Human Universe by Professor Brian Cox

years old, but the galaxy is almost as old as the universe. If we assume life is relatively common, and on at least some of these planets intelligent civilisations arose, it follows that there should exist civilisations far in advance of our own somewhere in the galaxy. Why? Our civilisation has existed for around 10,000 years, and we’ve had access to modern technology for a few hundred. Our species,
Homo sapiens
, has existed for a quarter of a million years or so. This is a blink of an eye in comparison to the age of the Milky Way. So if we assume we are not the only civilisation in the galaxy, then at least a few others must have arisen billions of years ahead of us. But where are they? The distances are not so vast that we cannot imagine travelling between star systems in principle. It took us less than a single human lifetime to go from the Wright Brothers to the Moon. What might we imagine doing in the next hundred years? Or thousand years? Or ten thousand years? Or ten million years? Even with rocketry technology as currently imagined, we could colonise the entire galaxy on million-year timescales. The Fermi Paradox simply boils down to the question of why nobody has done this, given so many billions of worlds and so many billions of years. It is a very good question.

 
     
     
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    FERMI’S PARADOX
    The Fermi Paradox is the apparent contradiction between the high probability of extraterrestrial civilisations’ existence and humanity’s lack of contact with, or evidence for, such civilisations.
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LISTEN VERY CAREFULLY
    For three days in 1924, William F. Friedman had a very important job. As chief cryptographer to the US Army, Friedman was used to dealing with National Security responsibilities, but from 21 to 23 August he was asked to search for an unusual message. On these dates Mars and Earth came within 56 million kilometres of each other, the closest the two planets had been since 1845, and they would not be so close again until August 2003. This offered the best opportunity since the invention of radio to listen in on the neighbours.
    To make the most of the planetary alignment, scientists at the United States Naval Observatory decided to conduct an ambitious experiment. Coordinated across the United States, they conducted a ‘National Radio Silence Day’, with every radio in the country quietened for five minutes on the hour, every hour, across a 36-hour period. With this unprecedented radio silence and a specially designed radio receiver mounted on an airship, the idea was to make the most of the Martian ‘fly-by’ and listen in for messages, intentional or otherwise, from the red planet.
    Conspiracy theories notwithstanding, William F. Friedman didn’t decipher the first message from an alien intelligence, and the American public soon tired of the disruption to their news bulletins, but the principle of the experiment was sound. The idea that we might listen in to aliens had first been proposed 30 years earlier by the physicist and engineer Nikola Tesla. Tesla suggested that a version of his wireless electrical transmission system could be used to contact beings from Mars, and subsequently presented evidence of first contact. He wasn’t right, but in 1896, one year before the publication of
War of the Worlds
, it was certainly a plausible claim. Tesla wasn’t alone; other luminaries of the time shared his optimism, including the pioneer of long-distance radio transmission, Guglielmo Marconi, who believed that listening to the neighbours would become a routine part of modern communications. By 1921 Marconi was publicly stating that he had intercepted wireless messages from Mars, and if only the codes could be deciphered, conversation would soon begin.
    The failure of the National Radio Silence Day brought a temporary halt to the organised search for extraterrestrial signals, and the idea dropped out of scientific fashion until the post-war flying saucer boom. One of the first scientists to make