reason to expect the temperature of the fireball radiation to be the same in all directions. Yet the observed cosmic microwave background does have nearly the same temperature throughout the heavenly dome. Current data indicate that temperatures fluctuate only a few parts in 100,000. Physicists call this situation the horizon problem.

Imagine that 100 high school alumni arrived at their 10-year reunion each clad in ruffled purple dresses or suits and that you found out that the classmates had been completely out of touch for the entire decade. No phone calls, e-mails or letters had been exchanged, except to announce the time and place of the event. How would you explain such a startling wardrobe synchronicity?

You could chalk it up to pure coincidence or shared fashion sense. Or if you did some detective work, perhaps you might discover hidden commonalities that led to such color uniformity. For example, maybe a mixer was held shortly before graduation that brought all the seniors together. Suppose the sponsors of the event asked students to dress like the pop star Prince, whose favorite color is purple. At the mixer, students shared smiles and came to associate their outfits with graduation. Therefore, even when they were beyond communication for years, they retained certain commonalities.

Different parts of the universe have been out of touch for far longer than that. Nevertheless, they are all costumed the same. Could there have been some kind of cosmic “mixer” well before the photons “graduated” and moved away?

In 1969, physicist Charles Misner of the University of Maryland proposed the Mixmaster universe as a potential way of resolving the horizon problem. The Mixmaster universe is an anisotropic variation of the Big Bang theory. In the standard Big Bang, the universe bursts forth at equal rates in all directions, like an evenly gushing fountain. The Mixmaster universe, on the other hand, behaves far more erratically. It expands in certain directions while contracting in others. Furthermore, the directions of expansion and contraction keep changing in an essentially unpredictable manner. Misner