"We are all asking ourselves, 'When can we play again? Is it appropriate to laugh in public? Is it all right to feel happy? When will our sadness and anxiety abate?' I don't have an easy answer," said Dacher Kelter, UC Berkeley professor of psychology.

But he said he knows from his research studying people responding to traumas, such as bereavement, that experiencing awe, amusement, love, compassion, pride and desire - the positive emotions - is an important path out of trauma, and "guilt about having these feelings, while it shows people's concern for others, may be misguided," said Keltner.

Keltner said that laughter is high on the list of things that bring about meaning and positive transformation after a traumatic event, such as the death of a spouse.

Judging from the research on bereavement and interpersonal conflict, which Keltner has contributed to over the past eight years, he has these three prescriptions for Americans dealing with the trauma of September 11:

1. Use laughter and feelings of beauty, elevation and awe to discover new meaning in the tragedy.
2. Look for opportunities for reconciliation and compassion.
3. Beware of anger, even though it is justified.

"In our studies, when people laughed during the six months after the death of their spouse, they were reveling in the absurdity of life. Sometimes that's the only option," said Keltner.

"Humans have a wonderful capacity to find humor in the juxtaposition of life and death. Many of our positive emotions are directed at transforming the distress and trauma that results from that human condition."

The emotion of anger, however, is more problematic.

Keltner said that it was appropriate to feel anger at the terrorist attacks on the World Trade Center and the Pentagon, but to "watch out."

"Anger is justified. Justice does need to be served," he said. "But the question is how much compassion will be involved alongside that administration of justice."

"Beware of anger," said Keltner. "It has a legacy and it can escalate."

By "legacy," Keltner is referring to his research findings that people who experienced anger and other negative emotions during the mourning period after the death of a spouse were more poorly adjusted years later. In his own and other research, he found that the anger tended to escalate, generating more anger, conflict and disharmony.

Four years later, in a follow-up study, the psychologist discovered that the more anger, disdain, and contempt people had expressed six months after the death, the more likely they were to be still preoccupied by the experience.

"Bereavement research shows us that anger leads to unhappiness for years following the death of a spouse, affecting the ability to form new bonds," said Keltner.

But can this research on individuals be transferred to the national, political level?

Keltner said he thinks it can, with one exception.

He said it is healthy now for people to laugh in their own personal lives, but they can't laugh at the events unfolding at the national level because they don't understand them.

"We don't know who did this or how to respond yet," said Keltner, explaining that humor and laughter depend both on understanding an event and seeing an alternative to it.

"Once those pieces are in place, we will be able to laugh," said Keltner. "But soul-searching is the appropriate thing to do right now."

Keltner also believes it is appropriate for people to continue watching and hearing the stories of loss displayed on national media, even though they stimulate feelings of sadness.