The Arrow of Time and the Meaning of Life

1. The Arrow of Time and the Meaning of Life Sean M. Carroll Caltech

2. Two aspects of time: • Repetition • Change

3. Repetition -- predictable, cyclic behavior -- is what allows us to measure time.

4. Rhythms of the heart, brain, and body provide us with internal clocks.

5. But change is the more interesting -- and mysterious! -- aspect of time.

6. Just as organisms change and evolve, so do stars, and so does the universe.

7. A profound difference between time and space: time has a direction, space does not. [NASA]

8. The arrow of time -- the difference between past and future -- is one of reality’s most blatant features.

9. Memory Cause & Effect Free Will Aging Aspects of Time’s Arrow

10. The fundamental laws of nature have no arrow of time. Macroscopic evolution is irreversible. Simple (“fundamental”) motions are reversible.

11. A single phenomenon underlies all manifestations of time’s arrow: increasing entropy. Entropy is a measure of disorderliness, messiness, randomness.

12. 2nd Law of Thermodynamics: entropy increases in closed systems as time passes. Entropy Time

13. Ludwig Boltzmann, 1870’s: Entropy counts the number of ways we can re-arrange a system without changing its basic appearance. [Martin Röll] low entropy: delicately ordered high entropy: all mixed up time

14. low entropy Entropy increases simply because there are more ways to be high-entropy than low-entropy. All makes sense, if the entropy was low to begin with. high entropy arrangements of atoms, grouped into sets that appear the same macroscopically

15. The Past Hypothesis: our universe started in a low-entropy state. 13.7 billion years ago, at the Big Bang.

16. correct reconstruction low-entropy past The past hypothesis helps reconcile reversible microphysics with macroscopic directionality. Why do we remember the past and not the future? possible futures possible pasts what we know about the present

17. Cosmologists are faced with a puzzle: why did the early universe have a low entropy? [Sky & Telescope]

18. Entropy vs. Complexity Entropy increases. Complexity first increases, then decreases.

19. 10100 yr 1015 yr 105 yr 1010 yr 1 sec Ephemeral Complexity in the Universe

20. Origin of life: Complexity isn’t merely compatible with the Second Law, it’s a consequence of increasing entropy. [Yung, Russell & Parkinson]

21. Sustaining life: energy is constant, but organisms take low-entropy energy and degrade it into high-entropy energy. [Penrose]

22. Two ways to be stationary • Microstasis: individualconstituents are static • Homeostasis: individualconstituents in motion,but regulatedmacroscopic stationarity.Requires entropy production.

23. Maxwell’s Demon as a model for life

24. Thinking and consciousness:the C. Elegans nematode [Bob Goldstein, UNC Chapel Hill, Wikimedia commons; OpenWorm project]

25. Evolution adapts memory to use for imagination. What role does thinking about the future play in the origin and nature of consciousness?

26. The span of life three billion heartbeats [Levine 1997]

27. Configuration space is big, the universe is young and small Age of observable universe: 1017 seconds Number of particles in observable universe: 1088 Human-sized DNA sequences: 101,000,000,000 Universal recurrence time: 1010 120 P vs. NP: it’s much easier to check solutions to problems than to find them

28. [NASA/Hubble]