Frontiers | Pages 178-179| See Linked Version

Multiple Universes?

One of the most intriguing questions in cosmology is: What came before the Big Bang? One hypothesis, illustrated here, is that our universe may be just one of many that materialized out of the inherent instability of the cosmic vacuum. These vacuum fluctuations may be similar to an era of fluctuating foam known as Planck Time, 10­43 second after the Big Bang, before which our current models and theories do not apply. Some researchers speculate that the writhing foam would have produced tiny bubbles that appeared and disappeared--or suddenly expanded into entire universes.

How SMALL Does Matter Get?

For another cosmic mystery, it's not necessary to peer billions of light-years into space or back to the beginning of time. This mystery is right at your fingertips: What is the essential nature of matter? From the atoms of Democritus to the atomic nuclei of Ernest Rutherford to the quarks of Murray Gell-Mann, our models of matter have shrunk to ever-smaller scales. It's natural to wonder whether this progression will continue, surprising us with even tinier nesting Russian dolls of matter. The answer is more than just a curiosity, because quantum mechanics tells us that energy and matter fluctuate on these tiniest scales. In the earliest moments of the Big Bang, continual quantum fluctuations dictated the future appearance of the universe--and they form the basis of all space and matter today.

Physicists peel back matter's layers by boosting electrons, protons, and other particles to exceptionally high speeds and smashing them together. Our Earthly machines are pale versions of natural particle accelerators in the cosmos. One of the closest is the Sun, which pierces the inner solar system with writhing magnetic fields. Charged particles in the solar wind zoom outward along these field lines like surfers catching steep waves. Pulsars, black holes in the centers of galaxies, and other energetic objects also fling particles into space at close to the speed of light. Accelerator energies on Earth are low by comparison, but they still allow physicists to simulate the conditions that existed fractions of a second after the Big Bang, albeit within volumes smaller than that of an atomic nucleus.

Decades of such research have constructed a scheme for the universe with a rather dry name: the standard model. This thorough model describes all known particles in the universe and their interactions with precision. Its main ingredients are the four forces of nature--gravity, electromagnetism, and the strong and weak nuclear forces --and two distinct sets of particles. One set consists of the basic units of matter as we know them today: quarks, electrons, and neutrinos. Each of these types of matter falls into one of three "families," divided according to their masses. For the most part, the stuff of our everyday world features particles in the least-massive family. The other two families arise mainly in particle accelerators, both on Earth and in space. The second set of particles in the standard model is fundamentally different.