Frontiers| Pages 176-177 | See Linked Version

vast event horizon. Here's another favorite topic: What came before the Big Bang? To answer that the laws of physics did not work before the Big Bang may sound as if we're dodging the issue. However, time and space were meaningless before the Big Bang; they simply did not exist. Just as you cannot go any farther north on Earth if you are standing at the North Pole, you cannot go farther back in time from the birth of the universe.

This does not stop some theorists from speculating. The cosmic microwave background tells us that the space-time fabric of our infant universe was roiled by fluctuations on the smallest possible scale--a quantum foam, if you will. One class of inflationary hypotheses describes a mega-universe with endless bubbles of expansion arising from this foam. Each bubble looks like a Big Bang universe from within, and it may sustain laws of physics that differ from the ones we know. Inhabitants of those other bubbles would face the same impossible mysteries, forever confined to their part of the "multiverse" (page 178). Testing this wild scenario will require some scientific advance that we can't envision today. At this point it's safe to say that our laws of physics don't exclude the existence of other universes; they simply can't explain them.

It's tempting to regard the Big Bang as little more than science fiction. However, our belief in the theory is bolstered by an impressive set of successful predictions--far more than most theories in progress enjoy. Indeed, nearly everyone in the community of astrophysicists now accepts the Big Bang. But we all recognize that, as cosmology progresses, it one day may become the core idea of something even bigger.

Signs of the Big Bang

The cosmic microwave background is the faint glow of radiation that remains from the primordial fireball--the Big Bang--that gave birth to the universe. Within a fraction of a second, the ultimate characteristics of our universe were set. Space-time expanded, the energy of the universe spread thinner and thinner, and the average temperature dropped--swiftly at first, more slowly later on.

Big Bang Plus 10­43 Second

This artist's conception represents the cosmos in the tiniest fraction of a second after the Big Bang. At this time the universe was much smaller and hotter and contained minute irregularities--bumps no larger than grains of sand would make under a bedsheet the size of a football field. Most theories then call for a period of rapid expansion known as inflation.

 Big Bang Plus 300,000 Years

In the Cosmic Background Explorer's sky map of the Milky Way, red indicates temperatures 0.005 percent warmer than the average sky temperature of 4.9 degrees Fahrenheit above absolute zero while blue represents temperatures 0.005 percent colder. Computer analysis shows a pattern of fluctuations that supports predictions based on the inflationary Big Bang theory.

 Big Bang Plus 13 Billion Years

Tiny differences in the gravitational fields in the young universe caused matter to start to clump together, weaving the "cosmic web" that is the large-scale structure of galaxies we see today.