The year 1915 was a big moment for physics. That was when Albert Einstein published his general theory of relativity, one of the most transformative ideas about the universe ever formulated. And that was the year mathematician Emmy Noether published her Noether’s theorem, which established the importance of symmetry, a central concept in physics and in theories attempting to unify the known forces of the universe.
Two public lectures at the Perimeter Institute for Theoretical Physics in Ontario this week will explore the genesis and impact of these landmark advances. Both will be broadcast live here on this page. On Monday, June 22 at 8 P.M. Eastern Time, mathematician Peter Olver will discuss Noether’s life and career, and physicist Ruth Gregory will detail the meaning of Noether’s theorem. On Tuesday, June 23 at 8 P.M., Perimeter physicists will celebrate Einstein’s theory of relativity, the role it has played in 20th century astrophysics and the challenges it presents to physicists who are trying to unite all of the universe’s forces in a single physical law. Both lectures are part of Perimeter’s Convergence conference about the future of fundamental physics.
Noether’s theorem states that for every symmetry of nature there is a corresponding law of conservation. In physics, a symmetry is something that remains unchanged under transformation—for example, the time translation symmetry tells us that the laws of physics are the same at all times. This rule corresponds to the conservation of energy—as time passes, energy cannot be created or destroyed, or else the laws of physics would have changed. Noether’s theorem remains highly relevant because symmetries are at the forefront of the search for deeper truths in physics. For example, the idea of supersymmetry suggests that all the known particles in the universe might correspond to mirror particles that are waiting to be discovered.
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General relativity, meanwhile, established that space and time are united in a concept called spacetime, and that gravity works by warping spacetime so that any object passing through it will travel along a curved path. The theory is still the most accurate tool for predicting the orbits of celestial bodies, but it does not play well with other foundational theories, such as quantum mechanics. The next century of physics will likely be dominated by quests to combine relativity with the other known laws of nature.