Britannica
Sources used in this answer
- Philosophy of physics - The special theory of relativity
- relativistic mechanics - Development of the special theory of relativity
- relativistic mechanics - Relativistic space-time
- Bertrand Russell on relativity - Relativity physics
- Bertrand Russell on relativity - Realism in relativity
- relativity - Einstein’s Gedankenexperiment s
- time: Top Questions
Why does Einstein’s theory of relativity not mean that all physical facts are relative?
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relativity
Brian Greene kicking off his Your Daily Equation video series with Albert Einstein's famous equation E = mc2.
It is a common misconception that Albert Einstein’s theory of relativity implies that all physical phenomena are relative. In reality, the theory was designed to establish that certain fundamental aspects of the universe remain objective and independent of any observer’s perspective.1
While Einstein demonstrated that measurements of time intervals, spatial distances, and simultaneity depend on an observer's frame of reference, the theory identifies a "residue" of physical facts that all observers must agree upon. For example:12
- Constancy of Light: The theory is built on the requirement that the speed of light in a vacuum is constant for all inertial observers.13
- Spatiotemporal Interval: All observers agree on the "spatiotemporal interval"—a specific algebraic combination of spatial and temporal distances between events—which confirms that space and time are part of a single, objective space-time structure.14
- Objective Laws: The fundamental laws of physics are formulated to be invariant under Lorentz transformations, ensuring they take the same form regardless of the observer's motion.154
Ultimately, relativity is a realistic framework; it posits that what all observers agree upon when recording a phenomenon constitutes objective reality, rather than a subjective contribution from the observer.2