Event Horizon At the Edge of the Universe

Abstract: In Found Mass Missing it was surmised that there was an event horizon around the Universe.
Theorem: There is an event horizon at the edge of the universe.
Problem: Demonstrate that the Universe in its various states of expansion either had or did not have an event horizon. An event horizon is defined as the line which a particle or photon crosses at the edge of a sufficiently dense body such as a black hole after which the gravitational attraction is sufficiently strong that the particle regardless of its energy is ever unable to escape again. This effect does not preclude the quantum mechanical states of being in other places simultaneously or spontaneously and thereby diffusing out of a black hole.
When the Universe was a singularity, it was of sufficient density to possess an event horizon. All matter that crossed this frontier was unable due to gravitation attraction to leave.
As the Universe expanded it had an event horizon as long as its density was greater than that of a black hole- the definition of black hole being a sufficiently dense body from which nothing can escape- i.e. with an event horizon.
When the expansion of the early Universe caused the density to fall below that of the definition of a black hole, what happened to the event horizon?
(A note is in order here. Two possibilities. The notion of an event horizon may have been moot since there were no events beyond the "Big Bang". Or once again there was that last in-rushing bit of late matter from the "Big Crunch" that got to cross the event horizon.)
So what happened to the event horizon? Did it shut off like a light bulb or did it slowly spread and diffuse before vanishing?