# Was our Universe born inside a Black Hole [duplicate]

Is there any possibility that our Universe was just born inside a Black Hole? If so, then mathematically prove that it happened and if it didn't happen, then please mathematically disprove it.

• This needs more details to be answerable. Perhaps you are refering to the observation that a black hole with a mass the size of the observable universe would have a radius about the same as the observable universe. – James K Oct 10 '20 at 9:17
• – user24157 Oct 10 '20 at 10:37
• No................ – Spin Foam Oct 10 '20 at 13:48
• Mine was, but it's a secret. – uhoh Oct 11 '20 at 1:18
• The math proof is hard and over my skills. But, what I know: the space-like slices of the Universe are flat, while of the Block Hole are curved. The Universe is not static in time, the black hole is. So, on the level of the formulas, these looks really very different, but... a physicist once explained to me that a bijection between them is still possible. So, really we do not know. They look very different on the first spot, but possibly these are not so different. – peterh Oct 15 '20 at 15:44

No. The reason is that black holes have a spacetime geometry that is very different from the universe.

The universe is known to have a nearly flat geometry, with perhaps some positive or negative curvature. Most importantly it is to a high degree isotropic: it looks the same in all directions. It is expanding, with more remote galaxies moving away faster from us than nearby galaxies.

Near a big black hole the geometry is very directional. The radial coordinate behaves very differently from the other two spatial directions: a spherical object even when falling freely is squeezed from the sides and pulled apart radially. When you are inside the event horizon this remains true, although the radial coordinate in some sense becomes like time: it is not possible to move towards larger $$r$$. The spaghettification still applies.

In a very big black hole these effects are milder than in a small one, but they still imply things very different from what we observe: a spatial anisotropy, objects moving towards each other rather than apart, and increasing curvature as we move towards the future.

• Hi, You have answered my question and also I have also accepted it, but no one has given a math proof. Please give a mathematical explanation for that so that it will become clear. – Spin Foam Oct 25 '20 at 9:15
• What level of mathematical proof do you want? Usually when people say "mathematically prove" in questions like this they mean it very informally, but do you really want a formal proof about the difference in metric tensor? – Anders Sandberg Oct 26 '20 at 8:20
• I want an Informal proof for that. – Spin Foam Oct 26 '20 at 9:14