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I am grappling with a big-rip scenario. Anyone knowledgable:

  1. Nov 7, 2008 #1
    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.
  2. jcsd
  3. Nov 7, 2008 #2

    “When the size of the observable universe is smaller than any particular structure, then no interaction between the farthest parts of the structure can occur, neither gravitational nor electromagnetic (nor weak or strong), and they will be ripped apart.”

    Eventually, the galaxies “fly apart”, then the stars, the planets and each of us as well (and all black holes) as gravity is overcome. As the electromagnetic force is overcome then all the molecules will dissociate. When the strong force is overcome, then the atoms and quarks will dissolve too (and any virtual particles). Nothing interacts with anything else in any way represented by the fundamental forces, so there is no force to slow the expansion.
  4. Nov 7, 2008 #3
    Yes, Arch, I understand that... but that seems to contradict something that an astute reader in another forum pointed out: That whenever the density of the universe is higher due to the observable universe becoming smaller, then that density itself should slow down the expansion of the universe, because space is so warped due to the density of matter left in the observable universe.

    Furthermore, there will be some time between when the electromagnetic force is overcome and the strong force is overcome. This should mean that there is a FLOOD of virtual particles that cannot recombine, thus becoming real particles. This by itself should dramatically increase the mass of the universe, perhaps either to a black hole density or at least, a density enough to significantly slow down accelerating expansion.

    This should occur even without the flood of virtual particles, because all of the real particles will take up the same amount of space, but the size of the observable universe itself is MUCH smaller, and thus, much more dense. This density should slow down the universal acceleration, in my mind, bellow the speed of light, allowing the size of the observable universe to begin increasing again.

    This is kind of like rebound/bounce theory.

    My question is this: Does the density of energy/matter in the universe stop the acceleration of the expansion of the universe (or slow it down bellow the speed of light) before the universe can collapse into a singularity, or does the universe first collapse into a singularity?

    Either of these has HUGE implications on our understanding of cosmogenesis.
  5. Nov 7, 2008 #4
    Look, I’m not an expert on this, but I haven’t read this astute reader’s insights on the Big Rip actually published anywhere by anyone. The density of the observable universe right now does not stop expansion and the amount of mass in these smaller event horizons won’t go up faster than the volume it occupies. If all the black holes fly apart, then any new black hole would fly apart too because anti-gravity rules. Right? As I posted, there would be no force to overcome expansion.
    Virtual particles borrow background energy, annihilate and return the background energy. The total mass of the system doesn’t change. So tell your astute reader that there would be no flood of mass and that these particles would still dissociate, along with all other particles. The energy density of the universe will not overcome the anti-gravity of Dark Energy (DE) anywhere, nor would anything else. That’s the theory.

    That said, it sounds like you are blurring the Big Rip, the search for Omega and Quantum Loop Cosmology (QLC). The Big Rip postulates that DE will overcome all forces and rip everything apart. The search for omega, the density of the universe, is an attempt to determine if the universe continues to expand or contracts into a singularity. QLC is a new/untested theory that the universe expands, then contracts and bounces, only to expand again.
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