By Davide Castelvecchi

A string of recent discoveries in astronomy has left scientists with an
unsettling realization: The stuff we know and understand makes up less than 5
percent of the universe. The rest has to be yet-unknown forms of “dark matter”
and “dark energy.”

At a time of momentous changes in our basic understanding of the universe, a new
document outlines the essential role of particle physics in deciphering the laws
of nature that govern dark matter, dark energy and more.

Conceived to make the science as accessible as possible, the Quantum Universe
report focuses on nine fundamental questions (see sidebar) in response to a
request by two major research funding agencies, the U.S. Department of Energy
and the National Science Foundation.

The report was prepared by a task force chaired by Persis Drell, director of
research at the Stanford Linear Accelerator Center (SLAC). The funding agencies
asked their joint High Energy Physics Advisory Panel to appoint the task force
and to charge it with explaining what particle physics can do, and what
facilities it needs, to answer “the truly exciting scientific questions of this
century.”

The 58-page report, published in June, argues that answering such fundamental
questions requires new knowledge from particle physics. “Quantum Universe makes
it clear: These new discoveries are our problem,” Drell said.

The report details how understanding the ultimate constituents of matter and the
fundamental forces of nature ties in with the cosmic picture. “Just saying,
‘It’s fundamental, so it’s important,’ is not enough,” said committee member
Steve Kahn, a Stanford astrophysicist and deputy director of the newly
established Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at
SLAC. “The agencies were asking us to tell them how all this stuff fits together.”

In response, the committee singled out nine crucial questions. Their report also
articulated how current and future U.S. experiments, as well as international
collaborations with U.S. participation, can address those questions. That
includes experiments using particle accelerators, underground laboratories and
space-based missions.

An unusual feature of the document — which went through some 24 drafts during
its five months of preparation — was the emphasis on communication. From the
beginning, the committee included two science communication experts — Neil
Calder of SLAC and Judy Jackson of Fermi National Laboratory in Batavia, Ill.

“It was so important to us that Quantum Universe be accessible and engaging,”
Calder said. “The physics is so cool, we wanted people to read the report and
go: ‘Wow!'”

Prompted by Calder and Jackson, the committee kept in close touch with its main
audience — the funding agencies, congressional staffers and policymakers in
Washington — for feedback. “We were able to remind people throughout the
process that we weren’t writing for ourselves, and we weren’t even primarily
writing for an internal physics audience,” Jackson said.

That was no easy task. Many of the issues — such as the possible existence of
extra dimensions of space — were “by definition esoteric,” as Kahn put it.

“We struggled a lot to explain the idea of symmetry,” Drell said. “It is
incredibly interesting and yet such an abstract concept. We rewrote that about
20 times.

Drell credited Calder and Jackson with making the document look, well, unlike
most official reports, beginning with its binding. “For some of us, the first
reaction was: ‘What? Twenty-first-century physics in a 19th-century cover?'”
Drell said, referring to its leather-logbook look. With its use of photography
and graphics, Quantum Universe is pleasing to the eye and includes playful
details such as a fake sticky note on the back. “We were totally unprepared for
what Judy [Jackson] and Neil [Calder] did with the layout of the document,”
Drell said, “and how that enhanced the science in it.”

Drell emphasized that all 17 members of the committee spoke for the physics
community as a whole, not for their respective institutions. At the same time,
she said, “The research being carried out at SLAC, especially through [the
particle-collider experiment] BaBar and KIPAC, and in the Stanford Physics
Department, is targeted to many of those questions. We cover just about all of
them.”

So far, the intended audience of Quantum Universe — the funding agencies and
all levels of Washington policymakers — has given it a warm welcome, Jackson
said. “People liked it, and that’s extremely gratifying. This is the first time
I have ever seen a report get this kind of response.”

But was it a fun job? “It was a blast,” said Drell, “the most fun committee I’ve
ever been on.”

The Nine Questions

I. Einstein’s dream of unified forces

1. Are there undiscovered principles of nature: new symmetries, new physical laws?

2. How can we solve the mystery of dark energy?

3. Are there extra dimensions of space?

4. Do all forces become one?

II. The particle world

5. Why are there so many kinds of particles?

6. What is dark matter? How can we make it in the laboratory?

7. What are neutrinos telling us?

8. How did the universe come to be?

9. What happened to the antimatter?

[Davide Castelvecchi is a science writing intern at the Stanford Linear
Accelerator Center.]

Editor Note: This article was written by Davide Castelvecchi, a science writing
intern at the Stanford Linear Accelerator Center. A portrait of Persis Drell by
science illustrator Alan Chou is available at http://newsphotos.stanford.edu

Relevant Web URLs:

* Quantum Universe report http://interactions.org/cms/?pid=1012346