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TRANSCRIPT
Einstein and Relativity
The Special Theory of Relativity (1905) underpins much of modern science and technology, from our view of the Big Bang to the harnessing of nuclear power for industry. A short description of the theory and the supporting evidence will be presented, and the impact of relativity on modern science will be described.
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Einstein and 1905
March 1905 - On the nature of light
Cornerstone of Quantum Theory
May 1905 - Brownian Motion
Verification of the existence of molecules
June 1905 - Special Theory of Relativity
Physics of bodies moving at high speed
1915 - General Theory of Relativity
Physics of accelerating bodies
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Special Theory of Relativity
- One of the world’s most successful scientific theories
- Dramatic impact on 20th century science and technology
- Changed our view of time and space
What is Special Relativity ?
“Modification of traditional physics required to describe bodies moving at tremendously high speed”
Special Relativity - bodies in uniform (non-accelerated) relative motion
General Relativity - bodies in non-uniform (accelerated) relative motion
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Galileo and Relativity
Galileo : Object released from a height on the deck of a ship experiences the same drop irrespective of motion of ship
→
Principle of Relativity
“..laws of motion indifferent as to whether a system is at rest or moving at constant velocity”
‘no absolute frame of reference for the laws of motion’
Note : motion of ship cannot be detected inside the ship
In tune with Copernican view of earth
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Relativity and the Ether
Maxwell - electricity and magnetism = EM
speed of EM wave = speed of light c
→
light = EM wave
→
c = speed of light wave relative to ether ?
(wave must travel through medium)
Absolute frame of reference for EM ?
- Experiments undertaken to measure earth’s motion relative to ether
o null result
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Einstein and Relativity
- EM theory in apparent conflict with Galilean relativity
- unsuccessful attempts to detect earth’s motion relative to the ether
- induction of an electric current in a loop of wire by a magnet depends only on the relative motion of magnet and loop
Relativity applies to EM ?
No absolute frame of reference for EM?
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The Special Theory of Relativity
Einstein 1905 : Galileo’s relativity must be replaced by new relativity principle that includes EM
1.“…the laws of all physics are the same for observers in uniform relative motion”
“the phenomena of electrodynamics as well as of mechanics possess no properties corresponding to the idea of absolute rest”
From EM, Einstein added a second postulate
2. “…the velocity of light in empty space has a constant value, independent of the motion of source or observer...”
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Derivation
Postulates could not be predicted by traditional mechanics
→
traditional ideas about time and distance must be revised!
→
New equations for distance and time assuming constancy of speed of light
Lorentz Transformation
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Predictions
No absolute values for distance, mass or time!
1. Length of body will shrink* when travelling at high speed
L = L0
* relative to a stationary observer
2. Mass of body will increase when travelling at high speed
m =
Note c = ULTIMATE SPEED LIMIT
3. Time interval will increase for body travelling at high speed
t =
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Implications
1. Time is relative
- two observers in relative motion could measure elapsed time differently and not agree that two events were simultaneous.
2. Mass is a form of energy
E = mc2
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Experimental Evidence
Mass increase
Mass of high-energy particles (β- rays of radioactivity)
Ultimate Velocity
Speed of high-energy particles
Speed of light emitted by high-energy particles
Time Dilation
Lifetimes of high-energy particles (muon detection at sea level)
Mass-energy
Radioactivity
Nuclear fission, fusion
Particle anti-particle creation
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High-energy particles conform to the speed limit set by the speed of light
Relativistic mass increase with increasing velocity
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