Quantum Space Loop Quantum Gravity and the Search for the Structure of Space, Time, and the Universe [Audiobook] (2024)

But, while they are both highly successful, these two structures leave a lot of important questions unanswered. They are also based on two different interpretations of space and time, and are, therefore, fundamentally incompatible. We have two descriptions, but as far as we know, we've only ever had one universe. What we need is a quantum theory of gravity.
Approaches to formulating such a theory have primarily followed two paths. One leads to String Theory, which has for long been fashionable, and about which much has been written. But String Theory has become mired in problems. Combining clear discussions of both quantum theory and general relativity, this book offers one of the first efforts to explain the new quantum theory of space and time.