1. Special Theory of Relativity Einstein pondered the question, “If I could ride a beam of light, what would I see?” Meaning, if a car moved at the speed of light, would the headlights shine ahead?

2. Speed of Light Speed of light (c) has a value of 300,000km/sec or 186,000miles/sec in a vacuum.

3. Relativity of Motion as we know it “Relativity”

4. Relative to the TRAIN, what is velocity of the man? Relative to the MAN, what is velocity of the woman? Relative to the WOMAN, what is velocity of the man? Relative velocities using Newtonian physics If the MAN starts walking at 4mph to right, how fast is he moving relative to woman? Relative to train? Train is moving at 40mph in relation to the ground

5. In the late 1800’s, scientists tried to apply Newtonian physics principles to the speed of light, where Newton’s Laws were king for 250 years.

6. Relative to the TRAIN, how fast is light beam moving? Relative to the WOMAN, how fast is light beam moving? Relative velocity of LIGHT using Newtonian physics Train is moving at 40mph in relation to the ground

7. However,… No matter how they measured the speed of light

8. Postulates of Special Theory See what thinking can do?...ages you…ignorance is bliss.

9. Relative to the TRAIN, how fast is light beam moving? Relative to the WOMAN, how fast is light beam moving? Revisit relative velocity of LIGHT problem (previous answer = c) (previous answer = v + c) According to EINSTEIN: NEW ANSWER = ?

10. Relative velocity problem How fast does the beam of light move relative to the person on ground? How fast does the beam of light move relative to the rocket ship that is moving at 0.9c relative to the ground? How fast would an observer moving towards light at 0.9c measure light beam to move?

11. SIMULTANEITY Are 2 events that are simultaneous to one observer ALSO simultaneous to another?

13. Einstein figured that if the speed of light is the SAME for 2 observers in different RF’s, then something else must be different for each of them.

14. Imagine 2 parallel mirrors separated by distance h, as shown below. This represents our ‘light’ clock where the time between a tick and a tock for the clock is: What happens if the same clock MOVES past YOU with velocity v. Imagine a pulse of light that bounces back and forth between the mirrors This clock is stationary where the ticks and tocks (events) occur at the same places according to person standing next to clock (proper time, t o )

16. Math for time dilation…just a simple right triangle

17. Gamma or Lorentz factor

18. The weird part… Moving RF does However, moving RF looks at the rest RF and states Time is However, our everyday speeds These effects are only

19. If v = 0.5c If v = 0.87c If v = 0.995c Means that if you move at 50% speed of light Means that if you move at 87% speed of light Means that if you move at 99.5% speed of light

20. Muons Muons at rest have lifespan of Muons are cousins of electrons. They are fast- moving (0.99c) unstable particles created in upper atmosphere & move quickly towards to ground. Using the muon speed and lifetime, muons HOW DO WE EXPLAIN

21. The Lifetime of a Muon v = 0.99c lifetime in muon RF, t o = 2.2x10 -6 s Find lifetime of muon from Earth frame:

22. GPS uses time dilation eqns 24 satellites orbit the earth with clocks that tick at a different rate then those on Earth because of their fast speeds. The satellite clocks need to be in perfect synch with those on Earth to allow it to nail down position to a precise degree. The high speeds of the satellites cause the atomic clocks to tick

23. Clocks and time Does this “time dilation” effect come about only because we used a special “light” clock?

24. Space Ride thought experiment Travel back to clock at high speed. What do you observe with hands of clock? Start moving away from clock at high speed. What do you observe as you watch clock hands? Starting at noon,how long to see 1pm?

25. As a spacecraft moving at 0.92c travels past an observer on Earth, the Earthbound observer and the occupants of the craft each start identical alarm clocks that are set to ring after 6.0 h have passed. According to the Earthling, what does the Earth clock read when the spacecraft clock rings?

26. Benny travels to Vega (5th brightest star in our sky) leaving 35yr old twin sister Jenny behind. Benny travels at 0.990c and Vega is 26.4ly from Earth. a) How long does the trip take according to Jenny? b) How long did the trip take for Benny according to his clock? c) How old is Benny and Jenny when he reaches Vega?

27. Twin Paradox - Who is really younger?

28. LENGTH & SPACE

29. Meterstick How fast does a meterstick need to move past you for you to measure it to be 0.50m?

30. Benny & Jenny, continued Benny travels to Vega (5th brightest star in our sky) leaving 35yr old twin sister behind. Benny travels at 0.990c and Vega is 26.4ly from Earth. How far does Benny measure the trip to be?

31. Space travel made possible, 2 viewpoints

32. Length Contraction only along direction of motion Moving observers see that objects contract along the direction of motion. Note that there is no contraction of lengths that are perpendicular to the direction of motion

33. Revisit Muon experiment Recall that muons should have decayed prior to reaching the Earth’s surface, but they didn’t. Why?

34. SPACE-TIME

35. Accelerators produce radioisotopes for use in medicine/cancer therapy. Some larger hospitals make their own radioisotopes in basement-cyclotrons. Particle accelerators need Einstein’s equations for the correct operation of the machines More applications for Einstein’s relativity equations

36. Barn & the Pole Paradox Consider a pole 20m in length and a barn 10m in length at rest. The barn doors can shut & open simultaneously via a switch. You are sitting inside the barn at rest. A runner moves with the pole at 0.90c towards the barn.

37. Relativistic Mass

38. So, how does light move at the speed of light?

39. An ordinary CRT television set is a simple form of particle acceleratorCRT Mass Really Does Increase with Speed Electrons in a color TV tube (moving at about 1/3 c) are about half a percent heavier than electrons at rest, and this must be allowed for in calculating the magnetic fields used to guide them to the screen.

40. E = mc 2

41. ‘Little Boy’ dropped over Hiroshima (9,000lbs), August 6 th, uranium bomb ‘Fat Man’ dropped over Nagasaki, August 9 th, plutonium bomb