Professor Seeks Answers to Billion-Year-Old Riddle

Everyone knows that the universe began billions of years ago with the Big Bang.

But for the past 20 years, a group of Harvard physicists have been trying to figure out why the universe still exists.

Physicists think the Big Bang produced equal amounts of both matter and anti-matter.

When the two meet, they annihilate each other in a burst of energy.

Puzzlingly, scientists see more matter than anti-matter in the universe.

A group of Harvard physicists led by Professor of Physics Gerald Gabrielse have taken the first steps towards answering this question.

They created anti-hydrogen in a lab last October, an important step toward finding out if matter and anti-matter have different properties. If encountered, these differences could explain why the universe did not explode into a burst of energy shortly after it started.

Though the riddle may be a billion years old, Gabrielse and his team are racing to solve it. A group of European physicists based in Geneva are also producing anti-matter, and the Harvard group is vying to make important discoveries in a field which it used to dominate.

But for now, both teams are waiting until a key component of their experiment can be used again.

Does Anti-Matter Matter?

Anti-matter has long fascinated physicists because it seems to be exactly like regular matter, but with certain properties exactly flipped.

For example, a normal electron has a negative charge, but an anti-matter positron has a positive charge, although it seems to be the same as an electron in every other respect.

“I don’t see any reason why we couldn’t, in principle, be made out of anti-matter,” said Gabrielse.

“It’s a fascinating question that we do not know the answer to right now,” he said. “It kind of gnaws at me a bit.”

Gabrielse and his team make their anti-matter at the European Centre for Nuclear Research (CERN) in Geneva, Switzerland.

Seven Harvard scientists, including graduate students and post-doctoral fellows work with Gabrielse in Geneva.

Their success in creating anti-hydrogen, the simplest form of anti-matter, was published in the journal Nature in October.

The Gabrielse team, which goes by the name of Antihydrogen Trapment Collaboration (ATRAP), was able to create an atom of anti-hydrogen, the anti-matter counterpart of hydrogen, by joining an antiproton, the counterpart of a proton, and a positron, the counterpart of an electron. Except for their charges, both the anti-proton and the positron are identical in nearly all respects to their antimatter counterparts.

The most difficult part of creating anti-hydrogen involves overcoming repulsive forces to bring together the oppositely-charged antiproton and positron.

A machine the size of a football field uses magnets to guide anti-protons into and positions together. When the two get close enough, anti-hydrogen forms.

The Competition

But ATRAP wasn’t the first to succeed.

A few weeks before, on Sep. 18, a competing group, called ATHENA, which also uses the accelerator at CERN, announced that they had succeeded in joining an antiproton and a positron. This group is composed of mainly European scientists, who had not been serious competition for the Harvard group before.

However, Gabrielse said that ATHENA’s success came in part from work Gabrielse had already done. He said that many of the devices and techniques used by ATHENA to create the anti-hydrogen—including the football field-sized machine used to trap and merge antiprotons and positrons—had been developed by ATRAP in years earlier.

“In science, first and second is always a little tricky,” he said. “I don’t think anyone really disagrees that the main techniques in the experiment are the ones that we have developed.”

ATHENA member Alessandro Variola, a scientist from the Italian National Institute for Nuclear Physics (INFN), says that such borrowing of techniques from other scientists is a natural and necessary component of scientific progress. “You can mix a huge amount of…different experiences, different techniques. You must be careful to choose the techniques that allow you the best [results],” he says. “And surely, some of the techniques of Dr. Gabrielse were useful for us.”

He also said that ATRAP and ATHENA experiments differed in several notable ways, including in methods of detecting the anti-hydrogen after creation and in the quantity of positrons used.

Gabrielse said that ATRAP had begun its anti-matter experimentation long before ATHENA.

“That was laid out about five or more years before ATHENA even existed,” he says. “They basically bought into the vision.”

Because ATRAP had been foremost in many technological innovations for the project, according to Gabrielse, it had been seen as the clear leader in anti-matter resarch—until Sept. 18.

No Hard Feelings

Though both research groups worked to be the first to achieve a shared goal, the competition was not clouded with animosity, Variola says.

“We have quite a gentlemanly concurrence,” he says. “This is what I would call ‘sane competition.’”

“There certainly is rivalry, but there is no bad feeling between the two groups,” says Paul Oxley, one of two Harvard graduate students who worked in the Geneva lab. “They do their experiments within 20 feet of our

experiments.”

According to Variola, the close proximity of the experimenters is unusual.

“It’s not so common in physics to have two experiments running on the same subject…two different experiments with the same setup and the same machine,” Variola says.

But for now, the competition is on hold.

The work in Geneva can go on for only six months per year because of required maintainance work on the massive machines. For now, the competition is frozen. The teams will start work again in May.

When ATRAP members are not working in at CERN alongside ATHENA, they are at Harvard, creating, slowing, and studying positrons.

“We store millions of positrons in a little container,” says Gabrielse.

But he must travel to Geneva to use the equipment that actually brings together anti-protons and positrons.

For the past two years, Gabrielse had been making once-a-week trips to Geneva to conduct research.

He still teaches classes, answering students’ questions by e-mail. Often, he says, students do not realize he answers their questions from thousands of miles away.

From Making to Studying

Now that the anti-hydrogen has been created, the Harvard team still must travel to Geneva to create more of it to study. They now hope to determine whether antihydrogen and hydrogen—and analogously, antimatter and matter—are exact mirror images of each other, or if other differences exist between the two.

If there are other differences, the notion of a perfect, symmetric universe espoused by physicists will no longer be accurate, having revolutionary implications on scientists’ understanding of the physical world.

“If we find any unexpected differences at all between anti-matter and matter, it will require a fundamental reform of basic physics theories,” says

Gabrielse. “And that intrigues me.”

—Staff writer Nura A. Hossainzadeh can be reached at hossainz@fas.harvard.edu.