relativity

According to standard electromagnetic theory, if the charge A is stationary and the charge B is moving along arbitrary trajectory then the electromagnetic force on charge A is: $$\vec{F}_A = q_A \left(-\nabla\phi - \frac{\partial}{\partial t}\vec{A}\right)$$ where $\phi$ and $\vec{A}$ are velocity dependent scalar and vector potentials (Lienard-Wiechert potentials), i.e. $$\phi = \frac{1}{4\pi\ep…

An exercise in Schutz's general relativity book states: "A body is said to be uniformly accelerated if its acceleration four vector $\vec{a}$ has constant spatial direction and magnitude, say $\vec{a}\cdot \vec{a} = \alpha^2$ " . Unfortunately, I don't understand what's meant by "constant spatial direction". I can find an explicit solution if, in a given referential frame, the speed is given by: …

Scientific Reports, Published online: 22 August 2026; doi:10.1038/s41598-026-67596-6 Comparative fits to identified-hadron spectra in relativistic p+p, p+Pb, Pb+Pb and Au+Au collisions including error covariances

Our universe emerged when spacetime’s building blocks “crystallized” into being, according to a controversial theory.

Textbooks say that for a distant external observer, an infalling object never reaches the horizon because $dr/dt$ tends to 0 as $r$ approaches $2M$ . But this conclusion assumes the object is a test particle with negligible mass. If we take the object's own mass $m$ seriously, then the exterior spacetime is determined by the total mass $M+m$ . The new horizon is at $2(M+m)$ , so the old surface $…

Confirming that Everettian quantum mechanics avoids ‘spooky action at a distance’ addresses longstanding concerns about its compatibility with relativity; however, the researchers acknowledge this work doesn't fully resolve debates surrounding wavefunction branching itself. Some interpretations, like those initially proposed by von Neumann, necessitate an instantaneous collapse of possibilities u…

The ability to simulate black holes offers a unique testing ground for fundamental theories attempting to reconcile general relativity with quantum mechanics; however, faithfully recreating these extreme environments remains computationally challenging. The researchers acknowledge that their chiral spin chain, a simplified mathematical analogue of a black hole’s edge, necessarily omits crucial as…

General Relativity (GR) serves as the foundational framework for modern gravitation, demonstrating exceptional consistency across local and intermediate cosmological scales. In this work, we propose a systematic, field-theoretic refinement of GR by incorporating effective viscoelastic responses into the spacetime fabric as higher-order constitutive corrections. Beginning from a modified least-act…

Textbooks say that for a distant external observer, an infalling object never reaches the horizon because dr/dt tends to 0 as r approaches 2M. But this conclusion assumes the object is a test particle with negligible mass. If we take the object's own mass m seriously, then the exterior spacetime is determined by the total mass M+m. The new horizon is at 2(M+m), so the old surface 2M is no longer …

Space-time isn’t an actual object or event, it’s a conceptual framework for understanding reality.