Einstein's special theory of relativity — where space and time merge into spacetime, clocks slow down near the speed of light, and simultaneity becomes relative. Interactive Minkowski diagrams and Lorentz transformations in your browser.
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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