|
all rights reserved 2002
|
Simultaneous Events There
is no such thing as simultaneity between two events when viewed in different
frames of reference. If you understand what we have talked about so far, this
concept will be a breeze. First let's clarify what this concept is stating. If
Meagan sees two events happen at the same time for her frame of reference,
Garret, who is moving with respect to Meagan, will not see the events occur at
the same time. Let's use another example. Imagine that Meagan is standing
outside and notices that there are two identical cannons 100 yards apart and
facing each other. All of the sudden, both cannons fire at the same time and the
cannonballs smash into each other at exactly half their distance, 50 yards. This
is no surprise since, the cannons are identical and they fire cannonballs at the
same speed. Now, suppose that Garret was riding his skateboard super fast
towards one of the cannons, and he was directly in the line of fire for both.
Also suppose he was exactly half way between the two cannons when they fired.
What would happen? The cannonball that Garret was moving towards would hit him
first. It had less distance to travel since he was moving towards it. Now,
let's replace the cannons with light bulbs that turn on at the same time in
Meagan's frame of reference. If Garret rides his skateboard in the same fashion
as he did with the cannonballs, when he reaches the halfway mark, he sees the
light bulb he is moving towards turn on first and then he sees the light bulb he
is moving away from turn on last. See the figure below for clarification.
In
the figure, the bulb on the right turns on first. I have shown Garret to be
moving in the same direction of the distance line between the bulbs, and he is
looking towards the moon. As stated earlier, when the bulbs turn on in Meagan's
frame of reference, Garret will see the bulb on the right turn on before the
bulb on the left does. Since he is moving toward the bulb on the right, its
light has a shorter distance to travel to reach him. Garret would argue with
Meagan that the bulbs did not turn on at the same time, but in Meagan's
perspective they did. Hopefully, you can see how different frames of reference
will not allow events to be observed as simultaneous.
|