Albert Einstein's famous letter to U.S. President Franklin D. Roosevelt on August 2, 1939, triggered the Manhattan Project to develop the atomic bomb. General Leslie R. Groves was in military charge, while J. Robert Oppenheimer was in scientific charge. The first successful test of an American atomic bomb took place on July 16, 1945, near Alamogordo in the Chihuahuan Desert of New Mexico. In August 1945, the new U.S. President Harry S. Truman decided to use this weapon to force Japan's surrender. On August 6 and 9, the cities of Hiroshima and Nagasaki were bombed and largely destroyed, killing over 100,000 people. On August 15, Japan’s Emperor Hirohito announced the unconditional surrender of his country.
Other countries, such as the former Soviet Union, Great Britain, France, China, and others, also built and tested atomic bombs – some also hydrogen bombs – first in the atmosphere, then underground. This led, especially in the Northern Hemisphere, to a worldwide increase in environmental radioactivity and, during the Cold War, to a balance of terror between the political East and the political West. Only the Comprehensive Nuclear-Test-Ban Treaty (CTBP) of 1996 – which, however, is still not in force – led to an end to nuclear weapons testing, a process that has lasted to this day. Whether this will continue, or whether other countries will develop and test atomic bombs to use them as a threat, for example, remains an open question.
The lecture is divided into three parts: some basic physics about nuclear forces and nuclear reactions, then the actual history of the atomic bomb, and finally the effects of atomic bomb testing on humans and the environment. However, the geopolitical impact of the atomic bomb cannot be addressed in a physics colloquium lecture.