Time Perception Physics

Time — the progression of events from past through present to future, measurable through the interval between events — is one of the most fundamental and least understood aspects of reality. Physics offers two perspectives: Newton's absolute time (a fixed, universal background against which events occur, the same everywhere); and Einstein's relativistic time (time is not fixed but depends on relative velocity and gravitational field — time dilation, confirmed experimentally). GPS satellites must correct for both special relativistic (moving clocks run slow) and general relativistic (clocks in lower gravity run slower) effects — without corrections, GPS would drift by 10km/day. The 'arrow of time' — the puzzling asymmetry between past and future — is not built into fundamental physics (Newton's and Einstein's equations work equally well in either time direction), but emerges from thermodynamics: entropy increases over time, giving time its direction. Why did the universe start in a low-entropy state (allowing entropy to increase)? This is one of the deepest unanswered questions in physics. Human time perception is highly subjective: boredom slows time; flow states (complete absorption) accelerate it; pain slows time; mortal danger produces time dilation (memories stored at high resolution, making the interval seem longer in retrospect).