Science desk
< January 6	<< Dec \| January \| Feb >>	January 8 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

January 7

This

How is Avobenzone formed? What is the science behind Methylchloroisothiazolinone? What is it's occurrence in nature?96.53.149.117 (talk) 00:53, 7 January 2009 (UTC)[reply]

Methylchloroisothiazolinone (also commercially known as Kathon CG when mixed with methylisothiazolinone) is a synthetic preservative. Thus it is made by humans via a series of chemical reactions and is not known to be generated in a naturally occurring process (at least not at significant levels). I'm not sure what you mean by the science behind it, but it is a known human allergen that can cause contact dermatitis, and has been shown to be mutagenic and cytotoxic in some studies. Rockpocket 08:43, 7 January 2009 (UTC)[reply]

Transistor configuration in a radio Tx/Rx

Picture:[1] I've been looking up simple radio transmitters/receivers on the net.

In many sites, as in the above picture there is capacitor connecting the collector and emitter of the transistor which is connected to the antenna. What is that for?
Also in the above picture of a receiver and many others, the input from the antenna seems to be given to the collector. As far a I know, in all three configurations of the transistor, base and emitter are used for input. what is this connection?

59.93.4.189 (talk) 09:36, 7 January 2009 (UTC)[reply]

For #1, maybe impedence-matching (see Antenna tuner)? Or wait, do you mean the "10" or the "50"? DMacks (talk) 18:31, 7 January 2009 (UTC)[reply]

Interesting circuit. It maybe looks like a self oscillating mixer at first sight. Perhaps the input signal is large. Since the detected output seems to operate a relay, perhaps this is a remote control Rx?--GreenSpigot (talk) 04:33, 8 January 2009 (UTC)[reply]

The first transistor is in sort of common base config. There may be coupling between the emitter coil and the collector coil which would make an oscillator. The input signal is fed to the collector and to a parallel tuned circuit in the collector and so would not see much loading at the res frequency of the collector tank.--GreenSpigot (talk) 04:39, 8 January 2009 (UTC)[reply]

Unless of course, the input signal is intended to make the input circuit oscillate (at its res freq) and thereby generate a signal that can be rectified later in the circuit to operate the relay!--GreenSpigot (talk) 04:42, 8 January 2009 (UTC)[reply]

The frequency f0 on the diagram is 27.145 MHz, which is RC Yellow Band. That first stage is an oscillator, no doubt, and it looks like it must drive that antenna; you can't take input on the collector like that. What it's using for input, I can't tell, and the mess leading to the relay is a mystery, too. That second transistor might be biased to chop the waveform into class-c, and the final has a little power supply in the bias, fed by the output signal, that looks like AGC. What the relay controls is anybody's guess. The 50p across the transistor is there because the circuit didn't work right unless it was there, basically; it shunts higher frequencies around the transistor so they're not amplified. --Milkbreath (talk) 15:39, 8 January 2009 (UTC)[reply]

It seems pretty obvious that the signal flow in the diagram is from left to right. In that case the oscillator is acting as a receiver (albeit a strange one). Otherwise there is no control of the oscillator and the rest of the circuit is junk. But I believe the rest of the circuit amplifies and detects the oscillator output to drive the relay.--GreenSpigot (talk) 16:52, 8 January 2009 (UTC)[reply]

It has to work because, not just in this site, but in many other sites there is similar diagram with the input from the antenna given to the collector with a capacitor connecting collector and emitter. I'm using Qucs and/or gnu spice right now to see what happens when the 50p is changed...
It is OK to rpleace the antenna with a signal source with 50 Ohm resistance in series, right?
Another funny thing is that if the o/p of the first stage is taken from above the 10uH i.e @ at the other end of 50p, the waveform there is stronger(!) than if o/p is taken from above the tank circuit. Since you said the first stage looks like an oscillator I'm going to take a look at regenerative receivers.
Another thing is that the 40n is a large value as far as 27MHz is concerned (.147 Ohm reactance). So even on the presence of the 5.6k Ohm resistor, the place that they take o/p of first stage is practically @ Vcc or ac-ground. Any way I'm probably going to try anther circuit. 59.93.21.70 (talk) 10:59, 9 January 2009 (UTC)[reply]

If you are going to simulate this circuit on spice, I would use a representative source impedance to simulate the aerial. However, I cant tell you what that would be as it depends on the design odf the aerial. its unlikely to be 50 ohms, more like 300 ohm i think.GreenSpigot (talk) 21:50, 9 January 2009 (UTC)[reply]

Quantum Physics - The double Split Experiment

The concusion for the double split experiment was that particles behave differently when 'being observed' - ie it was mysteriously just the ACT of us OBSERVING that changes particle behaviour. Is it not possible that it was the observing APPARATUS ITSELF that was interfering with the particle behaviour & therefore the experiment ? How exactly did they detect the respective particles (photons/electrons)- what type of apparatus did they use? No one ever questions this? —Preceding unsigned comment added by 165.145.151.160 (talk) 10:09, 7 January 2009 (UTC)[reply]

"The" double slit experiment isn't one experiment like the michelson-morley experiment, it's an experiment that can be performed in the classroom and has been repeated with several different variations. The idea that it's the observation that causes the wavefunction to collapse is the Copenhagen interpretation of quantum mechanics, which is still being debated. So yes people question this, but it's more a debate about interpretations of quantum mechanics than a debate on what apparatus to use. EverGreg (talk) 10:29, 7 January 2009 (UTC)[reply]

What that is referring to is simply that in order to measure anything of any order of magnitude or size, you must modify it. For example, if you wish to measure the piece of wood you are using to build a tree house, you must manipulate that piece of wood with your hands, use a tape measure of sorts, and determine a length. Not that the action really changes the size or shape of a piece of wood. But when you are dealing with attempting to observe something as small as a electron or photon etc, there's nothing small enough to really measure directly. So, when studying electrons, scientist bounce other electrons off of the object or subject and observe the trajectories after impact and deduce from the deflections the properties of the object/subject. If you wanted to observe a red wavelength photon, and bombard it with electrons or white wavelength photons (light), you are going to add energy to your subject and thus, change its color or in some cases, composition and structure completely. There are new encryptions for computer lines using this quantum mechanic. They are already calling it Quantum cryptography. Hope that helps a bit.... Operator873 (talk) 10:25, 7 January 2009 (UTC)[reply]

Thanks Operator873 - but surely knowing that alone - that there is no way to observe the electrons without disturbing them and their path, it brings renders the results of the experiment inconclusive? All I'm hearing is this massive hype about how this experiment has opened a whole new door into science in that things arent really there until we observe them - and all of this is based on an experiment which has 'fake' results? —Preceding unsigned comment added by Nickylaatz (talk • contribs) 11:12, 7 January 2009 (UTC)[reply]

One question is if the Heisenberg principle is caused by a real uncertainty of the underlying system, or is caused only by the fact that to measure a system, we necessarily need to disturb it. The surprising thing with the double slit experiment is that over time a double slit inference pattern forms even if we can guarantee that only a single photon (or electron for that variant of the experiment) is in the experimental apparatus at any one time. If we consider a photon as a discrete particle, each of these photons flies through exactly one of the slits and has no way to interact with the other slit, or other photons. Still, in sum the photons behave just as interfering waves would. This strongly suggests that photons (and electrons, and other particles) "really" have wave-like properties, and hence do not have one discrete position, but are spread out in space. --Stephan Schulz (talk) 11:59, 7 January 2009 (UTC)[reply]

Except that if we place a detector of some sort to determine WHICH slit the electron passes through... If we make any attempt to identify the specific slit, then we end up with two discreet bands immediately behind the slits, whether we fire one electron at a time or many. Again, the addition of the measuring device appears to change the nature of the light from wave-like behavior to particle-like behavior. Or, light is doing the same thing in both cases, and its our measuring device which changes the experiment... --Jayron32.talk.contribs 13:05, 7 January 2009 (UTC)[reply]

First off, we're talking about the observer effect. The Heisenberg uncertainty principle has nothing to do with it. Second, it's not so much that light has wave-like properties as theoretical waves have light-like properties. Also, theoretical particles have light-like properties. Third, Jayron, the measuring device doesn't change the nature of the light (or electrons or whatever you use). It just causes the waveform to collapse and expand from there, and behaves like it would if there was a single slit, which makes sense, as it's only going through a single slit. — DanielLC 16:26, 7 January 2009 (UTC)[reply]

There are at least three things being discussed in a big tangled mess here. Firstly - indeed it is impossible to measure the position and speed of an electron without disturbing it in some way. Secondly - even without that - the precise position and speed is unknowable because an electron is a fuzzy probability cloud not a solid 'dot'. Thirdly, the duality of particles and waves do indeed seem to act such as to make things like the double-slit experiment do different things depending on how you measure them. The first of these is (I think) easy to understand. You can't measure something without affecting it in some way - duh. If it's small enough then the way you affect it makes a HUGE difference - but for large objects, it doesn't. The second of these is definitely a bit strange - but it's clear that "this is how the universe works" - and just because it seems weird to beings like us that learned and evolved in a 'macro-scale' world doesn't make it any the less valid. The really REALLY disturbing one is the double-slit experiment where the outcome depends qualitatively on how you look at it. Fire one photon at a pair of slits - it interferes with itself just like a wave that's travelled through both slits and you get a diffraction pattern. Put a photon counter in the way to figure out which slit the photon went through and you get an answer as to which one it passed through - but as if by magic, the diffraction pattern goes away and the particle seems to say to itself "OK - if you want me to behave like a particle - so be it - so you don't get a diffraction pattern anymore."...but how did the part of the light that went through the other slit in the first experiment "know" that you had a detector on the other slit - which could be some distance away? That's weird...it IS a whole new thing for us to understand.

I've personally done the double-slit experiment (we did it in 1st year college physics) - and I have to tell you that it's completely compelling. It's not just some flakey result - or something that's open to interpretation - it works and it's a really simple experiment. At small scales, the universe is a very weird place - but that's because we're not equipped to think in terms of the way it works at those scales - not because it's wrong. The problem is with our brains - our "common sense" - which turns out to be a mere approximation of the way things are that's only valid at large scales. It's like an astronomer saying that bacteria don't exist because he can't see them with his telescope. Our minds are simply unable to do this...but the universe doesn't care about that - it works however it works. SteveBaker (talk) 18:02, 7 January 2009 (UTC)[reply]

SteveBaker (talk) 18:02, 7 January 2009 (UTC)[reply]

Steve, I've observed two copies of your signature, so you must have sent it through two slits. There's no interference pattern, however, so there must have been a detector used. :-) StuRat (talk) 19:04, 7 January 2009 (UTC)[reply]

No, not quite. For such a small number of Steves, you get a probabilistic result. He may constructively interfere with himself here. --Stephan Schulz (talk) 21:15, 7 January 2009 (UTC)[reply]

Probably Steve has built his own home setup to search for gravitational waves. Franamax (talk) 23:08, 7 January 2009 (UTC)[reply]

Steve, you did the quantum mechanical double slit experiment in a first-year physics lab? With individual particles, and a detector at one of the slits? And it was "a really simple experiment"? In 1970 or 1980 or whenever you went to college? I find that hard to believe. Plenty of physics labs include a "double-slit experiment" that consists of observing a diffraction pattern from a laser, but that's explainable with Maxwell's equations. -- BenRG (talk) 04:56, 8 January 2009 (UTC)[reply]

Just playing devil's advocate here, my professor demonstrated the double-slit experiment to us my freshman year in lab, and I performed it in my sophomore year. It really is simple, though the equipment involved (ultra-dim lightbulb, with a photodiode capable of detecting single photons) was a bit complex by itself. I was able to perform it, with multiple distances, comparing one- and two-slit results, in just 3 hours.-Running On Brains 05:33, 8 January 2009 (UTC)[reply]

Yep - it's been a long time - but I believe we used a sodium lamp as the light source (it produces nearly monochromatic light - not quite as good as a laser - but enough to show the effect) - the photon counter was some kind of electronic gizmo - a photo diode is a possibility. But the photoelectric effect (which is what you use to count photons with) was demonstrated in the 1850's - so it was certainly around in 1975. I kinda recall a techtronic's storage scope might have been the way we recorded photons arriving at the detector...but honestly, it's been too long for me to recall the details. We had pretty good science labs in British universities back then - they took this kind of undergrad stuff rather seriously compared to modern colleges who find it cheaper to teach it out of a text book. SteveBaker (talk) 16:39, 8 January 2009 (UTC)[reply]

It seems pretty obvious to me that the problem is your 'photon counter'. How does this photon counter work, exactly? This rather crucial aspect of the double slit experiment always seems to be glossed over. People say, "but if you watch to see which one the photon goes through, the interference pattern vanishes! Amazing!" and glide right over the part where you have to explain just exactly how you "watch" a photon. Like many ideas in quantum mechanics, this seems to be an impressive conclusion drawn from some very dodgy reasoning. Maelin (Talk | Contribs) 05:20, 8 January 2009 (UTC)[reply]

The photon counter works because of the photoelectric effect - which is important because that's the effect that led Einstein to show that light acts like particles. Einstein won a Nobel prize for that work. It's effectively a solar-cell - a photo-diode - which produces electrons when struck by a photon. If you can find a decent translation of Einstein's paper on the photoelectric effect - you'll find it pretty compelling as an explanation of why light "is composed of particles"...that guy was actually rather smart! SteveBaker (talk) 16:39, 8 January 2009 (UTC)[reply]

Aaaaaaaah - Maelin - this is PRECISLY what I'm on about!!!!! Maybe if we watched it in a different way, with different non-intrusive apparatus/method, it would NOT collapse after all. It might be OUR EQUIPMENT causing this MYSTIFYING, effect that so maany other science ideologies are BASED on!!!! One day we might think....OH...&#$*!.....it was our stupid equipment. —Preceding unsigned comment added by 165.145.103.161 (talk) 06:35, 8 January 2009 (UTC)[reply]

It's known that the effect isn't caused by interaction with the apparatus. See interaction-free measurement and the linked articles. In the case of the double-slit experiment, consider the fact that the "photon detector" at one of the slits, however it works, only detects half of the photons. If the measurement effect were due to physical interaction then you ought to see a 50% interference pattern on the screen from the photons that evaded the measuring device (combined with some other pattern from the photons that were detected). But that's not what quantum mechanics predicts and it's not what's observed. The photon's behavior is also modified by the fact that it could have interacted with the measurement apparatus but didn't. -- BenRG (talk) 10:38, 8 January 2009 (UTC)[reply]

Indeed. Quantum theory is SO bizarre and SO contrary to people's expectations that great minds have tried to wiggle their way out from under the experimental evidence pretty much since Einstein got everyone excited about the problem again. This is a very well proven thing. Much of our modern electronics wouldn't work if it wasn't true. Have you ever seen a blue LED? Ever used a flash memory? Well there you are then. No quantum theory - no MP3 players...you choose! SteveBaker (talk) 16:39, 8 January 2009 (UTC)[reply]

I'm perfectly happy to accept that light behaves neither like billiard balls nor like water waves, but I refuse to accept that the universe alters its behaviour on the basis of whether humans are looking at it. How does this photon detector work? Why does it only pick up half the photons? Why don't I just stick an opaque photosensitive screen over one of the slits? Now I've transformed it into two single slit experiments! There's a "photon detector" that won't miss ANY of the photons. Can anybody here who accepts the result of this experiment actually, genuinely explain the precise mechanism by which these photon detectors work? The linked articles on interaction free measurement are unintelligible. Maelin (Talk | Contribs) 00:26, 9 January 2009 (UTC)[reply]

Well, you may refuse all you like - but that's what happens. The photon detector works via the photoelectric effect - for which we have an article. I think BenG says it only picks up half the photons because he's imagining an experiment where only one of the slits has a photodetector behind it. Just imagine two photodetectors - one behind each slit - then you know exactly where the photons went...it doesn't help you. The diffraction pattern DOES disappear when you try to find out where the photons went. Yes, it's deeply weird. I know you're going to start looking for trivial errors in the experimental approach - but don't you imagine that far greater minds than either yours or mine have not been examining that question for the close to hundred years that we've known of this 'wave/particle duality' thing? The effect IS real - and we use it (and it's consequences) all the time in day to day electronics. Like I said - the universe is WEIRD at the quantum level. SteveBaker (talk) 06:03, 9 January 2009 (UTC)[reply]

To make it even more weird (correct me if I'm wrong though), if you use entangled pairs of photons and send each one of the pair to a different double-slit experiment, counting the photons at one of the experiments also destroys the interference pattern at the other one. At least I think I've read that paper... Franamax (talk) 06:42, 9 January 2009 (UTC)[reply]

Steve, I don't like this "my head hurts and so should yours" approach to explaining quantum mechanics (to quote you from a thread below this one). The basic quantum rules have been known since the 1920s. You can learn them and use them to figure out the outcomes of experiments of this kind. It's not magic. People are fond of saying that no one understands quantum mechanics—a virtually meaningless statement. Do you understand gravity? Sure you understand some things about it, but do you really truly understand it, at the deepest imaginable level? Of course not. The quantum rules are unsatisfying as a just-so story about the universe, but so is every aspect of current physics. Why are there three particle generations? Why is the strong force so elegant and the electroweak force so ugly? The explanations for these things, if we ever find them, will probably be unsatisfying themselves. That's the nature of the frontiers of physics.

Also, the quantum rules may be strange, but so are "the classical rules". People are just more used to them. They happily talk about "unbiased coins" that have a "50% probability" of coming up heads, blissfully unaware of what crazy nonsense they're spouting. It's impossible to make sense of classical probabilities, and all of science is based on them (all experiments have error bars), so all of science is meaningless. Yet somehow it works anyway. Quantum mechanics is no more absurd than that.

I think I'd better revise my previous response in this thread. The measurement effect is due to interaction with the device, in that it is the construction of the device—the nucleons and electrons that make it up—that dictates its effect on the experiment, not mysterious measurement dust that adheres only to measurement devices. But quantum mechanics happens to have a concept of null measurement, or null interaction, which doesn't exist in classical physics, and which says that an interaction that could (probabilistically) have taken place, but didn't, has an effect that's very similar to the effect when it does take place. The presence of the apparatus introduces a possibility of interaction, and that has an effect on the behavior of the system even in trials where no interaction actually takes place (in the ordinary classical sense—things bouncing off of each other, if you like). To put it another way, interference effects show up when information about which way the particle went is lost, and conversely, interference effects don't show up when information about the path is retained, in any form whatever. A detector at one of the slits yields which-path information whether or not it detects a particle (if it doesn't detect one, that's evidence that the particle didn't go that way). As a result it affects the interference pattern whether or not it detects a particle. This can all be formalized. -- BenRG (talk) 08:42, 9 January 2009 (UTC)[reply]

Actually - I agree with pretty much everything you just said. Of course there is no special status for the 'observer' - but that IS how the system appears to act in practice - you try any way you can to find out which slit the photon went through - and the diffraction pattern goes away. No matter how clever you try to be - no matter how you sneak up on the photons - they never seem to get caught in the act of being both wave and particle at the same time. The circumlocution required to say that without invoking "magic observer dust" is even harder for the general public to understand. SteveBaker (talk) 20:43, 9 January 2009 (UTC)[reply]

Sorry? The photoelectric effect? You mean the one where a photon hits a bit of metal and is absorbed and an electron pops out? So let's see. You have two slits, and photons go through them and, wow, even though we know that light has particle behaviour (due, in fact, to the photoelectric effect), it turns out to still have a wavelike behaviour because we get interference patterns even if we only send one photon through at a time. And then, what, you shove a bit of metal in front of one of the slits, and sit there catching the electrons that pop out as the photons are absorbed, and you say, "Look! The interference pattern has collapsed now that we are observing the system! Amazing!" Obviously you've ruined the experiment because you've stuck a bit of damn metal in front of one of the slits to catch the photons. If you still got interference patterns EVEN WITH one of the slits blocked up by your detector, now THAT would be really amazing. But this is like being amazed that a Magic Eye vanishes if you hold your hand over one of your eyes. Maelin (Talk | Contribs) 09:04, 9 January 2009 (UTC)[reply]

Maelin....spot on...you and I are of like minds. Theres all this scientific talk meandering off in a thousand directions, without actually adressing the plain and simple issue....The device/detection method..is there irrefutable proof, that its not the PHYSICAL equipment CAUSING this effect? If someone says No, fine. If someone says yes....without redirecting to any 'thought experiments' as backup, please explain in laymans terms (well as close as possible - this IS quantum physics) WHY this is the case... —Preceding unsigned comment added by 165.145.117.62 (talk) 10:24, 9 January 2009 (UTC)[reply]

I want to know exactly HOW it is that photons are detected, do they fire electrons at it? does someone have the details (in simple terms) of how they detect the photon? Where do they detect it? at the slit or anywhere between the slit and the screen? thise sort of details? Can someone tell me exactly how the experiemtn is set up? in a vacuum? whats the detector etc etc? —Preceding unsigned comment added by 165.145.117.62 (talk) 11:15, 9 January 2009 (UTC)[reply]

Here's a weird proposition for possible explanation of the double-slit experiment outcome ... Perhaps photons and electrons (and maybe even all things 'teeny tiny quantumy') naturally exist & travel around as WAVES (naturally being on their own without any interferrence of other particles) ...or frequencies if you will. BUT - As soon as you introduce another different tiny PARTICLE (in this case electron to a photon-wave or photon to an electron-wave) , the wave collapses, and photon-wave becomes photon-particle and suddlenly EXISTS and ofcourse visce verce.......

If all this were true, how scary would it be that in total darkness, nothing really exists ?? eeeeek!!!!! —Preceding unsigned comment added by 165.145.117.62 (talk) 12:45, 9 January 2009 (UTC)[reply]

Agh! Do you REALLY thing all of these scientists are so stupid that they didn't notice that they blocked up one of the slits?!? What kind of bozo's do you think these people are?! No - of course they didn't do that. If you're going to start congratulating yourselves for showing up an "obvious" flaw - and thereby dismissing all of fundamental physics as we know it - theories that actually work in practice to make things you probably use every day - then you REALLY need to crack open a book and read about it first. Einstein spent the largest part of his life (after General Relativity was complete) trying frantically to get rid of this result in some clever theoretical manner. If you think you can do what he failed to do over 30 years - and do it in the space of a few minutes - you are bigger fools than you can possibly know!

SteveBaker (talk) 20:43, 9 January 2009 (UTC)[reply]

Steve, try looking at this from our side. As I said, I will accept the particle-wave duality thing. But then this part of the double slit experiment gets turned into some incredible, ineffable nonobservability principle in which the quantum universe behaves differently when certain bipedal carbon based life forms are looking at it. That's terrible science. Positing that humans are somehow magical observers with the capability of altering quantum behaviour is on par with suggesting leprechauns to explain rainbows. I frequently see people explaining quantum mechanics to laypeople and they seem to be perfectly happy to draw totally ridiculous conclusions like "the universe knows when we're watching!" for the sake of eliciting a "wow" response. Surely the reason the quantum behaviour changes is more mundane. Surely the behaviour changes not because "humans are watching" but rather because "when humans want to watch they stick apparatus in that muck up the experiment". The problem is that nobody is ever willing to explain precisely how humans "watch" the experiment so we can never explore this more sensible explanation. Maelin (Talk | Contribs) 02:13, 10 January 2009 (UTC)[reply]

Many people are willing to explain, in fact we have an article about it. Note how that article has a "confusing" tag on it? That reflects why "because humans are watching" ends up being the explanation - the concepts are much more deep than why my car wouldn't start this morning in the rain. The incredible ineffable bit is in my comment above, when you use entangled photons and send them to two different experiments, and by "ruining" one experiment, you ruin the other one a mile away, at exactly the same time. That's like explaining why none of the cars started today. Steve already said, it's WEIRD!!! Franamax (talk) 12:15, 10 January 2009 (UTC)[reply]

dextrose & ct scans

why must dextrose be held for a period of time prior to performing a ct scan? —Preceding unsigned comment added by Cecollins64 (talk • contribs) 10:11, 7 January 2009 (UTC)[reply]

Have you read our article on Computed tomography? --Jayron32.talk.contribs 13:25, 7 January 2009 (UTC)[reply]

I can't see anything in that article that's relevant; perhaps I've overlooked it. In any case, I suspect that our questioner may be thinking of a PET scan (or a combined CT/PET scan) rather than a CT scan per se. The PET scan article indicates that dextrose should be held if the PET scan uses fluorodeoxyglucose (FDG) as its tracer molecule, as glucose/dextrose etc. would compete with the tracer for uptake. - Nunh-huh 13:58, 8 January 2009 (UTC)[reply]

Darting PVDF membrane magic trick

I recently prepared a peice of PVDF membrane by soaking breifly in methanol, and then transfering to a container of water. I noticed that the strip of membrane darted around the container, hitting the sides and bouncing back. Eventually it slowed down and stopped but what caused this? --129.125.160.178 (talk) 13:40, 7 January 2009 (UTC)[reply]

Sounds like Brownian motion. Apparently some reaction took place which gave off energy that became motion. Hopefully others will have the specifics. StuRat (talk) 18:54, 7 January 2009 (UTC)[reply]

Brownian motion only is visible at the microscopic level, it is probably osmotic pressure. Graeme Bartlett (talk) 21:01, 7 January 2009 (UTC)[reply]

The behavior sounds more like you get when you drop a small piece of dry ice onto water - the rapid liberation of gas from the dry ice makes it behave like a hovercraft and it rapidly zips around the surface. If this membrane absorbed a ton of methanol and then for some reason caused it to evaporate out when it came in contact with the water - then the methanol vapor would make it zip around like that. Sadly, I don't know enough about this weird membranous stuff to comment further. SteveBaker (talk) 15:47, 8 January 2009 (UTC)[reply]

Scabies

What causes intense itching in scabies? —Preceding unsigned comment added by 59.103.69.8 (talk) 14:34, 7 January 2009 (UTC)[reply]

Our article gives two causes: "action of the mites moving within the skin and on the skin itself", and "presence of the eggs produces a massive allergic response" - Nunh-huh 15:07, 7 January 2009 (UTC)[reply]

you better have an explanation for this

This question has been removed. Please do not start debates or soapbox on the Reference Desk. Matt Deres (talk) 17:10, 7 January 2009 (UTC)[reply]

I (Matt Deres (talk)) have reinstated the question:

In my heart I know that God simply cannot exist. Yet I keep finding things that seem to debunk current "scientific" understandings of how the universe, the earth and humanity came to be. How can there be identical lines of DNA coding in identical order for the structure of an eye in an octopus as in a human when they aparently evolved seperately and the order of the sequence wouldn't effect the program the lines were switched? Why do people cling to the idea that fossils don't form for millions of years when a quick trip to the local quarry will present fossilised mining equipment and boot prints? Why do we still place our faith in carbon 14 dating when it has proven inaccurate every single time sombody has tried to trick the system? Is there really a single scrap of evidence that supports evolution over intelligent design? Can anybody show me an intermediate fossil of any missing link which hasn't been found to have been tampered with? When Dawkins himself is saying that the only plausible explanation for this particular universe happening is that there are infinite parralel universes with every posibility, siting the existence of this universe as proof of this theory, what seperates the Athiests from every other faith based religion? —Preceding unsigned comment added by 194.80.240.66 (talk) 16:53, 7 January 2009 (UTC)

OK - I'll bite:

In my heart I know that God simply cannot exist. - If you want to treat things as a scientist then the "in my heart" stuff has got to go. You need a reason.
Yet I keep finding things that seem to debunk current "scientific" understandings of how the universe, the earth and humanity came to be. - When that happens, scientists get very, very excited - because it means we can learn something new.
How can there be identical lines of DNA coding in identical order for the structure of an eye in an octopus as in a human when they aparently evolved seperately and the order of the sequence wouldn't effect the program the lines were switched? - What makes you think that's true? I doubt very much that enough research has been done into the DNA responsible for the development of eyes in Octopii and Humans to know this. Where did you find this information? Sure, there will be proteins and other structures that are common between the two systems - but that's because those chemicals were probably used for something else before they came to be used inside eyes - and hence they would have evolved prior to the last common ancestor of man and cephalapod. My inclination is to yell "BOGUS!!!" at this claim - until/unless there is some solid proof that it's true.
Why do people cling to the idea that fossils don't form for millions of years when a quick trip to the local quarry will present fossilised mining equipment and boot prints? - Eh? There is no fossilised mining equipment. Boot prints are a different matter - a print can fill with something like concrete that sets hard in a short period - but technically that's not a fossil. Again - I don't believe this claim. Fossils do indeed take a very long time to form...and we can easily prove that.
Why do we still place our faith in carbon 14 dating when it has proven inaccurate every single time sombody has tried to trick the system? - Sure you CAN trick the system (eg by injecting some extra carbon-14 into your sample or irradiating it with a strong neutron source). But if you DON'T trick the system - if you use it honestly - it works rather well. But this is true of ANY scientific process. If I write a scientific paper that says that the rate that a pendulum swings is proportionate to the weight of the pendulum times it's length (which is NOT true BTW) - then should everyone rush off and build clocks on that basis? Hell no! You repeat my experiment first (and you find it's wrong - so you publish a report saying why - and then nobody trusts me anymore). Trusting the scientists that did the C14 dating in any particular case is certainly important - and that's why we have things like peer review and the general principle that we don't trust the results of some experiment until it's been independantly verified. The fact that it's POSSIBLE to cheat - doesn't make the testing any less valid providing we stick to the rules for scientific acceptance.
Is there really a single scrap of evidence that supports evolution over intelligent design? - YES! Absolutely! Ask anyone who runs a hospital about how bacteria evolve immunity to our drugs. Examine the way that humans have become lactose-tolerant in response to the domestication of cattle. Actually READ Darwin's book - it's really quite compelling. (Heck - I read the bible from cover to cover - it's the least you can do to return the favor!) I'd turn the question around - where is there any piece of evidence that intelligent design is true? I've never seen anything.
Can anybody show me an intermediate fossil of any missing link which hasn't been found to have been tampered with? - Sure - go to any decent natural history museum that has rows of fossil human skulls - what's on display is likely to be replicas - however, if you politely ask the curator whether you could please examine the original bones - they'll generally find a time when you can come and do that. You'll see a set of gradual changes from something that's clearly not "human" into something that is - with very small changes at each stage along the way. It's completely compelling. This claim from the intelligent design nut-jobs that there are these enormous gaps in the fossil record is completely bogus. Bear in mind that these people are more than happy to lie to you about stuff like this - they don't have independent testing and peer review - any idiot publishes something - and the rest parrot it as if it were truth. Take nothing on trust - go to a good museum and see for yourself.
When Dawkins himself is saying that the only plausible explanation for this particular universe happening is that there are infinite parralel universes with every posibility, siting the existence of this universe as proof of this theory, what seperates the Athiests from every other faith based religion? - I don't recall hearing or reading that Richard Dawkins said that. However, he's just one more person who has an opinion - your use of "himself" as though he were some great high-priest of science and/or atheism shows your need to have a heirarchy of priests telling you how to think. The world of both science and atheism don't work like that. He's just another guy with an opinion...and sometimes (albeit rarely) he's wrong.

We don't know (and almost certainly CAN'T know) about the existence of parallel universes. I personally find them to be a rather elegant (if deeply weird) explanation for things like the 'Schrodinger's cat' thought experiment - but there are no solid reasons why the alternative explanations involving the effect of observers on wave-function collapse is an equally valid explanation that is only slightly weird. Certainly, the explanation of why the universe happens to have the properties it has comes down to something like "well in order for there to be thinking beings to ask the question - it has to be how it is". So either the universe just happens to have properties that are suitable for us...and that's all just a coincidence...or perhaps no matter what properties the universe might have, some form of intelligent beings would have arisen - and it just happens that it come out this way...or PERHAPS it was all magicked into existance by The Great Pink Aardvark In The Sky...or perhaps there are an infinite number of parallel universes and the ones that have properties close to the one we happen to live in all have intelligent beings asking this question on THEIR Wikipedia reference desks. I don't think we have an answer for that one. Occam's razor (which is a great principle to live by) says that we should pick the simplest explanation until we have evidence to the contrary - so "it's all just a coincidence" is probably the best guess that most scientists would give...although if they are honest, they'll add "but we don't know for sure". Science is not 'finished' - there are things we don't know yet. It's still possible that something like string theory will come up with a reason why the fundamental constants of the universe come out the way they are - it's possible that there is some simple reason why the speed of light is what it is - why the charge on the electron is just right for making atoms and molecules work. Certainly you can be an atheist without subscribing to the "many worlds hypothesis".

SteveBaker (talk) 17:33, 7 January 2009 (UTC)[reply]

I'd also like to add, that while science will never be able to provide all the answers, as there's always more to learn, the same is true of religion. Just as we don't really know the reason for the existence of the universe, saying God created it doesn't help, as we then need an explanation for where God came from. If you accept that God was always there, or just mysteriously popped into existence, how is that any different from accepting that the universe was always there or just mysteriously popped into existence ? StuRat (talk) 18:50, 7 January 2009 (UTC)[reply]

Anyone who has spent any time in the usenet talk.origins debates would immediately recognize the questions above as creationist trolling, notwithstanding the "I believe God doesn't exist" disclaimer preceding them. I see this so often from creationists, it's hard for me to assume good faith here. ~Amatulić (talk) 19:08, 7 January 2009 (UTC)[reply]

I agree - but if you simply delete or refuse to answer, that will be a victory for the nut-jobs. "You suppressed me" is a rallying cry. So - I prefer to take the OP at face value, answer the questions as posed as honestly and accurately as possible...pretty much what we always do around here. Nothing the OP said is hard to explain or refute - except for the things that don't seem to be true. I'd be VERY surprised if there was any evidence that Octopus DNA has similar coding to Human DNA for the process of eye development. If there is no evidence for it - then it's almost certainly untrue. I have no clue why ANYONE would imagine that construction equipment becomes 'fossilised'?!? That can only be a misunderstanding of what the term means. All we can do for the people afflicted with this terrible meme-infection is to try to educate. It's what we do here. SteveBaker (talk) 19:35, 7 January 2009 (UTC)[reply]

It's at least controversial that the octopus and the human eye represent convergent evolution, as previously thought. There is about a 70% genetic similarity, probably traceable to a conserved ancestral gene set. For a discussion of the genetics of the convergent evolution of the camera eye, see Ogura, Atsushi (2004). "Comparative Analysis of Gene Expression for Convergent Evolution of Camera Eye Between Octopus and Human" (PDF). Genome Research. 14: 1555–1561. Retrieved 2009-01-08. {{cite journal}}: Cite has empty unknown parameter: |month= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help). It's not the data that's suspicious, but rather the idea that the data somehow does anything but support evolution. It's a good example of science being self-correcting (as new data is obtained, understanding changes), and nothing for creationists to be shouting "Aha!" about. - Nunh-huh 01:05, 8 January 2009 (UTC)[reply]

The problem with the creationist/ID people's take on data like this is that the work isn't done yet. I'd have no problem with their extreme brand of scepticism if only they applied the same standards to their own theories. Where are the peer-reviewed journals? Where are the chains of logic and evidence for this nutty idea they have? I can't be merely sceptical about their stuff because they don't HAVE any stuff. There is some dogma - but zero evidence. SteveBaker (talk) 03:27, 8 January 2009 (UTC)[reply]

I cannot help quoting myself from these desks. I apologize for this. So, I have a theory about the existence of God, that may possibly be of some help. I am convinced, with some good arguments indeed, that God exists, and does not exist, at the same time. This may sound contradictory at a first glance; but after a short reflection, you'll agree there is no real contradiction; clearly it looks paradoxical to us just because our mind is limited. But if you think, anybody is able to just exist, or, just not to exist: evidently God, in his/her omnipotence, is able to do both simultaneously. Of course I can't prove this as a theorem, but I wish to remark that this principle allows to explain quite easily any Religious Dogma, Sacred Mystery etc. (for instance: the Trinity Mystery, 3=1, follows as an exercise from 1=0). Moreover, this principle embraces and welcomes all different points of view in matter of faith and religion, including the heretical and the schismatic ones, and even atheism, and in fact smooths their differences, which are a source of animosity and misunderstanding between men. I am, correspondingly, believer and not believer at the same time. A position very suitable for tolerance indeed, and I am delighted to confront it with any other one (who created the stars? God. When? Never. etc)--PMajer (talk) 01:17, 8 January 2009 (UTC)[reply]

Great - so you have a theory. It's not falsifiable so I can't prove it's not true - and you have no evidence so you can't prove that it IS true. The trouble is that I could sit here all day and all night for weeks and weeks and type in other theories...my current 'Pink Aardvark' theory for example - the Russel's teapot-in-orbit-around-Mars theory. The problem for every thinking being on the planet is to know which theory to pick. Why a here-but-not-here-God and not a bunch of pink aardvarks? You have no evidence - neither do I - I can't disprove yours and you can't disprove mine...but the problem is that there are a million - or a billion - or a trillion of my crazy ideas and only one of yours. Mine are all just as plausible as yours. With no way to choose between them - they are all just as probable. So what are the odds that your's is true? Zero...near as dammit. So as rational beings, our only LOGICAL conclusion is that there are no gods - and that things that are unfalsifiable might as well be ignored - at least until we have some pretty solid evidence. It's POSSIBLE that you're right - but it's utterly, astronomically improbable. So I call "BOGUS" on your theory...like every other religion on the planet it's a complete pile of crap. SteveBaker (talk) 03:11, 8 January 2009 (UTC)[reply]

hey, hey, that's just irony... which doesn't mean I'm not serious. I personally do not feel the religious problem, nor I feel the need of having any belief about it more than about the teapot. But I equally respect who has a religious faith and who has not --with a small personal sympathy for the latter, statistically. But: as long as they remember that their belief is just a personal belief (in particular, that has nothing to do with science). So, I strongly agree and sympatize with what you wrote, except your last sentence, to whom I give, I'm sorry, a kind of self-referencing collocation.--PMajer (talk) 10:46, 8 January 2009 (UTC)[reply]

Your theory has certain resemblances to negative theology, PMajer. Deor (talk) 13:51, 8 January 2009 (UTC)[reply]

I hope you liked it. I invented it expressly for discussing with creationists, as a young student, one day that they knocked at my door, having great fun. And to their credit, they gave to my theory much more credit that I have gathered here --that's no problem of course, it's kind of friendly fire that I'm used too (after all Matt Deres knew very well what he did when removed the OP). So, I give you my theory for free, should they knok at your door too. As to the originality issue, I'm sorry to firmly decline any resemblance with negative theology ;) --PMajer (talk) 15:47, 8 January 2009 (UTC)[reply]

I cannot help quoting myself from these desks. I'm sorry - where was the quote? Anyway, if you want a good argument for the existence of god(s), how's this one? I'll even use science against itself. According to the many worlds interpretation of quantum mechanics, there may be an infinite number of alternate universes. If there are an infinite number of alternate universes, it is inevitable that god(s) will exist in at least one of these universes. After all, if an infinite number of monkeys can type out the script for Hamlet, an infinite number of universes will have god(s) in at least one of them. Now, where do I collect my Nobel prize? :) 216.239.234.196 (talk) 13:52, 8 January 2009 (UTC)[reply]

In one or more of these universes, for sure; most likely even in the present one according to it's level ;) --131.114.72.215 (talk) 14:02, 8 January 2009 (UTC)[reply]

There are several problems with '216s suggestion:

We don't know that many-worlds is true. We may never know that it's true - it's a neat explanation - but it's absolutely unfalsifiable right now - so it's up there with the teapot, the aardvarks, and god(s). Invoking an unfalsifiable claim in order to "prove" another unfalsifiable claim is exactly like me saying: "The universe is ruled by Pink Aardvarks and I believe that Pink Aardvarks create gods as a kind of hobby. Hence god exists."...that's an unbelievably stupid argument - but it's logically no different than claiming that god must exist because there are infinitely many universes when we can't prove that there are infinitely many universes.
Most versions of many-worlds say that the laws of nature would be the same in all of the universes because they are all created as a result of quantum events such as Schrodinger's cat. You stuff the cat into the box - the poison gas is either released by a quantum event or not - our universe splits into two copies that are utterly identical EXCEPT that the poison gas is release in one and not in the other. In this (more likely IMHO) version of many worlds, the only differences between them are the consequences of all of the quantum events since the big bang. However, it doesn't seem likely that the speed of light or the charge on the electron would be any different in any of those other universes. If the laws of nature are identical in all parallel worlds then gods (which require 'magic' in order to make them omnipotent) can't exist in the other universes any more than they can in this one. That busts your argument wide open. However, you may choose to define "gods" as "super-advanced life forms" and note that "any sufficiently advanced technology is indistinguishable from magic". But these so-called gods still can't fly faster than the speed of light or precisely measure both the position and momentum of an electron. Hence they are neither omnipotent nor omniscient - which I think disqualifies them from the "God" title for most religious nuts.
So maybe you're right - but who cares? These gods could not possibly affect us in any way shape or form - so we needn't bother worshipping them or fretting about whether they are planning to send us to hell for our little indescretions where we'll be tortured for an infinite amount of time by those guys with the pointy tails, tridents and bright red skin.
If you accept the common definition of a god as "a creature with omnipotent powers" - something with literally no limits on capability - then your claim that there are an infinite number of universes containing gods which (because they have literally no limits on their powers) would allow them to be able to cross the boundaries between universes. This would inevitably lead to an INFINITE number of them deciding to come to our universe and an INFINITE number of them would be messing around in our lives. An infinite number of them would choose to manifest themselves. If you believe THAT then you have a huge problem with the whole worship thing! No matter which one you pick - you're in deep trouble with the other infinity-minus-one of them!

So - no - you don't get to sneak God past the laws of physics like that. This is another very stupid theory. Sorry. SteveBaker (talk) 15:27, 8 January 2009 (UTC)[reply]

I think 216 was ironic too --PMajer (talk) 19:44, 8 January 2009 (UTC)[reply]

If so then both you and 216 need to stop making "ironic" posts because as far as most of us are concerned, the appropriate adjective is not "ironic" - it's "wrong". Stick to writing the truth please. (Personally - I think you're just falling back on that when I shred your crazy theories into teeny-tiny shreds with rather elementary logic.) SteveBaker (talk) 00:17, 9 January 2009 (UTC)[reply]

Steve, maybe you need to start asking if people are being ironic if their comments seem absurd. You seem to find it difficult to tell, even when it is the sort of thing that the person writing would have likely believed impossible to misunderstand. These were people who were actually supporting what you were saying, attempting to demonstrate the absurdity of some opposing views. There's nothing wrong with asking (particularly in a text-environment), and this could have been much jollier. :) 130.88.52.75 (talk) 17:40, 9 January 2009 (UTC) [reply]

Maybe you are right that irony is not appropriate here, and could be misleading for a simple-minded reader. Ok, bye. PS: As to my poor theory, it's even too kind of you to give it a microsopic, still non zero probability... thanks (you know, there is inside a minor problem with the Principle of contradiction... have a look to it btw, just to improve your elementary logic)--PMajer (talk) 14:07, 9 January 2009 (UTC)[reply]

Along with quite a few other people on the science and computing desks - I have Asperger's syndrome - and telling whether people are joking or being ironic is EXCEEDINGLY difficult for me because I can't put myself in your head as most people can. Hence, I have to take your words at face value and reply accordingly. Your reply didn't seem at all absurd - just WRONG...no more and no less wrong than many of the other posts to this thread. So it's not just 'simple minded' folk who'll have problems! In online conversation, you have to 'write defensively' - assuming that things that you don't say clearly (such as things that are intended as irony) will likely be misinterpreted. <joke>Feel free to use fake <irony> tags where necessary!</joke>SteveBaker (talk) 20:12, 9 January 2009 (UTC)[reply]

Steve, you know you have difficulty spotting irony. I assume you allow for this in everyday life, and people who know you also allow for this. Those of us here who know you well enough to realise the problem also allow for it. But since you are aware of the problem, when someone who cannot reasonably be expected to know you well enough to allow for this says something ridiculously wrong it would help if you considered the possibility that this could be irony. You could then ask them (indicating that this is a real question, because you have difficulty telling). All would be well. 79.66.109.89 (talk) 17:41, 10 January 2009 (UTC)[reply]

You don't need to has Asperger's to have difficulty spotting irony in written communication between people from different cultures with different native languages. It's important to take that into account when writing stuff. I think 216 did take it into account, though - the comment in question does have a ":)" at the end, which would normally suggest it isn't meant to be taken seriously (";)" would be clearer, though) - Steve probably missed it. --Tango (talk) 19:19, 10 January 2009 (UTC)[reply]

Simply sticking a smiley on the end of an entire paragraph quite utterly fails to convey the intended meaning. I saw the smiley - and paid good attention to it - but it seemed to me to apply only to the "Now, where do I collect my Nobel prize?" sentence at the end (which clearly WAS intended as a joke). Then when people say things like: "hey, hey, that's just irony... which doesn't mean I'm not serious."...I doubt that even the most capable non-Aspie could make sense of that! SteveBaker (talk) 15:29, 11 January 2009 (UTC)[reply]

It's not fair play to stir up debate and then object to the form your counterpart's discourse takes. I'm just sayin'. --Milkbreath (talk) 14:13, 9 January 2009 (UTC)[reply]

I appologize. I didn't mean for that post to be taken seriously. Anyway, it is not merely a very stupid theory, it is absurd. 216.239.234.196 (talk) 16:56, 9 January 2009 (UTC)[reply]

I don't think you need to apologize. Your joke was funny and with its sort of social utility. You even put a ":)" should one risk to take it seriously...--PMajer (talk) 19:03, 9 January 2009 (UTC)[reply]

Steve, as I said, it's no problem for me being misinterpreted when I am ironizing. The problem with irony is that one can not ironize saying "I'm ironizing", because that would kill the ironic effect --I suppose you know it very well as you are suggesting ironically the use of "irony tags". I was really convinced that was impossible to misunderstand "his/her omnipotence" or "1=0 implies 3=1" however. Anyway, I took my risk and then I found quite funny, and not at all offensive, finding myself victim of friendly fire, as I wrote. Your further reaction however sounded somehow authoritarian and priest-like (stop ironizing... write the truth...). Notice, by the way, that the hate of laughing, seen as diabolic manifestation, is an old Christian Church theme, an evergreen in fact. As to the truth, of course I do not have it, nor it is aim of science to get it, so I just can't write it. But I also understand that after you gave a very clear and valuable point-wise response to the OP, it might appear somehow a lack of respect towards science, or towards you, that somebody added an unnecessary remark, so that's no problem also. Anyway, the content of my ironical post was no joke, it's a remark that I believe important to repeat, although obvious. I agree that religion, when used to explain phisical phenomena, as pseudo-scientific theories like creationism claim to do, is bogus. The main and first reason (IMHO) being, that assuming that God sends comets does not even explain if there will be another one, not to say when. Nevertheless, as a personal, inner belief, religious faith has to be respected; which should be an obvious thing, and it is not in practise, as far as I can see reading news. Faith has to be respected even because we have no logic nor probabilistic argument against it. You can well argue that white-beard God is as likely to exist as one of the N = one Googol other weird mutually-exclusive deitys, including all Pink Aardvarks, just by an indifference principle, and that therefore each of them has probability not more than 1/N to be true. But this is quite a weak argument, for I can say that indifference is a good principle for you in absence of other reasons for you, but as I like spaghetti, Spaghetti Monster for me is kind of special, and not at all like the others, so I am free to grant him a larger probability. Or I can also say: ok I'm democratic, let's give equal probability to each weird deity, but then the same probability also to "no gods at all". As a result I get quite certainly one weird deity that I'm happy with --no matter which one it is, since I'm democratic (this was the content of 216's intelligent joke, as I intended it). Then you have to admit that "no gods at all" is a special hypotesis for you that you grant with a larger probability than existence of werid deitys. It's ok for me, but then our probabilistic proof of unconsistency of gods falls in a petitio principii: God has probability zero beacuse has probability zero. I personally do not feel the need of giving any measure of certainity to neither hypotheses, I am not even curious to know if there is a God or not. As soon as it remains a personal choice, let everybody be free of believing or not. The point of course is that we have to fight improper use of faith like: "since my God is omnipotent and he gave me this land, this land is mine", or "since my God is omniscient and gave me this booklet, what is written here is true", or "since my God knows all about sex, you shall do it this way and not that", or "my God gave you your life so you are not free to die". --PMajer (talk) 19:30, 10 January 2009 (UTC)[reply]

Does this represent inertia?

If I drop an egg on to a hard surface and the egg Breaks (obviously). Is this a representation of inertia at work?? —Preceding unsigned comment added by 65.184.51.249 (talk) 17:47, 7 January 2009 (UTC)[reply]

Eh... inertia is involved, to be sure, but I wouldn't consider that a good representation of "inertia at work" -- I'd think it's a better representation of acceleration/g-forces and structural load limits. Specifically, I don't think the tendency of the egg, or of the egg's contents, to remain in motion is what causes the egg to break.

I suggest that examples a fixed force on differently massed objects would be a more clear representation -- for example, it's easier to impart motion to a baseball than a shotput (a mass difference factor of about 50). — Lomn 18:08, 7 January 2009 (UTC)[reply]

Urgh...kinda related. Newton's 1st law (which is really talking about inertia) says that an object will keep moving in a straight line at constant speed until acted on by an external force. So your egg is trying to move at constant speed until it hits the hard surface. The inertia of the part of the egg furthest from the surface is still trying to do that when the front end hits...so it's resistance to that change in speed is what imparts a force against the surface. So the egg has to decelerate to a stop - and because F=ma (yep - that Newton fellow again...the second law this time) that accelleration imposes a force against the surface. Then (because every action has an equal and opposite reaction - per Newton's third law) the surface has to push back with an equal but opposite force...which cracks open the egg. So I suppose you could maybe argue that inertia started the whole chain of events (which in reality is just one event). If the egg had no mass or no velocity - then it would have had no inertia and it would have simply stopped without breaking. But the first law is really just a special case of the second. When F=0 (there is no force acting on an object), and m > 0 (it has mass) F=ma says that 'a' has to be zero...so no accelleration is possible. If you look at it like that, then the whole 'inertia' thing is a bit of a non-event because it's just a special case when there are no forces lying around. So I dunno. There are better examples. Swing an object around on the end of a piece of string - then let go of the string. As soon as the force due to the tension in the string drops to zero - the object goes off in a straight line...which is a perfect example of inertia in action. SteveBaker (talk) 18:30, 7 January 2009 (UTC)[reply]

This reminds me of bad test questions I always had, where the answer was "kind of, but not really". Unfortunately, they were always true or false questions and I never could quite guess which way the teacher was going to rule. StuRat (talk) 18:37, 7 January 2009 (UTC)[reply]

I'm going to go ahead and say "No". The law applies to objects not being acted on by outside forces. The law says nothing about when happens when you DO apply an outside force. So the only cases you can say Inertia applies is when there are no outside forces, or more realistically, no significant outside forces. In this case we have two forces: The force of gravity and the force of the ground acting on the egg. Both of these forces are significant since without either one the egg would not break. Anythingapplied (talk) 23:36, 7 January 2009 (UTC)[reply]

If an egg was on the seat of a moving car,going, say 60 miles per hour, not constrained from moving forward, and you suddenly applied the brakes, the egg would continue moving forward until it hit something. It might break on the dashboard. This is why wearing seatbelts/shoulder straps is a good idea. Edison (talk) 23:47, 7 January 2009 (UTC)[reply]

.249, are you sure you didn't mean to say entropy rather than inertia? Because, yes, the fact that intact eggs break all the time but broken eggs never become intact is a classic example of increasing entropy. --Sean 13:03, 8 January 2009 (UTC)[reply]

Buying Optical fiber

How much does it cost? (an estimation is enough) Where can I buy it? (and similar things) --Mr.K. (talk) 18:27, 7 January 2009 (UTC)[reply]

A Google search on "Buy optical fibre" turned up many possible places. However, you need to be MUCH more specific about what you need. There are many different things called "optical fibre". There is cheap, short glass fibre that is used in things like toys and those lamps that are made from a bundle of fibres. There is hugely pure glass for which a 20 mile length of the stuff is more transparent than a single pane of window glass. There is single-mode and multi-mode fibre which had graded refractive index that varies from the core to the outside to better 'steer' the light...there are bundles of fibres where the arrangement of the fibres is identical on both ends of the 'cable' so you can send pictures through it. There are bundles of fibres that are just to get light from A to B where the fibres can be all muddled up inside the cable. There are fibres encased in various sheaths to protect them and there are bare fibres with no sheaths. The length you need makes a MASSIVE difference to the price. If there are connectors on the ends of the fibres - or if the ends are cut at precisely 90 degrees and carefully polished so they make a good optical connection - then that's yet another parameter. In short - I can't give you even an estimate on price. But do the Google search and you'll find out for yourself. SteveBaker (talk) 18:37, 7 January 2009 (UTC)[reply]

If you don't want to buy them for industrial purposes, but for a DIY project you could try a company that buys electronic scrap. Old copiers and fax machines have a strip of (rather short) good quality optical fibers. Apart from that, as Steve said we can only guess. Lisa4edit76.97.245.5 (talk) 23:40, 7 January 2009 (UTC)[reply]

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

Contents