Big Think Physics: Are we forever trapped in the arrow of time? | Sabine Hossenfelder
Oct 29, 2025
In this intriguing discussion, Sabine Hossenfelder, a theoretical physicist and science communicator, tackles the enigma of time's one-way direction. She explains how fundamental particle laws are time-symmetric but macroscopic events are not—a concept known as the arrow of time. Hossenfelder dives into entropy, revealing its role in aging and the potential for lifespan extension. She even explores philosophical ideas on the universe's fate and its connection to science fiction, including Asimov's thought-provoking story on reversing entropy.
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Micro Laws Are Time-Symmetric
- Microscopic laws are time-symmetric, yet macroscopic reality is not because of how particles are arranged.
- This mismatch between microphysics and our everyday experience creates the observable arrow of time.
Entropy Gives Time Its Direction
- The arrow of time arises because entropy increases in one temporal direction, making forward and backward movies look different.
- Entropy's unidirectional growth is what gives time its apparent directionality in everyday phenomena.
Low-Entropy Past Is Required
- Entropy can only increase if it started very low, so the early universe must have had very low entropy.
- That low-entropy past is necessary for the arrow of time and for our existence today.
