There was plenty of room to stretch out in Sanders Theatre yesterday, as renowned physicist Stephen W. Hawking described the mathematical underpinnings of black holes in his second of three Loeb lectures.

Sanders Theatre was filled to capacity during the first lecture on Monday, and tickets for all three lectures sold out within an hour of when they went on sale at the Harvard Box Office.

Perhaps because of the technical focus of yesterday's lecture, though, a steady trickle of students began heading for the door after Hawking dove into topics like path integrals in 11 dimensions, leaving the theatre only partially full by the end of his speech.

"I was kind of disappointed that so many people got up and walked out," said Anna C. Gay '02. "I think they couldn't understand it."

But Hawking had warned audience members that the technical details of yesterday's lecture--which included a mathematical conjecture that the universe is a four-dimensional surface sandwiched between two five-dimensional regions--might elude them.

"The important thing is that you'll get the flavor of the formula for black hole entropy" rather than understand all the equations, Hawking said.

Hawking's speech concerned the nature of infinitely dense cosmic objects called "singularities," which are found at the center of black holes.

Black holes are formed when massive stars, having exhausted their nuclear fuel, collapse under the weight of their own gravity until they become so dense that nothing that enters their sphere of influence can escape--even light.

Since time stops at the center of a black hole, matter and information that fall into it are gone, forever frozen while the universe continues around the singularity.