martinbn said:
At a physics exam one relativity question involves two events, event A and event B. The question asks if the events are simultaneous. The student answers: A is simultaneous, B is not.
I see two possibilities here: a) the student believes that "simultaneity" is a property of an event (by itself), not a relation between two events, b) the student didn't accept the assumption that the simultaneity relation is symmetric (A can be simultaneous with B, while B is not simultaneous with A).
But what is
ahmadphy's view of this mysterious quality? Gathering from this quote:
ahmadphy said:
No in both frames it is emited from the same point simultaneously it's point event I mean the emission and hence relative to all frames the emission is simultaneous
one could either think that, again, the event has a property of being "simultaneous" on its own, and this property is dependent on a frame of reference, or (which I'm more inclined to consider) that
ahmadphy thinks that simultaneity is a relation of the event with itself in different frames of reference (i.e. the event A in the frame C is simultaneous with this event in the frame C'). I'm inclined to believe so, because I can sort of see this attempt to somehow connect two different frames in the starting post of this thread:
ahmadphy said:
Imagine one person standing on it and one approaching it from left at v and a photon approaching it from the right now relative to the standing person who is touching it the photon arrived and he died but relative to the moving observer since the speed of light is constant and the device is moving to the left the photon didn't arrive yet and hence the standing man is still. Alive .
i.e. we're looking at the events in one frame (the frame of the standing person) at a certain time, and the photon has arrived and killed that person, but when we're switching to a moving person's frame (who's approaching the standing person from the left) then
at that time the photon hasn't arrived
yet, and the person on the platform is still alive. The issue here, of course, we have no idea what is this implicit moment in time, and it seems that TS assumes that two different frames of reference can share a single moment in time and each look at the events in that moment of time from their own point of view, whereas (as we all know) each frame of reference has each own timeline, and what can be loosely considered a moment in time in one frame (a collection of all the events happening with the same time coordinate) is not a moment in time in another frame (all those events are happening at different times in the other frame, so one moment of time in one frame is spread across different moments of time in another frame).
Since there's no common timeline between frames of reference and simultaneity is relative, there's no point in trying to see some kind of contradiction the way TS is trying to see it, using the adverbs like "yet" and "still", in SR we look at the events unfolding throughout the whole duration of the thought experiment. In one frame we see a person (standing on a device) and the emitter (to the right of the person at some distance) at rest, the emitter emits a photon at a certain time towards the person, the photon arrives at the device and kills the person. In another frame we see both the person on the device and the emitter moving towards the left (incidentally, the distance between them is Lorentz-contracted), the emitter, again, emits a photon towards the person with the device, the photon catches up with the person (who is moving slower than the speed of light) and kills him (or her). It's the same set of events, nothing is changed except for some distances and timeframes, which is perfectly allowed. No contradiction in sight.