Event P is shown by a small x.

1
Event P is shown by a small x. At what time (in
the primed frame) does P occur? A at ct1 B
at ct2 C at ct3 D at ct4
2
Event P is shown by a small x. Where (in the
primed frame) does P occur? A at x2 B at
x2.5 C at x3 D at x3.3 E at x3.6
3
In the unprimed frame, which event occurs first?
Q or P A Q B P C they are simultaneous
4
In the primed frame, which event occurs first? Q
or P A Q B P C they are simultaneous
5
OK, which event really occurs first? A Q B
P C neither
6
The line connecting two events is called a
spacetime interval. If this line is rather flat,
a reference frame moving sufficiently rapidly
will have an x axis that is steeper than the
line, and the events will switch their time
order. If the line is steeper than 45, then no
reference frame can change the time order.
7
A flashbulb goes off in the exact middle of a
spaceship that is traveling very fast. (The
flashbulb is in the spaceship.)Does the light
hit the front and back mirrors at the same time,
according to an observer on the earth?A yesB
no
No. The speed of light is independent of the
speed of the source or the observer, so it will
hit the back mirror first. (The mirror is moving
toward the source, so it reduces the distance the
light must travel.)
8
According to an earthbound observer, a clock on
the spaceship, adjacent to the back mirror,
reads exactly 12 noon when the light hits the
back mirror. At exactly this time (according to
the earthbound observer), what does a clock on
the ship, adjacent to the front mirror read?The
clocks are synchronized and correct according the
spaceman.A a little before 12 noonB exactly
12 noonC a little after 12 noon
9
Clearly, spatially separated events that are
simultaneous in one frame are not in another.

• What other bizarre things might happen? Lengths
  could change, clocks could run fast or slow????
  Who knows???
• What cannot happen
• A pipe cannot contract or expand in the direction
  perpendicular to its motion.

10
Next the light clock