There are certain, pivotal discoveries in any century, findings that will in turn initiate a process of change that will affect society as a whole. Deciding which are the most important is a subjective activity - but can there have been any more profound discoveries in the past century than the development of nuclear weapons, the explanation of the nature of DNA and the introduction of digital computers? These have, in their turn, shaped society, and society would not be as it is had any one of these been taken from the equation.
Who do we have to thank for nuclear weapons? Clearly, the secret US Manhattan Project, begun in 1942 with the specific aim of creating atomic weapons, was the initial source of the bomb as we know it. This work, however, grew directly from the achievement by Enrico Fermi, in 1942, of the first self-sustaining nuclear fission reaction, and from the work by Cockcroft and Walton 10 years earlier when they used the first nuclear particle accelerator to split a lithium atom.
The scientists were working on aspects of fundamental physics, just as a new generation of scientists is today. The Manhattan Project scientists were working on a weapon they hoped would end a wicked war, despite the powerful wickedness of such a device. And so the various contributions were summed up over many years, with discovery being built on discovery, until the world was brought to the brink of annihilation. The scientists did not achieve this on their own, they needed the help of both lawmakers and society to make this all happen. Today scientists, with the help of society and governments, are taking weapons apart and trying to find ways to make their nuclear ingredients safe.
In the interim, however, the Cold War divided Europe, spawned the development of advanced rocketry able to carry nuclear weapons to enemies on the other side of the world, led idealogues under Stalin to kill off 25 million of their countrymen for fear of undermining the state, and brought about the development and massive stockpiling of chemical and biological weapons.
The Cold War also opened up research of a different kind, that into space travel. Success in rocketry and getting people into space became a matter of prestige and national pride. The Cold War and nothing else managed to land humans on the surface of the moon and the remnants of that space race - and the military advances that come from such research - remain, in efforts to create an international space station and in satellite launches to Mars.
For good or ill, science brings about these changes through the incremental steps and the occasional flashes of genius produced by research. The nuclear weapons persist, the military industrial complex still flourishes and the political maps still reflect the scars left by the Cold War and a dangerous time in the world's history brought about through scientific research.
We could blame the whole thing on Einstein, yet he was doing no more than trying to reconcile Sir Isaac Newton's fundamental physical laws and the laws describing electricity, magnetism and light assembled by Sir James Clerk Maxwell. In the process, Einstein established the link between time and space and between mass and energy. If this brought us the Cold War, it also brought us cosmology and the Big Bang and Black Holes and a whole new way of understanding our universe.