[acecharly (OP)]

From what ive heard galaxies are "generally" proportioned in relation to there black hole at the center. Has anybody ever theorised that we may be on the inside rather than the outside? Im imagining some reversed donut type shape.

[evan_au]

There is believed to be a supermassive black hole in the centre of our galaxy, known as Sagittarius A*.

The best measurements of its size put it at less than the radius of Earth's orbit. Since it is about 26,000 light-years away from us, we can't be inside this black hole.

However, the Big Bang theory suggests that the universe was in a very compact form about 13 billion years ago. If you work out the Schwarzchild radius of this mass, we could well be inside a universe-sized black hole.

[Mordeth]

However, the Big Bang theory suggests that the universe was in a very compact form about 13 billion years ago. If you work out the Schwarzchild radius of this mass, we could well be inside a universe-sized black hole.

Hi evan_au,

The curvature of the observable universe is currently measured to be flat, or very close to it. It appears that the density is at the so the called critical value.  As a consequence of flatness, not a black hole, the Schwarzchild radius of the universe equals its age multiplied by the speed of light(which is the observable radius in a flat universe).  This is a mathematical identity.  When you calculate the Schwarzchild radius, and assume a flat universe, ie., one whose critical density equals its actual density, the schwarzchild radius will yield an answer equal to the radius of the observable universe.  No black hole here.  I can show my work if you like.

Incidentally, in Friedman-Lemaitre-Robertson-Walker spacetime,  the metric is not the same as the schwarzchild metric.   The Schwarzchild equation for a black hole is not typically used to calculate a solution to a metric of time dependent, matter filled, homogeneous and isotropic conditions.

[Bill S]

Possibly the “Gravastar” (Gravitational Vacuum Star) of Mazur and Chapline is the nearest that we have to a serious theory that comes close to our being inside a black hole.  However, mainstream cosmology seems not to have accorded it much attention.