Definition
In physics, relativity is the principle that measurements of motion, speed, and even the timing of events depend on the observer's frame of reference. There is no single absolute vantage point; a passenger on a train and a person on the platform each describe the same scene differently, and both are correct.
As a mental model, relativity reminds us that perspective shapes perception. What looks fast, fair, large, or risky from one position looks different from another. Understanding a situation requires knowing which frame the observer occupies.
Why it matters
How it works
A frame of reference is the coordinate system from which an observer measures. Motion is meaningful only relative to such a frame — you are at rest relative to your chair but moving rapidly relative to the sun. Crucially, the laws of physics themselves stay the same in every frame, even though the measured numbers change.
The practical use is to ask, before judging, from what frame the judgment is made. A delay that feels slow to a customer feels fast to an engineer. By naming the frame and trying others, you separate what is genuinely true for everyone from what is merely an artifact of your vantage point.