As Einstein pointed out, simultaneity is relative to the reference frame one is observing from. His classic train example describes two concurrent flashes of light viewed as simultaneous to a stationary observer half way between the two sources yet not viewed as simultaneous to an observer moving towards one flash and away from the flash behind also situated at the midway point. If a buzzer was to go off when two events were simultaneous but not if not simultaneous, does this mean that the buzzer would go off in one time frame and not another (we are talking about the same two distinct yet concurrent events.) This was brought up somewhere in the past by JesseM. If one can observe two distinct events and make them simultaneous by adjusting the frame of reference, will the buzzer go off because we can find one frame of reference in which there is simultaneity? Can any two non-concurrent events be made concurrent or simultaneous by adjusting the frame of reference? (We are restricted to keeping within the light cone and staying below the speed of light.) Of course, if two events are too far apart that that the speed required to get from the first to the second is greater than the speed of light, they can never be simultaneous, but short of that, can any two non simultaneous events if within striking distance of the speed of light or less be made to appear simultaneous?