Life, the Universe and Everything (Part 2)

Part 2

This is the second in a series of essays exploring a chain of questions about complexity, life, consciousness, intelligence, and ethics. Together, they form a rough map of the journey, hopefully with not too many imaginary dragons along the way.

In the last essay, we argued that complexity is fundamental, and that it compounds naturally. Simple systems combine into more complicated structures, and those structures interact with other structures. Some arrangements vanish almost immediately. Others persist, because the properties of their parts make some patterns more likely than others. Ordered complexity does not require intention. It can arise naturally because atoms have specific properties, molecules take specific shapes, and local environments constrain what can happen.

If ordered complexity can arise naturally, then life may perhaps be understood as a later threshold in the same story. Even when the necessary conditions are there, the transition to life may be difficult and possibly quite rare. But still, it is a threshold inside nature, grounded in physics and chemistry.

Nature has had billions of years to explore these possibilities, but we have not yet demonstrated in controlled laboratory conditions exactly how non-living chemistry can give rise to life. What experiments have shown is that many of the ingredients associated with life can arise through natural processes. Amino acids and organic molecules, as well as sugars, fatty acids, nucleobases, and other useful building blocks, can appear under plausible conditions. We also know that some of these materials have also been found in meteorites and interstellar environments, so we know that the raw materials of life are not something completely exotic.

The laws of physics and chemistry, as far as we can tell, apply throughout the universe. Reactions between chemical elements, when subjected to similar conditions, follow the same set of rules everywhere we can test. Stars forge heavier elements inside their cores and stellar winds and supernovae distribute them in the surrounding space. Planets, moons, comets, asteroids, ice, dust, form during the same star-formation processes and provide the many environments in which chemistry can unfold.

Every living system must process energy in some form, because maintaining order requires work. Stars hosting planetary systems provide these planets with usable energy for billions of years. But direct sunlight is not the only possible source of energy that life can tap. Hydrothermal vents, tidal heating, radioactive decay, and chemical gradients may also provide usable energy in the right environments.

So if life requires ordered chemistry, usable energy, and suitable environments, then it would be reasonable to assume that the Earth is probably not unique in satisfying the basic conditions. The pertinent question is then how often do those ingredients arrange themselves into systems that preserve and reproduce their own organization? Carbon and water seem to be extremely important here.

Life, at least on Earth, and possibly elsewhere, is built on complicated carbon scaffolding and uses water as its solvent. That does not prove that all life everywhere must do the same, but it gives us a sober starting point, because carbon is extremely flexible chemically. It forms strong bonds with many atoms, including with itself, and can form long chains, rings, branches, and very large molecules that are stable enough to persist while remaining active enough to participate in complex chemistry. Carbon is so fundamentally important to life as we know it that it even has its own branch of chemistry, organic chemistry.

Silicon is sometimes proposed as an alternative because it sits below carbon in the periodic table and shares some bonding behaviour. The problem is that silicon is not nearly as chemically flexible as carbon. In the presence of oxygen, it tends to form silicon dioxide, which is extremely stable, and can form various minerals and quartz, which is great if one wants nice rocks, but it is far less promising if one wants flexible molecular machinery. But there will be more to say about silicon later. For now, the important things to take away here, are that there is far more Carbon than Silicon in the Universe and that, when it comes to forming complex scaffolding structures, Carbon beats every other element, including Silicon, hands down.

Biologists also insist on the role of liquid water, as a powerful solvent, which allows molecules to dissolve, move, meet, react, separate, fold, and recombine. Water can remain liquid across a specific range of conditions and one of its very useful properties is that it expands when it freezes. This means that when an ice layer forms, it can insulate and preserve liquid water below it.

There may be other solvents that can perform similar roles. Methane is discussed in relation to very cold worlds such as Titan, but colder chemistry tends to be slower, and we have not yet found any life that does not rely on carbon and water. So, for now, carbon and water are the best game in town. They are simply extremely good at the job.

Still, a chemical soup of complex structures, however promising, remains a soup until some deeper organization arises. The crucial shift comes when chemistry begins to preserve structure through time. A living system carries something forward: it maintains a boundary, stores information, regulates internal processes and uses energy to repair and rebuild. Its variations become exposed to selection, with earlier arrangements influencing later arrangements. Some patterns make successor patterns more likely, and some variants persist better than others under local conditions. The system becomes a lineage.

Schrödinger’s old question, “What is life?” helped move the discussion away from vague appeals to a mysterious life force and toward physics, chemistry, order, and information.

Once stored information enters the loop, chemistry can preserve instructions that influence future structure.

Whatever awkward boundary cases exist, the cell, at least here on Earth, is the first clear unit where all the relevant processes come together. It has a boundary and can process energy. It stores information and uses it to build and repair itself. It maintains internal conditions and can respond to its environment. And it can reproduce, belonging to a lineage shaped by variation and selection. The cell is a tiny chemical reactor with “memory”.

Once reproduction, variation, and inheritance exist, evolution enters the story. Evolution explores what is possible under local conditions. Sometimes lineages gradually drift and sometimes they remain stable for very long periods. Life evolves somewhere, under particular conditions, with particular materials and pressures. The laws of biology are constrained by the local environment.

Changes in the local conditions, or available materials, affect the possible forms that life can take. Life adapts to environments, but over time it can also alter them. Oxygen in the Earth’s atmosphere is largely a biological product, and its soil is full of life. Coral reefs are byproducts of life, and living forests shape local climates. Ecosystems become networks through which energy, matter, and information move. In that sense, life does not simply evolve within an environment, but it can become part of the environment’s machinery.

Now, we have to remember that we have only one clear example of life: that which exists on the Earth. And all known life on Earth appears to share a common origin; all Earth life belongs to one vast biological family tree. But we cannot infer from a single example how common life may be in the Universe, or what forms it may take.

It could be that life appears readily wherever conditions are suitable, and it may very well be the case that simple microbial life is abundantly scattered throughout the universe. Or it could be that the transition from chemistry to life is an extremely rare event. This may be especially true when discussing complex life. Long-lived complex organisms may require a chain of favourable conditions: the right kind of star, a stable orbit, liquid water, a suitable atmosphere, enough heavy elements, geological recycling, climate stability, shielding from destructive radiation, protection from excessive impacts, plate tectonics, a planetary magnetic field, and vast stretches of time without experiencing any catastrophic events. Conditions allow possibilities, they don’t guarantee outcomes. Habitable does not imply inhabited.

So there are at least a couple of questions we need to unpack here; How common is the transition from complex chemical structures to simple life? And once simple life is established and given enough time, how common is highly complex life?

It may turn out that microbial life may be very common in the universe, while complex animal life may be rarer. Or simple life may be uncommon, and technological intelligence extremely rare. But such deliberations belong to a later part of our journey.

We are well on the way to at least getting some real answers on the first question. The search for life elsewhere will probably begin indirectly. Of course we should not expect to see forests, animals, or cities on distant planets. This is impossible with current technology. If the first evidence comes from another world, it will likely be chemical: promising traces in an atmosphere, unusual combinations of gases, or signs that a planet is chemically out of balance in ways that are difficult to explain without life.

Detecting one type of biosignature molecule by itself will not prove much. Methane, for example, can have geological sources, and Oxygen can arise without any biology under some conditions. We will need patterns of evidence: multiple signals that fit together, a planetary environment where the interpretation makes sense, and alternative explanations ruled out as far as possible. The first convincing evidence could also come from closer to home, from Mars, Europa, Enceladus, Titan, or some other Solar System environment where chemistry has had time and shelter to become interesting.

So, where does all this leave us? A useful working definition might be this: Life is a self-maintaining form of organized complexity, sustained by energy flow, that stores heritable information and belongs to a lineage capable of adaptive evolution through variation, inheritance, and differential persistence.

This is a rough definition, but it maintains that life marks a real threshold. Before life, patterns may persist, but it is only with life that patterns begin to maintain themselves through time. Life interacts with its environment, responding to local conditions, moving toward some chemical gradients and away from others. It starts behaving as though some states are preferable to others, and optimizing for its own existence. Is that some kind of primitive awareness?

At what point can we start speaking about experience, and when does a complex living organism become a sentient life form?

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Further reading
Erwin Schrödinger’s “What Is Life?” for the classic question of how living order can be understood through physics, chemistry, and information; Jim Baggott’s “Origins” for a modern scientific account of the path from the Big Bang to life and consciousness; Lisa Kaltenegger’s “Alien Earths” for habitable worlds, biosignatures, and the search for life beyond Earth.

Related lighter and fun fiction
Olaf Stapledon’s Last and First Men imagines the long evolution of life, humanity, and successor species across deep time; Isaac Asimov’s fiction repeatedly explores life, intelligence, robotics, and civilization through clean thought experiments; Ursula K. Le Guin’s novels are excellent companions for thinking about life, culture, difference, ecology, and moral imagination.

Life, the Universe and Everything (Part 1)

This is the first in a series of essays exploring a chain of questions about complexity, life, consciousness, intelligence, and ethics. Together, they form a rough map of the journey, hopefully with not too many imaginary dragons along the way.

Part 1

What is life, how does it come about in the Universe, how rare is it? How should we think about the value of life, from a humble bacterium to a sperm whale? Is there some useful framework which could help us investigate this question soberly, unfettered from religious or ideological doctrines? In order to start exploring these questions, let’s begin with a simple but fundamental concept: complexity.

Consider a crystal. It is a conglomeration of atoms naturally arranged in a well-defined pattern. The pattern determines its form and rigidity, but a crystal is a static arrangement, it does not move, self-regulate, repair itself, adapt, or respond to the world except through ordinary physical interaction. The amount of information we need to communicate precisely what a crystal is can be simplified, because of these patterns.

Smoke, on the other hand, moves and changes its shape constantly. Smoke is also physical matter, made up of large numbers of particles that interact with each other, but here the particles are not arranged in well-defined patterns. They move around, collide, swirl, and spread. If we tried to describe all that microscopic activity in full detail, the description would be enormous. It would require that we track each individual particle and its interactions with surrounding particles. Smoke is hard to describe precisely, beyond some general statistical properties.

Considering these two simple examples, we can start to see why information matters when we talk about complexity.

But what kind of information is useful, and in what sense? A quick distinction may help. Data are recorded differences: positions, temperatures, symbols, measurements. Information is drawing inferences from data that reduces uncertainty in some context. Organized information is information embedded in relationships that produce stable effects. The last of these is the one that matters most here.

The crystal contains information in its structure, because the arrangement of its atoms reveals something fundamental about the rest of it. Describing the pattern compactifies the description. One no longer needs to describe exactly what each atom is doing, we describe the pattern without loss of information. Of course smoke contains information too, in a statistical sense. But that information is mostly not organized into stable patterns. It is hard to summarize because of its inherent messiness.

So complexity is not just about how much information is needed to describe something. There is something relevant about the nature of this information itself. What part of it is preserved, structured? Does local information carry over to other parts of the system in ways that are reproducible? Does it generate patterns that can persist, change in some predictable fashion, or be transmitted in some way or form? Or is the information indistinguishable from random noise?

Entropy measures the degree of disorder of a system. In information theory, it is more precise to think of it as a measure of uncertainty. Smoke for example, has high entropy because it is highly disorganized and we need excessive amounts of information to describe it precisely. It is not easily reducible. A random signal has high entropy because it is hard to predict. A regularly repeated signal has lower entropy because it is easier to predict. Noise can reveal broad statistical properties and temporary local patterns, but not patterns that persist, regulate, reproduce, or compound.

So the important question to ask is whether the information content is organized in some form. Does it carry patterns? Does the ordered structure regulate a process? Can it respond to changes without dissolving into noise? This is where complexity starts to become interesting, when it becomes organized and persistent.

Ok, but organized how?

A large pile of bricks and a house both have structure, but it is not organized in the same way. In the pile, the bricks are simply there, ordered or disordered. In the house, the position of each part relates to the function of the whole. Walls carry weight, doors allow passage without compromising the structure, windows let in light, and so on. The ordered complexity of the arrangement is necessary because each of the parts constrains and supports each other. All together, they serve some common function: to provide humans with a living space. This is artificial organization of course, but natural systems can also naturally develop ordered patterns that serve different functions.

A whirlpool, or a hurricane, also has some kind of organization that makes it more interesting than smoke. It can maintain an identifiable structure for some time. Energy flowing through its structure is one of the ways information propagates across the system. But these structures arise only under particular conditions. Remove those conditions, and the pattern quickly disappears.

So persistence of structures seems relevant when we are talking about ordered complexity, but persistence of ordered complexity alone is not a guarantee of compounding higher degrees of complexity. A rock can persist for a very long time, but its complex structure is not particularly exciting (unless you are a geologist, in which case, fair enough).

If we want to understand how organized complexity starts moving toward life, something more than persistence is required. A stable, reproducible pattern is needed, but additional activity is also necessary. Certain sufficiently complex patterns perform functions.

A flame maintains itself while fuel and oxygen are available. It replicates under the right conditions and converts energy. But it does not store information, does not alter its structure across generations, or build internal machinery to regulate itself. It operates in a limited fashion until the underlying conditions fail.

But there are also patterns that can preserve some part of their own organization across time. It happens all the time in chemical reactions across the universe, and one chemical element, Carbon, is exceptionally good at generating large complex structures by repeatedly bonding with itself.

Complex organized chemical structures gradually interacted in ways that produced more complex arrangements. They became larger organized structures with multiple components. Most of these arrangements formed, drifted, broke apart, or dissolved back into the chemical background, and nothing lasting came out of them. Remnants of such processes are in the dust and gas in the interstellar medium.

But there are places in the universe with abundant available energy and with very rich and diverse types of highly organized building blocks. And a tiny fraction of these building blocks randomly arranged themselves in patterns that began to chemically interact with their environment in more complex ways. Interactions between complex systems began to become complex themselves. Additional complexity compounds. Once a system has more parts interacting in more ways, it gains new degrees of freedom. More things can happen.

Chemistry determines what types of different complex molecules interact, and how, under local constraints. Some arrangements are more stable than others. Certain arrangements make other arrangements more likely. The degree of randomness is constrained because of energy conditions, molecular shapes, charges, relative concentrations, surface, temperature and pressure conditions, which all restrict what processes can take place. The possible combinations are vast, but not arbitrary.

If everything disperses immediately, the system has no local history. Useful products will drift away and reaction networks break apart. Locality means that the reactions take place in some kind of setting where their products remain near each other. This could take the form of a membrane, a droplet, a mineral pore, an ice pocket, or some other structure that preserves locality. The system needs enough separation from its surroundings for its internal state to matter. This sets up feedback loops inside that environment. Products accumulate, some reactions may become easier, structures can stabilize other structures, and some arrangements last longer, while others collapse.

Once variation exists, some versions persist better than others under those particular conditions. Certain patterns persist more efficiently and become more common. The loop now includes energy flow, locality, self-maintenance, information storage, imperfect copying and selection. The underlying system begins to participate in its own persistence.

The whole process acts as a filter. The pattern becomes part of a process that preserves and reproduces structure. Ordered complexity and information are no longer merely present in the arrangement. They begin to play a role inside the arrangement. This is the first major threshold.

Ordered complexity becomes the foundation of structures that persist, interact, regulate, and help generate more structure. The road toward highly complex systems, and perhaps toward very simple life, starts to barely become visible, though by no means inevitable. Under the right conditions, matter can organize itself into patterns that participate in their own continuation.

So the natural next question is this: at what point do some complex organized patterns become identifiable as life?

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Further reading
If you want to dig deeper, here are some recommendations that explore these ideas: James Gleick’s Chaos for how simple rules can produce complex and unpredictable behaviour; Philip Ball’s Patterns in Nature for the way natural forms and structures arise without design; and Max Tegmark’s Our Mathematical Universe for thinking about reality as mathematical structure and pattern.

Related lighter and fun fiction
Olaf Stapledon’s Star Maker approaches cosmic order, life, mind, and civilization on the largest possible scale; Arthur C. Clarke’s 2001: A Space Odyssey explores intelligence, evolution, tools, and encounters with higher-order mystery; and Iain M. Banks’ Excession imagines advanced minds confronting something beyond their own frame of understanding.

Κλιματική αλλαγή (ξανά)

 Πριν από σχεδόν δέκα χρόνια είχα γράψει ένα μικρό κείμενο για την κλιματική αλλαγή, επειδή είχα απηυδήσει να διαβάζω διάφορες ανοησίες στα ελληνικά social media. Δέκα χρόνια μετά διαβάζουμε ακόμη τις ίδιες σαχλαμάρες.

Μια μπούρδα ολκής είναι το επιχείρημα «Το κλίμα πάντα άλλαζε.»

Ναί, και οι άνθρωποι πάντα πέθαιναν, αλλά αν βρεις κάποιον με μια χαντζάρα στην πλάτη δεν λες, ναί μωρέ,  «οι άνθρωποι πάντα πέθαιναν». Το ξέρουμε ότι το κλίμα της Γης έχει αλλάξει στο παρελθόν. Οι αλλαγές αυτές είναι γενικά σταδιακές και παίρνουν εκατομμύρια χρόνια. Το ερώτημά μας είναι τι προκαλεί τη σημερινή, ραγδαία εξελισσόμενη θέρμανση του πλανήτη τα τελευταία περίπου 100 χρόνια. Κι εδώ επίσης ξέρουμε την απάντηση.

Δεν υπάρχει ουδεμία αμφιβολία οτι τα κύρια αίτια είναι η ανθρώπινη δραστηριότητα, κυρίως η καύση ορυκτών καυσίμων, η αύξηση των αερίων του θερμοκηπίου και οι αλλαγές στη χρήση γης. Δεν είναι πολιτικό το θέμα. Είναι αυστηρά επιστημονικό και στηρίζεται σε τεράστιο όγκο δεδομένων. Όχι επειδή το λέω εγώ, ή κάποιος τυχάρπαστος σε ένα πάνελ. Δεν είναι κάποια «ατζέντα». Είναι το συμπέρασμα πολλών δεκαετιών μετρήσεων, φυσικής, μοντέλων, δορυφορικών παρατηρήσεων, παλαιοκλιματικών δεδομένων, ισοτοπικών ενδείξεων, μετρήσεων CO₂, ενεργειακού ισοζυγίου και ατμοσφαιρικής φυσικής. Από επιστημονικής άποψης, είναι λυμένο πρόβλημα. Οι πολιτικές προεκτάσεις είναι άλλο θέμα. Πρώτα αναγνωρίζουμε πώς έχει πραγματικά η κατάσταση, και μετά συζητάμε ώς κοινωνίες τί μπορούμε να κάνουμε. Δεν χώνουμε το κεφάλι στην άμμο και τραγουδάμε λαλαλά.

Κάποιοι προσπαθούν να θολώσουν τα νερά γιατί είτε δεν καταλαβαίνουν πώς να διαβάσουν τις μετρήσεις, είτε γιατί πιστεύουν σε θεωρίες συνωμοσίας, είτε γιατί έχουν κάτι να κερδίσουν, είτε γιατί δεν πιστεύουν ότι μπορούμε να κάνουμε τίποτα, είτε γιατί αμφισβητούν κάποια από τα δεδομένα, πάντα επιλεκτικά.  Αυτό λέγεται cherry-picking. Παίρνουν δηλαδή μία συγκεκριμένη πηγή, έναν επιστήμονα, ένα γράφημα χωρίς πλαίσιο, ή μία περίοδο δέκα ετών που τους βολεύει, και τα παρουσιάζουν ως δήθεν αντίβαρο απέναντι σε ολόκληρο το σώμα της επιστημονικής γνώσης. Παιδιά, αυτό δεν είναι σκεπτικισμός. Είναι επιλεκτική άγνοια.

Ο πραγματικός σκεπτικισμός κοιτάζει όλα τα δεδομένα. Ρωτά αν η υπόθεση εξηγεί το σύνολο των παρατηρήσεων. Αντέχει στον έλεγχο; Κάνει προβλέψεις; Συμφωνεί με τη φυσική που γνωρίζουμε; Εξηγεί γιατί θερμαίνεται η τροπόσφαιρα και ψύχεται η στρατόσφαιρα; Εξηγεί την άνοδο της θερμοκρασίας των ωκεανών; Εξηγεί την αύξηση της συγκέντρωσης CO₂ και την ισοτοπική του υπογραφή; Εξηγεί γιατί οι φυσικοί παράγοντες, όπως ο Ήλιος ή τα ηφαίστεια, δεν αρκούν για να εξηγήσουν τη σημερινή θέρμανση; Η άρνηση δεν τα εξηγεί αυτά. Απλώς αναποδογυρίζει τη σκακιέρα και βγάζει γλώσσα. Και, ειλικρινά, έχει αρχίσει να γίνεται κουραστικό.

Δεν είμαστε στο 1990. Δεν είμαστε κάν στην αρχή της συζήτησης. Δεν περιμένουμε ακόμη να βεβαιωθούμε αν είναι πραγματικά ανθρωπογενής ή όχι. Η επιστημονική συζήτηση σήμερα αφορά τις λεπτομέρειες, τα εύρη αβεβαιότητας,τις  περιφερειακές επιπτώσεις, την ταχύτητα των αλλαγών, διάφορα σενάρια εκπομπών, πιθανές προσαρμογές, πιθανές τεχνολογικές λύσεις, πολιτικές αποφάσεις και κόστος.

Ανεξάρτητες μελέτες, με διαφορετικές μεθόδους, διαφορετικά δεδομένα, διαφορετικά μοντέλα και διαφορετικές αρχικές υποθέσεις, συγκλίνουν στο ίδιο συμπέρασμα επειδή αυτό εξηγεί καλύτερα την πραγματικότητα. Και όταν τα δεδομένα αλλάζουν, η επιστήμη διορθώνεται. Αυτό είναι το ακριβώς αντίθετο της ιδεολογικής τύφλωσης.

Η ειρωνεία είναι ότι πολλοί από αυτούς που φωνάζουν ότι «η επιστήμη πρέπει να αμφισβητείται» δεν αμφισβητούν τίποτα από αυτά που τους βολεύουν. Αμφισβητούν μόνο το συμπέρασμα που δεν τους αρέσει. Παιδιά, σας έχω νέα. Δεν είναι ελεύθερη σκέψη να αγνοείς συστηματικά τα δεδομένα, ούτε είναι θαρραλέο να προωθείς μπούρδες, ούτε είναι έξυπνο να ψάχνεις στο διαδίκτυο μέχρι να βρεις έναν άνθρωπο, κάπου, που λέει αυτό που ήθελες να ακούσεις εξαρχής.

Σας ενοχλεί που το θέμα έχει πάρει πολιτικές διαστάσεις; Σας τη δίνουν μερικοί ακτιβιστές και το γενικότερο τοξικό κλίμα του διαλόγου; Πάρτε αριθμό και μπείτε στη σειρά. Αλλά το θέμα δεν είναι πολιτικό, είναι επιστημονικό. 

Με αυτό ώς δεδομένο, μπορούμε μετά να συζητήσουμε για πολιτικές λύσεις. Να συμφωνήσουμε ή να διαφωνήσουμε για πυρηνική ενέργεια, ΑΠΕ, φόρους άνθρακα, τεχνολογική καινοτομία, προσαρμογή, κόστος, δικαιοσύνη, ανάπτυξη, γεωπολιτική. Αλλά το να επιστρέφουμε κάθε τόσο στο «το κλίμα πάντα άλλαζε» είναι σαν να επιστρέφουμε συνεχώς στην ιδέα οτι η Γή είναι επίπεδη, και είναι σπατάλη χρόνου και δημιουργικής ενέργειας. Άντε, γιατί κάποια στιγμή πρέπει να τελειώνουμε με τα προσχήματα.

Η ανθρωπογενής κλιματική αλλαγή είναι πραγματική. Η βασική φυσική είναι γνωστή. Τα δεδομένα είναι συντριπτικά. Η επιστημονική συναίνεση είναι εξαιρετικά ισχυρή. Και η επιλεκτική χρήση πηγών για να συντηρείται η άρνηση είναι αισχρή παραπληροφόρηση.

Στην τελική, αν ακόμα έχετε αμφιβολίες, ρωτήστε κι εμάς που ξημεροβραδιάζουμε μέσα στην επιστημονική βιβλιογραφία να μάθετε περισσότερα. Εδώ είμαστε.

Πηγές:

1. Cook, J. et al. (2013), “Quantifying the consensus on anthropogenic global warming in the scientific literature”, Environmental Research Letters, 8, 024024.
   Μελέτη 11.944 επιστημονικών περιλήψεων για την κλιματική αλλαγή. Από τις εργασίες που εξέφραζαν θέση για την αιτία της υπερθέρμανσης, το 97,1% υποστήριζε την ανθρωπογενή εξήγηση.
   https://doi.org/10.1088/1748-9326/8/2/024024
2. Cook, J. et al. (2016), “Consensus on consensus: a synthesis of consensus estimates on human-caused global warming”, Environmental Research Letters, 11, 048002.
   Σύνθεση έξι ανεξάρτητων μελετών για την επιστημονική συναίνεση. Το συμπέρασμα είναι ότι 90-100% των ενεργών επιστημόνων του κλίματος συμφωνούν πως οι άνθρωποι προκαλούν τη σημερινή υπερθέρμανση.
   https://doi.org/10.1088/1748-9326/11/4/048002
3. Lynas, M., Houlton, B. Z. & Perry, S. (2021), “Greater than 99% consensus on human caused climate change in the peer-reviewed scientific literature”, Environmental Research Letters, 16, 114005.
   Επικαιροποιημένη ανάλυση 88.125 επιστημονικών εργασιών από το 2012 έως το 2020. Το συμπέρασμα είναι ότι η συναίνεση στην επιστημονική βιβλιογραφία υπερβαίνει το 99%.
   https://doi.org/10.1088/1748-9326/ac2966

Western civilization is not rooted in Christian values

A common line I keep hearing from modern Christian conservatives is that “Western civilisation is rooted in Christian values.” Well, fine, yes. But also, no. Mostly, it’s complicated, which is what people who do bumper-sticker history tend to dismiss as mere details. So let’s go into the details. 

Christianity is certainly one of Europe’s important civilisational layers, especially in the medieval world. But “the West” most certainly did not begin with Christianity, nor can its foundations be reduced to it. 

Long before Christianity arrived in Europe, the Greeks and Romans had already built many of the foundations of Western thought: philosophy, logic, mathematics, law, political theory, republican ideas, drama, history, ethics (and not all of these are exclusively Western ideas). Plato, Aristotle, Epicurus, the Stoics, Cicero and others were part of the house well before Christianity moved in and started rearranging the furniture. 

Christianity itself emerged from Judaism inside the Greco-Roman world and absorbed and assimilated a great deal from that world. Medieval Christian thinkers and theologians leaned heavily on Greek metaphysics and Roman law. Ideas like natural law, logos, virtue ethics, rational inquiry and civic duty were not Christian inventions. Stoicism was a huge influence. 

Later, the Renaissance and the Enlightenment revived and reinterpreted many pre-Christian traditions, often in direct tension with Church authority. Lucretius and Epicurean thought are a useful example: materialist, empirical, suspicious of fear-driven religion, and focused on reducing suffering in this life rather than preparing for some deferred afterlife. 

In fact, modern Western thought draws from many different streams simultaneously: Athens, Rome, Jerusalem, Renaissance humanism, science, secular critique, classical republicanism, and yes, Christianity too. 

So I find the claim that Western civilisation is “rooted in Christian values” rather silly. Western civilisation is a layered, quarrelsome inheritance, full of argument, borrowing, rebellion and reinvention. It also absorbed ideas from other civilisations and influenced them in return. 

I think it is probably more helpful to think of it as a compost heap, rather than as a refined cathedral. As with most compost heaps, quite a lot grew out of it. Some of it quite good. Some of it rather nasty.