1 Light’s Arrival Starship Enterprise is headed straight for the star Betelgeuse at a speed of 0.6 c. When the Enterprise is 2 light-years (in the Enterprise frame) from Betelgeuse, Betelgeuse goes supernova. The Enterprise continues toward Betelgeuse, not knowing yet that it has gone supernova. They only realize that it has gone supernova when the light reaches them. How long does the light from the supernova take to reach them, in their frame? a)2 yr b)More than 2 yr c)Less than 2 yr

2 Just How Proper is it? You are on Earth, an astronaut goes by at high speed. Who measures the proper time between your heartbeats? Who measures the proper time between the astronaut’s heartbeats? a)You, you b)You, the astronaut c)The astronaut, you d)The astronaut, the astronaut

PAL Nikos travels to a planet 12 light-years away at a speed of 0.6 c. Juan stays on Earth. 1) Apply d = vt in Juan’s (Earth’s) frame to find time as measured by Juan. (Think about what consistent set of units you want to use.) 20 yr 2) Who measures the proper time? Use definition to justify. Nikos 3) Apply time dilation equation to find the time as measured by Nikos. 16 yr

4 Simultaneity If two events are simultaneous in your reference frame, then they are simultaneous to all observers. True or false?