I have been grappling with a big rip scenario that I've read on a forum and then expanded on in my own mind. In my opinion, the big rip seems to be the likeliest end to the universe. Universal expansion is happening at an accelerating rate, and it seems inevitable that this expansion WILL be able to overcome all of the other forces, with time. As the universe is expanding at a faster rate, more and more galaxies will disappear beyond our event horizon. As the intensity of expansion overtakes gravity, things will start to fly apart. All that will be left are non-gravitated particles. Likewise, as the universe expands at an accelerating pace, the event horizon to our observation point shrinks dramatically. Someone talked to me about this the other day, and I was wondering if there were any major flaws with this theory... As the universal expansion continues to accelerate, there should be a time where the event horizon is quite small compared to the mass contained within this event horizon. The ratio of mass to space will increase because of this. The "density" of the universe should, theoretically, increase approaching infinity, because the event horizon of the universe is so small compared to the mass contained within it. Whenever the density of the universe goes up, doesn't this theoretically slow expansion down? Alright... so expansion is slowed down. My question is this: Does the expansion slow down to the point that the event horizon of the universe can return to expanding faster than space itself is expanding? OR does the universe collapse into itself because the density is too high? What I'm asking is this... what happens first: Does the universe reach critical density to form a black hole before the density in the universe is enough to slow down the accelerating expansion of space to the point that it is NOT expanding faster than light? Or does the universe slow down the accelerating expansion of space to sub-luminal speeds before it reaches the critical density to form a black hole? Another question regarding this: What happens to virtual particles when the accelerating expansion of the universe overtakes their ability to recombine? Won't the local area be flooded with real particles, because they cannot recombine? Thanks for the help. These are things I've been thinking HEAVILY about lately.