Science: quotes, facts and reflections - Page 6

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WonderScience

Voyager 1 and 2 were launched in 1977, thirteen years before Tim Berners-Lee's first web server went online at CERN at the end of 1990. Both probes are still working, run by onboard computers that carry out about 8,000 instructions a second; a modern phone manages billions.

The probes date from the dawn of the home computer: they left Earth in the same year that the Apple II, one of the first mass-produced personal computers, went on sale. Each Voyager carries three kinds of computer, two of each for safety: one runs commands, one keeps the craft pointed in the right direction and one packages the science data. Together the six hold about 68 kilobytes of memory, far less than a single photo taken on a modern phone. Data were stored on a tape recorder and sent home by radio. In November 2023 a failed memory chip left Voyager 1 sending meaningless data. Each command took nearly a day to reach it, yet engineers moved the affected code to other parts of its memory, and by April 2024 the probe was sending usable data again.

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WonderScience

Venus takes 243 Earth days to rotate once relative to the stars, longer than its 225-day orbit around the Sun. It also spins backwards compared with most planets, so on Venus the Sun would rise in the west.

The 243-day figure is Venus's sidereal rotation period, measured against the distant stars. Because Venus spins backwards while it moves around the Sun, a solar day, from one local noon to the next, lasts about 117 Earth days. So 'a day on Venus' can mean 243 or 117 Earth days, depending on what is being measured. Someone on the surface would see the Sun rise in the west and set in the east about 58 Earth days later, if the thick clouds ever let it through. Why Venus turns so slowly, and backwards, is still debated. It probably formed spinning differently. Over billions of years the Sun's gravity, which tends to slow a planet's spin, and tides raised in its thick, sun-heated atmosphere may have brought it to the slow backward turn seen today.

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WonderScience

During the First World War Marie Curie fitted cars with X-ray equipment and took them to field hospitals near the front, sometimes at the wheel herself, so surgeons could see bullets, shell fragments and broken bones inside wounded soldiers. The cars became known as 'petites Curies', little Curies.

When the war began in 1914, X-ray machines were found mainly in city hospitals, far from where soldiers were wounded. Curie studied radiology, anatomy and car mechanics, learned to drive, and gathered X-ray equipment, vehicles and generators. As director of the Red Cross radiology service she equipped 20 mobile units and oversaw about 200 fixed X-ray rooms in field hospitals. Her 17-year-old daughter Irène worked beside her, and Curie trained 150 women to operate the machines. More than a million wounded soldiers are estimated to have been X-rayed during the war, yet the French government never formally recognised her work. Years of exposure to radiation, in the laboratory and at the front, are thought to have caused the aplastic anaemia, a failure of the bone marrow to make blood cells, that killed her in 1934.

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DriveScience

In 1905, while working as a technical expert at the Swiss Patent Office in Bern, Albert Einstein, then 26, published four papers that changed physics: on the photoelectric effect, on Brownian motion, on special relativity and on the link between mass and energy, E = mc². Physicists call it his miracle year.

Einstein had failed to find a university post after graduating, and in 1902 he joined the patent office in Bern, helped by the father of his friend Marcel Grossmann. His job was to assess patent applications, many of them for electrical and mechanical devices. In his spare time he debated physics and philosophy with friends in a small reading group they jokingly called the Olympia Academy, and he talked his ideas through with a colleague, Michele Besso, the only person thanked in the relativity paper. Alongside the four papers he completed a doctoral thesis on measuring the size of molecules. His paper on Brownian motion, the jittery movement of tiny particles suspended in a liquid, gave strong evidence that atoms really exist. He stayed at the patent office until 1909, when he became an associate professor at the University of Zurich.

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DriveMind

Neuroplasticity is the brain's ability to change its connections, and even its structure, in response to experience. It is strongest in childhood but continues through adult life, which is why adults can still learn a language, an instrument or a new skill, even if it often takes them longer.

For much of the 20th century scientists believed the adult brain was more or less fixed. Brain scans changed that view. In 2004 researchers in Germany taught adults to juggle three balls over three months; scans showed extra grey matter, the tissue packed with nerve cells, in areas that track moving objects, and it shrank back once they stopped practising. A follow-up in 2008 found the same kind of change in volunteers around 60 years old, although they learned less well than 20-year-olds. The best-known example comes from London, where Katherine Woollett and Eleanor Maguire followed trainee taxi drivers for four years as they memorised the city's 25,000 streets. Those who passed the exam gained grey matter at the back of the hippocampus, a region involved in finding our way; those who failed, and people who never trained, showed no such change.

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When you practise a skill, the same groups of nerve cells become active together again and again, and the connections between them grow stronger. This strengthening, part of what scientists call neuroplasticity, is how practice slowly turns effort into ability.

The Canadian psychologist Donald Hebb proposed the idea in his 1949 book The Organization of Behavior: when one nerve cell repeatedly helps to fire another, the link between them becomes more efficient. It is often summed up as “cells that fire together wire together”. In 1973 Timothy Bliss and Terje Lømo found such strengthening in the brains of rabbits in Oslo: after bursts of electrical stimulation, connections in the hippocampus, a region vital for memory, stayed stronger for hours. The effect is called long-term potentiation. Practice can reshape the brain within days. In 1995 Alvaro Pascual-Leone and colleagues at the US National Institutes of Health had volunteers practise a one-handed, five-finger piano exercise for two hours a day. After five days, the area of the motor cortex that controls the finger muscles had grown larger.

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WonderArt

Leonardo da Vinci (1452–1519) filled thousands of notebook pages over his life. On a single sheet a study of muscles can sit beside a flying machine, a weapon, notes on flowing water or sketches for a painting. For him, drawing was a way of understanding the world, not only of recording it.

Leonardo wrote most of his notes from right to left in mirror writing; he was left-handed. When he died in France in 1519, he left his papers to his pupil Francesco Melzi. After Melzi's death they were scattered, and in the late 16th century the sculptor Pompeo Leoni cut up some notebooks and mounted the sheets in large albums. The biggest, the Codex Atlanticus (codex is an old word for a bound manuscript), is named after the atlas-sized paper used for mounting. It holds 1,119 sheets dated from 1478 to 1519 and is kept in the Biblioteca Ambrosiana in Milan. Other notebooks are in Paris, London and Madrid, and the Royal Collection at Windsor holds many of his anatomical drawings. The Codex Leicester, his notes on water, rock and light, was bought by Bill Gates in 1994 and is the only major scientific notebook of his in private hands.

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WonderHistory

When it was finished about 4,500 years ago, the Great Pyramid of Giza stood 146.6 m tall. For more than 3,800 years nothing built by people rose higher, until the timber spires of medieval English cathedrals overtook it.

The pyramid was built for the pharaoh Khufu from an estimated 2.3 million blocks of stone and faced with polished white limestone brought by boat from Tura, across the Nile. In the Middle Ages most of that casing was stripped away and reused in Cairo, and the top is missing, so today it stands about 138.5 m. Sources disagree about which building beat it first. Some point to Old St Paul's Cathedral in London, completed in the 13th century; others to Lincoln Cathedral, whose central spire is said to have reached about 160 m in the early 14th century. Both spires were made of wood covered with lead, and both are gone: Lincoln's blew down in a storm in 1548, and St Paul's burned after a lightning strike in 1561.

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WonderScience

The English word ‘disaster’ comes from the Italian for ‘ill-starred’, from a time when misfortune was blamed on the stars. Other everyday words keep old history too: ‘quarantine’ comes from the Italian for forty days, and ‘robot’ from a Czech word for forced labour.

Disaster reached English in the 1590s through French désastre, from Italian disastro: dis-, meaning bad, and astro, star. In astrology a planet in the wrong position was thought to bring calamity, and English still says ‘ill-starred’. Quarantine goes back to plague-era ports. In 1377 the city of Ragusa, now Dubrovnik in Croatia, made new arrivals wait 30 days in isolation, and in 1448 Venice extended the wait to 40 days, quaranta giorni in Italian. Robot first appeared in Karel Čapek's 1920 play R.U.R., about artificial workers. Čapek said his brother Josef suggested the word, based on the Czech robota, the unpaid labour serfs owed their lords. The American writer Ralph Waldo Emerson put the idea neatly in 1844: ‘Language is fossil poetry.’

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WonderScience

Only 65 years separate the Wright brothers' first powered flight, 37 m (120 ft) in 12 seconds on 17 December 1903, from the Moon landing of July 1969. Neil Armstrong carried a piece of the Wright Flyer's wing fabric and a sliver of its propeller wood with him to the Moon.

Aviation moved fast between those dates. In 1919 John Alcock and Arthur Brown made the first non-stop flight across the Atlantic. In 1947 Chuck Yeager flew faster than sound in the rocket-powered Bell X-1. In 1957 the Soviet Union launched Sputnik, the first artificial satellite, and in 1961 Yuri Gagarin became the first person in space. Orville Wright, who piloted that first flight, lived until 1948. The Flyer itself spent 20 years at the Science Museum in London: the Smithsonian Institution had credited its former head, Samuel Langley, with the first machine capable of flight, and Orville sent the Flyer abroad in protest. It returned to the United States in 1948 and is on display at the National Air and Space Museum in Washington. In 2021 another scrap of its wing fabric flew on Mars, fixed to NASA's Ingenuity helicopter.

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WonderScience

A solar cell turns sunlight straight into electric current. Most are thin slices of silicon, a semiconductor: a material that conducts electricity well only when its electrons gain extra energy. Sunlight supplies it, and an electric field between two layers of the cell drives the freed electrons out through a wire as current.

The two layers are silicon with tiny amounts of other elements added: one has spare electrons, the other is short of them. Where they meet, a boundary called a p–n junction forms, and with it an electric field. This effect, called the photovoltaic effect, was first seen in 1839 by the French physicist Edmond Becquerel, who noticed a small current when light fell on metal plates in a liquid. It is related to, but not the same as, the photoelectric effect, in which light knocks electrons out of a metal surface. The first practical silicon solar cell was shown at Bell Labs in the United States in April 1954 and turned about 6 per cent of sunlight into electricity. Ordinary panels today convert around a fifth. One cell gives only about half a volt, so a panel links dozens of cells together.

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WonderScience

A digital camera's sensor is a silicon chip covered with millions of tiny light-sensitive squares called pixels. Light falling on each pixel frees a little electric charge: the brighter the light, the more charge. The camera measures every pixel's charge and turns the pattern into an image.

The key invention was the charge-coupled device, or CCD, created in 1969 by Willard Boyle and George Smith at Bell Labs. It passed each pixel's charge across the chip, step by step, to be measured at the edge. CCDs transformed astronomy, and Boyle and Smith shared the 2009 Nobel Prize in Physics with Charles Kao. Most cameras and phones now use CMOS sensors, built with the same technology as computer chips and developed in the early 1990s, including at NASA's Jet Propulsion Laboratory; they read each pixel where it sits and use less power. Pixels cannot tell colours apart, so tiny red, green and blue filters sit on top in a pattern devised by Bryce Bayer at Kodak in 1976, with twice as many green ones to match the human eye. The idea behind it goes back to Einstein's 1905 explanation of how light frees electric charge.

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WonderMind

The human brain contains about 86 billion neurons, the nerve cells that carry signals, and roughly as many other cells that support them. Each neuron can connect with thousands of others. The figure comes from a 2009 study that counted the cells instead of estimating them.

For decades textbooks said the brain had 100 billion neurons and ten times as many support cells, called glia, but nobody had actually counted them. In 2009 the Brazilian neuroscientist Suzana Herculano-Houzel and colleagues in Rio de Janeiro used a method she had developed with Roberto Lent, the isotropic fractionator. Brain tissue is dissolved into an even liquid of cell nuclei; a small sample is counted under the microscope, with a stain that marks only neurons, and the result is scaled up. In adult men's brains they found about 86 billion neurons and 85 billion other cells, so the famous ten-to-one ratio was wrong. Another surprise: only about a fifth of the neurons sit in the cerebral cortex, the brain's wrinkled outer layer. Most are packed into the cerebellum, at the lower back of the brain.

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WonderMind

An adult brain weighs about 1.3 kg, roughly 2% of body weight, yet it uses about 20% of the energy the body burns at rest. Most of that energy pays for the brain's constant background activity, not for the extra effort of thinking hard.

The brain's main fuel is glucose, the sugar carried in the blood; during long fasts it can also run on ketones, which the liver makes from fat. Much of its energy powers tiny pumps that move charged particles in and out of nerve cells, keeping each one ready to send a signal. Brain scans by the American neurologist Marcus Raichle and others showed that a hard mental task raises the brain's total energy use only slightly, often by less than 5%, and he called the constant background activity the brain's “dark energy”. In most vertebrates the brain takes 2 to 8% of resting energy, so humans are unusual. The share peaks in early childhood: a 2014 study estimated that at about four years old the brain uses around two thirds of the body's resting energy.

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Dopamine, a chemical messenger in the brain, is central to motivation and learning. Its activity changes most when things turn out better or worse than expected, which helps the brain learn which cues are worth paying attention to.

The key experiments were made in the 1980s and 1990s by the neuroscientist Wolfram Schultz, then at the University of Fribourg in Switzerland, who recorded dopamine cells in monkeys. When a drop of juice arrived unexpectedly, the cells became active. Once a light or a sound reliably came before the juice, they responded to the signal instead and barely reacted to the juice itself. If the expected juice did not arrive, their activity dropped below normal. The cells were tracking the gap between what was expected and what happened, now called the reward prediction error, and some computer learning methods use a similar signal. This is how a phone's ping can become a cue that grabs attention: it hints that something interesting may be waiting. That is different from saying every notification gives everyone the same burst of pleasure.

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WonderScience

In a vacuum, light travels 299,792 kilometres (186,282 miles) every second. At that speed it reaches us from the Moon in about 1.3 seconds and from the Sun in about 8 minutes 20 seconds.

The exact figure is 299,792,458 metres per second, and it is exact by definition: since 1983 the metre has been defined as the distance light travels in a vacuum in 1/299,792,458 of a second. The first estimate came in 1676, when the Danish astronomer Ole Rømer noticed that the eclipses of Jupiter's moon Io came later when Earth was farther from Jupiter, because the light had further to travel. Light slows down inside materials such as water or glass. Einstein's theory of relativity showed that nothing with mass can reach this speed, which is why it is called the universe's speed limit. Scientists still time laser pulses bounced off mirrors that Apollo astronauts left on the Moon; the round trip takes about 2.5 seconds.

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A light-year is a distance, not a length of time: how far light travels in a year, about 9.46 trillion kilometres. The nearest star after the Sun, Proxima Centauri, is about 4.25 light-years away, so the light we see from it set off over four years ago.

Astronomers define it precisely using a year of 365.25 days, which gives 9,460,730,472,580.8 kilometres. The unit grew out of the first measurement of the distance to another star: in 1838 the German astronomer Friedrich Bessel found that the star 61 Cygni was so far away that its light took about ten years to reach us. The term itself first appeared in 1851, in a German popular astronomy article by Otto Ule, who compared it to measuring a walk in hours. Professional astronomers usually prefer the parsec, about 3.26 light-years. Because light takes time to arrive, looking far away means looking back in time: we see the Andromeda Galaxy by light that left it about 2.5 million years ago.

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More than 99.9% of an atom's mass is packed into its nucleus, a centre tens of thousands of times smaller across than the atom itself. The rest of the atom is filled by a thin cloud of electrons. If an atom were a large stadium, its nucleus would be about the size of a pea.

The nucleus, made of protons and neutrons, was discovered in 1911 by Ernest Rutherford in Manchester. His colleagues Hans Geiger and Ernest Marsden had fired tiny charged particles at thin gold foil; most passed straight through, but a few bounced back, which only made sense if the atom's positive charge and mass were packed into a tiny core. Electrons are not little balls in orbits; they are better described as a cloud showing where each is likely to be found. Solid things feel solid for two reasons. The negatively charged electrons of neighbouring atoms repel one another, and a rule of quantum physics called the Pauli exclusion principle stops electrons from crowding into the same state. Together these keep atoms from being squeezed into each other.

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A neutron star packs more mass than the Sun into a ball only about 20 to 25 kilometres across, roughly the size of a city. Its matter is so dense that a single teaspoonful would weigh billions of tonnes on Earth.

A neutron star is what remains when a star of more than about eight times the Sun's mass runs out of fuel. Its core collapses, and the outer layers are blown away in a supernova, a vast stellar explosion. The collapse forces electrons into protons to make neutrons, the particles that give these stars their name, packed as tightly as in the nucleus of an atom. Walter Baade and Fritz Zwicky predicted such stars in 1934. The first evidence came in 1967, when Jocelyn Bell, a PhD student at Cambridge, and Antony Hewish picked up regular radio pulses that proved to come from spinning neutron stars, now called pulsars. The fastest known spins 716 times a second. In 2017, detectors recorded for the first time the gravitational waves, ripples in space and time, from two neutron stars colliding.

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WonderScience

The Sun holds about 99.86% of all the mass in the solar system. It is roughly 330,000 times as massive as the Earth and 109 times as wide, so the planets, moons, asteroids and comets together make up only about 0.14%.

The Sun formed about 4.6 billion years ago when a cloud of gas and dust collapsed under its own gravity. Most of the material fell to the centre and became the Sun; the rest flattened into a spinning disc in which the planets grew. That is why the Sun ended up with nearly everything. It is made mostly of hydrogen (about 73%) and helium (about 25%), and in its core hydrogen fuses into helium, releasing the energy that reaches us as sunlight. Of the small share left over, Jupiter and Saturn hold more than 90%. The four rocky planets, Earth included, together with all the dwarf planets, moons, asteroids and comets, make up less than 0.002% of the solar system's mass.

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WonderScience

Pi, the ratio of any circle's circumference to its diameter, can never be written out in full. Its digits after 3.14 go on for ever without settling into a repeating pattern, because pi is irrational: no fraction of two whole numbers equals it exactly.

People have approximated pi for thousands of years. Around 250 BC the Greek mathematician Archimedes trapped it between 3 10/71 and 3 1/7 by drawing many-sided shapes inside and outside a circle. The Swiss scientist Johann Heinrich Lambert proved in the 1760s that pi is irrational. In 1882 Ferdinand von Lindemann went further, showing that pi cannot be produced from whole numbers by any finite combination of arithmetic and roots. That settled an ancient puzzle: with only a compass and straight edge, it is impossible to draw a square with exactly the same area as a given circle. The Welsh mathematician William Jones first used the symbol π for this number in 1706. Computers have now calculated hundreds of trillions of digits, yet NASA's engineers use just 15 decimal places for their most precise spacecraft navigation.

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Prime numbers, whole numbers above 1 that divide exactly only by 1 and by themselves (2, 3, 5, 7, 11 and so on), never run out: however far you count, there is always a larger one. Euclid proved this about 2,300 years ago.

The proof is in Euclid's Elements, written in Alexandria around 300 BC. Suppose you had a complete list of all the primes. Multiply them all together and add one. The new number leaves a remainder of 1 when divided by any prime on the list, so either it is prime itself or it is divisible by a prime missing from the list. Either way the list was not complete, so the primes can never end. In October 2024 Luke Durant, working with the volunteer project GIMPS, found the largest prime known at the time: 2 to the power of 136,279,841, minus 1, a number with 41,024,320 digits. Primes also help keep online payments secure, because some encryption relies on how hard it is to split a huge number into its prime factors.

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Indian mathematicians were the first to treat zero as a number in its own right, not just a gap or a mark for an empty place. In AD 628 Brahmagupta wrote down rules for adding, subtracting and multiplying with it.

The Babylonians used a sign for an empty place by about 300 BC, and the Maya invented their own zero independently, but for both it marked a position rather than a number to calculate with. Brahmagupta, an astronomer in western India, gave its rules in his Brāhmasphuṭasiddhānta (“The Correctly Established Doctrine of Brahma”); he also tried to divide by zero, though that rule was wrong. The oldest firmly dated zero in a written number, a dot, is carved on a stone from Sambor in Cambodia dated AD 683; in India, a temple inscription at Gwalior dated AD 876 shows it as a small circle. The idea spread through Arabic mathematics and reached Europe with Fibonacci's Liber Abaci in 1202. The word travelled the same road: Arabic ṣifr, “empty”, used to translate Sanskrit śūnya, is the source of English zero and cipher, and of Turkish sıfır.

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In quantum physics, a particle such as an electron can be in a superposition: not in one definite state, but in a combination of several, for example of two different positions. When it is measured, one definite result appears, and the odds of each result are set by that combination.

The clearest evidence is the double-slit experiment. Fire electrons one at a time at a barrier with two narrow openings, and the dots they leave on a screen slowly build a striped pattern that can only form if each electron's state included both routes. In 1935 Erwin Schrödinger imagined a cat whose life depended on a single atom, to show how strange it would be to apply the idea to everyday objects. Large things do not show superposition because the slightest contact with their surroundings quickly destroys it, a process physicists call decoherence. Even so, molecules of 2,000 atoms and, in a 2026 experiment, clusters of more than 7,000 sodium atoms have been put into superposition. Quantum computers rely on the same principle: their qubits can be in a superposition of 0 and 1.

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