In order to know if life exists outside the Earth, we must deal with our own significance in the universe. Are we something unique or are we nothing special?
We all live on a small planet orbiting a middle-aged star that is one of an estimated 200 billion stars in the vast swirl of matter that makes up the Milky Way galaxy. Our galaxy is one of, presumably, several hundred billion similar structures in the observable universe, and its extent today in all directions from us is more than 270,000,000,000,000,000,000,000 (2.7 × 1023) miles.
By any paltry human standard, the universe is an enormous amount of matter and a gigantic amount of space. Our species was formed in an insignificant moment of colossal history, and it seems that there will be an even longer future with or without our participation.
Attempts to define our position, to establish our importance may seem like some kind of hypertrophied joke. We must be monstrously stupid if we imagine we can find any meaning for ourselves at all.
Yet we are trying to do just that, despite our apparent mediocrity, which became visible when the Renaissance scientist Nikola Kopernik, about 500 years ago, stopped considering the Earth as the center of the solar system. His idea has become one of the largest scientific discoveries over the past several hundred years, as well as an important indicator on our path to understanding the inner structure of the cosmos and the nature of the real world.
In our attempts to assess our worth, we are faced with a riddle: some discoveries and theories suggest that life may well be ordinary and ordinary, while others claim the opposite. How should we begin to piece together our knowledge of space - from bacteria to the Big Bang - to explain whether we are important or not? And as we learn more about our place in the universe, we are trying to understand what all this means for our attempts to find out if there are other living things in space? What will be our next steps in this direction?
What do we know
Promotional video:
In the 1600s, trader and scientist Antony van Leeuwenhoek, using his own hand-made microscopes, became the first person to see bacteria - a journey that took him into the alien world of the microcosm. This remarkable descent, this slide down the stairs of physical dimensions into the wildly growing world within us, was the first step towards understanding that the components of our body, our mass of molecular structures, exist at the very far end of the spectrum of the biological scale. I doubt that before Levenguk's amazing discovery, people had the opportunity to think about this fact, not on a superficial level, but on some other, deeper level.
Streptococcus pyogenes bacteria
There are organisms on Earth that are physically larger and more massive than we are - look at whales or trees. However, we are much closer to the upper end of the life scale than to the microscopic end. The smallest reproducing bacteria are hundreds of billions of times smaller than a meter, and the smallest viruses are still ten times smaller. The human body is about 10 or 100 million times larger than the simplest life we know.
Among warm-blooded terrestrial mammals, we are also among the large specimens, but not at the very top of the scale. At the opposite end are our smallest relatives, tiny shrews - very small creatures of wool and flesh weighing only two grams. They exist on the edge of the possible, and their bodies constantly lose heat, which they can hardly compensate with the help of abundant food.
However, most mammals are closer to their size than ours - especially when you consider that the average body weight of the mammalian population is 40 grams. Our sophisticated cell-based smart bodies are at the very top, and relatively few mammals are larger than us.
There is no doubt that we are on this very edge, on this border between the complex diversity of the biologically small and the limited capabilities of the biologically large. Now imagine our planetary system. Our star is not one of the most abundant types of stars (most of them are smaller in mass), our orbits are currently more rounded and more spaced from each other than in most other exoplanetary systems, and we do not have any super- Earth among our planetary neighbors.
This kind of world, several times larger than the Earth in mass, is represented in at least 60% of all systems, but in our solar system it is not. If you were the architect of planetary systems, then you would consider our design to be isolated, slightly different from the norm.
Some of these characteristics are based on the fact that our solar system has escaped a major dynamic reorganization that most other planetary systems have failed to do. This does not mean that we are assured of a quiet and peaceful future - the latest gravity simulations show that within a few hundred million years our system may be affected by a more chaotic period.
And in another five billion years, the sun may expand with the onset of a spasmodic aging period and significantly change the irradiation of the planets. All indicators indicate that we are now living in an intermediate or borderline time, in the transition period between stellar-planetary youth and the coming period of weakness.
Our relatively calm existence during this period, if we evaluate it retrospectively, is not surprising. As with other aspects of our situation, we live in a temperate place, not too warm and not too cold, chemically our environment is not too active and not too inert, it is not too volatile and not entirely devoid of change.
In addition, today it is obvious that this astrophysically calm neighborhood extends far beyond the boundaries of our galaxy. From the point of view of the universe as a whole, we exist in a period that is much older than the fast and violent period of a young, hot space. The process of making stars is slowing down everywhere. Other suns, other planets are forming at an average rate that is only 3% of what was in the period from 11 to 8 billion years ago.
These stars begin to slowly move through the universe. And, if we talk in large cosmological terms, it was only 6 or 5 billion years ago that our universe began to slow down after the Big Bang. Dark energy, born from the vacuum itself, accelerates the growth of space and helps suppress the development of larger cosmic structures. But this means that life is ultimately doomed in a separated future to dull isolation in an increasingly incomprehensible universe.
Put all these factors together, and then it becomes clear that our view of the inner and outer space is severely limited. This is a view from a narrow pole. In fact, our intuitive understanding of random events and our scientific development in the field of statistical inference, perhaps, would be different if there were other circumstances in the field of order or chaos, space and time.
And the very fact that we are too far away from any other life in space - to the point where we have not yet been able to capture any of its signs or encounter it - has a strong impact on the conclusions we can draw.
conclusions
We have ample evidence to support Copernicus's basic idea that we are nothing special. But at the same time, there are several characteristic features of our environment that indicate the opposite.
Some of these qualities have given rise to the so-called anthropic principle, according to which certain fundamental constants in nature appear to be "fine tuned", and thus the fundamental qualities of the universe are balanced near the boundaries that allow the earth and life on it to exist. If you go too far in either direction, then the nature of the cosmos can be completely different.
Change the relative strength of gravity slightly, and then stars will either not form at all and no heavy elements will arise, or huge stars will be created and then quickly disappear, leaving no traces, no descendants, no path to life. And if you change the electromagnetic forces, then the chemical bonds between atoms will be too weak or too strong to create a variety of molecular structures that allow such incredible complexity in space.
Spiral galaxy NGC 4258
What do we think about all these contradictions? In my opinion, the facts are pushing us towards a new scientific idea of our relative place in space, to parting with both Copernican principles and anthropic ideas, and I also think that moving in this direction, this new idea will become an independent principle. Perhaps we can call this new idea the cosmo-chaotic principle, the platform between order (the original meaning of the Greek word kosmos) and chaos.
Its essence lies in the fact that life, and, in particular, life on Earth, will always be in the place of contact or at the junction of zones determined by such characteristics as energy, location, scale, time, order and chaos. Factors such as stability or chaos of planetary orbits, or variations in climate and geophysics on the planet, are direct manifestations of these characteristics.
If you move too far from these boundaries, then the balance will shift towards an unfavorable state. Our life requires the right combination of ingredients, a mixture of calm and chaos - the right combination of yin and yang.
Approaching these boundaries makes such changes and variations possible, but one should not get too close so as not to constantly overwhelm the system itself. There are obvious parallels with the concept of a habitable zone (Goldilocks zone), according to which the temperature of the space environment for a planet around a star is in a narrow range of parameters.
Leaving aside the existence of life, the habitable zone can be much more dynamic - it does not have to be fixed in space and time. Rather, it is a constantly moving, wriggling and bending trajectory with many parameters - like the paths laid by the arms and legs of a dancer.
If the universal rule is that life can only exist under these conditions, then some intriguing possibilities arise regarding our importance in space. In contrast to Copernicus' stern ideas, which emphasize our mediocrity and therefore assume the presence of many similar conditions in space, the notion that life requires adjusting various and dynamic parameters reduces the number of options.
The possibilities for life resulting from this new approach are also different from anthropic ideas, which in their most radical part predict only one place for the formation of life in space and time in general. Instead, the new rule defines where life should arise, as well as the potential frequency with which it does so. The new rule clarifies the fundamental characteristics necessary for living within a possible space with many waltzing parameters - it indicates the fertile zones.
This kind of rule about life does not necessarily turn living beings into some special part of reality. Biology is probably the most complex physical phenomenon in our universe - or in any universe that obeys certain laws. But this, perhaps, is the extreme limit of a feature: an extremely complex natural structure that arises under the right conditions, on the border of order and chaos.
And this formulation of the concept of where exactly life fits into the larger scheme of nature leads directly to the solution of the riddle, in which there are convincing, but not definitive arguments that life should exist in abundance and that it is extremely rare.
Caleb Scharf
Caleb Scharf is director of the interdisciplinary Astrobiology Center at Columbia University; he is the author of Gravity's Engines: How Bubble-Blowing Black Holes Rule Galaxies, Stars, and Life in the Cosmos.