Knocking on Heaven's Door - Lisa Randall [172]
The Cosmic Microwave Background Explorer (COBE), a four-yearlong satellite mission launched in 1989, measured this background radiation extremely accurately, and the mission scientists found that their measurements agreed with predictions to better than one part in 1,000. But COBE measured something new as well. By far, the most interesting thing that COBE measured was a tiny bit of nonuniformity in temperature across the sky. Although the universe is extremely smooth, tiny in-homogeneities at the level of less than one in 10,000 in the early universe grew bigger and were essential to the development of structure. The in-homogeneities originated on minuscule length scales, but were stretched to sizes relevant to astrophysical measurements and structure. Gravity caused the denser regions where the perturbations were especially large to become more concentrated and form the massive objects we currently observe. The stars, galaxies, and clusters of galaxies that we discussed earlier are all the result of these initial tiny quantum mechanical fluctuations and their evolution through the gravitational force.
The microwave background measurement continues to be critical to our understanding of the universe’s evolution. It’s role as a direct window into the early universe cannot be underestimated. More recently, along with more traditional methods, CMB measurements have provided experimental insights into several other more mysterious phenomena—cosmological inflation, dark matter, and dark energy—subjects that we turn to next.
CHAPTER TWENTY
WHAT’S SO LARGE TO YOU IS SO SMALL TO ME
When I was an MIT professor, the department ran out of office space on the third floor where the particle physicists worked. So I relocated to the open office next door to Alan Guth’s on the floor below, which at the time housed theoretical astronomers and cosmologists. Although Alan started his career as a particle physicist, he is known today as one of the best cosmologists around. At the time of my office move, I had already explored some connections between particle physics and cosmology. But it’s a lot easier to continue such research when your neighbor shares those interests—and is as messy as you are so that in his office you feel right at home.
Many particle physicists have gone further afield than a single floor and crossed over into a wide variety of other research areas. Wally Gilbert, a cofounder of Biogen, started life as a particle physicist but left to do biology and Nobel Prize–winning chemistry research. Many since have followed in his footsteps. On the other hand, many of my graduate student friends left particle physics to be “quants” on Wall Street where they could bet on changes in future markets. They chose just the right time to make such a move since the new financial instruments to hedge such bets were only just being developed at the time. In the crossover to biology, some ways of thinking and organizing problems carried over, whereas in finance some of the methods and equations did.
But the overlap between particle physics and cosmology is of course far deeper and richer than either of the above. Close examination of the universe on different scales has exposed the many connections between elementary particles on the smallest scales and the universe itself at the largest. After all, the universe is by definition unique and encompasses everything within it. Particle physicists, who look inward, ask what type of fundamental matter exists at the core of matter, and cosmologists, who look outward, study how whatever it is that is out there has evolved. The universe’s mysteries—most not ably what it is made of—matter to cosmologists and particle physicists alike.