Inertial frames

• Why Is Time Dilation Reciprocal in Special Relativity?
  In special relativity, each inertial observer sees the other’s moving clock run slow; differing simultaneity conventions resolve the apparent symmetry.
• Is Einstein’s Second Postulate an Axiom?
  Einstein’s second postulate is an empirical physical principle in the 1905 formulation of special relativity, not a mathematical axiom proven from nothing.
• Would a Car’s Headlights Become Gamma Rays Near Light Speed?
  A headlight remains visible in the car’s rest frame, but a forward observer sees relativistic blueshift; calculate the speed needed for gamma rays.
• Why Does Every Moving Observer Measure the Same Speed of Light?
  A moving observer still measures light in vacuum at c because Lorentz transformations change space and time together, preserving light’s speed.
• Could the Speed of Light Vary While Time Is Absolute?
  Special relativity makes vacuum light speed invariant and time frame-dependent. An absolute-time model is possible.