Interferometer A coherent light source can be split and
recombined. Phase shifts for different paths A Michelson
interferometer observes the spacing between fringes. Time-of-flight
differences mirror 2 mirror 1 semi- silvered mirror
Slide 3
Michelson-Morley In 1887 Michelson and Morley used the
interferometer to try to measure the relative velocity of the
ether. One path into and against etherOne path into and against
ether One path across etherOne path across ether The time
difference depends on the velocity of the ether.
Slide 4
No Ether The earth changes velocity direction as it orbits the
sun. Changing v relative to the etherChanging v relative to the
ether Measure fringes in different orientationsMeasure fringes in
different orientations Measure in different seasonsMeasure in
different seasons The experiment saw no shift in fringes. Theories
to preserve ether failedTheories to preserve ether failed
Slide 5
Relativity Principle FitzGerald (1887) and Lorentz (1892)
developed transformations consistent with electromagnetism.
FitzGerald-Lorentz contractionFitzGerald-Lorentz contraction
Explains Michelson-MorleyExplains Michelson-Morley Poincare (1898)
proposed that the speed of light must be the same for all
observers. Unprovable postulateUnprovable postulate Still accepted
etherStill accepted ether
Slide 6
Einsteins Theory In 1905 Einstein independently derived
Lorentzs equations from two principles. No need for ether I. The
laws of physics are the same in all inertial frames. II. The speed
of light in a vacuum is the same for all inertial frames, from all
sources.
Slide 7
Simultaneity Einsteins special theory of relativity required
that neither distance nor time was absolute. Only the speed of
lightOnly the speed of light Simultaneity is relative to the
observer. Simultaneous pulses for ASimultaneous pulses for A
Slide 8
Relative Time Another moving observer sees events as separate
in time. Time is relative Like coordinates and velocity Neither
observer is wrong. Each correct in their frame next