Collider physics is one way to probe the unobservable early universe. Another is to observe its aftermath, by analyzing the dimples and wrinkles in the cosmic microwave background (CMB), which is what paper #4 attempts. The CMB is imprinted with sound waves from the hot plasma epoch. CMB fluctuations in temperature and polarization on a scale smaller than 1° are particularly interesting, as many cosmological models predict acoustic peaks in the angular power spectrum at sub-degree scales. The amplitudes and positions of the fluctuations are highly sensitive to cosmological parameters. Paper #4 gives results from the first season’s operations of the Degree Angular Scale Interferometer (DASI). DASI is a 13-element interferometer designed to study the CMB radiation over a large range of scales with high sensitivity. The instrument operates from the NSF Amundsen-Scott South Pole station, at an altitude of 2800 m, ideal conditions for microwave astronomy.

Clem Pryke, University of Chicago, and his colleagues have benchmarked their data against a seven-dimensional grid of dark matter models. The upshot is that they find 2.2% of the universe is baryonic matter, about 14% to 20% dark matter, and at least 60% the vacuum energy driving the acceleration of the universe. These results are in accord with many recent cosmological experiments, but an important new finding is that the baryonic density is consistent with big-bang nucleosynthesis.

Some theorists toy with universes that probably do not exist, and that’s a feature of Hot Paper #7. Superstring theory is our only candidate for a consistent unification of quantum field theory and gravity. This paper is one of many exploring the rich physics of 10-dimensional superstrings, but the profession still seems a long way from the confrontation of ideas with reality.

Finally, carbon nanotubes get into our Physics Top Ten for the first time in many years. Paper #10 is a contribution on bottom-up electronics. Microelectronics is evolving into nanoelectronics, where chemical synthesis and self-assembly will increasingly be used to make electronic components. Until the mid-1990s, molecular electronics was at a standstill because nobody could work out how to manipulate single molecules into working circuits. Then, carbon nanotubes came along: they can behave as metals or semiconductors. Many groups quickly succeeded in attaching electrodes to them, and making devices similar to field-effect transistors. But there was a large problem looming over all the hype in the literature: none of the transistors could be used to build a logic circuit because the gain was too small.

Cees Dekker, Delft University of Technology, Netherlands, and his coworkers have succeeded in making chemically synthesized nanotubes as an important component of the transistor, and they show explicitly that they can be used to build a logic circuit. For Science Watch, coauthor Peter Hadley has this comment: "Our transistor is bigger than a silicon transistor in one direction, and too narrow to drive much current. For now, silicon is still king. No other technology even comes close. But lots of people are betting on bottom-up electronics in the long run, which is why our paper has excited so much interest. The front-runner devices are carbon nanotubes and semiconducting nanowires."