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I've read everywhere that the universe is expanding, and accelerating the expansion. But it is our single point observations of the universe enough to resolve this result?

What gives us 100% conclusion that the universe is expanding, and not contracting, aren't this equivalent?


Imagine there is massive black hole (orders of magnitude bigger than all the mass measured in the observable universe), which contains all the remaining mass of the big bang that did not manage to escape its own gravity. This black hole is outside our observable cone of spacetime.

Every object in the universe is falling towards it.

  • Object A (close to it) is being attracted a lot
  • We are further away from it, but we still get attraction
  • Object B (far away from it) would be still falling but slowly.

From our point of view, both objects are accelerating away from us, and their acceleration is not constant but increases over time (as we all get closer to the gravity source).

This effect may even be accentuated by the long distances and the time the gravitational waves take to travel.

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  • $\begingroup$ What gives us 100% conclusion that the universe is expanding, and not contracting, aren't this equivalent? Physics is a cautious science with no 100 percent certainty claims, it's more based on very strong evidence leading us to accept a theory, (including the expansion theory ) which may later be replaced by one with stronger evidence. $\endgroup$ – user146020 Feb 25 '17 at 0:20
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You are right that objects arrayed radially with respect to a black hole will move apart from each other. This would mean they would appear red shifted according to any observer looking along this radial direction. However, along the plane perpendicular to that radial direction objects would appear blue shifted. They would be moving towards the observer. If we lived in a black hole universe then galaxies would appear red shifted or blue shifted in an anisotropic fashion. This is not what is actually observed in the universe.

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