Step One: EMPTY UNIVERSE
Each panel represents a three-dimensional membrane. The observable universe exists within the panel on the right; the other membrane is invisible to us. At the end of one cosmic cycle—after about a trillion years of accelerating expansion—matter is so spread out that space is essentially empty. This stage corresponds to the distant future of our universe. All is not static, however: The membranes still contain energy, and a force of attraction gradually draws them together again.