Assume that you are at the origin of a laboratory reference system at time t=0 when you start your clock (event A). Determine whether the following events are within the future light cone of event A, within the past light cone of event A, or elsewhere.
(a) A flashbulb goes off 7 m away at time t=0.
(b) A flashbulb goes off 7 m away at time t=2 s.
(c) A flashbulb goes off 70 km away at time t=2 s.
(d) A flashbulb goes off 700,000 km away at time t=2 s.
(e) A supernova explodes 180,000 ly away at time t=−5.7×1012 s.
(f) A supernova explodes 180,000 ly away at time t=5.7×1012 s.
(g) A supernova explodes 180,000 ly away at time t=−5.6×1012 s.
(h) A supernova explodes 180,000 ly away at time t=5.6×1012 s.
For items (e) and (g), could an observer in another reference frame moving relative to yours measure that the supernova exploded after event A? For items (f) and (h), could an observer in another frame measure that the supernova exploded before event A?