Special Relativity The Death of Newtonian Physics

Classical Relativity 1,000,000 m/s ■ How fast is Spaceship A approaching Spaceship B? ■ Both Spaceships see the other approaching at 2,000,000 ms -1. ■ This is Classical Relativity.

Einstein’s Special Relativity 1,000,000 m/s 0 m/s 300,000,000 m/s Both spacemen measure the speed of the approaching ray of light. How fast do they measure the speed of light to be?

Special Relativity Stationary man  300,000,000 ms -1 Man travelling at 1,000,000 ms -1  301,000,000 ms -1 ?  Wrong! The Speed of Light is the same for all observers

2 Postulates of Special Relativity 1. “The laws of physics are the same in every inertial frame of reference” -The Principle of Relativity 2. “The speed of light in vacuum is the same in all inertial frames of reference, and is independent of the motion of the source” -Invariance of the speed of light Inertial Reference Frame: Inertial Reference Frame: A system that is not accelerating

Frames of Reference

The Principle of Relativity

Spacetime The 3 spatial dimensions are not independent of time. Relativity links space and time together to make a four dimensional quantity.Relativity links space and time together

Simultaneity of Events Events which are simultaneous in one frame may not be in another—time is not special!another—time is not special! Each observer is correct in their own frame of reference

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Time Dilation Time between ‘ticks’ = distance / speed of light Light in the moving clock covers more distance  …but the speed of light is constant…  …so the clock ticks slower! The faster the speed, the slower the time Observed in caesium clocks flown at high speed V

The Twin Paradox A Tale of Two Twins A classic mental test of Special Relativity involves twins, one who stays on Earth, while the other travels in a spaceship and then returns home. The twin who travels will have aged less than the twin who stays at home.

Concept Check Click for Answer

Length Contraction Observers measure moving objects to be shorter than if they were at rest. Only applies to the direction parallel to the motion.

Objects do not contract; the measurement of the object from another frame of reference contracts, because it is in a different spacetime. The measure of distortion of time when clocks are found to run slowly is also a distortion of spacetime.distortion of spacetime

Concept Check Click for Answer

The Ladder Paradox Another classic mental test of Special Relativity involves a ladder that is longer than the width of a shed. The ladder moves at relativistic speeds and fits in the garage in both reference frames. When the observer is in the shed, the ladder contracts to fit in. When the observer is on the ladder, the back door closes and the opens before the front door closes. Reference: Shed Reference: Ladder

Einstein not only linked space and time, he also linked mass and energy. Mass has “energy of being” (in effect a kind of potential energy) that is called rest energy. This equivalence was derived through special relativityderived through special relativity Energy Mass Equivalence This leads to General Relativity

Doppler Effect The pitch of the siren:  Rises as the ambulance approaches  Falls once the ambulance has passed. The same applies to light!  Approaching objects appear blue (Blue-shift)  Receding objects appear red (Red-shift)

Headlight Effect Beam becomes focused. Same amount of light concentrated in a smaller area Flashlight appears brighter V

What famous landmarks would look like at relativistic speeds Eiffel Tower Stonehenge

The Speed of Light If the speed of light is the same in all reference frames, does that mean that nothing can go faster?  Neutrinos in Switzerland did/might have. Neutrinos in Switzerland  HUGE consequences to this Backwards time travel Infinite mass The death of Relativistic Physics Futurama makes fun of Modern Physics