3 ms·

Can someone explain that to me. When the observer is in the train, he sees the right tower future? Or maybe another way of saying it, the left and right tower t

Can someone explain that to me. When the observer is in the train, he sees the right tower future? Or maybe another way of saying it, the left and right tower time are not the same? Or yet another way of saying it would be, two points of an observed moving object are not at the same position AND not at the same time? Two points of a moving object got different delta positions and delta times?

red75prime 9y ago
What you see on the diagrams are pictures taken by the drone swarm which moves alongside the train. In other words the pictures show events happening on a plane of simultaneity. Observer in the train can only see events which happened in their past light cone. So they definitely cannot see right tower's future. ('They' is used as gender neutral version of gender neutral 'he')
- quadcore 9y ago
  Why is the left tower "in the past"? Because it "goes further away" from the train? What is "going further away" determined by? Position delta? So if position delta T->pA > position delta T->pB, time offset T->pA < time offset T->pB?
  - red75prime 9y ago
    It depends on what you mean when you say "left tower is in the past". Space-time intervals are defined for the pairs of events, which are points in space-time. Left tower is not an event. In the bridge plane of simultaneity both towers lighted at -100 units of time. In the train plane of simultaneity left tower lighted at -65, right one did at -150. The values are determined by the Lorentz transformation which includes speed of the observer. So "what's in the past" depends on the positions of the events, the times of the events, and the speed of the observer.
    - quadcore 9y ago
      Wow it's so cool. So I guess the left tower lighted is not an event of the past, it will just appears differently depending on the observation frame. So let me rephrase my initial question. Why is the left tower lighted before right tower is lighted when observed from the train frame? Because the train "goes further away" from the left tower? What is "going further away" determined by? Distance delta? So, is the following correct: let two events A and B occurring respectively at positions pA and PB in the same frame, a mobile at position pM, if delta_distance(pM, pA) > delta_distance(pM, pB), then follow that observed_time(A) < observed_time(B) assuming observed_time(A) == observed_time(B) in pA and pB frame? Please note, it's not delta_position but delta_distance I've written. Also, by delta, I mean difference. (edit: I get that "distance delta" is velocity)
  - deleted 9y ago
    [deleted]
jules 9y ago
From a modern perspective the relation of the time axis to the x axis is roughly the same as the relation between the x axis and the y axis. Saying that two events happened at the same x coordinate (delta x is 0) is a statement that depends on the observer. Another observer who is rotated with respect to the first will see the events at different x coordinate (delta x is not 0), because some of the x axis has been rotated into the y axis. Similarly, saying that two events happened at the same t coordinate (delta t is 0) depends on the observer. Another observer who is moving with respect to the first will see the events at different t coordinate (delta t is not 0), because some of the t axis has been "rotated" into the x axis. This notion of "rotation" only differs from ordinary rotation by a minus sign. If you rotate the xy plane around the origin then points move in a circle x^2 + y^2 = const. If you rotate in the xt plane then points move in a hyperbola x^2 - t^2 = const. Physically you "rotate" in the xt plane by accelerating in the x direction. This causes points to move along that hyperbola, which means that some delta x manifests as delta t and vice versa. We don't see that in ordinary life because we only move with respect to one another at incredibly low speeds, which corresponds to very small "rotations". Imagine a world where all creatures are facing along the x axis with only very small deviations. These creatures may think that the x coordinate has physical meaning independent of the y and z axes. They might think that there is something special about their x axis. Similarly, we are all moving with roughly the same velocity through the universe. We initially thought that there was something special about our velocity, namely, we thought that we were at rest with respect to the aether.
- quadcore 9y ago
  edited 10 thousand times Very good explanation, thanks for your time. Still something that's unclear to me. Let say I'm observing a star moving away from me at speed of light. Will I see the star? If yes, it means that, those photon-things, have a property which I haven't. Some "move at speed of light" type of property. So now, we have two points on a line, the "value" of a photon (speed of light) and my "value" (speed x), do we? What about that? We cant call that speed because we are saying speed is relative. How do you call that property then? And what is the other bound? Cant be x right? Or another solution is that, light depends on the observer. Ok got it. 100% got it. Light both has a speed (speed being always dependent from the observer) and both has a property I havent. The key is that light has a special property I havent, but it isnt about speed. Am I correct?

red75prime 9y ago

What you see on the diagrams are pictures taken by the drone swarm which moves alongside the train. In other words the pictures show events happening on a plane of simultaneity. Observer in the train can only see events which happened in their past light cone. So they definitely cannot see right tower's future. ('They' is used as gender neutral version of gender neutral 'he')

quadcore 9y ago
Why is the left tower "in the past"? Because it "goes further away" from the train? What is "going further away" determined by? Position delta? So if position delta T->pA > position delta T->pB, time offset T->pA < time offset T->pB?
- red75prime 9y ago
  It depends on what you mean when you say "left tower is in the past". Space-time intervals are defined for the pairs of events, which are points in space-time. Left tower is not an event. In the bridge plane of simultaneity both towers lighted at -100 units of time. In the train plane of simultaneity left tower lighted at -65, right one did at -150. The values are determined by the Lorentz transformation which includes speed of the observer. So "what's in the past" depends on the positions of the events, the times of the events, and the speed of the observer.
  - quadcore 9y ago
    Wow it's so cool. So I guess the left tower lighted is not an event of the past, it will just appears differently depending on the observation frame. So let me rephrase my initial question. Why is the left tower lighted before right tower is lighted when observed from the train frame? Because the train "goes further away" from the left tower? What is "going further away" determined by? Distance delta? So, is the following correct: let two events A and B occurring respectively at positions pA and PB in the same frame, a mobile at position pM, if delta_distance(pM, pA) > delta_distance(pM, pB), then follow that observed_time(A) < observed_time(B) assuming observed_time(A) == observed_time(B) in pA and pB frame? Please note, it's not delta_position but delta_distance I've written. Also, by delta, I mean difference. (edit: I get that "distance delta" is velocity)
- deleted 9y ago
  [deleted]

jules 9y ago

From a modern perspective the relation of the time axis to the x axis is roughly the same as the relation between the x axis and the y axis. Saying that two events happened at the same x coordinate (delta x is 0) is a statement that depends on the observer. Another observer who is rotated with respect to the first will see the events at different x coordinate (delta x is not 0), because some of the x axis has been rotated into the y axis. Similarly, saying that two events happened at the same t coordinate (delta t is 0) depends on the observer. Another observer who is moving with respect to the first will see the events at different t coordinate (delta t is not 0), because some of the t axis has been "rotated" into the x axis. This notion of "rotation" only differs from ordinary rotation by a minus sign. If you rotate the xy plane around the origin then points move in a circle x^2 + y^2 = const. If you rotate in the xt plane then points move in a hyperbola x^2 - t^2 = const. Physically you "rotate" in the xt plane by accelerating in the x direction. This causes points to move along that hyperbola, which means that some delta x manifests as delta t and vice versa. We don't see that in ordinary life because we only move with respect to one another at incredibly low speeds, which corresponds to very small "rotations". Imagine a world where all creatures are facing along the x axis with only very small deviations. These creatures may think that the x coordinate has physical meaning independent of the y and z axes. They might think that there is something special about their x axis. Similarly, we are all moving with roughly the same velocity through the universe. We initially thought that there was something special about our velocity, namely, we thought that we were at rest with respect to the aether.

quadcore 9y ago
edited 10 thousand times Very good explanation, thanks for your time. Still something that's unclear to me. Let say I'm observing a star moving away from me at speed of light. Will I see the star? If yes, it means that, those photon-things, have a property which I haven't. Some "move at speed of light" type of property. So now, we have two points on a line, the "value" of a photon (speed of light) and my "value" (speed x), do we? What about that? We cant call that speed because we are saying speed is relative. How do you call that property then? And what is the other bound? Cant be x right? Or another solution is that, light depends on the observer. Ok got it. 100% got it. Light both has a speed (speed being always dependent from the observer) and both has a property I havent. The key is that light has a special property I havent, but it isnt about speed. Am I correct?