Astronomers Friday said the big-bang theory of the origin of the universe is alive and well, despite major questions about the subsequent evolution of the cosmos and the formation of galaxies.

The big-bang theory holds that time and space - the universe - exploded into existence some 15 billion years ago. Since then, the space has been explanding in all directions with galaxies rushing away from each other like dots painted on an inflating balloon.A key question mark about the theory involves the density of the universe. Astronomers have been unable to explain how the expanding universe grew from a supposedly uniform explosion into the "lumpy," galaxy-ridden cosmos they see today.

Despite recent claims raising questions about the big bang, astronomers said Friday the theory is alive and well.

"The big bang is in very good shape," Alan Guth of the Massachusetts Institute of Technology in Cambridge, Mass., told the American Association for the Advancement of Science's annual meeting.

A recent study published in the British scientific journal Nature said some measurements of the density of matter in the universe were in conflict with the big bang theory, raising questions about its validity.