The Coming Crisis

1
The Coming Crisis

• Galileo Natural state is constant motion
• If at rest, stay at rest
• If in motion, stay in motion
• Newton Laws of motion
• Vast in scope
• Roemer, and others
• Speed of light well known
• Is light a wave or particle?
• 1800 Youngs double slit experiment evidence
  light is a wave
• 1860s Maxwells work unifying electricity and
  magnetism

2
Combining Waves - Interference
Constructive Interference Waves
constructively combine
Destructive Interference Waves destructively
combine Interference pattern
3
Maxwells Work

• James Clerk Maxwell
• Unifies electricity and magnetism in 1860s
• Crowning proof?
• What do ? and ? physically represent?
• Unification encoded in 4 equations Maxwells
  Equations

4
Physics Bravado Circa 1900
Optimism in idea of a deterministic, mechanistic
universe

• Galilean Relativity Principle
• Laws of Physics are equally true for anyone in
  uniform motion, independent of your frame of
  reference
• No experiment can be developed that will answer
  the question Am I in (uniform) motion?
• All that matters is relative motion
• Newtonian Mechanics
• Obeys relativity principle
• Explains sweeping range of phenomena
• Maxwells Electromagnetism
• Explains electromagnetic phenomena
• Visible light, radio waves, X-rays, microwaves
• Electromagnetic waves travel at speed c

• Light travels at speed c.with respect to what?

5
What is a wave?

• A disturbance (of a medium) that propagates
  through that medium
• Example sound A pressure wave (in air) that
  travels through air
• (Alien In space, no one can hear you scream)
• So, what medium does light, a wave, disturb and
  travel through?

The luminiferous ether
6
Why is this ether idea so important?

• Prediction of Maxwells theory
• Electromagnetic waves travel at the speed of
  light, c, in a frame at rest with respect to the
  ether
• Observers in other frames will measure a
  different speed of light, and thus have
  different laws of electromagnetism
• According to 19th century physics, Maxwells
  equations are only valid in a frame that is at
  rest with respect to the ether
• That is, the thought is that
• Newtons Laws
• Valid in ANY frame of reference in uniform
  motion
• Obey relativity principle
• Maxwells Equations
• Valid ONLY in frame of reference at rest with
  respect to the ether
• Dont obey relativity principle

7
What of this ether?

• What properties must it have?

• Must be a fluid
• Must be very tenuous
• Must be very stiff
• We must be moving slowly through it

A simple question Is the earth moving relative
to this ether?
If yes, how do we detect this ether wind?
8
The Michelson-Morley Experiment

• 1881 Albert Michelson tries to detect difference
  in speed of light in two directions
• Ether hypothesis Speed of light depends upon
  velocity of apparatus relative to the ether
• To his dismay, finds no difference Null
  result
• 1887 Joins with Edward Morley
• Again, no difference although
• apparatus is designed to detect
• 40x (later 400x) expected effect
• Speed of light does not depend upon
• motion of source, or observer
• Web demonstration

9
What of Copernicus?

• Physics paradigms circa 1900 force us to reason
  that there is an ether through which light
  propagates
• Michelson-Morley experiment cannot detect ether,
  although it is more than 40x more sensitive than
  required
• Are we are rest with respect to this ether????
• What of Copernican ideas???
• A crisis is brewing!