it is thought that the universe is just one of many that started, they all resided in a cosmic soup and due to particular circumstances the dot in the soup that is our universe started to expand in the big bang. the universe has been proved recently to be expanding forever (thats not to say that someone will prove otherwise in the future), with the result that the matter in the universe will spread out creating a less dense universe as time goes on. this will take trillions and trillions of years, and will be after the last black holes evaporate. i have never read anything that contemplated what would happen if two universes collided, but i imagine that this would bring eternity to a stand still in our universe if it did
Cheers
~M


Anyway, "eternity can't have a first second" - this assumes that eternity goes into both directions (past and present).

Current theories of the Universe propose that it started some 15,000 million years ago. At that moment (the moment of the Big Bang) - according to some - the Universe started to exist. This includes not only matter, but also space and time itself! In other words, time itself could have had a beginning.

Of course, there are other theories according to which this is only a part in an even larger structure, which (in several theories) would be outside of what we can grasp with our senses or our instruments.

At one moment, it was thought that the Universe, which is currently expanding, would some day contract, placing a limit to "eternity". However, recent observations found that the expansion of the Universe is actually accelerating, as if there was some sort of "anti-gravity" on a large scale. In this case, there would be no end to time (into the future), although the Universe would get quite empty after a while.