In this solo episode, Sean Carroll explains the discovery that the universe's expansion is accelerating—the most surprising result of his career. He traces the history of the cosmological constant from Einstein's original introduction through the puzzle of why quantum field theory predicts a disastrously large vacuum energy, to the 'coincidence problem' of why dark energy dominates at the present epoch. This is the first of two connected solo episodes; the next will cover alternative dark energy theories.
This summary was generated from show notes and public descriptions, not from a full transcript review. Details may contain inaccuracies.
Canon
•
The Cosmological Constant as the Explanation for Cosmic Acceleration
A positive cosmological constant, or vacuum energy, is the simplest explanation for the observed acceleration of the universe's expansion.
Einstein's Introduction and Dismissal of the Cosmological Constant
Einstein added the cosmological constant to his field equations to permit a static universe and later called it his 'greatest blunder' after the expansion of the universe was discovered.
Quantum field theory predicts a vacuum energy that is 120 orders of magnitude larger than the observed value, creating the 'cosmological constant problem.'
The density of dark energy is roughly equal to the density of matter at the current epoch, raising the question of why we happen to live in this brief window of cosmic history.