The ultimate fate of an expanding universe
Top: Diagrams of three possible geometries of the universe: closed, open and flat from top to bottom, corresponding to a density parameter Ω0 which is greater than, less than or equal to 1. The closed universe is of finite size and, due to its curvature, traveling far enough in one direction will lead back to one’s starting point. The open and flat universes are infinite and traveling in a constant direction will never lead to the same point.
Bottom: The age and ultimate fate of the universe can be determined by measuring the Hubble constant today and extrapolating with the observed value of the deceleration parameter, uniquely characterized by values of density parameters (ΩM for matter and ΩΛ for dark energy). A “closed universe” with ΩM > 1 and ΩΛ = 0 comes to an end in a Big Crunch and is considerably younger than its Hubble age. An “open universe” with ΩM ≤ 1 and ΩΛ = 0 expands forever and has an age that is closer to its Hubble age. For the accelerating universe with nonzero ΩΛ that we inhabit, the age of the universe is coincidentally very close to the Hubble age.
HAHH!!!! FRIEDMANN’S EQUATION! This right here is why I love physics, we define things with a definite system like math and then we generalize! Rounding means nothing to physics, to tell you the truth, working out the equation we get 0.3, but it’s really “hand wavy” so we just say it’s close enough to 1 and call it a day. It’s beautiful really! But on top of that, Dark Energy!!! Put it all together and you get something called quintessence, not only is the flat (because fuck you Christopher Columbus) but it is expanding and accelerating! Not what you’d expect, right? Wouldn’t gravity fuck shit up and bring it all back to a point to force a new big bang? Well dark energy doesn’t like that Idea, so it does it’s own thing and so we expand! Now it’s not your normal expansion, like radial motion from the origin of the big bang, but we find that it’s like we are sitting on the outside of a balloon thats being inflated, everything spreads evenly! Sad thing is, this will keep going and it is stated that the universe will reach infinite size at infinite time, most everything will be void. But that could allow for virtual particles, a phenomenon that occurs in voids such that particles pop into existence and just as soon pop out… I don’t know anything about those really, but I wonder about them… What do you think?