Wikipedia:Reference desk/Archives/Science/2008 March 28

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March 28

Shape of the Milky Way Galaxy

I remember when I was younger and more interested in astronomy reading that the Milky Way was a spiral galaxy, like the Andromeda galaxy, but while browsing various articles, I came upon the Milky Way article, which said that it was a barred spiral galaxy, which surprised me. When did astronomers figure out that it's a barred spiral galaxy instead of a spiral galaxy? Was there some discovery in the past decade that allowed them to see that it is in fact a barred spiral instead of a spiral galaxy? How do astronomers know what shape the Milky Way is and where the arms are? By judging the distance of tons of stars and laying out a map? How are astronomers able to guess at what lies on the other of the core? Thanks in advance. – Psyche825 _(talk) 04:28, 28 March 2008 (UTC)

Adaptive optics is certainly one breakthrough during the last ten years, that has helped astronomers to dramatically enhance the accuracy and resolution of star charts among other things. I cannot elaborate as I am by no means an expert in astronomical modelling. Sandman30s (talk) 09:36, 28 March 2008 (UTC)

Yes, this conclusion must have been reached by an analysis of the distribution of stars and interstellar gas and dust clouds using observations at various wavelengths. Radio astronomy, for example, allows us to see details of the Galactic Center that are hidden at visible wavelengths. Apparently the crucial evidence that clinched the case for a barred spiral structure were infrared observations made in 2005 using the Spitzer Space Telescope. Gandalf61 (talk) 11:13, 28 March 2008 (UTC)

Ah, thanks. A quick Google search about the Spitzer telescope turns up quite a few articles with more information. – Psyche825 _(talk) 06:09, 29 March 2008 (UTC)

Quantum: Measurement vs. Schrödinger Equation

1. Article Copenhagen interpretation: Each measurement causes a change in the state of the particle, known as wavefunction collapse.

2. Article Schrödinger equation: The Schrödinger equation is commonly written as an operator equation describing how the state vector evolves over time.

Although I don't fully understand quantum mechanics, the two items above seem to be related to each other.

When an observable of a quantum system is measured, the state $|\psi (t)\rangle$ of the system can be expressed as

$|\psi (t)\rangle =\sum _{i}\psi _{i}|i\rangle$ (1)

where $|i\rangle$ is the $i$th eigenfunction, which is associated to eigenvalue $i$, of the observable and

$\psi _{i}=\langle i|\psi (t)\rangle$ (2)

which will "suddenly" or "discretely" collapse from $|\psi \rangle$ to one of terms, say $\psi _{a}|a\rangle$, of the right-hand side of (1). The rest of the terms not associated to eigenvalue $a$ simply vanish after the measurement.

On the other hand, Schrödinger equation

${\hat {H}}(t)\left|\psi \left(t\right)\right\rangle =\mathrm {i} \hbar {\frac {d}{dt}}\left|\psi \left(t\right)\right\rangle$ (3)

where

${\hat {H}}(t)=-{\frac {\hbar ^{2}}{2m}}\nabla ^{2}+V\left(\mathbf {r} ,t\right)$ (4)

describing how the state vector $|\psi (t)\rangle$ evolves over time. When the state $|\psi (t)\rangle$ of the system is measured, the apparatus measuring the system will interact with the system and makes change to the potential field $V\left(\mathbf {r} ,t\right)$. Therefore, the state $|\psi (t)\rangle$ should evolve "smoothly" or "continuously" according to the varying potential $V\left(\mathbf {r} ,t\right)$ during the measurement. According to Schrödinger Equation (3) and (4) together with $V\left(\mathbf {r} ,t\right)$, we should be able to figure out the final state of the system after the measurement.

It seems that the measuring process can be explained by the two ways, wavefunction collapse & Schrödinger equation, above. Do they contradict? Is "wavefunction collapse" compatible with "Schrödinger Equation"? - Justin545 (talk) 08:12, 26 March 2008 (UTC)

Yes, they do contradict. There is no place for a collapse in Schrödinger's Equation, which is one reason why David Bohm concluded that there can be no collapse of a wave function, that it's a figment of the model. — kwami (talk) 08:34, 28 March 2008 (UTC)

Figment of the model? I'm amazed that they do contradict since the two items are considered to be postulate of quantum mechanics in some textbook of quatum mechanics IIRC. It should imply at least one of the two items is wrong. So has David Bohm or some one else solved the contradiction? And how about the experimental evidence? Experimental evidence supports which one? - Justin545 (talk) 08:55, 28 March 2008 (UTC)

The Copenhagen interpretation is just that, an interpretation. It has no empirical support (or at least it didn't some years ago) and is in no way an axiom of QM. I've heard people who use it make the excuse that none of the other interpretations have any empirical support either, even though some of them are less counter-intuitive than Copenhagen. Bohm attempted to create a deterministic hidden-variable QM, but was unable to solve some fundamental problems before he died. One of his students continued with his work, but I don't know if he ever got anywhere. — kwami (talk) 09:04, 28 March 2008 (UTC)

I think neither Schrödinger equation nor wavefunction collapse could be axiom of QM. Therefore, they are considered to be "postulates" of QM. Schrödinger equation seems to correctly predict the spectral lines of each atomic models. On the other hand, wavefunction collapse seems to correctly predict the phenomenon of quantum entanglement. And both of the predictions has been observed by many experiments. The experimental results seem to support both of the two items. But there may be some subtle differences are missing (enough precision? relativity?). When reading the article Copenhagen interpretation, we should also notice the sentence "The Copenhagen interpretation consists of attempts to explain the experiments and their mathematical formulations in ways that do not go beyond the evidence to suggest more (or less) than is actually there." - Justin545 (talk) 09:41, 28 March 2008 (UTC)

>> "There is no place for a collapse in Schrödinger's Equation"

Theoretically, is it possible to build a thought experiment in which the measuring process is simulated and use the Schrödinger equation to find out the result of the experiment? Had some one done this job before? - Justin545 (talk) 10:02, 28 March 2008 (UTC)

As above, it is an open problem. There are ongoing efforts to create "measurement" systems that can be fully modeled quantum mechanically via Schrodinger's equation for all parts of the system. Observationally it is certainly true that wavefunctions "collapse", by which one means that a single particle state interacting with a much larger collection of particles will usually be observed to reside in an eigenstate, however the mechanics of how this occurs is not well understood. The dynamical timescale is apparently quite short, and the systems that need to be modelled fairly large (e.g. 30 or 40 plus particles evolving simultaneously). Dragons flight (talk) 16:02, 28 March 2008 (UTC)

It is likely to get only numerical solution to Schrödinger's equation for so many particles. Finding the solution of exact expression for so many particles seems impossible.

After reviewed the article wavefunction collapse this morning, I noticed this:

By the time John von Neumann wrote his famous treatise Mathematische Grundlagen der Quantenmechanik in 1932, the phenomenon of "wave function collapse" was accommodated into the mathematical formulation of quantum mechanics by postulating that there were two processes of wave function change:

1. The probabilistic, non-unitary, non-local, discontinuous change brought about by observation and measurement, as outlined above.

2. The deterministic, unitary, continuous time evolution of an isolated system that obeys Schrödinger's equation (or nowadays some relativistic, local equivalent).

In general, quantum systems exist in superpositions of those basis states that most closely correspond to classical descriptions, and -- when not being measured or observed, evolve according to the time dependent Schrödinger equation, relativistic quantum field theory or some form of quantum gravity or string theory, which is process (2) mentioned above. However, when the wave function collapses -- process (1) -- from an observer's perspective the state seems to "leap" or "jump" to just one of the basis states and uniquely acquire the value of the property being measured, $e_{i}$, that is associated with that particular basis state. After the collapse, the system begins to evolve again according to the Schrödinger equation or some equivalent wave equation.

It seems that we should treat wave function change as an if-then-else statement in programming. If the change is discrete then use wavefunction collapse method else if the change is continuous then use Schrödinger's method. Not quite a an elegant way in science. - Justin545 (talk) 02:30, 29 March 2008 (UTC)

Any mathematical model that involves "alakazaam!" is obviously fundamentally flawed. However, QM is also the most precisely confirmed theory in human history. As a result, you get the null "Shut up and calculate!" interpretation, which seems to be what most people actually abide by. — kwami (talk) 18:19, 28 March 2008 (UTC)

It sounds like you (kwami) are really sick of quantum theories and those people who are learning it. Unfortunately, I am not here trying to pick a fight with someone over my post. I mean maybe you want to ignore this post and take a rest for a while. - Justin545 (talk) 00:41, 29 March 2008 (UTC)

Nuclear fission

What is the formula for the typ eof Nuclear fission used in power plants? The article has no formulae at all. —Preceding unsigned comment added by Anthrcer (talk • contribs) 09:36, 28 March 2008 (UTC)

The reaction in the top picture is ²³⁵U + n → ²³⁶U → ⁹²Kr + ¹⁴¹Ba + n + n + n. I think that would be fairly typical for anything other than a breeder reactor. The daughter nuclei aren't always the same though. There are a range of possibilities, but the first two steps stay the same. AlmostReadytoFly (talk) 09:48, 28 March 2008 (UTC)

In the case of fission, formulae don't tell you much, as there is a fairly even chance as to what the end-products (the fission products) will be. Pick two arbitrary fission products and you can figure out how many neutrons will be released, and by doing the binding energy calculations, how much energy will be released (in one of a few forms). Power plants don't use a different type of nuclear fission than anything else; where they differ is in the arrangements used to facilitate the fission reactions in different concentrations of uranium, etc. --Captain Ref Desk (talk) 11:18, 28 March 2008 (UTC)

Our article on fission product yield tabulates the most common products of uranium-235 fission, though it doesn't give specific formulae for the fission reaction. In general, the products will be as AlmostReadytoFly says—pick a couple of nuclei from the table that account for all your protons, any 'leftover' neutrons are free neutrons released by the fission. TenOfAllTrades(talk) 13:48, 28 March 2008 (UTC)

STS-123

Why was the hydrazine exhaust more pronounced in this flight than others? Nick (talk) 12:47, 28 March 2008 (UTC)nicholassayshi

I don't know, but here's our article: STS-123. One factor that can make exhaust more visible is humidity in the atmosphere. While on a dry day water vapor will instantly become invisible, on a humid day it can remain indefinitely as an exhaust trail. Under ideal conditions any exhaust particles can also serve as nucleation sites to cause cloud formation. Shock waves can have the same effect. Light conditions will also make the exhaust more or less visible. If it is lit up against a dark sky, that's when it will show up best. This lighting condition is most common before dawn or right after sunset, so the 2:30 AM launch doesn't seem likely to be illuminated by the Sun, but could still be illuminated by the rocket combustion. That seems to be the case in this pic: [1]. StuRat (talk) 16:22, 28 March 2008 (UTC)

doctors whose expertise is diabetics

How do you call a doctor whose expertise is Diabetics ? 'Diabetician' is probably wrong. BentzyCo (talk) 15:55, 28 March 2008 (UTC)

I would think that it's a sub-specialty of endocrinology. -- Coneslayer (talk) 15:56, 28 March 2008 (UTC)

(Which means that the physician's business card may describe him as an endocrinologist.) Individuals interested in a career in endocrinology will first finish a regular medical degree (MD). To become an endocrinologist usually requires at least a two- or three-year fellowship on top of their general training. Many endocrinologists specialize on a specific area within the field (diabetic medicine, reproductive medicine, etc.). TenOfAllTrades(talk) 16:07, 28 March 2008 (UTC)

There are also nutritionists/clinical dieticians who will advise you on a new diet for diabetics. I'm not sure if any handle diabetes alone or if they all handle multiple special diet planning. Also, many may not hold doctorate degrees. StuRat (talk) 16:20, 28 March 2008 (UTC)

It would be a metabolic sub-specialty of endocrinology. Wisdom89 _{(T / ^C)} 18:47, 28 March 2008 (UTC)

I looked up on the internet a doctor (in the US) who is an expert in treating diabetes. The website describes him as "Specialties: Diabetes, Endocrinology & Metabolism, Internal Medicine" and he is Board certified in Internal Medicine and Endocrinology. In the UK I found one who described himself as "Consultant Diabetician and Endocrinologist." So the terminology may vary regionally. Even in the UK "diabetician" seems to be more of an informal usage by patients rather than a professional certification. Edison (talk) 00:15, 29 March 2008 (UTC)

"Diabetologist" has some currency in the U.S. - enough to merit an entry in Merriam-Webster's Dictionary that dates the first use of the term as 1970. - Nunh-huh 01:41, 29 March 2008 (UTC)

That could also refer to a scientist who studies or specializes in or researches diabetes as well - probably why you might find mentions of the term floating around in literature. Wisdom89 _{(T / ^C)} 02:54, 29 March 2008 (UTC)

Well, I suppose it could, but in actual use, it generally doesn't. - Nunh-huh 00:15, 30 March 2008 (UTC)

We call them "Diabetes Specialists." There are CME courses for diabetes specialists and national testing to be officially titled as a diabetes specialist. Right now, I'm beginning a study on how much treatment of diabetes is improved in clinics that employ diabetes specialists. None of them call themselved diabeticians or diabetologists or anything of the sort. -- kainaw™ 03:00, 29 March 2008 (UTC)

Climate change

Given the clearly disturbing events that have just happened a few days ago regarding a 160 km piece of an ice shelf buckling, just how concerned should the world be. Also if the ice shelf does collapse, which areas will most likely be affected, the northern or southern hemisphere? I think we can all agree that we need to start looking for a new planet --77.100.6.191 (talk) 18:37, 28 March 2008 (UTC)

Take it easy. An ice shelf buckling is not going to destroy all life on Earth. Ice floating on water doesn't even increase sea levels when it melts. Ice on land does, but likely only a fraction of an inch worldwide. If all of the ice on Antarctica and Greenland melted, then you would have a significant sea level rise of tens of feet. That would be trouble for some low-lying coastal areas, especially those below sea level. However, as long as this happens slowly enough, we will be able to compensate by moving inland or constructing sea walls. Human life will survive. Now, would it be wise to take some of the resources we would otherwise put into evacuating coastal areas and spend that on slowing global warming, instead ? Sure, that would be a more efficient use of those resources. StuRat (talk) 18:51, 28 March 2008 (UTC)

Okay, this is an excuse to advertise my own work on an interactive tool for seeing regions vulnerable to sea level rise: http://www.globalwarmingart.com/sealevel A complete melt-down would be 65 m (210 feet) and have a dramatic effect, but that is very unlikely and would require a very long time even if it did happen. More likely is somewhere between 0.3 and 2 m (1-6 feet) during the next hundred years, which is important only to isolated regions, like New Orleans and the Netherlands, that are already very close to sea level. Speaking of efficient use of resources, another good one would be to stop building so many beach front properties. Property losses due to hurricanes in the US have increased 10-fold in recent decades, but that is mostly because so much more construction is being built in vulnerable areas. Dragons flight (talk) 21:05, 28 March 2008 (UTC)

Hi. Wow, that looks like a really useful tool, and perhaps just as useful as Flood Maps. The Wilkins Ice Shelf, even if it melts completely, should not be a global catastrophe. However, if Pine Island Bay melts, well, uh, that's another story. Hope this helps. Thanks. ~AH1^(TCU) 21:35, 28 March 2008 (UTC)

Hi. Woah, a mere 25-metre sea level rise would flood large areas around the Caspian sea, acording to that link. Thanks. ~AH1^(TCU) 23:00, 28 March 2008 (UTC)

One problem with these kind of maps is that they usually take into account only elevation, thus showing things like a greatly enlarged Caspian Sea, or a water-filled Death Valley, etc. This one seems a bit better in that its legend is labeled "Elevation Relative to Sea Level" -- which does not necessarily mean "filled with water". Pfly (talk) 18:55, 29 March 2008 (UTC)

Wilkins Ice Shelf

The spectacular series of pictures of a large piece breaking off from the Wilkins Ice Shelf clearly show the broken piece turn from white to blue as the crack progresses through Feb and March. Why is that? Surely it would not have got noticeably thinner in that short space of time. SpinningSpark 18:43, 28 March 2008 (UTC)

I think there was a subtle change in the angle that caused it to reflect light differently (it appears to be higher up on land and lower by the water). In Antarctica the sunlight is coming in at such a shallow angle that any change in the surface angle can put the entire surface in shadow. Shadows on snow and ice often appear blue. StuRat (talk) 18:58, 28 March 2008 (UTC)

Hi. How is it impossible for ice to melt in the space of a month? If it never melted, then it would refreze the next winter, and events like Larsen B would be impossible. Could it be that as the ice became detached from the main shelf, it started to crack, and the colder water, interspersed with large chunks of ice, created a "gel-like" structure overall and became a combination of ice and fresh water? Or, is it really impossible for it to melt that quickly in the space of a month? Didin't Larsen B turn blue when it was melting? How could Arctic ice, similar albeit less thick, melt so quickly if the ice cannot change in thickness? Will the Wilkins Ice shelf, the part that broke off at least, refreze around May and June? Thanks. ~AH1^(TCU) 21:43, 28 March 2008 (UTC)

Earth Hour - feasable or not?

As far as I know about power stations and electricity, it costs more power to halt a power station for an hour and restart it afterwards, than to keep it running. So, what if the Earth Hour succeeds in an impressive way, and everyone turns off everything for an hour. What could possibly happen? Where goes all the generated power? Wouldn't it be dangerous if suddenly everyone turns everything off? Wouldn't all the power stations blow off? with a 10% drop as last year, certainly not, but what about a 95% drop? --V. Szabolcs (talk) 20:04, 28 March 2008 (UTC)

Power networks have pumped-storage hydroelectricity facilities which consume excess electrical power during periods of low demand, using it to pump water from a low reservoir into a high reservoir. The water is then released during periods of high demand, when it generates electricity by driving turbines. In effect, these facilities act as huge rechargeable batteries. This allows the energy company to even out fluctuations in demand on the grid and to run their base load power plants at or near a constant peak efficiency. Gandalf61 (talk) 20:25, 28 March 2008 (UTC)

Thanks for the quick answer. I knew about the water pumping at the hydroelectric stations, but aren't those fluctuations statistical, so they usually never change very much too quick? If everybody at the same time turns everything on or off, wouldn't it cause strange effects? --V. Szabolcs (talk) 21:07, 28 March 2008 (UTC)

(ec) Well that's one solution. Other, not so widespread, options include undergound compressed air storage and NaS batteries (molten sodium batteries have ridiculous capacities, but only operate at high temperatures). For the large part though, much of the power infrastructure is still managed by taking plants on and off-line and allowing voltages to drift by several percent as you do so. Most electronics are tolerant of minor changes in the voltage which gives power suppliers room to adjust the amount of energy they are delivering without having to always react instantly to changes in demand. Dragons flight (talk) 21:16, 28 March 2008 (UTC)

Different types of power plants can be shut down and restarted on different time scales. Base load power plants (conventional coal or nuclear facilities) take hours or days to start up. Peaking power plants (oil-fired and especially gas turbines) can be started or shut down in minutes. The output of most hydroelectric plants can be regulated easily (often in seconds) by adjusting the flow of water through their turbines. Extremely rapid changes in demand (on time scales shorter than a few seconds) will result in brief increases or decreases in the grid's voltage. How easily the power grid can respond to rapid shifts in demand depends on how fast those changes occur, the size of the change, and the makeup of the grid's generating capacity.

The condition you're describing – where a power plant running at full output faces a sudden sharp drop in demand – is called load rejection. Power plants are designed to shut down safely when this occurs (as can happen during a major transmission line failure, for example—see Northeast Blackout of 2003), though restarting tripped plants can take hours or days. TenOfAllTrades(talk) 21:25, 28 March 2008 (UTC)

Hi. Should someone add Earth Hour to the on this day for the main page March 29, as well as edit the article on March 29 to mention Earth Hour, or should I do that myself? Thanks. ~AH1^(TCU) 21:46, 28 March 2008 (UTC)

I've mentioned Earth Hour in the March 29 artcle. --Bowlhover (talk) 04:37, 29 March 2008 (UTC)

Sounds like an interesting experiment, and I plan to do my part. An imbalance between generation and load due to everyone turning off lights at the same instant would cause the power frequency in the affected region to increase a bit above the normal 60 Hz until the steam valves could react by decreasing the input power to the generators. Most people will not alter their usage during the appointed hour. Other load which will not be affected includes electricity used to operate in full or in part the heating plants, refrigeration systems,stores, electricity used in industry, that used to operate electric trains,for operating elevators, restaurants, streetlights, sewage plants, hospitals, broadcasting operations, and many other portions of the load. The baseload plants will be dispatched according to the expected load. Baseload plants could be tripped offline if the load dropped too abruptly, and they would takw a while to restart. Peakers are smaller units designed to start rapidly and to change their output rapidly to follow loadswings. If folks in each timezone turned off their lights frop 8 to 9 pm local, there would be interesting swings in the powerflow on the tielines between utilities on either side of the time zone boundary. The US is connected a grid,(or rather grids) with large areas interconnected to allow one area to back up the next when load is added or when generation drops. It sounds like a field day for burglars, if residential security lights are turned off. Edison (talk) 22:28, 28 March 2008 (UTC)

I suspect it's a truism in control theory (and if someone can confirm this, I'd be grateful) that the best regulation can be achieved only with anticipation of future events. Machines aren't good at predicting unpredictable events in the future, but people can be. I suspect that, as the publicity surrounding Earth Hour has increased, the word has gone out to all the power plant operators everywhere (via whatever bulletin-board or chat system they use) that they'd be well-advised to have their finger closely on the throttle at 8:00 tonight.

I wonder, too, how far this observation goes in explaining what I hear has recently been discovered to be the inherent instability of large-scale electric power generation and transmission networks. We'd like to think that those networks, and all their regulation and protection mechanisms, are fully automated, removing us unreliable people from the loop. But if the systems are operating close enough to the edge (of capacity or stability or any other factor) that the best possible regulation is absolutely required, and if the best possible regulation requires more anticipation than "dumb" machines can possibly handle, then humans may be unavoidably part of the system, meaning that the possibility of human error (with arbitrarily catastrophic results) can't ever be entirely eliminated. —Steve Summit (talk) 18:50, 29 March 2008 (UTC)

"People can be good at predicting unpredictable events"?!?!? Would you, ah, care to rephrase that? --Anon, 21:45 UTC, March 29, 2008.

Well, okay, if you want to be pedantic about it, would you settle for "People can be good at reading the newspaper and anticipating events that couldn't have been predicted when the power grid management system was designed N years ago"? :-) —Steve Summit (talk) 22:52, 29 March 2008 (UTC)

How about Earth Away From Home? I now have my breaker box wired with contactor relays for each and every circuit and the contactor relays setup for remote control so that instead of shutting everything down for just an hour I can shut everything down including such electric appliances as the electric water heater when I leave for work. Except for the security system my house is dead until I return. That's everything off for at least eight hours a day. 71.100.15.236 (talk) 00:06, 29 March 2008 (UTC)

Well, I killed the main breaker in my home at 8 and restored power at 9. I did not see much of a blackout at neighbors' homes. During the hour I had a battery radio on, a fire in the fireplace, and a few battery lights, candles and kerosene lamps burning. It was a pleasant interlude, for what it's worth. It will be interesting to see if the experiment caused a measurable change in power demand. Edison (talk) 02:19, 30 March 2008 (UTC)

what causes water drops to join up?

I'm not talking about condensation, or the formation of water drops. I'm asking what is the name (if one exists) of the phenomenon of water drops clumping up to join a larger mass.

There are two scenarios in which i've seen this: first, when it's raining outside, and water drops slide down my car window, as they travel, they absorb more drops, gaining in mass and velocity. Second, if given enough time, and the frequency is right, free falling water drops will seem to clump up and form larger clumps.

I heard this refered to as the 'Moydo (Moydow?) Effect' but can't find any reference to it. Does anyone have a clue if this phenomenon has a name (other than water clumping, of course)204.154.43.244 (talk) 21:53, 28 March 2008 (UTC)

It's largely a function of surface tension. The most volume enclosed by a given surface area (or the least surface area required to enclose a given volume) is a sphere, and water tends to sit as spherically as possible given the constraints of gravity, intervening surfaces, and so forth. — Lomn 21:57, 28 March 2008 (UTC)

Do you mean the Marangoni effect ? SpinningSpark 22:16, 28 March 2008 (UTC)

More generally, perhaps coalescence? Sadly we don't seem to have much info on that, although it can be fascinating. 81.157.46.230 (talk) 01:44, 29 March 2008 (UTC)

Also, capillary action might be at work here, although this is related to/involves surface tension effects, in addition to intermolecular forces. Wisdom89 _{(T / ^C)} 03:03, 29 March 2008 (UTC)

Thermal ballast

Is it more energy efficient to keep a freezer and a refrigerator as empty as possible or to keep them loaded to the max.? —Preceding unsigned comment added by 71.100.15.236 (talk) 23:35, 28 March 2008 (UTC)

Personally, I believe it makes little difference, although having it fuller will probably make it slightly more efficient. And my hero agrees with me. —Steve Summit (talk) 00:49, 29 March 2008 (UTC)

I would define efficiency in terms of how much food is kept cold per dollar. In that case, an empty freezer is running at 0% efficiency. StuRat (talk) 04:02, 29 March 2008 (UTC)

If you have the type of freezer with a front-opening door and shelves, then every time you open the door the cold air flows out and it replaced by warm air from the room, which then has to be cooled again. In that situation it's more efficient to keep it full, since frozen food doesn't convect! I did see a suggestion somewhere though that you could reduce that problem by filling excess freezer space with empty cereal boxes to hold the cold air in place. Freezers with drawers also solve the problem. Eve (talk) 13:26, 29 March 2008 (UTC)

However, when you do put food in, you would then need to remove a cereal box full of cold air, and that won't help efficiency. StuRat (talk) 14:21, 29 March 2008 (UTC)

If it was a cereal-box-sized piece of food you put in, it would have displaced the equivalent volume of cold air anyway. —Steve Summit (talk) 14:54, 29 March 2008 (UTC)

Talking Budgerigars - sex difference

Why is it (usually) easier to teach a male Budgerigar to talk than a female? Why do male birds usually develop a larger overall vocabulary than females? --90.242.159.224 (talk) 23:45, 28 March 2008 (UTC)

Probably to impress the females. Male birds usually have many distinguishing features, like more colorful feathers, for the same purpose. --V. Szabolcs (talk) 08:28, 29 March 2008 (UTC)

Puck of the most words made the Guiness Book of Records in 1995[2] – he was a bloke, too. Julia Rossi (talk) 08:49, 29 March 2008 (UTC)

See sexual selection. --Captain Ref Desk (talk) 20:04, 29 March 2008 (UTC)