On the Meaning of General Covariance and the Relevance of Observers in General Relativity

TL;DR

This paper clarifies that in General Relativity, the concept of observers is fundamental and not to be dismissed, emphasizing the importance of observer-dependent quantities despite the theory's general covariance.

Contribution

It argues against the common misconception that general covariance implies observer-independence, highlighting the essential role of observers in the interpretation of General Relativity.

Findings

Observers are crucial for meaningful physical quantities in General Relativity.

Misinterpretations of covariance can lead to neglecting the observer concept.

Examples demonstrate the importance of observers in the theory.

Abstract

Since the appearance of General Relativity, its intrinsec general covariance has been very often misinterpreted as implying that physically meaningful quantitities (and conclusions extracted from the theory) have to be absolutely independent on observers. This incorrect point of view is sometimes expressed by discarding the very concept of observer in the structure and applications of the theory. As we shall stress in this essay, through some examples, the concept of observer is as essential to General Relativity as it is to any physical theory.