4 ms·

> The malleability of space and time mean that two events occurring far apart might even happen in one order when viewed by one observer, and in the opposite or

by choxi 8y ago

> The malleability of space and time mean that two events occurring far apart might even happen in one order when viewed by one observer, and in the opposite order when viewed by another. Why doesn't this break the rules of causality? I found this answer on Quora (https://www.quora.com/Is-chronological-order-of-events-preserved-for-different-observers https://www.quora.com/Is-chronological-order-of-events-prese...) but I don't understand it.

simonh 8y ago
It doesn't break the rules of causality because this can only occur for non-causally connected events. In other words, we only see this for independently occurring events, which both happen before a light signal could have travelled from the location of one event to the other.
- jpindar 8y ago
  However, you can hear (which is a form of observation) it for events that are not independent. If a rifle is fired toward you (hopefully you are safe behind a berm) you hear the bullet impact first, then you hear the shot because the bullet travels faster than sound.
  - simonh 8y ago
    But not faster than light, so in theory you could ‘see’ (optically detect) the gun firing and the sound wave travelling through the air before it reached you. The information about what is happening is theoretically available and could be collected given a well designed experiment. What you’re describing is just an illusion created by our limited aural perception.
whb07 8y ago
It doesn’t break the rules of causality because they arent even related. Let’s say I poke a balloon with a needle, the poking event causes the balloon to pop. The pop will never ever occur without me first poking it, irrespective of any number of viewers across all possible distances. Now for the distortions in time perception, it does matter as to who the viewer is. Everyday you wake up you experience energy that’s being radiated from the Sun that’s roughly 8 minutes away (at the speed of light). And yet, there’s cosmic events which have released energy that have happened millions and millions of years ago which have yet to reach us because we are so far away. So from our perspective the Sunlight from today is an older event than the truly much older supernova explosion that has yet to reach our planet. That which when we finally detect it, it will be a “new” event which again is much older than our Sun.
- whatshisface 8y ago
  The travel time of light is classical, it's not what relativistic time is about. In SR we usually "subtract out" the details of the measurement (light travel time, whatever else) implicitly so that we can make statements about the actual geometry of spacetime itself.
- glitchc 8y ago
  Your example belies the very core of the argument in the article, in that the sequence you just described as causal is in fact an illusion. Certainly from the human perspective, these events in sequence look causal. But our perception of time is finite and our mind is constructing the order of those events. But the human perspective is subject to the limitations of our sense of scale, our faulty sense impressions and our faulty logic in reconstructing those events. At the scale of molecules, the distances between the molecules of air, the rubber of the balloon and the metal of the pin are vast. It is impossible to perceive, looking at a subset of molecules of air within the balloon far from the site of the pinprick, why the molecules of metal interacting with the molecules of rubber have any effect on the molecules of air around them. There is no correlation. Going deeper, at the intra-atom scale, it is difficult to fathom an incontrovertible connection between cause and effect when two atoms interact, as mostly empty space encounters mostly empty space. That their nuclei are close enough to influence each other is determined probabilistically, not deterministically. The odds that any two atoms interact is quite small. The probability improves with their relative number and density in a given volume of space and gives us some measure of reliability that we treat as causality.
  - 21 8y ago
    Atoms are not mostly empty space, because electrons are not little balls spinning around like planets. Electrons are more like continuous clouds surrounding the atom. > The picture of an atom being mostly empty stems from the childhood of atomic structure analysis, where most of the atom's extension was found to be transparent for alpha rays, and the early models explained that by pointlike nuclei and electrons. Similarly the picture of a proton or neutron being essentially empty apart from three quarks embedded in it arises because deep inelastic scattering shows that protons are essentially transparent for very energetic electrons, except when the latter meet an almost pointlike quark. But both pictures are quite limited: We don't think glass doesn't occupy space because it is transparent for light. https://www.mat.univie.ac.at/~neum/physfaq/topics/touch.html https://www.mat.univie.ac.at/~neum/physfaq/topics/touch.html
empath75 8y ago
If there's a causal effect between the two events, then a signal must have time to propogate between them, which is limited by the speed of light and introduces a delay between the two events. Which means that you will always see the cause happen before the effect.

by choxi 8y ago

simonh 8y ago

It doesn't break the rules of causality because this can only occur for non-causally connected events. In other words, we only see this for independently occurring events, which both happen before a light signal could have travelled from the location of one event to the other.

jpindar 8y ago
However, you can hear (which is a form of observation) it for events that are not independent. If a rifle is fired toward you (hopefully you are safe behind a berm) you hear the bullet impact first, then you hear the shot because the bullet travels faster than sound.
- simonh 8y ago
  But not faster than light, so in theory you could ‘see’ (optically detect) the gun firing and the sound wave travelling through the air before it reached you. The information about what is happening is theoretically available and could be collected given a well designed experiment. What you’re describing is just an illusion created by our limited aural perception.

whb07 8y ago

It doesn’t break the rules of causality because they arent even related. Let’s say I poke a balloon with a needle, the poking event causes the balloon to pop. The pop will never ever occur without me first poking it, irrespective of any number of viewers across all possible distances. Now for the distortions in time perception, it does matter as to who the viewer is. Everyday you wake up you experience energy that’s being radiated from the Sun that’s roughly 8 minutes away (at the speed of light). And yet, there’s cosmic events which have released energy that have happened millions and millions of years ago which have yet to reach us because we are so far away. So from our perspective the Sunlight from today is an older event than the truly much older supernova explosion that has yet to reach our planet. That which when we finally detect it, it will be a “new” event which again is much older than our Sun.

whatshisface 8y ago
The travel time of light is classical, it's not what relativistic time is about. In SR we usually "subtract out" the details of the measurement (light travel time, whatever else) implicitly so that we can make statements about the actual geometry of spacetime itself.
glitchc 8y ago
Your example belies the very core of the argument in the article, in that the sequence you just described as causal is in fact an illusion. Certainly from the human perspective, these events in sequence look causal. But our perception of time is finite and our mind is constructing the order of those events. But the human perspective is subject to the limitations of our sense of scale, our faulty sense impressions and our faulty logic in reconstructing those events. At the scale of molecules, the distances between the molecules of air, the rubber of the balloon and the metal of the pin are vast. It is impossible to perceive, looking at a subset of molecules of air within the balloon far from the site of the pinprick, why the molecules of metal interacting with the molecules of rubber have any effect on the molecules of air around them. There is no correlation. Going deeper, at the intra-atom scale, it is difficult to fathom an incontrovertible connection between cause and effect when two atoms interact, as mostly empty space encounters mostly empty space. That their nuclei are close enough to influence each other is determined probabilistically, not deterministically. The odds that any two atoms interact is quite small. The probability improves with their relative number and density in a given volume of space and gives us some measure of reliability that we treat as causality.
- 21 8y ago
  Atoms are not mostly empty space, because electrons are not little balls spinning around like planets. Electrons are more like continuous clouds surrounding the atom. > The picture of an atom being mostly empty stems from the childhood of atomic structure analysis, where most of the atom's extension was found to be transparent for alpha rays, and the early models explained that by pointlike nuclei and electrons. Similarly the picture of a proton or neutron being essentially empty apart from three quarks embedded in it arises because deep inelastic scattering shows that protons are essentially transparent for very energetic electrons, except when the latter meet an almost pointlike quark. But both pictures are quite limited: We don't think glass doesn't occupy space because it is transparent for light. https://www.mat.univie.ac.at/~neum/physfaq/topics/touch.html https://www.mat.univie.ac.at/~neum/physfaq/topics/touch.html

empath75 8y ago

If there's a causal effect between the two events, then a signal must have time to propogate between them, which is limited by the speed of light and introduces a delay between the two events. Which means that you will always see the cause happen before the effect.