Lecture 12: Threshold 5—Life

Threshold 5—Life .............................................................................

LECTURE

Most of the Universe as I’ve described it so far is still technically dead.

It’s not alive. It can do lots of interesting things, as we’ve seen, but

it’s not—strictly speaking—alive, not alive in the sense that you and

I are alive.

W

e have described the creation of our Universe, our Sun, and our

Earth. This lecture crosses a new threshold with the appearance of

life. What is life? Life is one of those things that may seem easy

to de¿ ne until you try. Traditional accounts have often seen life as a divine

gift, dependent on some kind of life force. But it has proved impossible

to demonstrate scienti¿ cally the existence of a creator-deity, and as we

have seen, deistic theories always generate a new question: How was the

creator created?

Until the early 19th century, many scientists argued that there was a basic

difference between the “organic” chemicals from which living organisms

were made and the “inorganic” chemicals from which nonliving things were

made. This idea was disproved in 1828 when German chemist Friedrich

Wöhler (1800–1882) synthesized a simple organic chemical (urea) in a

laboratory. Just as Newton has argued that the same physical laws applied

in the heavens and on Earth, so this suggested that the same chemical laws

applied to living and nonliving things. This implies there is a continuum

between life and non-life, which may be why it is so hard to distinguish

rigorously between life and non-life.

Nevertheless, living organisms are different. First, they count as a higher

level of complexity. Like all complex things, their existence depends

on very speci¿ c ways of organizing matter. Get the plan wrong and the

organism dies. They have a degree of stability but eventually die. They display

new, emergent properties. And they depend on À ows of energy to maintain

their complexity. Indeed, these À ows seem to be denser than in all the other

complex things we have seen, which justi¿ es the claim that living organisms

represent a higher level of complexity. Eric Chaisson has argued that energy