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I dont know if this question belongs on the physics SE or here but I'll take a punt within philosophy.

Observers within the universe all move relative to one another. Take any two Observers A and B such as in the twin paradox, with relativity the Observers are both moving away from one another so A would measure time slower than B and B would measure time slower than A.

This has attempted to be resolved by an non inertial reference frame when one of the observers is acted upon by a force such as the observer leaving the earth that is accelerated for a period of time and then returns to the earth to find his twin has aged more then them.

This time dilation is regarded as a result of special relativity or the time dilation observed by motion. Time dilation occurs also as a result of two Observers in different locations within a gravity well and this is known as general relativity and there is evidence to support this.

My question is this. Would an external observer of the universe be the absolute frame of reference to all the movement that it observes within that universe and thus the absolute measure of the passage of time? Would that observer also not be subject of a location within the gravity well of the universe and the resulting time dilation?

I dont know the phillosopical implications of this if there are any. However, it occurred to me, and I just wanted to express my thoughts and hoped I would get a response however disparaging.

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    I find "external observer of the universe" as illogical. How can something be outside of the universe? Isn't the universe that, that contains everything? Nov 16, 2023 at 14:28
  • @IoannisPaizis Only by definition, does an inside have an outside?
    – 8Mad0Manc8
    Nov 16, 2023 at 14:30
  • not always: see Moebius strip. Nov 16, 2023 at 14:35
  • @IoannisPaizis Does the universe contain itself?
    – 8Mad0Manc8
    Nov 16, 2023 at 14:41
  • Only an outside observer would know!!! In math (set theory) terminology a set which contains all objects, including itself does not exist, strange isn't it? Nov 16, 2023 at 15:58

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I would add to Mikhail's excellent answer that even if you could swallow the idea of what it would mean for an observer to be outside the Universe, they would be outside of spacetime. If they had any notion of time at all it would not be the time we experience, and even if they considered their frame to be 'absolute' it would be entirely irrelevant to us inside the Universe, since, as far as we know, the laws of physics are the same regardless of which inertial frame you pick.

You ought to be careful when you consider two observers to 'measure time slower' than each other. That's not really what time dilation means in SR.

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There is no use of speculating about an observer who is per definition outside of our universe. We know nothing about the external of our universe. We do not even know whether the concept is meaningful.

In former times and from a religious perspective the idea is named the view from "the eye of God". This already shows that one leaves the realm of physics and of science.

Similarly, to Archimedes is ascribed the saying "give me a fixed point and I will move the whole world".

But the hypothetical observer resp. fixed point is external to our world and cannot be incorporated into a physical theory. In particular, he is not appropriate to be used as a point of reference.

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Superficially it seems like an appealing image to envision an outside observer, so to speak observing the universe as we would a fish tank. However, consider the following simplified model. Consider the universe as a (x,y)-plane (you can choose a (1,1) metric on it if you like, by analogy with what goes on in relativity). Now place the observer at the point (0,0,1) outside the plane. It seems as though she might have an "absolute" perspective on what is going on in the plane.

But a moment's thought reveals otherwise: if the motion in the plane is relative to the choice of a frame of reference, then the same applies to the observer, by considering her (x,y)-coordinates. So we don't gain any absoluteness by placing the observer outside the universe, since there is no reason to assume absoluteness anymore than within the universe itself.

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For all we know, to an observer outside the universe, the universe could be a 4, 5, or infinite-dimensional lattice, a crystal. The "reference frame" of the outside observer wouldn't be comparable to the reference from of you or me -- it would be a layer above that.

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Observation is interaction, and a universe is the set of all that can interact. Observer who is not part of the universe is a contradiction.

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