Relativity of Simultaneity
- One of Einstein's postulates, as
stated by Kenneth Krane, is that, "The speed of
light in free space has the same value c in all
inertial reference frames" (p. 31). In other
words, the speed of light is the same for all
observers!
- This means that both observers
in the image above would measure the speed of
the light coming toward them to be the same
value.
- The two events, A and B, are a
lightning bolt hitting tree "A" and a different
lightning bolt hitting tree "B." Events A and B
are in the same reference frame.
- The observer on the train is in
a different reference frame than events A and B.
This person observes event B happening first
because they are traveling towards B (and away
from A) at a relativistic speed. Therefore, the
light from B reaches them first.
- Standing in the same reference
frame as and equidistant from trees A and B, the
observer on the ground sees events A and B occur
at the same time.
- Concerning a similar situation,
Einstein explained it this way:
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