On Time

Causality and the Quantum Gravity Conflict

De: Jan Zaanen

Narrado por: Richard Trinder

This text revolves around a new and unusual view on the most fundamental puzzle of physics. It focuses on the key aspect that makes the role of the time dimension fundamentally different: causality. The implicit and intuitive way by which causality is usually taken for granted is just made explicit and less self-evident, shedding a new light on the gravity-quantum conflict. The case is made that gravity is a necessary condition for a causal universe. But upon turning to the "pure" unitary quantum physics explaining the nature of matter one is dealing with the strictly a-causal time expressed through the thermal quantum field theory machinery. When this a-causal microscopic and causal macroscopic world meet, one encounters the wavefunction collapse, that itself may be rooted in the quantum-gravity conflict. Modern ideas are discussed resting on eigenstate thermalization showing how this may lie eventually at the origin of irreversible thermodynamics. The case is anchored in the sophisticated modern mathematical machinery of both general relativity and quantum physics which is normally barely disseminated beyond the theoretical physics floors.

The book is unique in the regard that the consequences of this machinery are explained in an original, descriptive language conveying the conceptual consequences while avoiding mathematical technicalities.

©2024 Oxford University Press (P)2024 Tantor Media

Very intersting ideas well presented

This book refers to figures and equations but there is no associated PDF.
The figures and equations appear in the digital book version.
Nevertheless, anyone can understand these ideas without the PDF.
ONE THING – if you don’t know about the AdS/CFT correspondence you should google it and understand it before starting this book. The author LOVES this correspondence and uses it without explaining what it is first.

The author makes several interesting points. Firstly, that causality only exists in non-equilibrium states and the non-equilibrium state of our universe is due only to gravity. Thus causality only makes sense in theories including gravity. He also points out that in Quantum Field Theory (QFT), time is unitary and there is no causality built in. To get causal results from QFT explicit causes must be added to the equations. He then proposes that the causal nature the thermodynamics in our real world, is due to the repeated collapse of wave functions due to gravity.

The author also describes several ideas on how science might investigate the collapse of the wave function, including computing how long it would take for a small mass (a bacteria) to collapse a superposition.

In the Epilogue the author goes a little off the rails making a very weak argument that the ability of humans to tell a good new story (while AI is currently unable to do this) hints that something about human consciousness may be required to collapse the wave function. I was not convinced. Although I agree that current AI’s cannot create a good new story, this is only because of the way AI’s are currently trained. I don’t see any reason to believe this implies some limit on the creativity of future AI’s. I understand Penrose and Zaanen seem to believe in the specialness of consciousness. I suspect a lot of humans want to believe they are special.

The narration was very clear and handled the technical material very well.