Carlo Rovelli

Carlo Rovelli Image source: Edge

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Carlo Rovelli is an Italian theoretical physicist and cosmologist who wrote the book on Quantum Gravity.

Quotes by Carlo Rovelli in Time One

[G]eneral relativity and quantum mechanics appear to be fully inconsistent with one another.

Since the discovery of general relativity we no longer are sure of what spacetime is, and since the discovery of quantum mechanics we no longer are sure of what matter is.

The very distinction between spacetime and matter is likely to be ill-founded....

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.

I think that the responsibility for the search for the new synthesis is not for physicists alone.

We do not have a new synthesis.

General relativity is structured in such a way to imply that there is something external to the system described.

… the very notion of a system’s state depends on the fact that an observer is observing it.

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. . . .

[A]t small scales there should be quanta of space and time ….

At the foundations of physics there is today confusion and incoherence. … GR and QM have opened a revolution. The revolution is not yet complete.

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.

Physics always deals with two distinct temporalities, which I may denote as the system’s time and the observer’s time.

I believe that the essential discovery about nature encoded into general relativity is … that position with respect to a “background” spacetime is a meaningless concept.

The “fundamental scientific view of the world” of the present time is characterized by an astonishing amount of perplexity, and disagreement, about what time, space, matter and causality are.

[In the Loop Quantum Gravity picture] these “quanta of gravity” do not live immersed in a spacetime. They are space. The idea of space as the inert “container” of the physical world has disappeared.

Einstein’s major discovery is that spacetime and gravitational field are the same object.

QM is not the theory of micro-objects. It is our best form of mechanics.

[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?

I think it is fair to say that there isn’t even a single complete and consistent candidate for a quantum theory of gravity.

Quantum gravity is therefore the study of the structure of spacetime at the quantum scale.

The most appealing aspect of loop quantum gravity is that it predicts that space is not infinitely divisible, but that it has a granular structure.

[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.

The search for a quantum theory of gravity raises once more old questions such as: What is space? What is time? What is the meaning of “moving”?

The world may not be the way it appears in the tiny garden of our daily experience.

The key difficulty of quantum gravity may therefore be to find a way to understand the physical world in the absence of the familiar stage of space and time.

Fundamental physics is today in a peculiar phase of deep conceptual confusion.

Everybody says they want background independence, and then when they see it they are scared to death by how strange it is. … Background independence is a big conceptual jump.