A fascinating book I read recently is by a famous science writer, Lawrence Krauss. The title of the book is “The Edge of Knowledge: Unsolved mysteries of the cosmos.” It is a fairly dense book, difficult to understand sometimes, that deals with five topics: Time, Space, Matter, Life and Consciousness. According to him, the two most inspiring mysteries of nature are the last two: Life and consciousness. Here is my attempt to describe his take on Life, which I find very interesting.
The first issue he deals with is what exactly is a living organism and how do you separate it from the non-living collection of molecules. He says that “Living organisms are generally thought to be an open-systems that maintain homeostasis, are composed of cells, have a life cycle, undergo metabolism, can grow, adapt to their environment, respond to stimuli, reproduce and evolve (Wikipedia).” In this rather lengthy definition, “homeostasis” is a moderating feedback loop to maintain a kind of static equilibrium. So, one could say that a fire is not a living organism because it does not maintain homeostasis. This is a fairly comprehensive definition, in my opinion that adds several parameters I had not thought about, such as responding to stimuli.
He then describes four key attributes associated with observed life on earth: 1. Informational molecules/genomes to enable faithful reproduction, 2. The building blocks of metabolism, typically molecules called ATP that allow life forms to store and manipulate energy, 3. Protein catalysts to allow biological reactions to proceed, and 4. Compartments/membranes that separate the workings of living things from their environment. If you are familiar with what a cell is composed of, this list makes sense. A cell is an incredibly creation of nature which forms the building block of all things living.
Now we are entering the religious and philosophical domain. How could such a complex thing come about without the hand of god or an intelligent designer?
Krauss says that it is possible to have an explanation about origin of life that does not require god or an intelligent designer. Although the final answer is not found at present, there are three possibilities: 1. Scientists have identified exotic environments where there is new chemistry that creates complex biomolecules, 2. Many basic organic building blocks of life, including amino acids have been discovered in meteorites and comets, 3. RNA (which has both genomic and catalytic functions) provides a possible pathway to replicating structures in advance of biology. Krauss believes that eventually we will find the answer to origin of life using science, since we already have several strong candidates. I agree with him.
One most obvious next question is what about life elsewhere, outside of earth? What should we expect?
Regarding extraterrestrial life, Krauss sees three possibilities: 1. Extraterrestrial life might be based on exactly the same chemistry that we see on earth. 2. We discover life that has different rules, different genetic backbones than RNA and DNA, different metabolic pathways, and different sources of energy. 3. Life that bears no resemblance to life on earth. Perhaps we are too conditioned to expect life looking similar to what we are familiar with. That may not be the case.
The question is: Will we find extraterrestrial life? In fact, do civilizations exist elsewhere in the universe?
In 1961, Frank Drake estimated a way of estimating active, intelligent and communicative civilizations in the Milky Way. It is composed of a number of probabilities that begins with number of stars in the galaxy X Fraction that have planets around them (which we know is approximately one, given the number of exoplanets we have already found) X Fraction of planets that can potentially develop life X Fraction that do indeed develop life X Fraction that develop intelligent life X Fraction that develop communications technology X Fraction that attempt to communicate.
At the moment, we are busy trying to find planets that can potentially develop life whether they do develop or not is a separate question. For example, three moons of Jupiter (Europa, Ganymede, and Callisto), plus two of Saturn (Enceladus, and Titan) have potential for life development. Several space probes will further enhance our knowledge of these potential cradles of extraterrestrial life. Let’s see what happens. The other fractions in Drake’s equation are still wild guesses.
At some point, life will not be tenable on earth. Whether a solution is found to manage these catastrophic events or human beings will find home elsewhere is a question that keeps science fiction writers busy. Krauss thinks that we are not that well suited for interplanetary travel much less interstellar. He thinks that it will not be human beings but the instructions to make humans that will go beyond our solar system. Also, who is to say that the dominant intelligence on earth may not become silicon based rather than carbon based? In that case, life might never end in the universe; it just won’t be the same life that survives.
Many folks argue that so many things in universe had to go right for life to exist, and therefore there has to be a divine intervention. Krauss says that the universe is not fine-tuned for life, rather life is fine tuned for the universe.
