The fine-tuning of the universe for life

March 31, 2022

The fine-tuning of the universe for life

Luke Barnes

Whether or not there is life on planets elsewhere in our universe, there certainly is on Earth! But how likely is it that a universe like ours would generate life? Against considerable odds, Luke Barnes survived childhood to crunch the numbers for us.


As kids, my siblings and I thought we’d cracked the secret of flight. The key, we determined, is a good launch. An early test flight of our prototype—a cardboard box, pushed off a table—had been a one-way ticket to the floor. But the principle was sound. If we could just get our cardboard box up onto the roof, the sky was ours. Tragically, our parents grounded this record-breaking endeavour before it became an arm-breaking endeavour. We turned to a more achievable project: big plastic bag = parachute?

Just because something is familiar, doesn’t make it easy. Birds can fly, but that doesn’t mean that a cardboard box can. Face-plant into the floor a few times, and you’ll stop taking birds for granted.

In this article, I want to point you to a familiar fact, and ask whether we’re taking it for granted. Are we confusing the familiar with the easy?

The fact is this: our universe contains physical life forms.

Our story comes in three parts. Firstly, we consider the wonders of the natural world. Secondly, a variety of thinkers use the authority of science to claim that—actually, really, deep-down—nature is accidental, pointless, mechanical, and mindless. Finally, some actual, real, deep-down science has a surprise for us.

First impressions: ‘Something natural and beautiful’

Nature is amazing. A few minutes spent watching slow-motion footage of a hummingbird will establish this point, if it was ever in doubt. Aristotle wrote memorably of his wonder at the natural world in a passage known as the ‘Invitation to Biology’,

There is something awesome in all natural things. … One should approach research on animals of whatever type without hesitation. For inherent in each of them there is something natural and beautiful. Nothing is accidental in the works of nature: everything is, absolutely, for the sake of something else. The purpose for which each has come together, or come into being, deserves its place among what is beautiful.[1]

As Aristotle says, we see that nature fits together. Experiences of beauty, order and ingenuity in nature reassure us that we can thrive here. Nature makes a place for us.[2] We perceive what philosopher Stephen C. Evans calls beneficial order.[3] This goes some way to explaining why it is an almost universal belief amongst human beings across all cultures and times that intelligence and purpose lie behind the wonders of the natural world. We can call this our design intuition.

But first impressions can be mistaken. What happens to our design intuition as science looks deeper into the inner workings of the universe?

Second thoughts: The accidental universe

We are just ‘accidental collocations of atoms’, wrote Bertrand Russell in 1903. The argument seems to go like this. Humans once thought that nature was pushed and pulled by gods, whose actions explained both the regularity (sunrise/sunset) and unpredictability (sunshine/thunderstorm) of the world around us. If there were no gods, then why is all this stuff arranged just so, and why does it keep moving and changing?

However, the argument continues, we discovered that the real mover and shaker of the natural world is, in fact, nature herself. Water and air and heat can make a thunderstorm all on their own. Thor need not apply; the position is taken. Purposes and designers are unnecessary, because mere mechanism will do the job. The more science discovers, the fewer gods we need. Our desire for explanation should lead us deeper into the workings of nature herself, not beyond or outside of nature. If the natural world inspires awe, wonder or gratitude in you, direct those feelings back to nature herself.


It is not always noticed that this argument has some small print, some terms and conditions. Yes, science leads us deeper into the workings of nature. The world is composed of space and time, fundamental particles, and quantum fields. In short, the stuff of physics. So, if you’re hoping that the progress of science erodes and ultimately dissolves the design intuition, the stuff of physics had better not invoke this same intuition. Richard Dawkins sees this quite clearly in The Blind Watchmaker:

Physics is the study of simple things that do not tempt us to invoke design … [T]he only watchmaker in nature is the blind forces of physics. … [From the point of view of] a physical scientist, the Creator could be infinitely lazy. … I am a biologist. I take the facts of physics, the facts of the world of simplicity, for granted.[4]

Of course, it’s fine to take physics for granted when doing biology. But Dawkins is doing more than this. He’s taking it for granted that physics won’t tempt us to invoke design. Is that true? Should we assume that there is nothing about the fundamental constituents of the universe that appeals to our design intuition?

What if, down in the small print of physics, things didn’t look so blind?

The third degree: Asking deeper questions

A common sense interpretation of the facts suggests that a superintellect has monkeyed with physics … and that there are no blind forces worth speaking about in nature.[5]

How did Fred Hoyle, Cambridge astrophysicist and atheist, come to this conclusion? What would it look like to see design in the fundamental laws of physics?

In fact, Dawkins provides us with a method. What is it about life that invokes the design intuition? Why think that life needs an explanation? Because, says Dawkins,

You may throw cells together at random, over and over again for a billion years, and not once will you get a conglomeration that flies or swims or burrows or runs, or does anything, even badly, that could remotely be construed as working to keep itself alive.[6]

Note the principle: of all the possible arrangements of cells, an extremely small proportion are ‘good for something’—in this case, will do something alive (or alive–ish). Thus, living arrangements of cells need an explanation. Darwin provides such an explanation, says Dawkins, as long as we can take physics for granted.

We can apply this principle to physics. Rather than imagining throwing cells together, we imagine throwing a universe and its physical laws together at random. Modern physics offers us a remarkably robust way to perform this thought experiment. In the deepest laws of nature that we know (which we can call the Standard Models), there are a set of numbers called the fundamental constants. They represent features of our universe that we can measure but not predict. For example, you may remember the electron from highschool science: it’s the particle that orbits in atoms. We can measure the mass of an electron: about a thousandth of a trillionth of a trillionth of a gram. But we have to put it into our equations; we can’t get it out of those equations.

Thirty-one of these constants appear in the Standard Models, putting a number on quantities such as the masses of fundamental particles, the strengths of fundamental forces, and the structure and contents of the universe as a whole. With these numbers in hand, the Standard Models are remarkably successful in predicting a wide range of observations of the universe.

What if these constants had been different? What if we could make a universe with heavier electrons, or stronger gravity, or more matter packed in? This would be the physics equivalent of being able to ‘throw cells together at random’ to see if they fly. We could investigate a host of possible universes, to see what they can do.

This might seem like science fiction, but actually it’s just theoretical physics. Given a mathematical description of the laws of a universe, including its fundamental constants, it is my job as a theoretical physicist to work out the consequences of those laws. That’s what we do. We’re not looking for places where science fails, but asking deeper questions of the deepest laws that succeed in describing our universe.

If the design intuition dissolves in physics, we would expect the following. Life-supporting universes will be typical, even unremarkable. Most possible universes will be capable of producing complex structures. Their basic ingredients can and will be combined into a variety of arrangements, making it plausible that they are ‘good for something’, perhaps even something life-like, whatever your definition of life.

Going forth into the unknown: Exploring other universes

So, using our method, we ask: what’s a typical universe like? Answer: Almost always, deadly dull and good for nothing.

An illustration will help. There are three fundamental particles that constitute the matter we’re made of: the electron, the up quark and the down quark. (With up quarks and down quarks, you can make protons and neutrons.) Let’s call these the three Lego bricks. Each of the three Lego bricks has a mass, and in common with the electron mentioned previously, the quarks are extremely light. What if their masses had been different?

You might think that this would simply make a universe in which everything was heavier or lighter than our universe. But the effect of these constants is more pervasive than one might think. As Einstein famously taught us, energy equals mass times the speed of light squared, or more economically, E = mc2. Mass is a form of energy, and energy has a big say in what processes can and can’t happen in a universe. If a certain hypothetical process—like two particular particles forming a bond with each other—can’t balance its energy budget, then it won’t happen.

This is the key connection between stability and energy: if you want a certain configuration of matter to be stable, make sure it doesn’t have enough energy to pull itself apart. On the other hand, if you want to rearrange something, ensure there’s enough energy around to make it happen. In particular, if you want to make a system that can process information, you’ll need basic physical constituents that are both changeable and stable, depending on what the system needs.

This, it turns out, is not easy. Like some kids trying to fly a cardboard box off the roof, most universes face-plant. Looking at the range of possible values for the masses of the three Lego bricks,[7] we can focus on universes that pass two minimal tests: a) can fundamental particles bind together to make complex arrangements, without falling apart, and b) can gravity squeeze particles together, to make them bind?[8] If you choose the masses of the three Lego bricks at random, the chances of getting fundamental particles that can stick anything to anything are less than one in a million trillion trillion. That’s a number with more than 30 digits.[9]

Kids playing in cardboard box

In these face-planting universes, fundamental particles can combine into objects with a maximum size of two or three particles. (A grain of sand, by way of comparison, contains around a billion billion fundamental particles.) Anything larger would have enough energy to pull itself apart. Objects are inherently unstable. In Dawkins' words, they aren’t ‘good for anything’, especially compared to the astounding complexity of our Universe.

This phenomenon is called the fine-tuning of the universe for life. At the bottom of physics as we know it, we find numbers that describe our universe, which we can measure but not predict. For some of these numbers, the overwhelming majority of their possible values would result in a universe incapable of sustaining complexity. In short, if you throw a universe together at random, it won’t fly.

The fifth element: A classic case of fine-tuning

Until the 1990s, our universe was thought to be composed of four types of energy: ordinary matter (made from the three Lego bricks), light, dark matter, and neutrinos.[10] In 1998, two groups of cosmologists discovered evidence that there is a fifth form of energy in our universe. While the attractive pull of the other four forms of energy causes the expansion of the universe to slow down, this fifth form is responsible for causing the expansion of the Universe to speed up. Distant galaxies are not only moving away from us; they are moving faster today than they were yesterday. This fifth form of energy acts as a kind of antigravity. Given that we don’t know much else about it, cosmologists called it dark energy. As best we can tell, the amount of dark energy in our universe can be captured by one number, known as the cosmological constant.

If you’re brave enough to ask the question ‘what if we threw a universe together at random?’, then we should try spinning the cosmological constant dial, to see what happens. There is a minimum and maximum on the dial, encompassing the range of values for this number that the Standard Models can handle. What happens in between?

If we turn the dial too far clockwise (positive values), the universe has too much antigravity. It expands extremely quickly, pulling everything away from everything else. The universe dilutes into a thin hydrogen soup. Every fundamental particle in the universe is surrounded by a few squillion light-years of empty space. Even if matter was capable of forming life, it would never have the chance.

On the other hand, turn the cosmological constant dial too far anticlockwise (negative values), and the universe re-collapses very quickly. The expansion of the universe is halted, and turns into contraction. Everything collides with everything else at enormous temperatures, and the universe ends in a fiery crunch in a fraction of a second.

Compared to the full range of dial settings, the subset that gives the matter in the universe a chance of getting together into anything interesting is extraordinarily small: at most one chance in 1090. That’s a number with 91 digits. I’d love to give you some intuitive idea of the size of that number, but it is beyond astronomical.

Cases can be multiplied. The fundamental forces, which push and pull on the fundamental particles, must be not too weak and not too strong. Fred Hoyle, quoted above, was the first to work out that the carbon nucleus must have finely-tuned internal properties in order to be produced in stars. The early universe must be not too smooth and not too lumpy, not too dense and not too sparse. Neutrinos must be not too heavy and not too light. Our universe’s ability to make complex life forms requires a remarkable confluence of factors, making it a rare talent indeed. For more examples and links to the scientific literature, see Barnes (2019), and my 2016 book with Geraint Lewis.[11]

Note well: there is nothing mathematically wrong with these other, lifeless universes. Nothing in the equations tells us that they are inconsistent or illicit or forbidden. As a theoretical physicist, these other universes are wonderfully simple—much easier to analyse than ours! These other universes obey the same laws as ours, and have been analysed with the same mathematical and computational methods. Theoretical physics is more than capable of throwing together a universe at random. It was an unexpected and startling discovery that they don’t fly.


On the sixth day: Our place in the cosmos

Are we just ‘accidental collocations of atoms’, tossed to and fro by ‘blind’, mindless forces of nature? If we’re made of electrons, and electrons don’t have eyes and minds, then nature is blind and mindless. If nature conforms to patterns—in the form of mathematical laws and equations—that don’t mention minds, then those laws are mindless. If the laws act consistently, then nature is merely mechanical. If the laws of nature tell us that electrons merely react to the way the universe is, rather than planning for the future and seeking to fulfil a purpose, then nature is an accident.

If you can’t see the logical leaps here, consider some analogous cases. A sheet of steel can’t fly, so aeroplanes made of steel can’t fly. I can mathematically describe the Mona Lisa without mentioning Leonardo da Vinci, so no painter is required. Bob wakes up at 8:25am every morning and goes for a walk, so he must be a robot. My car doesn’t know or care what direction it travels in, so you can’t use it to purposefully go anywhere.

Nikita Khrushchev famously said of the first Russian in space: ‘Gagarin flew into space, but didn't see any god there.’ Perhaps he expected to see a towering, bearded figure looming in the depths of space, shuffling stars for fun and occasionally pulling galaxies from a top hat. Like the arguments above, this is looking for God in the wrong place. It’s looking for the Creator as if they were a mere creature. To quote C.S. Lewis,

Shakespeare is in one sense present at every moment in every play. But he is never present in the same way as Falstaff or Lady Macbeth. Nor is he diffused through the play like a gas. … If God does exist, He is related to the universe more as an author is related to a play than as one object in the universe is related to another.[12]

What would it look like if the Universe had a good and powerful Creator? We would expect the universe to be good for something. To do something that, perhaps, the typical, randomly-thrown-together universe wouldn’t do. Something with moral value. We might expect a universe in which finite creatures can live morally meaningful lives, consider right and wrong, be able to make real decisions with real consequences, and experience knowledge, beauty and love. To facilitate this, we would expect the natural world to display consistency, precision and rationality in its inner workings. We might even expect to be reminded of our own finitude by the rest of creation, to be ‘engulfed in the infinite immensity of spaces’ (Blaise Pascal), lest we imagine ourselves to be the centre of existence.

The design intuition was not touched by Darwin. The scientific status of Darwinian evolution is a distraction. If you are amazed by a hummingbird, then go and learn some theoretical physics: you’ll be amazed by the fundamental properties of our universe as well. The design goes all the way down.

Dr Luke A. Barnes is a lecturer in astrophysics at Western Sydney University, and the coauthor with Prof Geraint Lewis of A Fortunate Universe: Life in a Finely-Tuned Cosmos and The Cosmic Revolutionary's Handbook, both published by Cambridge University Press.



[1] Quoted in Armand Marie Leroi, The Lagoon: How Aristotle Invented Science (Bloomsbury, 2014), p10.

[2] Roger Scruton, Beauty: A Short Introduction (OUP, 2009), p66.

[3] Stephen C. Evans, Natural Signs and Knowledge of God: A New Look at Theistic Arguments (Oxford University Press, 2012), Chapter 4.

[4] Richard Dawkins, The Blind Watchmaker (Penguin Books, 1986), Chapter 1.

[5] Fred Hoyle, ‘The Universe: Past and Present Reflections’. Ann. Rev. Astron. Astrophys. Vol.20, 1982, pp1–36.

[6] Dawkins, Op.cit., p12.

[7] This range is not infinite. The Standard Models rely on both quantum mechanics and general relativity, and so cannot describe a single particle with a mass larger than the so-called Planck mass. This places an upper limit on how much we can change fundamental constants that are masses in the Standard Models. A lower limit is provided by zero—negative masses can’t be handled by the theory either. See Luke. A Barnes, ‘A Reasonable Little Question: A Formulation of the Fine-Tuning Argument’. Ergo, 2019, p6.

[8] An object that uses gravity to bind smaller arrangements of particles into larger ones is effectively a star. In our universe, it binds smaller nuclei like hydrogen into larger ones like carbon.

[9] The justification of a number like this requires some careful footwork in probability theory. The technical details can be found in Barnes (2019).

[10] We don’t have space here to delve into the joys of dark matter and neutrinos, unfortunately. See Luke A. Barnes and Geraint F. Lewis, The Cosmic Revolutionary's Handbook: (Or: How to Beat the Big Bang) (CUP, 2020).

[11] Geraint F. Lewis and Luke A. Barnes, A Fortunate Universe: Life in a Finely Tuned Cosmos (CUP, 2016).

[12] C.S. Lewis, ‘The Seeing Eye’. Christian Reflections, ed. Walter Hooper (Eerdmans, 1995), pp167-169, 171.

Leave a comment

Comments will be approved before showing up.