Assume that you are at the origin of a laboratory frame of reference at time t=0

Question

Assume that you are at the origin of a laboratory frame of reference at time t=0 when you start your clock (event A). Determine whether the following events are within the future lightcone or past lightcone 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=-5.7x1012 s.

f) A supernova explodes 180,000 ly away at time t=5.7x1012 s.

g) A supernova explodes 180,000 ly away at time t=-5.6x1012 s.

h) A supernova explodes 180,000 ly away at time t=5.6x1012 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 explodedbefore event A?

Explanation / Answer

Future light cone is cone opening towards larger time and past cone is towards lesser time.

a) past light cone

b) past light cone

c) past light cone

d) future lightcone

e) past light cone

f) future lightcone

g) past light cone

h) future lightcone

yes in both cases

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