Time is an illusion, and these physicists say they know how it works [video]
Physicists’ claims that “time is an illusion” prompt wide-ranging reflections on whether time is fundamentally real or just a way humans describe change, memory and experience. Commenters contrast everyday and philosophical intuitions about time with formal treatments in classical mechanics, relativity, quantum mechanics and thermodynamics, including the idea that only entropy gives time an arrow. The thread also touches on why gravity is modeled differently from other forces and how assertions about time’s illusory nature intersect with debates over consciousness and free will.
Conceptual views of time
- Many participants equate time with change: no change → no meaningful time.
- Several argue awareness and memory are required to perceive time, though others say physical time would exist even in an unconscious universe.
- Thought experiment: in a universe with a single particle, some say time is meaningless (no relative change or position); others say the particle’s internal changes or universe size still allow time.
Time, change, and measurement
- Clocks are seen as devices that track regular changes (atomic transitions, orbital motion, mechanical cycles).
- One view: “time = distance / velocity”; without motion or distance, no time. Others push back that this is just one formula, not a definition.
- Some compare time to derived quantities like temperature or pressure: measurable and useful but not obviously fundamental.
- Debate over whether time has a “fundamental unit”; skepticism that it’s a particle-like thing or discretely sampled.
Physics frameworks and the arrow of time
- One summary contrasts:
- Classical mechanics: time as a continuous axis in a 4D geometry.
- Relativity: same, but spacetime can be curved.
- Quantum mechanics: algebraic evolution of states; time enters equations but superposition changes the picture.
- Thermodynamics: introduces an arrow of time via entropy increase and information-theoretic considerations.
- Others stress entropy decrease is locally possible but globally overwhelmingly unlikely.
Gravity and spacetime
- Multiple comments explain why gravity is “special”: GR treats it as spacetime curvature, while other forces fit quantum field theory with force carriers.
- Attempts to quantize gravity like other forces run into non-renormalizability; no confirmed graviton.
- Some note you can reformulate GR in force-like terms, but it becomes ugly and loses the geometric elegance.
Is time an illusion?
- Some argue time “doesn’t exist” and is just narrative or bookkeeping for change.
- Others respond that physics treats time as a measurable quantity with high-precision clocks, giving it strong operational reality, even if our intuition about it is misleading.
- Several emphasize that calling something an “illusion” usually means “not as it naively appears,” not “nonexistent.”
Free will digression
- The video’s claim that free will is an illusion sparks debate.
- Positions range from strict determinism, to chaos/quantum-based unpredictability, to compatibilist views where predictability doesn’t negate “making choices.”
- Some argue free will has little scientific utility; others stress its role in explaining agency and responsibility.