Technology

80 cards about Technology, with explanations, methods and source links.

Cards about Technology

• Did a brain scan prove that writing by hand teaches better than typing?

  The headline went everywhere: a brain scan had settled it, and handwriting beat typing. Underneath sat a real result, wider connectivity across the brain in EEG while people wrote by hand. Then a published critique pointed at the step from that result to the claim. What was missing?

  Source: Pinet and Longcamp, Frontiers in Psychology

• What would happen to the navigation on your phone without relativity?

  A navigation receiver works out where it is by trilateration: from minute differences in the arrival times of signals from several satellites. So the accuracy of their clocks is everything. Relativity says two opposite things about such a clock: its high speed should slow it down, and the weaker gravity up there should speed it up. Which one wins, and what does it cost?

  Source: Ashby, Living Reviews in Relativity

• What does the router in your house know about who is in the room?

  A Wi-Fi router sends out radio waves that bounce off walls, furniture and people, which gives the receiver several copies of the same signal arriving by different paths. The receiver is already measuring the strength and the shift of each one at every frequency. When somebody moves in the room, that pattern changes. What can be read out of it?

  Source: Adib & Katabi, ACM SIGCOMM

• Why does a reactor that has already been shut down still need cooling?

  Stop the chain reaction in a reactor and the fission stops at once. But the radioactive material it made while it was running does not vanish at the same moment, and it carries on decaying by itself. What does that leave behind, and why does it mean cooling for years?

  Source: U.S. NRC, decay heat

• Which wall of lava lamps is guarding part of the internet?

  Good encryption needs numbers that are genuinely random, and a computer is a deterministic machine that on its own produces only pseudo-random sequences. So it needs a source of noise from the physical world, something nobody can predict and nobody can reproduce. Where do you get one of those?

  Source: Cloudflare, LavaRand in production

• Why does a QR code still work when part of it has been erased?

  A QR code looks like a picture of the information, and every pixel in it looks necessary. And yet you can print a logo right through the middle, crease it and dirty it, and it still scans. How does that work?

  Source: Reed & Solomon, J. Soc. Indust. Appl. Math.

• How did a dead spider become a ready-made robotic arm?

  Spiders straighten their legs with fluid pressure rather than with a pair of opposing muscles as we do, so after death the pressure goes and the legs curl up. What happens if you put the pressure back?

  Source: Yap et al., Advanced Science

• Why does the cheese in a cacio e pepe sometimes seize into one lump?

  Cacio e pepe is supposed to hold nothing but pasta, pecorino, pepper and water, and that is the whole secret. Except that heating the cheese brings on protein coagulation, and the proteins clamp together into a single lump. The researchers mapped the conditions and varied them systematically. What prevents it?

  Source: Bartolucci et al., Physics of Fluids

• They had an alligator bellow in helium. Which part of its voice changed?

  A voice is made in two stages: the vocal folds vibrate, and the cavity of the mouth and throat filters the result. Out of the two comes one sound, and separating them is hard without dissecting the animal. So a female alligator was put in a chamber with helium. What changed?

  Source: Reber et al., Journal of Experimental Biology

• Why does a toughened window crumble into thousands of small pieces instead of long blades?

  Toughening heats glass and then cools its surfaces fast, so they stay in compression while the center stays in tension. That compression is what stops scratches and shallow cracks. And what happens when something gets through anyway?

  Source: Zaccaria & Overend, Journal of Materials in Civil Engineering

• Is virtual reality really an “empathy machine”?

  A virtual reality headset is sometimes called an empathy machine, because it places you inside the experience. But empathy includes at least two things: feeling with a person, and understanding their point of view. Which of them moves?

  Source: Martingano et al., Technology, Mind, and Behavior

• Does a long password have to be complicated as well to be strong?

  Many sites demand a capital letter, a digit and a special character, on the assumption that complexity equals strength. To find out, fifteen kinds of password rules were tested on more than twenty thousand participants, for strength and for convenience alike. Which won?

  Source: Shay et al., ACM Transactions on Information and System Security

• Why does a drop of water flee a very hot pan in particular?

  In a moderately hot pan, water touches the metal and boils quickly. Logic says that the hotter the pan, the faster the drop should evaporate. Above a certain temperature exactly the opposite happens. Why?

  Source: Quéré, Annual Review of Fluid Mechanics

• An air dryer spreads more bacteria than a paper towel. Is that always true?

  The claim that an air dryer spreads more bacteria than a paper towel comes round again and again, sometimes on signs in the washroom. Except that the results in the literature contradict one another. Here volunteers dried their hands both ways while instruments sampled the air. What came out?

  Source: Gião & Vardoulakis, Frontiers in Public Health

• A cockatoo wants the seed inside a hard fruit. Why is one tool not enough?

  Using a single tool is familiar in many animals. On an island in Indonesia, Goffin’s cockatoos were seen opening a hard fruit, and every stage of the job demanded something different of them. Why did one tool not do?

  Source: O’Hara et al., Current Biology

• A chain pours from a cup to the floor. Why does it rise into the air first?

  When a long bead chain pours from a tall container, it does not pass straight over the rim but climbs into the air first. The weight of the falling part can pull downward, not push upward. So what lifts it?

  Source: Flekkøy et al., Frontiers in Physics

• Why does a magnetic liquid grow spikes when you bring a magnet near it?

  A ferrofluid is a liquid holding tiny magnetic particles that stay dispersed, and in a weak field its surface is almost smooth. As the field strengthens it grows orderly spikes. A liquid is not supposed to hold a shape. So what is going on there?

  Source: Engel et al., Journal of Magnetism and Magnetic Materials

• A pig at a screen with a joystick. Does it understand that its movement moves a cursor?

  Moving a joystick is one thing, and understanding that your movement moves a cursor on a screen is another thing entirely. Four pigs were trained to push a joystick with the snout and bring a cursor to a colored wall. What did they understand?

  Source: Croney & Boysen, Frontiers in Psychology

• A parrot touches a picture of another parrot on a screen. Does it really want to call?

  A parrot touching a picture on a screen may only be learning to press for a stimulus, which says nothing about wanting company. Eighteen parrots learned to ring a bell, choose a photograph of another parrot and open a video call. What did they do with it?

  Source: Kleinberger et al., CHI 2023

• You open a bag of nuts and the big ones are on top again. Why does shaking not mix them?

  You open a bag of nuts and the big ones are always on top, although the shaking on the way should have mixed them. A granular material, a pile of particles, does not behave like a liquid. So what is actually going on in there?

  Source: Möbius et al., Nature

• A drop of coffee dried on the table. Why is most of the stain at the rim?

  A drop of coffee dries and leaves a dark ring at the rim with an almost empty middle. If the liquid evaporated evenly, the particles would stay evenly spread. What moves them to the edge?

  Source: Deegan et al., Nature

• A lotus leaf grows in mud and stays clean. What does the rain do differently on it?

  A lotus leaf grows in mud and stays clean, and the obvious explanation is a smooth surface that dirt cannot catch on. Under a microscope the opposite turns out to be true: the surface of the leaf is extremely rough. What does the rain do there?

  Source: Barthlott & Neinhuis, Planta

• A gecko runs across a smooth ceiling with no glue. What holds each step?

  A gecko runs across a smooth ceiling with no glue at all, and comes off the instant it wants to. Real adhesive does not behave that way, because it sticks and then fights being removed. To find the mechanism, researchers pulled on one hair from a gecko toe, and on the toes of live animals, across surfaces of opposite chemistry. What held?

  Source: Autumn et al., PNAS

• A water strider pushes backward, and its legs barely break the surface. What is it pushing?

  Water-repellent hairs keep a water strider’s legs from wetting, and surface tension carries its weight. To move forward it has to push something backward, and the legs hardly break the surface at all. For decades the assumed answer was waves. So what are they pushing?

  Source: Hu et al., Nature

• A salt flat cracks into polygons of almost equal size. What marks their borders?

  A salt crust breaks into polygons about a meter across, and the old account put that down to the crust shrinking as it dried. Two things do not fit. The polygons keep much the same size for kilometers, and their borders stand up as ridges rather than opening as gaps. So what draws the pattern?

  Source: Lasser et al., Physical Review X

• How does a tide from the sea turn into a wave that runs up a river?

  In most rivers the tide raises the water quietly, over hours. In a few places it arrives as a single steep front that travels upstream, while the current under it still runs out to sea. Researchers modeled the conditions that produce one. What makes it?

  Source: Viero and Defina, Water Resources Research

• How does a flat fire on the ground turn into a tall spinning column?

  A fire lying flat across the ground can gather itself into a rotating column of flame. Nobody adds fuel at that moment, and nobody adds spin either. Because the real thing is too dangerous to instrument, almost everything known about it comes from scale models in a laboratory. So where does the column come from?

  Source: Tohidi et al., Annual Review of Fluid Mechanics

• What does the color of a soap bubble know about its own thickness?

  The wall of a soap bubble is thinner than the wavelength of some of the light hitting it, so light reflects twice, once from the outer surface and once from the inner. The two reflections travel different distances before they meet again. What does that do to the color?

  Source: Princen and Mason, Journal of Colloid Science

• Which feather silences an owl in flight? There is no single answer

  An owl wing carries several adaptations at once: a comb of stiff bristles along the leading edge, a velvety texture across the feather surface, and a soft flexible fringe at the trailing edge. It is tempting to look for the one responsible for the silence. Which of them does it?

  Source: Jaworski and Peake, Annual Review of Fluid Mechanics

• How do you defend data against a computer nobody has built yet?

  Post-quantum cryptography is meant to survive an attacker holding a powerful quantum computer, and the name invites an obvious guess: that the defense is quantum too. It is not. It runs on the laptop you already own. So what is it leaning on instead?

  Source: NIST

• Does hot water really freeze faster than cold?

  The claim is that water starting out hotter reaches a given low temperature sooner, and references to it go back at least as far as Aristotle. It sounds wrong, and at first thought it even looks like a breach of thermodynamics. Two physicists checked both halves of that.

  Source: Burridge and Linden, Scientific Reports

• Can you sort live worms the way a lab sorts molecules?

  Chromatography separates polymers by pushing them through a confined space, where transport rate depends on size. Living things are also long and flexible, and they wriggle. Whether that activity could serve as the sorting property, the way size does, was the open question.

  Source: Heeremans et al., Science Advances

• How do you make a robot swim like an eel?

  A propeller is the obvious way to move something through water, and no fish uses one. An eel swims by sending a wave down its body, which needs a body that bends continuously rather than joints that hinge. So the robot has to be soft, and softness is hard to control.

  Source: Chen et al., Smart Materials and Structures

• Why does sand on a vibrating plate draw lines?

  Scatter sand on a metal plate, drive the plate with a tone, and the grains gather into a clean geometric figure. The pattern is the plate telling you where it is not moving. Reproducing one from theory, rather than admiring it, means knowing the plate’s resonant frequencies first.

  Source: Tuan et al., The Journal of the Acoustical Society of America

• Can a message tell you it was intercepted?

  Classical encryption hides a message and says nothing about who looked. Quantum cryptography uses the rules of quantum mechanics, with devices such as sensors that record individual photons, and its advertised advantage is detection rather than concealment. One early protocol put that to work.

  Source: NIST

• Was there ever a real bug in a computer?

  The word bug for a technical fault originates with Thomas Edison in the 1800s, long before computers existed. On 9 September 1947 a team working on the Harvard Mark II in Cambridge, Massachusetts reported one of a different kind, and the logbook entry survives.

  Source: Computer History Museum

• Can an adult cell be sent back to the beginning?

  Differentiated cells could already be reprogrammed to an embryonic-like state, by transferring nuclear contents into oocytes or by fusion with embryonic stem cells. Both routes work and neither explains itself: little was known about which factors actually induce the reprogramming.

  Source: Takahashi and Yamanaka, Cell

• Did a nuclear reactor ever start without people?

  At Oklo in Gabon, uranium ore went critical on its own about two billion years ago, when natural uranium still held enough of the fissile isotope to sustain a chain reaction. That much was established. How the reaction behaved over time was not, because nothing was there to record it.

  Source: Meshik, Hohenberg and Pravdivtseva, Physical Review Letters

• How small a difference in height can a clock feel?

  Relativity says two clocks disagree if one moves relative to the other, or if one sits deeper in a gravitational field. Both predictions had been checked, but with spacecraft speeds and with clocks carried up mountains. The question is how far down the scale the effect can be followed with hardware on a bench.

  Source: Chou et al., Science

• Can you vaccinate somebody against a false story?

  Psychological inoculation borrows the logic of a vaccine: show people a weakened version of a manipulation technique before they meet the real thing. Dozens of experiments have tried it with misinformation. What stayed unclear is whether it sharpens the line between false and true, or just makes everyone more suspicious.

  Source: Lu et al., Journal of Medical Internet Research

• Who else can tell a benign slide from a malignant one?

  Pathologists and radiologists spend years acquiring and refining their visual skills, and nobody can fully say which image features carry the diagnosis. Animal models have cracked open other human abilities that resist introspection. The pigeon visual system shares a great deal with ours, which makes it a candidate.

  Source: Levenson et al., PLOS ONE

• Why has nobody fixed the splatter problem?

  Urinals are a staple of public spaces, and their designs have remained essentially stagnant for over a century. The splatter they produce costs cleaning hours, chemicals and water, and lands on floors and users. Impinging stream angle is one of many factors involved, which makes it a candidate to solve.

  Source: Thurairajah et al., PNAS Nexus

• Which health data does nobody collect, every single day?

  Technologies for the longitudinal monitoring of a person’s health sit poorly inside clinical workflows, and have rarely produced biometric data a provider can act on. Wearables read the body from outside. Excreta carry a standard-of-care signal that currently goes straight down the drain.

  Source: Park et al., Nature Biomedical Engineering

• Full or empty, which beer bottle survives the impact?

  Beer bottles turn up in physical disputes, and forensic pathologists have to say afterwards what happened. A bottle that breaks produces sharp trauma; one that stays intact produces blunt injuries. Nobody had measured which of the two a full bottle delivers.

  Source: Bolliger et al., Journal of Forensic and Legal Medicine

• Was the keyboard really laid out to stop people typing too fast?

  The story is repeated everywhere: early typewriters jammed when neighboring type bars were struck in quick succession, so Christopher Latham Sholes scattered the common letter pairs to slow typists down. It explains an awkward layout that has survived 150 years of better ideas. It also has a problem sitting right in the middle of the keyboard. What does the layout itself say?

  Source: Smithsonian Magazine

• If nothing happened at midnight in 2000, was the millennium bug ever real?

  Until the 1990s many programs abbreviated four-digit years to two digits to save memory, so a machine reading 98 as 1998 would read 00 as 1900. The predicted consequences ran from banking and utilities to elevators and medical equipment. Then the date arrived and almost nothing broke, which is now often told as proof the whole thing was invented. What came in between?

  Source: Britannica

• Why is a wireless standard named after a tooth?

  Bluetooth is not an acronym and does not stand for anything, which is unusual for a technical standard. It also does not sound like one. The Bluetooth special interest group tells the story itself. It runs through a tenth-century Scandinavian king, a meeting of three companies in 1996, and a placeholder nobody managed to replace in time.

  Source: Bluetooth SIG

• What was the first thing ever sent between two computers on the network?

  Samuel Morse opened the telegraph with a line he had chosen in advance. When the ARPANET sent its first host-to-host message in October 1969, nobody had prepared anything, because the task at hand was mundane: log in to a machine at Stanford Research Institute from one at UCLA. Leonard Kleinrock, who ran the receiving end, tells the story. The message is two letters long, and not by design.

  Source: ICANN

• What was the first webcam pointed at?

  The first webcam was not built to broadcast anything. It was built to solve a nuisance in a university computer science department, where the coffee pot sat in one room and most of the people wanting coffee sat in others. The walk was short and the disappointment was real. Their solution predates web browsers being able to show images at all.

  Source: History of Information

• Who built the first digital camera, and who did they build it for?

  The company that dominated film photography also built the first digital camera, which is the sort of detail that sounds like hindsight and is not. A supervisor at Eastman Kodak handed a young engineer a question about a newly invented light-sensing chip and complete autonomy to answer it. The National Inventors Hall of Fame records what he built, and what the company then did about it.

  Source: National Inventors Hall of Fame

• How often does a quantum computer make a mistake?

  The best quantum computers today hold hundreds of interconnected qubits, and they make an error roughly once in every thousand operations. A classical computer makes about one error for every quintillion calculations. That gap is not a matter of engineering polish. It comes from what a qubit must be if it is to be useful at all.

  Source: NIST

• What did the first computer virus actually do?

  Creeper, written by Bob Thomas at BBN around 1971, is usually called the first computer virus. It did not steal anything, encrypt anything or break anything. It copied itself from one machine to the next and printed a line: “I’m the creeper, catch me if you can!” Someone then had to write a second program to chase it down.

  Source: History of Information

• Do undersea cables really carry almost all the world’s data?

  The claim that over 99 percent of intercontinental data traffic runs through submarine cables gets quoted everywhere, usually with no source attached. TeleGeography went looking for where it came from and found it traced back to their own FAQ, which rested on FCC filings. The figure holds up. The data behind it stopped being collected a decade ago.

  Source: TeleGeography

• What was in the first email ever sent?

  Ray Tomlinson sent it at BBN in late 1971, between two computers standing side by side in Cambridge, Massachusetts. He had joined two existing TENEX programs, SNDMSG and READMAIL, to a transfer capability so a message could cross the network instead of staying put. Nobody recorded the contents. The most common guess is QWERTYUIOP, the top row of the keyboard.

  Source: EBSCO Research Starters

• Should you take notes when watching a lecture at double speed?

  Students watched recorded lectures at normal or double speed, some taking notes and some not. Test scores drifted downward as speed went up. Note-taking helped either way, by laptop or by hand. And students who took notes at double speed did no worse on the test than students who took no notes at normal speed.

  Source: Chen et al., Applied Cognitive Psychology

• What is a block of aerogel actually made of?

  Almost nothing. Silica aerogels are roughly 95 percent air by volume, and the remaining few percent is a continuous silica network holding the whole thing in shape. That is why a block of it looks like solid smoke, and why it insulates so well. The hard part was never building the structure. It was getting the liquid out without collapsing it.

  Source: Particle & Particle Systems Characterization

• What had to change before glass could carry a phone call?

  The glass had to get purer, and somebody had to work out how much purer. In 1966 Charles Kao calculated how to transmit light over long distances through optical glass fibers. The fibers then available carried a signal about twenty meters. Kao showed that with glass of sufficient purity the distance would be a hundred kilometers.

  Source: The Royal Swedish Academy of Sciences

• Why did a blue light take thirty years longer than a red one?

  Red and green diodes had been around for a long time, but white lamps could not be made without blue. Despite serious effort in universities and industry, the blue light-emitting diode stayed out of reach for three decades. Akasaki, Amano and Nakamura produced bright blue beams from semiconductors in the early nineteen nineties, and shared the 2014 Nobel Prize in Physics for it.

  Source: The Royal Swedish Academy of Sciences

• Can two metal plates be pushed together by nothing at all?

  Lamoreaux measured it. Between two closely spaced conducting surfaces there is a vacuum stress, arising because the surfaces modify the zero-point fluctuations of the electromagnetic field between them. His experiment showed the force conclusively over separations from under a micrometer to a few micrometers, and the measurement agreed with theory to within five percent.

  Source: Lamoreaux, Physical Review Letters

• Why did the first lithium battery have to be redesigned?

  Because it was liable to explode. Whittingham built an innovative cathode from titanium disulphide, whose structure has spaces that can house lithium ions, and paired it with an anode partly of metallic lithium. The result had real potential, just over two volts. It was also too reactive to sell. Goodenough and Yoshino between them made it safe.

  Source: The Royal Swedish Academy of Sciences

• Can a sound wave make a bubble glow?

  It can, and the light is strange. Hold a gas bubble in place with sound, drive it hard enough, and each collapse focuses so much energy that the bubble emits light. The spectrum tends to peak in the ultraviolet, and it depends strongly on which gas is dissolved in the liquid. Traces of noble gas can change the brightness dramatically.

  Source: Brenner et al., Reviews of Modern Physics

• What happens to helium below two degrees above absolute zero?

  Its internal friction disappears. In 1938 Pyotr Kapitza discovered the superfluidity of helium, meaning that below about 2.2 kelvin the viscosity of the liquid vanishes. Allen and Misener made the same discovery independently at the Mond Laboratory in Cambridge. Kapitza shared the 1978 Nobel Prize in Physics for his inventions and discoveries in low-temperature physics.

  Source: The Royal Swedish Academy of Sciences, 1978 award ceremony speech

• Why did an expensive early watch come with a sundial inside the lid?

  Because the watch could not be trusted. A portable horizontal sundial with a folding compass, usable at forty-two degrees of latitude, is screwed to the inside of the cover of a Dutch clock watch made around 1605. The Met’s entry is blunt about why: the sundial would have been useful for setting and correcting the watch.

  Source: The Metropolitan Museum of Art

• What did the physicists at Murray Hill actually find?

  A way to unblock a blocked contact. Bardeen and Brattain moved a tiny probe across a semiconductor surface under a microscope, using a micrometer screw, mapping the region near a negative electrode where the charge carriers had fled. When they made the probe positive and close to the electrode, the blockade lifted. The probe was injecting holes, and that is transistor action.

  Source: The Royal Swedish Academy of Sciences, 1956 award ceremony speech

• Why does the water in a reactor glow blue?

  An electron is outrunning light. Not light in a vacuum, which nothing beats, but light in water, which travels more slowly. A charged particle moving faster than light does in the surrounding medium builds a bow wave, exactly as a boat does when it outpaces the waves on the water. The bow wave here is visible blue light.

  Source: The Royal Swedish Academy of Sciences, 1958 award ceremony speech

• How slippery is a banana skin, really?

  Mabuchi and colleagues put a number on it. They set a six-axis force transducer under a flat linoleum panel and laid a banana skin on it. A foot then pushed and rubbed a shoe sole across it, while both frictional and vertical force were recorded. The coefficient came out at about 0.07, which is the range of a well lubricated surface.

  Source: Mabuchi et al., Tribology Online

• Do market anomalies pay more when everyone is watching?

  They do, on this evidence. Jiang, Liu, Peng and Wang find that returns to financial market anomalies tend to be higher following high-attention days. The result survives controls for news, and it survives a natural experiment in which a stock market regulation and rounding errors produce variation in attention that has nothing to do with the anomalies themselves.

  Source: Jiang et al., Review of Finance

• Can you measure how people move through a museum?

  At the Galleria Borghese in Rome, Centorrino and colleagues did. Visitors carried portable Bluetooth Low Energy beacons while fixed Raspberry Pi receivers sat in the museum rooms. Two algorithms cleaned the signal strength readings, and the result was visitor trajectories reconstructed accurately at the scale of individual rooms.

  Source: Centorrino et al., Journal of Computational Science

• Can a traffic jam form with nothing blocking the road?

  Sugiyama and colleagues put cars on a circular track with no bottleneck at all, spaced evenly, all moving at the same speed, at a density chosen to sit at the edge of instability. Even a tiny fluctuation grew. The even spacing could not hold, and a jam cluster appeared and traveled backward around the circuit like a solitary wave.

  Source: Sugiyama et al., New Journal of Physics

• What did Gordon Moore actually predict, and for how long?

  A decade, not half a century. A special issue of Electronics asked Moore in 1965 to predict the next ten years. He observed that the number of components in integrated circuits had roughly doubled each year, and extrapolated that annual doubling forward. He estimated microcircuits of 1975 would hold sixty-five thousand components.

  Source: Encyclopaedia Britannica

• What were all those distorted words actually used for?

  Transcribing books. CAPTCHAs block automated programs by asking humans to do something computers cannot, such as deciphering distorted characters. Von Ahn and colleagues asked whether that effort could be put to use, by serving scanned words from old printed material that optical character recognition had failed on. The transcription accuracy exceeded ninety-nine percent per word.

  Source: von Ahn et al., Science

• Why does every major league baseball get rubbed with the same mud?

  Because nothing synthetic has replaced it. Before it leaves a pitcher’s hand, every ball in Major League Baseball is massaged with a finger-sized dollop of Lena Blackburne Baseball Rubbing Mud, scooped from a secret location in New Jersey. The league has tried and failed to find substitutes more than once.

  Source: Eos, American Geophysical Union

• How good are perovskite solar cells, measured independently?

  The confirmed record in the 2024 tables is 25.2 percent for a perovskite cell, measured at Newport in July 2023 for Northwestern University, with an uncertainty of plus or minus 0.8. A perovskite minimodule reached 22.6 percent. For comparison, the thin-film chalcogenide leaders sit at 23.35 for CIGS and 21.0 for cadmium telluride.

  Source: Green et al., Progress in Photovoltaics

• Why do dried mud cracks meet at right angles rather than hexagons?

  Because of the order in which they opened. When cracks form in a thin contracting layer they break it sequentially into smaller and smaller pieces, and a later crack tends to meet an earlier one at a right angle. Goehring’s point is that the rectilinear pattern therefore records its own history, while a hexagonal pattern has had that history erased.

  Source: Goehring, Philosophical Transactions of the Royal Society A

• What did Douglas Engelbart show an audience in 1968?

  A working version of how everyone now uses a computer. At a conference in San Francisco in December 1968, Engelbart showed NLS, the oN-Line System, a real-time collaborative computer system. Before his inventions, controlling a computer meant laborious and error-prone keypunch cards or manually set switches, and data had to be printed before anyone could look at it.

  Source: Encyclopaedia Britannica

• What makes a whirlpool in the open sea?

  Tides working against each other. A whirlpool is a rotary oceanic current, a large-scale eddy produced by the interaction of rising and falling tides. Similar currents with a central downdraft are called vortexes, and they occur where coastal and bottom configurations provide narrow passages of considerable depth.

  Source: Encyclopaedia Britannica

• What makes an error-correcting code perfect?

  Using no more redundancy than the job requires. A binary Hamming code is a linear code whose parity-check matrix has columns consisting of all the nonzero binary vectors of a given length, each used exactly once. MathWorld states the consequence plainly: Hamming codes are perfect single error-correcting codes.

  Source: Wolfram MathWorld

• What does a droplet do when sound holds it in mid-air?

  Two things a solid sphere will not. Emulsion droplets trapped in an ultrasonic levitator spin rapidly about an axis parallel to the trapping plane, and coaxially spinning droplets form long chains aligned with their common axis of rotation. Solid spheres in the same trap do something different: they form close-packed planar crystals.

  Source: Ultrasonic chaining of emulsion droplets

• Why would a spacecraft send its data home by laser?

  Because radio is the bottleneck. The amount of scientific data that can be transmitted from deep-space probes is very limited by the constraints of radio communications. Free-space optical communication can relieve that, increasing the data rate while reducing the weight, mass and power of the communication equipment the spacecraft has to carry.

  Source: CTA telescopes as deep-space lasercom ground receivers

• How did you pack a full place setting for a hunt in 1709?

  By making the handles come off. A conical case holds a silver beaker along with a knife, fork, spoon and marrow spoon, all with removable handles. The Met dates the set to 1709 or 1710, with the cup by the London silversmith Charles Overing and the cutlery by two makers identified only by initials.

  Source: The Metropolitan Museum of Art

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