Usually physicists aim for extremes. They want to understand the smallest building blocks of matter, or the biggest cosmological bang. So it might seem strange, at first, that physicists supported by the US Department of Energy (DOE) are issuing a rallying cry to study the middle.

But according to members of the DOE’s Basic Energy Science Advisory Committee (BESAC), the ‘mesoscale’ is where it’s at. On Friday, at meeting in Bethesda, Maryland, they approved the final steps in the roll-out of a report that is supposed to galvanize physicists towards an understanding of the mesoscale — a regime of medium-scale lengths, energies and times that sits between the quantum world of atoms and the classical world in which we live. The report will be the culmination of an effort that began earlier this year with town halls throughout the United States, and which has gathered dozens of white papers.

Roughly speaking, the mesoscale is a regime between 100 nanometres and one micrometre, says John Sarrao, a condensed-matter physicist at Los Alamos National Laboratory in New Mexico and co-chair of the committee authoring the report. He cites the example of atomic defects. To a nano-scientist studying individual atoms, defects don’t exist and don’t matter. But for a mesoscale scientist seeking to study, say, the catalytic surface of a battery, defects must be understood.

In 2001, the DOE established the National Nanotechnology Initiative, which pushed physicists deep into the quantum world. Now, Sarrao says, they need to start working in the other direction, to understand the messy behaviour that emerges as atoms are stuck together in groups. “What we now need to do is come back up from the bottom,” he says.

The committee needs a few more weeks to polish its report. But at the BESAC meeting, Sarrao presented the six areas in which the mesoscale effort will be focused:

* Mastering defect mesostructure and its evolution
* Regulating coupled reactions and pathway-dependent chemical processes
* Optimizing transport and response properties by design and control of mesoscale structure
* Elucidating non-equilibrium and many-body physics of electrons
* Harnessing fluctuations, dynamics and degradation forcontrol of metastable mesoscale systems
* Directing assembly of hierarchical functional materials

The group hopes that the report will help the DOE organize funding in support of the mesoscale, but it will not call for any new facilities; mesoscale physicists would continue to take advantage of existing light sources.