Einstein's special theory of relativity — where space and time merge into a single four-dimensional spacetime, clocks slow down near the speed of light, and simultaneity becomes relative. This category covers the phenomena that reshaped twentieth-century physics: time dilation, length contraction, the Lorentz transformation, mass–energy equivalence (E=mc²), the relativity of simultaneity and the geometry of Minkowski diagrams. By dragging events across an interactive spacetime grid and pushing the velocity toward c, you can see for yourself how the Lorentz factor γ stretches time and shrinks distance, why the spacetime interval stays invariant, and how causality is preserved by the light cone. It matters because these effects are not abstractions — they govern GPS satellites, particle accelerators and the muons raining through the atmosphere every second.
Each simulation runs fully in the browser — no server, no installation
The four fundamental equations of special relativity for a boost along x
From postulates to Minkowski geometry — explored interactively
Special relativity (Einstein, 1905) rests on two postulates: the laws of physics are the same in all inertial frames, and the speed of light c is constant in all frames regardless of the motion of source or observer. These simple postulates force a radical restructuring of space and time into a unified four-dimensional spacetime.
The Minkowski diagram is the most direct way to visualise this new geometry. Each point (event) in spacetime has coordinates (x, ct). Two inertial frames S and S′ — where S′ moves at velocity v = βc relative to S — are related by the Lorentz transformation. In the diagram, the S′ axes appear tilted toward the 45° light cone as β increases: both axes tilt symmetrically, which ensures c remains the same in both frames.
The most counter-intuitive consequence is the relativity of simultaneity: events that are simultaneous in S (same ct coordinate) generally have different ct′ values in S′. There is no absolute "now" — only the spacetime interval s² = c²t² − x² is invariant. Timelike separated events can be causally connected; spacelike ones cannot (and their time-ordering can be reversed by boosting).
Topics and physics you'll find in this category
Common questions about special relativity
Every Relativity simulation here runs instantly in your browser, so you can learn Relativity online without any downloads or accounts. Each interactive Relativity model lets you adjust velocity, drag spacetime events and watch time dilation, length contraction and the Lorentz factor respond in real time. From the Minkowski diagram to the twin paradox and E=mc², these visual tools turn abstract equations into something you can manipulate by hand. The same physics underpins the GPS navigation in your phone, where clock corrections for relativistic time dilation keep positioning accurate to within a few metres.