Wikipedia:Reference desk/Archives/Science/2010 November 23

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November 23

Inserting pipes when drilling for oil etc.

When drilling through soft material like mud, clay etc., presumably some sort of pipe has to be inserted into a bore hole as the drilling progresses to prevent the hole from simply collapsing? As the hole becomes longer and longer, how is that achieved? I would have thought it would soon become impossible to ram in new sections of pipe from the top of the borehole due to increasing friction? 86.173.36.159 (talk) 01:03, 23 November 2010 (UTC)

You'd be surprised. One thing they do is use a type of wet "mud" to lubricate the pipes, but basically, they just keep feeding pipe section after pipe section into the hole. At the end of the last pipe is the drill bit, which leads the way, but as the drill bit clears out enough rock to put in another pipe length, you just add another one. Wikipedia's article on Boring could use some work, but it is really not a complex process. --Jayron32 01:43, 23 November 2010 (UTC)

Do you know whether it is pressure from above that forces the pipe down or the weight of the pipe above? Intuitively I feel that as the hole gets deeper the gaps in the pipe form somewhere near the top, as the weight of the pipe forces it downward as the hole deepens. If this is this case you are not pushing the pipe all the way to the bottom but just filling a gap. -- Q Chris (talk) 09:13, 23 November 2010 (UTC)

To expand on Jayron32's explanation, during the drilling of a soft section, the collapse of the hole is prevented by keeping the pressure of the drilling mud high (although not too high or you may hydraulically fracture the well bore). To prevent later problems it is necessary to line the unstable sections of the wellbore using a metal liner known as a casing, after they've been drilled. Once the liner has been set, the borehole is drilled on using a smaller bit, leading to a hole that gets progressively narrower with depth. This starts at the surface by drilling out (or digging out in the case of onshore drilling) the uppermost tophole section and it is into this that the blowout preventer is set once it has been lined. Mikenorton (talk) 11:00, 23 November 2010 (UTC)

So, please excuse me for adding a related question or two, when the drill bit needs replacing the whole pipe has to be drawn up leaving the bored hole without any lining? With a long pipe, won't the friction become very high and make it difficult to turn the bit? 92.15.6.86 (talk) 13:18, 23 November 2010 (UTC)

Yes, a broken drill bit (or any other tool breakage in the hole) would be a "minor catastrophe" and could delay drilling operations anywhere from several hours to many days, depending on how long it takes to physically remove the drill string. If there are shards of metal in the bore, then a special grinding tool might need to be put down the hole to chomp up the metal fragments, increasing the costs and delays. And with a very long pipe, friction is very high - so powerful motors (topdrives) are used at the surface. In very "high-tech" drilling, a drillbit can be hydraulically actuated (meaning that instead of turning a drillstring, energy is conveyed by pumping pressurized fluid down the bore, and that pressure provides energy to a mechanical contraption that turns the bit). Alternatively, electric motors can be used down-hole. Neither of these solutions are standard-practice. You might find the Schlumberger Oilfield Glossary a helpful resource - bottomhole assembly has diagrams of the bit and related mechanical parts, and a bunch of links to related terms. Nimur (talk) 14:47, 23 November 2010 (UTC)

At least for smaller water wells there exists drill-bits that expand when turned in one direction and contract enough to fit in the casing when turned in the wrong direction a few turns. This works by a bearing of centre and a part that is turned in or out due to friction. This linck shows an other method [1]. --Gr8xoz (talk) 12:00, 24 November 2010 (UTC)

Is there anything equivalent to a stent used in drilling, a collapsed object which can be moved into place, then expanded into it's final form using a balloon ? StuRat (talk) 17:54, 23 November 2010 (UTC)

Yes. Indeed, a component of the infamous MC252 lower marine riser package was a (hydraulically) inflatable "gasket" called an annular preventer. (Actually, there were at least two independently-actuated annular preventers, described in detail in the BP Accident Investigation Report). Both of these were intended to seal the annulus, not the bore. The trouble with annular preventers, like any high-pressure seal or valve, is that they must withstand the gauge pressure of any fluid across the zone they are trying to seal. In the case of the MC252 well, the fluid-pressures in the bore (i.e., gas and oil squeezing up the well annulus) were higher than the hydraulic pressure supply for the annulus - even if the hydraulic system had been functional, the annular preventers still could not have sealed against such high pressures. These "inflatable" seals were at the "top" of the well (at the LMRP), but similar apparatuses exist in the bore-hole near the cement shoe (almost at the bottom of the hole). A float collar can include a hydraulically inflated valve (though usually use a mechanical check valve instead); it is more common to use controlled injection of drilling fluids with known densities (weights) to seal the bore at great depth - in other words, a fluid seal; or to insert a cement or polymer plug. Obviously, by definition, a blowout will blow out such a seal. Nimur (talk) 19:12, 23 November 2010 (UTC)

Altering the refractive index of air molecules. —without different gases or high temperatures

I have a question about how one can cause air to become "blurry" —AT ROOM TEMPERATURE— by altering the refractive index of the air molecules in a small area.

I know that a similar effect can be engineered through either raising the temperature tremendously (in a small part of a much larger area), or by pumping a gas with a different refractive index into said area (which is usually a sign to leave IMMEDIATELY!)

I'm curious, however, if one can create a similar effect using a certain frequency of radio waves (or microwaves, etc.), or some other extant technology. To wit, be able to change the refractive index of the air in small area, so that it would appear "blurry" from farther away.

Does any such technology exist? Thank you for reading this! Pine (talk) 01:17, 23 November 2010 (UTC)

No, because it would be the equivalent of heating the air. Physchim62 (talk) 01:35, 23 November 2010 (UTC)

What you would have to do is change the density of air in a local area; the only option you may have from the other two you have ruled out is to generate a pressure wave of some sort; unfortunatly in order to be detectable, such a pressure wave would probably be large enough to rip you to shreds; it also could not be localized, so it would travel out causing death and destruction. The problem with all of this is air is a gas; which means that any perterbations you make to density, locally, are VERY quickly dissipated. You just can't do what you are proposing. --Jayron32 01:39, 23 November 2010 (UTC)

Increasing the pressure in a local area will also inherently increase the temperature in the same local area. Googlemeister (talk) 16:20, 23 November 2010 (UTC)

Robert Boyle would like to have a word with you. DMacks (talk) 16:56, 23 November 2010 (UTC)

Just an off-the-cuff thought, but what about using two beams of microwaves of differing frequency which, intersecting at a localised spot, would yield a beat frequency (of, say, 2.54 GHz) that would have a strong dielectric heating effect on the moisture content of the air? 87.81.230.195 (talk) 12:52, 23 November 2010 (UTC)

Wouldn't the microwave heating cause the air heated to be at a higher temperature from the rest of the room? I suppose a technically correct but unhelpful response would be to have a room where the temp was way different from 70 F but have the "blurry air" be at exactly 70, by heating or cooling. If some air were compressed, then released through a slot in the viewing area, the pressure drop would cause the air to suddenly cool, perhaps with moisture condensing. This is done in some dew point measurement apparatus. Again, there is a temperature change, but the "delivery temperature" of the air could be the required 70 F. Edison (talk) 14:46, 23 November 2010 (UTC)

What you see when the apparent refractive index of air changes with temperature is an effect of changing air density. (Denser, cooler air contains more molecules per cubic centimeter and has a higher refractive index than less-dense, warmer air.) As suggested, in principle one could use focused infrared or microwave radiation of an appropriate frequency to locally heat a small volume of air from a distance; as it expanded its refractive index would fall, but it would fail your criterion of maintaining 'room temperature' conditions.

You can temporarily increase the density (and refractive index) of air by passing a shock wave through it. (See, for example, this YouTube video; between roughly 0:02 and 0:04 you can see an expanding ring of visible distortion around the exploding automobile.) In principle, I wonder if you might accomplish something similar (and somewhat less destructive) by setting up some kind of standing acoustic wave. It would be awfully loud, however — sound pressures comparable to atmospheric pressure are up around 195 decibels. TenOfAllTrades(talk) 15:06, 23 November 2010 (UTC)

Or more destructively, with a nuclear weapon. See [2] for some info. DMacks (talk) 15:32, 23 November 2010 (UTC)

Shock waves (especially nuclear ones) also cause temperature to rise. Googlemeister (talk) 16:21, 23 November 2010 (UTC)

"In principle, I wonder if you might accomplish something similar (and somewhat less destructive) by setting up some kind of standing acoustic wave. It would be awfully loud, however — sound pressures comparable to atmospheric pressure are up around 195 decibels."

Could that be done with NO SOUND, though, through active noise cancellation? Pine (talk) 18:50, 23 November 2010 (UTC)

It could be done at frequencies people can't hear, such as 5 Hz or 100,000 Hz, though a human might still be able to "feel" sound that they can not hear at that level of intensity. Actually, 195 decibels might be harmful to people, even if they can't hear it. Googlemeister (talk) 20:22, 23 November 2010 (UTC)

Active noise cancelling would actually cancel the wave.. As for the standing wave, I wonder if you could do it using a lot of smaller speakers all around the target producing small waves that add up in the centre. I saw a clip of an amazing wave pool in Japan once which had hundreds of computer controlled baffles around the outside that could produce precise small waves at the edge that would all travel to the centre barely more then a ripple to begin with, but they'd line up perfectly just for a moment in the middle making various shapes, like a triangle, or a heart shape. For the "grand finale" all the baffles made a wave that "added up" in the centre and created a wave so violent that it sent a big ball of water shooting up into the air. I wonder if you could do something similar with speakers. Vespine (talk) 22:13, 23 November 2010 (UTC)

equilibrium constants units

in formation of ammonia from nitrogen and hydrogen

      N2 + 3H2 <--> 2NH3

units of k_c doesnt cancel. i read about unit of k_c on net and came to know that k_c do have units in the form of (mol/L)⁺ⁿ or(mol/L)^-n.

if it so why dont we write the units , neither it is wrong to not write the units why?

is there any other logic behind not writing units of equilibrium constant except that it is the ratio of same things ie concentrations --Myownid420 (talk) 01:48, 23 November 2010 (UTC)

Assuming you mean K_c, which is the equilibrium constant (k is the rate constant). Equilibrium constant is ALWAYS a unitless value. When you calculate K_c or K_p, you are using standins for the real value. The equilibrium constant is dependant on a value called activity, which, by a bit of circular logic, is the value which determines how fast a substance reacts in a chemical reaction (and thus, its effect on rate and equilibrium). Activity is unitless, so equilibrium constant is also unitless. It is actually an unmeasurable value, however for most measurements, the ratio of concentrations is close to equal to the ratio of activities so we use concentration as a stand in for it. K_c indicates that concentration is used as the standin for activity, and works for all solutions, and for all gases in a constant pressure environment. In a constant volume environment, we use K_p instead of K_c, which uses pressure values instead of concentrations (normalized to atmospheres). The article Equilibrium constant discusses most of this. In summation, equilibrium constant is always unitless, even though you use "concentration" as an approximation to calculate it; thus if you actually do the dimensional analysis on your calculation, you will often get a "unit" for the equilibrium constant. Ignore that. Equilbrium constant is unitless, period. --Jayron32 04:55, 23 November 2010 (UTC)

The logic behind the fact that the equilibrium constant is unitless comes from the fact that it is related to the Gibbs free energy change for the reaction by ΔG = −RTlnK. You can't take a logarithm of a quantity that has units. Physchim62 (talk) 12:54, 23 November 2010 (UTC)

No, that's plainly not true. pH is the -log of the molarity of the hydronium ion concentration. Concentration has units of moles/liter, but pH is unitless. You cannot take the log of the unit and get a meaningful second unit, but you certainly can take logs of measurements with units and get useful numbers. --Jayron32 01:49, 24 November 2010 (UTC)

Human-caused / Life-caused

Non-scientist here, so forgive the obliviousness. I know the term used for human-caused (or man-caused) is "Anthropogenic". Two questions: 1) Is there a term used for something caused collectively by life in general? 2) What are some examples of this? I know early plant life had something to do with the early atmosphere changing to something we can breathe today -- could that be considered "life-caused" (or that might be too specific of an example, so it would be limited to "plant-caused" I guess)? If you can point me to a WP article, I would be appreciative. Rgrds. (dynamic IP, may change) --64.85.215.81 (talk) 07:27, 23 November 2010 (UTC)

Biogenic means "created by life". So, yeah: Biogenic oxygen, biogenic methane, etc. I don't know of an equivalent for "plant-caused". I was thinking floragenic, but that seems to be a company. Someguy1221 (talk) 07:32, 23 November 2010 (UTC)

I would probably use "phytogenic" for plant-caused. --Jayron32 07:36, 23 November 2010 (UTC)

But it's sort of a moot point, since the initial oxygenation of the atmosphere was probably caused by cyanobacteria billions of years before there were any plants. Looie496 (talk) 07:46, 23 November 2010 (UTC)

That would make it "bacteriogenic", which means "bacteria-caused".

Another word pertaining to things caused by life is "zoogenic", which means "animal-caused". Red Act (talk) 08:17, 23 November 2010 (UTC)

"Biogenic" appears to be what I was looking for and seems to point me in the direction I was hoping, thanks Someguy. ("Zoogenic" is too specific-- I was looking for an all-inclusive term.) Rgrds. --64.85.215.81 (talk) 08:45, 23 November 2010 (UTC)

Mass flow rate of Refrigerant

what relation can I use to solve mass flow rate problems when given temperatur, pressure and specific volume —Preceding unsigned comment added by 41.221.209.6 (talk) 10:08, 23 November 2010 (UTC)

what appropriate relations can i use to determine changes in potential and kinetic energies and enthalpy when given temperature, pressure and mass flow rate —Preceding unsigned comment added by 41.221.209.6 (talk) 10:13, 23 November 2010 (UTC)

In the absence of an empirical equation of state, you can use the Ideal Gas Law or its more accurate form, the Van der Waals equation, to model gas volumes and pressures. Use the assumption that the flow is adiabatic, unless you know there is a pump, heat source, or heat sink. Conserve energy, calculate temperature using a specific heat value for the gas, and assume a phase change at the boiling-point temperature. You can apply the enthalpy of vaporization to conserve heat across the phase-transition. You can assume the fluid is incompressible when in liquid form, unless you have parameters for compressibility. Nimur (talk) 15:39, 23 November 2010 (UTC)

The Doppler Effect

If one were using the Doppler Effect to determine the speed of an object, how would the angle at which the object is moving in relation to the observer effect the determination? Can the speed still be accurately calculated even if the moving object isn't moving directly away from or at the stationary observer?--160.36.38.212 (talk) 15:41, 23 November 2010 (UTC)

For the acoustic Doppler effect, only the radial speed matters, so you just add a $\cos \theta$ and you're done. For the relativistic Doppler effect, that effect occurs but there is also the transverse Doppler effect (very small at, say, highway speeds). In either case, there's only one value you measure (frequency change), so you can't determine two values (speed and direction). But if you know one of those two, and measure the frequency change, you can get the other. --Tardis (talk) 16:23, 23 November 2010 (UTC)

What about in the instance of, let's say, determining the speed of a baseball with a radar gun. Since we are trying to determine the speed and can't be sure about the angle of observation, how accurately can the frequency change be used to determine the speed of the baseball?--160.36.38.212 (talk) 16:47, 23 November 2010 (UTC)

You'll never overestimate its speed (because the error is that if it's moving across your line of fire you'll get 0). The ratio of its true speed to your measurement is the secant of the angle its velocity makes with your line of fire. If you assume that that's, say, no more than 10°, then the true speed is no more than 1.5% above your measurement. But look at the graph of that function to see what happens if the direction isn't known at all. --Tardis (talk) 16:55, 23 November 2010 (UTC)

I see, not much to worry about as far as error is concerned. Thanks for your help.--160.36.38.212 (talk) 17:03, 23 November 2010 (UTC)

The "error" will always favour the driver, yes. Physchim62 (talk) 18:33, 23 November 2010 (UTC)

When you say it will always "favour the driver" I assume you are thinking of a police control for speeding speeding and no attempt at setting a speed record or similar. This is true as long as you are measuring the speed of a point like object, if you let the radar gun sweep along a stationary wall you will get the speed at which the point of intersection of the wall and the radar beam moves away from you. You can get similar errors if you don't hold the radar gun steady at a vehicle. --Gr8xoz (talk) 11:29, 24 November 2010 (UTC)

Does the sun drop faster on the equator?

As headline. —Preceding unsigned comment added by 84.12.125.33 (talk) 16:02, 23 November 2010 (UTC)

Yes. On visiting Texas from the UK I just couldn't get used to not having a twilight, its light one minute and dark 10 minutes later. The movement of the sun across the sky is also consistent, they can say "15 minutes for each finger-width (at arms length) the sun is above the horizon. In the UK it varies with the time of year but could be hours at midsummer!

The sun moves at that angular velocity all the time and everywhere. But in what direction? If it's moving "horizontally", it's not dropping as fast even though it's moving as fast. The sun typically moves more vertically near the equator and more horizontally near the poles, so there's the effect you're thinking of. However, it varies over the year and day even at one location; clearly at noon the sun is neither rising nor dropping. At the solstices, the sun crosses the horizon closest to one of its stationary points in altitude, so twilight is exaggerated there. During the midnight sun, of course, the sun never (fully) drops even over many days! --Tardis (talk) 16:20, 23 November 2010 (UTC)

"The sun moves at that angular velocity all the time and everywhere" -- Are you sure? I'm not convinced that the (apparent) angular velocity of the sun is exactly the same at all times everywhere on earth. How big the variation is is another matter... 86.174.40.11 (talk) 21:24, 23 November 2010 (UTC).

Well, it does 360 degrees in 24hr, doesn't matter where on earth you stand right? Vespine (talk) 21:58, 23 November 2010 (UTC)

No, if you’re standing on one of the poles, the sun will have almost no motion over the course of a day. The "15 minutes for each finger-width" rule of thumb (rule of finger?) fails miserably at or near the poles. Red Act (talk) 22:16, 23 November 2010 (UTC)

No, it really does go through 360 degrees in 24 hours no matter where on Earth you are. Its apparent angular velocity is the same everywhere on Earth. The angle subtended by your outstretched finger is also the same, even at the poles, and so it takes the sun the same amount of time to "travel" that (angular) distance there as the equator. WikiDao ☯ (talk) 22:40, 23 November 2010 (UTC)

You are obviously wrong, the sun may be close to the horizon all the day but it moves around the horizon. (Obviusly we are talking about apparent motion on the sky, the sun has a real motion relative to the galaxy of 0.13 AU/day or relative to the cosmic microwave background 0.21 AU/day) --Gr8xoz (talk) 22:36, 23 November 2010 (UTC)

Whether the sun apparently moving approximately 360 degrees per day is accurate depends on how you're measuring the angle. If you're measuring the angle around the Earth's polar axis, then yes, 360 degrees is about right. But if you're measuring the angle along the sun's apparent path, then the rate can be much less than 360 degrees per day. Red Act (talk) 22:41, 23 November 2010 (UTC)

Hm, you're right -- on a Uranus-like planet with exactly 90° tilt, you need not have the sun move at all (though of course it'll only be truly overhead for an instant per year, but that's practically irrelevant since years are long). But the slowest it can get on Earth (i.e., at the poles on a solstice) is $\cos 23.4^{\circ }=91.8\%$ of its maximum 360°/d speed, so that's a relatively minor effect compared to the 0–100% variation caused by the apparent direction. --Tardis (talk) 22:48, 23 November 2010 (UTC)

Yeah, you're right, the 23 degrees at the Tropic of Cancer isn't all that big of an angle. I was picturing it as being bigger in my head when thinking about it. Red Act (talk) 23:05, 23 November 2010 (UTC)

Whoops, yes, my statement that the sun has "almost no" motion over the course of a day at the poles was an overstatement, because the Earth's axis isn't tilted enough. But the apparent motion is less than 360/24 degrees per hour, measuring along the sun’s apparent path. Red Act (talk) 22:54, 23 November 2010 (UTC)

(e/cx2) Yes, the explanation of the original question has to do with "apparent" path. It is true that the sun "sets" faster at the equator than at higher latitudes.

At a pole, in summertime, the sun at most just dips below the horizon, but travels all around the horizon (360°) over the course of the day. When it does slip below the horizon, it slides along it as it slowly sinks before slowly rising again.

At the equator, when the sun sets, it does so directly downward, ie. with apparent motion perpendicular to the line of the horizon.

At a latitude of say 45°, the sun is apparently moving at the same angular rate, but some of that motion is a bit sideways, along the horizon. The "vertical" component of its motion is therefore less than at the equator, and more than at the poles, so the time it takes to set at that latitude is slower than at the equator and faster than at the poles. WikiDao ☯ (talk) 22:54, 23 November 2010 (UTC)

• In case it is unclear, when I originally doubted the exact accuracy of "The sun moves at that angular velocity all the time and everywhere", I was talking about the apparent angular velocity along the sun's path, as viewed from a fixed point on Earth. To put it another way, you fix your frame of reference to the horizon, then look at the speed the sun is moving through the sky relative to that, in whatever direction it happens to be moving. I am not convinced that that speed is always the same. 86.174.40.11 (talk) 01:50, 24 November 2010 (UTC).

Angular velocity is the same for any observer at any location on the surface of Earth. This is because the Earth rotates at a constant rate.

But angular velocity is a vector, so it is useful to consider that velocity as having "vertical" (define as perpendicular to the horizon) and "horizontal" (parallel to the horizon) components. At the equator, there is relatively small (and sometimes no) "horizontal" component, so the sun approaches the horizon and disappears beneath it very rapidly compared to at higher latitudes, where there is an increasingly large "horizontal" component and therefore a correspondingly decreasing "vertical" component. That is, the vertical and horizontal component velocity vectors do change according to latitude, while the angular velocity vector itself remains constant. WikiDao ☯ (talk) 03:01, 24 November 2010 (UTC)

It's not exactly the same angular velocity at all locations and times, because the Earth's axis isn't exactly perpendicular to its orbital plane. Tardis' calculation above looks right to me. The magnitude of the angular velocity at a pole on a solstice is about 8.2% less than it is anywhere on earth on an equinox. But the direction of the sun's path relative to the horizon is a much bigger effect. Red Act (talk) 03:48, 24 November 2010 (UTC)

Your latitude doesn't matter (except in an extremely small way due to parallax effects), only the Sun's current declination, which is determined by the time of year. The Sun's angular velocity is 8.2% slower (if the calculation is correct, and I think it is) at the solstices than at the equinoxes anywhere on the Earth. Remember that the whole sphere of the sky rotates as a unit (in your frame of reference), one rotation per sidereal day, and everyone sees it the same way; only the Sun's position on that sphere gradually changes with the seasons (progressing along the ecliptic, which is angled at 23.5° to the celestial equator, corresponding to the inclination of the Earth's axis).

Incidentally, another source of minor variation are the facts that the Earth's orbit is not circular and that consequently the Earth's orbital speed is not constant. This causes the Sun's motion to drift alternately ahead of clock time and behind it; see equation of time. But the variation in angular velocity for this reason is only on the order of 0.1%, I would estimate. --Anonymous, 11:03 UTC, November 24, 2010.

I probably should also have made it clear that I am not claiming that a variation in apparent angular velocity is the reason why the length of twilight varies across the earth. I understand the stuff about angle of setting relative to the horizon just fine. My original thinking was that at the equinoxes the polar sun travels right around the horizon in 24 hours, whereas at the summer solstice it travels right around the sky in the same time, but at a higher elevation, so it actually travels a shorter "distance". Therefore the "speed" cannot be the same. This theory seems to be borne out by the calculations, and the 8.2% figure, given above. 86.174.162.130 (talk) 12:33, 24 November 2010 (UTC)

Perpetual stew

I have a batch of perpetual stew going (and have for a couple weeks now). My Q is if there is any concern that some of the foods, by being cooked far more than is typical, might lose their nutritional value or morph into something harmful. I've noticed that everything turns brown after some period of time, is this a sign of chemical changes which may be harmful ?

So far, I have added the following:

Tomato soup
Ham bone
Carrots
Corn (kernels)
Corn (baby cobs)
Green beans
White lima beans
Beets
Broccoli
Tender cactus
Sweet potato
Potato
Cilantro
Hot peppers
White onion

Next, I intend to toss all the leftover turkey from Thanksgiving in there. Is there any reason for concern ?

And, for the inevitable bunch who always claims that any Q is a medical Q and can't be answered, this is a food safety Q, and you don't need to have a medical degree to legally offer advice on food safety, so it's not a problem. StuRat (talk) 17:45, 23 November 2010 (UTC)

Well, you'll obviously get some vitamin loss, but that's not terribly harmful. As long as you heat it frequently enough to prevent bacterial growth, I can't see anything that would cause problems. Looie496 (talk) 18:27, 23 November 2010 (UTC)

In my household, such a pot of stew, fitted with a padlock, would not survive until the next day, let alone perpetually. Be that as it may...

Think that these romantic cooking traditions survive partly because they serve as a focus for romantic memes and partly because long periods of slow cooking can produce a stew, pottage, gruel etc., with lots of umami. However, with the exception of saturated fats, all other fatty acids degrade with prolonged exposure to heat. In other words: it encourages the formation of trans fats. The essential fatty acids get destroyed. Vegetables and grains also contain these fatty acids, so a purely vegetarian stew is not going to avoid this degradation. Obviously, prolonged heating will also destroy all the heat liable vitamins. Prolonged containment in a non-stick pot may also impart unwanted levels of perfluorooctanoic acid. On the plus side. This type of food preparations was popular in England during the period were the average life span vacillated between 25-45years and thus may have helped these emerald isles from suffering over-population. Other than that: bon appétit and enjoy! --Aspro (talk) 19:24, 23 November 2010 (UTC)

I suspect that the primary cause of the short life span was poor sanitation, and particularly the habit of dumping raw sewage directly into their water supply.

Trans fats are bad all right. But there are some veggies and tubers with virtually no fats, so they should be OK. I may have to rethink the turkey leftovers, though. What's the time frame for this change ? Would a day do it ? A week ? A month ? Let's assume it's at boiling temp half the time, and cooling off at night. StuRat (talk) 19:53, 23 November 2010 (UTC)

I should also mention that it's an aluminum pot, but not a non-stick surface. Any worries about ingesting too much aluminum ? I heard that aluminum causes senility, but can't recall any details. :-) StuRat (talk) 19:53, 23 November 2010 (UTC)

I forget where I read it, but I thought elevated levels of Aluminum was found in Alzheimers patients. Googlemeister (talk) 20:14, 23 November 2010 (UTC)

Good question. With frying, the higher temperature mean that the fats are degraded whilst the food is cooked. Simmering -as in a stew, is certainly OK for a single or leftover cooking. I have never come across any convincing reason why ordinary aluminium oxide from utensils presents a problem (but other aluminium compounds show growing concern that they cause laboratory rats immune problems). The connection between aluminium and Alzheimer's disease is still debatable, but has never worried me because ordinary aluminium oxide is so inert and the science has not yet come up with anything convincing. The secret, I think, is to always use fresh unprocessed food. Even those tasty German sausages are processed food. A technology which dates before the time we had refrigeration. --Aspro (talk) 20:24, 23 November 2010 (UTC)

The Alzheimer's disease#Prevention section, at least, lists more studies that conclude that there is no connection between aluminum and Alzheimer's than studies that suggest that there might be. Red Act (talk) 22:02, 23 November 2010 (UTC)

I understand that acrylamide is produced when browning food (although apparantly not from oxidative browning such as when you cut an apple) and is a Substance of very high concern. Before it was discovered in food it was thought to be likely to be a carcinogen: I'm personally sceptical of the reports that all of a sudden say it isn't really. Heterocyclic amines are produced when cooking meat at high temperatures, as are Polycyclic aromatic hydrocarbons - I don't know if stewing for days on end would have similar results. 92.15.13.42 (talk) 20:40, 23 November 2010 (UTC)

Some good points were made about high temperature changes, but do any of those apply at boiling temp ? Assuming I never let it run dry, I see no reason the temp would ever exceed that inside the pot. StuRat (talk) 21:38, 23 November 2010 (UTC)

You say "I've noticed that everything turns brown after some period of time" and I pointed out that browning is associated with acrylamide production. I've also noticed: "Let's assume it's at boiling temp half the time, and cooling off at night". A heating/cooling cycle would be the sort of thing that encourages some bacteria to grow. 92.15.13.42 (talk) 21:56, 23 November 2010 (UTC)

The browning in his stew has nothing to do acrylamide - that comes from high heat + gases (frying)...assuming he's simmering as stew should be done and it's under/in fluid. Apples slow-cooked will brown that way.
⋙–Berean–Hunter—► ((⊕)) 22:35, 23 November 2010 (UTC)

Gases? What gases? What do you mean please? 92.15.6.122 (talk) 23:29, 24 November 2010 (UTC)

Not just frying, but baking, barbecuing and even microwaving too. 92.15.15.224 (talk) 12:38, 24 November 2010 (UTC)

Not all forms of barbecuing have this result. The barbecue that I had in my slow cooker before this thread began didn't have any of this acrylamide production as it was produced from low heat. As for gases, it is evident that the process like most other processes also rely on the gases in air or the foodstuff itself combined with high temp heating. Boiling doesn't do it, and there is an apparent reduction of acrylamide when foods are cooked under a vacuum which seems to substantiate that gaseous compounds play a part.
⋙–Berean–Hunter—► ((⊕)) 13:50, 26 November 2010 (UTC)

You must be unique in calling cooking in a slow-cooker "barbecuing". That is not the common meaning of barbeque. 92.24.178.149 (talk) 22:00, 26 November 2010 (UTC)

I hear they slow cook Barbecue in Texas. Will this thread ever end?! WikiDao ☯ (talk) 22:26, 26 November 2010 (UTC)

As for bacteria, yes, I would expect some to grow at night, but for them to be killed by the boiling the next day. And dead bacteria are edible in small quantities. If there was ever any visible growth on the surface, I'd toss the whole batch out. StuRat (talk) 22:58, 23 November 2010 (UTC)

Dead bacteria I wouldn't worry about. The toxins (some of which may be carcinogenic) that those bacteria and particularly fungi (if any) produced before they died I would worry more about. Also any endospores or spores that may have been produced. (There's a reason people aren't encouraged to simply cook spoilt food well. And usually by the time you actually start to see something it's starting to get to late.) These problems would seem to be particularly concerning if you are growing a fresh batch every day at the temperatures the encourage high replication. Nil Einne (talk) 05:32, 24 November 2010 (UTC)

One of the fundamental things about food hygeine I was taught long ago on this side of the pond was that you must not re-heat food more than once. There is some reason to do with bacteria going into encysted form; I forget the details. The advice about never reheating food more than once is given many times on this website: http://www.eatwell.gov.uk/keepingfoodsafe/germwatch/ Other government advice says: "If food is allowed to cool down over a long period of time any food poisoning bacteria or bacterial spores that survive the cooking process (bacterial spores are heat resistant so they will be present) will be able to grow and multiply to a level that may cause illness." So if you are doing this repeatedly, the bacteria will build and build, for example Bacillus cereus and other mentioned in the Foodborne illness article and here http://www.eatwell.gov.uk/healthissues/foodpoisoning/abugslife/ . As mentioned elsewhere, the toxins survive cooking. 92.15.15.224 (talk) 12:38, 24 November 2010 (UTC)

The "reheating" they mention seems to be just warming it to a comfortable eating temperature, and I agree that this is a bad idea; just reheat what you intend to eat. However, bringing it to a boil for a long period will kill off all the bacteria, and start the clock over again, so I don't see the issue there. I also don't quite follow the bit about bacteria spores surviving boiling and regrowing when temps are right. After all, isn't the entire basis of canning that food can be 100% sterilized by boiling ? If not, cans of food would all go bad after a couple weeks sealed in the can. StuRat (talk) 18:19, 24 November 2010 (UTC)

You've forgotten about the toxins - they make you ill. Boiling something in a saucepan is very different to sterlising it in a can under high pressure. I believe the cans are stored for a while and the improperly sterilized ones explode. The germ spores survive the cooking, as well as the toxins, and become active again afterwards. Its the repeated heating and cooling that is dangerous. 92.15.6.122 (talk) 22:40, 24 November 2010 (UTC)

AFAIK, most authorities recommend you reheat food to above comfortable eating temperature (too hot to eat) and then allow the food to cool down somewhat. If currently you only reheat food to eating tempereature I guess you have other problems with safe food practices. Also as 92 has said as does our article, most sterilisation for canning usually involved high pressure and significantly above 100 degrees C. I'm pretty sure with commercial canning at least, properly sterilised equipment is used (even if the canning occurs at 100 degrees C) and fresh food whereas in your case it sounds like you're going to be growing more and more each day so once some bacteria with heat resistant spores do get in there's a far change they're going to stay there. Nil Einne (talk) 11:16, 25 November 2010 (UTC)

Maybe you should get a slow cooker. 92.15.13.42 (talk) 21:51, 23 November 2010 (UTC)

What does that do for me that a pot on the stove doesn't ? StuRat (talk) 22:56, 23 November 2010 (UTC)

It allows more careful regulation of temperature in the stew. Stoves heat strictly from the bottom, but a good slow cooker tends to heat from all sides. Also, slow cookers tend to maintain a more constant temperature over time without much maintenance. On a stove top, you often have to cycle the heat up and down to keep the temperature at an ideal point. The slow cooker has an internal thermostat which cycles the heat for you, often more efficiently than you can do it. --Jayron32 01:45, 24 November 2010 (UTC)

A non-pressurized pot also seems to be self-regulating, as far as temperature goes. The temp increases from the burner, until boiling occurs. At that point the boiling action cools the stew such that it remains at that temp until all the water boils off. With the size of the pot, that would take days, if loosely covered. That gives me plenty of time to add more water. The boiling also evenly distributes heat throughout the pot. StuRat (talk) 03:05, 24 November 2010 (UTC)

Sort of. Often, the optimum temperature for cooking is just below the boiling temperature, called by cook books and the like as a bare simmer. There are several problems with cooking at the boiling temperature. First of all, it can actually toughen meat rather than tenderize it; the gelatin-forming reactions that occur at slightly lower temperatures still occur, however at the boiling point, the fibers in the meat itself can undergo a sort of crosslinking creating tough meat. Optimum meat-cooking occurs at temperatures some level below the boiling point, say 180-200 degrees or so. Also, rapid boiling can aggitate the food, causing vegetables to break up in ways that may be undesirable in the final product. Slowcookers are optimized to cook at this bare-simmer temperature, say 200 degrees, and maintain it pretty much indefinately. With stovetop cooking, you are basically stuck at the boiling point itself. Yes, you can maintain lower temperatures, but it requires more watching. --Jayron32 03:16, 24 November 2010 (UTC)

...and the cooking results are just different. You can't get that pork roast as tender on the stovetop as you can in a slow cooker. You're much less likely to burn your food and there is no open element like a stovetop so you can leave your home or sleep (or edit on the Wiki :)) and not worry about it. I am able to get a pretty good rendition of pit-cooked barbecue with 12-14 hours of slow-roasting that I would never dream of doing on a stovetop...and heating your oven for that long would cost more. The cooker puts off less heat, too.
⋙–Berean–Hunter—► ((⊕)) 02:32, 24 November 2010 (UTC)

Well, I only make perpetual stew in the winter, when the extra heat and humidity are welcome. I'm not worried about leaving burners on, as there are no kids or pets in the house. Since my burners are gas, which is 1/3rd the cost of electricity, this should cost less than a slow cooker. There is some concern that leaving the gas on for hours may deplete oxygen levels and increase levels of combustion products (other than water vapor) and unburned gas. However, it's on a very low level on one burner only, and not in a part of the house where I hang out, so the risk is minimal. StuRat (talk) 03:02, 24 November 2010 (UTC)

Given your observation of "extra heat and humidity", it's obvious that your cooking method (pot on burner) is not very efficient. You seem to welcome that inefficiency, but it is an indicator that other methods (like a slow cooker with lid) could result in much more efficient heating if the power sources were equivalent. Whether the difference in the price of gas (vs electric) and the "welcome" nature of the heat loss into the room are offset by the waste and risk involved in heating a pot with an open flame is complex and at least partly subjective. Heating your home with a stove is notoriously inefficient. -- Scray (talk) 04:16, 24 November 2010 (UTC)

Why would heating a home with a stove be inefficient ? It seems to me that 100% of the heat goes into the room, versus with a central heater, where much of it goes up the chimney or is lost heating the ducts and walls. I certainly wouldn't choose to heat a house that way, but not due to inefficiency, but because that much burning gas would indeed deplete the oxygen and create dangerous levels of combustion products inside the house. Then there's the issue of distributing the heat from the kitchen to the rest of the house. So, in winter, the added heat and humidity is that much less which is required from the furnace and humidifier, so it isn't lost at all, but is 100% reused. That's highly efficient. In summer, that's another matter, requiring extra A/C, so I don't do that. StuRat (talk) 04:29, 24 November 2010 (UTC)

Because you're heating your home unevenly. Unless your house has very good insulation and airflow your kitchen will be warmer for the rest of the house even though you probably spend little time there. And since your thermostat is probably not in the kitchen this extra heat is not actually saving you much on your other heating bill.

This is typically what people mean when they claim that electrical area-heaters are "inefficient". They don't literally mean that energy is disappearing into the aether.

Of course, I have no idea if it works out like that in your home; I've never been. APL (talk) 08:23, 24 November 2010 (UTC)

The very advantage of electrical space heaters is that they do heat unevenly, so you can heat the room you're in and let the rest get colder, thus only heating a small portion of the house. If my central heat went out and I needed to use the oven for heat, then I would spend my time in the kitchen, until the furnace was fixed.

Something else I've noticed is that, while heat doesn't flow very quickly from one room to another, humidity does. It would be nice to be able to quantify this observation in some way, so if anyone knows of one, I'd be interested. StuRat (talk) 18:27, 24 November 2010 (UTC)

If you go back 50 years then in many working-class UK homes the kitchen was the centre of the home, at least in winter, for this very reason. The range used to cook meant it was warm and poorer families would not be able to heat other rooms in the house. -- Q Chris (talk) 09:22, 24 November 2010 (UTC)

Also many homes have an air vent that let the air exit the home from the kitchen and also from the bathroom in order to not spread smells in the home. In that case you may heat the air just before it is vented out. I assume you are not using an Extractor hood that vent out the warm air. --Gr8xoz (talk) 11:06, 24 November 2010 (UTC)

There was a kitchen vent, but it's blocked off now for insulation reasons. StuRat (talk) 18:14, 24 November 2010 (UTC)

The other reason not to keep your stew for ever is that it won't be so nice to eat after a while. Suggestion: do your stew again, eat it over two days, maximum three. Then do another batch, varying the ingredients a bit. Soupe au pistou is a nice way to use a ham bone, tomatoes and white beans; online recipes are a better guide than our article. Itsmejudith (talk) 13:15, 24 November 2010 (UTC)

That approach requires washing the pot frequently, and also necessarily means that some of the detergent residue will be ingested. StuRat (talk) 18:31, 24 November 2010 (UTC)

Rinse the pot out after with clean water and dry thoroughly. It is this very rapid dehydration of any remaining bacteria which kills them off. --Aspro (talk) 18:55, 24 November 2010 (UTC)

Well, there is some fat in the pot, from the ham, so I would need detergent to remove that coating. StuRat (talk) 06:15, 27 November 2010 (UTC)

"Perpetual Stews" are a time honored technique. Some stews are maintained for decades and remain allegedly delicious the whole time. APL (talk) 16:21, 24 November 2010 (UTC)

I think it would be a very good idea StuRat for you to first get to understand a bit of basic food safety. Not all toxins are destroyed by 'boiling' such as those produce by Bacillus cereus which has already been mentioned. Canning undergoes higher temperatures than 100 deg C which includes an adequate dwell time, because not all bugs and spores are destroyed at the normal atmospheric boiling point. Foods should be cooled quickly and the larger the pot the longer it will take to cool. I have often read of large fatalities at Indian wedding parties because this aspect of bigger than normal pots has been overlooked. Sounds like you have been lucky up to now. This site has some tips.[3]Aspro (talk) 18:55, 24 November 2010 (UTC)

If, as many indirect references here suggest, perpetual stews are a time-honored tradition, then Aspro's comment reminds me of the frequent clash between empiricism and extrapolation. Perhaps major illnesses resulting from perpetual stews have been overlooked - this is worth investigating (and I would do so before indulging in this practice); however, I suspect something more interesting is at work - extrapolation from other situations is being applied to a specific, well-tested practice, with the extrapolation predicting major problems that actual experience does not support. I think there's much to be learned from these situations, but I've also learned to trust empirical evidence more than extrapolation (with a pinch of caution, which StuRat has already expressed). -- Scray (talk) 20:18, 24 November 2010 (UTC)

There is no clash as I see it. The wife of the house whom learnt the tradition from her mother, whom in tern learnt from her mother etc., was only able to do so because they had learnt a safe technique which enabling them to cheat an early death and so pass the method on to their daughters. Rediscovering a successful way to recreate this gastronomic medley in a cauldron, using trail and error methods with a pinch of ignorance here-and-there, will - I fear - ensure that such a stew will kill off its paddle stirrer and its chances of ever becoming a proper perpetual stew worthy of such a title. Do you see my point? --Aspro (talk) 20:58, 24 November 2010 (UTC)

LOL @ "trail and error" ... go down one trail until you hit a dead end, then try another ? I don't think it can be quite so dangerous as you suppose, or people would have learned to avoid the practice centuries ago. For example, tomatoes apparently leached out lead from the leaded plates and bowls of the day, and thus poisoned people. They had no idea that this was the problem, but still thought of tomatoes as poisonous and avoided them. Something similar would happen if perpetual stews regularly killed people who got the technique wrong. Perhaps they would develop a theory that slow-moving invisible demons invade the stew if it's left uneaten for too long, which isn't really all that far off. :-) StuRat (talk) 21:45, 24 November 2010 (UTC)

A bigger point is I don't see any evidence perpetual stews were cooked the way StuRat cooks them. My guess is they were kept heated for the whole day (not necessarily boiling but usually enough to reduce problems) rather then Sturat's attempts to grow microbes with heat resistant spores. Of course humans have managed to learn to deal with a number of potentially dangerous foodstuffs like Cashew nuts and tapioca. Also the consumption of carcinogenic but not acutely dangerous toxins wasn't generally a big deal. Nil Einne (talk) 11:16, 25 November 2010 (UTC)

Then how would they have cooked them, if not bringing them to a boil during the day and letting them cool off at night, exactly as I do ? Would they stay up all night to stoke wood under the fire ? StuRat (talk) 17:16, 25 November 2010 (UTC)

In old times there would be a coal-fired kitchen range, a large iron thing that would stay hot overnight, with the coals probably still smouldering and its big thermal mass taking a long time to cool. In the UK they were normally built into the wall, adding more thermal mass. More importantly, people often died of infectious diseases etc, so some food poisoning wouldnt have been noticed. Goodness knows why you want to play russian roulette with your food - I'm detecting that North Americans think any food is wholesome (hence the eating of pop tarts without shame or self-loathing} and cannot get their heads round the idea that some foods can be bad for you. 92.28.251.194 (talk) 17:53, 25 November 2010 (UTC)

I don't think coal-fired stoves were common, say 1000 years ago, when wood would have been the norm for cooking. So, how did they keep their perpetual stew hot then ? StuRat (talk) 05:06, 26 November 2010 (UTC)

In 1010AD, they probably didnt have your "perpetual stews", little or no idea of hygeine or medicine, and people usually died young for unidentified and unspecified reasons. 92.28.241.63 (talk) 12:15, 26 November 2010 (UTC)

To get temps higher than 100°C in something that's mostly water, you would need to pressurize it. Yet I don't believe this is normally used in home canning, so how do all the bacteria get killed there ? StuRat (talk) 20:17, 24 November 2010 (UTC)

Canning often involves hypertonic solutions (e.g. salt and sugar). In addition to providing a higher boiling temperatures, such solutions are relatively inhospitable to many food pathogens. -- Scray (talk) 20:22, 24 November 2010 (UTC)

Home canning has been the cause of many a multiply deaths ( the whole family can be affected). The article gives some pointers on how to do it safely. Even something as traditional as the sausage has been subjected to ancient laws stipulating how they should be made in order to avoid botulism. The name of this bug itself, comes from the Latin for sausages with which it was so often associated. --Aspro (talk) 21:11, 24 November 2010 (UTC)

But, of course, there are many deaths from each stage in food production: preparation, distribution, and serving; both at home and on an industrial scale, so the question is whether deaths from home canning are a higher proportion than from those other sources. Myself, I seem to get food poisoning about 1/10th the time I eat out, so that's a rather low target to try to beat. I don't get sick nearly so often from home cooking, and I attribute this to one factor: If I see food that looks suspicious, I won't eat it or serve it to others I know, but the restaurant workers don't know or care about the people they serve, so are likely to just remove the visible mold from the top of the food and serve it anyway. The chances that they personally will be punished for this are low enough that it's not a concern.

I have a specific example from a Wendy's salad bar (do any of them have those any more ?). They apparently were just "refreshing" the salad bar periodically, meaning adding fresh food to the top. I saw no evidence that they ever dumped out the old food. The cucumbers were fresh on top and gradually got worse going down, to where they were all decomposed into something like snot at the bottom of the container. I complained to the management, and they pointed out that there are holes in the bottom of each container where the decomposed cucumber juice can drain out, so they weren't concerned about it. StuRat (talk) 21:32, 24 November 2010 (UTC)

However do they get any customers? 92.15.6.122 (talk) 22:49, 24 November 2010 (UTC)

Well, I didn't go back after that, and I suspect the same is true of others, as most (or maybe all ?) Wendy's seem to have discontinued their salad bars. Perhaps they do a better job at what they serve now. StuRat (talk) 01:26, 25 November 2010 (UTC)

The Botulism article gives some relevant details. 92.15.6.122 (talk) 22:49, 24 November 2010 (UTC)

The first line in that says that anaerobic conditions are required, but this pot is opened up daily and stirred, while boiling, so plenty of oxygen should be available. StuRat (talk) 17:21, 25 November 2010 (UTC)

That was just an example. There are many germs that can make you ill or kill you, not just botulism. This List of foodborne illness outbreaks in the United States says there were 76 million illnesses from food in a year - I'm beginning to see why. 92.28.251.194 (talk) 17:53, 25 November 2010 (UTC)

But why refer me to an article which clearly isn't relevant ? And that last list also doesn't seem relevant, unless there are perpetual stew cases listed in there. The closest thing I saw was the case where botulism in peppers served at the Trini and Carmen restaurant in Pontiac, Michigan caused the largest outbreak of botulism poisonings in the United States. The peppers were canned at home by a former employee. Fifty-nine people were sickened. But, again, that's botulism, so not relevant to perpetual stew. StuRat (talk) 05:03, 26 November 2010 (UTC)

The botulism article is relevant to canning, which was discussed above, and is one example of food-borne illness. Of the 76 million illnesses, most of them were domestic rather than being those listed. I'm puzzled why you want to persist with a practise that is likely to make you ill or worse, despite all the advice to the contrary. 92.28.241.63 (talk) 12:26, 26 November 2010 (UTC)

If you have some specific evidence that perpetual stews cause illness, I'd like to see it, but unrelated articles about industrial food contamination aren't helpful, and neither is citing the number of food-caused illnesses, if not broken down to include perpetual stews. StuRat (talk) 18:05, 26 November 2010 (UTC)

So the fact that its "perpetual stew" means that it is absolved from all the rules of normal food hygiene? When you start heaving, I hope you can realise why. It's your funeral. 92.24.178.149 (talk) 21:57, 26 November 2010 (UTC)

It's subject to the same rules of evidence as anything else. If you have any actual evidence it is harmful, present it. Otherwise, be quiet. Evidence that other foods are harmful just makes perpetual stew look safer by comparison. StuRat (talk) 05:45, 27 November 2010 (UTC)

Darwin Award. 92.15.11.45 (talk) 13:10, 27 November 2010 (UTC)

And yet again you've provided a link to people killing themselves in other ways, having nothing whatsoever to do with perpetual stew. StuRat (talk) 17:59, 27 November 2010 (UTC)

If you want to incubate things, try making your own yogurt. 92.15.6.122 (talk) 23:31, 24 November 2010 (UTC)

Energy to Mass

Ok it seems that with exotic materials such as antimatter, it is pretty easy to grasp how to convert mass to energy, but are there known ways to convert energy to mass? For example, say there a huge number of photons, do we know a way, even only a theoretical one, to convert them into something recognizable, like say aluminum or carbon? Googlemeister (talk) 20:28, 23 November 2010 (UTC)

Nucleosynthesis, particularly stellar nucleosynthesis, is the only practical way to assemble any reasonable quantity of heavy atomic nuclei out of smaller "pieces". To fuse together two hydrogen atoms, a proton–proton chain reaction takes place - this is actually exothermic, and it requires "a starting ingredient" - hydrogen. To produce hydrogen out of "pure energy", see Baryogenesis and Big Bang nucleosynthesis - at present, we can not do this in a laboratory. (In other words, we don't have any machine or particle accelerator that can take photons in and spit out hydrogen). At best, we have a theoretical understanding of the mechanism involved. This conversion from large quantities of undifferentiated energy, into distinct particles, is the process we call the "big bang." In the beginning, a hyper-dense region of energy must exist. It begins to expand, which causes the energy density to decrease and symmetry-breaking begins to occur (notably, the separation of fundamental interactions). As energy density decreases, inhomogeneity develops, and different "zones" begin behaving as various elementary particles, exhibiting the first fundamental interactions. We call this stage a "quark plasma." These quarks begin the process of coalescing into light nuclei - protons, mostly; and electrons; and thus is born the first hydrogen. For this process to occur, we need extraordinarily dense energy. It is still not clear whether a homogeneous, isotropic clump of energy will inherently begin to break symmetry (i.e., whether this is "built in" behavior); or if we began with a non-homogeneous or non-isotropic universe. We do not understand the requirements for symmetry-breaking in the universe-at-large, so we don't have a method to reproduce baryogenesis experimentally. Nimur (talk) 20:51, 23 November 2010 (UTC)

See Gamma ray#Properties#Matter Interaction, Pair production. It is basically the reverse of annihilation. This reaction cannot as of yet be finely controlled enough to stop the produced pair from self annihilating and reverting back to energy. Even if there is a way, electrons alone do not make an atom. It simply needs to much energy, and is too inefficient to be considered an experiment just to see if you can. Plasmic Physics (talk) 21:10, 23 November 2010 (UTC)

See also Hawking radiation, which is a peculiar effect of pair production which occurs near black holes. --Jayron32 01:42, 24 November 2010 (UTC)

So, assuming that the questioner is really asking "can we create macroscopic amounts of matter out of radiation" (so avoiding the whole "energy - mass - aren't they the same thing ?" minefield), then I think the answer is "not with known technology or any feasible extension of it", because (a) we cannot confine a large enough amount of radiation in a small enough space for a long enough time to create enough particles and (b) we have no idea how to prevent the creation of equal amounts of matter and antimatter, or stopping the matter/antimatter pairs turning back into radiation. Gandalf61 (talk) 12:13, 24 November 2010 (UTC)

If energy such as changing electromagnet fields were used to accelerate an object, such as a small steel ball, or an ion, wouldn't the ball or ion be more massive, thus demonstrating energy turned to mass? (even if no new protons or electrons or neutrons were created). 67.48.228.68 (talk) 20:35, 25 November 2010 (UTC)

"...thus demonstrating energy turned to mass" - not really, because energy has mass and mass has energy - see mass–energy equivalence (yes, yes, I know this depends on which definition of mass you use). Despite the title used by the original questioner, I think it is clear that they intended to ask about turning radiant energy into matter, which is quite different. Gandalf61 (talk) 12:05, 26 November 2010 (UTC)

Remove strong smell from plastic and aluminium?

OK, so this is a weird question, but I still think the science desk is my best bet. I just bought an external Disk enclosure; it's in parts - aluminium heatsink, acrylic/plastic outside, and the circuit board. The heatsink and plastic both smell VERY strongly (with the same smell), and I'm very sensitive to smells. Since they are 100% separated from any electronics, I can clean them easily. The question is: with what? Any advice on how to get rid of the smell, or even a hint as to why it's there in the first place? (Since the materials are different, I don't get why they smell the same.) I'd describe the smell a bit like "burnt plastic". -- Aeluwas (talk) 20:50, 23 November 2010 (UTC)

I suspect outgassing, which is normal for some new synthetic materials. The only solution I know of is to put it somewhere where it won't bother you while it does this, perhaps a few weeks ? Of course, you could just leave all that stuff off indefinitely, and the hard drive may actually air cool even better without it. However, there is a risk of spilling something nasty into it and also dust accumulation, so perhaps it is best to put the enclosure back on after it stops stinking up the place. I would guess it was made in China, as many such products have flaws like you describe. One warning, don't put it in sunlight, or the plastic portion may be degraded by the UV light.

Now, let's also consider it actually being coated with something smelly. Does a cloth stink after you rub it on the object ? If so, then cleaning may help, after all. I'd just use liquid dish-washing detergent, preferably fragrance-free, if you are sensitive to that, too. Don't use bleach, as that could damage it. If some stink still remains, then go back to the first idea of leaving it where it won't bother you until it stops stinking, or maybe return it and get one that smells better. StuRat (talk) 21:28, 23 November 2010 (UTC)

"Now, let's also consider it actually being coated with something smelly."

I noticed that this morning. EVERYTHING in the entire package (including the package itself) has the same smell. Antistatic bags, the components, the small plastic bag for the screws, both the USB and FireWire cables, and their plastic bags. All the same smell. Since these are so different materials, it must have been added for some reason... Any ideas why (which of course would lead us to what)?

This is, by the way, the second time ever I can recall being bothered by how computer parts smell (unless you stick your nose right down to a PCB!), the other being when I got my UPS. It also had a weird smell for the first month or two of use, possibly because of something protective burning off the battery, IIRC. (I've had it for two years so I don't recall the details of what I looked at back then.) -- Aeluwas (talk) 08:59, 24 November 2010 (UTC)

Well, this seems to confirm that it is indeed coated with something smelly. They might coat everything with something to give it a nice sheen and make it more marketable, but your description of it smelling like burning plastic makes me think they had a plastic fire in the factory, causing smoke damage to everything in it, but just packaged it up and sold it anyway. You can wash most of those items with dish-washing detergent, and maybe just toss out the bags, but returning it all and getting a replacement sounds like a good alternative to me. I'd check the batch number to make sure it isn't the same, or, better yet, get a different brand that hopefully doesn't also try to sell smoke damaged items to the public as new ones. StuRat (talk) 18:05, 24 November 2010 (UTC)

Sounds to me, that this smell is from the remaining free, unbound and volatile plasticizer in the plastic. See: Plasticizer#For_plastics. Heat plastic and more gets driven off. It should disperse in time. Can't think off-hand of anything that will help which wont risk making the plastic brittle, other than perhaps an alcohol wipe which might be effective. Alcohol wipes should be safe to use on plastic surfaces, which is why they are made for electrical equipment servicing. Some types of potting compounds and conformal coating can also smell a bit strong with an acrid tint to it. Think this is the real origin to the Skunk Works name, because they used ******** to stick black project planes like the ********* together. I don't believe the Lockheed explanation at all. --Aspro (talk) 19:28, 24 November 2010 (UTC)

Whatever this stuff is, it won't give in easily. FWIW: the plastic bags etc. are obviously irrelevant, I only brought them up because it all smells the same, as if it's sprayed on or something. Anyway, what smells by far the most is the aluminium heatsink; the plastic is acceptable. By now the heatsink has been in water for about... 22 hours, 10 hours of which with (quite a lot) of dish soap massaged onto it and in the water, and just now I wiped it thoroughly with pure isopropyl alcohol, rinsed with water... and absolutely ZERO difference. What gives? -- Aeluwas (talk) 20:40, 24 November 2010 (UTC)

Well, anything which can dissolve is usually water-soluble, alcohol-soluble, or oil-soluble (detergent handles the last case). So, this leaves us with something that isn't soluble at all. I'm going back to my theory that it's out-gassing of some substance within the aluminum, which then apparently also deposits on nearby items. So, are you ready to return it, yet ? If not, put it in the garage or somewhere out of nose-shot and it will eventually lose most of it's smell. StuRat (talk) 21:16, 24 November 2010 (UTC)

Hydrated Salts and Coordination Compounds

Hello. If all the water of crystallization in copper(II) sulfate pentahydrate evaporates at 200°C, is CuSO₄·5H₂O a coordination compound? If so, are the water molecules covalently bonded to the metal centre, Cu²⁺? (Covalent bonds need higher temperatures to break.) Are most hydrated salts coordination compounds? Thanks in advance. --Mayfare (talk) 23:48, 23 November 2010 (UTC)

It can be complex. The individual water molecules can be bonded in any number of ways, sometimes multiple ways in the same compound. It can be bonded as a ligand to either the copper(ii) ion or the sulfate ion, or it can simply occupy locations in the crystal lattice without being bonded directly to either ion. The article water of crystallization uses copper(ii) sulfate as a specific example; I'll let you read it to discover for yourself the particular bonding. --Jayron32 01:40, 24 November 2010 (UTC)

If the water molecules attract to the metal centre by hydrogen bonding, why is CuSO₄·5H₂O a coordination compound? Shouldn't ligands be covalently bonded to the metal centre in such compounds? --Mayfare (talk) 02:05, 24 November 2010 (UTC)

The water molecules are NOT attracted to the metal center by hydrogen bonding. The metal center is bonded to six oxygen atoms, four of them water molecules and two of them sulfate ions. The fifth water molecule is not bonded directly to the metal ion; it is basically free-floating in the interstices of the crystal latice, weakly hydrogen bonded to all of the various oxygen atoms surrounding it. The oxygen-copper bond is called a "coordinate bond", which generally means that both electrons are donated by the lewis base (in this case water). However, as Physchim62 implies below, electrons have no memory of which atom they came from. In the end, it just matters that there is are oxygen-copper covalent bonds. These bonds can be explained by either hybridization theory or molecular orbital theory, which basically provide different perspectives on bonding, but such an explanation is probably outside of the scope of this reference desk. --Jayron32 02:25, 24 November 2010 (UTC)

The bonding in such compounds (coordination compounds) is midway between covalent and ionic. You can describe it in many different ways, the electrons don't care! Physchim62 (talk) 02:15, 24 November 2010 (UTC)

Are coordinate covalent bonds so weak that 200°C is sufficient to evaporate all the water of hydration including the four water molecules bonded to the metal centre? --Mayfare (talk) 19:53, 24 November 2010 (UTC)

Quite possibly. What you would need to do is to find the equilibrium constant for the reaction CuSO₄·5H₂O <--> CuSO₄ + 5H₂O, and convert this to ΔG via the equation ΔG = -RTlnK (alternately, you could calculate ΔG directly). Then, from ΔG = ΔH - TΔS, and find the exact temperature when ΔG changes from positive to negative. The way you usually do this experimentally is to find K at two different temperatures, which lets you find ΔG at two different temperatures. This allows you to solve a system of equations to isolate ΔH and ΔS values. Then substitute in these found values of ΔH, ΔS and set ΔG = 0. The temperature you find would be the minimum temperature to cause the reaction. --96.255.208.104 (talk) 21:46, 24 November 2010 (UTC)