An artist's rendition of a universe containing a black hole (Image: Unattributed).
A black hole is a region of space from which light and matter cannot escape. It is twice as wide as its Schwarzschild radius and contains a singularity of infinite density and zero volume at its center. Here is an article from the National Geographic website that describes just how every black hole may contain another universe.
So, after reading this article, I was interested to know if anyone else was silently questioning their Earthly existence and what they thought about this. I wasn't about to get too excited before Discover Magazine was amusingly there to remind me just how our universe is not a black hole by clearing up the confusion.
"If anything, our universe bears a passing resemblance to a white hole" with a singularity in the past and no singularity in the future (source).
In this article, I learned that a solution to Albert Einstein's equation that describes the universe expanding from the Big Bang can be used to show how the time-reversal of a black hole is actually very similar. The author Sean Carroll is also careful to compare the extent of our observable universe (characterized as the Hubble length) with the Schwarzschild radius of a black hole in order to validate how the universe is spatially flat.