|
|
Simultaneity |
|
What events are simultaneous? How can we observe when two things happen at the same time? Taking our statement that the speed of light is always the same, if a light source is placed in the centre of a room, then the light reaches the opposite ends of the room at the same time. Now let us suppose the room is in constant motion – to an observer within the room, the light would still appear to reach both ends of the room at the same time. However to a person stood outside the room, watching it go past they would see light reaching the back of the room before it reaches the front. The two events are now no longer simultaneous to one of the observers. An event’s position in time is dependent on the reference frame of both the event and the observer. So, seeing as an events simultaneity depends on the reference frame involved, you can attend two events that are happening at the supposed time, provided you can get everybody at the correct speeds compared to each other. Handy if your mother’s birthday and an exciting party are kicking off at the same time for example. Or if you need a hard and fast alibi proving you were somewhere else at the time the crime you committed occurred. Of course, you may have to travel faster than the speed of light to get between said locations to appear to be in both at once, but if you can engineer everyone to be travelling at the correct speed anyhow, would have thought that is no problem. [http://www.phys.unsw.edu.au/einsteinlight/jw/module4_time_dilation.htm#simultaneity] |
