Chapter 32 Special Theory of Relativity
Chapter 32 Special Theory of Relativity
Classical physics Theory of relativity Quantum theory Albert einstein (1879-1955) Modern physics Special theory of relativity: inertial frames Relationship between space, time motion
Albert Einstein （1879 - 1955） Theory of relativity Quantum theory Classical physics Modern physics Special theory of relativity: inertial frames Relationship between space, time & motion
Galilean-Newtonian relativity Relativity principle The basic laws of machanics are the same in all inertia reference frames or: All inertial reference frames are equivalent for the description of mechanical phenomena No one inertial frame is special in any sense There is no experiment to tell which frame is really"at rest and which is moving
Galilean-Newtonian relativity 3 Relativity principle: The basic laws of machanics are the same in all inertia reference frames. or: All inertial reference frames are equivalent for the description of mechanical phenomena. No one inertial frame is special in any sense. There is no experiment to tell which frame is “really” at rest and which is moving
M-equations speed of light Maxwell: light >electromagnetic wave Speed of light from M-equations: c=3.00X 108m/s In what reference frame is this valid? Speed relative to the medium ether But it does not satisfy the relativity principle Reference frame of ether is a special frame!
M-equations & speed of light 4 Maxwell: light → electromagnetic wave Speed of light from M-equations: c=3.00×108m/s In what reference frame is this valid? Speed relative to the medium —— “ether” But it does not satisfy the relativity principle Reference frame of ether is a special frame!
Michelson-Morley experiment Speed of earth relative to ether c-v C+y 2 C-1 M ∧t, Rotating No significant fringe shift
*Michelson-Morley experiment 5 1 l l t c v c v = + − + 2 2 2 2l t c v = − No significant fringe shift! v C < < < M M’ S Speed of earth relative to ether? t, Rotating
Einsteins two postulates First postulate(the relativity principle) The laws of physics have the same form in all inertial reference frames Second postulate(constancy of the speed of light) Light propagates through empty space with a definite speed c independent of the speed of the source or observer Give up commonsense notions of space and time
Einstein’s two postulates 6 First postulate (the relativity principle): The laws of physics have the same form in all inertial reference frames. Second postulate (constancy of the speed of light): Light propagates through empty space with a definite speed c independent of the speed of the source or observer. Give up commonsense notions of space and time!
Simultaneity Time is no longer an absolute quantity! Simultaneity of events depends on the observer Same time at same place /timing by light A BB (a)Observer o(b)Observer O
Simultaneity 7 Time is no longer an absolute quantity! Simultaneity of events depends on the observer A1 B1 O1 . A2 O2 B2 . v (a) Observer O1 (b) Observer O2 Same time at same place / timing by light
Time dilation(1) Mirror Mirror MOTION D Event 1 Event 2 Event I Event n B (b)Observer C on Earth 2D (a Observer B on spaceship
Time dilation (1) 8 (a) Observer B on spaceship (b) Observer C on Earth 0 2D t c =
Time dilation(2) Mirror Mirror MOTION D Event I Event 2 Event I Event 2 B B 2D 2L2v△t △t C C 2/×/c1)2 △t= >△ 1/C
Time dilation (2) 9 0 2 , D t c = 2L t c = 2 2 0 2 2 2 v t c t c = + 0 0 2 2 1 / t t t v c = −
Time dilation(3) △t △t v/C Clocks moving relative to an observer are measured by that observer to run more slowly(as compared to clocks at rest) 1)Proper time(events occur at same point 2)Relativity factor y=1//C2 3)Relativistic effect universalit 4)Space travel twin paradox 10
Time dilation (3) 10 Clocks moving relative to an observer are measured by that observer to run more slowly (as compared to clocks at rest). 0 0 0 2 2 2 1 / 1 t t t t v c = = = − − 2) Relativity factor 3) Relativistic effect & universality 4) Space travel & Twin paradox 1) Proper time (events occur at same point) 2 2 = − 1/ 1 / v c
