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Machine learning lets a computer learn a task from examples instead of following rules written by hand. A spam filter, for instance, is shown thousands of emails already marked as spam or not spam, and works out for itself which patterns give spam away.

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The term was coined in 1959 by Arthur Samuel, an IBM researcher whose draughts-playing program got better the more it played. A learning system has many internal settings. During training they are adjusted again and again until its answers on the examples are as accurate as possible, and the system then uses them on cases it has never seen. A turning point came in 2012, when AlexNet, a system from the University of Toronto, recognised objects in photos far better than earlier methods, using layered 'neural networks' loosely modelled on the brain. Machine learning now powers translation apps, voice assistants, film and music recommendations and the analysis of medical scans. Because it learns from data, gaps or biases in that data carry through into its answers.

Türkçe oku
Makine öğrenmesinde bilgisayar bir işi, elle yazılmış kurallara uyarak değil, örneklerden öğrenerek yapar. Örneğin istenmeyen e-postaları (spam) ayıklayan bir filtreye, önceden spam olup olmadığı işaretlenmiş binlerce e-posta gösterilir. Filtre, spam'i ele veren ipuçlarını kendisi bulur.

Terimi 1959'da IBM araştırmacısı Arthur Samuel ortaya attı; Samuel'in dama oynayan programı, oynadıkça ustalaşıyordu. Öğrenen bir sistemin çok sayıda iç ayarı vardır. Eğitim sırasında bu ayarlar, sistem örneklerde olabildiğince doğru yanıt verene kadar defalarca değiştirilir. Sistem sonra aynı ayarlarla, daha önce hiç görmediği durumları değerlendirir. Dönüm noktası 2012'de geldi: Toronto Üniversitesi'nde geliştirilen AlexNet, fotoğraflardaki nesneleri önceki yöntemlerden çok daha iyi tanıdı. AlexNet, beynin çalışmasından kabaca esinlenen, katman katman dizilmiş “yapay sinir ağları” kullanıyordu. Bugün çeviri uygulamaları, sesli asistanlar, film ve müzik önerileri makine öğrenmesiyle çalışıyor; tıbbi görüntülerin incelenmesinde de bu yöntem kullanılıyor. Sistem verilerden öğrendiği için verideki eksikler ve önyargılar da yanıtlarına yansır.

Sources and further reading

Background reading: Machine learning
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WonderHistory

When Neil Armstrong radioed “Houston, Tranquility Base here. The Eagle has landed” on 20 July 1969, his words reached Earth about 1.3 seconds later. Radio waves travel at the speed of light, and the Moon is about 384,000 km (239,000 miles) away.

Eagle was the lunar module that carried Armstrong and Buzz Aldrin down to the surface. Light, and so radio, travels at almost 300,000 km per second. At the Moon's average distance of about 384,400 km, a signal takes roughly 1.28 seconds each way, so every exchange with Mission Control in Houston had a built-in pause of about 2.6 seconds before an answer could arrive. Large dish antennas at Goldstone in California and at Honeysuckle Creek and Parkes in Australia picked up the signals; the clearest pictures of the first steps came through Australia and were watched live by an estimated 600 million people. Before leaving, the crew set up a panel of reflectors on the surface. Scientists still fire lasers at it and time the light's return, which is how we know the Moon is drifting away from Earth by about 3.8 cm a year.

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Telomeres are stretches of repeated DNA that cap the ends of chromosomes, a little like the plastic tips on shoelaces. They get shorter as many of our cells divide, but their length cannot predict how long a particular person will live.

In the mid-1970s the Australian-born biologist Elizabeth Blackburn, working at Yale, found that chromosome ends carry a short DNA “word” repeated many times; in humans it is TTAGGG. She shared the 2009 Nobel Prize in Physiology or Medicine with Carol Greider and Jack Szostak for showing how telomeres, and an enzyme called telomerase that rebuilds them, protect chromosomes. Each time most body cells divide, the copying machinery cannot quite reach the very end, so a little telomere is lost; when it gets too short, the cell stops dividing, which is why telomeres are often called a clock. But it is a poor clock for comparing people or species: mice have much longer telomeres than humans yet live only two or three years, and telomere length varies widely between people from birth. Many scientists therefore doubt commercial tests that claim to read your “biological age” from them.

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WonderTechnology

The atomic clocks on GPS satellites run about 38 millionths of a second a day faster than clocks on the ground, an effect predicted by Einstein's theories of relativity. Left uncorrected, the drift would put your position out by about 11 km within a single day.

A GPS receiver, such as the one in your phone, works out where it is by timing signals from several satellites orbiting about 20,200 km up. Radio signals travel about 300 metres in a microsecond, a millionth of a second, so even tiny clock errors matter. Relativity pulls the clocks apart in two ways. Special relativity says moving clocks run slow: travelling at almost 4 km a second, the satellite clocks lose about 7 microseconds a day. General relativity says clocks in weaker gravity run fast: high above Earth they gain about 46. The net gain is about 38 microseconds a day. So before launch, each satellite clock is set to run slightly slow, at 10.22999999543 million cycles a second instead of 10.23 million, and in orbit it keeps step with clocks on the ground.

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The Apollo Guidance Computer that steered astronauts to the Moon had about 4 kilobytes of rewritable memory and 72 kilobytes of permanent memory. Its programs were woven by hand into “rope memory”: a wire threaded through a tiny magnetic ring stored a 1, and a wire passing it by stored a 0.

Designed at the MIT Instrumentation Laboratory and built by Raytheon, the computer was one of the first to use silicon chips (integrated circuits) and fitted into about 28 litres. Its memory was counted in “words” of 16 bits, or binary digits: 2,048 rewritable and 36,864 permanent. During Apollo 11's descent on 20 July 1969 it flashed 1202 and 1201 alarms: a radar left on in case the landing had to be abandoned was stealing processing time and overloading it. Its operating system, designed by J. Halcombe Laning, dropped less urgent jobs and restarted in a moment while the landing programs kept running, so Mission Control told the crew to carry on. The flight software was written by a team led by Margaret Hamilton, who received the Presidential Medal of Freedom in 2016. Its power was similar to that of the first home computers of the late 1970s.

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WonderTechnology

In 1984 and 1985, John Clarke, Michel Devoret and John Martinis showed that a whole electrical circuit on a chip, cooled almost to absolute zero, can behave as a single quantum object, just like an atom. The discovery earned them the 2025 Nobel Prize in Physics.

The experiments were done at the University of California, Berkeley, in Clarke's group; Martinis was his doctoral student and Devoret a postdoctoral researcher. Absolute zero, −273.15 °C, is the lowest temperature possible. At the heart of the circuit was a Josephson junction: two superconductors, metals that carry current with no resistance when very cold, separated by an insulating layer only a few atoms thick. Vast numbers of electrons moved together as if they were one particle. The team saw two signs of quantum behaviour: the circuit escaped from a trapped state by tunnelling, slipping through an energy barrier it could not climb over, and it absorbed microwave energy only in fixed steps, or quanta, as an atom does. Circuits of this kind are now the qubits, the basic units of information, in the superconducting quantum computers built by companies such as Google and IBM.

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