The Quantum Universe

Arrows of Time
As far as we know, the fundamental dynamical laws are time neutral --- preferring no direction of time over another. Yet our universe exhibits a number of `arrows of time' --- general phenomena that distinguish directions in time. There is the thermodynamic arrow of time --- the fact that presently isolated systems are mostly evolving towards equilibrium in the same direction of time. There is the electromagnetic arrow of time --- electromagnetic radiation is retarded. 

There is the psychological arrow of time --- we remember the past, experience the present, and predict the future. There are the arrows of time supplied by the expansion of the universe and the growth of inhomogeneity. And then, there is the quantum mechanical arrow of time defined in Copenhagen quantum mechanics by the direction in time the wave function of a subsystem is reduced on measurement. The papers below in various ways show how arrows of time arise in quantum cosmology from asymmetries in quantum conditions that specify our universe even though the dynamical laws are time neutral.   READ MORE...

The Entropy of Quantum Entanglement

Bartosz Regula from the RIKEN Center for Quantum Computing and Ludovico Lami from the University of Amsterdam have shown, through probabilistic calculations, that there is indeed, as had been hypothesized, a rule of entropy for the phenomenon of quantum entanglement.


This finding could help drive a better understanding of quantum entanglement, which is a key resource that underlies much of the power of future quantum computers. Little is currently understood about the optimal ways to make effective use of it, despite it being the focus of research in quantum information science for decades.


The second law of thermodynamics, which says that a system can never move to a state with lower entropy, or order, is one of the most fundamental laws of nature, and lies at the very heart of physics. It is what creates the "arrow of time," and tells us the remarkable fact that the dynamics of general physical systems, even extremely complex ones such as gases or black holes, are encapsulated by a single function, its entropy.     READ MORE...