Why do they always go on about whether conditions elsewhere ‘may support life’? Why don’t they think outside the box? Life could be completely mental surely? Time-travelling, wispy spirit creatures with a form we couldn’t even comprehend, specifically.
That was my thought process on the matter until I discovered a great little book called ‘Life in the Universe’ by Lewis Dartnell. I really enjoyed reading it.
Sometimes when I read non-fiction I do it in a dutiful way. My attention will drift now and then from the book to the sensation of the ‘attentive’ face I’m pulling. I also fall in to daydreams where an opportunity has arisen for me to impart my knowledge in the course of conversation, so I do, but apologetically. Madness. With this book though, for the most part, I was totally engrossed.
What I took from it:
The visible universe is composed of chemical elements (for the purposes at hand). What those elements are can be determined by spectroscopic analysis of the light received through telescopes. Unknown elements have been identified this way, but still, the universe doesn’t turn in to Heaven or something round some corner.
Any life out there is a feature of this observable system. That imposes limitations on what it could be like.
As well as involving the ability to replicate, life is by definition an energy disequilibrium. Naturally occurring processes are unnaturally sped up, a disequilibrium is created, and life uses the resulting energy gradient to do work (in the case of complex life- through the processes of respiration or photosynthesis)
The complexity of information storage molecules on earth, RNA and DNA, suggests that metabolism must have preceded them and resulted in them. There is consensus on how metabolism emerges, says the book: Pre-organic pools of chemicals engage in reactions, the product of one catalysing the next. In a large enough pool engaging in a variety of reactions there is a good chance some will catalyse each other. The products produced become more common and as a greater diversity of reactants is generated the pool of potential catalysts gets bigger and the process accelerates, the network of catalytic interactions becomes denser until a single self-sustaining network emerges. As the network becomes increasingly complex it begins producing small organic molecules that had not previously existed.
Having molecules available in a dissolved state is crucial for the rapid chemical reactions of life. It wouldn’t be possible in a solid or gaseous state. Water is the solvent used by life on earth, yet there’s no reason to say the solvent couldn’t have been ammonia or formamide, both of which can handle organic substances in water-like ways. Under other temperature and pressure conditions, methane or liquid nitrogen are also possibilities.
An oxygen-rich atmosphere may be essential for complex life. Respiration releases more energy than any other reduction-oxidation process (bar the reduction of fluorine or chlorine, which are too reactive to accumulate in an atmosphere). Therefore it is possibly the only way complex life could support its huge power demands.
Life on earth is carbon based. It forms the backbone of all the key molecules, like DNA, amino-acids and sugars. What a biochemistry based on some other molecule would be like, scientists ‘cannot even begin to guess’. Silicon has been suggested because it’s close to carbon on the periodic table and can form four bonds at a time in the same useful way carbon can. However, carbon polymers can be oxidised, such as during respiration, to release carbon dioxide. If silicon was switched in the end product would be silicon dioxide- sand. That would be difficult for life to process. Also, carbon is rife in the galaxy.
Designing tests to identify exotic metabolic systems like those is not possible because scientists have no idea what it would be like or how it would work. So all they can do is ‘follow the water’. Their reasonable hope is to find boring bacterial life this way. It is known that bacteria exist on earth in conditions that match those on other spots in the solar system.
There are only a few feasible ways to solve particular survival problems. In terms of sensing light, eyes have independently evolved on earth many times. Sight would therefore be likely on aliens.
Complex alien life would be subject to many of the same physical laws as here. A reasonable guess can made about what it would look like given gravitational, temperature, or other conditions. If it has evolved to swim through liquid for instance, it would need to have a tapered smooth skinned body.
Intelligent complex life would have to be land-based. Building, handling tools and exploiting fire have been necessary in the development of technology/intelligence.