The Michelson-Morley Experiment :

• Before Michelson and Morley conducted their experiment, it was believed that light travelled through a medium called Aether
• Michelson and Morley designed an experiment to use interference effects of light to calculate the speed of light in aether.
• Similar to the change in speed of sound with respect to the relative movement of its medium, the speed of light on earth was expected to be different with respect to the relative speed of aether and earth.
  

  

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• But the speed of light seemed to remain unaffected by the relative speed of earth and aether.

Galileo was one of the first to propose that the laws of physics should remain same irrespective of the relative speed of observer.

• He proposed that if we conducted experiments below deck in a ship as it was moving on a calm ocean we would observe same results as when the ship was at the dock.
• Evidence from electromagnetic experiments also show that equal currents are induced with charges in a changing magnetic field, as by charges moving into a constant magnetic field. Thus laws of physics are same irrespective of velocity of reference frames.

Extract from Physics Stage 6 Syllabus © 2017 NSW Education Standards Authority (NESA)