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Dark matter seems to give off no light and absorb none, so no telescope can see it. Astronomers detect it through its gravity and estimate that there is about five times as much of it as the ordinary matter that makes up stars, planets and people.

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In 1933 the Swiss astronomer Fritz Zwicky found that the galaxies in the Coma Cluster were moving far too fast to be held together by the matter he could see, and suggested unseen ‘dark matter’. In the 1970s Vera Rubin and Kent Ford showed that stars at the edges of spiral galaxies orbit about as fast as those nearer the centre, which suggests that each galaxy sits inside a large halo of invisible mass. Gravitational lensing, the bending of light from distant galaxies by the gravity of mass in front of them, maps the same hidden mass. Dark matter makes up about 85 per cent of all matter, yet after decades of experiments no one knows what it is made of. A minority of physicists argue instead that gravity itself works differently where it is extremely weak, as at the edges of galaxies.

Türkçe oku
Karanlık madde, bildiğimiz kadarıyla ne ışık yayar ne de ışık soğurur; bu yüzden hiçbir teleskop onu göremez. Gökbilimciler varlığını kütleçekiminden anlar. Hesaplara göre evrende, yıldızları, gezegenleri ve bizi oluşturan sıradan maddenin yaklaşık beş katı kadar karanlık madde var.

İsviçreli gökbilimci Fritz Zwicky 1933'te Coma Kümesi'ndeki galaksilerin çok hızlı hareket ettiğini fark etti: Görünen madde, bu hızla dolanan galaksileri bir arada tutmaya yetmezdi. Zwicky bu yüzden görünmeyen bir “karanlık madde” olması gerektiğini öne sürdü. 1970'lerde Vera Rubin ile Kent Ford, sarmal galaksilerin kenarındaki yıldızların da merkeze yakın olanlar kadar hızlı döndüğünü gösterdi. Bu, her galaksinin görünmez kütleden oluşan büyük bir halenin içinde durduğunu düşündürür. Kütleçekimsel merceklenme, yani uzak galaksilerden gelen ışığın aradaki kütlenin çekimiyle bükülmesi de aynı gizli kütlenin haritasını çıkarmaya yarar. Karanlık madde, evrendeki bütün maddenin yaklaşık yüzde 85'ini oluşturur; ama onlarca yıldır süren deneylere rağmen neyden oluştuğu hâlâ bilinmiyor. Az sayıda fizikçi ise karanlık madde yerine başka bir açıklama öneriyor: Onlara göre kütleçekimi, galaksilerin kenarları gibi çok zayıf kaldığı yerlerde farklı işliyor.

Sources and further reading

Background reading: Dark matter
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The historian E. P. Thompson traced this change in a famous essay of 1967, “Time, Work-Discipline, and Industrial Capitalism”. Farm and craft work, he argued, had been measured by tasks: milking, harvesting, finishing a piece. Factory work was measured in hours. Cromford Mill, opened in 1771, was the world's first water-powered cotton-spinning mill. It started with about 200 workers, most of them women and children, the youngest only seven. Bells rang at 5 in the morning and 5 in the evening, the gates were shut at exactly 6, and anyone late lost that day's pay and was fined another. In industrial towns, where alarm clocks were not yet cheap or reliable, “knocker-ups” were paid a few pence a week to tap on upstairs windows with long poles.

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Less than 66 years, well within a single lifetime, separate the first powered aeroplane flight from the first Moon landing. Orville Wright flew for 12 seconds and 37 metres on 17 December 1903; Apollo 11 landed on the Moon on 20 July 1969.

The Wright brothers, bicycle makers from Dayton, Ohio, flew near Kitty Hawk, North Carolina, and that first hop was shorter than the wingspan of a Boeing 747. What followed came fast. In 1919 John Alcock and Arthur Brown flew non-stop across the Atlantic; in 1927 Charles Lindbergh did it alone, from New York to Paris; and in 1947 Chuck Yeager flew faster than sound. Orville Wright died in 1948, nine years before the Soviet satellite Sputnik opened the space age. Yuri Gagarin orbited the Earth in 1961, and in July 1969 Neil Armstrong took a scrap of the 1903 Flyer's wood and fabric with him to the Moon.

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The Cold War between the United States and the Soviet Union (1947–1991) was fought mostly without direct battles between the two. They competed instead through weapons, science, sport, films, propaganda and the race into space.

George Orwell used the phrase “cold war” in 1945, and the American journalist Walter Lippmann made it popular in 1947. Because nuclear weapons made open war between the superpowers too dangerous, the rivalry spread into other arenas. After the Soviet Union launched the Sputnik satellite in 1957, the United States passed the National Defense Education Act of 1958 to fund science, maths and language teaching. In 1959, at an American exhibition in Moscow, Vice-President Richard Nixon and the Soviet leader Nikita Khrushchev argued about capitalism and communism in a model kitchen, an exchange remembered as the Kitchen Debate. In 1972 in Reykjavík, the American Bobby Fischer beat the Soviet champion Boris Spassky for the world chess title. The Olympics were boycotted in turn: the United States and many allies stayed away from Moscow in 1980, and most of the Soviet bloc from Los Angeles in 1984.

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The computer was designed at the MIT Instrumentation Laboratory from 1962 and built by Raytheon, and one flew in every Apollo command module and lunar module. The chip was still a new invention: Jack Kilby and Robert Noyce had made the first ones in 1958 and 1959. MIT used almost a single type throughout, a simple logic circuit designed by Fairchild Semiconductor, repeated thousands of times. According to the Computer History Museum, Apollo bought some 200,000 of them at 20 to 30 dollars each, and by 1965 the Minuteman missile programme had become the bigger buyer. Orders like these kept the young industry going until prices fell: the average chip cost 50 dollars in 1962 and 2.33 dollars in 1968. The Space Race is often credited with GPS too, but GPS was a separate US Department of Defense project, begun in 1973.

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On 12 April 1961 the Soviet cosmonaut Yuri Gagarin, aged 27, became the first human in space. His Vostok 1 spacecraft circled the Earth once, and the flight lasted 108 minutes from launch to landing.

Gagarin, who had trained as a foundry worker before becoming an air force pilot, was launched from Baikonur, in today's Kazakhstan. As the rocket lifted off he called out “Poyekhali!” (“Let's go!”). His orbit took him as high as 327 kilometres. On the way back he ejected from the capsule about 7 kilometres above the ground and came down by his own parachute near Engels, in the Saratov region, where a farm worker and her granddaughter were the first to meet him. Because the record rules of the day required pilots to land inside their craft, the Soviet Union claimed he had, and admitted the truth only in 1971. Gagarin became famous around the world. He died in a training-jet crash in 1968, aged 34. Since 2011 the United Nations has marked 12 April as the International Day of Human Space Flight.

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