I What does Causality really mean?

[InfiniteMonkey]

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.

 

[Bandersnatch]

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.

 

[diezir]

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).

 

[Drakkith]

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.

 

[berkeman]

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.

 

[geshel]

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!

 

[hmmm27]

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.

 

[geshel]

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”.