Hacker News Reader

Comment by yaks_hairbrush | Hacker News Reader

There a germ of the right idea here, but our universe is really more of a black hole backwards. Within the event horizon of a black hole, the singularity is always in the future. Within our universe, we see a singularity in our past.

In short, our universe looks more like a white hole than a black hole.

View on HN

Couldn’t we just be perceiving time backward? I’m no physicist, but AIUI the equations work either way. As a sci-fi–head, sometimes I just like to speculate—“What if the ‘point’ of the universe is the singularity of the big bang?” (Yeah, pun intended.)

If we’re in a simulation, maybe it’s the final result of the computation. If we’re in a black hole, maybe it’s in the past of the universe within, but in the future of the one without. All good material for a short story, one of these days…

Black hole does not imply singularity.

Why not? You can’t have a black hole without a singularity. A black hole is formed only when >3 solar masses collapse in a singularity. Maybe the opposite is theoretically possible, the so called naked singularity in which a singularity is not hidden by an event horizon.

A black hole is a region that light cannot gravitationally escape. It has nothing to do with singularities which often but not always exist inside of a black hole. Small black holes often have singularities just to have enough mass density to capture light. It is not required though — imagine a binary system of two neutron stars that are each just below the mass threshold to collapse into a singularity. It would be a black hole to external observers. Oddly larger black holes require less mass density. More oddly still as you approach the size of the observable universe, the required mass density crosses the cosmic mass density, meaning light emitted from Earth cannot gravitationally escape the universe created by the Big Bang, meaning we exist inside of a black hole as big as the observable universe.

I’m not sure why I’m being so heavily down voted for stating this fact you can find in any cosmology textbook.

> More oddly still as you approach the size of the observable universe, the required mass density crosses the cosmic mass density, meaning light emitted from Earth cannot gravitationally escape the universe created by the Big Bang

This is true...

> meaning we exist inside of a black hole as big as the observable universe.

This is an unwarranted jump. I'd recommend looking at the reference [0] from Sean Carroll.

[0] http://www.preposterousuniverse.com/blog/2010/04/28/the-univ...

There is nothing to be learned in that article. He says that the question is nonsense because we don’t know what is outside the observable universe. That’s not a very interesting thought restriction.

Reply on news.ycombinator.com