Carlo Rovelli is an Italian theoretical physicist and cosmologist who wrote the book on Quantum Gravity.
Quotes by Carlo Rovelli in Time One
Thus the picture of reality that emerges by taking quantum mechanics and general relativity seriously is quite radical: spacetime as [a background] “entity” has fully disappeared…. What the world is beyond these [background] regimes, and how we can describe, measure, or just think about it, are issues still immersed in a profound mystery.
The quest for quantum gravity can be separated into three main lines of research. … They are often denoted “covariant,” “canonical,” and “sum-over-histories,” even if these names can be misleading and are often used interchangeably. They cannot be characterized by a precise definition. . . .
I believe that we are going through a period of profound confusion, in which we lack a coherent general picture of the physical world capable of embracing what, or at least most of what, we have learned about it.
[P]hysics is once more facing conceptual problems: What is matter? What is causality? What is the role of the observer in physics? What is time? What is the meaning of ‘being somewhere’? What is the meaning of ‘now’? What is the meaning of ‘moving’? Is motion to be defined with respect to objects or with respect to space?
[T]he formal content of special relativity is entirely coded in the Lorentz transformations, which were written by Lorentz, not by Einstein, and several years before 1905. What was Einstein’s contribution? It was to understand the physical meaning of the Lorentz transformation.