Wikipedia:Reference desk/Archives/Science/2009 October 12

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October 12

Rattlesnake Anti Venom avalibility

I did not get bitten but it sure was close today when I almost stepped on a very large Timber Rattler.

We both startled each other and I sure did jump quick. The snake is still alive and out behind the house somewhere as I don't kill wild animals that have as much right as I do to live.

My question goes more to "What if" I had been bitten and needed the Anti Venom quick.

Do hospitals keep this stuff on hand?

How long might it take for the hospital to locate it and get it in an emergency?

I live in the NY Catskill Mountains, Sullivan County. These snakes are here but not very common, I have seen only 3 in almost 60 years. —Preceding unsigned comment added by Gamalot52 (talk • contribs) 00:33, 12 October 2009 (UTC)

It is my understanding that US hospitals keep antivenoms for all native snakes. As for how long can the hospital locate it? I'm sure they could have it to you quicker than it would take them to identify the snake. In any case, be careful. By all accounts, rattlesnakes hurt a lot, and can make you pretty sick. Call your local hospital and ask. They'll know if they have it on hand. Falconus^{p t c} 01:48, 12 October 2009 (UTC)

In my experience as a medical student in Kentucky, your antivenom would have been CroFab. It's expensive. If a small hospital were to stock it, have no patients, and let it expire, it would cost the hospital thousands of dollars per vial [1] and several vials are necessary to treat even one adult. This scenario is very likely given the sporadic nature of snake bites. Thus by pure economics, most small rural hospitals will not have it on hand, and you would be transferred to a tertiary care center if you really needed it. - Draeco (talk) 05:56, 12 October 2009 (UTC)

Why is sneezing convulsive?

As we now know, many animals sneeze. That's understandable, but why does it have to be convulsive - why does the individual have (almost) no control over it? Why can't it be just like other processes that clean the body (defecation and urination), that give the individual some discretion about the timing? It's not hard to think of circumstances in which it could be disastrous for an animal to sneeze at the wrong time - such as a when it means being detected by a predator or prey. I doubt that it's always of such life threatening importance that it has to be done immediately. Waiting a bit, while just breathing through the mouth for the time being, seems like a much better adapted alternative. Why can't we do that? — Sebastian 00:45, 12 October 2009 (UTC)

Coughing is a similar deal though - we can't help doing that either. SteveBaker (talk) 02:54, 12 October 2009 (UTC)

You're right. But coughing is convulsive for a reason: If something's stuck in our windpipe, we need to get it out quickly before we suffocate - there's no way to bypass the windpipe by breathing some other way. — Sebastian 03:02, 12 October 2009 (UTC)

Actually I remember reading somewhere that if a human isn't systematically toilet trained from a young age then they will most likely fail to develop an ability to control when they go to the toilet, to a greater extent. I think the fact that you have mucous membrane in your nose and throat probably plays a large part, it's probably more sensitive to infection and such, so there is probably a biological advantage to not let dirt or whatever sit on your membranes for longer then possible. Vespine (talk) 04:57, 12 October 2009 (UTC)

So i just had a quick read of the mucous membrane article and it actually says that the mucous acts against infection by trapping it, i'm sure it's still more prone then epidermis and your body still probably rather avoid (relatively) large bits of dirt sticking to it. Vespine (talk) 05:01, 12 October 2009 (UTC)

Its thought that the ancestral mammalian condition was obligate nose breathing (that is, our evolutionary predecessors used to only be able to breathe through their nose, and not their mouth). For many (but not all) non-human mammals that is still the case. Thus having a semi-autonomous mechanism in place to clear the airway of obstruction/infection would be quite advantageous, as Sebastian notes about coughing. Note also that human neonates are pretty much obligate nose breathers for the first few months, so they don't really have the option of waiting a bit, while just breathing through the mouth for the time being. I expect uncontrollable sneezing is a physiological artifact from before oronasal breathing was an option. Rockpocket 06:53, 12 October 2009 (UTC)

Thanks, that sounds plausible! — Sebastian 15:58, 12 October 2009 (UTC)

I frequently can control coughing and sneezing. Also, just because you can't consciously control something doesn't mean you can't unconsciously control it. The sneeze and cough responses may well be suppressed during times when they would cause trouble, such as when sleeping or hiding. StuRat (talk) 15:23, 13 October 2009 (UTC)

Interesting! From Vespine's post, I conclude that you must have been hanky trained as a child! And you're right, unconscious control would address the predator/pray situations I mentioned. This non-RS says "Experts say that you cannot or one is incapable of sneezing while at sleep." (With a quick google search, I couldn't find research on that, but I did find this related discussion.) But if it's true that we can't sneeze in our sleep, doesn't that negate the assumption that sneezing is vital to prevent us from suffocating? — Sebastian 16:44, 13 October 2009 (UTC)

"Can't sneeze" is a bit strong. The response is somewhat suppressed at times, but you would still sneeze if you really needed to, such as if someone blew pepper up your nose. StuRat (talk) 21:45, 18 October 2009 (UTC)

Windmill? Wind turbine? Wind Widget?

The article windmill makes it clear that that term refers to a wind powered grinding mill. Wind turbine refers to a wind powered electrical generator. These two devices have something in common, a big spinny bit. What is the spinny bit called? I'm looking for a name that includes both windmills and wind turbines, but excludes other similarly appearing spinny bits, such as propellers.

Alternately, I'm asking this question. What is the name for a device which captures wind energy, regardless of what purpose that energy is channeled into?

gnfnrf (talk) 01:25, 12 October 2009 (UTC)

Does this diagram help? Intelligentsium^review 02:07, 12 October 2009 (UTC)

They are called sails - see Windmill_sail. Exxolon (talk) 02:09, 12 October 2009 (UTC)

They seem to be called "sails" on a windmill and "blades" on a wind turbine. I guess it depends on their shape and purpose; blades are designed to move a lot faster.--Shantavira|^{feed me} 07:57, 12 October 2009 (UTC)

As far as I can tell, it looks to me like the difference between a sail and a blade may be a matter of the construction. A sail is generally made of a flexible material attached to a rigid frame, whereas a blade is one solid rigid piece. So modern wind turbines uniformly have blades, old-style windmills have sails, and typical (relatively) modern windmills as were commonly found in the American West have metal blades. I'm not certain that's the defining distinction between a sail and a blade; I'm just making an observation based on how the terms are used in the windmill and wind turbine articles. Red Act (talk) 12:23, 12 October 2009 (UTC)

The third sentence of the windmill article implies, without making it quite clear, that in popular parlance they all tend to be called windmills. If you read the whole article carefully, you'll see that the word is in fact used therein to refer to devices other than grist mills. I know that I've never heard the water-raising devices used on the American plains (as described in the section Windmill#In Canada and the United States) referred to as anything other than windmills; and the existence of articles such as Boardman's Windmill and List of drainage windmills in Norfolk suggest that usage isn't confined to grist mills in England, either. Deor (talk) 12:31, 12 October 2009 (UTC)

In fact, the more I look at the lede of the windmill article, the more it seems to me dead wrong. If you look at the dictionary definition linked in note 2 of the article, you'll see that windmill is in fact the correct word for any "device which captures wind energy, regardless of what purpose that energy is channeled into." Deor (talk) 15:23, 12 October 2009 (UTC)

Mytoses question

In my Biology class, we are doing a experiment about cells and mytoses (or howrevr you spell it. There's a question I can't figure out, and the page here is to complicated for me. The question is "What two differences are apparent at the poles of plant and animals cells?" (during mitoses). I thought the difference was that there is only a cell wall in a plant cell, but not in a animal. But there have to be 2! I've already tried, could someone explain it to me? Im not aksing for you to gimme the answer, just to explain. Help would be appreciated! Warmly, --Amber. —Preceding unsigned comment added by 69.210.134.227 (talk) 02:04, 12 October 2009 (UTC)

Mitosis -- you're sort of asking for the second difference. If you'd tell use what you don't understand about the second thing, we can explain it to you in easier-to-understand words. DRosenbach ^{(Talk | Contribs)} 02:30, 12 October 2009 (UTC)

It's spelled mitosis; please check out that article, it mentions at least two differences. — Sebastian 02:31, 12 October 2009 (UTC)

I checked the article -- and it doesn't specifically speak of two differences at the poles. Perhaps there are unmentioned differences, such as regarding the asters, the microtubal arrangements, the centromeres/-somes, etc. I'd hardly say that cleavage vs. cell wall formation occurs "at the poles." DRosenbach ^{(Talk | Contribs)} 02:33, 12 October 2009 (UTC)

You're right - I just didn't read the question thoroughly. Your reply was better than mine anyway; mine was only there due to an edit conflict, so I am striking it. I do take exception to your editing my reply though; it was meant as a reply to the question, not to your reply, and I'm undoing that herewith. — Sebastian 03:38, 12 October 2009 (UTC)

Higher plants have neither centrioles nor their product centrosomes. Perhaps that's your answer - Draeco (talk) 04:47, 12 October 2009 (UTC)

Silver in a plastic cutting board - antimicrobial/antibacterial or just BS?

I see in the Silver Nitrate article that there are legitimate disinfection uses for it, but I'm having a hard time seeing how scattering a few silver (cat?)ions across a plastic cutting board can cut down on the nasties living thereon... despite what the bodacious labeling wants to scream at me.

Can someone clear this up? 218.25.32.210 (talk) 02:08, 12 October 2009 (UTC)

Probably BS. I think any antiseptic properties would be short-lived at best. Either (A) the silver is covalently bound to the plastic which is permanent but doesn't allow it to interact with bacteria or (B) it's free to dissolve in water (which is the key to most medical uses of silver) making it possibly effective during the first use but subject to having all the ions washed away for subsequent uses. Having said this, I don't know of any real scientific evidence on cutting boards in particular, and I doubt it exists. Asking the manufacturer might be your best bet. - Draeco (talk) 05:04, 12 October 2009 (UTC)

I don't know about this specific product or what material is used, and I wouldn't be surprised if a manufacturer replied with the same marketing BS (if indeed that's what it is). However, there is literature about the effectiveness of silver in this type of use. See [2] for example. DMacks (talk) 05:10, 12 October 2009 (UTC)

Abrasive toothpastes

If toothpaste (and probably dentist cleaners too) contain abrasives which are at least as hard as teeth, then what is to prevent it from wearing them down to nothing? (well, at least polishing all the way through the enamel) If I guess a molecule of enamel is at least 600pm, and you brush twice a day for 25,000 days that's 0.03 mm. The dentist probably does at least that much again with his tools and his goops. Add to that that many people have really fast toothbrushes instead of manual ones, and it's remarkable that they could put sand in it and still have it remove so little each time. Sagittarian Milky Way (talk) 02:53, 12 October 2009 (UTC)

I'm no expert on dental care products, but you began with an "if" that might be important! How do you know those abrasives are "at least as hard as teeth"? Wouldn't it be smart to make them a little harder than plaque, but softer than tooth enamel? -- Scray (talk) 03:28, 12 October 2009 (UTC)

I know for a fact that silica is harder than teeth and calcium phosphates are just as hard (Mohs scale 7 and 5 respectively). Carbonates, sufates, organics, some elements, and halides tend to be soft. It only has to equal the hardness of something to scratch it. Sagittarian Milky Way (talk) 03:53, 12 October 2009 (UTC)

I would think that toothbrush bristles do not press the abrasives against the enamel with enough force to do damage. - Draeco (talk) 04:39, 12 October 2009 (UTC)

Actually, worn down enamel at the neck of the tooth is a very common problem caused by wrong brushing technique (too much force, to vigorous back-and-forth). To avoid it, follow best practices (little pressure, circular motion) and avoid brushing when the enamel has been weakened by recent acid contact (e.g. shortly after eating fruit). --Stephan Schulz (talk) 12:41, 12 October 2009 (UTC)

This recent article[3] mentions that tooth enamel and dentin can repair themselves. Usually the body is constantly repairing small amounts of damage.Cuddlyable3 (talk) 14:25, 12 October 2009 (UTC)

Dentist here -- enamel and dentin will not repair themselves after having been worn away by overzealous toothbrushing. DRosenbach ^{(Talk | Contribs)} 23:01, 12 October 2009 (UTC)

Somehow, I'd be too lazy to push either zealously or fast even if dentistry said it was better. I'd brush more often if that were the case. Sagittarian Milky Way (talk) 03:38, 13 October 2009 (UTC)

I once asked my dental hygienist a question of this nature and she told me that teeth are organic and do regenerate themselves spontaneously. Assuming adequate health. Vranak (talk) 17:03, 12 October 2009 (UTC)

Amazing, after all you hear about cavities you would've thought it was inert as a rock. Sagittarian Milky Way (talk) 20:00, 12 October 2009 (UTC)

Suffice to say that there are many many people out there driving around very nice cars because of the widespread belief that only a dentist can keep your teeth from rotting away to stumps. Perhaps there is some truth to that notion but it's far from being the whole story. Vranak (talk) 22:45, 12 October 2009 (UTC)

Tooth enamel "remineralizes" (so said the article on the main page for October 12th). I guess this is not the same thing as growing new enamel. I haven't been to a dentist for 20 years, still have all my teeth and they still seem good. Perhaps a dentist could give them a deep clean and make them better and likely to last longer, but as you say, very nice cars. —Preceding unsigned comment added by 81.131.7.241 (talk) 20:04, 13 October 2009 (UTC)

I'm sure excessive use is harmful, as toothpaste manufacturers and the American Dental Association all give upper limits for the recommended amount of brushing. 66.65.140.116 (talk) 20:28, 12 October 2009 (UTC)

The main component contributing to tooth abrasion is overzealous brushing, hence the name "toothbrush abrasion." Without enough force, the abrasive content of toothpastes will not wear away tooth structure, and with excessive force, toothbrush bristles will cause abrasion even without any paste at all. Thus controlling for both false negatives and false positives, it is the force of the brushing and not the abrasive that does it -- the abrasives may add to the effect, but the majority of brushing time finds the toothpaste already dissipated in large part. As for manual vs. electric toothbrushes, little force used to push the bristles of the latter against tooth structure doesn't add any forces that are not present with manual brushing. DRosenbach ^{(Talk | Contribs)} 23:01, 12 October 2009 (UTC)

Let's back up a bit to discuss why toothpaste contains abrasives. During the day (or night) deposits build up on the teeth. Everyone gets a buildup of plaque, and some also get tartar. The abrasives are to wear those off. Beyond this, they may indeed wear off a bit of the enamel, but, as previously stated, it can regrow if it's worn down at a slow enough rate. And, even if your teeth are worn down too fast for this, as long as it's slow enough that you die before the enamel has a hole in it, then you will keep your teeth your entire lifetime, which is the goal, after all. I suspect that those who manage to wear their teeth down by brushing are suffering from an obsessive-compulsive disorder which causes more frequent and vigorous brushing than is recommended. StuRat (talk) 14:53, 13 October 2009 (UTC)

when is dQ different from dH?

I'm having a hard time separating these two concepts.

In addition the enthalpy article states dH = TdS which can be greater or equal than dQ?! John Riemann Soong (talk) 04:28, 12 October 2009 (UTC)

Also, I really don't get the equation H = U + PV -- how is enthalpy more than the internal energy, and why does an object having a finite volume against environmental pressure contribute to its enthalpy? John Riemann Soong (talk) 04:31, 12 October 2009 (UTC)

Enthalpy is a defined value. It means absolutely nothing. The reason it was defined that way is to simplify expressions in constant-pressure processes, which is often what happens in research. Tim Song (talk) 05:18, 12 October 2009 (UTC)

More specifically, pressure exerted on the walls of a container is itself a form of potential energy (it becomes kinetic when the walls blow out...) so even under constant pressure conditions there is potential energy which must be taken into account. The PV part of your enthalpy definition is that little bit of potential energy, which is added on to the potential energy internal to the molecules. It should be noted that internal energy is a finite and real, but immesurable quantity, a property that is passed on to enthalpy as well. Thus, we tend to deal in ΔH rather than H, since enthalpy changes should equal the total energy changes to a system as a result of a chemical change, so long as pressure does not change. In cases where the reaction vessel is open to the atmosphere, any minute pressure changes are "washed out" as the "system" becomes the entire atmosphere, and since lots of chemistry is done in open air, enthalpy is a convenient way to measure energy changes. In situations where you have a sealed reaction vessel, then enthalpy must also taken into account the changes in potential energy due merely to changes in pressure, complicating the calculations significantly. --Jayron32 06:06, 12 October 2009 (UTC)

Which is why plain internal energy is used in those cases - constant volume => no pV work => dU = dQ if there is no other work. Tim Song (talk) 06:38, 12 October 2009 (UTC)

Okay, so enthalpy is any internal energy plus that little bit of potential energy due to "previous" work done against atmospheric pressure? I'm also having a little problem with the derivation of dH.

So H = U + PV; dH = dU + PdV + VdP

since U = H - PV, then dU = dH - PdV - VdP; does dH - VdP = dQ?

I still don't know how to make sense of the difference between dH and dQ. How can the increase in enthalpy be greater than the increase in heat added? John Riemann Soong (talk) 06:45, 12 October 2009 (UTC)

If the heat added also does work; for example, thermal expansion is a form of work. The confusing thing for a chemist is that chemists don't like to think about work as a form of energy. All chemists care about is the "q" factor; heat energy changes as measurable by temperature change. However, in situations where real work is done, then that ALSO has to be taken into account. PdV and VdP are the "work" factors in your equations. All of these factors are interrelated, so its a complete mess if you are trying to work out all of the details. For example, a decrease in internal energy could cause both changes in the surroundings temperature (a change in q) OR it could do work on the surroundings. You could also envision situations where a process is exothermic, but endergonic, that is work is done ON the system, but heat is release BY the system. For us simple chemists, if we ignore work, all of this mess goes away. --Jayron32 06:51, 12 October 2009 (UTC)

Okay, yeah, I can do that with my specific situation equations ... (isobaric, isochoric, etc.) but I just want to know facts that hold universally. So, let's say I transfer 1 J of heat to a system from the environment ... the enthalpy can increase by 1 J and on top of that, work can also be done? How does that not violate some form of conservation energy principle? John Riemann Soong (talk) 07:20, 12 October 2009 (UTC)

No, if you transfer 1 joule of energy from the system to the environment (dH = - 1), that energy can do both work and heat; in other words dW + dQ = - 1 Joule. For most common processes, dW is so close to zero it might as well be zero; however you aren't doing work ON TOP OF the heating of the environment. Its just that in some situations, releasing 1 joule of energy from a chemical reaction will not result in 1 joule of heating; it may result in MORE than 1 joule of heating (if the surroundings do work on the system WHILE the system is also heating the environment) OR it may result in LESS than 1 joule of heating (if the system does work on the surroundings WHILE the system is heating the environment). Remember that dQ and dW can be opposite signs. Ignore what Dauto says below about enthalpy not obeying the laws of conservation. Enthalpy does obey the laws of conservation; unless you ignore work. If you ignore work when you shouldn't, then you are introducing an error which makes it appear to not obey the laws of conservation. --Jayron32 18:32, 12 October 2009 (UTC)

It doesn't violate energy conservation because enthalpy isn't energy (even though it is also measured in Joules). U is the internal energy that must be subjected to the internal energy conservation. From the equation H=U+PV you get dH = dU + d(PV) = (dQ - PdV) + (PdV + VdP) = dQ + VdP. And that's that. Dauto (talk) 15:00, 12 October 2009 (UTC)

So wait -- as heat is withdrawn from a system enthalpy decreases faster than U does? I'm also trying to think of this in terms of heat capacity at constant pressure versus heat capacity at constant volume. Heat capacity at constant volume is less than heat capacity at constant pressure because of the heat transfer during a constant pressure process is diverted to work i? So at constant pressure, is the q that becomes part of U less than the q that the environment gave to the system?

Also, how do I distinguish between pressure of the system and pressure of the environment? John Riemann Soong (talk) 16:45, 12 October 2009 (UTC)

If the system is isolated from the environment, in a sealed container, than the two may have a different pressure. If the system is open to the environment, then you have the definition of a constant pressure situation, which is what is required for dQ to equal dH. If you did not have a constant pressure situation, then you would have two energies to keep track of; dQ and dW (heat and work). It really doesn't matter whether we say that dQ = dH - dW or dQ + dW = dH; that is conceptually it doesn't matter whether the work factor causes us to misestimate the enthalpy or the heat if we assume that dQ = dH. However, if the reaction is open to the surroundings, then no meaningful work is done (strictly speaking, work is almost always done, but when the denominator on the fraction is the moles of gas in the entire atmosphere, then for all intents and purposes that number is so small as to be meaningless). So, to answer your question again, the two pressures are the same unless you have a closed system, and in that case, you need to account the work factor in calculating the enthalpy (the PdV + VdP). --Jayron32 18:24, 12 October 2009 (UTC)

Jayron, dH = dQ + VdP which is not the same as dQ + dW because dW = PdV

OK, yes, you are right about that bit. Technically, VdP does not represent actual work, since nothing moves; however VdP is the potential energy change generated by the change in pressure; functionally it behaves like work in this case. Its much easier to think conceptually that there are two factors here; heat energy and mechanical energy. Mechanical energy has two forms; kinetic (work) energy (PdV) and potential energy (VdP). Any deviations between Q values and H values are due to mechanical energy changes, either kinetic or potential. The crux of the OP's problem is ignoring these mechanical energy issues. Since mechanical and heat energy could be the same sign OR opposite signs, the deviation between dQ and dH could be either positive or negative. --Jayron32 19:13, 12 October 2009 (UTC)

I agree with everything you said except with the carachterization of PdV and VdP as being kinetic and potential energies. I don't see how that fits. Dauto (talk) 19:40, 12 October 2009 (UTC)

Kinetic energy means something is moving. If the volume of a container is changing (a non-zero dV) then something must be physically moving, so it is kinetic energy. If there is no movement, but there is a change in pressure, then there is a change in the force on the walls of the container, and that change in force is a potential energy. To see that, imagine what would happen if the pressure, say, ripped a hole in the wall of the container. That would represent the conversion of that potential energy into kinetic energy. Increasing pressure increases the forthcoming kinetic energy involved in such a rupture, which is the definition of potential energy. So changes in volume are kinetic changes, while changes in pressure are potential changes. --Jayron32 20:31, 12 October 2009 (UTC)

"So at constant pressure, is the q that becomes part of U less than the q that the environment gave to the system?"

Yes, that's right. If you heat the gas at constant pressure, it will expand and do useful mechanical work on the environment, which means some of the energy you put in as heat is now gone from the system (for example off powering a generator), and not included in U. Change in enthalpy includes that work portion, which is why it's larger in this case than the actual energy that ends up in the gas. Rckrone (talk) 04:37, 14 October 2009 (UTC)

map distances and multiple crossovers

So let's say I have a cis genotype AB/ab (linked on the same chromosome) test-crossed with ab/ab and I'm supposed to find the amount of progeny that will end up AB/ab. If A and B are 10 m.u. apart, is this proportion 45% or 47.5% (or something a little larger than that?). Basically, if two genes are 1 m.u. apart, is the chance of no crossing over equal to 99%, or is that the chance of having parental type gametes? I'm trying to sort this out from the idea that the longer distances lead to underestimated recombination frequency. John Riemann Soong (talk) 06:39, 12 October 2009 (UTC)

1 map unit = 1% observed recombination. Therefore, given 100 meioses containing two loci 1 m.u. apart, one would expect to see 1 with a cross over event between the loci and the other 99 will not cross over. You should be able to apply this up to your experiment, which has two loci 10 m.u. apart. Bear in mind you would start off with half (50% is the value you would get with no crossing over at all) then subtract the percentage of those alleles that will have recombined between the two loci. Rockpocket 07:10, 12 October 2009 (UTC)

blood platelets

[Removed paraphrase of existing medical question.] APL (talk) 12:48, 12 October 2009 (UTC)

Time-matter conversion

I once read about some scientist's theory that said, among other things, that time and matter are just different forms of the same thing, much like heat and work are just different forms of energy. In this theory:

• Tachyons are the elementary particle that mediates time, just like the graviton would mediate gravity.
• When tachyons decelerate below the speed of light (I don't remember the exact process for this described in the paper), they "decay" into quarks, leptons and bosons, and when matter accelerates above the speed of light, it "decays" into tachyons. Therefore, c is not an absolute barrier, just a door between the realms of time and space.
• General relativity seems to preclude the transmission of information or matter above the speed of light; this is because it fails to consider the transformation from matter into time. Therefore, the only reason that matter cannot travel above the speed of light is because when it does it automatically becomes time.

I find it difficult to accept this theory, but because I have little knowledge of fundamental particle physics, I would appreciate it very much if someone could please tell me what is the observational evidence against the above theory. Thank you. --Leptictidium (mt) 13:08, 12 October 2009 (UTC)

I don't think you need observational evidence against it - it just doesn't make sense. Time is the progression from cause to effect, it makes no sense to talk about it being mediated by a particle. --Tango (talk) 13:45, 12 October 2009 (UTC)

I think the point here is to re-think what the definition of "time" is, so replying that "time" isn't what he says it is seems a little tautological. Again, I don't know the theory, but dismissing it just because "it doesn't make sense" in a very basic explanation seems silly to me, and unscientific. As one writer put it, the theory that the Earth sits on an endless series of turtles isn't wrong because it is ridiculous, it's wrong because we don't find any turtles at the South Pole... --Mr.98 (talk) 14:41, 12 October 2009 (UTC)

Time is time. If you want to define a new concept you need to give it a new name. There is a difference between ridiculous and nonsense - the theory as described doesn't make sense, the Earth sitting on turtles makes perfect sense, it just happens to be wrong. --Tango (talk) 15:11, 12 October 2009 (UTC)

A theory is scientific only if it has Falsifiability. This one doesn't. Cuddlyable3 (talk) 14:07, 12 October 2009 (UTC)

That seems, uh, to be a little premature of a judgment, no? I mean, I don't know the first thing about this reported theory, but I do know that a lot of new theories and high-end physics sounds pretty silly and out-there for a non-practitioner, especially when it is new. --Mr.98 (talk) 14:39, 12 October 2009 (UTC)

No. To clarify, my post did not conclude that the reported theory is wrong, just that it is not scientific i.e. ameanable to the scientific method. Cuddlyable3 (talk) 16:06, 13 October 2009 (UTC)

How could the speed of light be a "door"? It's a speed, not a door. In a diagram of space or time intervals, the speed of light is the locus of points that is identical in all frames of reference and separates definitely-space-like from definitely-time-like intervals; but this is not a "door". If you're looking for an analogy, consider it more of a wall. You might want to read the article spacetime for an overview. As has been pointed out, there's not observational evidence against these postulates because they don't make claims about observable phenomena. Nimur (talk) 14:14, 12 October 2009 (UTC)

Where did you read this theory? And which scientists believe it?

I don't ask to be contrary, I ask because the way you described it, it seems very confused. Perhaps if we could see the source... APL (talk) 14:33, 12 October 2009 (UTC)

Yes, I think we'd need to know the details a little bit better to even start to get a sense of it. If it is a "real" theory and not just on-the-internet speculation, then there is likely a lot more to it. --Mr.98 (talk) 14:39, 12 October 2009 (UTC)

I wouldn't take very seriously any theory that depends on the actual physical existence of tachyons in order to make sense. It smells like crackpot to me. Dauto (talk) 16:35, 12 October 2009 (UTC)

Er, why not? I mean, yeah, nobody has any evidence yet for tachyons, and they seem a little fishy, but there's no reason that one can't say, "if they exist..." and so on. Scientists have been doing that for a long time. (Remember that there was very little hard evidence for atomism at all until the early 20th century, yet it proved a pretty useful concept before then.) Again, I don't know about this purported theory at all... but I think dismissing things just because they sound weird is a little silly, given how weird the reality of things is (I think complementarity is pretty weird, but that doesn't mean it's wrong). --Mr.98 (talk) 18:20, 12 October 2009 (UTC)

Tachyons don't sound a little weird to me. They sound plain wrong. That theory described here doesn't pass the smell test. Atomism is not a good analogy. Dauto (talk) 18:38, 12 October 2009 (UTC)

The observational evidence against any theory that says time and matter are interchangeable is that no-one has observed time changing into matter or vice versa. You would think the effects would be quite noticeable - "hey, I just lost 5 seconds and lost of tracks have appeared in my cloud chamber". Equivalence of work and heat is easily demonstrated; equivalence of matter and energy is demonstrated in every nuclear reactor; but there is no demonstration of the equivalence of matter and time. Gandalf61 (talk) 17:00, 12 October 2009 (UTC)

...though it's of note that the matter-energy equivalence was not observed until the twentieth century, even though it was technically happening all the time. --Mr.98 (talk) 18:20, 12 October 2009 (UTC)

In the early 20th century, many well regarded scientists said relativity was a crackpot theory. Edison (talk) 19:11, 12 October 2009 (UTC)

True and irrelevant. Dauto (talk) 19:14, 12 October 2009 (UTC)

I'm sorry that I can remember no more details: I read about the theory in a magazine in an English library and only remembered about it the other day when watching a documentary about M-theory, but I don't remember the author or the name of the theory. Leptictidium (mt) 21:05, 12 October 2009 (UTC)

Weather

I need some good weather websites. Anyone have some? Surface maps, radars, cool graphics, stuff like that. I would like that. Thanks! <(^_^)> Pokegeek42 (talk) 14:03, 12 October 2009 (UTC)

Google is your friend. Entering "Weather forecast" gave[4] me 37 million "hits". Cuddlyable3 (talk) 14:10, 12 October 2009 (UTC)

If you're interested in weather in the United States, you should check out the National Weather Service, http://nws.noaa.gov. Their website provides the most authoritative forecasts in the country (in fact, it is the source for most redistributed commercial forecasts); and you can also access much of the raw data, including maps, radars, satellite imagery, and atmospheric conditions data. Being both a government website, and a website run by scientists, the imagery has a little less gloss and veneer than you might be used to if you mainly pull from commercial weather websites... but that rustic rawness is scientific accuracy. Nimur (talk) 14:20, 12 October 2009 (UTC)

Depending on what you need... Unisys or NRL TC might be useful. -Atmoz (talk) 16:21, 12 October 2009 (UTC)

And don't forget Wunderground (a.k.a. "Weather Underground") at http://www.wunderground.com/ and the amazing Masters's blog [5]. Bielle (talk) 16:55, 12 October 2009 (UTC)

Age hardening of Mild steel under water

Could anyone please advise on this topic.

I am designing a Remote underwater drilling rig. I will drill Mild Steel (Grade 43 A) at 600 RPM, with a Diamond Tipped Rotary Drill. The current force I have calculated to drill throught the 6mm thk plate is 1.7kN. Do I need to concider the effects of Age Harding during this underwater drilling process or not. If so presumably the effects of Age-Hardening could increase the surface hardness of the Mild Steel to four times, is this correct?

Please confirm

Regards,

Lyndon —Preceding unsigned comment added by Longone02031966 (talk • contribs) 14:25, 12 October 2009 (UTC)

I have some follow-up Q's for you:

1) How long has the mild steel been underwater ?

2) How deep ?

3) Is this ocean water ?

4) What is the temperature of this water ?

5) Is there any corrosion (rust) on the mild steel ? StuRat (talk) 14:39, 13 October 2009 (UTC)

North Texas weather

Why is it rainier than usual?Accdude92 (talk) (sign) 15:06, 12 October 2009 (UTC)

The extra 6 inches of rain (beyond the average) since September 1 appear to be due to a series of four heavy-rain days (as opposed to steady drizzle over the entire month). My guess is that these were all part of this front (visible in this satellite IR image). Take a look at climate and weather - explaining deviations from average values is not always possible. This is a pretty significant statistical variation, though. One really big weather system can knock off the statistics pretty strongly. Nimur (talk) 15:21, 12 October 2009 (UTC)

It's all the more weird because it follows a record-breaking series of 100 degF days through the summer. SteveBaker (talk) 01:05, 13 October 2009 (UTC)

You seem to be getting our rain! We had over fifteen inches of rain in July alone here in northern UK, and August was mainly wet, too, but the autumn is unusually dry here. We would gladly exchange climates! Dbfirs 08:55, 13 October 2009 (UTC)

Texas weather has no "why". When I moved from Denton to Toronto, long about November sometime, it was a little bit chilly, maybe around freezing. So I went on the web and looked up Denton. It was eight degrees. Fahrenheit!!!. --Trovatore (talk) 09:47, 13 October 2009 (UTC)

Urinary Tract Infections

It has commonly been stated that human females, generally, are more susceptible to urinary tract infections. One reason would logically be the shorter length of the urethra tract of females, and it being closer to the anus compared to males, but my question is do you know of any components in urine that might differ from male to female resulting in males not being as susceptible as females. I know that in old age there seems to be an equal frequency of infection between men and women as stated on the wiki UTI page. It also states that women lack bacteriostatic properties secreted from the prostate in males. This is not referenced, and if that is right would that "property" be prostatic acid phosphotase (PAP)? Pjohnso8 (talk) 21:38, 13 October 2009 (UTC)pjohnso8 —Preceding unsigned comment added by Pjohnso8 (talk • contribs) 19:13, 12 October 2009 (UTC)

Time speed shift

In some days I have a quite strong feeling that the time, particularly, the minutes, run faster. Ultimately, the way which usually takes me say 30 minutes to walk, eats 35 min or so. Is there any explanation? 85.132.109.227 (talk) 19:39, 12 October 2009 (UTC)

Our sense of time article is in sorry shape, but some of the reference links might be interesting, as might googling for time perception. --Sean 19:53, 12 October 2009 (UTC)

Perception is a purely psychological phenomenon; that is such differences between expected time differences and actual time differences are entirely products of your own mind. The world itself is unchanged. It is a very common human trait to ascribe psychological effects to the world itself rather than to recognize them as purely internal processes. There is a real phenomenon where time for two people will pass at different rates, called time dilation, but that is a very different thing than what you are describing. --Jayron32 20:27, 12 October 2009 (UTC)

Jayron32's phrases "products of your own mind" and "internal processes" should be interpreted liberally; some drugs alter the perception of time. Comet Tuttle (talk) 20:54, 12 October 2009 (UTC)

As noted in this recent news story. --Sean 00:20, 13 October 2009 (UTC)

The story is ok but the newsreaders' sniggering is juvenile. Cuddlyable3 (talk) 15:44, 13 October 2009 (UTC)

Yes, but the drugs don't actually change the way time works. They change the way your mind works. That's the whole point. Doing drugs of this type doesn't expand your capacity for knowledge or wisdom, as was often claimed, it merely increased your own perception of your own knowledge or wisdom. You don't expand your consciousness, you just think you do. Nothing changes in the way the world works, just in how you perceive how it works. --Jayron32 02:39, 13 October 2009 (UTC)

KC135 boom

How long can the refueling boom on the KC135 be extended? Googlemeister (talk) 21:23, 12 October 2009 (UTC)

This photograph of the boom operator's instrument panel has a dial labeled "Telescoping" which appears to range from 0 to 20 feet. It is not clear to me whether this is the full extended length or merely the extra length added by telescoping; also, the units ("feet") are obscured by the dial needle so I may be reading it incorrectly. Nimur (talk) 21:57, 12 October 2009 (UTC)

I don't recall the actual length of the telescoping boom - 20 feet seems way too short. If you look at photos of the boom, it looks to be about as long as the vertical stabiliser fin is tall. The fin is 40 feet tall - so I'd guess the boom was at least that. I do know that the alternative 'hose and drogue' system used by some aircraft types (eg when refuelling two planes at once) extends to about 75 feet...so again, 20 feet for the boom system seems way too short. It's possible the dial is indicating how far one section of the telescoping boom is extended - rather than the total length. SteveBaker (talk) 00:56, 13 October 2009 (UTC)

I think the US military uses metric units Metrication_in_the_United_States#Military. 20 metres would be about right, 65 feet or so. Our article on aerial refueling says the receiver pilot flies "directly below and 50 feet behind" the tanker, which matches up well. Franamax (talk) 15:44, 13 October 2009 (UTC)

It's possible that it's in meters - but I rather doubt it. I have a kinda half-suspicion that the dial is telling the operator something much more important. I think that the center section of the boom is designed to telescope in and out in order to take up the slack between the tanker and the plane that's being refuelled. After all, neither of them can fly perfectly straight and level - and it would be expected that they would drift around and that center section would need to be able to telescope in and out. However, if the pilots ever got so close together (or so far apart) that they ran out of telescopability (is that even a word?) - then the boom might run into some kind of end-stop limiter - and it might get really nasty. So perhaps the guy on the boom station is required to watch that gauge and either yell out warnings on the radio - or perhaps manually disengage the boom - if the two planes get too far away from their optimum positioning. Now THAT distance could easily be as little as 20 feet. So out of a 60 foot boom (or whatever it is), it is easily possible that only 20 feet of it might be telescopic. SteveBaker (talk) 21:42, 13 October 2009 (UTC)

I just took another look at the photo - and now I'm 100% convinced that my explanation above is right. The center section of the dial is marked with a green arc - with red markers at either end. That surely has to mean that so long as the telescoping of the boom falls between those two red marks, everything is OK - and that if it ever compresses so much that it's in danger of sticking and ramming itself through the pilot's windshield - or stretches so much that it's going to be yanked off of the plane - then you're outside of the green band. Even more convincing is that the danger zone on the full-extension side of the dial is smaller than the one on the left. That too would make sense since if the boom is stretched too far, it'll simply disconnect - but if it's squashed up more than it can handle - then there would be a hard collision with the refuelling plane - which could easily get someone killed. Hence, the dial is in feet - but that tells us nothing about the overall length of the boom. Oh - except that it must be at least 40 feet at fullest extension in order to allow 20 feet of telescoping with a single rigid sliding section. SteveBaker (talk) 21:50, 13 October 2009 (UTC)

Lump on penis

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Time over distance...

... I have heard that clocks on the top of really tall buildings go through an hour a few minutes either fast or slower than a regular clock. But due to them being so high up, the time difference equals out so they match a regular clock on the ground. Is there any truth to this, if so, where can I find more information?

Thanks in advance!

74.218.50.226 (talk) 22:25, 12 October 2009 (UTC)

No building on Earth is tall enough to experience any measurable time dilation from either the gravitational difference nor the net difference in rotational motion - certainly not minutes on the hour. Nimur (talk) 22:32, 12 October 2009 (UTC)

How about the buildings on other planets? Just kidding... I didn't think there was that big of a differance. Thanks!74.218.50.226 (talk) 22:38, 12 October 2009 (UTC)

Not on other planets - but perhaps a tall building built on a neutron star might show some serious weirdness - but making a building more than a millimeter or two tall would be an impressive engineering feat! SteveBaker (talk) 00:47, 13 October 2009 (UTC)

Clocks at tops of buildings run very slightly faster than clocks at bottoms of buildings, due to gravitational time dilation. The difference is big enough to measure, but only if extremely precise equipment is used. The Pound–Rebka experiment, which was the first experiment to show this effect, took place in a building that wasn't even all that tall. The height difference between the bottom and top was only 22.5 meters (73.8 feet). Red Act (talk) 23:12, 12 October 2009 (UTC)

Sorry, but it just sounds bogus. It is very surprising and counter-intuitive that there should be an easily measurable effect in such a small distance in such a gravitational field. Edison (talk) 03:40, 13 October 2009 (UTC)

The original Pound-Rebka paper (1959) states that there should be a factor of 1.09x10^-18 frequency multiplier for each centimeter above the earth's surface. The derivation seems dubious; the approximation seems more dubious; and the prospect of measuring an effect on the order of 10^-18 even today, let alone in 1959, seems very dubious. Finally, the paper states a method for observing this effect - by observing hyperfine structure on nuclear gamma ray emission spectra (which can be measured very accurately) - but does not actually state that the gravitational redshift experiment has been performed. Thus the theoretical derivation of the frequency redshifting was not validated with experimental data. Nimur (talk) 04:01, 13 October 2009 (UTC)

The 1960 followup paper, Apparent Weight of Photons, does explicitly claim to have completed experimental measurement. Again, I have to call "dubious" all over this paper - the introduction outlines their "systematic measurement errors" that they attempt to mitigate by what I would consider data cherry-picking (using only certain combinations of experimental results and measuring a delta); they compensate for the temperature shift by what appears to be an arbitrary multiplication; etc. I'm not a relativistic physicist; I know little about hyperfine structure of gamma ray spectra - but I am an experimental physicist - and I don't like claims that are buried so far below the noise floor that you have to subtract elaborate models of the noise to "find" your result. I think it speaks volumes that this work, published in the early 1960s, has not been brought up since then as a bastion of scientific method and empirical proof of relativity - it's been cited once or twice in five decades. The discerning wikipedian will probably want to read the paper series themselves and decide whether my harsh judgement of "dubious" is warranted; after all, these papers were peer-reviewed and published - but needless to say, the effect is miniscule if it is measurable at all. Nimur (talk) 04:14, 13 October 2009 (UTC)

For context, Gamma ray spectrometer shows several plots from modern equipment (with about 12 bits of frequency resolution, or ~ 1000 "channels"). This is the top-of-the-line gear in 2009. To measure a frequency deviation of 10^-18, one would need to pull about 64 bits (equivalent) of resolution - fifty years ago - out of a custom-built analog experimental apparatus. Nimur (talk) 04:29, 13 October 2009 (UTC)

Pound-Rebka isn't some forgotten experiment that's been ignored by mainstream physicists. The experiment is widely referenced as being an important confirmation of general relativity in general relativity textbooks. For example, MTW, which is generally considered to be the "Bible" of general relativity, devotes more than two pages to the experiment (see pages 1056-1058). Other GR textbooks I happen to have that reference Pound-Rebka are "Gravity" by James Hartle, which devotes half of p. 118 to it, and "A first course in general relativity" by Bernard F. Schutz (see p. 120).

The experiment didn't need to measure anything accurate to one part in 10¹⁸. The 10^-18 is the relative amount of change per centimeter of height. But the apparatus had a height difference of 22.5 meters, so it was only necessary to measure a relative change of about 2.5x10^-15.

A relative change of 2.5x10^-15 is enormous compared to what is measured by modern gravitation experiments. For example, LIGO measures relative changes down to 10^-21, i.e., more than a million times smaller than what needed to be measured by Pound-Rebka. Red Act (talk) 05:45, 13 October 2009 (UTC)

Here is a document by Dr. John Mester, a physics prof at your school, which refers to the Pound-Rebka experiment. So you could stop by his office and ask him about Pound-Rebka, if you're still dubious about it. Red Act (talk) 07:59, 13 October 2009 (UTC)

I'll follow up on that lead. As I disclaimed earlier, I'm not an expert in this field - and the experiment did get published in a reputable peer-reviewed journal - so as much as I flail around shouting "dubious", my opinion is only worth so much. The Gravity Probe B mission, and the LIGO, also seeking to measure relativistic gravitational effects, also both suffer from tiny signal amongst huge noise. I think the ultimate answer here is that the OP's suggestion of "minutes per hour" is very far from reality; the predicted changes should be femtoseconds - which cannot be measured by even the most accurate atomic clocks. To measure these, it seems necessary to build a complex custom "device" and extrapolate a time dilation via a frequency shift. Nimur (talk) 11:47, 13 October 2009 (UTC)

I'd be really cautious about suggesting that the Pound-Rebka device needs 64 bits of precision to make a successful measurement. Remember, the experimenters don't need to measure the frequency from scratch. They just need an apparatus sensitive to minor differences in frequency — which the universe handily provides in the form of crystalline iron-57. It's the difference between measuring elapsed milliseconds between two events on the bench (trivial) and attempting to measure elapsed milliseconds since the start of the universe, twice, and taking a difference (ludicrous). TenOfAllTrades(talk) 12:38, 13 October 2009 (UTC)

It took me an hour to write one lousy sentence, but I put that little factoid into our Isotopes of iron article. People with some actual understanding of the topic may wish to review my wording.[6] Franamax (talk) 16:51, 13 October 2009 (UTC)

Y'all think you're so smart talking about gravitational redshift that you endded up missing the trivial answer to that question that a grandfather clock's period will change as you go up a building because the formula for the period of oscilation of a pendulum pendulum#Period of oscillation depends on the local acceleration of gravity that changes as you move higher up a building. Dauto (talk) 15:00, 13 October 2009 (UTC)

Like the original poster, I vaguely remember hearing that the effect of gravitational time dilation is exactly canceled by the effect of the changing gravity on a pendulum clock. Unfortunately, unless I miscalculated, they only half-cancel—the change in the swing rate is half the change from time dilation. That only applies for small height differences (where both effects are negligible anyway) and only for pendulum clocks, of course. -- BenRG (talk) 19:47, 13 October 2009 (UTC)

Viscous damping by air slows a pendulum clock slightly. This is why pendulums often have sharp edges to minimise air friction. At the top of a building the air pressure is lower which contribures to a clock going faster. (But something is wrong with the clock if the time difference is as much as minutes in an hour.) Cuddlyable3 (talk) 15:38, 13 October 2009 (UTC)

Air pressure changes over time just due to different weather - that variation is more significant than the change in air pressure for all but the tallest buildings. --Tango (talk) 16:56, 13 October 2009 (UTC)

So how many experiments published in peer-reviewed journals in the 50 years since the original publication have managed to replicate the Pound-Rebka experiment? Science is not about citing some teacher or book writer who "believes" the result. For a miniscule effect buried down in the noise and rescued by post-hoc correction factors, actual replication is appropriate. Edison (talk) 17:49, 13 October 2009 (UTC)

Edison, your excepticism is very healthy but in that specific case it is unfounded. Indeed, the Mossbauer effect effect, (which is the effect used in this experiment), can measure extremely small frequency shifts. This experiment is not bogus. Dauto (talk) 19:12, 13 October 2009 (UTC)

The Mössbauer effect is sensitive to very tiny frequency shifts; the Pound-Rebka experiment is famous and cited by every relativity textbook; the theoretical prediction of time dilation follows directly from the equivalence principle; and it's been empirically detected in other ways (like the GPS). But looking at P&R's actual published data (top of page 340) I see why Nimur and Edison are complaining. It looks too noisy to justify even the claimed 10% accuracy of the result. -- BenRG (talk) 20:13, 13 October 2009 (UTC)

That was just the initial experiment. By 1964, Pound and Snider had improved on the precision of the Pound-Rebka experiment by a factor of 10. See Pound and Snider's 1964 paper.[7] Red Act (talk) 21:13, 13 October 2009 (UTC)

Actually, Pound and Snider's 1965 paper might be better. That's the one MTW cites. See [8]. Red Act (talk) 22:02, 13 October 2009 (UTC)