Wikipedia:Reference desk/Archives/Science/2011 March 5

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March 5

An attempted desription of Eternity,

Would someone identify the writer of this attempt to illustrate the idea of Eternity which I read decades ago and will now try to re-create. Try to imagine a block of granite 100 miles long by 100 miles wide by 100 miles high.Once every 10,000 years a small bird alights on it to sharpen it's beak.After the last bird has worn away the last granule of the block this will represent the first second of Eternity. J.Cowell00:27, 5 March 2011 (UTC) —Preceding unsigned comment added by 124.185.229.128 (talk)

I think it may be HG Wells in his book about the history of the world. 92.24.182.238 (talk) 00:44, 5 March 2011 (UTC)

It sounds like a bit of the sermon on Hell in A Portrait of the Artist as a Young Man by James Joyce. AndrewWTaylor (talk) 13:34, 5 March 2011 (UTC)

Yes, it is from Portrait:

Now imagine a mountain of that sand, a million miles high, reaching from the earth to the farthest heavens, and a million miles broad, extending to remotest space, and a million miles in thickness; and imagine such an enormous mass of countless particles of sand multiplied as often as there are leaves in the forest, drops of water in the mighty ocean, feathers on birds, scales on fish, hairs on animals, atoms in the vast expanse of the air: and imagine that at the end of every million years a little bird came to that mountain and carried away in its beak a tiny grain of that sand. How many millions upon millions of centuries would pass before that bird had carried away even a square foot of that mountain, how many eons upon eons of ages before it had carried away all? Yet at the end of that immense stretch of time not even one instant of eternity could be said to have ended. At the end of all those billions and trillions of years eternity would have scarcely begun.

. See here for the full text. AndrewWTaylor (talk) 13:38, 5 March 2011 (UTC)

The bird with the grain of sand illustration did not start with Joyce. The evangelist Charles Finney used it in 1855. See, "On Neglecting Salvation" from April 11, 1855 by Finney [1]. However, it may be older than Finney. The granite and the sand are variations of the same sort of illustration. I'm also interested to know the original source.

I'm not convinced that is it. I still recall something in one of the several history books by HG Wells. I think I remember an illustration that went with it. 92.15.18.16 (talk) 14:41, 6 March 2011 (UTC)

Since this found its way to the Science desk rather than Humanities, I should point out that such a vision of eternity does not have a basis in the world as we know it. When we look at physics with a particular set of laws, as for atoms and molecules, the universe seems to have a beginning in a Big Bang, and an ending in (probably) cold and endless space. When we look at the universe as an eternity (by considering the logarithm of time, or something similar) we encounter all sorts of different physics without beginning nor end, from quark-gluon plasmas to decaying protons. The stage of eternity is one on which bird and sand and observer and probably even space itself are fundamentally transformed, become unrecognizable, and transformed again, a continual ferment of raw creativity following a plan of supreme beauty, which is unknown to all those who lack infinite energy and infinite time for experiment. Wnt (talk) 21:10, 6 March 2011 (UTC)

What makes tape sticky

I find myself on this board, randomly contributing to answer a question, and figured I'd throw one out there that I came across today. So, I was doing my expense report and taping receipts to a piece of paper for photocopying, and I wondered: What makes tape sticky? I mean, I know it has something to do with an adhesive, and tacki-ness (sp), but more specifically what exactly is going on? Is it a chemical bond? What physical process is going on that makes it stick, but not bind permanently? Also, it seems when you peel scotch tape off paper, the tape is "less" sticky but the paper is not sticky at all. Is it absorbed? Deep thoughts, by David Able 04:51, 5 March 2011 (UTC)

Adhesion is the article, but it's unfortunately confusing. The most important thing is that adhesives flow into microscopic gaps in the surface, giving a much larger contact area. In the case of scotch tape that happens when you press the tape against the surface. When you pull something apart (i.e., put it under enough tension that it breaks), the weakest bonds break first. If you're lucky those will be the bonds that formed when you applied the adhesive, but that's not a foregone conclusion. No bond is really permanent. As for the actual bonding mechanism of scotch tape, I'm not really sure. It's some kind of van der Waals force. -- BenRG (talk) 11:07, 5 March 2011 (UTC)

I keep wondering if electrostatic attraction isn't involved in "stickyness" in some molecular/nanoscale fashion. Edison (talk) 03:10, 6 March 2011 (UTC)

energy

It is sometimes, but not always, possible to obtain "energy" via a differentiation of a spatial coordinate; (for example, kinetic energy is related velocity squared - which is a nonlinear operation on the first derivative of a spatial coordinate). So, "energy" is rarely a useful coordinate in most physical treatments. But you must know the mass to get the actual energy, right? — Preceding unsigned comment added by 98.221.254.154 (talk • contribs)

I would say that energy is very often a useful concept of most physical systems. Dauto (talk) 06:04, 5 March 2011 (UTC)

The OP is directly quoting my response to the question about "Dimensions" from March 2, 2011, but out of context. I was discussing whether "energy" would be a useful generalized coordinate, not whether it would be "useful." Nimur (talk) 13:32, 5 March 2011 (UTC)

Yes, you need to know the mass to get the (classical, kinetic) energy. 83.134.170.152 (talk) 06:32, 5 March 2011 (UTC)

Exactly - if you mean classical, kinetic energy, you must know the mass of the object - which is a constant. Nimur (talk) 13:35, 5 March 2011 (UTC)

Food spoilage rates

Why does meat spoil faster than fruits and vegetables? And why do flour, cookies, potato chips, and crackers just go stale instead of spoiling like the aforementioned meat, fruits, and vegetables? —SeekingAnswers (reply) 08:03, 5 March 2011 (UTC)

A few thoughts:

1) Moisture content is critical, and dryer things may not rot at all, like crackers and flour.

2) Trans fats are specifically used because they increase shelf life, in products like cookies, potato chips, and crackers. Apparently they are as unhealthy for microbes as they are for us.

3) Hi salt content also retards bacterial growth.

4) In other cases, some partially rotten products may still be considered edible. This is the case with fruit, for example. There are examples of fermented meat which people still eat, but most people find such things more distasteful than fermented fruit.

5) In the case of fruit, vegetables, and, in particular, potatoes, then may remain "alive" for some period after they are removed from the rest of the plant, and thus their own immune system may continue to fight bacterial growth. Since potatoes and onions can grow new sprouts, under the right conditions, this means that they must still be alive.

6) Fruit often has a skin designed to act as a barrier to bacteria, and that provides some period of protection. StuRat (talk) 18:21, 5 March 2011 (UTC)

Trans fats are not intentionally added, dude. They are a byproduct of catalytic hydrogenation of alkenes. John Riemann Soong (talk) 22:59, 5 March 2011 (UTC)

I'm not following you. If they aren't intentionally added, are you saying they are accidentally added ? StuRat (talk) 07:07, 6 March 2011 (UTC)

Thanks, but the answer to my two questions are still not entirely clear. I'm rather confused by the listing out of so many factors; which of them are most important? I don't think the question of why meats are so much more prone to spoilage than fruits and vegetables has been completely addressed; salted meat will still spoil faster than fruits and vegetables. Anyone else have anything to add? —SeekingAnswers (reply) 01:27, 6 March 2011 (UTC)

Beef jerk is salted and dried meat. I lats a long time. Dauto (talk) 01:47, 6 March 2011 (UTC)

Ethene and fermentation are articles of particular interest. ~AH1^(TCU) 03:11, 7 March 2011 (UTC)

The simple answer, and the one I would give to someone asking this for the first time, is that certain things are needed by the micro-organisms that decompose food, so an absence of those things can slow down or stop food spoilage.

First, there needs to be some micro-organisms or their spores (abtut like tiny eggs) present: when we sterilise something, we try to kill any micro-organisms and their spores. This is why sterilised food has to be sealed completely airtight, because micro-organisms and their spores are in the air around us everywhere. Canned food, and food you buy in a sealed jar, relies on this.

Secondly, there needs to be a source of food for the micro-organisms. Obviously, all things which are food to us also contain food for micro-organisms.

Thirdly, there needs to be enough available water for the micro-organisms. That's why drying food slows spoilage, because it's hard for micro-organisms to live in such dry conditions. Crackers are generally very dry, although they start to spoil as they absorb water from the air. It's also why food with a lot of sugar or salt lasts longer, because the high levels of sugar or salt dry the micro-organisms out! Think of how dry your mouth feels if you eat a lot of sugary or salty food without drinking anything.

Fourthly, it needs to be warm enough for the micro-organisms. At room temperature or warmer, micro-organisms tend to multiply very quickly, break food down quickly, produce toxins very quickly. At fridge temperatures, they do everything more slowly. At freezer temperatures, not only have they slowed right down but the water is frozen! And micro-organisms need water. And, of course, get them hot enough for long enough and they die.

These are the basics, and they are all important. We have an article on food preservation. 86.163.4.134 (talk) 12:58, 7 March 2011 (UTC)

Your answer addressed why wet things spoil faster and why sealed, salty, or frozen things spoil slower, but not why meat spoils faster than fruits and vegetables. —SeekingAnswers (reply) 14:51, 8 March 2011 (UTC)

Yes, these basics easily answer your second question. They also largely answer your first, although there are additional relevant details I excluded for simplicity's sake. One large part of the answer is that more dangerous micro-organisms or their spores are already present on the meat than the fruit, so meat spoils in the sense that it is unsafe to eat more quickly than fruit. Another is that the fruit and veg is often still sort-of alive, with functioning cells that continue their resistance to micro-organisms: some more so than others. Fruit is also typically sugary. Etc, etc. Check out the article I linked. 86.163.4.134 (talk) 16:46, 8 March 2011 (UTC)

Run Lola Run “sideways thru time” question

In the film Run Lola Run, and in many other sci fi films, the theme of “how would a small difference in the order of events affect long-term consequences as time moves on?” is explored. In this film’s case, (and it takes its philosophy pretty seriously) , Lola has to run somewhere in order to save her boyfriend. That run is shown three times, and each time there is some small difference, for example, she bumps into some people which slows her down a little. That difference ends up completely changing the results of her efforts at the end of the day. No one seems to think there is anything odd about this, and other films explore this theme with similar outcomes.

I have thought about it, and in my thought experiment, the whole platform on which Run Lola Run rests can be demonstrated to be false. Yes, it is true that a single, small event can change a whole life. For example, a young man attends a party that he had not intended to go to, meets a girl, and they end up getting married. But such life changing events that are the result of a small deviation in routine are rare. Run, Lola, Run implies that EACH such deviation has long-term consequences that radically alter one’s life.

I feel that can be refuted decisively by reflecting on one’s own life. In my case, for example, I lived in the same place for over 10 years. Each day, something unexpected would occur; I’d meet an old friend by accident and go and have a few drinks and so on. But at the end of each day, however many deviations from the norm occurred, I would end up back in my own little bed, safe and sound. If small deviations in the norm changed outcomes like they do in Run Lola Run, one’s life would be a huge storm of chaos, each day would be a major alteration of direction. It would be impossible to live like that. I feel surprised that no one seems to mention this when the scientific and philosophical themes of such films are discussed: that the structure of lives has a sturdiness that is not NORMALLY perturbed by chance meetings and intervening events. We are put off course briefly but we get back on course. We miss a train, so we catch the next one. If that means we miss a meeting, we discuss it with someone else. So our lives end up pretty much where they were before.

I’ve got no argument with Run Lola Run in the depiction of a small PARTICULAR event having a radical impact on the outcome of an entire enterprise, but it is only feasible that it happens once. The film puts forward the idea that EVERY such deviation from the norm has a radical effect, but the general ordinariness of our own lives provides ample refutation of that notion. I think this is a scientific question as well as a philosophical one, and I would be interested in the opinions of other WIkipedians. Myles325a (talk) 09:01, 5 March 2011 (UTC)

Have you checked out butterfly effect and perhaps Butterfly effect in popular culture? Nil Einne (talk) 09:24, 5 March 2011 (UTC)

You might also wish to consider the sum over histories theory of Richard Feynman. --TammyMoet (talk) 11:37, 5 March 2011 (UTC)

For an even more detailed (and in my opinion more delightful) "study" of this question, see Groundhog Day, where the same day is run through hundreds of times with only one variable (Bill Murray) changing. In any case, the idea that the little things in life get overwhelmed (most of the time) by the big trends is indeed a valid criticism, I think. I'm not sure it holds universally, though. In the context of history, this is discussed in some detail in Carr's What Is History?, where he talks about attributing too much to "accidents" of history (e.g. the entire fate of the Russian revolution to the fact that Trotsky got a cold on the wrong day). Carr says that these explanations miss out on the fact that huge forces have been previously put into motion anyway behind these "accidents" — that focusing on the tip misses you the rest of the iceberg. --Mr.98 (talk) 14:15, 5 March 2011 (UTC)

I think the answer is somewhat in between. That is, while not all seemingly insignificant events in your life have a dramatic effect on the outcome, many do. I think of it in terms of equilibrium, and will use a glass bowl analogy. Which events upset the equilibrium, like pushing a bowl off a table where it shatters, and which are self-correcting, like pushing a bowl, having it wobble a bit, then settle back down ? Your "missing a train" example could be self-correcting, if you get on the next train. However, what you do during that period or what you would have done, had you been on the earlier train, are also events which need to get back onto the original path. The longer it takes, and the more subsequent events occur, before you "catch the next train", the less likely it is that the time-line will be fully restored. StuRat (talk) 18:10, 5 March 2011 (UTC)

The real problematic part here is strictly speaking, as far as we know, time just doesn't work this way. Film gives us the impression that we can divide it into little indefinite segments, and possibly reloop "time lines" in different ways. But as far as science tells us (odd interpretations of quantum theory notwithstanding), the arrow of time is one way (although it can run at different rates depending on your reference frame, etc.). This is not a pedantic point; it was the foundation of a great deal of the philosophy of time, by people such as Henri Bergson, who explicitly criticized film as giving people very bad ideas about how to visualize "time" and "events". Bergson would say about your comment: "there is no time-line to be restored; there is just one time-line, and it plays out how it plays out, irrespective of how you imagine it in a more ideal form." Only in fiction do we get to have multiple "time-lines" in the sense you mean. To very much bastardize Bergson, he would say, when you try to make broad statements about the nature of time based on metaphors from film, you are making as big a category error as you would if you were trying to make broad statements about the nature of violence based on cartoons. --Mr.98 (talk) 19:47, 5 March 2011 (UTC)

The OP seems to assume that there exists a sequence of events, called the norm, from which various degrees of deviation occur i.e. 1) deviations that cause only a temporary disturbance to the sequence that is supposed to be in equilibrium to which it returns, and 2) deviations that have expanding repurcussions that irrevocably change everything that follows. The assumption is appealing because it allows unlimited speculation about Counterfactual history. However it is impossible to prove the speculation that any future sequence of events is more "normal" than any other, and the grading of "deviations" is an Anthropomorphism. Example: the corrosion of an electric contact may cause an innocuous click in a telephone conversation or prevent a nuclear bomb exploding, but the corrosions were equally inevitable in the given environments. Cuddlyable3 (talk) 23:12, 5 March 2011 (UTC)

All physical systems respond elastically to perturbations below some threshold and plastically to larger perturbations. It's universal. I see no way to avoid the conclusion that human history, considered as a physical system, behaves in this way also. You could treat Earth's weather as external to the system, or you could treat it as internal and have the external perturbations come from micrometeorites or something. In the end it doesn't matter much.

You can't escape this by arguing that it's impossible to define a notion of alternate history, because that's an argument against the scientific method. If you believe that experimental data is noisy, and that one must ignore the noise when looking for patterns, then you believe in counterfactuals. That's what a counterfactual is. For that matter, if you believe that there's such a thing as entropy then you believe in counterfactuals. It's the same thing.

I realize that it's disturbing to think that human history could have gone entirely differently, and it's tempting to argue against it for that reason alone, but this is the science desk and that's the science. If you can come to terms with trillions of other galaxies that probably harbor intelligent life, or with the eventual demise (by heat death or spacetime singularity) of everything the human race has ever created, then you can come to terms with this. -- BenRG (talk) 01:55, 6 March 2011 (UTC)

Suppose we consider two sets of spacetimes, with identical pasts, one where you turned right, and one where you turned left. You were able to turn right or left from the same past because physics is indeterminate. Likewise, it is possible that the worlds where you turned right or turned left have the same future, because of the same indeterminacy. So if you select out a set of parallel spacetimes and arrange to travel between them by the twisting of a knob on a machine, then whether you travel among worlds with the same pasts and different futures, or different futures and the same past, or same pasts and same futures, or, of course, different in every regard, depends solely on how this very hypothetical machine is contrived.

If it is not necessary to build a machine - notably, if one supposes a connection between such parallel spacetimes based on religious faith - then there is no physical law to prove or disprove that one's consciousness moves between these parallel worlds as the process of divine creation continues to unfold. Wnt (talk) 20:58, 6 March 2011 (UTC)

The whole question seems to reduce to whether potential outcomes in a walk of life are oscillatory or deviatory. The situation could branch into almost an infinity of possible outcomes or the outcome of a decision could have two or three possible outcomes. This is another issue involving whether humans have free will and how deterministic human interactions are (or whether our decisions cause quantum collapse) and the simple answer is: we don't know. ~AH1^(TCU) 03:09, 7 March 2011 (UTC)

I've always thought Terry Pratchett summarised this idea particularly well in the Discworld novel, Lords and Ladies:

The universe doesn't much care if you tread on a butterfly. There are plenty more butterflies. Gods might note the fall of a sparrow but they don't make any effort to catch them. Shoot the dictator and prevent the war? But the dictator is merely the tip of the whole festering boil of social pus from which dictators emerge; shoot one, and there'll be another one along in a minute. Shoot him too? Why not shoot everyone and invade Poland? In fifty years', thirty years' ten years' time the world will be very nearly back on its old course. History always has a great weight of inertia.

--Kateshortforbob _talk 15:57, 7 March 2011 (UTC)

Kolmogorov complexity

Hi. I'm pretty new to computer science, but am fascinated by the term Kolmogorov complexity. The article has an example that contains the letters "ab" repeated 32 times, and encodes it as "ab 32 times". However, what if the actual string given is "ab 32 times"? How could we differentiate that from an encoded version of the abab... string? 88.112.51.212 (talk) 12:13, 5 March 2011 (UTC)

The example we use in our article is a bit "invalid" (for the sake of simplicity) - it's missing a complete description of an escape character that would be required. Some piece of information (at least one single bit) is required to indicate whether the substring "32 times" should be interpreted literally or as a "modifier" to the preceding characters. This extra information can be included by using an escape-character that is always specially-interpretted; but then you can never print the escape character! So you need a little more sophistication in the scheme. This problem pops up a lot in the implementation of encoding-algorithms; the answer invariably is either "indicate the special interpretation using side-channel information" or "indicate the special interpretation by using in-band escape-characters." Naturally, trouble arises when trying to convey the literal value of the escape-character; but again, this can be done with either in-band or side-channel information.

You might find it helpful to consider actual implementations of run-length encoding or lossless data compression to see the practical implementations of these theoretical requirements.

I will also point out that a complete information-theoretical description of complexity of a data-stream should account for the complexity of both the data-stream and the algorithm or machine that must be used to decode it. Abstract machines (or decoding-algorithms) require some minimum number of bits to define them - and this is often the "forgotten" information-container when "infinite compression" schemes are proposed. You may find Turing completeness interesting, and the principle of the quine program concept. Nimur (talk) 13:45, 5 March 2011 (UTC)

It is not true that in constructing a data compression code one must invariably indicate the special interpretation by using in-band escape-characters. In LZW compression thst is used in GIF image files the coding algorithm starts by expanding all characters slightly rather than compressing them. The trick lies in the encoder then teaching (up to a limit) the decoder about every string of characters that might repeat, so that only one character suffices to convey each repetition. The resulting compression ratio can be very high. Cuddlyable3 (talk) 15:52, 5 March 2011 (UTC)

I think this talk about escape characters is a red herring. Escape characters are an irrelevant implementation detail, and they're not even commonly used in real compressed stream formats. The important thing is that compressed and uncompressed streams are kept separate. You don't have to distinguish your compressed stream from an identical uncompressed stream because your decompressor will never get an uncompressed stream. If you compress abababababababababababababababababababababababababababababababab to "ab" 32 times then you probably will compress "ab" 32 times to something like '"ab" 32 times' 1 time—or at any rate, to something other than a copy of the uncompressed string. Yes, the compressed string is longer than the uncompressed string; that's unavoidable in general (by the pigeonhole principle, aka the counting argument).

The other important thing is that the compressed formats used in discussions of algorithmic complexity have to be Turing-complete programming languages. Most (all?) real-world compressed formats aren't. The reason you need Turing completeness is that every compressed format must be "convertible" into any other by prepending a description of a decompressor for the other format to compressed data in that other format. This makes the optimum compression ratio format-independent in the limit of arbitrarily large files, which means that you can define algorithmic complexity (in the limit of arbitrarily large files) without tying it to any particular compressed format. -- BenRG (talk) 23:31, 5 March 2011 (UTC)

Are gays and lesbians fertile?

If a gay man had sex with a straight woman or a lesbian was raped by a straight man, would they produce viable children? —Preceding unsigned comment added by 93.29.254.150 (talk) 12:18, 5 March 2011 (UTC)

Most likely. Sexual orientation has no effect on fertility necessarily. See Clay Aiken (specific example) and artificial insemination (the method that he used). Finalius (Say what?) 13:09, 5 March 2011 (UTC)

Yes, of course they are. Many have had children. And the millions of those who were married but "in the closet" over the years had children as well. --Mr.98 (talk) 14:11, 5 March 2011 (UTC)

Residents of France, of whom the OP seems to be one, are not AFAIK famous for such ignorance about sexuality. The OP poses scenarios that are incompatible with consensual sex. A child conceived in such abnormal encounters is as likely to be biologically viable and grow as any other, but its mother will need to compensate somehow for the lack of a normal father figure. Cuddlyable3 (talk) 15:25, 5 March 2011 (UTC)

@Cuddlyable3: I don't know anything of mothers having to compensate for the lack of a normal(?) father. Actually, I don't even know what a normal father is.Quest09 (talk) 02:22, 6 March 2011 (UTC)

Also, the first case can perfectly well be consensual. Happens now and then. Aaronite (talk) 03:11, 6 March 2011 (UTC)

Although gay parents are not unknown, I don't know if they are equally fertile. If their hormonal levels are different, they certainly could be less fertile. Quest09 (talk) 02:23, 6 March 2011 (UTC)

@Quest09, on this ref. desk we try to provide sourced information and references to questioners. You have posted "I don't know..." 3 times[2] [3] which is unhelpful. Cuddlyable3 (talk) 04:36, 6 March 2011 (UTC)

@Cuddlyable3: Saying "i don't know" is a polite way of saying "I've never heard about this shit before."Quest09 (talk) 13:18, 6 March 2011 (UTC)

Yes CA3, we should provide sources and references, and not provide unasked for opinions (which of course can not have proper source or reference). For instance, the phrase "its mother will need to compensate somehow for the lack of a normal father figure." True, many editors opine here, but in this case the OP asked only about viability of offspring, and not about your feelings on family life. SemanticMantis (talk) 15:54, 6 March 2011 (UTC)

I think Cuddlyable3's point is that these desks are not conversations between one editor and the rest of the world. If an editor has something positive to contribute, they're welcome. If they don't know the answer to a question, nothing is gained, and space is wasted, by them coming here to tell the world that they don't know. The OP certainly couldn't give a tinker's cuss that some anonymous bloke on the internet does not know the answer to their question. -- Jack of Oz [your turn] 20:55, 6 March 2011 (UTC)

You would be right if my "I don't know" were simply expressing the fact that I don't know something. However, I was reacting to the assertion of Cuddlyable3 that: "its mother will need to compensate somehow for the lack of a normal father figure" (is that a sourced reference?) and also pointing out to the fact that homosexuals could have a different fertility level. I was actually saying: "THAT's fishy!"Quest09 (talk) 21:58, 6 March 2011 (UTC)

You could make an argument either way for possible differences in homosexual fertility. Some would say that homosexuality could potentially be associated with physically intersexed phenotypes, but for example, I think that all suggestions of a correlation with Klinefelter syndrome or Turner syndrome have been rebuffed. Though there's still a chance for a small unobserved effect. On the other hand, I remember seeing something in print a decade or two ago saying that female relatives of gay men actually had higher fertility, which was used in support of kin selection; however, the typical formulation neglects this effect and focuses on non-genetic benefits.^{[4]PMID 18810630} I wouldn't rule out that homosexuals themselves could have higher fertility rates for other reasons - for example, women who avoid men should not suffer allergic reactions to sperm. The problem is that getting data is difficult. If you look at this the way you'd look at a mouse experiment, then Utah has a far higher fertility rate than other states, ^[5] but of course this doesn't prove anything. What is clear is that many gays and lesbians who decide to have children are able to do so; to a zero-order approximation, there is no known difference. And there is a wide variety of difference among heterosexuals - for example, a steadily falling sperm count in the U.S. and western Europe. Eating specific foods like hemp seeds can cut sperm count by 50%. So you're looking for a tiny signal in a sea of noise, under circumstances that make even crude counts unreliable. Wnt (talk) 20:46, 6 March 2011 (UTC)

Skyscraper

Let's say, in strictly theoretical terms, that there is a skyscraper so tall it reaches all the way up into the higher atmosphere, space even. Would the building look like it was bending upwards from ground level according to the Coriolis effect, or would it still look perfectly straight? Thank you.--Editor510 ^{drop us a line, mate} 14:33, 5 March 2011 (UTC)

A viewer standing on the ground is in the same inertial frame of reference as the skyscraper and therefore observes its true straight shape, with minor modifications due to obscuration by clouds, and refraction due to the atmosphere's temperature gradiant. Cuddlyable3 (talk) 15:31, 5 March 2011 (UTC)

A viewer standing on the ground is in the same inertial frame of reference as the base of the skyscraper. Except at the poles, a skyscraper on the surface of the rotating Earth will be experiencing a slightly different acceleration at each height. TenOfAllTrades(talk) 16:02, 5 March 2011 (UTC)

So? Cuddlyable3 (talk) 21:51, 5 March 2011 (UTC)

As Coriolis effect says, the Coriolis effect is an apparent deflection of moving objects when they are viewed from a rotating reference frame. The skyscraper is not moving in the reference frame of somebody standing besides it, so there is no Coriolis effect. However, if somebody dropped an object from the top then, due to the Coriolis effect, it wouldn't fall straight down. This can be observed from far smaller heights. A gunner or sniper at the bottom aiming for the top would also see the projectile curving and would have to not aim straight at the goal even if gravity is ignored. PrimeHunter (talk) 17:47, 5 March 2011 (UTC)

Thank you.

Resolved

--Editor510 ^{drop us a line, mate} 22:29, 5 March 2011 (UTC)

Will the frame dragging effect of twisted spacetime cause a theoretical if not appreciable bend in a similarly tall object? —Preceding unsigned comment added by 129.67.37.227 (talk) 15:01, 6 March 2011 (UTC)

Looking for an electronic engineering journal

Hi there, hope this is the right place to ask! I was wondering if someone could recommend a good journal on electronic engineering, preferably one that can be subscribed to in paper form from the UK. Kind regards, Raywil (talk) 19:54, 5 March 2011 (UTC)

Are any of these any good to you? List of Institute of Electrical and Electronics Engineers publications--Aspro (talk) 20:19, 5 March 2011 (UTC)

Thanks for replying. There are definitely some interesting titles there and I didn't realise the IEEE published so many things. I'm still looking for a particular recommendation though if anyone has one. Raywil (talk) 21:11, 5 March 2011 (UTC)

Electronic Design Magazine is free and though Electronics (magazine) 1930 - 1995 is no longer published you may find copies in library collections. Cuddlyable3 (talk) 21:59, 5 March 2011 (UTC)

Any recommendation would really depend on what the OP is hoping to gain from it. If it is just for general interest, then pop along to a local WHS and paw through a copy of Electronics World. If it is to prepare for an electronics course then it would be best to ask the course lecturer or whoever for their recommendation. Local public reference libraries should have a subscription for one or two of the more popular publications. Or let your imagination rip! One of my student flat-mates, got his dear aunt to fork out for a Playboy subscription. After all - he was studying anatomy (an' 'e ended up with first class 'onours to boot!).--Aspro (talk) 22:57, 5 March 2011 (UTC)

Thank you very much for all of your suggestions so far. I've sent off for a copy of Electronic Design and will have to look out for Electronics World next time I'm in WHS as I've never noticed it there before. I'm considering studying the subject at uni so thought I'd better get myself some related reading material. Any more appropriate suggestions would definitely be much appreciated. Raywil (talk) 00:54, 6 March 2011 (UTC)

IEEE Spectrum is a good one too - it's not too technical or domain-specific, but provides a "generalist" viewpoint into the cutting edge of electronics. I would say Spectrum is the magazine you should read (IEEE calls it the "flagship publication"). You can read online versions at http://spectrum.ieee.org or order paper subscriptions. Nimur (talk) 15:33, 6 March 2011 (UTC)

In my recollection, it is very expensive to join IEEE and get their journals. Edison (talk) 00:48, 7 March 2011 (UTC)

adaptive features of fish

tell me about adaptive features of fish —Preceding unsigned comment added by 220.225.96.217 (talk) 20:35, 5 March 2011 (UTC)

Have you tried searching the web or searching for relevant articles on Wikipedia? We are somewhat unlikely to write an essay on the subject for you. Please ask us about specific issues when you have done your own research. 88.112.59.31 (talk) 21:03, 5 March 2011 (UTC)

It also helps to narrow down the question. Just one example is symbiosis of clown fish to the sea anemone. ~AH1^(TCU) 02:49, 7 March 2011 (UTC)

inverting integrators and time integral of voltage

When I take the time integral of voltage, what unit do I get? I'm trying to use an equation similar to that in Operational_amplifier_applications#Inverting_integrator and I want to know if I have an RC value of 1.06 milliseconds how much that would scale my output by. John Riemann Soong (talk) 21:54, 5 March 2011 (UTC)

You can get the Time constant you mention using R = 1060 ohm and C = 1 uF. If there is a step change of +v at the input then during the next 1.016ms (assuming the integrator output is not saturated) the output will change negatively by −0.632v. Cuddlyable3 (talk) 22:16, 5 March 2011 (UTC)

Can you walk me through that? I totally understand the RC part -- what I don't get is that is that if I take this integral of a sinusoidal function, I seem to get an output integral reported in V/s, not V. This is because the inverted integral of sin t dt is cos t -- thus I get cos(t2)/RC-cos(t1)/RC as my theoretical output.

Which of course I am puzzled by, because my output should be in V, not V/s. If I do a square wave I am fine -- the inverted integral of a constant +v is -v*t/RC, which gives me an output in volts. How do I calculate how to scale my output for sinusoidal functions? John Riemann Soong (talk) 22:36, 5 March 2011 (UTC)

The sinewave input is V_in = V_pk sin ( ω t ) where ω = 2 π f

You omitted the frequency f. The angular velocity ω is in radians sec^-1. Cuddlyable3 (talk) 00:09, 6 March 2011 (UTC)

Exactly. In fact sin t is not a physically meaningful statement because it is a non-polynomial function of a dimensional quantity which makes no sense. Dauto (talk) 02:04, 6 March 2011 (UTC)

This non-polynomial?

${\begin{aligned}\sin t&=t-{\frac {t^{3}}{3!}}+{\frac {t^{5}}{5!}}-{\frac {t^{7}}{7!}}+\cdots \\[8pt]\end{aligned}}$ Cuddlyable3 (talk) 05:06, 6 March 2011 (UTC)

Yes, it is non-polynomial. see the first sentence of polynomial. The problem is that every term in the expansion above has a different dimension (it is measured with different units) so they cannot be added in a physically meaningful way. Dauto (talk) 06:17, 6 March 2011 (UTC)

Huh? ω t is (radians / sec)* sec, i.e. radians. Which are handled as non-dimensional units in the sin expansion above. They can all add up. Doing sin of something in radians is quite ordinary. Wnt (talk) 07:16, 7 March 2011 (UTC)

Image of a moleclue

OK, how would the researchers this image? After all I've learned of quantum mechanics, I thought it wasn't possible to narrow down the location of an atom so closely. Magog the Ogre (talk) 23:02, 5 March 2011 (UTC)

That's an electron density map. You can theoretically predict it using calculators. It's important because we can now measure electron density empirically rather than merely theoretically. John Riemann Soong (talk) 23:11, 5 March 2011 (UTC)

As long ago as 1989, IBM used a scanning tunneling microscope to position 35 Xenon atoms to spell out IBM. SpinningSpark 01:04, 6 March 2011 (UTC)

Then what is all this quantum physics nonsense about not knowing an atom's state at any place and time? Magog the Ogre (talk) 02:51, 6 March 2011 (UTC)

See quantum uncertainty. Bear in mind that the scale of an atom is very different from the scale of a nucleon or an electron, and that while quantum uncertainty is quite real at all physical scales, it's only really relevant once you're subatomic. — Lomn 04:04, 6 March 2011 (UTC)

So that means a telescope that's 10000x as powerful as this one could probably not exist? Magog the Ogre (talk) 08:21, 6 March 2011 (UTC)

Microscope, not telescope. Unlikely, for different reasons. Plasmic Physics (talk) 08:36, 6 March 2011 (UTC)

It's also worth noting that you can't really tell the precision of those images very well from the image alone. At the level of an atom, uncertainty principle says there will be limits to your precision — not that you can't know anything. It's a ratio of how precise your understanding of both position and momentum can be. It is only when you get to the level of, say, a bare electron, that the ratio gets so extreme that you start being able to know only one or the other. It is a common entry-level physics problem to ask students to calculate how much precision in position/momentum you can have for visualizing things on that level, how "in focus" they can maximally be. --Mr.98 (talk) 14:36, 6 March 2011 (UTC)

That's a truly gorgeous image, but note that you see rings, not points. The uncertainty principle tells us that we can't follow individual electrons zipping around that racetrack, but it does not in any way prohibit us from calculating nor observing the shape of molecular orbitals in breathtaking detail. Wnt (talk) 20:01, 6 March 2011 (UTC)