8- The relativity of simultaneity

What do we at O observe about the two light flashes (E1 and E2)?

We observe them as occurring simultaneously because we are at rest in the reference frame where the two trains have equal length.

What does observer B, standing at the midpoint of train AC, conclude?

B sees E1 before E2 and concludes that train PR is shorter than train AC.

What does observer Q, standing at the midpoint of train PR, conclude?

Q sees E2 before E1 and concludes that train PR is longer than train AC.

Why do B and Q disagree on the simultaneity of E1 and E2?

Because each assumes they are at rest and that light travels at the same speed in all directions in their respective reference frames.

What does the thought experiment conclude about simultaneity?

Simultaneity is relative—events that are simultaneous in one frame may not be in another moving frame.

What fundamental concept of Special Relativity does this experiment illustrate?

That length and simultaneity are not absolute but depend on the observer’s frame of reference.