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Interstellar Medium. Aristotle reasoned that if water carries water waves, something between the Sun and Earth’s atmosphere must be carrying the sunlight waves He called the medium the ether Root word for ethereal (heavenly) Everyone believed him for ~ 2000 years. Michaelson.

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Aristotle reasoned that if water carries water waves, something between the Sun and Earth’s atmosphere must be carrying the sunlight waves
  • He called the medium the ether
    • Root word for ethereal (heavenly)
  • Everyone believed him for ~ 2000 years
  • The Michaelson-Morely experiments began in 1887
  • Professor Michaelson also believed Aristotle and did experiments to put numbers on the ether such as viscosity, density, specific gravity, etc.
  • An analogy of the Michaelson-Morely experiments:Take a tank of some fluid and observe the action of some stuff in that fluid. Tell me what the fluid is and define its nature. I feel that this is a realistic view of the Michaelson-Morely experiments.
  • Michaelson used an instrument called an interferometer
  • The instrument splits a beam of light into two beams
  • Staring with one beam ensures that the 2 split beams are in phase
Interferometers have a number of optical applications. They are used to study and measure interference phenomenon. Hence the name Inerfero-meter. The Michaelson interferometer has been replaced by the Fabrey-Perot interferometer in most optics applications.
constructive and destructive interference
Constructive and Destructive Interference
  • Light that travels through a medium would be slower than light that travels through a vacuum
  • One of the split beams would travel through a vacuum while the other would travel through the ether
each split beam hits a mirror and returns
Each split beam hits a mirror and returns
  • Both of the split beams hit a mirror and return to the source
  • Each beam travels the same distance
constructive interference
Constructive Interference
  • If the beams return to the source at the same time, constructive interference occurs and a bright spot results
  • This would be the case if there were no ether and both split beams traveled through a vacuum
destructive interference
Destructive Interference
  • If the beams return to the source at different times, constructive interference occurs and a dark spot results
  • This would be the case if one beam traveled through the ether which would slow down the light beam ever so slightly
he saw a bright spot
He saw a bright spot!
  • This meant that each beam had the same speed of light
  • What did he conclude?
got funding for a better instrument
Got funding for a better instrument
  • He repeated the experiment over and over again with bigger and better interferometers
  • What did he conclude?
He died believing that he was a failure
  • Is it so bad to have an experiment fail?
  • Lessons are learned from failed experiments
  • What 2 lessons resulted from Michaelson’s experiments?
Speed of light is constant regardless of the observer – Einstein’s Special Relativity Theory
  • Existence of the ether is doubtful
The supposed failure of the Michaelson-Morely experiments presupposes that some outcome would be defined as a success. The failure is not in the outcome but in the assumptions and the interpretation.
modern theory shows that the speed of light is not constant, nor is wavelength, but that frequency remains constant in a given inertial reference frame (see optics)
In light of modern theory, what we call light should be separated into two or three distinct phenomenon.
The energy that exists surrounding a given body of mass (see field theory and black body radiation), the photons that result from interaction with other energy fields from other bodies with mass (reflection, refraction, interference, et al), and the perception of EM radiation by sensory organs.
When discussing fields, their existence is measurable only when they interact with matter. We are material and perceive by material interaction.
Electromagnetic radiation must be assigned an apparent mass at its moment of interaction. Fields are generally considered to be infinite, i.e. constant times some quantities divided by distance, usually squared. Constant fields are very local things.
The energy density of space has been theorized to be a result of Hydrogen that remains uncaptured by large gravitational fields.
If quantum theory is to be believed, one point must be accepted. The material universe is finite. If a minimum quantity truly exists and all space is built of this building block, or system of building blocks, then a finite system is all that can be created.