the measure because the favored plants were best at that measure. The final determinant is replicability in other labs which do not share the biases or expectations of the original experimenter. Edison (talk) 17:05, 11 April 2008 (UTC)

This article on the effects of microwave ovens is probably more appropriate. -- MacAddct  1984 ^{(talk • contribs)} 17:13, 11 April 2008 (UTC)

(ec)As to the DNA, that's complete and utter nonsense. Microwaves are non-ionizing radiation they can't change DNA, and even if it did, whatever you're cooking is dead, its cells aren't dividing, it isn't producing new proteins, it's completly inert. That argument makes me immediately discount any other findings he states since he sounds like he is just throwing out words to sound scientific. 192.45.72.26 (talk) 17:19, 11 April 2008 (UTC)

This article is the number 3 google hit for "microwaves", so your fearful friend is in good (or at least plentiful) company. In it I learned the following:

1. "use of artificial microwave transmissions for subliminal psychological control, a.k.a. "brainwashing", has also been proven"
2. you should not microwave your blood
3. microwave ovens cause "a breakdown of the human "life-energy field"", and lead to "magnetic deposits" in the lymphatic system
4. microwave ovens' use of alternating current is what makes them dangerous, while the sun's microwaves are safe because they operate on direct current

--Sean 17:37, 11 April 2008 (UTC)

Wow, that last one made me snort out loud at my desk. Luckily everybody else seems to have gone home early! --LarryMac | Talk 18:20, 11 April 2008 (UTC)

You can also buy an economy size order of bioTHIN, algae pigment guaranteed to make you loose weight, happy days! -- MacAddct  1984 ^{(talk • contribs)} 17:46, 11 April 2008 (UTC)

If you run the experiment until one of them dies, then even if the experiment is conducted perfectly, there's an expected 50% chance that'll be the one you're interested in. To prove that microwaved water is dangerous (to plants) you'd need to show that the microwaved water plants died more often than could be attributed to random chance. An the double-blind requirement mentioned above would be important too.APL (talk) 17:59, 11 April 2008 (UTC)

Also, using more than 2 plants would be beneficial too. To be statistically significant, you would probably need a sample size of at least 30. -- MacAddct  1984 ^{(talk • contribs)} 18:09, 11 April 2008 (UTC)

Over time, microwave ovens may also affect your Purity of Essence/Our Precious Essence. Seriously, your friend's concerns are, ahem, overstated.

Atlant (talk) 18:00, 11 April 2008 (UTC)

Are we talking about that big clock that sometimes cooks things? 200.127.59.151 (talk) 19:50, 11 April 2008 (UTC)

The DNA argument is nonsense. Any DNA you ingest will be broken down in your stomach, so whether it is broken down beforehand or not, it makes no difference. Also, the food in the oven is no longer alive, and the DNA is no longer being used to make proteins, mutated or not Cambrasa 19:59, 11 April 2008 (UTC)

I find tea made with water boiled in a kettle to have a more agreeable taste than with water boiled in the microwave. It's a more natural experiment than buying two plants and feeding them water over two weeks. Nevermind scientific literature – try it yourself for first-hand knowledge. Vranak (talk) 00:01, 12 April 2008 (UTC)

Or maybe it's just placebo effect. --antilived^{T | C | G} 00:42, 12 April 2008 (UTC)

Or maybe it's not. Vranak (talk) 01:33, 12 April 2008 (UTC)

When doing taste experiments I strongly recommend blinding. Experience shows that many people will be convinced that something tastes better just by e. g. some clever advertisement and a higher price. You'll also find some examples of this if you search with Google Scholar. Icek (talk) 01:52, 12 April 2008 (UTC)

I am aware of the double-blind with-placebo experiment and its uses. That said, I know a funny taste when I taste it. Vranak (talk) 05:08, 12 April 2008 (UTC)

One possible explanation that occurs to me is that water boiled in a microwave could have fewer impurities than water boiled in a kettle, and so could taste different. What does the inside of your kettle look like ? Gandalf61 (talk) 08:44, 12 April 2008 (UTC)

I have noticed the effect that Vranak mentions. I put it down to smells adsorbed on the steel lining of the oven, or perhaps lurking in the numerous crevices in the interior. If I put my head right inside the oven (who doesn't?) I can detect this smell, which never goes away regardless of how carefully I clean the thing. It smells like all 57 varieties of soup mixed together. After all, it's pretty unnatural to cook food in a tiny steel box that never gets a proper clean - it never gets immersed in hot soapy water like a pressure cooker or saucepan, or roasted at 200 °C like a conventional oven. I certainly wouldn't blame the taste on some undocumented property of the Deadly Radiation. What's your hypothesis, Vranak? --Heron (talk) 09:30, 12 April 2008 (UTC)

It's been about four years since I've had tea made with microwaved water, so it's hard to recall. I think the water just feels 'buzzy', it's not so much a matter of flavor. Vranak (talk) 23:49, 12 April 2008 (UTC)

I'd go along with the "absorbing smells from the microwave oven's interior" hypothesis. I suppose a "microwave kettle" could be made, perhaps out of glass, that would be sealed until the water boils, then would whistle as it let's the steam out. A glass bottle with a small opening would be a good compromise until such a device becomes available. Always avoid microwaving water in plastic, as it may absorb chemicals that leach from the plastic when heated. StuRat (talk) 15:17, 12 April 2008 (UTC)

Then again, so does everyone who experiences the placebo effect, do they not? That said, I'm not denying the possibility of your experience, simply suggesting without a double blind, we will never know whether it's a true difference or a placebo... Bear in mind any good experiment will also need to take into account all possible factors. Water same temperature, brewed for the same time, using similar tea bags, your are in same condition etc (ideally the person doing the brewing should be single blind). For example, if you only make tea from microwaved water when you are in a hurry then there are obviously many possibilities as to why the tea thats different. Nil Einne (talk) 17:38, 12 April 2008 (UTC)

You seem to be suffering from the scientist's classical delusion that anything can be finally regarded as 'true' or 'proven'. Such thinking is vanity. "There are no moral facts, just as there are no eternal truths." -- Nietzsche. Vranak (talk) 23:52, 12 April 2008 (UTC)

Is someone forgetting mathematics? But about the microwaving of tea, I've never noticed an odd taste when I reheat tea in the microwave but, like you Vranak, I do when I make it in the microwave. I think it's because the microwaves mess with the teabag, but that's just OR. Michael Clarke, Esq. (talk) 00:04, 13 April 2008 (UTC)

Hi. Keep in mind, however, that just because something hasn't been proven doesn't mean you shouldn't at least be a bit cautious. Thanks. ~AH1^(TCU) 01:23, 13 April 2008 (UTC)

Wait, you were microwaving the water with the teabag in?! No wonder it tasted weird. I'd also imagine, making the tea properly, there'd be a difference with microwaving the water vs boiling in the kettle because it's harder to get the water evenly boiling in the microwave. A decent cup of tea requires freshly boiled water poured onto the tea while still as close to 100°C as possible. 79.66.105.94 (talk) 01:27, 14 April 2008 (UTC)

Vranak, if you didn't do it double-blind then you couldn't possibly know if it really tasted different. People report that heavy water tastes totally totally different than regular water if they know it's heavy water. If they don't, they say it tastes like regular water. The mind is a subtle thing, and taste is even more subtle—color, smell, and expectations can change how things taste a LOT. I read recently of an experiment in which a researcher gave people beer with red wine vinegar; when they didn't know what the additive was, many of them claimed to enjoy it, when they knew what it was, they all said it tasted disgusting! Don't stick by your perceptions unless you have some reason outside of them to believe it. Microwaved water shouldn't have a different taste—if you don't expect it to, you probably won't find one. I used to think I could taste the difference between all the different colors of Froot Loops until I actually tried it with my eyes closed once and realized they were all identically ambiguously fruity! --Captain Ref Desk (talk) 05:15, 13 April 2008 (UTC)

As a person who still seems to have full faith in science, I shouldn't expect that we'll be able to come to an understanding. So, we'll have to agree to disagree for now. :) Vranak (talk) 15:54, 13 April 2008 (UTC)

You haven't the slightest ideas what my opinion on science in general is. What we're talking about here is just reasoning about what makes a logical conclusion and what's a good way of coming to it. If you want to throw out reason, please feel free, but if you're going to do that I hardly see what benefit your contributions are going to be. As for the question of whether microwaved water tastes different from non-microwaved water, it's easy to come up with reasonable, reliable, and reproducible results. Your method is obviously not the way to do this, and watching you sticking by it even in the face of its obvious methodological difficulties makes me wonder if you are ignorant or just stubborn. --Captain Ref Desk (talk) 00:00, 14 April 2008 (UTC)

Captain Ref Desk your above reply to Vranak is out of line. In particular saying “if you're going to do that I hardly see what benefit your contributions are going to be” is borderline personal attack. After all 86% of people in the world believe things without evidence. -- S.dedalus (talk) 21:48, 14 April 2008 (UTC)

In support of the good Captain, you've taken it slightly out of context there. He said "If you want to throw out reason", which is a valid complaint, really. Conclusions reached without the use of reason are significantly less valuable. And just because the majority of people do something, that doesn't mean it's the right thing to do. The Captain had a valid point about the reliabilty of conclusions drawn from experiments performed at home with no control measures, and to suggest that we should accept answers to queries posted here that are clearly not based on the principles of logic and reason simply because a lot of people hold beliefs that do not stand up to scientific scrutiny is ludicrous. Sorry if I'm a bit blunt but I really fail to see the problem with Cap Ref Desk's comments. Michael Clarke, Esq. (talk) 22:02, 14 April 2008 (UTC)

Vranak: Science doesn't work on "faith", nor does it aim to "prove" anything. All a scientific experiment does is corroborate a claim, or falsify it. That's a far cry from "proving" a claim. In this case, it's perfectly valid to demand an unbiased experiment to support or falisify a claim, in this case the claim is that tea made with microwaved water tastes different than tea made with water boiled in a kettle on a stove.

It's perfectly fine to have faith in one's own senses, but even professionals in the wine tasting business know that their sense of taste is easily altered by other influences such as color, knowledge of price, brand, etc. -- which is why California wines didn't win competitions in France until the blind tasting Judgment of Paris. Until one actually experiences the brain's influence on flavor perceptions, there's no point criticizing a proposal for a simple experiment. ~Amatulić (talk) 22:23, 14 April 2008 (UTC)

“Comment on content, not on the contributor.” (Wikipedia:No personal attacks) and “Wikipedians define incivility roughly as personally targeted behavior that causes an atmosphere of conflict and stress.” (Wikipedia:Civility) At the very least Captain Reference Desk’s remarks seem highly argumentative. He could just as easily have let it go and ended the discussion amiably as Vranak seemed to be trying to do. It doesn’t matter whether Vranak is right or wrong. We would never say to an editor “Because you are a Presbyterian I hardly I hardly see what benefit your contributions are going to be.” Yet to a scientist most Christian beliefs are as illogical as microwaves changing the taste of water. Vranak is entitled to hold his beliefs without harassment. --S.dedalus (talk) 22:40, 14 April 2008 (UTC)

Fellows, there are plenty of scientists who do believe in God, just as some believe in UFOs. You probably believe Ceasar's account of his conquest of Gaul, yet the oldest manuscripts of his account are from around the 13 century and there are only 5 of them. There are over 5,000 manuscripts are or manuscripts of books of the Bible, many dating back several thousnad years. 129.112.109.250 (talk) 16:33, 16 April 2008 (UTC)

Earth Hour

Most of my appliances have a wattage or amperage rating. For instance, my microwave has a rating of 500 watts and my room AC has a rating of 5,000 watts. It takes 3 minutes, 33 seconds for the microwave to heat up a 900 ml container of water from 72.1 F to 138.4 F, raising the temp by 138.4 - 72.1 = 66.3 degrees Fahrenheit. I've used .5 kW for (3 + (33 / 60)) / 60 = 0.0591666667 or 0.0295833334 kWh. The cost of my electricity is

• Energy Charge $.05061/kWh
• Fuel Charge $.05241/kWh
• Total Charge $0.10302

So it costs me 0.0295833334 kWh x $0.10302 or $0.003047675 or about a third of a cent to heat water to make coffee using electricity. However, it costs me $0.07625 to burn 1 ounce of Isopropyl during Earth Hour at $2.44 per 32 oz. So if I want coffee during Earth Hour using Isopropyl to heat the water it will cost me 25 times as much.

What then is the least cost, yet most convenient, replacement for electricity I can use to heat water during Earth Hour? (Not a homework question BTW although it should be.) 71.100.160.37 (talk) 17:50, 11 April 2008 (UTC)

Only you may be able to answer the question about convenience, but in terms of low cost and most environmentally friendly/efficient, consider perhaps a solar cooker. May not work in all climates and times, so I guess that could reduce your measure of "convenience". :-) --Prestidigitator (talk) 20:43, 11 April 2008 (UTC)

Generally speaking, the least expensive thing is the most environmentally friendly. If it costs 25 times as much to cook it with isopropyl, that probably reflects it being more labor-intensive to get, or simply less efficient. If it's less efficient, then you're burning less to get the electricity to heat the coffee then you are if you heat it by burning isopropyl. If isopropyl is more labor-intensive to get, that labor is using some form of energy (electricity, gas, etc.) that's presumably environmentally unfriendly. If you want to be able to tell people that you did your part to help the environment by observing Earth Hour, use the stove. If you want to actually do your part, rather than telling people you did, use the microwave when it's more efficient, and conserve energy in ways that actually do something. — DanielLC 22:02, 11 April 2008 (UTC)

If you want to go really old-school, you could try a wood burning stove, or just a small wood fire. That'll heat water pretty fast. Michael Clarke, Esq. (talk) 01:53, 12 April 2008 (UTC)

Or indeed the Kelly kettle. Ingenious design! BrainyBabe (talk) 19:36, 16 April 2008 (UTC)

Thanks for the suggestions. I've taken a second look and have decided the best way to provide myself with coffee during Earth Hour is to, er... to make a lot more of it in the microwave before Earth Hour starts and store it in a thermos until Earth Hour is over. 71.100.160.37 (talk) 04:16, 12 April 2008 (UTC)

That was going to be my suggestion. This question brings up, however, flaws with the concept of Earth Hour. If people switch to less efficient forms of energy or use more energy before and after Earth Hour, this really doesn't help the environment, does it ? I object to "feel good solutions" which do nothing to actually solve the core problem. Replacing incandescent light bulbs with compact fluorescent bulbs is an example of something everyone can do which will actually save energy, versus this Earth Hour silliness, which does nothing to save energy. What's worse, people who participate in Earth Hour will then say "hey, I've already done my part, no need to go changing light bulbs, too". I almost wonder if Earth Hour wasn't started by some oil company to intentionally distract people from actually doing anything that will really save energy. StuRat (talk) 15:00, 12 April 2008 (UTC)

Hey, now there is a thought... Earth Hour Revised - ride the bike to work instead of the SUV. 71.100.160.37 (talk) 16:41, 12 April 2008 (UTC)

Yes, that would actually do some good. I used to walk to lunch every day rather than drive. StuRat (talk) 03:16, 13 April 2008 (UTC)

The emphasis of Earth Hour is on switching off lights, as hinted at by the official slogan 'See the difference you can make'. The organisers do not suggest that anybody go without hot food. Their website also recommends [1] using compact fluorescent bulbs, as mentioned by StuRat. I think that most of the points made above are straw men - "Look, I had to burn polar bear cubs to keep warm during Earth Hour: how environmentally friendly is that?"

Actually they no longer need to recommend using compact fluorescent bulbs since retailers have begun selling low cost incandescent bulbs that may say 1000 hours but that are lucky in some cases to make it to 300. Of those bulbs you might be considered lucky for only one out of ten to pop on first use. 71.100.160.37 (talk) 05:01, 14 April 2008 (UTC)

Earth Hour is a just a stunt to make people think about their energy usage for a few days. It isn't going to save the planet (assuming that it needs saving), but as a piece of agitprop it works just fine. --Heron (talk) 13:02, 13 April 2008 (UTC)

I look at it as people having a finite amount of effort they will put into any endeavor, in this case saving energy. If they waste that effort on "Earth Hour", they will take less of an effort on other actions that will make a permanent difference in energy usage. Even if Earth Hour was a huge success (reducing energy usage by 10% during that hour and not increasing energy usage before or after to compensate), that still would only result in around a 1/1000 of 1% reduction in energy usage for the year. StuRat (talk) 15:14, 13 April 2008 (UTC)

Actually we do already have Car Free Days in some places Nil Einne (talk) 13:19, 13 April 2008 (UTC)

Cheap nuclear power ?

Okay, maybe I should post this as a new question but here goes... What about nuclear fusion that was suppose to make the cost of electricity so low it would be too cheap to meter so we would not need to conserve? 71.100.171.178 (talk) 03:29, 14 April 2008 (UTC)

(I made it a subquestion instead.) That seems absurdly optimistic to me. Even if energy could be produced absolutely freely, the cost of distributing it via power lines and maintaining those lines alone would be worth metering, unless you want to broadcast electricity as Tesla envisioned (with people occasionally bursting into flames if their fillings happen to pick up that frequency). At present we can't even make net energy from fusion at any price. It may provide a low cost energy source several decades from now, but certainly not that low. StuRat (talk) 18:21, 14 April 2008 (UTC)

Here's a really good article on the subject. The phrase comes from a speech made in 1954 and is now a byword for unfounded scientific optimism. The world at that time was full of daft predictions, so it's a bit unfair to single out this quote, as some people do, as if it underpinned the modern nuclear industry. The guy didn't even say that nuclear power would be source of this cheap electricity, although that's what most listeners would have inferred. --Heron (talk) 14:00, 15 April 2008 (UTC)

Well, he meant it as nuclear. He was Lewis Strauss, chairman of the AEC, all-around atomic blowhard. Strauss was only doing his normal thing: being totally unrealistic in his scientific advice and happily defying people who knew better. After Sputnik, Eisenhower finally realized that Strauss's scientific advice was so bad that he decided to set up better ways of getting it (ergo the birth of PSAC). --98.217.8.46 (talk) 02:50, 13 September 2008 (UTC)

What elements glow green?

I understand spectral analysis shows the colors different elements emit. What elements emit the color green? This includes all shades of the color from blue-green to yellow-green to just plain green. (you don't have to include compounds.) Am I right in saying, first of all, that Oxygen appears green? If you look in the sky with a telescope and see a green mass, what does that tell you about the object chemically? Wrad (talk) 22:20, 11 April 2008 (UTC)

A great example of an element emitting green, or rather, appearing green is Chlorine gas. Wisdom89 _{(T / ^C)} 22:36, 11 April 2008 (UTC)

Also, Oxygen is a colorless gas. Wisdom89 _{(T / ^C)} 22:37, 11 April 2008 (UTC)

Hi. Does Copper count? Apparently it glows green when fired. BTW I'm not an expert on this. Thanks. ~AH1^(TCU) 23:35, 11 April 2008 (UTC)

I've seen copper mentioned, yes. Wrad (talk) 23:37, 11 April 2008 (UTC)

He's right, oxygen does have a green 5007 Å emission line. You see it in nebulae and aurorae. -- Coneslayer (talk)

Does Chlorine emit green or does it just absorb all but green light? Wrad (talk) 23:58, 11 April 2008 (UTC)

I think Chlorine just reflects green. I'm not sure of it's spectral properties. Wisdom89 _{(T / ^C)} 01:28, 12 April 2008 (UTC)

... Or a pale blue liquid: liquid oxygen. -- 128.104.112.85 (talk) 20:27, 12 April 2008 (UTC)

If you want pure green try burning some thallium. 71.100.160.37 (talk) 00:24, 12 April 2008 (UTC)

And the anon is absolutely correct. Wisdom89 _{(T / ^C)} 01:30, 12 April 2008 (UTC)

And with emission spectra, as in the flame test, barium and boron will make a green flame. At that article you can see a few more greenish elements. Graeme Bartlett (talk) 12:15, 13 April 2008 (UTC)