Unit 18: Relativity

What is an inertial frame of reference?

A frame of reference that is not accelerating.

It is said that Einstein, in his teenage years, asked the question, "What would I see in a mirror if I carried it in my hands and ran at the speed of light?" How would you answer that question?

He would see his reflection as normal. Since light moves at the same speed for all observers, it does not matter if he is at rest or moving.

b. How would the observer of the Michelson-Morley experiment determine if an ether existed?

If the beams form a certain interference pattern when they meet then an ether exists.

Explain why Galilean relativity does not work when applied to light emitted from a moving source.

Light moves at the same speed for all observers regardless of the source.

What are the two postulates of special relativity?

Light moves at the same speed for all observers regardless of the source. The laws of physics are the same in all inertial frames of reference.

There are objects in the universe that are moving away from Earth at speeds of nearly half the speed of light called quasars. What is the speed of the light that we receive from these quasars? Explain.

Light moves at the speed of light for all observers.

Explain the apparatus of the Michelson-Morley experiment.

Light moves to the right and strikes the mirror. Some passes through and some is reflected upward. Both beams are then reflected back to the mirror. The upper beam passes through while the beam coming from the right is reflected down.

What were the results of the Michelson-Morley experiment and what conclusion were drawn from these results?

They found that light moved at the same speed regardless of the earth's motion through space. The conclusion was that there was no ether.

Define proper time.

Time measured by the observer who sees events occur at the same point in space