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?
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2 Answers
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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.
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$\begingroup$ 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. $\endgroup$– JoeCommented Jul 16, 2020 at 22:33
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$\begingroup$ @Joe, a "relative" event horizon (as in special relativity) would be a Rhindler Horizon. $\endgroup$ Commented Jul 22, 2020 at 0:49
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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.
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$\begingroup$ It is not so,, the Andromeda galaxy we see is younger, because it is in the past $\endgroup$– SK DashCommented Jul 17, 2020 at 0:50
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$\begingroup$ You're not disagreeing with me. $\endgroup$ Commented Jul 17, 2020 at 8:08
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$\begingroup$ 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. $\endgroup$– SK DashCommented Jul 17, 2020 at 10:42
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$\begingroup$ 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. $\endgroup$ Commented Jul 17, 2020 at 19:16
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$\begingroup$ 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 $\endgroup$– SK DashCommented Jul 18, 2020 at 0:55