somanystylez

But the point here is that the direction of their velocity relative to those 2 blades isn't the same, so they techincally don't have the same velocity (the direction of the velocity is different).

Hi guys, I was recently analyzing the famous train and tunnel paradox which is based on length contraction. If somebody isn't familiar to it, here's the link: . So in the example there are two guillotines and the most important thing is that all observers agree that none of them hits the train. The first observer is at rest with respect to the tunnel and in his reference frame the guillotines went off simultaneously, but the train got contracted so nothing happened to the train. The second observer is moving towards the first guillotine and away from the second so in his reference frame the first guillotine went off and the second followed, so nothing happened to the train because enough time passed that the front parts came off the tunnel and the rear parts followed. The point that is troubling me here is the situation in which we imagine a third observer that has the same velocity as the one located in the train, but isn't moving towards the first guillotine and away from the second. Let's say he's moving towards both of them (he is outside of the tunnel). What situation will happen in his reference frame? After all if he is moving towards both of them, he should see them simultaneously, but 'before' the ground observer sees them, and the tunnel will still get length contracted. I hope you understand my question, thanks for reading. Regards

How large the mentioned portion of space is, is there some kind of barrier which limits the local notion of simultaneity?

Hi guys, in most relativity articles on the internet, and in books, relative simultaneity is always mentioned in the context of special relativity, and that it depends on the state of motion of the intertial reference frame (or observer). But curiosity has brought me another question, which is related to general relativity, and its take on the relativity of simultaneity. The most known effect on time which is related to GR is gravitational time dilation which is mostly discussed when people talk about GR, but does GR change anything (or add anything) to the definition of relative simultaneity in special relativity. By this, I mean any new criteria or conditions when observers disagree about simultaneity or something like that. I hope somebody could answer me this with a concrete example, similar to the train example by Einstein which describes relative simultaneity of moving observers. I apologize in advance if my language is not very scientific, I'm pretty new to this topic so I hope you don't mind. Thanks for the answers in advance.

What if one observer (the one that is moving with respect to Andromeda) is much closer to it then the one on Earth? Would it make a difference?

Hi, I've been reading recently on the, let's call it famous, Andromeda paradox stated by Riejdtnik/Putnam. So I understand what happens, or why the motion affects plane of simultaneity, but I don't understand why is there such a big time lapse between what's happening on the Andromeda galaxy right now according to the observers. It is clearly stated that because it is distant, the lapse between events is huge (about a day if they are walking slowly). So when we compare it to the train experiment, when the difference is only a few seconds, it seem confusing. What role does the distance of event to the observer play here, and how does it affect the judgement of the temporal order of events?

It does, thank you for your very well formed answer.

My opinion is that everything else than 'yes, from its frame the events are simultanoues' would be illogical, since then we wouldn't be able to define the object which serves as a reference frame itself

I mean parts in the sense of temporal parts which are extended in space and time. So basically I'm refering to stages of the parts of that object. The stages make the object what it is at a particular time.

For instance, take an intertial frame, let's say a cell phone which is at rest with respect to the earth. From its perspective it's parts are simultaneous with one another and simultaneous with the object itself. That's what I mean.

But if an object has parts, surely from its rest frame it must be simultaneous with its parts at some time. Otherwise we couldn't even define the object because without its parts it doesn't exist.

Hi guys, this is my first post here, and I've just recently started studying special relativity. I don't understand some thing so I hope to get an appropiate answer. If we have an object that serves as an inertial reference frame, is this object simultaneous with itself from its own rest frame? And are all of its parts mutually simultaneous when viewed from the rest frame of that object? I hope you can answer me.