Choices in The Quantum Universe

Strange universe of Einstein initially seemed uncomfortable with quantum implications
Credit: Einstein archives

"It was a blast," said Persis Drell, director of research at the Stanford Linear Accelerator Center (SLAC), "the most fun committee I’ve ever been on."

This kind of enthusiasm is rare oftentimes: as the questions get bigger, the answers that a committee can contribute often become more narrow and legalistic. But that kind of binary choice, either between a fun or tedious task, hardly seemed worthy when considering the biggest questions, particularly when the questions concern quantum mechanics.

Drell chaired a group of particle physicists charged with authoring the Quantum Universe report.

Their 58-page analysis focuses on nine fundamental questions in response to a request by two major research funding agencies, the U.S. Department of Energy and the National Science Foundation. Their conclusion answering such fundamental questions requires new knowledge from particle physics. "Quantum Universe makes it clear: These new discoveries are our problem," Drell said.

What can particle physics do to answer "the truly exciting scientific questions of this century"? In response, the committee singled out nine crucial questions.

Higher dimensional universe of complex topologies, loops and strings
Jacket Credit: The ATTIK, NY

"It was so important to us that Quantum Universe be accessible and engaging," said Neil Calder, also of SLAC. "The physics is so cool, we wanted people to read the report and go: ‘Wow!’"

It’s one thing to write science fiction about antimatter engines to the stars or speculate on worm holes that tunnel vast distances across the galaxy. But to do the hard work of putting down compelling experiments and theories was one charter for the Quantum Universe committee.

Many of the issues — such as the possible existence of extra dimensions of space — were "by definition esoteric," as the predicatment was described by Steve Kahn, a Stanford astrophysicist and deputy director of the newly established Kavli Institute for Particle Astrophysics and Cosmology (KIPAC). "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."

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?

The Planck Satellite. The cosmic microwave background is polarized — the photons have preferred "orientations" at different parts of the sky — and that polarization contains information about gravity waves that rattled around the universe since a tiny fraction of a second after the big bang. The Planck satellite or its successors should be able to extract that information
Credit: European Space Agency

Not only does the question of how the universe began come up, but subtle recipes for how to build up the necessary particles and energy come into play.

Cosmologists today are trying to answer these age-old questions, according to Science magazine writer, Charles Seife, who also authored the book, Alpha and Omega. Seife told Astrobiology Magazine that "Quantum mechanics and relativity were incredibly important and dramatic changes of the rules that occurred after several centuries of scientific observation and theory."

On an historical timeline, he summarized many of these questions as attempts to understand the role of "depth" in our broad world view. When looking at the night sky, the naive observer sees a flat blanket of blackness marked with twinkling stars. What’s behind?

Seife noted that "It doesn’t take much imagination to think of the night sky as a sphere enclosing the Earth. It took a lot of work to show that the heavens had depth — vast depth. Astronomers have to use subtle clues to flesh out that extra dimension: parallax,Cepheid variables, the Tully-Fisher relation, and supernovae are all tools which gave scientists more and more understanding of how deep the universe really is."

"The acoustic waves and big bang were important," summarized Seife, "until the universe was 400,000 years old and set the pattern for the clumping of matter in the cosmos; until then, the important forces were gravity and the radiation pressure of photons bouncing off of matter, set against the backdrop of an expanding universe. And don’t forget dark energy in addition to gravity and the initial energy of the big bang as a driver!"