Wikipedia:Reference desk/Archives/Science/2011 September 14

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September 14

Chainsaw as weapon

Seeing a suggestion in an earlier section on how to "improve" a sword by adding a cutting chain to it, would a chainsaw make a very effective weapon? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:16, 14 September 2011 (UTC)

Maybe? --Jayron32 00:18, 14 September 2011 (UTC)

Please be serious. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:21, 14 September 2011 (UTC)

Not really. It's fairly easy to derail chains, especially when using them to flail away at things; and once derailed, they're pretty useless. They look and sound scary, and they can of course intimidate and do real damage. But they're surprisingly fragile for the reason stated. --Tagishsimon (talk) 00:24, 14 September 2011 (UTC)

Maybe if you held the chain on with superstrong magnets or such? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:25, 14 September 2011 (UTC)

But that would tend to stop it from rotating, as much as it stopped it from derailing. So maybe not. --Tagishsimon (talk) 00:47, 14 September 2011 (UTC)

If you moved the magnet along with the chain... Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:53, 14 September 2011 (UTC)

How are you going to do this without greatly increasing friction? You could as easily suggest an I shaped tooth such that the bottom of the I prevented the chain from being pulled free of the chain bar. This, too, would inevitably increase friction. A key problem for chainsaws is that chains stretch when they heat up. One of the reasons that by design the chain is lubricated with a continuous flow of oil is to minimise friction to prevent lengthening. Under either scheme - magnet or I - you're trading a perception of "more difficult to derail" for more friction, more heat, and thus chain lengthening. And if the chain is now held such that it cannot stretch as it heats, it will try to get free of its restraints, which will cause more heat and more stretching until the point that it snaps, or binds up. And all that would be why chains are not I shaped. Back to the drawing board for you, I'm afraid. You could, I suppose, argue that you could dynamically adjust the chain bar length to obviate the lengthening problem. But then when you turned the thing off, your mechanism would have to deal with chain contraction. It's one thing to control chain lengths as a bicycle does with derailleur gears. Quite another to do so at the speed a chainsaw chain is revolving. --Tagishsimon (talk) 01:06, 14 September 2011 (UTC)

How about if the only part that was magnetic was the part furthest from the axis of rotation? (Either that or use extremely strong metal...) Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:13, 14 September 2011 (UTC)

They already use extremely strong metal ;). You're trying to eat you cake and have it, by saying, in essence, use fewer magnets to decrease the added friction, but hope that they provide as much protection against derailing as was previously the case. You have to face it that the chainsaw business is big and very long established business, and were there a better solution, the probability is that one or other of the manufacturers would have arrived at it by now. But they haven't, and I think a) we can take it that that is for good practical reasons and b) in considering the suitability of chainsaws as weapons, we're going to have to stay within the bounds of the possible and not drift into wishful thinking. --Tagishsimon (talk) 01:20, 14 September 2011 (UTC)

This, for completeness, is the nearest thing to your ideal; the Stihl MS 460 Rescue Saw, designed to cut through metal sheet. The majority of the saw is shrouded to prevent derailling, and only the tip has protruding teeth to do the cutting. I confess I should not wish to meet you, unarmed, on a dark street at night, were you wielding one of these. You may now say "¡Ay, caramba!". --Tagishsimon (talk) 01:44, 14 September 2011 (UTC)

Okay. ¡Ay, caramba! Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:03, 14 September 2011 (UTC)

I think the main weaknesses of a chainsaw as a weapon are it's weight and short reach. If someone was chasing you with a running chainsaw, you could probably outrun them, especially if they were being careful not to injure themselves. If you had much of a weapon, you could probably get at them first. You could shoot them, stab them with a sword, or throw a knife at them before they got close enough to use the chainsaw. And then there's the lack of stealth. You can't exactly sneak up on somebody with a running chainsaw. The weight would also make the attacker likely to fall over (especially if you helped them by hitting them with a chair). If they fell on the running chainsaw, or it fell on them, that might take the fight out of them. StuRat (talk) 02:18, 14 September 2011 (UTC)

Chainsaws pose a serious danger to the user. At the "Stihl MS 460 Rescue Saw" site I read: "IMPORTANT INFORMATION/WARNING: The occurrence called “kickback” can cause serious or fatal injury." Kickback is also mentioned in this article. Bus stop (talk) 02:37, 14 September 2011 (UTC)

There's a risk of kickback, but you have to be using a chainsaw fairly inattentively to be injured by it. If you're gripping it correctly and it kicks back, the front-most of your two hands will trip a lever which brakes the chain. I guess if you're leaning over the bar as you're cutting, and you don't have a hardhat and face visor then ... maybe you;re asking for it. --Tagishsimon (talk) 20:10, 14 September 2011 (UTC)

Have there ever been any real life murders with chainsaws even? If there weren't, I wouldn't be surprised. They are slow, heavy, large and cumbersome. Not to mention loud as hell, that would attract a lot of unwanted attention. ScienceApe (talk) 03:26, 14 September 2011 (UTC)

Well, if the victim was previously knocked out or tied up, there's no reason they couldn't be finished off that way, although you'd need good luck to clean up that crime scene. StuRat (talk) 04:03, 14 September 2011 (UTC)

I'm surprised no one has mentioned this yet. here is a nice model that is being given away in a competition. Vespine (talk) 03:55, 14 September 2011 (UTC)

Chainsaws in popular culture mentions the problems with using them as weapons: Brian de Palma claims the chainsaw killing in Scarface was based on a real murder, but there's no evidence about the actual details of the crime. --Colapeninsula (talk) 11:47, 14 September 2011 (UTC)

Whereas Health & Safety authorities and Accident & Emergency departments continue to deal regularly with the consequences of incautious use of a chainsaw [1]Elen of the Roads (talk) 22:40, 14 September 2011 (UTC)

Solid light

Is it possible to solidify light? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:24, 14 September 2011 (UTC)

Not that I know of. 67.169.177.176 (talk) 00:35, 14 September 2011 (UTC)

What if you compressed lots of photons into a crystal of light? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:36, 14 September 2011 (UTC)

Doesn't work this way -- you can't "compress" photons because they're massless, uncharged and travel at the speed of light. You could focus a beam of light, but that's not the same thing -- even if you focus it to a width of one angstrom, it won't turn into a solid. 67.169.177.176 (talk) 00:42, 14 September 2011 (UTC)

You can't crystalise or compress photons. However, there does exist a type of object called a photonic crystal - type of substance that is composed of microparticles, that forms a quasicrystal in the presence of a certain frequency of light, held together by induced electrostatic attraction between the particles. It is a quasicrystal, because its components does not consist of discrete atoms or molecules. This technique has been demonstrated on polystyrene microbeads. Plasmic Physics (talk) 01:04, 14 September 2011 (UTC)

¡Ay, caramba! Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:07, 14 September 2011 (UTC)

Not solid, but still interesting... Count Iblis (talk) 01:17, 14 September 2011 (UTC)

That is interesting, though the military application may be worrisome. Somebody should set a SETI project looking for such things from deep space... Wnt (talk) 13:59, 15 September 2011 (UTC)

Put the light in a black hole? A Black hole isn't solid though... Has mass, but it's not solid. Very strange thing. ScienceApe (talk) 03:21, 14 September 2011 (UTC)

Mercury has mass but is not solid (it's a liquid, to be exact). 67.169.177.176 (talk) 00:51, 15 September 2011 (UTC)

What are you talking about? Plasmic Physics (talk) 23:05, 15 September 2011 (UTC)

Trying to make a point that objects don't have to be solid in order to have mass. 67.169.177.176 (talk) 01:45, 16 September 2011 (UTC)

Who said they did? Plasmic Physics (talk) 11:51, 16 September 2011 (UTC)

ScienceApe did, when he/she said that a black hole "has mass but it's not solid... very strange thing". 67.169.177.176 (talk) 19:57, 17 September 2011 (UTC)

He didn't make that point. He was proposing that if light enter a black hole, the light is somehow solidifies onto the singularity. He corrected himself, since the definition of a solid does not apply to a singularity. Then, he remembered you statement, "you can't "compress" photons because they're massless," and concluded that even though a black hole is not massless, neither is it a solid. It short, he refuted his own statement. Plasmic Physics (talk) 23:54, 18 September 2011 (UTC)

Using an ultracentrifuge for almost-suspended animation

Dear Wikipedians:

Modern ultracentrifuge are capable to reaching an acceleration of millions of g's. Since Einstein's General Relativity says time dilates in strong gravity fields, and the equivalence principle states that millions of g's of centrifuge acceleration is equal to millions of g's of gravity field, wouldn't time in a modern ultracentrifuge be massively dilated? And can I then use the ultracentrifuge for almost-suspended animation by placing some fresh food into it, spin it for 5 years, and retrieve the food to find it still warm and hot?

Interestingly, the article g-force states "Recent research carried out on extremophiles in Japan involved a variety of bacteria including E. coli and Paracoccus denitrificans being subject to conditions of extreme gravity. The bacteria were cultivated while being rotated in an ultracentrifuge at high speeds corresponding to 403,627 g. Paracoccus denitrificans was one of the bacteria which displayed not only survival but also robust cellular growth under these conditions of hyperacceleration which are usually only to be found in cosmic environments, such as on very massive stars or in the shock waves of supernovas."

But how can Paracoccus denitrificans cellular growth be observed by humans in the lab's resting frame when the bacteria is massively accelerated to 403,627 g, and hence experience massive time dilation, so that typical cellular growth time for the bacteria might translate into thousands of years for human scientists in the resting lab frame?

Thanks,

174.95.169.5 (talk) 00:28, 14 September 2011 (UTC)

400000 g is still way too low to see noticeable time dilation effects. For that you'd really need something more like a hundred billion g's. Dragons flight (talk) 00:44, 14 September 2011 (UTC)

It works out to roughly (acceleration in gees) × (centrifuge radius in light years) = (time dilation factor)² − 1. For a time dilation factor of 2 and a centrifuge radius of 1 km, you need an acceleration of 3×10¹³ g. -- BenRG (talk) 23:01, 14 September 2011 (UTC)

You're not applying the equivalence principle correctly. In fact you should expect zero time dilation in this situation. Of course there will be time dilation due to the relative motion but that's another matter. Dauto (talk) 02:19, 14 September 2011 (UTC)

Let me give a more elaborate answer to that question.

• Starting with a thought experiment on a building on the Earth's surface. Suppose that a laser located at the bottom floor of the building sends a signal to the top floor of the building where it is detected and its frequency is carefully measured and it is observed that this frequency is slightly lower than the emitted frequency.

1. This frequency shift - a redshift - can be interpreted as gravitational time dilation.
2. Another way to look at this redshift is that the photons lost some of their energy because they climbed the gravitational potential well and, like anything else, had to pay the toll (gravitational potential energy) with some of its own energy. From Planck's relation $E=h\nu \,$ we see that this imply a redshift.
3. Note that what matters here is the gravitational potential $\phi =-{\frac {GM}{d}}$, not the gravitational acceleration $g={\frac {GM}{d^{2}}}$, so it is incorrect to say that the local gravitational acceleration causes the redshift. The local acceleration might even be zero (a point right in between two identical masses) and it would still be possible to observe time dilation. In short, gravitational time dilation has nothing to do with gravitational acceleration.

• Now apply the equivalence principle and replace the building on Earth with an accelerated building floating in out space away from any gravity source.

1. The equivalence principle states that if we make a similar experiment, an identical redshift shall be observed.
2. An observer that is not accelerating and see the building passing by as the experiment is performed interprets this redshift as a Doppler redshift because the detector at the top of the building is moving faster than the light source at the bottom of the building. It is moving faster because the detection happens after the emission giving it a bit of time to accelerate to a slightly higher speed.

The bottom line is: a non-accelerated observer (The scientist in the experiment you described) sees zero time dilation associated with an accelerated environment (The bacteria culture in the experiment you described). All he sees is Doppler effect. Dauto (talk) 18:48, 14 September 2011 (UTC)

You've messed up somewhere or else you're trying to make a distinction that I don't understand. It's a fact that an object in a spinning centrifuge will experience a shorter proper time than an object at rest in the lab. It's not strictly general relativity, since there's no spacetime curvature, but you could treat it as a gravitational redshift of the edge of the centrifuge relative to the center (where the acceleration is zero). -- BenRG (talk) 23:01, 14 September 2011 (UTC)

Yes, and it's quite easy to see this. The gamma factor to lowest order is 1 + 1/2 (v/c)^2. Working in the co-rotating frame, the centrifugal potential is V(r) = 1/2 omega^2 r^2, and sqrt[1 + 2 V(r)/c^2] which is the time dilation factor in the weak field limit, becomes 1 + 1/2 (v/c)^2. Count Iblis (talk) 23:43, 14 September 2011 (UTC)

I didn't mess up anything. I am indeed making a distinction, and I quote from my first post "Of course there will be time dilation due to the relative motion but that's another matter." If you read the OP's post carefully you will see that he is under the impression that there should be another time dilation factor beyond the normal time dilation factor due relative motion per special relativity. This extra time dilation factor would somehow be related to the local frame acceleration. That extra factor doesn't exist and that's what I was trying to demonstrate. Dauto (talk) 04:07, 15 September 2011 (UTC)

So what's the concensus? Do we have a time dilation? And would the 403,627g that bacteria experience in the centrifuge be equivalent to 403,627g of gravity experienced near a black hole? Thanks. L33th4x0r (talk) 03:00, 15 September 2011 (UTC)

No, there is no time dilation due to the 400 000 gees experienced by the bacteria. There is only the time dilation due to the relative motion which is negligible in this case. Dauto (talk) 04:14, 15 September 2011 (UTC)

Assuming a radius of $r=0.1m\,$, and an angular frequency of $\omega =60000RPMs\approx 6300rad/s\,$, we get the centripetal acceleration $a=\omega ^{2}r=3969000m/s^{2}=405000g$. We also get $v=\omega r=630m/s$, and the time dilation is $\gamma ={\frac {1}{\sqrt {1-{\frac {v^{2}}{c^{2}}}}}}=1.0000000000022$. Clearly that is not much to look at. Dauto (talk) 04:43, 15 September 2011 (UTC)

We agree about everything except (possibly) wording. There is time dilation and it's easy to calculate the amount using special relativity alone. Instead of calculating it as an SR time dilation, you can treat it as a gravitational effect and get the same answer. There aren't separate SR and gravitational effects that add together; there's just the one effect that can be calculated in two different ways. That's what Dauto and I were trying to say, in different ways. The rate (relative to a distant clock) of a clock near a black hole experiencing 400,000 g will not be the same as the rate (relative to the lab) of a clock in a centrifuge experiencing 400,000 g. The amount of time dilation isn't a function of the acceleration. Acceleration, as such, doesn't cause time dilation. -- BenRG (talk) 08:54, 15 September 2011 (UTC)

So what you and Dauto mean to say is that the 400,000 g in a centrifuge is just an acceleration whereas the 400,000 g near a black hole is not just an acceleration, it is an acceleration caused by gravity of the black hole and the gravity is responsible for the massive time dilation. But in this case I would argue that Einstein's EP would say that a rocket accelerating at 400,000 g would also give its riders the same massive time dilation that the black hole would, in this case the time dilation has nothing to do with gravity at all but rather to do with the pushing force of the rocket exhaust. Arguing along this same line, would the normal force exerted by the wall of the centrifuge on its content be ultimately responsible for giving its content the 400,000 g of acceleration? Then wouldn't this normal force give the centrifuge's content a massive time dilation just the same way as the pushing force of the rocket and the gravity of the black hole? Thanks. 76.68.7.220 (talk) 22:43, 16 September 2011 (UTC)

I am sorry for adding a bit more to what I was just saying. I have always been taught that the starting point for GR is when Einstein took his axioms of SR and applied them to accelerated frames of reference. So I have always understood the absolute time dilation of GR to be a by-product of acceleration since the EP implied that there is nothing special about gravity as compared, say, to more mundane forces such as the exhaust of an accelerating rocket. However, what you and Dautos are arguing here seems to be that in addition to the acceleration, there is something special/magical that is present in gravity/rocket exhaust that is missing in the force of containment (normal force) provided by the wall of the centrifuge, such that even though all three forces can go up to 400,000 g, the time dilation one get with 400,000 g of gravity/rocket exhaust is missing in the normal force of the centrifuge wall. I am wondering what this special/magical element is that makes gravity/rocket exhaust able to dilate time, but not the normal force of the centrifuge wall. Even though all three should be equivalent under the EP. Thanks. 76.68.7.220 (talk) 22:56, 16 September 2011 (UTC)

No, you still don't seem to understand it. What we are saying is that time dilation has nothing to do with acceleration, neither in the centrifuge, nor in the blackhole. The time dilation in the blackhole can be related to the gravitational potential by the formula given by Count Iblis above. But that relationship is only valid in the weak field approximation. Dauto (talk) 01:34, 17 September 2011 (UTC)

Then what about time dilation experienced from accelerating rockets, as in the case of the twin paradox? There is surely no gravity in that scenario. Thanks. L33th4x0r (talk) 01:38, 17 September 2011 (UTC)

The fundamental rule is that the elapsed proper time is the length of the worldline. In other words, a clock marks off equal spacetime intervals on its own worldline. Spacetime geometry isn't the same as Euclidean geometry, but it's closely related mathematically. In Euclidean geometry there's a theorem that the shortest distance between two points is a straight line. In special relativity, there's a similar theorem: the longest spacetime interval (proper time) between two events is a straight (nonaccelerating) worldline. In the Euclidean case, if you have two curves connecting points A and B, one straight and the other not, the straight one will always be shorter. So straightness and length are related in a way. But the extra length of the other curve doesn't "happen during" the parts where it deviates from straightness. The length is a global property, it isn't concentrated in any particular part of the curve. The twin effect is the same. If one twin accelerates and the other doesn't, the one that accelerates will experience less proper time between the meeting events. But the difference doesn't "happen during" the acceleration, and isn't really caused by the acceleration as such.

An object in a centrifuge has a helical worldline in spacetime. An object at rest in the lab has a straight worldline that runs parallel to the helical worldline (or to the cylinder that contains it, at least). Although these worldlines can go on forever and never meet, it should be clear that they have different lengths, in some sense. In the Euclidean case, the helix is longer. If the slope of the helix is v/c, i.e., it moves a distance v "around" for each distance c that it moves "up", then the helix is longer by a factor of ${\sqrt {1+(v/c)^{2}}}$, by the Pythagorean theorem. In the case of spacetime geometry, the helix is shorter by a factor of ${\sqrt {1-(v/c)^{2}}}$, by the spacetime counterpart of the Pythagorean theorem.

It's much harder to visualize an object hovering near a black hole, because spacetime is curved in this case. But I hope it's not hard to believe what I said above, that the same acceleration (worldline curvature) does not translate into the same ratio of lengths in this very different situation. There's no formula relating a particular amount of curvature to a particular amount of time dilation. You have to consider the geometric relationship of the worldlines. -- BenRG (talk) 09:04, 17 September 2011 (UTC)

Wow! That is fascinating. I never thought of it before! So fundamentally it is the change in the geometry of spacetime caused by a given scenario that determines whether the given scenario will result in time dilation or not. I would like to learn more. Is there any book that I can read that can teach me how to do calculations to allow me to figure out whether there would be time dilation, and by how much, there is in any given scenario, be they black wholes, traveling twins, centrifuges or other scenarios involving forces/relative motion/other scenarios of GR/SR/Q. Thanks for teaching me. I feel enlightened. L33th4x0r (talk) 18:05, 17 September 2011 (UTC)

Lightsaber vs. chainsaw

Suppose a Jedi armed with a lightsaber encounters a zombie armed with a chainsaw. Assuming that both of them have equal skill in using The Force, who do you expect will win?  :-D 67.169.177.176 (talk) 00:54, 14 September 2011 (UTC) Die, zombie scum! :-D 67.169.177.176 (talk) 00:58, 14 September 2011 (UTC)

Lightsaber can cut chainsaw, chainsaw can't cut lightsaber, Jedi wins. (Unless you have ten thousand zombies attacking one Jedi...) Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:03, 14 September 2011 (UTC)

And if lots of folks go see that movie, George Lucas wins. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:14, 14 September 2011 (UTC)

Interesting idea for an Expanded Universe movie (or perhaps a Hardware Wars-style parody). Of course, you'd prob'ly have to get the old man's permission first... 67.169.177.176 (talk) 01:36, 15 September 2011 (UTC)

Yes, I would choose "light saber" in that scenario. Course', I can't imagine a scenario in which I wouldn't choose a light saber :) Quinn ^{░ RAIN} 03:44, 14 September 2011 (UTC)

Light saber vs. Tommy gun. Now THAT would be interesting. Quinn ^{░ RAIN} 03:46, 14 September 2011 (UTC)

I thought the Jedi had superhuman reflexes that allowed them to block bullets with their lightsabers? 67.169.177.176 (talk) 00:44, 15 September 2011 (UTC)

If it was zombie superman? I don't think a light sabre would cut superman. Then you'd want a cryptonite sword.. Mind you if superman ALSO had a chainsaw, then I think your best bet is to run and hope zombie superman can't gather up much speed. Vespine (talk) 03:48, 14 September 2011 (UTC)

Where did you get the idea that Superman is a zombie? 67.169.177.176 (talk) 00:45, 15 September 2011 (UTC)

As an aside, wrt the questioner's piped link, there were no zombies in the Texas Chainsaw Massacre (at least in the films I've seen) Jebus989^✰ 12:31, 14 September 2011 (UTC)

What about Leatherface? 67.169.177.176 (talk) 00:49, 15 September 2011 (UTC)

Where did you get the idea that Superman is a zombie? Same place the OP got the idea that you could fight zombies with light sabres: I made it up. It was a reply to I can't imagine a scenario in which I wouldn't choose a light saber. Vespine (talk) 01:17, 15 September 2011 (UTC)

In that case, would a lightsaber made of krypton plasma be effective against the abovementioned chainsaw-armed zombie Superman? ;-) 67.169.177.176 (talk) 01:23, 15 September 2011 (UTC)

If you'll excuse me for asking, what the heck is this discussion doing in the reference desk for science? Jedis? Lightsabers? Zombies? Since none of them even exists, the question, although a well-formed, grammatically valid English-language utterance, has no real-world meaning. Guess I just can't take a joke...—PaulTanenbaum (talk) 01:30, 15 September 2011 (UTC)

Just for the record, in case you haven't been paying extra careful attention to previous discussions, what started this whole thing was a previous discussion about swords, where someone mentioned adding vibration technology to the sword to improve cutting power, and I replied (in jest) that they might as well just add a cutting chain to get the same effect. And then the discussion took on a life of its own. 67.169.177.176 (talk) 01:44, 15 September 2011 (UTC)

And in fact, I'm taking issue with your claim that "lightsabers don't exist", because they actually do. :-) 67.169.177.176 (talk) 04:23, 16 September 2011 (UTC)

Automobile engines and altitude

If I've got an ordinary (non-whatever-charged) internal combustion automobile engine that's rated for a maximum power of 100 horsepower at sea level, is there a way to calculate its maximum power output at other altitudes (say, 10000 feet)? --Carnildo (talk) 01:00, 14 September 2011 (UTC)

The power output is an approximately linear function of manifold pressure (I know -- they don't talk about that outside flight training), so for a non-supercharged engine, the power output will fall off with the atmospheric pressure (by about 3.3% for every 1000 feet when below 9000 feet, slower at higher altitudes). Turbocharged engines will deliver an approximately constant power output regardless of altitude, and engines with gear-driven superchargers (generally only found on aircraft) will deliver a constant power output up to a certain altitude (generally up to about 10000 feet) and then experience a drop in power output in a similar way to unsupercharged engines. FWiW 67.169.177.176 (talk) 01:12, 14 September 2011 (UTC)

(non)Existence of God

Is there any evidence (other than religious texts) for or against the existence of God? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:01, 14 September 2011 (UTC)

AFAIK -- none either way (unless you count the Resurrection -- I know, a circular argument...) 67.169.177.176 (talk) 01:03, 14 September 2011 (UTC)

You can't find evidence, if you don't know what to look for. So, it would be impossible look for evidence if you exclude religious texts. What reasoning could you use otherwise? Plasmic Physics (talk) 01:17, 14 September 2011 (UTC)

There are lots and lots of arguments both for and against God. See Existence of God for a long run down. There are not limited to religious texts. None are generally recognized as uncontestable either way, though. Natural evidence (e.g. empirical evidence) plays a role in some of the arguments (e.g. Argument from evil, Argument from design). But there isn't any single piece of evidence that as of yet can distinguish between existence and lack of existence of God. --Mr.98 (talk) 01:35, 14 September 2011 (UTC)

There never will be such evidence, see Russell's teapot. Count Iblis (talk) 02:04, 14 September 2011 (UTC)

Russell's teapot says no such thing. It says there can be no ultimate evidence for a total negation, but it says nothing about evidence for, and it says nothing about evidence against specific, falsifiable conceptions of a God (e.g. I believe in a God who gives everyone free fish on Tuesdays). --Mr.98 (talk) 11:46, 14 September 2011 (UTC)

Yes, but then the "God hypothesis" all but falsified, that's the situation we're in. Count Iblis (talk) 15:28, 14 September 2011 (UTC)

If you could prove it, there would be no debate. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:07, 14 September 2011 (UTC)

The problem with trying to prove the existence of an omniscient omnipotent being is that you can't. Anything and everything becomes proof, the reason why I think the belief in a 'deity' ('architect[s]', if you will) can actually coexist with being a scientist.

But most religions are contradictorily literalist. It's fairly ridiculous how people claim a god that can not be comprehended and yet try to confine the idea in definable terms - like the way the words are arranged in a book, or worse, actually making him in a male human's image. Like a caveman worshiping an astronaut because the astronaut came from the flying ship and has magical things, a cargo cult perpetually concerned with retconning. That kind of man-made god - the wizard in the sky - seems rather weak to me.

If we do find evidence of design sometime in the future woven into the very fabric of the universe, it would be frankly exhilarating, imo. But in the meantime, it's really just a rather pointless question when our brains aren't even equipped to comprehend infinity yet.(Disclaimer: I'm an agnostic atheist)-- Obsidi♠n Soul 02:22, 14 September 2011 (UTC)

There is no evidence for the existence of god. Asking for evidence against the existence of god is as absurd as asking for evidence against the existence of the flying spaghetti monster. Long story short, god is just a fairy tale for adults. ScienceApe (talk) 03:16, 14 September 2011 (UTC)

Well, let's weigh the evidence: Against: Cancer; child molesters; natural disasters, etc. For: Unicorns and magic...Oh, wait...damn! Quinn ^{░ RAIN} 03:31, 14 September 2011 (UTC)

Saying you "can't" offer any kind of proof I think is only a very small piece of the question. Probably you can't offer proof of SOME kind of supernatural being, but most religions have a silly habit of actually making specific CLAIMS about their deity some of which CAN be empirically tested, i.e. God created the world in 6 days. This has been happening for centuries, as science discovers more and more, the "gaps" for God to exist become smaller and smaller and more and more of the core "beliefs" become figurative or allegorical instead of literal. If you are actually interested in the subject, I recommend a book called God: The Failed Hypothesis. It takes a far more scientific approach to the question then the popular "New Atheist's" books. Vespine (talk) 03:42, 14 September 2011 (UTC)

Some active practitioners say that justifiable evidence is recognisable in the form of conditioning. For instance, if one actively practices, they may find that otherwise improbable fortuitous events occur more often (I guess, it is analogues to Karma.) I do not know whether a statistical study has been done on this. Plasmic Physics (talk) 04:43, 14 September 2011 (UTC)

See Efficacy of prayer (not that this answers the question - because it isn't answerable) AndyTheGrump (talk) 04:57, 14 September 2011 (UTC)

It's not all about prayer, it's a lifestyle which requires 24/7 commitment, and active persuit. It's not like an ointment, that you apply only when you need it. Neither is it like an umbrella that you put away, just because the rain stopped. Plasmic Physics (talk) 05:24, 14 September 2011 (UTC)

Note that while it's impossible to prove that God doesn't exist, just like how it's impossible to prove the flying spaghetti monster doesn't exist, it IS possible to prove the opposite. If I ask God to show me a miracle and he rearranges the stars to say "GOD IS HERE", that would be solid evidence. If I ask God to violate the laws of physics and make light travel 50% slower, and he does so, that would be solid evidence. --140.180.16.144 (talk) 05:31, 14 September 2011 (UTC)

Nope. That would prove that either (a) God exists/Gods exist, (b) you are dreaming/deluded, (c) the world is being run by people determined to make you think that God/Gods exist, (d) that free will doesn't exist, and you had no choice but to ask God/the Gods to make it happen, and it had no choice but to happen, or (e)... Well, there are probably an infinite number of possible explanations - none of which can be disproved. The thing about Gods is that they (allegedly) can do inexplicable things. If something inexplicable happens, 'God did it' isn't an explanation. AndyTheGrump (talk) 05:45, 14 September 2011 (UTC)

I agree, also there's Clarke's third law. If you showed primitive people fire production from your hand, or could drop someone dead instantly at a distance with just a loud bang, they would no doubt think you are a god. Maybe there's some crazy advanced race of mischievous aliens that can read minds and teleport stars around at whim. Of course that's incredibly unlikely, but without further evidence, I'd say it's MORE likely then "God did it". Vespine (talk) 05:50, 14 September 2011 (UTC)

OR! The stars were just going to arrange them selves like that for some inexplicable but perfectly natural reason, and you just happened to be one of the people to be gazing up into the sky wondering if there was a God at that precise moment, lol.. Vespine (talk) 05:54, 14 September 2011 (UTC)

Andy, what a goofy thing to say. Perhaps true from a purely philosophical sense, but the same reasoning could be applied to all scientific or mathematical proofs. You don't normally see headlines saying "FERMAT'S LAST THEOREM PROVED, OR ALL MATHEMATICIANS CRAZY", or text books that say "All mammals require oxygen, or there is a global conspiracy to make all scientists believe that mammals require oxygen."

If the stars were suddenly rearranged to say "GOD IS HERE" in a language well-known before the stars were rearranged, I think we could count that as a "proof" of the existence of a god. That would be a proof more solid than any other scientific proof I can think of off the top of my head. APL (talk) 06:33, 15 September 2011 (UTC)

Why do you think that He will reveal Himself in such a way. He's not genie in a lamp. Plasmic Physics (talk) 06:39, 14 September 2011 (UTC)

How can you tell? There's just as much reliable evidence that God is a genii in a lamp as there is that he exists at all. It's just as hard to try to prove that he isn't a genii in a lamp as to try to prove that he doesn't exist at all. The same kind of rationalizations that work to explain why god is undetectable work equally well to explain why it isn't obvious to everyone that he's a genii in a lamp. I mean, sure you can't see his lamp, but obviously an all-powerful Genii is perfectly capable of making the Holy Lamp become invisible whenever he wants to. My guess is that he usually keeps his Lamp invisible as way of testing humans' faith, but that's just a guess, as mere humans can't be expected to be able to comprehend Genii's motives. Red Act (talk) 16:49, 14 September 2011 (UTC)

Something like that would defeat the whole purpose of a faith-based relationship. Plasmic Physics (talk) 06:42, 14 September 2011 (UTC)

It's interesting to debate why God would want such a relationship, back in the old testament he certainly didn't Jebus989^✰ 07:02, 14 September 2011 (UTC)

He changed His ways, since it didn't seem to work very well. Plasmic Physics (talk) 07:34, 14 September 2011 (UTC)

You have to admit it's awfully convenient that God has apparently set things so the world is fairly indistinguishable from there being no God at all. --Mr.98 (talk) 11:46, 14 September 2011 (UTC)

Convenient to who? Plasmic Physics (talk) 13:31, 14 September 2011 (UTC)

I think Mr.98 is saying that theists try to rationalize the real world so that it fits into their preconceived belief that god exists. It's kinda like saying "God always watches out for me". But when something bad happens, you rationalize it to yourself and say "it happened by god's will for a reason." It's basically just a way to delude yourself. ScienceApe (talk) 14:06, 14 September 2011 (UTC)

There is no evidence that can be provided to finite Man to prove the existence of an infinite God. An infinite God would know this and so any evidence offered must be faked, either by the hands of Man or by sufficiently advanced yet mortal aliens. Hcobb (talk) 13:39, 14 September 2011 (UTC)

How about a burning bush? Jebus989^✰ 13:44, 14 September 2011 (UTC)

"If I could just see a miracle... a burning bush, or the seas part, or my Uncle Sasha pick up a check." --Woody Allen in Love and Death ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:18, 15 September 2011 (UTC)

Consider God as described in the Bible in the way people interpreted it before the 17th century, so before major advances in science were starting to be made. Then, you have to consider if that interpretation is consistent with the scientific knowledge that has transpired since that time. It is wrong to adjust the interpretation of religious texts to make it compatible with scientific knowledge and then argue that this interpretation is consistent with the scientific knowledge. Count Iblis (talk) 15:45, 14 September 2011 (UTC)

You know what else is wrong? People who don't believe in a religious precept telling people who do that their method of believing it is incorrect. It's not a scientifically analyzable concept. It's like telling someone they are wrong for liking the music of Billy Joel or wrong for finding the poems of Robert Frost to be entertaining. --Jayron32 15:51, 14 September 2011 (UTC)

Yeah! It's not like religions ever proselytize. Oh wait, they do it all the time. Religions are unverifiable, and it bugs me when people say "Well, atheism is unverifiable too!" because atheists aren't the ones making extraordinary claims about magic being real without offering a single shred of evidence. --Goodbye Galaxy (talk) 17:13, 14 September 2011 (UTC)

Did I do any of that? --Jayron32 17:46, 14 September 2011 (UTC)

Did I claim you did? --Goodbye Galaxy (talk) 18:00, 14 September 2011 (UTC)

God is said to be unknowable. If God is unknowable, isn't it futile to ask whether or not something that is unknowable—exists? Bus stop (talk) 18:19, 14 September 2011 (UTC)

Said by whom? --Goodbye Galaxy (talk) 19:04, 14 September 2011 (UTC)

I find this sort of idea supported at for instance this web site in statements such as this:

"Some Christians, and most Jews and Muslims, say that God is beyond knowledge or understanding. The prophets talked with him, but the age of prophets has past. We can never personally experience God." Bus stop (talk) 20:16, 14 September 2011 (UTC)

I heard them say that too. If that's the case, why do they say all these things about him in their holy books? Religious people contradict themselves all the time. ScienceApe (talk) 20:33, 14 September 2011 (UTC)

Religious experiences can be caused by temporal lobe epilepsy. Count Iblis (talk) 21:41, 14 September 2011 (UTC)

Reminder, can we keep it civil? There is no need for patronising comments.

By "unknowable", it refer to His motives, rationale, and complete comprehension. You can assemble a pretty good character profile from religious texts.

Jebus: The burning bush is not external evidence, which is what the original question included. Plasmic Physics (talk) 22:23, 14 September 2011 (UTC)

Science can do a lot of things, but one area where it utterly fails is in the realm of spiritual guidance. That's where religion or faith comes in. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:11, 15 September 2011 (UTC)

The short answer is: there is no unargueable evidence for or against the existance of God. It can only for reasoned for or against. Plasmic Physics (talk) 02:33, 15 September 2011 (UTC)

The existence of God is not provable from science, because no matter how miraculous the composition of the world, natural philosophy must accept it as law. But there are events in human relations where all logic demands that nothing but endless cruelty and conflict are possible, and even if something else were attempted it would be crushed - yet someone acts instead in an inspired way and things turn out very differently. Just as a hunter would follow an animal by its tracks, one seeking to prove the existence of God must carefully note, explain, trace and follow the signs of goodness in the world. Wnt (talk) 14:48, 15 September 2011 (UTC)

Best kind of lightbulb?

I want to replace all of the old incandescent light bulbs in my house with something better. In terms of energy consumption, light emitted, and lifespan, what is the best? My guess is LEDs, but I'm not sure. ScienceApe (talk) 03:14, 14 September 2011 (UTC)

LEDs have the lowest energy consumption and longest life spans. Of course, there might be other things to consider such as up front price and light aspects such as tones brightness, etc... Dauto (talk) 03:18, 14 September 2011 (UTC)

LEDs are still quite expensive, and not much better than compact fluorescents, so you might do better economically to go with those, until the price comes down on LEDs. An exception seems to be for dim and maybe bright lights, where the compact fluorescents cost far more. I've noticed that you can get CF bulbs equivalent to 60-100W incandescent bulbs for $1 each, but be prepared to pay 10x as much outside that range. StuRat (talk) 03:25, 14 September 2011 (UTC)

Thought I'd chip in here - my summer job last year was as an LED lightbulb salesman. They are remarkably efficient - they'll outlast halogen bulbs (not sure about incandescents) by a factor of about eight or ten, and pay for themselves about thrice over in energy savings. You can also get "warm white" bulbs, which have a tone just a little colder than halogen/incandescent bulbs, but not by much – perhaps 3800K vs 3500K. However, we were selling 3W bulbs (equivalent to a 30W halogen) at £11, and 6W (equivalent to a 50W halogen) at £16, and a couple of pounds extra for dimmable bulbs, so I got a lot of cold shoulders from people who simply didn't have the spare cash to invest in efficient lighting. Shop around and you'll probably find some a lot cheaper. But as StuRat says, if you don't mind compact fluorescents, which take a little while to reach full brightness, these are probably the best choice. They are much cheaper up front, the light is more diffuse (LEDs are best used as spotlights) and they won't cost much more to run in total, in terms of bulb cost plus energy savings. Brammers (talk/c) 07:53, 14 September 2011 (UTC)

Depending on the electronic ballast, some fire up quite quickly, although I prefer the slower ones, at times, so my eyes have time to adjust. StuRat (talk) 22:48, 14 September 2011 (UTC)

LED bulbs have it all over compact fluorescents in some respects. The upfront cost is higher, but the higher efficiency and longer life make up for it. I object to the mercury content of CFLs, and at the end of life they often fail by making a popping noise, with the base becoming charred or turning dark brown, and by putting out bad smelling smoke which the manufacturers assure us is harmless. Earlier LEDs had poor color quality, and were mostly very low brightness bulbs only advertised as being for "accent purposes," with no more brightness than a 30 watt or 40 watt incandescent, but finally some are on the market which are as bright as a 60, 75, or 100 watt incandescent, if I recall correctly, at about 100 times the price of the incandescent equivalent. Obviously they only make sense for the long run, and not for temporary use or for use where someone can unscrew them and steal them. If the price is too high now, it will likely be much lower in a year. One big problem with LEDs is that they are intolerant of heat; if placed in a fully enclosed light fixture, the lifetime and light output can be degraded, since they still produce some heat in operation. They generally are not suited for operation on a conventional dimmer, but some can be dimmed by other means. In new construction, it will be common to have "permanent" LED fixtures with no provision for unscrewing and replacing the LED, and with the fixture providing assurance of proper ventilation. Edison (talk) 03:26, 15 September 2011 (UTC)

Wow. Are they really that certain they will last for the life of the building, or do they just not care ? StuRat (talk) 03:29, 15 September 2011 (UTC)

Installing new light fixtures, and providing sockets into which you plan to screw LED bulbs, is reminiscent of having a 1902 automobile with a socket for a buggy whip, just because vehicles always had a buggy whip socket. Will a new fixture with nonreplaceable LED last the lifetime of the building? Most of the cost would be in the LED and its electronics, not the metal/plastic/glass/ceramic portions of the light fixture. We are used to unscrewing the burned out incandescent bulb after a year, or the CFL after 4 years, but after 20 years or longer of an LED lamp being in service, when the LEDs burn out, , I would not feel too bad about replacing a 50 dollar fixture with the current style rather than screwing a new 45 dollar LED into the old fixture and saving 5 dollars (mileage may vary). As we transition to LED lights, there will certainly be a market for screw-in LED bulbs, but as mentioned above they may not be suitable for fully-enclosed fixtures. Edison (talk) 21:26, 16 September 2011 (UTC)

I personally don't care about this, but women tend to want things to match. Thus, when one LED burns out, it wouldn't just be necessary to replace that fixture, but every fixture in the house, so they all match. And if one (more frequently used) LED burns out in one-tenth the time of the rest, you've now increased the cost tenfold. Considering that LEDs are pricey to begin with, this is becoming a rather expensive and time-consuming proposition. StuRat (talk) 04:51, 17 September 2011 (UTC)

Are you heating or air conditioning the room that the bulb is in? Hcobb (talk) 17:55, 15 September 2011 (UTC)

For most people the answer is yes in summer, but, in winter, they provide needed heat where people are present, similar to space heaters or zone heating. So, the overall cost of this is negligible. I suppose you could use LEDs in summer and halogens in winter, though. StuRat (talk) 17:58, 15 September 2011 (UTC)

Lightbulbs aren't the best heating anyway, because they tend to be placed in the ceiling. Lightbulb waste energy all goes to heat, but that heat manifests as a warm spot on the ceiling, you would have been better off with LED lights, and baseboard heaters. (Even assuming that electricity is the cheapest form of energy available to you, which is not a safe assumption.)

Well, many bulbs are in lamps, too. And those on the ceiling might heat the floor above, which might be OK, if that floor is occupied, too. StuRat (talk) 05:19, 16 September 2011 (UTC)

Be careful of cheap, generic-brand LED bulbs. I bought a few of them and they lasted less than a year! The LED elements themselves were fine, but the accompanying electronics burned out making the "bulb" as a whole worthless. APL (talk) 22:40, 15 September 2011 (UTC)

Re; The transfer of coldsores or herpes labialis by touch- 13th September 2011-04.52am

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

--Jayron32 04:05, 14 September 2011 (UTC)

We can't give medical advice. See you doctor. But, on a personal note, I would avoid touching other person's genitalia with your nostrils until you get this figured out. Quinn ^{░ RAIN} 04:06, 14 September 2011 (UTC)

(edit conflict) Wikipedia has articles about herpes labialis but if the person who left the question is genuinely concerned about the issues they noted, they should ask their doctor pretty much the exact same questions they tried to ask here. --Jayron32 04:07, 14 September 2011 (UTC)

Fast cars

How many BHP, HP, PS, CV, LB-FT do you need to make a car that weighs 2,500 lbs, and has a drag of 0.28, and a frontal area 6 sq ft, to go 350, and 150 MPH?--213.107.74.132 (talk) 07:08, 14 September 2011 (UTC)

If Adrian Newey or any of his peers know the answer, they will probably keep it very much to themselves for as long as they can. {The poster formerly known as 87.81.230.195} 90.197.66.205 (talk) 15:10, 14 September 2011 (UTC)

One may apply this equation[2]

                              3
                  ( velocity )
    hp = weight x ( -------- )
                  (   234    )

to estimate the required horsepowers:

150 mph: 659 hp

350 mph: 8366 hp Cuddlyable3 (talk) 16:27, 14 September 2011 (UTC)

                             3
                 ( velocity )
   hp = weight x ( -------- )
                 (   234    )

What does this formula mean? Please explain it in the steps you do when you use the calculator, like hp*weight/drag or whatever. Do you get it?--213.107.74.132 (talk) 17:49, 14 September 2011 (UTC)

Cuddlyable3's equations don't work out in reality, particularly because they don't factor in the vehicles Cd. They also appear to be designed to determine trap speed in quarter mile drag racing, not top speed. Obviously a vehicle like the one you described would not need 650 hp to attain a maximum speed of 150 mph. These questions are hard to answer as there are many more variables at work here than you provide. To take a vehicle to 350 mph is very difficult, the only real world examples of vehicles that approach this speed are Top Fuel drag racers which reach about 325 mph (of course they can do it in a space of a quarter mile). Top Fuel cars have between 8000 and 10000 hp. A very rough estimate for your hypothetical vehicle to reach 350 mph would be 3000-5000 hp. --Daniel 18:04, 14 September 2011 (UTC)

Quote

One may apply this equation[3]

                              3
                  ( velocity )
    hp = weight x ( -------- )
                  (   234    )
 

::to estimate the required horsepowers:
::150 mph: 659 hp
::350 mph: 8366 hp Cuddlyable3 (talk) 16:27, 14 September 2011 (UTC)

You are wrong. The McLaren F1 has 2,500 lbs and less hp, yet can go 240 mph. — Preceding unsigned comment added by 213.107.74.132 (talk) 17:53, 14 September 2011 (UTC)

Yes as I said, Cuddlyable3's equation is not appropriate for your question which concerns top speed, not quarter mile trap speed. --Daniel 18:06, 14 September 2011 (UTC)

You may be interested in Land speed record. Modern attempts use jet engines whose output is generally not measured in HP. I just noticed that your hypothetical vehicle has tiny frontal area, less than that of a rocket car, but the Cd is a very mundane .28, similar to many common road cars. In any event there are some piston driven HP numbers that you can use to make rough guess. One attempt was made at 450 mph with a 2500 hp engine, although the Cd was certainly far less than .28. --Daniel 18:15, 14 September 2011 (UTC)

Red snow and snow plant

Are the two names equal? namely Red snow and snow plant. The concise oxford dictionary says so.But wiki search shows them to be an algae and a flowering plant. Also I could not locate this: protococcus nivalis, but only got the other nivalis for red snow. — Preceding unsigned comment added by 59.96.40.46 (talk) 10:34, 14 September 2011 (UTC)

In various dictionaries the two terms are sometimes confused (and also some use the term red snow plant), but the term snow plant is usually applied to a fleshy parasitic herb (Sarcodes sanguinea), whereas red snow is a term used for the alga protococcus nivalis which you mention. - David Biddulph (talk) 11:04, 14 September 2011 (UTC)

are Saturn's rings perfectly flat?

i am wanting to confirm whether Saturn's rings are perfectly flat. in other words, at the furthest known extension (distance from the surface), do they orbit at exectly the same longditude as the inner most circle? or is it slightly concave or convex? or is it a bit of both, with some rings tending up and others down?

i'm curious as the shape might suggest a bent space effect from the gravity of Saturn. 58.171.106.110 (talk) 12:47, 14 September 2011 (UTC)

See Rings of Saturn. -- kainaw™ 12:54, 14 September 2011 (UTC)

They're independently orbiting and of different thicknesses so with a strict definition of 'perfectly' flat, no. Differences in thickness and composition alone would lead me to favour 'some up some down', but as you can see from the images on the above-linked article, they are 'pretty' flat Jebus989^✰ 13:03, 14 September 2011 (UTC)

I believe the question is about the angle of the tilt of the rings. If so, it is answered in the introduction of the article that I linked. -- kainaw™ 13:04, 14 September 2011 (UTC)

Ah ok, I may have misunderstood. Though I can't find that information in the lead, only that pheobe is at 27 degrees to the others Jebus989^✰ 13:10, 14 September 2011 (UTC)

The Phoebe ring to which you refer, discovered only in 2009, is a much larger, diffuser and separate entity from the better (and longer-)known rings, as are other faint dust rings associated with some of the other satellites, and these might be better treated as somewhat different kinds of object. {The poster formerly known as 87.81.230.195 } 90.197.66.205 (talk) 15:24, 14 September 2011 (UTC)

Yeah I know, that's why I queried where the angle of tilt of the rings is in the lead Jebus989^✰ 15:27, 14 September 2011 (UTC)

I remember watching a Discovery Channel the other day, where it was mentioned that there are irregularities in the rings. The main ring can have a density variance as high as Everest from the mean. Plasmic Physics (talk) 13:38, 14 September 2011 (UTC)

With Saturn itself being something like 9 times as wide as the earth, a disk with a thickness of 29,000 feet is relatively quite thin. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:24, 14 September 2011 (UTC)

As this picture shows and the associated article explains, the rings are not perfectly flat, they have small vertical perturbations. Looie496 (talk) 15:30, 14 September 2011 (UTC)

Saturn's rings are rocks, so they can't be flat. →Σ _{^talkcontribs} 01:50, 15 September 2011 (UTC)

Not all rocks are round, as noted here: "It's hard to take a round stone / And try to bounce or flip it / And if you find a flat stone / You might as well just skip it." --Wiley, of B.C. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:01, 15 September 2011 (UTC)

There were also a couple of recent articles in Science (journal) about waves detected in Saturn's C ring, which, along with the previously known corrugations in the D ring, point to an impact from a debris cloud (likely from a comet) in 1983. [4]. In the same issue, scientists also examined photos of Jupiters rings, and concluded that waves seen there were from the Shoemaker-Levy 9 impact of 1994, when the entire ring system was tilted about 2 km [5]. It must be stressed that these pertubations are extremely minor, on the scale of their respective ring systems. Planetary rings are extremely thin and flat. Buddy431 (talk) 03:38, 15 September 2011 (UTC)

meaning of a steeper curve in a oxygen–haemoglobin dissociation curve

Assuming you're familiar with the typical shape of the (say, human) oxygen–haemoglobin dissociation curve, imagine a different curve, much further to the left, with a much less pronounced 'S' shape, where it rises very steeply, very quickly, over short partial pressure changes, and also approaches the plateau fairly quickly. Mammals are benefited by having a dissociation curve not shaped like the one I've just described. But why? The only answer I have come up with so far is that the mammal would experience very sudden changes in affinity for oxygen over very small changes in the partial pressure of oxygen. However, as well as seeming somewhat simple, I need to relate this benefit to the efficiency of oxygen release. I have trouble getting my head around these dissociation curves and wonder how a much steeper curve equates to lower oxygen release efficiency? Any help very much appreciated! 82.71.20.194 (talk) 13:51, 14 September 2011 (UTC)

A couple of things first, "human oxygen-dissociation curve" is vague, we have different curves for fetal and adult haemoglobin, as well as for myoglobin. This seems to be a homework question and you're on the right track, so to help you out myoglobin, found in muscle tissue, has a curve in the shape you describe, why do you think that would be an advantage in muscles? Jebus989^✰ 14:18, 14 September 2011 (UTC)

Okay, myoglobin binds oxygen very readily. I can see how that is an advantage in muscles! In my 'homework' question, it's plotted on the same graph as a 'normal' human adult oxygen-haemoglobin dissociation curve (very sigmoidal). It's steep as described, but it will still take up and give up its oxygen over a range (albeit a very narrow range) of partial oxygen pressures. How is that different in 'efficiency' from haemoglobin? For example, at 5 kPa it will be almost 100% saturated, and only 20% saturated at 1.5 kPa. How is that 'less efficient' than the range for the normal curve, where 100% is around 20 kPa and 20% is at 4 kPa. You could almost say that myoglobin is more efficient, because it can take up and release with smaller changes in partial pressure? I do understand that myoglobin doesn't form tetramers like that of the haem group, and so therefore it doesn't have a situation where the loss of one oxygen molecule makes it easier for the other ones to go, too. If that's the 'answer', I don't know how to relate it to the curve! My textbook even says, "The shape of the curve is crucial to how efficiently a pigment can act as an oxygen carrier.", but there isn't any explanation on other shapes or how they influence this. I feel very stupid. I've answered more complex questions on this graph, including an exercise/pH/carbon dioxide Bohr shift to the right and its consequences, but for some reason this part is really really confusing me!  :| Hopefully with more insight into my thoughts you will work out what obvious thing I am missing?! 82.71.20.194 (talk) 14:46, 14 September 2011 (UTC)

You're pretty much there. You know about co-operative binding, so you can see how that fits into haemoglobin's function as an oxygen carrier. When oxygenated blood enters the tissues, we want the oxygen to transfer to active muscles. So looking at the curve, in low pO₂ muscle capillaries, haemoglobin will dissociate from oxygen, releasing it to diffuse across into muscle tissue. Now, the myoglobin, with much higher affinity at lower pO₂, is able to efficiently bind this free oxygen (almost all of it) and transport to respiring cells. Also of interest, if that it will only release the oxygen when really needed (at lower pO₂ than haemoglobin), so this allows more efficient muscle use. The myoglobin article reminded me that Whales have shed-loads of myoglobin to utilise this kind of 'muscle oxygen storage'.

The basic idea/exam answer they are looking for is that the right-shifted, steep dissociation curve will more easily 'pick up' oxygen at lower partial pressures. I'm not sure what level you're studying it, so the biological context may or may not be relevant (but I think it helps to think of the overall process anyway, rather than just looking at datapoints on a curve). Hope that's helpful Jebus989^✰ 15:11, 14 September 2011 (UTC)

Another point I should have mentioned, myoglobin having such a curve means it can act as if operated by a switch: sucking up all the oxygen as it diffuses across from capillaries, and then releasing it all when required for respiration. So efficiency, in terms of oxygen transport, is heightened by taking up all the delivered oxygen, and by delivering it all quickly when required for respiration Jebus989^✰ 15:23, 14 September 2011 (UTC)

(e/c) Thank you very much. I hate to say this, but I'm still kind of confused. The biological context is the more important thing for me here (this is university level, second year (believe it or not), but I study on my own so have no tutor to ask!). I think I see fairly clearly how these two (haemoglobin and myoglobin) work together, and the necessity of myoglobin operating at a much reduced pO₂. But the question is about the curve's shape, not its position to the far left on the graph. I guess that's what is essentially perplexing me. I don't necessarily see how that shape affects efficiency of oxygen release. After all, it seems from the graph that, given the right pO₂, it will still keep or give up its oxygen just fine. The question is not so much about why or where that curve operates (which I understand) but about why it's 'so much more advantageous for the mammal' to have a haemoglobin dissociation curve be sigmoidal like it is, instead of more like the myoglobin dissociation curve. If I wasn't so bloody determined to get a first, I'd have made something up and moved on by now! 82.71.20.194 (talk) 15:28, 14 September 2011 (UTC)

Right ok, in that case I apologise for my tone earlier, I wasn't trying to be condescending but I remember A/AS-level questions along these lines (but I remember we did recover it on my Biology degree course too). As a final punt, the steep curve acts as a switch (explained above) while the shallow S sigmoid utilises co-operative binding, the biochemistry of the haemoglobin subunits is an interesting read to understand the mechanism. You wouldn't want an all-or-nothing response in normal haemoglobin. But it seems my explanations are not hitting the mark so I'll let someone give it a go! Jebus989^✰ 15:41, 14 September 2011 (UTC)

Generating MIST from still water

How much velocity / acceleration (linear) is needed to be imparted to water lying at rest (at atmospheric pressure) to convert it into MIST ? (pipeyoga 17:10, 14 September 2011 (UTC)) — Preceding unsigned comment added by Pipeyoga011 (talk • contribs)

Water is not converted to mist by velocity or acceleration. It's converted to mist by turbulent air flow on its surface. Dauto (talk) 17:19, 14 September 2011 (UTC)

let me re-phrase a bit as ;

 " I put water in open conduit (half pipe section for example) and put it 
   on top of Bullet Train (assuming conduit is welded to bullet train).
    Now will the water Lump ( mass) split into fine droplets (mist) ? "

(pipeyoga 17:43, 14 September 2011 (UTC)) — Preceding unsigned comment added by Pipeyoga011 (talk • contribs)

Yes, for the reason described by Dauto above: the flow of air over top the train is not laminar flow, but has a component of turbulent flow. This is also how mists are formed e.g. over the ocean. It is an interesting question to consider how fast the train must go to generate mist, but I will leave that for the fluid dynamicists :) (also, please sign your posts with four tildes (~)). SemanticMantis (talk) 18:04, 14 September 2011 (UTC)

I think they are using four tildes, but it looks like they have modified their signature so that it no longer has a link to their user or talk page. —Akrabbim^talk 18:12, 14 September 2011 (UTC)

I thought 'unsigned comment' (Autosigned by Sinebot) only occurred when no signature was added by user... SemanticMantis (talk) 18:21, 14 September 2011 (UTC)

See User:SineBot#What it looks for. - David Biddulph (talk) 07:35, 15 September 2011 (UTC)

Note that the most energy efficient means of creating mist may be to force water through small orifices (holes). Spray bottles do this. The velocity required there is very low. StuRat (talk) 21:49, 14 September 2011 (UTC)

Dear Friends, I know from my barbers shop that spray bottles can generate mist / mist like phenomenon!

But my question is pertaining to CALCULATION ....!

If I consider the drag equation :- F(drag) = 1/2 C*Rho*A*v^2

Problem No 1 is what profile should I consider viz Speherical / Conic / Parabolic / irregular ? Ther value ranges from 0.5 to 2 according to SERWAY depending on the profile. Rho = air density A = cross section area v = velocity .

Problem No 2 is What to equate the F(drag) to Van der Waal's Forces / Atomic Bond Forces ? The F(drag) must be > the Structural Stablizing force of the Water Bulk ! And Van der Waal's Eq in simple form ; (p+ a'/v^2 )(v-b') = kT; where a' = inter particle force, b= volume of particles, v= voulme of container !! Considering p = 1 bar ( open to atmosphere) , T = (25deg C+ 273 ) Kelvin & k = 0.008314. Please help through this sequence of thought process (pipeyoga 10:00, 1 October 2011 (UTC))

Gentlemen, is there any other forum inside wiki wherin I can post this query ? (pipeyoga 07:38, 9 October 2011 (UTC))

How to show TB test results?

HELP ME. I would like to know what is the propper way to show a negative 2-step TB test results on a lab report? — Preceding unsigned comment added by Jl1018 (talk • contribs) 17:45, 14 September 2011 (UTC)

I'm sorry, but the Wikipedia Reference desks cannot give medical advice. Looie496 (talk) 18:00, 14 September 2011 (UTC)

We assume the intended meaning of TB is Tuberculosis. Wikipedia has an article about Tuberculosis diagnosis which notes that many test methods are in use. A lab report should state the name of the tester, date, and concisely using accepted terminology what test was made, what result was obtained, and what conclusion was drawn. Cuddlyable3 (talk) 18:29, 14 September 2011 (UTC)

Pyruvate/Pyruvic Acid article in Wikipedia

I am no expert, but when looking at the figures of the molecule pyruvate in the "Biochemistry" subsection of the main article titled "Pyruvic Acid" I noticed that the figures represent pyruvic acid not pyruvate. To be precise, Pyruvate is the right molecule in that biochemical process but the figure itself represents the conjugate acid of pyruvate, which is pyruvic acid. I believe the carboxylate anion should be drawn there instead of the protonated molecule. I think the figure should be corrected but like I said, I am no expert and want to make sure this is correct. Any ideas? — Preceding unsigned comment added by Larios.leo (talk • contribs) 18:02, 14 September 2011 (UTC)

Yes, you are technically correct. Officially, the -ic acid ending is reserved for the protonated form and the -ate difference is for the deprotonated form. In practice, however, the difference is a purely pedantic one; most chemists understand that the two forms often coexist in equilibrium, which is highly dependent on small changes in pH, and so the -ate ending is often used for both forms interchangably. It is not purely, technically correct in the IUPAC sense, but in the actual language used by actual chemists, it is very common to here the -ate ending used even for the protonated form. --Jayron32 18:21, 14 September 2011 (UTC)

Pedant**2...it's common among biochemists to conflate the two because they tend to coexist (or at least equilibrate) and the difference doesn't matter in general pathway discussions because of that. Chemists often care because they're not always under equilibrating conditions or at a pH and solvent where both are reasonable possibilities. DMacks (talk) 18:39, 14 September 2011 (UTC)

True enough... It's one of those things that in contexts where it matters, the distinction will be made, and in contexts where it doesn't, then it doesn't. --Jayron32 01:32, 15 September 2011 (UTC)

Is there an upper limit for the amount of energy a single photon can carry?

The article "Absolute hot" seems to only apply to matter. --Goodbye Galaxy (talk) 19:59, 14 September 2011 (UTC)

No, there isn't because you can always postulate another observer moving relative to the first towards the direction the photon is coming from. That observer would see the same photon with a higher energy due to blue-shift Doppler effect. Dauto (talk) 21:22, 14 September 2011 (UTC)

"Absolute hot" would apply to a gas of photons as well as to ordinary matter. At very high temperatures there's no difference between photons and matter anyway. The energy of a single photon is meaningless, because for any single photon, and any given energy, there's an inertial reference frame in which that photon has that energy. (This is another way of saying what Dauto said.) But experiments that detect "high-energy photons" are really detecting the energy relative to the detection device, and that could have an upper limit—Dauto's argument doesn't apply any more because the only legitimate reference frame is the rest frame of the detector. In fact I'd expect general relativity to impose an upper limit of some sort for the usual reason: anything higher and the detector collapses into a black hole on impact instead of detecting the photon. -- BenRG (talk) 22:23, 14 September 2011 (UTC)

Yes, let's say for a single reference frame. --Goodbye Galaxy (talk) 04:37, 15 September 2011 (UTC)

Low-tech atmospheric reentry.

I'm writing a short story involving low orbital space travel in a somewhat "steam punk" setting. Putting aside the improbability of any kind of space travel with that low level of technology, what would be the simplest way of surviving atmospheric entry at orbital velocities? What shape would the entry vehicle need to be? What materials would it need to be made of? Would it be possible at all to survive such high temperatures without the aid of modern materials? 209.182.121.46 (talk) 20:41, 14 September 2011 (UTC)

The Apollo program's method would probably be the easiest. Heatshield, parachute, splashdown. I'm not sure what the heatshield would have to be made of, I don't think Victorians would have the advanced ceramics that NASA used, but if weight is no concern, I'm sure you could come up with a substitute. (It's OK if most of it burns away in the process.)

Really, the hardest part would be making sure you hit the atmosphere at precisely the right location and angle. I'm not sure how you'd do that without modern technology. APL (talk) 20:50, 14 September 2011 (UTC)

Tungsten could conceivably be used for the heat shield, couldn't it? 67.169.177.176 (talk) 01:18, 15 September 2011 (UTC)

If you have rocket launchers to get you to orbit - then you can launch enough material (possibly over multiple launches) to build an enormously large, thick heat-shield - which ought to be able to do what the few-inch-thick NASA shields did. From then it's a matter of parachutes - which we might reasonably assume they'd have because the parachute was invented in 1470 and successfully tested in 1617. APL's concerns over getting the right location and angle might require you to shoot a very large Babbage engine into orbit - but the data to feed it in terms of horizon angle, etc, ought to have been well within Victorian engineering capabilities. As for what it would look like, I would expect them to build a spherical heat shield - so that they wouldn't get into trouble if the aerodynamics were all wrong - and have it split in half to reveal the spacecraft within once sufficiently deep in the atmosphere for parachutes to be effective. You don't want the weight of what remains of your heat shield to have to be supported by the parachute...so you'd certainly have to jettison it. Also, if you have the rocketry (or whatever) to get you up there in the first place, you could also have retro-rockets to slow you down again and also to maintain attitude control. The problem for me is how the heck they'd get up there in the first place. They'd be able to make oxygen and hydrogen gasses from electrolysis (widely available in 1869) - but the control of such things would be tough without computers and electronics. But liquification of oxygen wasn't around until 1883 - and then only in microscopic quantities. So you simply couldn't get enough energy density into a small enough craft. 216.136.51.242 (talk) 21:06, 14 September 2011 (UTC)

Solid-fueled rockets could in principle be used both for the boosters and for the retro-rockets (possibly with some kind of gas vanes for control). As for the parachutes, the Garnerin design would be MUCH more practical than either the original Da Vinci design or any other early parachute designs. 67.169.177.176 (talk) 00:15, 15 September 2011 (UTC)

See Atmospheric entry. --Carnildo (talk) 22:31, 14 September 2011 (UTC)

How about room-temperature liquid fuels and oxidizers? Seem to recall that working for Goddard and the Nazis (in the liquid-fuel part at least...) Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:13, 15 September 2011 (UTC)

Godard used kerosene and LOX, von Braun used ethanol and LOX. In both cases LOX was used as an oxidizer. The Walther engine (used e.g. in the Me-163 Komet) used hydrazine and concentrated hydrogen peroxide, while the related Yangel engine (developed by the Russians after WW2 and used in the Proton rocket and in many Russian ICBMs) used hydrazine and nitric acid. Of these chemicals, concentrated nitric acid would have been available in the Victorian era, and possibly hydrogen peroxide as well (it's usually obtained as a byproduct from the manufacture of anthracene dyes), but I'm not so sure about hydrazine. FWiW 67.169.177.176 (talk) 00:30, 15 September 2011 (UTC)

According to the article, hydrazine was first synthesized in 1889 "by a circuitous route" (therefore could not be made in large quantities or at an acceptable cost), and was not produced industrially until 1907. 67.169.177.176 (talk) 00:33, 15 September 2011 (UTC)

Very low tech means could slow an orbiting object enough to de-orbit it. It only needs to lose about 1% of its orbital velocity in a typical reentry burn; the atmosphere does the rest. A compressed air or steam operated piston, a slingshot device, or a small rocket could slow an astronaut enough for de-orbit if he did not have to bring the spaceship down with him. The distance of application of the de-orbit deceleration would have to be long enough that the applied force was survivable. The heating during reentry is related to the area and shape of the heat shield and to the mass it must slow down. Canvas bags and a video camera survived reentry without being incinerated after the Columbia blowup, for instance, because their surface area was large relative to their density. MOOSE was a low tech proposal for a lightweight reentry system for an individual: a 1/4 inch thick ablative heat shield and a manually aimed small retro rocket, and a parachute. There was to be no capsule around the astronaut during reentry: his space suit and an oxygen bottle sufficed. Apparently it was a feasible way of getting a person down from orbit. The Atmospheric entry article describes an inflatable heat shield. Edison (talk) 03:14, 15 September 2011 (UTC)

An alternative would be to use an extremely large parachute to slow down while still in the upper atmosphere (the Russians had proposed something along these lines in the late 50's -- use a specially made parachute and deploy it at ~300,000 feet for initial braking, then cut it loose, freefall for a while, and deploy a second, more normal-sized parachute below 100,000 feet). The question is, would this profile be survivable for an unprotected cosmonaut? From what I remember, the article did say something about the aerodynamic pressure being enough to rip the first chute to shreds if it remained deployed below the cut-loose altitude (~150,000 feet if I remember rightly), so it would prob'ly be enough to cause considerable kinetic heating. 67.169.177.176 (talk) 03:54, 15 September 2011 (UTC)

As it's fiction (and you've already gotten into orbit in a rocket made of brass and teak that's fuelled by powdered anthracite, or something unlikely like that), I figure the amount of fun you have is proportional to how far you're willing to bend the laws of nature. So the following is a bit bendier than the more sensible ideas others had above:

• If you must have a heat-shield, it has to be made of asbestos (or similar materials like vermiculite); asbestos was the miracle nanomaterial of the steam age. If ordinary asbestos is too prosaic, use some fanciful "green asbestos from the lava tubes of the Kimberley deposit" to explain away the unpossible properties your heatshield needs.
• An atmospheric reentry to Earth typically uses a fast entry through the atmosphere, converting the massive kinetic energy of an orbiting body to heat (by friction). Because the reentry is so fast (90 minutes or less) that heat builds up faster than it can radiate away, so you get very hot, and so you need a heatshield to be able to survive. If you can reenter slowly then that heat doesn't build up. The trouble with that is that the upper atmosphere is so rarefied there's too little of it to "grab a hold of". If you can generate a massive drag very high in the atmosphere then you can deorbit gradually. The atmospheric entry article Edison linked to describes a "shuttlecock reentry", which does this a bit; it doesn't seem practical to do this for a full ex-orbital reentry, but you're writing fiction so you may wish to fudge that (with some bizarre fanfold wing arrangement that incrementally retracts as the vehicle falls). It's much the same idea with the ballute reeentry that 67.169.177.176 talks about - it's not totally inconceivable to build a bunch of these with some steampunky material ("the finest vermiculated Kweichow silk"), and it's a rather poetic image to have your little capsule trailing hundreds of massive diaphanous silken ballutes (each with dragons or whatever painted on them), shedding them like tears as it descends.
• If you're willing to seriously fudge the dynamics of the solar system, your intrepid spaceonauts can "capture" a comet, attach that to their capsule, deorbit the whole lot, and ride home on an explosively steaming icey heatshield.
• Heatshield/parachute/aerofoil reentries are the sensible choice for Earth, because Earth has a nice atmosphere suitable for aerobraking. But some bodies don't (Luna, Mercury), which means you have to shed all that KE with retro alone. That's very difficult to do with a conventional power source, but the Victorians did so love the (alleged) power of radium. You'd still need to eject reaction mass, so perhaps you'd retro brake with some crazy railgun that fires ball bearings.

Jules Verne fired people out of a cannon and H.G.Wells just used antigravity "stuff", demonstrating that ignoring the laws of physics (rather than trying simply to bend them) gives you better immunity from allegations of incredibility. -- Finlay McWalterჷTalk 11:01, 15 September 2011 (UTC)

As mentioned in our article Nose cone, some of the early Chinese vehicles apparently used wood as an ablative re-entry shield. {The poster formerly known as 87.81.230.195} 90.200.79.217 (talk) 15:38, 15 September 2011 (UTC)

Victorians were masters of ceremics manufacture. I'm sure Armitage Shanks could have knocked-up a decent heat shield. BTW, old H G Wells also used the giant gun spaceship in Things To Come. Alansplodge (talk) 22:22, 15 September 2011 (UTC)

If music is a universal component of human existence...

...why does it require years to learn? Using a vehicle is much easier for us humans, and we didn't drive vehicles along evolutions. Quest09 (talk) 22:37, 14 September 2011 (UTC)

How young were you when you first started to sing, vs. when you first drove a car? ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:42, 14 September 2011 (UTC)

Most children learn the basics of music (like singing and keeping a beat with their hands and feet) without any formal training, soon after they learn to speak. If you mean learning how to read music or more advanced techniques, then I'd say those things aren't universal. StuRat (talk) 22:45, 14 September 2011 (UTC)

Singing and driving a car are pretty simple. Learning to read music and learning to be a mechanic are more difficult. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:49, 14 September 2011 (UTC)

I'm not sure that music is a "universal component of human existence". It wouldn't surprise me at all if there have been cultures and tribes with no concept of music.

But ignoring that, I think most people learn to sing or whistle well before they learn to drive. Most people, even without practicing, could hum a tune well enough to be recognizable.

Finally, tool use is very much a part of our evolution, so the ability to gain basic proficiency with bicycles and cars with only a little practice is definitely something that we evolved.

It may take "years" to master the Trumpet, but you can get one to belt out a simple tune with only a couple week's of practice. Similarly, it may take years to master a car to the point where you could win a pro-level road race, but you could safely get yourself to work with only a couple week's of practice.

So, uh, basically, I question every single premise your question is based on. APL (talk) 01:09, 15 September 2011 (UTC)

Also, if using a vehicle is so easy, how come there are so many auto accidents? ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:35, 15 September 2011 (UTC)

Because using an auto while talking on the phone and eating a Big Mac is less easy. Googlemeister (talk) 13:27, 15 September 2011 (UTC)

If Muficke be the food of Loue, play on, Giue me exceffe of it: that furfetting, The appetite may ficken, and fo dye. Cuddlyable3 (talk) 15:04, 15 September 2011 (UTC)

"Singing... (is) pretty simple". OK Bugs, try the tenor part for the Faure Requiem. Let us know how you get on! Alansplodge (talk) 22:09, 15 September 2011 (UTC)

I would have to agree that music is a universal component of human existence, beginning with the exposure to our mother's rhythmic heartbeat in the womb when we are a fetus. It is thought that it is in the womb where music appreciation begins, and we all share that experience. Most importantly, music is not something you hear. It is something you feel. See Touch the Sound (2004) for more insight. Viriditas (talk) 13:49, 18 September 2011 (UTC)

Identification of a caterpillar

Beautiful caterpillar at Strandfontein, in the False Bay area of Cape Town.

I would appreciate it if someone who is knowledgeable about caterpillars in general, or at least about this one specifically, would reply with its name so that I can find out more about it from there. Kind regards, Adriaan Joubert. Adriaan Joubert (talk) 22:52, 14 September 2011 (UTC)

It's a Pine Emperor Moth caterpillar, Nudaurelia cytherea cytherea. Dominus Vobisdu (talk) 23:08, 14 September 2011 (UTC)

Wow—that is a totally awesome photograph! Bus stop (talk) 23:18, 14 September 2011 (UTC)

@Dominus Vobisdu, thanks so much, I really appreciate it!

@Bus stop, thanks, I used the Nikon Coolpix S9100. It still amazes me sometimes with its picture quality. Adriaan Joubert (talk) 23:22, 14 September 2011 (UTC)