Key Concepts:

1. What is Relativity?
2. What is Special Relativity?
3. How are time, length, and mass affected at high speed?
4. Can we travel to a star hundreds of light years away?
5. What is the Twins Paradox? and how is it resolved?

Exam 2

Quiz 16A: Monkey Hunter

What is Relativity?

• Measurements of motion, time, and space make sense only when we describe whom or what they are being measured relative to -- there are no absolute answers (e.g., a lumberjack).



• Classical ("Newtonian" or "Galilean") Relativity -- perceived motions are relative to the observer's point of view

A Paradox in Relativity?

TWO things in the universe are absolute:

1. The laws of nature are the same for everyone.
2. The speed of light is the same for everyone. (Michelson-Morley experiment)

Quiz 16B: Say, what???

"Special Relativity" at High Speeds: time, length, and mass are relative measures (and not absolute)!

Time dilation time differs in different reference frame time runs slower in the reference frame of anyone moving relative to you Relativity of Simultaneity: sequence of events are not absolute and dependent on the observer's frame
Length Contraction lengths (or distances) differs in different reference frame lengths of objects in the reference frame of anyone moving relative to you are shorter in their direction of motion
Mass Increase objects moving relative to you have greater mass than they have at rest. the kinetic energy (mass) of an object with velocity approaching the speed of light would approach infinity. Quiz 16C: A Fast Parking Job...

Space Travel: more plausible than you think (in theory)

Quiz 16D: the Twins Paradox

Reading assignment for next lecture: Unit 68