Special and general relativity (SR/GR) describe nature from a subjective perspective. Mathematically, they are correct. Here I show: (1) Physically, SR/GR have an issue. Science should always strive for an objective description of nature. This is not possible in relative spacetime. In particular, observers cannot agree on what is past and what is future. Even so, the Lorentz factor and gravitational time dilation are correct. This is why SR/GR work so well in an observer’s reality. (2) Euclidean relativity (ER) describes nature from an objective perspective. Any (!) object’s proper space d₁, d₂, d₃ and its proper time τ span “natural spacetime”, which is 4D Euclidean space (ES) if we take cτ as d₄. All energy is moving through ES at the speed of light c. Each observer’s reality is created by projecting ES orthogonally to his proper space and to his proper time. These axes are reassembled in SR/GR to a non-Euclidean spacetime. Because information is lost in each projection, the performance of SR/GR is limited. However, the SO(4) symmetry of ES is not compatible with waves. This is fine because ER tells us that wave and particle are subjective concepts: What I deem wave packet, deems itself particle at rest. We must distinguish between an observer’s reality described by SR/GR (with waves) and the “master reality” ES described by ER (without waves). ER improves cosmology and quantum mechanics by solving the Hubble tension, dark energy, and non-locality.