ONE of the most basic facts about the universe is that it is expanding. This observation, made by Edwin Hubble (pictured) in 1929, leads to all sorts of mind-stretching ideas. That the universe is growing implies it was smaller in the past—possibly a lot smaller. Which leads to the thought that a “Big Bang” kicked everything off. It also opens the question of whether the universe will expand for ever, or will eventually see its expansion halted and reversed by gravity, thus ending in a Big Crunch.
Things got stranger in 1998, when a group of astrophysicists discovered that the rate of expansion is increasing, for this finding raised another question in turn. The acceleration of the expansion was so great that it seemed something was actively pushing the universe apart. Thus was born the notion of “dark energy”—a new component of the cosmos, invoked to balance the equations.
Trying to work out what dark energy...Continue reading