Special Relativity Contents: The End of Physics Michelson Morley Postulates of Special Relativity Simultaneity Time Dilation

The End Of Physics 1900 +/- 5 The End of physics Black Body Radiation -> Quantum mechanics Velocity of light With Respect to ether Maxwell’s Equations… But what does light move through? Ether TOC

Michelson Morley So what does light travel through ? Path parallel to ether should take a bit longer Tried it in January Tried it in June… The Earth is at rest in ether Or the path parallel to the ether shrinks Or, there is no ether So what does light travel through ? TOC

Einstein’s Gedanken If we caught up to an EM wave what would we see:                                 B and E fields with nothing to create them This is impossible Therefore we cannot catch up to light waves… TOC

Postulates of Special Relativity First Postulate: The laws of physics are the same in all inertial frames of reference There is no experiment you can do to ascertain whether you are moving. (i.e. all motion is relative) Second Postulate: The speed of light is the same no matter what speed the source or observer is going (i.e the speed of light is a law of physics) (examples of this with cars/observers)                                 TOC

Simultaneity We can measure speed of light, and time of arrival                                 We can measure speed of light, and time of arrival Observer 2 sees pulses at same time Observer 1 sees the light from B first, then A Simultaneity is relative… TOC

Time Dilation                                 How the clock works What proper time is TOC

Time Dilation Earth observer sees light traveling at speed of light                                 Earth observer sees light traveling at speed of light Time is longer (i.e the clock runs slower) Derive Moving clocks run slower Examples: (time elapsed, velocity, factor of c) TOC

factor You can safely ignore relativistic effects to about .5 c

Whiteboards: Time Dilation 1 | 2 | 3 | 4 TOC

Moe and Joe have clocks that tick every 10. 00 seconds Moe and Joe have clocks that tick every 10.00 seconds. Joe is flying by at .85 c. What time does Moe see Joe’s clock take to tick? W 19 s

Two stopwatches, one sitting still, one moving in a very large circle Two stopwatches, one sitting still, one moving in a very large circle. The clock at rest ticks every .800 s, the moving one ticks every 1.200 s. What speed is the moving watch going? answer W .75 c or 2.24 x 108 m/s

Moe and Joe both have identical watches Moe and Joe both have identical watches. Joe is moving with respect to Moe at .85c. If 15 s elapse on Moe’s clock, how much time has elapsed on Joe’s clock? answer W 7.9 s

Muons have a mean life of 2. 2 x 10-6 s at rest Muons have a mean life of 2.2 x 10-6 s at rest. What speed are they traveling if they they have an average lifetime of 2.6 x 10-6 s? How far would they travel before decaying on the average? answer W .53c, 1.6 x 108 m/s, 415 m

Paradoxes Planet X Joe stays on earth                                 Planet X Joe stays on earth Moe goes to planet x that is 30 Ly away at .99 c Comes back How old Moe is/Joe is Does this violate Special relativity? Inertial means no acceleration What they see TOC

Paradoxes Planet X Planet X It’s all relative                                 Planet X Planet X It’s all relative Moe sees our clocks slow down too Postulates only apply to inertial frames of reference TOC