A look at how the world has changed since September 11	Day 4: Science vs. terrorism

Investigators emerging last fall from a house in Chester, Pa., where officials suspected hazardous materials were being produced. Protecting the nation from nearly invisible weapons is a priority of antiterrorism research. (KRT Photo)

New threat sets scientists on a patriotic mission Deeply aware that new scientific ideas - from radar to the atomic bomb - gave America a crucial edge in World War II, scientists across the country are working on weapons for the war against terrorism. Security analysts trying to narrow list of possible targets The guessing game has gone on across the nation since Sept. 11: Where might terrorists strike next? Cities, for their concentration of people and because they are centers for commerce, top the list.

FROM THE ASSOCIATED PRESS Tracking technologies have improved Year of surprises for Mass. anti-terror company DNA ID work forges new forensic tools Afetr loss, Avid aids 9/11 probe

MESSAGE BOARD The US government has unleashed a host of high-tech weapons in the war on terrorism. Will American technological might prove to be the decisive factor in thwarting potential terrorists? Read messages  CHAT TRANSCRIPT Science vs. terrorism: Globe science writer Gareth Cook talked about how science and technology are being harnessed in the battle against terrorism.