Electromagnetic radiation

• If Atoms Are Mostly Empty Space, Why Doesn’t Light Pass Through Everything?
  Atoms are not hard little obstacles, but their electrons interact with light. A material’s structure and energy levels determine whether it transmits, absorbs.
• How Do Mirrors Work?
  Mirrors reflect light because charges in their surfaces respond to incoming electromagnetic waves and emit fields that form a reflected wave.
• Can a Monochromatic Pulse Exist?
  A strictly monochromatic wave cannot be a finite pulse: localization in time requires a range of frequencies, though that range can be very narrow.
• How Are Electromagnetic Radiation and Blackbody Radiation Related?
  Blackbody radiation is the electromagnetic spectrum emitted by an ideal absorber; temperature sets its shape, while Planck’s law and Wien’s law quantify it.
• Are Electromagnetic Waves the Only Way to Transmit Information?
  No. Sound, mechanical motion, particles, and other physical signals can carry information; relativity limits causal signaling to at most light speed in vacuum.