16 July 1945: The Atomic Age begins

Dangling from a steel tower in the desert at 5.29am on 16 July 1945 was a device so devastatingly powerful, even its creators weren't sure what they'd made. The physicists who had spent years working on their terrible weapon made bets on how terrible it would be from the safety of their laboratory at Los Alamos, New Mexico.

Some guessed the bomb's blast would be the equivalent of around 45,000 tons of TNT. Nobel Prize-winning scientist Enrico Fermi is said to have offered side odds on the weapon having the power to wipe out all life on earth. But what everyone knew for sure was that the world would never be the same again.

When the plutonium bomb, nicknamed theGadget, dropped a minute later on that wet morning in 1945, it unleased a wave of destruction with a force of 18.6 kilotons of power. The steel tower that cradled it turned to dust, and the heat from the blast was so great, it turned the asphalt into shards of green glass, known as trinitite, named after the test site, Trinity.

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J Robert Oppenheimer, who led the research into the atomic bomb (the Manhattan Project), chose the name Trinity after a religious-themed poem by John Donne, such was his awe of the new weapon. As he watched the mushroom cloud rise to the sky, his thoughts turned to the Hindu holy text, the Bhagavad Gita: "If the radiance of a thousand suns were to burst at once into the sky, that would be like the splendour of the mighty one. Now I am become Death, destroyer of worlds".

The Manhattan Project had its roots in a letter Albert Einstein sent to US president Franklin D Roosevelt in 1939. In it, he explained how an atomic bomb could be made. Between 1942 and 1946, the US put all its energy into making the bomb a reality, spending $29bn in today's money, according to Bloomberg.

The next day after the Trinity test in July 1945, the Potsdam Conference began in Europe with the Allies drawing up plans for a defeated post-war Germany. News of the trial's success filtered back to US president Harry S Truman, who had one eye on ending the war with Japan. When the Japanese refused to surrender, atomic bombs were dropped on Hiroshima and Nagasaki the latter modelled on the one trialled at Trinity. Nobody knows for sure how many people died, but it's been estimated at around 185,000.

"I made one great mistake in my life", Einstein is reported to have said shortly before he died, "when I signed the letter to President Roosevelt recommending that atom bombs be made." The Atomic Age had begun, and nobody could say for sure how it would end.

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