Speed of light

• Does Matter Become Energy at the Speed of Light?
  Matter does not turn into energy at light speed: massive objects cannot reach that speed, and their rest mass remains part of their total energy.
• Do Echolocating Bats Experience the Terrell Effect?
  Bats do not experience the relativistic Terrell effect, though sound-travel delays and Doppler shifts can influence their echo perception.
• Do the Laws of Physics Apply to Non-Observers?
  Relativity’s laws do not require a conscious observer: they apply to physical events, while reference frames describe how those events are measured.
• 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.
• At What Speed Is the Universe Expanding?
  The universe has no single expansion speed: its current rate is about 70 km/s per megaparsec, so more distant galaxies recede faster.