What does Causality really mean?

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Discussion Overview

The discussion revolves around the concept of causality, particularly in the context of the observable universe and how events influence one another across vast distances. Participants explore the implications of causally disconnected regions and the limitations of influence based on the speed of light and the structure of spacetime.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • One participant questions the meaning of "causally disconnected," suggesting that influences from outside the observable universe could still affect events within it.
  • Another participant argues that while events can be observed by multiple observers, no influence can propagate between causally disconnected observers, using an example of two observers separated by the observable universe's radius.
  • A definition of causality is provided, describing it as a genetic connection between states of matter and their changes over time, but this is met with a request for source attribution.
  • Some participants emphasize the importance of considering events rather than just locations, noting that influences from outside a light cone cannot be observed until the light reaches the observer.
  • There is a reiteration that effects cannot propagate fast enough to be seen by observers outside their light cones.
  • Clarifications are made regarding the definitions of events and locations, with a focus on how influences are defined within the context of observable universes.

Areas of Agreement / Disagreement

Participants express differing views on the nature of causality and the implications of being causally disconnected. There is no consensus on whether influences from outside the observable universe can affect events within it.

Contextual Notes

Participants discuss the limitations of observable influences based on the speed of light and the structure of spacetime, but these points remain unresolved and are contingent on definitions of causality and observable universes.

InfiniteMonkey
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In the wikipedia article of the observable universe I have read the following:
"Both popular and professional research articles in cosmology often use the term "universe" to mean "observable universe". This can be justified on the grounds that we can never know anything by direct experimentation about any part of the universe that is causally disconnected from the Earth"

Im confused about the term causally disconnected, I get the main idea but:
When we define the universe as beeing much bigger then the observable universe, then every point in space has his own observable universe which is presumably as big as ours. Isnt then anything inside our observable universe and outside our viewpoint influenced by (for example radiation) from a different observable universe, therefore indirectly we get influenced from the outside of our observable universe too because of cause and effect?
Which of my assumptions is wrong.
 
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InfiniteMonkey said:
therefore indirectly we get influenced from the outside of our observable universe too because of cause and effect?
It does not follow.

You can have an event that lies within the past lightcones (i.e. observable universes) of two causally disconnected observers, and that event will have influenced both observers. But no event at either observer's location could have influenced the other.

E.g. let's imagine two observers A and B, today separated by twice the radius of the observable universe (same for both). A flash of light emitted when the universe was very young from point C, located midway between A and B, can by now be observed by both A and B. But neither observer could have ever sent a flash of light to be observed by the other. Both A and B can say something about the state the point C was in long ago, i.e. about the edges of their respective observable universes. Neither can say anything about the state of the other's location. They couldn't have used the existence of point C to communicate anything to, or otherwise influence, one another.
 
Causality, a genetic connection between individual states of types and forms of matter in the processes of its movement and development. The emergence of any objects and systems and the change in their characteristics (properties) in time have their defining grounds in the previous states of matter. These reasons are called causes, and the changes they cause are called effects (sometimes actions).
 
InfiniteMonkey said:
Isnt then anything inside our observable universe and outside our viewpoint influenced by (for example radiation) from a different observable universe, therefore indirectly we get influenced from the outside of our observable universe too because of cause and effect?
No, because the effects can't propagate to us fast enough to ever be seen.
 
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diezir said:
Causality, a genetic connection between individual states of types and forms of matter in the processes of its movement and development. The emergence of any objects and systems and the change in their characteristics (properties) in time have their defining grounds in the previous states of matter. These reasons are called causes, and the changes they cause are called effects (sometimes actions).
Do you have a link to where you got this text from? It's best to post a link in order to avoid copyright violations. Thanks.
 
Think in terms of events, not just location. An event outside of your light cone may “have already” influenced something within your light cone, but you can’t see any evidence of that until the light from that intermediate point reaches you. By this time, ignoring the expansion of space, the original event will be within your light cone!
 
geshel said:
Think in terms of events, not just location. An event outside of your light cone may “have already” influenced something within your light cone, but you can’t see any evidence of that until the light from that intermediate point reaches you. By this time, ignoring the expansion of space, the original event will be within your light cone!
By definition - where you have A (here), B (there) and C (there there) - if C influenced B which is subsequently observable by A, then C was within A's observable universe when the influence left C to go to B.
 
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hmmm27 said:
By definition - where you have A (here), B (there) and C (there there) - if C influenced B which is subsequently observable by A, then C was within A's observable universe when the influence left C to go to B.
Event C is in event A’s observable universe.

“Location” C is not in “location” A’s observable universe at the ill-defined “when the influence left C”.
 

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