The Quantum Mechanical Arrows of Time

  • James B. HartleEmail author
Conference paper


The familiar textbook quantum mechanics of laboratory measurements incorporates a quantum mechanical arrow of time—the direction in time in which state vector reduction operates. This arrow is usually assumed to coincide with the direction of the thermodynamic arrow of the quasiclassical realm of everyday experience. But in the more general context of cosmology we seek an explanation of all observed arrows, and the relations between them, in terms of the conditions that specify our particular universe. This paper investigates quantum mechanical and thermodynamic arrows in a time-neutral formulation of quantum mechanics for a number of model cosmologies in fixed background spacetimes. We find that a general universe may not have well defined arrows of either kind. When arrows are emergent they need not point in the same direction over the whole of spacetime. Rather they may be local, pointing in different directions in different spacetime regions. Local arrows can therefore be consistent with global time symmetry. [Editors note: for a video of the talk given by Prof. Hartle at the Aharonov-80 conference in 2012 at Chapman University, see]


Quantum Mechanic Quantum Fluctuation Quantum Cosmology Spacetime Region Emergent Feature 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



The author thanks Thomas Hertog for many discussions of the arrows of time in quantum cosmology and Murray Gell-Mann for discussions on the quantum mechanics of the universe over many decades. He thanks the Santa Fe Institute for supporting many productive visits there. The this work was supported in part by the National Science Foundation under grant PHY12-05500.


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Copyright information

© Springer-Verlag Italia 2014

Authors and Affiliations

  1. 1.Santa Fe InstituteSanta FeUSA
  2. 2.Department of PhysicsUniversity of CaliforniaSanta BarbaraUSA

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