In the previous chapter NDT discussed the opposing forces of coagulation and dilution. Up until very recently, everyone believed the universe is a steady-state, not expanding or contracting. In the 1920s and 30s Edwin Hubble observed the expansion of the universe. Next came a raging question of whether it expands forever or contracts periodically. Now we have that answer due to measurements of the effects of dark energy.
Since both mass and energy cause space-time to warp, or curve, omega tells us the shape of the cosmos. If omega is less than one, the actual mass-energy falls below the critical value, and the universe expands forever in every direction for all of time, taking on the shape of a saddle, in which initially parallel lines diverge. If omega equals one, the universe expands forever, but only barely so. In that case the shape is flat, preserving all the geometric rules we learned in high school about parallel lines. If omega exceeds one, parallel lines converge, and the universe curves back on itself, ultimately recollapsing into the fireball whence it came.
We know omega does equal one, but only after considering the huge amount of dark energy in the universe. This was understood only after very detailed measurements showed the expansion of the universe is accelerating
, a paradox that lead towards dark energy.
A potentially depressing thought, but they won't know any better.