Let’s talk about the concept of life. How do you tell the difference between something that is alive and something that isn’t? What is the difference, for example, between a living entity and a dead one? A living entity respirates, consumes energy and reproduces, whereas a dead entity does not. Is that the difference? What if an entity did not do one of those things, but it did do the other two, would it still be regarded as being alive? How do you know that you are alive? How do you know that I am?
Imagine that a clone of yourself was produced in a laboratory and was released at your age today. This clone has fully functional organs, it breathes, eats, sleeps and thinks. Would it be alive? How would it be different to you?
What if we constructed a machine that could do the same? Modern computers are capable of “thought”: they store and process information, assess options and probabilities, and take actions based on this assessment. We could power the computer with a battery that would need to be replenished regularly, and we could provide it with the ability to reproduce itself. Would this machine be a living entity? If not, why not?
What is this property called life? Can it be defined scientifically? In this edition of Ides of Science I would like to put aside supernatural explanations like souls and spirits, and consider whether there is a scientific basis for being alive, and what implications it may have.
The Origin of Life
At some point in the distant past there was a time when the Earth changed from being a planet without life to a planet with life. As far as we currently know, it is the only planet that has accomplished this, but the search continues for evidence that there may be others (more on that later in this blog).
So where did life come from? What is it? Before moving onto the origins of life, it is important to address various different terms that are sometimes confused. Firstly, the Big Bang Theory does not describe the origin of life. It is a model describing the formation of the universe. Secondly, the formation of the Earth does not describe the origin of life. The Earth was lifeless for a long time before it was not. And thirdly, the Theory of Evolution does not describe the origin of life. Evolution is a model describing the development of life after it formed. The origin of life involves a topic that is commonly known as abiogenesis. I will leave the current theories and experiments involving abiogenesis to the experts, but in very simple terms we are referring to a chemical process involving the development of complex organic molecules.
My simple-minded take on the development of life is as follows. In chemistry there is a property known as Le Chatelier’s Principle. It states that when a chemical reaction achieves equilibrium it will move in a direction that will prevent changes to that equilibrium. For example, if one was to add heat to an exothermic reaction then the reaction would produce more reactants on the endothermic side. Adding more reactants shifts the reaction towards producing more products, and so forth. The complex compounds involved in the formation of life would probably have relied on this process to resist changes to its formation, and possibly to enable the further development of more complex organisms over long periods of time.
Via Le Chatelier we have a chemical method by which a complex chemical compound can prevent itself from destruction. Could natural instincts be sophisticated extensions of the same chemical process? At their base level, instincts are mechanisms that prevent damage and destruction to the living entity. The need to fight or fly, consume and reproduce are all needed for its continued existence. As the chemical complexity evolved, perhaps the rules governing the survival of that complexity evolved along with it. We can see evolutionary advantages in being able to move around, having sensory equipment at the front of the “body”, having the organism that processes the sensory information in close spatial proximity to the sensory equipment itself, and so on. Perhaps the instincts from which much of animal behavior is governed can be derived from the simple chemical process that prevents changes to the equilibrium state.
Searching for Extra Terrestrial Life
What about life on other planets? You have probably heard of the SETI program, but may not know much about its objectives. SETI was set up to search for intelligent life; specifically life that was deliberately sending a signal towards us. The idea is that humanity on Earth has been transmitting signals for a century or so with our broadcasts, and that an alien on some planet has received this signal and is now sending one back to us. This is a noble first step and one worthy of taking, but there are some obvious limitations to this approach. Firstly, we must assume that the life that we are searching for is capable of recognizing our signals as coming from intelligent life, and that they understand how to transmit a signal in a manner that we would understand. What are the chances that an alien somewhere in the universe has this capability? I would estimate it to be quite high. What are the chances that one is within range? I would estimate that to be quite low.
What do I mean by “within range”? Consider the distances that we have to work with. The first wireless telegraph was transmitted in 1901 and radio has been broadcast since around the 1920s. So let’s say that we have been broadcasting signals into space for 100 years. These signals travel at the speed of light, and we need to accommodate for the round trip for an alien to receive our signal and then transmit one back to us. This gives us a radius of around 50 light years from the Earth within which our aliens would need to reside. There are only 132 stars within 50 light years of the Earth, only 32 of which are lone G type stars like our Sun. Three of them are known to have planets. Given all of the conditions that need to be balanced for life to form on Earth, the chances of there being technologically advanced life on a planet orbiting one of these stars are extremely small.
If we are looking for life on other planets, the presence of oxygen in the atmosphere would be an excellent clue. Oxygen is highly reactive and does not remain in its gaseous state for long, and so if it is present in an atmosphere it must be because there is something on the planet that is producing (replenishing) it. Our plant life on Earth produces oxygen at such a rate that it occupies over 20% of our atmosphere. Is this an essential ingredient for life? Or do we depend on oxygen simply because it was abundant in our atmosphere while we were evolving? Of all of the exoplanets that have been discovered from which we have been able to get an elemental spectrum measurement, none of them contain large quantities of oxygen in their atmospheres.
As with so many things in science, it appears that identifying life requires a definition of one’s selection criteria. How close does an entity need to be to living things on Earth for it to be regarded as being alive? Does it need to be carbon based? Does it need to consume? Reproduce? And how far from being like life on Earth would it need to be before we no longer recognized it as being alive?
If we limit our selection to things that are just like life on Earth, then how similar to conditions on Earth would a planet need to be to be able to support life? Here is a list of some things that Earth has that was important for the development of life here:
(1) It has a substantial abundance of water (2/3 of the planet’s surface is covered with it);
(2) Its distance from the Sun is in the “goldilocks” zone, where the temperature is such that liquid water is supported for much of the planet, most of the time;
(3) It has a moon that is massive enough to invoke tides, that aid in mixing organic material up and encouraging chemical reactions;
(4) It has a magnetic field strong enough to deflect away the solar wind that can strip away the upper atmosphere;
(5) The moon is not too massive as to destroy life emerging from the water to dry land;
(6) The solar system has a large planet (Jupiter) that can draw comets and asteroids towards it, reducing the number of catastrophic impacts at the Earth;
(7) The Sun is stable in its activity such that the temperature at the Earth is roughly the same for long periods of time.
Are these all required for life such as that on Earth to evolve? How many planets in the universe possess all of these properties? Maybe life on Earth is somewhat unique, or maybe our perception of life requires a change in perspective. With the age of Artificial Intelligence about to dawn, I suspect that these questions will need to be addressed sooner rather than later.