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I feel like this is a silly question but I am having trouble wrapping my head around it. Lets use Andromeda as an example, since it has its own observable universe (slightly shifted from ours but with the same radius) does that mean that it would have that sliver of space and energy/mass within it acting on it but not us? and then we also have a sliver of space acting on us but not it?

Joe
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Yes they can be influenced by objects outside our Hubble Sphere. The point we need to note is that objects can be influenced by other objects inside their Hubble Sphere, and we are just a part of their Hubble Sphere.

However the edge of the Hubble Sphere isn't exactly an event horizon. An event horizon is the place from where nothing can escape. We could view the observable universe as a 3d map, if we were to scan it and see, moving in any direction would be like visiting the distant past.

An event horizon is the point of no escape, but the edge of the observable universe is the point beyond which light hasn't had enough time to reach us.

SK Dash
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  • Is the edge of a Hubble sphere analogous to a relative event horizon? This is the part that gets me and I think the answer of the "relative" piece of it. – Joe Jul 16 '20 at 22:33
  • @Joe, a "relative" event horizon (as in special relativity) would be a Rhindler Horizon. – Hierarchist Jul 22 '20 at 00:49
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No. The Andromeda Galaxy we observe is younger than us and has a Hubble Sphere smaller than ours. Any causal influence on it would be observable to us.

Hierarchist
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  • It is not so,, the Andromeda galaxy we see is younger, because it is in the past – SK Dash Jul 17 '20 at 00:50
  • You're not disagreeing with me. – Hierarchist Jul 17 '20 at 08:08
  • here's what I want to say, I am considering the Hubble Sphere to be just a spatial boundary, and I assume the Andromeda galaxy's Hubble Sphere looks at us in the same way, so even it's Hubble Sphere would be 98 Billion Light Years in diameter, which means they have access to places that we do not. – SK Dash Jul 17 '20 at 10:42
  • Then you need to explain how a younger Andromeda can have a Hubble Sphere the same size as ours. Since, the Hubble Sphere grows with age. – Hierarchist Jul 17 '20 at 19:16
  • we observe the Andromeda galaxy to be younger, but at this moment it isn't younger than what it actually is, according to someone in the Andromeda galaxy, we are younger than what we actually are, so the Andromeda galaxy's Hubble Sphere would be of the same size as ours – SK Dash Jul 18 '20 at 00:55
  • We are causally disconnected from that conception of Andromeda. – Hierarchist Jul 18 '20 at 01:19
  • I understand that we are seeing Andromeda of the past, but Andromeda doesn't see itself in the past, so someone in Andromeda galaxy can actually see something which we can not – SK Dash Jul 18 '20 at 01:26
  • You can never observe that. Even when Andromeda and us meet, there will never be a historical record in either of the two galaxies that the other galaxy does not agree with. Every historical record will be independently verifiable, and the age of that historical record will match. Remember that for Andromeda to meet us, it will need to travel 200 million years into the future to do so. – Hierarchist Jul 18 '20 at 09:03