science tumbled

Soap Bubbles, Honeycombs, Snowflakes, Oranges on top of Each...

Fri, 24 May 2013 06:05:00 +0200

Soap Bubbles, Honeycombs, Snowflakes, Oranges on top of Each Other, and Programming Language Compilers

The Beijing National Aquatics Center, aka the “Water Cube”, constructed for the 2008 Summer Olympics, is based on the Weaire–Phelan structure. The what now?

In 1887, Lord Kelvin, notable for his achievements in thermodynamics, asked himself the following question: what is the most efficient bubble foam? To be precise, what is the structure of bubbles of equal volume with the least surface area? Kelvin proposed a slightly curved variant of the bitruncated cubic honeycomb, inspired by the honeycombs of bees. This structure, Kelvin thought, must be the most efficient way to construct a foam, like the one you’d observe when blowing soap bubbles.

An aside about bees. Two hypotheses about the hexagonal nature of bee cells have been proposed. One says that its efficiency at filling space while minimizing surface area (i.e., resource use) is why this design evolved. Another says that, far from geometric perfection, it is simply the way cells get deformed when bees try to squeeze their cells into each other—and observes that individual cells constructed outside the grid are irregular and not at all space-efficient.

For a hundred years, mathematicians considered Kelvin’s solution to be optimal. It seemed obvious, but no one could produce a formal proof of its efficiency. Then, in 1993, physicist Denis Weaire and his student Robert Phelan made a computer simulation and discovered a different structure, now bearing their names, which was slightly more efficient. This structure is non-obvious in that it employs two different kinds of cells, which nevertheless fulfill the formal criteria by having equal volume.

Something to think about when considering the similar ball stacking problem, which is even more obvious on first look. In 1611, the astronomer Johannes Kepler conjectured that the face-centered cubic packing—also known as the way to stack balls that results naturally from putting one ball on top of the other, in the way seen at any supermarket stack of oranges—is the most efficient packing. Slightly less than 26% of space is left unfilled by this arrangement. There are other known ball stackings with the same efficiency, but none that are more efficient. There’s a funny story about Kepler’s essay, On the Six-Cornered Snowflake: Kepler didn’t have money to buy his friend a Christmas present, because his employer hadn’t paid him for some time. Instead, Kepler wrote his friend a meditation on nothing, since he had nothing to give, in which he considers the closest things to nothing that were then known, such as snowflakes.

In 1998, mathematician Thomas Hales produced a proof of Kepler’s conjecture. This proof is widely accepted by mathematicians, but since it is a computer-assisted proof by exhaustion, meaning it runs through all the possibilities and checks to see if any is better than Kepler’s, it’s very hard to follow and to verify. This is why mathematicians remain skeptical to computer-aided proofs and prefer ones that aren’t. Another famous theorem, the four-colorem theorem, which states that any map can be colored with no more than four different colors such that no adjacent regions share the same color, was also proven by a computer-assisted proof by exhaustion.

But mathematicians aren’t Luddites. They don’t distrust computers by reflex. In fact, there is a theoretical result that is grounds for optimism about the future of mathematical proofs. Known as the Curry-Howard isomorphism, it establishes a correspondence between computer programs and formal proofs. The Coq proof assistant has a programming language designed with this isomorphism in mind. One of its applications is programming language semantics. Semantics is the field that studies meaning, and programming language semantics is about how compilers and interpreters—the programs that translate code written in a higher-level programming language into machine code—actually translate. Does the compiler translate the code as intended, or could there be bugs that make it mistranslate? Coq can help verifying that a compiler translates the code exactly as intended.

How the price of paint is set in the hearts of dying stars

Fri, 17 May 2013 02:16:58 +0200

How the price of paint is set in the hearts of dying stars:

Why are barns painted red? Because red paint used to be cheapest. But why is red paint cheaper than other colors? Ultimately, nuclear physics. Yonatan Zunger explains. For more on stellar nucleosynthesis, see: we are all made of star stuff.

Making gold green: New non-toxic method for mining gold

Wed, 15 May 2013 14:31:00 +0200

Making gold green: New non-toxic method for mining gold:

The traditional method of extracting gold from other materials, first discovered more than two hundred years ago, involves cyanide. Cyanide is very toxic. But now, scientists have stumbled upon a method of extracting gold by using alpha-cyclodextrin, a carbohydrate that can be derived from corn starch. The gold forms tiny nanowires. From a press release:

The supramolecular nanowires, each 1.3 nanometers in diameter, assemble spontaneously in a straw-like manner. In each wire, the gold ion is held together in the middle of four bromine atoms, while the potassium ion is surrounded by six water molecules; these ions are sandwiched in an alternating fashion by alpha-cyclodextrin rings. Around 4,000 wires are bundled parallel to each other and form individual needles that are visible under an electron microscope.

This method can be used, among other things, to recycle gold from consumer electronics. Hopefully they can find a way to make it work for ores, since the initial mining still accounts for the majority of gold cyanidation, and consequent environmental danger. One of the co-authors of this paper, Dennis Cao, is on reddit answering questions about the research.

Why can't you tickle yourself, but schizophrenics can?

Fri, 26 Apr 2013 14:03:00 +0200

Why can't you tickle yourself, but schizophrenics can?:

An interesting fact I learned from a reddit today, and which is supported by the scientific literature: schizophrenics can tickle themselves. Why is that?

The brain has a predictive model of the sensory results of different motor movements. For instance, if I move my hand in this way or that way, where is it going to end up? When you make the movement, this “predictor” is informed and forms a prediction about the sensation that will result—say, the sensation of a feather moving against your skin. When this sensory data comes in, it is compared to the prediction, and if they match up, the brain assumes that it was your self-generated movement, and thus can compensate for it. This is how we can distinguish between the exact same stimulus when applied by an external force or when applied by ourselves.

In an experiment, healthy subjects were instructed to tickle themselves by moving a piece of foam on their palm with their other hand. As predicted, the subjects did not find the sensation of their own tickling ticklish. Then their hand was hooked up so that, instead of directly tickling themselves, their hand movements were replicated by a robot hand. The researchers then introduced various delays or rotational translations of the movement—in effect, increasing the difference between the brain’s predictive model of the movement and the end result. The subjects reported that the sensation grew increasingly ticklish as the delay or rotation increased. In another experiment, however, schizophrenics reported no difference in the amount of ticklishness, whether the tickling was self-applied or applied by another person.

A current hypothesis about the origin of delusions of passivity, e.g., the idea that someone else is making you say or do the things you do, a classic symptom of schizophrenia, is that it is due to faults in this predictive model. Evidence suggests that schizophrenics fail to generate this predictive model of what their own movements will result in, which manifests as the inability to distinguish external and internally generated stimuli, like in the tickling example. In healthy non-schizophrenics, the predictive model and the sensory input that results from a movement will reinforce each other; the brain predicts that the movement of a hand will result in a certain sensation, and the sensation confirms it. This also allows us to self-correct before we even begin a movement if we detect that the intended result and the predicted result don’t match up. But schizophrenics tend not to make such self-corrections. One can imagine how delusions of passivity could result if the “predictor” fails to make a prediction: when it then tries to compare the end result to a non-existent prediction, it is as if someone else had willed the action. After all, in healthy subjects, when we receive “unexpected” (i.e., not predicted by the model) stimuli, it is usually of external origin. As in, when another person tickles us.

Extraordinary Vision: Polychromacity, Polarization in Mantis Shrimp

Mon, 15 Apr 2013 14:28:00 +0200

You may have heard of mantis shrimp. They are members of the order Stomatopoda, a group of marine crustaceans with some extraordinary properties. They’re hard-hitting bastards, but the most interesting property about them is their magnificent vision. Their vision varies between different species, but some species are capable of seeing light that is invisible to us, distinguishing more shades of visible light than us, and detecting properties of light impossible for humans to comprehend.

In order to understand the mantis shrimp’s vision, we need to understand some fundamental properties of light. Humans, of course, can distinguish millions of colors, but these are all detected by three different kinds of photosensitive cells in the eye, cone cells which have a peak sensitivity at three different wavelengths. Sophisticated visual processing in the brain then combines the varying intensities of these three types of cells to distinguish the millions of shades we see. Our cone cells can only see a very small sliver of the entire spectrum of light; most of the spectrum is invisible to us, either because the wavelengths are too short (ultraviolet) or too long (infrared), and on either side of that are even more extreme kinds of light, like X-rays. In addition to that, we also have rod cells, which are more sensitive to light than cones, but which can’t discriminate between different colors. These are mainly responsible for low-light vision and for detecting movement; this is why all cats are gray in the night (we rely for night vision on cells that cannot discriminate color).

So, we have three different kinds of cones and one kind of rod cell, for a total of four different photosensitive cells. Some women may be tetrachromats, that is, they have four different kinds of cones and can distinguish more colors than everyone else. That doesn’t even begin to compare to mantis shrimp. Some species have as many as sixteen different kinds of photosensitive cells! Here is a diagram:

Not only can this species see ultraviolet light that is invisible to us, it can also distinguish much better between shades of visible light than us! However, this is kind of misleading. It’s true that the eyes of mantis shrimp have much more sophisictated color vision than human eyes; at the same time, however, they have much smaller brains. The visual center in the human brain is much more sophisticated than the mantis shrimp’s. As a result, it’s hard to compare color vision directly. What we can say for sure is that the raw input from the eyes is much better for color vision than the raw input from human eyes.

But that’s not all. Mantis shrimp can also detect polarization of light, which is a property that is completely invisible to us, as difficult to imagine as color would be to someone with monochromatic vision. To understand polarization, we need to understand a few things about the wave nature of light. Waves can be transverse or longitudinal. Here is a diagram:

Sound waves propagating through air are longitudinal. The air compresses and expands, carrying energy along. Light waves, on the other hand, are transverse. To simplify, they move “up and down.” Longitudinal waves, by definition, are moving “left and right” along the direction of the wave. The “up and down” movement of transverse waves, however, can go in different directions. This means that transverse waves, such as electromagnetic (light) waves, can be polarized.

Unpolarized waves basically move up and down in random directions. Polarized light, however, “waves” in a specific pattern, for lack of a better description. Light coming from the Sun is unpolarized, but becomes partially polarized when it passes through the atmosphere. Thus most light we see is partially polarized, but we are completely blind to this. Light of different polarizations looks the same to us, all else being equal. Some animals can distinguish different polarizations, however.

It’s been well known for some time that some animals can perceive linear polarization. Here is an illustration of linear polarization (look at the blue line):

The waving is confined to a given plane along the direction the wave is traveling. However, this is not the only way for light to be polarized. There is also circular polarization. Until recently, it was believed that no animal could perceive circular polarization. Here is a circularly polarized wave that goes clockwise from our vantage point:

And here is one that goes the opposite way:

Stokes parameters are a mathematical construction that completely describes a state of polarization. If you know these parameters, you basically know all there is to know about the kind of polarization (or non-polarization) that characterizes whatever light you’re looking at. Scientists recently demonstrated that the Gonodactylus smithii species of mantis shrimp can perceive all the Stokes parameters, or, in other words, they have perfect polarization vision.

Why would this be useful? Well, polarization information can be used to navigate, or it can be used to identify prey that would be transparent to humans (the light doesn’t change intensity or color when it passes through, but it may change polarization). It could also be used to communicate in a way that other species couldn’t detect. Below you see a signalling structure (viewed through filters to make the direction of circular polarization visible to humans) on the mantis shrimp:

Fun fact: in organic chemistry, one way of naming different enantiomers (molecules that are mirror images of each other) is by the direction they rotate polarized light.

Voyager 1 Encounters New Region in Deep Space

Tue, 26 Mar 2013 00:44:05 +0100

Voyager 1 Encounters New Region in Deep Space:

Voyager 1 is the man-made object farthest from the Sun, steadily traveling towards the edge of the solar system and beyond. A recent paper analyzing data from the probe, which is still sending data back to Earth, states that as of August, 2012, the probe has entered a new region of space which they dub the “magnetic highway.” Radiation levels from inside the solar system dropped to 1 percent of previous levels while radiation from outside the solar system increased dramatically in a matter of days, leading some to propose that Voyager 1 has finally—and as the first man-made object ever—left the solar system for good. NASA, however, was quick to clarify that they do not consider the probe to have entered interstellar space quite yet, as they expect magnetic field lines to change direction when this occurs. The boundary of the solar system is kind of fuzzy, but one thing is clear: this little piece of metal humanity sent out 35 years ago is really, really far away and traveling in unexplored territory. Here be ~~dragons~~ cosmic rays aplenty.

Miraculin

Fri, 22 Mar 2013 05:03:56 +0100

Miraculin:

Miraculin is a taste-modifying protein found in the fruit of Synsepalum dulcificum, also known as miracle berries. By itself, miraculin doesn’t have much of a taste, but after dissolving miraculin on the tongue, sour things like lemons taste sweet. The effects last for up to an hour. Miracle berry pills are available online.

Miraculin doesn’t affect the brain, it operates directly on the taste receptors. Experiments have shown it to have an interesting property: at neutral pH levels, it acts as an antagonist of sweet taste receptors, but in an acidic environment it turns into an agonist. This means that it will actually block the taste of things that are usually sweet, like table sugar or artificial sweeteners like aspartame. However, for some reason, when you add something acidic (sour), the effect changes, strongly activating the sweet receptor, known as hT1R2-hT1R3. Sour things taste sweet, and sweet and sour together tastes really sweet. Scientists hypothesize that the acid donates protons to the hT1R2-hT1R3-bound miraculin, causing it to change shape and go from inactive to active.

Weird Words

Tue, 19 Mar 2013 17:05:14 +0100

A couple odd linguistic phenomena.

A morpheme is the smallest unit of language that carries meaning. A cranberry morpheme is a morpheme that has no independent meaning. We know what “sub-” or “super-” mean regardless of what comes after, but the “cran-” in cranberry or the “-ceive” in “conceive”, “receive” and “perceive” have no meaning outside those words. Another example is the “cob-” in “cobweb”, which comes from an old word for spider, “attercop”, literally “poison-head”. (Cf. Norwegian “edderkopp.”)

Unpaired words are words that look like they should have a twin, but don’t. You can be unkempt, but hardly kempt, and one can be untoward but not toward, disgruntled but not gruntled. Frequently it’s the negative senses of such words that survive. Here is an article that explains the origins of many unpaired words. The word “ungainly”, for instance, ultimately comes from the adjective “gain”, meaning “straight, near”, which was used in the phrase “the gainest way”, meaning the shortest, most direct route. A word like “dishevelled”, on the other hand, comes from the Old French ” deschevelé”, and was never the negative of a positive “shevelled.”

An interviewer asks Richard Feynman how magnets work. This seems...

Fri, 01 Mar 2013 15:14:00 +0100

An interviewer asks Richard Feynman how magnets work. This seems like a perfectly reasonable question to ask of a scientist who won the Nobel prize for his work on quantum electrodynamics. But Feynman launches into a long rant that does everything, I suppose, but explain how magnets work.

You might say that Feynman is being a bit rude or mean to this interviewer, but at the same time, his rant gets to the heart of what science is and Feynman’s approach to it. Magnetism is both simple and complex, as Feynman explains. It is simple in that the electromagnetic force is one of the four fundamental forces of nature. It is simply a fact of the universe, in fact one of the simplest facts, that the electromagnetic force exists. At the same time, physicists have spent millions of man-hours learning exactly how the force works, to a high degree of accuracy, but this can’t be explained to a layman:

If you’re somebody who doesn’t know anything about [physics], all I can say is that there’s a magnetic force that makes [magnets] repel. And that you’re feeling that force. But then you say, “That’s very strange, because I don’t feel a force like that in other circumstances.” When you turn them the other way, they attract. There’s a very analogous force, the electrical force, which is the same kind of a question. Then you say, “that’s also very weird.” But you’re not at all disturbed by the fact that when you put your hand on the chair, it pushes you back. But we found out by looking at it that that’s the same force as a matter of fact—the electrical force, not the magnetic exactly in that case—but it’s the same electric repulsions that are involved in keeping your finger away from the chair…

I can’t explain that in terms of anything else that’s familiar to you. For example if we say the magnets attract like as if they were connected by rubber bands, I would be cheating you. Because they’re not connected by rubber bands, I shouldn’t be in trouble. You’d soon ask me about the nature of the bands, and secondly, if you were curious enough you’d ask me why rubber bands tend to pull back together again and I would end up explaining that in terms of electrical forces, which are the very things I’m trying to use the rubber bands to explain, so I’ve cheated very badly, you see.

Feynman is all about how you can always ask deeper, more interesting why? questions. And you can dumb down science by making analogies, but chances are if you keep asking why? eventually the analogies will break down as begging the question: to explain the analogies, you need to use the very concepts which the analogies were supposed to explain the first place.

This video displays some of Feynman’s charisma. He was a very funny guy, as anyone who has read Surely You’re Joking, Mr. Feynman! knows. Definitely check out that book if you haven’t read it. It’s not a scientific book, it’s more a series of humorous anecdotes from his life, but they provide a glimpse into the mind of one of the great scientists of the 20th century. And it’s very funny in a way that both nerds and non-nerds can appreciate.

The Ganzfeld Effect

Wed, 27 Feb 2013 13:21:15 +0100

The Ganzfeld Effect:

The Ganzfeld or “whole field” effect is a simple way to trick the brain and induce hallucinations. The most common setup is to cut up a white ping pong ball in two halves, put them over your eyes and illuminate them from the outside. The effect will be of staring into a uniform white field. In the absence of any structure to sensory input, or in the absence of any input whatsoever—as in sensory deprivation—the brain will start to amplify the noise inherent to perception, eventually producing simple or complex hallucinations. The effect can be extended to several senses, typically by wearing headphones blasting white noise or other unstructured sound.

Ganzfeld experiments are darlings of “paranormal researchers”, who use the setup in attempts to prove extrasensory perception. (Using red light is popular, I suspect for the sole purpose of giving photographs of the seance an otherworldly vibe.) Unsurprisingly, the results of these experiments don’t improve on chance.

Five hundred million years ago, evolution was still a moody...

Mon, 18 Feb 2013 20:17:25 +0100

Five hundred million years ago, evolution was still a moody teenager undergoing an experimental phase. Of course, evolution is experimenting continually—that is kind of the nature of genetic mutation—but the animal life during the pre-Cambrian and early Cambrian periods was something else. This is an animation of Herpetogaster collinsi, a bizarre creature found fossilized in the Burgess Shale. No one knows quite where it belongs in the tree of life, although it may be related to sea stars and acorn worms. See more weird evolutionary experiments from this time period here, or read more on this blog: when life got big, or, a forgotten architecture of life; and check out Hallucigenia, another specimen from the Burgess Shale that definitely lives up to its name.

Watercolor painting of a Mycoplasma mycoides cell, by David S....

Sat, 09 Feb 2013 18:26:20 +0100

Watercolor painting of a Mycoplasma mycoides cell, by David S. Goodsell. This cell would be about 250 nanometers in diameter. M. mycoides are parasitic bacteria that live in cattle and goats, causing lung disease. You can see the plasma membrane surrounding the cell, but Mycoplasma, like animal cells and unlike most bacteria, are distinguished by the lack of a cell wall. This means they are immune to antibiotics like penicillin which target cell walls. M. pneumoniae is a species that causes disease in humans.

Mycoplasmas are interesting because they’re the smallest self-replicating organisms that exist. Since mycoplasmas represent nature’s most minimal self-reproductive machinery, their study could help define the essential nature of biological life itself. (Viruses are smaller still, but require their hosts to do the replication for them.)

Observing a solar eclipse on January 1, 1907, in the Tian-Shan...

Mon, 04 Feb 2013 20:08:18 +0100

Observing a solar eclipse on January 1, 1907, in the Tian-Shan mountains, probably in modern-day Uzbekistan. This is a photograph taken by Sergey Prokudin-Gorsky, a chemist and photographer who invented a new process for color photography and used it to document the Russian empire in the time period 1905-1915. You can view many of the photos on Flickr or at the Library of Congress.

Cold War Science

Mon, 04 Feb 2013 14:32:00 +0100

In case you missed it, the New Yorker published a great, but terrifying look into science’s sordid past this last December. Operation Delirium and High Anxiety: LSD in the Cold War detail the US army’s experiments in mind control and chemical warfare during the cold war, centered around Edgewood Arsenal, in Maryland.

The efforts were led by Colonel James S. Ketchum, who wanted to develop a more humane approach to war: the enemy was not to be killed, only incapacitated using various chemical agents. Never mind that those agents might well be nerve gas, and the mechanism of incapacitation extreme mental or physiological stress. His best bet for such an incapacitating agent was BZ, an anticholinergic drug like scopolamine or atropine which causes delirium. (These drugs work by blocking the transmission of the important neurotransmitter acetylcholine.) At one point Ketchum’s team resorted to building “an entire Hollywood-style set in the form of a makeshift communications outpost.” Soldiers were placed on the outpost and dosed with either placebo or varying doses of BZ. Then Ketchum set about trying to fuck with their heads in any way he could think of:

Two hundred phony tactical messages, warnings of chemical attacks, and intelligence were fed to the men in the room. At one point, Ketchum and the others ran out of script. “In an urgent brainstorming session, we put our heads together and came up with an agonizingly improvised scenario,” he recalled in his memoir. “We told the military communicators to start sending new intelligence to the group inside the room—in a simple code. The messages informed the men that enemy forces were planning to move a train loaded with chemical weapons along a certain route.” Eventually, Ketchum and the technicians resorted to gibberish, using poker terms, referring to “the dealer” and a “full house,” as the BZ-addled soldiers struggled to interpret their code.

Ketchum was flanked by Dr. Van Murray Sim, who founded the Edgewood program on psychochemicals in 1956. Sim’s grand idea was the use of LSD-25 to loosen the tongue of what might today be euphemistically called “enemy combatants,” or if that didn’t work, make them so mad that they’d tell any secrets they had just to escape the torture. Maybe it was cruel, but surely, the logic went, the Communists were doing the same, and the US could not afford compassion. Besides, Sim figured, if he was willing to test the chemicals on himself first and he was fine, surely he could test them on others.

One chilling story is that of Private James Thornwell. Throwing informed consent to the wind, Sim theorized that expectations about a drug’s effect would influence the intoxication, and so it was vital that the subjects did not know what they were given, or even that they were given anything. When word got around about the kind of experiments going on at Edgewood, Sim was forced to relocate his experiments to Europe and, eventually, to Asia. James Thornwell was the only African-American working at an American military-communications station in France. After a falling out with his superior, Thornwell was accused of stealing classified documents. After three months of torturous interrogations, Thornwell insisting on his innocence, he was released—not to freedom, but into the hands of Sim’s special investigators, who repeatedly dosed an already half-mad man with LSD without his knowledge. Thornwell never recovered. The experiment was deemed a success.

It wasn’t only the military who were carelessly experimenting on humans. Under the innocuous-sounding title Effect of some Indolealkylines in Man, a 1959 medical paper details some rather cruel experiments. Ostensibly, the scientists set out to study the effects of a psychedelic snuff used across Central and South America. Failing to achieve any effect from the snuff, they isolated two pure chemical compounds for further study. They were n,n-DMT, a powerful psychedelic also found in the traditional brew ayahuasca, and bufotenine, a chemical cousin of the neurotransmitter serotonin. These chemicals were injected intravenously into schizophrenic patients.

Here is a description of one of the experiments:

In several subjects who had more than 10 mg of bufotenine injected quickly, there was intense salivation. The present subject could easily have drowned in her own saliva, and she had to be turned on her side. (…) Responsiveness returned at about 23 minutes, at which time the patient was entirely lucid and, in response to a query related to a preinjection question, spoke of a long-repressed memory from the age of three years, when she came into the bathroom and saw her mother die of a uterine hemorrhage.

But this revelation “had no therapeutic consequence.”

In further experiments, we read, three patients—as if they were patients undergoing treatment, not guinea pigs for mad scientists—were injected bufotenine after receiving reserpine or chlorpromazine (both antipsychotic drugs). “Each of these injections almost proved fatal in small amounts.” After one subject almost died, they repeated the experiment two more times just to make sure. It’s the same absurd logic which prompted Sim’s LSD researchers to respond to adverse reactions by doubling the dose in the next trial.

The LSD trials were suspended in 1963, but the Edgewood experiments continued into the 1970s.

Diagonal cross-section of the Menger sponge, a 3-dimensional...

Fri, 11 Jan 2013 17:34:45 +0100

Diagonal cross-section of the Menger sponge, a 3-dimensional fractal. In the limit, this fractal has infinite surface area and zero volume.

Bonus lulz: apparently, there is a Taiwanese horror film where a “crippled scientist” uses a Menger sponge to “capture the energy of the spirit of a child”. I don’t even know.

The media are abuzz with news of an experiment that manages to...

Sat, 05 Jan 2013 01:40:05 +0100

The media are abuzz with news of an experiment that manages to create negative absolute temperature. Phys.org:

In order to bring water to the boil, energy needs to be added to the water. During heating up, the water molecules increase their kinetic energy over time and move faster on average. Yet, the individual molecules possess different kinetic energies – from very slow to very fast. In thermal equilibrium, low-energy states are more likely than high-energy states, i.e. only a few particles move really fast. In physics, this distribution is called Boltzmann distribution. Physicists around Ulrich Schneider and Immanuel Bloch have now realized a gas in which this distribution is exactly inverted: Many particles possess large energies and only a few have small energies. This inversion of the energy distribution means that the particles have assumed a negative absolute temperature.

The Boltzmann distribution can be illustrated with balls that are distributed on a hilly landscape, which provides both a lower and upper bound for the potential energy of the balls. At positive temperatures (left figure), as they are common in everyday life, most balls lie in the valley around minimum potential energy. They barely move and therefore also possess minimum kinetic energy. States with small total energy are therefore more likely than those with large total energy – the usual Boltzmann distribution. At infinite temperature (central figure) the balls spread evenly over low and high energies in an identical landscape. Here, all energy states are equally probable. At negative temperatures (right figure), however, most balls wander on top of the hill, at the upper limit of potential energy. Also their kinetic energy is maximal. Energy states with large total energy are occupied more than those with small total energy – the Boltzmann distribution is inverted.

Coffee appears to be good for you.

Tue, 25 Dec 2012 19:22:00 +0100

Coffee appears to be good for you.:

This large study published earlier this year and involving tracking more than 400,000 participants over twelve years looked at the correlation between coffee drinking and mortality. It found that, all else being equal, there is an inverse correlation between coffee drinking and mortality, or, in other words, people who drink a lot of coffee died less often:

In this large, prospective U.S. cohort study, we observed a dose-dependent inverse association between coffee drinking and total mortality, after adjusting for potential confounders (smoking status in particular). As compared with men who did not drink coffee, men who drank 6 or more cups of coffee per day had a 10% lower risk of death, whereas women in this category of consumption had a 15% lower risk. Similar associations were observed whether participants drank predominantly caffeinated or decaffeinated coffee.

However, all else is rarely equal. The study also found that coffee drinkers were more likely to have other habits, particularly smoking, that correlate with higher mortality. When not correcting for these factors, coffee drinkers were a bit more likely to die. In other words, coffee appears to be good for your health, but if you drink a lot of coffee, statistically you’re more likely to have other, unhealthy habits that increase mortality.

2012 Roundup

Thu, 20 Dec 2012 14:24:00 +0100

Some of the more interesting things that passed through these pages in 2012.

The Brocken Spectre is an optical phenomenon in which the observer’s shadow appears to be magnified on clouds or fog below.

Psychedelics are back in science. After decades of little research due to drug hysteria, scientists have started exploring the therapeutic potential of psychedelics and similar drugs again. Here is the New York Times reporting on a promising study of MDMA-assisted therapy for PTSD.

On February 9, 1913, a unique procession of meteors was observed from North America. This meteor shower may have been the breakup of a short-lived, small second moon.

Rare earth metals are important for a number of modern technologies. China has a near-monopoly on the world’s supply, and they’re prepared to use it for political gain.

Synthetically grown bismuth crystals.

How long is the coast of Britain? Depends on the size of your measuring stick, of course. Enter fractal dimensions.

Wolbachia pipensis is an interesting group of bacteria that do funky things to reproduction.

(Previous years: 2011, 2010.)

Organic chemistry explained with cats.

Thu, 06 Dec 2012 02:35:39 +0100

Organic chemistry explained with cats.:

Some people might point out that “conformations” and “configurations” are also concepts in organic chemistry that mean much the same thing, and that this post is a thinly disguised effort to teach concepts in organic chemistry through a discussion of cats. Horseshit. This is 100% cat content here people! This is a cat blog.

Sometimes, the ways science goes wrong are as interesting as the...

Sat, 01 Dec 2012 17:05:00 +0100

Sometimes, the ways science goes wrong are as interesting as the ways it goes right. Nowadays, it seems uncommon for major discoveries which have been accepted by the scientific establishment for centuries to be proven completely wrong; they are more likely to be incrementally improved upon. Newtonian physics wasn’t wrong, it just wasn’t as right as Einstein’s relativity (which is to say, in most everyday situations, the two are indistinguishable, but Newton goes wrong in border cases he had no way to test, or even conceive of). But in the early days of modern science, some theories were put forth and widely accepted which turned out to be not only less than complete, but spectacularly wrong. One of my favorites is the phlogiston theory of combustion, which turned out to be the exact opposite of correct.

Another is the theory of preformationism. It holds that living beings are not assembled from parts, but that their form has actually existed since creation. Human beings come from homunculi, from the Latin for “little man”: in other words, humans grow from tiny versions of themselves which are identical in form to an adult. Even after Antonie van Leeuwenhoek, pioneer in microscopy, in 1677 discovered sperm cells, some scientists continued to hold that there must be tiny humans inside each cell (illustrated above). There was even scientific debate about whether the homunculi resided inside the ovum or the sperm cell. Today, this sounds like a “how many angels can dance on the head of a pin?” type of question.

Of course, one consequence of such a theory would be that humanity has a predetermined lifespan. After all, if humans nest inside each other like Russian dolls, at some point, the chain must end. A single sperm cell cannot contain an infinite amount of tinier humans with even tinier sperm cells with tinier humans.

I’m going to do something I don’t usually do on this blog and recommend some science-minded fiction. Notice that I don’t say “science fiction”. A lot of sci-fi is indistinguishable from fantasy, introducing impossible premises and then ignoring them when convenient, applying them when the plot requires. Science-minded fiction, on the other hand, would be fiction that takes false or impossible premises and then works out, in logical fashion, what the consequences would be.

One of my favorite authors of such fiction is Ted Chiang. He is not a very prolific author, but almost everything he publishes is gold. Every year he publishes a story, he earns at least a nomination for a Hugo or Nebula award. You should check out his collection of short stories, Stories of Your Life and Others. In that book, there is a story called Seventy-Two Letters, which imagines a world where Jewish mysticism and the preformation theory are true. Division by Zero is a story about a mathematician who discovers that mathematics is inconsistent. The title story is perhaps the best one in the collection, dealing with the now discredited Sapir-Whorf hypothesis and some other stuff I’m not going to spoil. If this sort of thing interests you, do check it out. Most of the stories in the collection have been available online at one time or another, so you might be able to find them if you’re cheap or impatient.