Towards Unification of Forces

Unification is one of the recurring, deepest ambitions of physics (as noted in the opening section), and many of physics's greatest advances have been exactly this: showing that two phenomena that looked unrelated are really the same thing viewed differently. Newton unified the terrestrial and celestial domains by showing that one law of gravitation governs both a falling apple and an orbiting planet. Oersted's and Faraday's experiments showed that electricity and magnetism cannot really be separated. Maxwell went further still, unifying electromagnetism with optics by showing that light itself is an electromagnetic wave. Einstein tried, and did not succeed, to unify gravity with electromagnetism — but that failure did not stop physicists from continuing to chase the goal.

Real progress has followed since: the electromagnetic force and the weak nuclear force have now been unified into a single "electroweak" force (what this unification precisely means is beyond the scope of this course). Efforts continue to fold the strong force into this electroweak picture, and ultimately to bring gravity in as well — much of this remains speculative and unsettled. The milestones so far: