Questions for Chapter S2

1. What is the theory of relativity?  How does special relativity differ from general relativity?
2. List five major predictions of the special theory of relativity.
3. According to the theory of relativity, what are the two absolutes in the universe?
4. What do we mean by a frame of reference. What is a free-float frame?
5. Suppose you see a friend moving by you at some constant speed. Explain why your friend can equally well say that she is stationary and you are moving by her.
6. What is time dilation? Explain how and why your measurements of time will differ from those of someone moving by you.
7. Explain why observers in different reference frames will not necessarily agree about the order of two events that occur in different places.
8. What is length contraction? How will your measurements of the size of a spaceship differ if the spaceship is moving by you compared to when it is at rest in your reference frame?
9. What is mass increase? How does the mass of an object moving by you compare to its rest mass?

10.  Briefly describe several experimental tests that support special relativity.

11.  If you watch a friend moving by you, you'll say that her time is running slowly, her length is contracted, and her mass is greater than her rest mass. How will she perceive her own time, length, and mass? Why! How will she perceive your time, length, and mass?

12.  Suppose you could take a trip to a distant star at a speed very close to the speed of light. How does relativity make it possible for you to make this trip in a reasonably short time? What will you find when you return home?

1. How does a photon "see the universe" [time, size]? What can travel at the speed of light?
2. How did the development of relativity theory represent a paradigm shift? Did it mean throwing out old ideas, or only modifying them? Defend your opinion.

Decide whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false). Explain clearly; not all of these have definitive answers, so your explanation is more important than your chosen answer.

1. Einstein proved that everything is relative.
2. An object moving by you at very high speed will appear to have a higher density than it has at rest. (Hint: Think about the effects on both length and mass.)
3. Suppose you and a friend are standing at opposite sides of a room, and you each pop a peanut into your mouth at precisely the same instant. According to the theory of relativity, it is possible for a person moving past you at high speed to observe that you ate your peanut before your friend ate hers.
4. Suppose you and a friend are standing at opposite sides of a room, and you each pop a peanut into your mouth at precisely the same instant. According to the theory of relativity, it is possible for a person moving past you at high speed to observe that you ate cashews rather than peanuts.
5. Relativity is "only a theory" and we really have no way to know whether any of its predictions would really occur at speeds close to the speed of light.
6. If you could travel away from Earth at a speed close to the speed of light, you would find yourself feeling uncomfortably heavy because of your increased mass.
7. We do not have rockets that can reach the speed of light today, but someday we will be able to build more powerful rockets that will allow us to travel much faster than the speed of light.
8. If you see someone's time running slowly in a different reference frame, that person must see your time running fast.
9. If you had a sufficiently fast spaceship, you could leave today, make a round trip to a star 500 light-years away, and return home to Earth in the year 2050.