The Arrow of Time and How to Reverse It
Summary
This PBS Space Time episode explores the arrow of time, explaining why the universe moves forward despite time-symmetric physical laws. The host details how the second law of thermodynamics and increasing entropy break this symmetry, using the Big Bang as the initial low-entropy state that dictates time's direction. The discussion also touches on the potential for a symmetric universe and includes a segment addressing viewer comments on electroweak theory and the physics of free will.
Topics discussed
Sponsorship: Progressive Commercial Insurance
Introduction: The mystery of time's direction
Time symmetry in physical laws
Defining the arrow of time: external vs internal
Reversibility of motion and the block universe
Entropy and the Second Law of Thermodynamics
Sponsorship: Progressive and UKG
Entropy fluctuations and time symmetry
How entropy minima create the arrow of time
Cosmic expansion and the Big Bang's low entropy
Speculating on a time-reversed universe
Sponsorship and transition to Q&A
Q&A: Electroweak theory and vacuum decay
Q&A: Free will, determinism, and information
Q&A: Philosophical labels and QED humor
Sponsorship: Progressive and UKG
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