If the universe weren't filled with unimaginably unlikely coincidences and anomalies, life--here or anywhere else--could not exist, Higgins Professor of Biology Emeritus George Wald said to several hundred Harvard students and Cambridge residents in the Science Center last Wednesday.

His talk, called "Life and Mind in the Universe," was one of the Science Center's monthly lectures specifically desiged for nonscientists.

The Nobel Prize-winning eye researcher began by describing how our universe is probably "permeated with life."

One out of every hundred stars might host a planet capable of supporting life and our own galaxy could contain a billion such stars.

Multiply that by one hundred billion galaxies, and the Earth seems less overpopulated, Wald said.

But "if any of the properties of our universe were different, that life that now - seems so prevalent would become impossible."

Atomic warfare

Wald said that once during a conversation with Albert Einstein, the great physicist suddenly piped, "Why do you think all the natural amino acids are lefthanded.... You know, I always wondered why the electron came out negative; it must have won the fight."

The "fight" occurred in the early universe between matter and antimatter, which annihilate each other into energy on contact.

Theoretically, the universe should have contained equal amounts of both--matter and antimatter which would have wiped each other out completely, leaving nothing but energy.

The only reason we exist is that for every 100 billion primordial particles, there was one more particle of matter than antimatter.

"The residue--that one one-billionth--that's our universe," Wald said.

Another lucky break is that protons and neutrons (both of which are nucleons) are nearly 2000 times heavier than electrons.

Consequently, an atomic nucleus stays relatively stili compared to the electrons whipping around it; this makes atoms stable.

"If nucleons and electrons were closer in mass, we could not have such structures as molecules. Under these circumstances, there could be no life," Wald added.

He stressed that life needs four elements to evolve: hydrogen, oxygen, nitrogen, and carbon.

Chemically, only carbon can form the extra-strong double bonds with other elements needed to make certain complex molecules, the building blocks of life.

Sandman

Wald refuted the claim that silicon, not carbon, could be the basis of other life. Silicon cannot form chemical double bonds, and therefore, forms crystalline chains instead of discreet molecules.

"When you're finished, you've got a rock," said Wald. "But if you want to make living organisms, you have to use carbon.

But Wald called water the most important molecule of life. And if water didn't break all the rules of chemistry, life could not exist.

Most solids are denser than their corresponding liquids; for example, an iron nail sinks to the bottom of a cauldron of molten iron.

But ice is actually less dense than liquid water; an ice cube floats in a drink. "Nothing else does that--it's just crazy," said Wald.

Therefore, when a pond freezes, the ice forms an insulating layer on the top, and the pond does not freeze all the way through.

If ice were "normal," it would sink and ponds would freeze from the bottom up and ponds would turn to solid ice.

Come spring, these icebergs would not melt completely. The warm, watery environment in which life evolved would not have existed.

Fortunately for life, water can be found throughout the universe, Wald added.