Life in the Universe
Evolution is an intrinsic and proper characteristic of the universe. Neither the universe as a whole nor any of its ingredients can be understood except in terms of evolution. And evolution is a daily happening. We, for instance, are constantly exchanging atoms with the total reservoir of atoms in the universe. Each year 98% of the atoms in our bodies are renewed. Each time we breath we take in billions and billions of atoms recycled by the rest of breathing organisms during the past few weeks. Nothing in my genes was present a year ago. It is all new, regenerated from the available energy and matter in the universe. My skin is renewed each month and my liver each six weeks. In brief, human beings are among the most recycled beings in the universe.
Life has made a relatively late appearance considering the total age of the universe. Life is thought to have emerged about three billion (3 x 109) years ago in its first microscopic forms. This was about eleven billion years after the Big Bang and about six billion years after the formation of the first stars. Why did it take so long for life to emerge? In order to provide the chemical abundances required for life it is estimated that three generations of stars were required. It is only through nucleosynthesis in stellar interiors that the heavier elements can be created and at the death of a star this material is regurgitated to form the matrix for a new generation of stars. The lifetime of a star depends upon its total mass and can vary from several millions of years for a very massive star to tens of billions of years for lower mass stars. At any rate it took about ten billion years of stellar evolution to produce carbon, nitrogen, oxygen, etc. I repeat that the universe is by its nature evolutionary and it had to evolve to be big and old before it could contain us. I was tempted to say, “in order to contain us”, but that would have introduced a finality which may not be justified scientifically.
The question is further complicated by the following consideration. As the universe evolved the appearance of life required a very fine tuning of the various constants of nature and the laws whereby the universe applies those constants. Let me give a few examples. If the velocity of expansion of the universe at its beginning were one millionth greater or smaller than it was, we would not be here, because the universe would either have expanded so fast that no complex systems could come to be or it would have almost immediately collapsed in upon itself. If the mass of the proton and the electron differed by an extremely small amount, we would not be here, because stars like the sun would not have stable enough energy mechanisms to provide for the long time required to generate the chemical abundances necessary for life. If the energy level of the carbon molecule, which is created by two nuclear reactions beginning with four helium atoms, were only slightly less than it is, the abundance of carbon in the universe would be millions of times less than it is and totally inadequate to provide the chemical processes which led to life. Now all the constants of nature, a few examples of which I have just mentioned, are empirical values, discovered as it were in a laboratory. They could have different values and, if they did, we would not be here. Would you allow me to ask as a scientist: WHY are we here? To the best of my knowledge, no satisfactory scientific explanation has been given for this fine tuning of the universe. Life in the universe is a marvel; its origins are not completely understood scientifically.