How the Arrow of Time Emerges from the Big Bang

Why do we experience time flowing in one direction — from past to future — when the laws of physics themselves are mostly time-symmetric?

The Special Initial State

The key lies in the special initial condition of the universe — a low-entropy, unstable equilibrium at the moment of the Big Bang.

The “tipping” of this unstable state set a cosmic arrow of time:

• Low entropy → high entropy.
• Smooth early universe → structured late universe.
• Expansion of spacetime defines a direction of evolution.

The Cosmic Arrow

Because of this, we observe:

• Cause preceding effect.
• Memories of the past but not the future.
• Entropy always increasing, not decreasing.

The arrow of time is not a feature of fundamental physics per se — it is an emergent consequence of the Big Bang’s unstable beginning.