Time in a quantum universe

Lee Smolin

Shi‐Xin Zhang, Shuai Yin

Quantum computers promise a highly efficient approach to investigate quantum phase transitions, which describe abrupt changes between different ground states of many-body systems. At quantum critical points, the divergent correlation length and entanglement entropy render the ground state preparation difficult. In this work, we explore the imaginary-time evolution for probing the universal critical behavior as the universal information of the ground state can be extracted in the early time relaxation process. We propose a systematic and scalable scheme to probe the universal behaviors via imaginary-time critical dynamics on quantum computers and demonstrate the validness of our approach by both numerical simulation and quantum hardware experiments. With the full form of the universal scaling function in terms of imaginary time, system size, and circuit depth, we successfully probe the universality by scaling analysis of the critical dynamics at an early time and with shallower quantum circuit depth. Equipped with quantum error mitigation, we also confirm the expected scaling behavior from experimental results on a superconducting quantum processor which stands as the first experimental demonstration of universal imaginary-time quantum critical dynamics.

George Jaroszkiewicz

Some principles underpinning the running of the Universe are discussed. The most important, the machine principle, states that the Universe is a fully autonomous, self-organizing and self-testing quantum automaton. Continuous space and time, consciousness and the semi-classical observers of quantum mechanics are all emergent phenomena not operating at the fundamental level of the machine Universe. Quantum processes define the present, the interface between the future and the past, giving a time ordering to the running of the Universe which is non-integrable except on emergent scales. A diagrammatic approach is used to discuss the quantum topology of the EPR paradox, particle decays and scattering processes. A toy model of a self-referential universe is given.

Andrew Soltau

The nature and topology of time remain an open question in philosophy. Both tensed and tenseless concepts of time appear to have merit. Quantum mechanics demonstrates that both are instantiated, as complementary aspects of the time evolution of physical systems. The linear dynamics is tenseless. It defines the universe probabilistically throughout space-time, and can be seen as the definition of an unchanging block universe. All properties of the universe are defined for the whole extent of the linear time dimension of space-time. The collapse dynamics is the change to the linear dynamics: time evolution of the physical system in the quantum concept of time. This is tensed: different definitions of the probabilistic definition of the space-time universe exist from moment to moment in the quantum concept of time. Thus the linear time dimension of space-time is tenseless, while time in the quantum concept of time is tensed. Exercise of the linear dynamics is experienced as the passage of time, while the exercise of the collapse dynamics is experienced as change.