PHYS20040:
From Classical to Modern Physics
From Classical to Modern Physics
Schedule
Quantum theory
- Quantum theory was making its appearance.
- M. Planck, 1900: black-body radiation
- electromagnetic energy is exchanged in quantized form
1905: Einstein’s Annus Mirabilis
- Four major papers:
- Photoelectric effect
- Brownian motion
- SR I: ‘on the electrodynamics of moving bodies’
- SR II: ‘does the inertia of a body depend upon its energy content?’
Inertial Frames of reference
- Definition
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- A frame in which Netwon’s laws hold.
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- If Newton’s laws apply in a frame, they also apply in every reference frame in uniform translational motion with respect to the first.
Galilean transformations
\[ \begin{aligned} & x' = x - vt \\ & y' = y \\ & z' = z \\ \end{aligned} \]
\[ \begin{aligned} & \dot x' = \dot x - vt \\ & \dot y' = \dot y \\ & \dot z' = \dot z \\ \end{aligned} \]
\[F = m \alpha = m \alpha'\]
Michelson-Morley experiment
- Michelson & Morley, 1887 published the most conclusive negative result.
- They setup a very sensitive experiment to measure the impact of the motion of the Earth through the Aether.
Michelson-Morley experiment
- A beam is split in two.
- Split beams travel at different angles compared to the aether.
- Beams interfere with each other.
Michelson-Morley experiment
- From Galilean transformations, we expect variation in speed.
- A fringe pattern would appear, with predicable strength.
- Variations measured are very small, compatible with the Earth being at rest with the Aether.
