Wikipedia:Reference desk/Archives/Science/2008 August 3

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August 3

Amount of energy needed to reach the speed of light: Infinite. Amount of atoms to destroy the sun: 1?

Essentially the faster an object with mass is moving, the more kinetic energy it has. In order to reach the speed of light, it would require an infinite amount of energy. The amount of energy it would take to blow apart the sun, is a finite amount. With that in mind, would it be fair to say that you could (in theory) destroy the sun with just one hydrogen atom, as long as you throw it at an extremely high fraction of the speed of light? ScienceApe (talk) 00:04, 3 August 2008 (UTC)

You seem to be invoking relativity and quantum mechanics at the same time. I'm no expert in either field, but my initial guess would be that any energy high enough to destroy the sun would surely be enough to split your hydrogen atom before it even gets there. --Russoc4 (talk) 00:20, 3 August 2008 (UTC)

Not exactly; the hydrogen atom can be accelerated to any speed below c at any non-zero rate. This implies that any non-zero force would due. --Bowlhover (talk) 02:31, 3 August 2008 (UTC)

But velocity is relative. So it doesn't matter which one is moving, as long as it's relative. So alternatively the sun could be moving at that velocity and collide with a single hydrogen atom that's at rest. Also I'm not sure how a Hydrogen atom would split just because it's moving at high velocity in a vacuum. This is kind of a hypothetical question, we are ignoring how to accelerate the atom to such ludicrous velocities. ScienceApe (talk) 00:27, 3 August 2008 (UTC)

Very well, then you are just using the hydrogen atom as an example of something extremely small. Alas, I don't have any answer for this one. --Russoc4 (talk) 01:40, 3 August 2008 (UTC)

You could certainly give the hydrogen atom enough energy to destroy the sun, but that doesn't mean it would actually do so. In order to destroy something you have to transfer the energy to it. I expect such a fast atom would just go straight through the sun and keep going, rather than destroy it. --Tango (talk) 02:19, 3 August 2008 (UTC)

There is a similar situation with bullets. A faster, higher energy bullet can actually do less damage, by going straight through a body and essentially taking a "core sample", while a slower, lower energy bullet bounces around inside and rips the body apart. StuRat (talk) 02:31, 3 August 2008 (UTC)

From my very limited knowledge of quantum physics, once you impute that much energy into the small mass, and it approaches the speed of light, the matter takes on wave-like properties. That's what advanced general relativity is about. Sentriclecub (talk) 02:46, 3 August 2008 (UTC)

Sorry Sentriclecub, but that's completely untrue. The more energy something has, the less quantum-mechanically it behaves, and general relativity has nothing to do with the quantum mechanical world at this point. Special relativity can be applied in something called quantum field theory, which is the likely source of confusion. SamuelRiv (talk) 02:53, 3 August 2008 (UTC)

Admittedly, my knowledge of quantum physics is just from 6 TTC lectures. They said that quantum mechanics and general relativity has some overlap, but they also have parts the other can't explain. The most advanced stuff of general relativity is trying to expand it into something called unified field theory which explains everything that quantum mechanics seperately covers. So that's why I called it "advanced general relativity" because it is something I'm very interested in. Einstein spent 30 years of his life unsuccessfully working on relativity trying to explain natural phenomenon using the propositions he laid out in his theories of special and general relativity. I have skimmed his book Relativity: The special and general theory with commentary by Richard Geroch" and follow updates to other scientists continuing his search. I believe I may have misunderstood the application of at appreciable fractions of the speed of light, matter breaks down and subsumes purely wavelike properties and maybe not relevant to this guy's question. Again my answer reflects my limited knowledge which was hopefully prefaced well enough enough in my first answer, that the reader knows I'm just providing an educated guess. I don't quite get what you say with the more energy something has, the less quantum-mechanically it behaves could you explain? I thought it was related to the more mass something has? Sentriclecub (talk) 03:18, 3 August 2008 (UTC)

$E={\sqrt {m^{2}c^{4}+p^{2}c^{2}}}$, so energy is linearly proportional to mass. —Preceding unsigned comment added by SamuelRiv (talk • contribs) 03:28, 3 August 2008 (UTC)

Thanks SamuelRiv, I used the wrong word also. Unified field theory is about expanding relativity into the field of electromagnetism, not quantum mechanics. I dont remember the term for unifying relativity with quantum physics. One last question, given the nature of mass-energy equivalence-- does a high energy object (with high mass) behave equally less quantum-mechanically than a particle with the same amount of energy (but exorbitantly less mass)? Thanks and I appreciate your response. Sentriclecub (talk) 03:43, 3 August 2008 (UTC)

The gravitational binding energy of the sun is around 10⁴¹ joules; I'll take that as an estimate of the energy needed to blow apart the sun (although stars are perfectly capable of blowing themselves apart without external input, so maybe I shouldn't). The mass of a hydrogen atom is about 10⁻¹⁰ joules. So we're talking a gamma factor of 10⁵¹. The sun's diameter is about 5 light seconds, so the hydrogen atom will pass through in about 10⁻⁵⁰ seconds of its proper time. Compare this to the Planck time of 10⁻⁴³ seconds. The orders of magnitude involved here make me think that you need a theory of quantum gravity to predict what will happen. My best guess is that you'd destabilize the vacuum, destroying the Sun, the Earth, and everything else. -- BenRG (talk) 11:54, 3 August 2008 (UTC)

Thanks for the followup, I was lurking awaiting followup so that I could go to sleep peacefully. Sentriclecub (talk) 12:00, 3 August 2008 (UTC)

You only need enough energy to disturb the balance between the sun's gravity and the radiation pressure to the point of causing an explosion - I have no idea how much energy that is, but it's presumably significantly less than the total gravitational binding energy. Either way, what does "destabilize the vacuum" mean? It sounds like something out of science fiction! --Tango (talk) 20:53, 3 August 2008 (UTC)

See False vacuum#Vacuum metastability event. Algebraist 21:01, 3 August 2008 (UTC)

A valid criticism of this hypothetical question is: we have never observed such high energy particles; while current theory may not prohibit them outright, it's conceivable that some upper bound on energy per particle will prevent this situation. Take a look at Tevatron - it's no easy task to get particles to have high energy, and you're suggesting that one may result from a random astrophysical process (or something). I conclude that it's not very likely, whether it's possible or impossible! Nimur (talk) 17:33, 3 August 2008 (UTC)

There's nothing in physics that prohibits it. There is no upper bound on energy per particle. According to special relativity, you can approach the speed of light as much as you like. You'll never hit it, but there's nothing stopping an object with mass from achieving a very high fraction of c. I never suggested that one may result from a random astrophysical process (or something) at all. Strictly a hypothetical question. ScienceApe (talk) 23:46, 3 August 2008 (UTC)

Such a high energy particle will strike a strong headwind of cosmic microwave background photons. These will appear to be ultrahard gamma rays in the frame of the proton and will cause massive reactions, as well as slowing it right down. This sort of effect Greisen-Zatsepin-Kuzmin limit puts an upper bound on the energy of cosmic rays. Graeme Bartlett (talk) 00:29, 4 August 2008 (UTC)

In this question we really aren't taking into account such things, nor am I asking about cosmic rays. Also I'm not sure how photons would significantly slow down a such a fast moving particle. The particle would have tremendous more momentum than a bullet. And photons don't slow down bullets very well. The Greisen-Zatsepin-Kuzmin limit applies to cosmic radiation, but not a particle that I'm referring to. Ultra-high-energy cosmic ray actually exceed that limit, but even they only have the energy of a baseball moving at 60 mph. But again, this is only referring to cosmic radiation, which isn't what I'm asking about. ScienceApe (talk) 02:13, 4 August 2008 (UTC)

Cosmic radiation just means really fast particles originating from space, like the one you suggested. — DanielLC 03:05, 4 August 2008 (UTC)

Originating from space, or from naturally occurring sources. In that case, it would be impossible for the particle to achieve such high velocities for the reasons mentioned above. ScienceApe (talk) 04:54, 4 August 2008 (UTC)

I don't understand Schrödinger's cat

I was trying to find out if there were any evidence of randomness in the universe and was led to Schrödinger's cat. I think I understand that the universe is random (right?)...but I don't understand why the cat would be both alive and dead. Louis Waweru  Talk  02:23, 3 August 2008 (UTC)

You're question is essentially one of microcausality. watch parts 1 through 5 and the answer is essentially that there isn't randomness, because the causal relationships between past and present are tied together and this must hold true at the quantum level. Also the guy who is prominently mentioned in I believe lecture 4, is a youtube professor from stanford.edu (the person who was invited to a physics meetup and got terrified by hawking's conclusion) you'll like it, since you are probably the right demographic that the video is aimed for. A pretty decent ability to comprehend concepts of higher science stuff. Sentriclecub (talk) 02:41, 3 August 2008 (UTC)

Professor suskind was his name. Sentriclecub (talk) 02:43, 3 August 2008 (UTC)

Thanks, just finished downloading this, going to watch it tonight =) Louis Waweru  Talk  02:11, 4 August 2008 (UTC)

Heh, everyone in that video is a complete ass, especially Hawking and Krauss. I'm not sure to what you're referring by saying there isn't randomness, because in our universe there is and has to be. It's simply fact. Now having not finished the videos, I think you might be referring to certain multiverse ideas to resolve the apparent paradox of randomness, but it really doesn't matter, because our universe is independent of that. SamuelRiv (talk) 03:38, 3 August 2008 (UTC) Edit: okay, it's about the information paradox, which has nothing to do with quantum randomness. SamuelRiv (talk) 04:11, 3 August 2008 (UTC)

Sorry Sentriclecub, but you have misunderstood what was being said in the video. It has nothing to do with quantum mechanics, but rather the information paradox applied to a general relativity problem. Causality must hold true, but this doesn't mean true randomness can't exist and particles can't appear out of nowhere. And Hawking is a pathetic self-promoter, as are many of the others in the video, and while the paradox is unresolved, it is mostly because we still do not fully understand what happens when black holes are created (a classical/statistical/QFT/GR problem) nor the nature of the singularity (a quantum gravity problem), either of which will likely resolve the paradox, for better or worse. SamuelRiv (talk) 04:07, 3 August 2008 (UTC)

Eh, it's more of an allegory than a principle of physics. There's too much "observation" that the cat has with itself (just through normal particle interactions that occur with any dense object) that would collapse any such uncertainty. If you'd like to understand the fundamental idea of randomness, maybe quantum mechanics is a good start. Let us know if you have questions, as it's a difficult subject.

Another type of randomness relies on a property called "sensitivity to initial conditions", and is formally known as chaos theory. Unlike quantum mechanics, it can be observed all the time in macroscopic systems (it's why we can't make accurate weather forecasts more than a day or two in advance). However, since such systems are all essentially Newtonian, it isn't true randomness. Rather, the data needed to predict what is going on is extremely difficult to obtain, and even a small error in the data is enough to catastrophically throw off predictions.

The final step in the randomness ladder is quantum chaos, about which I know nothing. Happy hunting! SamuelRiv (talk) 02:47, 3 August 2008 (UTC)

You speak of observation that the cat has with itself, but that's controversial, right? Doesn't your statement assume Objective collapse theory or something like that? Wouldn't others say that if the box was magically sealed from the outside world, the system would remain in superposition until the seal was broken? (Copenhagen interpretation?) --Allen (talk) 04:52, 3 August 2008 (UTC)

A common misunderstanding - which it sounds like you might be having from the statement in the original post - is that the cat is both alive and dead. The wavefunction does not express this, but rather it expresses our knowledge of the state of the cat. The cat is definitely one or the other, but we don't know until we look (observation). Therefore the wavefunction expresses our uncertainty (or lack of knowledge) about the state of the cat. After an hour, all we can say is that there is a 50% chance of it being alive. When we look inside (make an observation) we collapse the wavefunction to one state or the other. PhySusie (talk) 10:49, 3 August 2008 (UTC)

Again, you call it a misunderstanding... but are there not interpretations both ways? Are there not physicists who interpret the wavefunction as expressing something real about the system? --Allen (talk) 12:53, 3 August 2008 (UTC)

Thinking about this more, though my line of argument is similar (i.e. "hey, isn't what you're saying controversial?"), it doesn't seem to me that you're saying the same thing as SamuelRiv. It seems to me that SamuelRiv is saying that the wavefunction collapses without us looking from the outside -- the system observes itself. You seem to be saying that the wavefunction does not collapse until we open the box, but then you're also saying that the wavefunction doesn't imply a real superposition of the state of the cat. --Allen (talk) 13:02, 3 August 2008 (UTC)

PhySusie, you were right about how I was viewing it. Amcbride, what I think you're saying is what I was hung up on. Superposition is still really confusing, but I think what my friend told me about waveform collapse helps me make sense of it. Now I look at it as the collapsed waveform being what is reality...are you saying that the other possibilities are real as well? Louis Waweru  Talk  02:11, 4 August 2008 (UTC)

I'm no physicist so I don't know... I'm just saying it seems to me that a lot of physicists think that the other possibilities are real. So I'm not saying PhySusie is wrong; I'm just saying I think she's expressing one side of a controversy among physicists, rather than a consensus view. I could be wrong about that too, but so far no one has said so. --Allen (talk) 06:44, 4 August 2008 (UTC)

Schrödinger's cat was a silly parenthetical comment by Schrödinger in a much longer paper which took on a life of its own. The point Schrödinger was trying to make is that the rules of quantum mechanics imply that you can't confine it to the microscopic systems it was invented to describe; you can set up thought experiments where quantum behavior (modeled by Schrödinger's equation) is transferred from a microscopic system to a familiar macroscopic one, like a cat. In fact this always happens, since we can't measure properties of microscopic systems except by amplifying them. But in reality cats aren't fuzzy the way quantum systems are. (They're fuzzy in a different way—aren't you, widdle kootchie wootchums? Now get in the box.) People often get this backwards, thinking that Schrödinger was saying that the cat is, in reality, a superposition of alive and dead. He was really saying that the lack of alive-dead combinations in the real world means that Schrödinger's equation can't be the whole story. At any rate, he was wrong; cats are constantly interacting with their environment, and there's no way to prevent or shield this because of the second law of thermodynamics. When you model this interaction instead of treating the cat as an isolated system, you find that Schrödinger's equation does predict classical behavior for thermodynamic systems (see quantum decoherence). It might have been better all around if the cat had ended up on the cutting room floor. The whole cat paragraph could have been deleted from the paper without affecting the thrust of the argument at all, since it just reiterates the point of the previous paragraph in a sensationalistic way. And the point was wrong anyway. -- BenRG (talk) 13:35, 3 August 2008 (UTC)

When you talk about taking the cat as an isolated system, do you mean that as shorthand for taking the whole box as an isolated system? I don't see how any interpretation of Schroedinger's cat involves assuming that the cat itself is isolated from the rest of the box, though I'm sure I could be wrong. --Allen (talk) 18:25, 3 August 2008 (UTC)

Thank you for the help everyone! Honestly, I had to get a friend to interpret what you guys were saying for me. I think I understand now though...he had to explain things to me first though, like waveforms, the idea of superposition, waveform collapse, what happens when something is measured...the idea of an observer. All fascinating stuff, amazing... But I think in the end the point was that the Copenhagen interpretation is one of many interpretations and the cat is just meant to get people thinking. Louis Waweru  Talk  02:12, 4 August 2008 (UTC)

A bit near the question above...

Doesn't the cat live a normal lifespan? Assuming that if lives its entire life without ever being poisoned/shot, then wouldn't it eventually die? And, is the 50-50 chance that it lives applied to every second? Or nano second? Or microsecond? Eventually, if you narrow it down to smaller and smaller measurements of time (like Planck seconds), then wouldn't the trigger go off even without 2-3 seconds passing by with no incident? And, assuming that this argument is valid, wouldn't that ensure that the cat would die almost instantaneously after the experiment began?

Thanks! ❦ECH3LON❦ 03:38, 3 August 2008 (UTC)

Eventually, the cat would die, but that isn't the point of the experiment. It isn't a 50/50 chance of death. It is just that if you concern yourself with wondering about the hidden cat's state of being, you are uncertain. If you instead check the control of the trigger (decaying atoms in his example), there is no uncertainty. -- kainaw™ 03:48, 3 August 2008 (UTC)

First off, it's an allegory, not a real experiment, so it would indeed live a normal lifespan. Now how quickly the cat lives or dies depends on how you formulate the problem. Let's say that each ray of radiation emitted by a bit of radioactive material in the box is enough to kill to the cat instantly. So let's say it has a 1/2 chance of emitting one ray each second, then extrapolate the math from there, so the cat only has a 1/4 chance of surviving after two seconds, etc. Extrapolating to a singular point doesn't work, I'm afraid, with applied math, so you can never count an infinite number of probabilities in an infinitely small time to get a 100% chance of death. This is because in the physical world, radiation is well-defined, not some point-particle emitted in point-time as this exercise describes. SamuelRiv (talk) 03:56, 3 August 2008 (UTC)

The probability that the cat is alive at any given point in time is $p(t)=0.5^{\frac {t}{h}}\,$ where h is the half-life of the trigger (for instance, a radioactive sample) and t is the time that has passed since you set the trigger.71.77.4.75 (talk) 04:10, 3 August 2008 (UTC)

(2 ec's) "Doesn't the cat live a normal lifespan? Assuming that if lives its entire life without ever being poisoned/shot, then wouldn't it eventually die?" Yes, but Schrodinger's cat is a thought experiment about when a system ceases being a quantum superposition of states (both alive and dead) and becomes one state (either alive or dead). Whether the cat eventually dies is irrelevant; the experiment involves its state at the end of the experiment.

"And, is the 50-50 chance that it lives applied to every second?" No, radioactive decay, the process used in the experiment, has a certain possibility of occuring within a certain time. Half-life is the time it takes half a sample to decay, so it's also the time in which any given atom/other particle has a 50% chance of decaying. When the time is shortened, the possibility of decay also reduces; it doesn't remain at 50%.

Of course, the experiment does not necessarily have to use radioactive decay. Any quantum mechanical process that introduces randomness would work.

SamuelRiv: Surely extrapolating to a single point would give a 0% possiblity of emitting one ray? Also, the thought experiment doesn't involve a point-particle emitted in point-time; real particles can be used too, and Schrodinger used 1 hour as his time. --Bowlhover (talk) 04:13, 3 August 2008 (UTC)

You might like looking at quantum immortality. Jkasd 04:45, 3 August 2008 (UTC)

You might also like looking at Quantum Zeno effect. I you kept monitoring the cat so quickly it would never die :) Dmcq (talk) 08:48, 3 August 2008 (UTC)

Thanks for all your answers!! ❦ECH3LON❦ 22:49, 3 August 2008 (UTC)

Double alkylation of carboxylic acid derivatives

I have in my notes that acid anhydrides, unlike the more reactive alkanoyl halides and the less reactive esters, do not undergo double alkylation in the presence of a Grignard reagent. Does anyone know 1. if this is correct and 2. why this is? Instinctively, I would assume that, since you're making a ketone with the first alkylation, the Grignard could alkylate the ketone to yield a tertiary (or possibly secondary, if you started with a methanoic acid anhydride) alcohol, because you can do that with regular ketones that you didn't prepare from an anhydride. --M1ss1ontomars2k4 (talk) 03:54, 3 August 2008 (UTC)

Your analysis is reasonable - however look at this page http://designer-drugs.com/pte/12.162.180.114/dcd/chemistry/p2p.grignard.ac2o.html see the diagram (intermediate product) note that acetate has not left as a leaving group, in fact the acetocy group is capable of chelating the Mg in a six membered ring here..

eg from acetic anhydride and 'RMgBr' the intermediate could be:

        Me
         \
          C=O
         /   \
        O     MgBr
         \   /
          C-O
         RMe

Breaking the C-O bond to make ketone plus Mg(Br)(acetate) won't be very favoured (cf acid chloride) —Preceding unsigned comment added by 87.102.5.5 (talk) 13:46, 3 August 2008 (UTC)

However if you boiled this I would expect it to decompose..

Look at this patent from the preparation of a methyl ketone http://www.wipo.int/pctdb/en/wo.jsp?IA=WO2000076948&WO=2000076948&DISPLAY=CLAIMS note that the grignard is added to excess acetic anhydride.

I'd guess that if you added excess grignard to acetic anhydride with heat you'd get full reaction.

The results quoted are often under specific conditions and may not be an apples to apples comparison. There's often a big difference say if you do a grignard reaction at -78C or 25C - the text books often don't make that clear..87.102.5.5 (talk) 13:05, 3 August 2008 (UTC)

Extremes of earth's atmosphere

I remember an article, very probably on wikipedia, telling there was a time in earth's history when the atmosphere had oxygen levels up to 35%. Another article (or the same?) told about the solar system flying through a denser region of space, resulting the earth in catching hydrogen from space and burning the atmosphere. Now I can't find the articles again nor anything similar. Was I dreaming? 93.132.182.221 (talk) 10:00, 3 August 2008 (UTC)

As to the first question, oxygen catastrophe has a diagram showing a max at just about 35 per cent if I'm not mistaken. You won't get much more, anyway, because of spontaneous fires breaking out (already at ~25% IIRC).

As to the Earth's previous path, I think that's quite hypothetical. Also today, the solar system sits in a dust bubble, too, from a previous nearby supernova we moved to, so something similar as you say should happen now, too, but doesn't, probably because of the magnetic field shielding us. --Ayacop (talk) 10:13, 3 August 2008 (UTC)

Thanks for the link. The article I remember was different, telling for example that those giant flying insects of the past where only possible for the high oxygen concentrations to keep the muscles going when air could only enter through the trachea. I couldn't have mad up stuff like that in a dream, could I? 93.132.182.221 (talk) 14:11, 3 August 2008 (UTC)

Perhaps Carboniferous is what you are thinking of? Try the section "Rocks and coal" in particular. I've never heard anything about "burning the atmosphere" with hydrogen though. That seems unlikely to me. Dragons flight (talk) 16:28, 3 August 2008 (UTC)

Yes, that is the article!!! Thanks a lot! 93.132.182.221 (talk) 19:00, 3 August 2008 (UTC)

As for the second article, was it related to the late heavy bombardment or the hydrogen-and-helium atmosphere that escaped around this time? --Bowlhover (talk) 20:26, 3 August 2008 (UTC)

Baked limestone

Can you tell me if mixing baked limestone with water to produce heat would cause irritation to human skin?. —Preceding unsigned comment added by 217.42.237.185 (talk) 13:03, 3 August 2008 (UTC)

Yes - baking limestone enough makes quicklime which reacts with water giving heat. —Preceding unsigned comment added by 87.102.5.5 (talk) 13:08, 3 August 2008 (UTC)

Assuming there is enough lime, the water will reach a pH of about 12. Such very basic solutions are bad for skin. Given enough time, this would go beyond irriation and cause real damage. ike9898 (talk) 17:08, 3 August 2008 (UTC)

Shining Metals dug from the mountains

I was wondering if there are any metals that actually shine enough for us to be able to see it in the dark?

Let's say you're in a dig-site DEEP INSIDE the mountains, and you find yourselves standing in a tunnel looking down in a really dark hole with a huge gold-ore or silver-ore or any metal (but especially and preferably more commonly known metals!) And the only reason you can see it is because it gives out a slight glimmer that you can spot in the dark..

I'm not really thinking that there is any metal that shines and glimmers that strongly by itself, but what if you stood with a torch in your hand and maybe the light from the torch reflected in the metal so you could see it glimmer, despite the darkness surrounding it down in the hole. Is that possible ?

I have read that gold is kind of shiny compared to other metals and that the "grayness" that most metals has to them when you dig them out isn't as present in gold. because the electrons and/or atoms are more different and varied or somesuch. (whatever - that part about why and how isn't that interesting to me at this point) But i don't know if gold ore could ever reflect such light, or if any other metal could..

You familiar with MITHRIL for example? The fictional type of metal created by Tolkien. It was supposed to glimmer quite strongly, and have the beauty of silver... I know that no real metal shines that strongly but I was looking for one that maybe shines a little as I said, like maybe reflecting lights from torches etc. in the dark..

Krikkert7 (talk) 15:28, 3 August 2008 (UTC)

Shining is the reflection of light. Darkness implies lack of or no light. Therefore, no metal can shine in complete darkness and it's unlikely for it to shine brightly with little light. —CycloneNimrod^Talk? 15:51, 3 August 2008 (UTC)

They didn't say it would shine in darkness, but only that it would reflect a flashlight beam. Yes, gold does that, because it doesn't oxidize when exposed to air, as most metals do. However, you're not very likely to see an exposed gold vein in a cave wall. Other formations, like cave crystals, are far more likely to be sources of such a reflection. Then, to add a shiver to your spine, that reflection you see in the dark might be the eyes of a black panther hidden in the cave, stalking you. StuRat (talk) 16:37, 3 August 2008 (UTC)

What will you do? If you want draw your weapon and continue investigating the cave, turn to page 175. If you think the risks are too great and wish to leave this dark place, turn to 247.87.102.5.5 (talk) 17:04, 3 August 2008 (UTC)

If you do not wish to be eaten by a grue, put the book down and walk away.91.143.188.103 (talk) 21:15, 3 August 2008 (UTC)

If it is a real metal, it should abide by conservation of energy, and cannot shine brighter than the torch or flashlight you used to illuminate it. Assuming the only process is reflection, the "shininess" will necessarily be dimmer than the source flashlight. (This does not account for phosphorescence or chemiluminescence, which are photo-chemical effects - in these cases, the glow may be dimmer, although maybe longer in duration, than the source light. In some exotic cases it seems conceivable that you might even catalyze some chemical change which could release previously stored energy in the form of light, but I know of no such mineral which does this when exposed to a flashlight). Nimur (talk) 17:40, 3 August 2008 (UTC)

Well, Radium shines in the dark, and, as far as I know, some of it's salts shine brighter. I can see an Unholy Avenger of Oppenheimer that shines in an eerily green colour and causes disease and deformity... --Stephan Schulz (talk) 03:06, 4 August 2008 (UTC)

Radium in nature is found in vanishingly small concentrations. It does indeed have a deadly glow when concentrated, but it seems very doubtful that it would ever be concentrated enough to glow in the ore as found in a mine, with milligrams of Radium mixed with tons of ore. Edison (talk) 03:24, 4 August 2008 (UTC)

Why do we care about faces?

Why do we care about how our partners look like? As far as they are healthy, why does it matter to have a harmonic face, a hooked nose or big ears? Evolutionarily fit children can be perfectly born from ugly parents, can´t they? —Preceding unsigned comment added by Mr.K. (talk • contribs) 19:04, 3 August 2008 (UTC)

There are lots of theories around human mate selection, you may want to read them for a better idea. But it appears there are some obvious errors in your thinking. The first obvious flaw is that you seem to have forgotten there is no way we can know how healthy someone (or is going to be, remember for greatest probability of successful children we tend to want the mate to be around and in good health for 20 years+) is by magic, we have to use something. Bearing in mind human mate selection largely evolved before doctors or anything remotely similar, going on what people look like seems a decent choice even if far from perfect. Also, it's not just how healthy someone is, for example a female wants her mate to stick around to look after the children. And of course you can be as healthy as you want, it doesn't help if you can't hunt/raise children/successful give birth. Then of course it's all very well successfully raising children but if no one wants to mate with your children because they look ugly you're not doing very well in evolutionary terms so even if looking a certain way isn't actually a predictor of reproductive fitness in most others ways, the fact that it affects mate choice may be enough in itself (see Sexual selection). Finally remember that evolution is all about probabilities. Even if 'ugly' parents can have 'evolutionarily fit' (this is poor usage of terminology BTW) children, if 'beatiful' parents have a greater chance of having 'evolutionarily fit' children then the beatiful parents win in evolutionary terms Nil Einne (talk) 19:22, 3 August 2008 (UTC)

Beauty can also indicate age and injuries, both recent and past. For humans, living conditions affect one's looks drastically, and poverty causes problems such as disease, aggression, crime, and low intelligence. --Bowlhover (talk) 20:04, 3 August 2008 (UTC)

There are theories (and studies) which claim that facial symmetry can be indicators of mutations, pathogen load, and other indicators of mate quality. Here is one paper discussing issue of attractive faces. Also of interest is research into what fluctuating asymmetry can be an indicator of.

As Nil Einne does point out, this desire for attractive faces (which typically are the most symmetrical) is more complicated than just wanting the most attractive mate possible, since as the mate increases in attractiveness, competition will increase in suitors.

But in response to Nil Einne's claims about health not helping to raise children/hunt/etc, the idea isn't that facial symmetry needs to predict those behaviors (although they might). Those factors can be partially determined by actual interaction (ask fellow tribe members how reliable X is at hunting, or ask fellow tribe members how nurturing Y is with children). If beautiful faces are predictors of factors like pathogen load (especially during development) or number of detrimental mutations, then they would provide information that actual interaction may not (or additional information to supplement information received through normal channels). So, you wouldn't need to look at the face of someone to tell whether they have parasites on them right now; you'd look at the face of someone to tell how resistant they are to parasites (again, assuming the data supports the link between facial symmetry and parasite resistance, which it may well not).--droptone (talk) 12:46, 4 August 2008 (UTC)

You may have misunderstood what I was saying. I was not saying that health isn't important in helping determine other factors, like how good someone is at raising kids, but there are additional factors besides health that matter and that some of these factors may be partially predicted by how someone looks. Remember that someone can be as healthy as they want in every other respect, but if they are infertile, well they aren't a good mate (at least if you're male, things get a little complicated if your female where the person who helps you raise your kids does not have to be the person who impregnates you). Remember that looking at beauty from a more complete sense, it includes things like body type (which I haven't discussed much but I'm not sure if Mr. K really wants to restrict this discussion to facial type since he talks about ugliness and beauty in a generic sense for part of his question, in any case it doesn't make sense to ignore other factors completely when we talk about beauty). I agree it's a combination of interaction and what the person looks (and possibly smells) like as you point out. But of course, just because it may seem likely that it would be better to determine something in another way, doesn't mean beauty didn't play a role as well in telling us. Remember also that in some cases, e.g. if you kidnap people from another tribe, your interaction experience may be limited. And that a big part of our evolution happened before we had the level of communication we have now. In other words, it's almost definitely the case that beauty played a multifaceted role in telling primative humans which mate to choose and that it's beyond a simple predictor of current and future health (future health obviously includes issues such as resistance). For example, I'm sure I've read of a study which seem to show woman prefer a more feminine looking face (or body?) most of the time except when she was most fetile in which case she prefers a more masculine looking face (or body?). The idea here is that the female wants the masculine looking person to impregnate her, because his (particularly male) children may be the most successful in evolutionary terms but wants the femine looking person to care for her children, because he's the most likely to stick around. (This is an idea which comes up a lot in menstrual cycle linked differences.) Nil Einne (talk) 14:01, 4 August 2008 (UTC)

Mechanical pencil uses chuck?

What do you call the type of mechanical pencil that uses a chuck (engineering)-type mechanism?--Sonjaaa (talk) 21:06, 3 August 2008 (UTC)

Don't they all use a chuck? --Russoc4 (talk) 02:38, 4 August 2008 (UTC)

The types of mechanical pencils are listed in the article you cite under Mechanical_pencil#Types. Presumably you haven't found the answer you want there though? I would say the clutch type best describes a chuck type mechanism since the 'claws' clamp the graphite piece in place. Jdrewitt (talk) 07:35, 4 August 2008 (UTC)

I read the article, but I'm not an engineer, and I don't understand which type of mechanical pencil uses a chuck, or if like Russo says, they all use a chuck? It's the article about chuck that's not clear to me.--Sonjaaa (talk) 13:32, 4 August 2008 (UTC)

i seem to remember a term 'propelling pencil' from my younger days. This now redirects to mechanical pencil. So there you are!

That's not a very good article. Any kind of mechanical pencil I've ever taken apart uses the "clutch" type (which I would term a collet) to hold the lead in place. That's the little three-claw thing with a sleeve overtop, pushed down by a spring. The sleeve pushes the claws together and they hold the lead in place. A Faber-Castell or Staedtler drafting pencil would be chuck-type, gravity-based - you push the button at the top and let the lead drop out as far as you want. (I used those back when drafting was done by hand). The Pentel (and is that an article in need of cleanup!) mechanical pencils I use every day would possibly qualify as ratchet-based, you click-click-click and the lead advances a little bit at a time, if you hold down, you can push the lead all the way back in. They also use a collet/chuck mechanism to hold the lead in place. The screw-based and twist-based designs mentioned in the article undoubtedly exist, but I can't say I've ever seen one. I have probably 25 mechanical pencils in my house (yeah I know, geeky) and all of them use a collet (or chuck if you want) to hold the lead. Franamax (talk) 11:20, 5 August 2008 (UTC)

You can buy brightly-coloured disposable twist-end mechanical pencils for not much more than wooden pencils, so they're fairly ubiquitous to me :) No need for sharpeners, messy shavings, loose rubbers (since they have one on the end), and no worries about losing or lending them (unlike with reusable ones). Now, if only there were somewhere to send the used up pencils to be refilled and recycled. So yeah, look for brightly coloured plastic pencils if you want to see screw types. 79.66.32.107 (talk) 15:24, 6 August 2008 (UTC)

Plant defences and herbivory in the African savanna

I was watching a special on TV about life in the African savanna, where several animals, namely elephants, deer, giraffes, and monkeys, were going about their normal business maneuvering the limbs and branches of fairly thorny trees, and eating the leaves off very thorny twigs. The giraffes and deer seemed to eat the leaves with the greatest calm, not minding the thorns at all. The monkeys were jumping about just as easily, and the elephants were knocked down trees with no complaints. If theses thorns evolved in part to deter herbivory, then how come these animals eat off these trees so easily. And how come they can move about on the branches with no difficulty. I wondered if it was because they mightve had thicker skin, so the spines dont penetrate, or in the case of eating they might actually pull the leaves off with their tongue, and then chew. Any thoughts? —Preceding unsigned comment added by 189.34.103.78 (talk) 21:35, 3 August 2008 (UTC)

You're too absolute. Maybe the damage from those animals isn't enough to give the evolutional pressure that's necessary for really different solutions holding away the animals completely. Maybe the plant evolved in that direction but died out because the fruits weren't eaten any longer by apes, and so seeds couldn't be transported to new places? Maybe such evolved plants died out because the fleas that can be found on that giraffes no longer ate those ticks sitting on the plant and sucking. Nature is much more complex than you think, even if you don't dive into the chemistry of it. --Ayacop (talk) 09:59, 4 August 2008 (UTC)

You may also be interested in Plant defence against herbivory. Shyamal (talk) 10:03, 4 August 2008 (UTC)

Ah, that has it all, thanks. What's missing is that seeing an animal eating a plant doesn't always mean it's on its daily diet. It has been observed that apes use specific plants when they're ill or for digestion. The cost/benefit ratio of evolving against such minimal threats would be forbidding. --Ayacop (talk) 10:11, 4 August 2008 (UTC)

On the subject of human cloning (not sure if this is the right desk for this)

I assume that a human created by humans using cloning technology would be sapient and have his/her own separate consciousness, barring any unforseen flaws in the system, but would these 'manufactured humans' have a soul, as such? --84.71.59.70 (talk) 22:12, 3 August 2008 (UTC)

Do you? Seriously, there is no scientific basis for the existence of a soul, hence it is not a scientific question. I would suggest you are better off asking a religious or spiritual adviser. Baring that, you might try the humanities reference desk. Dragons flight (talk) 22:32, 3 August 2008 (UTC)

You might find the novel Never Let Me Go an interesting read related to this question. But no, it is not scientific. But if I were to speculate: a "soul", as it is usually understood, is something that surrounds human life. It does not seem to be something that is dependent on the combination of female and male gametes. So it shouldn't be a problem. A clone would still be a human in every way. --98.217.8.46 (talk) 23:05, 3 August 2008 (UTC)

Many experiments have been done to try and detect the soul but they have failed, e.g. killing a person in a closed room with just a small hole for the soul to get out and watching the hole, or putting people who are dying on scales to see if the scales move when they die. I can't find references to such experiments in Wikipedia, I'd have thought they were notable. We'd have to a) clone a person and b) be able to detect a soul to give a really definitive answer to your question. Until then I think we have to be content with what is said in the Philosophical zombie article. Dmcq (talk) 08:25, 4 August 2008 (UTC)

The experiments involving weghing dying patients on scales were carried out by Duncan MacDougall in 1907. By comparing results from human patients to results from a control group of dogs (which were assumed not to have souls) he concluded that the human soul had an average weight of 21 grams. MacDougall's methods and objectivity were called into question and his results have never been replicated.

In answer to the original question - if you assume that humans have souls, why should a clone not have its own soul too ? Identical twins are "natural" clones, with identical DNA, but each twin presumably has their own individual soul. Gandalf61 (talk) 09:17, 4 August 2008 (UTC)

This position, while common, is not universal. I don't know what the Yoruba think about cloning. Algebraist 11:58, 4 August 2008 (UTC)

That's very interesting about the Yoruba, thanks. I've looked it up and Frederick II, Holy Roman Emperor was the one who did the earlier experiment but it's not described on wiki, there's a small reference in http://www.youngscientists.co.uk/node/106 Dmcq (talk) 20:19, 4 August 2008 (UTC)

Anyone here a doctor?

Hi there. I am writing an essay regarding about the writing practices of physicians today. I am conducting an interview for physicians as part of the research of the essay. Here is the interview. It consists of 12 simple questions:

1. Approximately what percentage of an average work week do you spend on written tasks?
2. Please discuss how written communication skills are important (or not) to your field.
3. What sorts of documents you write on a daily/weekly basis? What about longer term?
4. Who are your primary audiences (internal? external? any international? If so, where?)?
5. Do you write collaborative documents (as part of a team)? If so, please describe a common collaborative situation (number of people, length of document, situation, etc.).
6. What software tools do you use to prepare documents in your field (Word? Excel? PowerPoint? Other?)? In other words, what (non-technical) general software should professionals in your field be prepared to use for written or oral communication?
7. What online tools are important to your field (examples include virtual meeting tools like WebEx, collaborative tools like Google docs or wikis, communication tools like blogs, online research tools, and professional networking sites)?
8. Do you see increasing use of multimedia tools (audio/video, for example) by professionals in your field? If so, please describe the use, tools, or applications.
9. Do you see the internet impacting information sharing and/or communication in your field in other ways not yet described? If so, please explain.
10. What is most difficult about the documents and/or presentations you write for your job?
11. What top three essential writing skills should new graduates have when entering this field?
12. Describe how especially written communication practices changed in your field in the past 5 years.

I would really appreciate if a physician could answer these questions. I will need them ASAP. Thanks in advance! NittanyLion08 (talk) 23:32, 3 August 2008 (UTC)

Keep in mind that it will be hard to verify whether any responses are from a legitimate physician, so if you value the data results very highly, you might want to use a non-internet-based survey method. Nimur (talk) 00:04, 4 August 2008 (UTC)

I'm waiting for the "I'm not a doctor, but I play one on Wikipedia..." answers. -- kainaw™ 01:12, 4 August 2008 (UTC)

I doubt you will receive more than a few responses, NittanyLion, but I may be surprised. --Bowlhover (talk) 02:26, 4 August 2008 (UTC)

I see a lot of professional surveys created by marketing / sociology researchers who have no concept of what a professional's time is worth. I remember one academic sending out a dollar with each survey questionnaire, and getting some of them (if at all) returned with one question answered, with comments that a dollar isn't sufficient compensation for even that one question. Good luck finding a physician with sufficient patience for your questions. Physicians are busy people, and their time is valuable. The questions you pose are too time-consuming to answer, unless you pay them for their time. It might help if you streamlined it, providing meaningful multiple choice responses. ~Amatulić (talk) 22:45, 4 August 2008 (UTC)