The Science of Can and Can’t

Description

A luminous guide to how the radical new science of counterfactuals can reveal that the scope of the universe is greater, and more beautiful, than we ever imagined

There is a vast class of things that science has so far almost entirely neglected. They are central to the understanding of physical reality both at an everyday level and at the level of the most fundamental phenomena in physics, yet have traditionally been assumed to be impossible to incorporate into fundamental scientific explanations. They are facts not about what is (the actual) but about what could be (counterfactuals).

According to physicist Chiara Marletto, laws about things being possible or impossible may generate an alternative way of providing explanations. This fascinating, far-reaching approach holds promise for revolutionizing the way fundamental physics is formulated and for providing essential tools to face existing technological challenges–from delivering the next generation of information-processing devices beyond the universal quantum computer to designing AIs. Each chapter in the book delineates how an existing vexed open problem in science can be solved by this radically different approach and it is augmented by short fictional stories that explicate the main point of the chapter. As Marletto demonstrates, contemplating what is possible can give us a more complete and hopeful picture of the physical world.Praise for The Science of Can and Can’t:

“Marletto’s call to probe counterfactuals is novel and interesting . . . Replete with stories from classical Greek mythology and examples of ideas drawn from biology and physics, The Science of Can and Can’t is worth delving into.” —Wall Street Journal

“[A] revolutionary recasting of physics . . . Marletto’s contributions to ‘constructor theory’ reconcile what we think of as physical laws with the open-ended possibilities thrown up by biology and information theory. It is a paradigm that, for all its rigor, re-enchants the world and enriches our place in it.” —New Scientist

“[A] cerebral yet intellectually satisfying journey with a simple description of the two kinds of counterfactuals in physics . . . Marletto’s style resembles a frank conversation with the reader. Sophisticated concepts in physics, like information and knowledge, are explained using clear analogies to everyday life.” —Booklist

“[A] lyrical yet complex debut . . . References to Greek mythology, Shakespeare, chess, and Legos add life to her survey . . . Marletto’s love of physics shines through . . . Those with an interest in physics will appreciate her passion and her provocative approach.” —Publishers Weekly

“[T[here’s plenty of food for thought for those interested in the processes of conceptual breakthrough [in The Science of Can and Can’t].” —Kirkus Reviews

“Marletto has a clear, sharp and imaginative style of explaining science . . . [The Science of Can and Can’t] will open the doors to a dazzling, deep set of new concepts and ideas that will change and affect deeply the way you look at the world. Let her story unfold. It will be an open-ended exploration of the endless possibilities that the laws of physics allow for.” —David Deutsch, author of The Beginning of Infinity

“Hugely ambitious, Chiara Marletto is the herald for a revolutionary new direction for physics. This book is essential reading for anyone concerned with the future of physics.” —Lee Smolin, author of Life of the Cosmos

“I enjoyed this book very much, not least because of the freshness of its approach to a subject that can easily become hard for the non-scientific mind to grasp. The theory of ‘can and can’t’ is an intriguing way of describing problems that are not only scientific (it describes very well what a storyteller does, for instance), and Marletto’s account of some things I thought I more or less understood (the nature of digital information, for one) illuminated them from an angle that showed them more clearly than I’d seen them before.” —Philip PullmanChiara Marletto is a research fellow at Wolfson College and the University of Oxford Department of Physics. Her main research focus is theoretical physics, but she enjoys dabbling in theoretical biology, epistemology, and Italian literature. This is her first book. 

1.

 

Such Stuff As Dreams Are Made On

 

Where I explain how to look at the laws of physics in a

far broader way, including counterfactuals (statements

about what transformations are possible or impossible);

and you become acquainted with knowledge-defined

objectively, via counterfactuals, as information that

is capable of perpetuating its own existence.

 

Most things in our universe are impermanent. Rocks are inexorably abraded away; the pages of books tear and turn yellow; living things-from bacteria, to elephants, to humans-age and die. Notable exceptions are the elementary constituents of matter-such as electrons, quarks, and other fundamental particles. While the systems they constitute do change, those elementary constituents stay unchanged.

 

Entirely responsible for both the permanence and the impermanence are the laws of physics. They put formidable constraints on everything in our universe: on all that has occurred so far and all that will occur in the future. The laws of physics decree how planets move in their orbits; they govern the expansion of the universe, the electric currents in our brains and in our computers; they also control the inner workings of a bacterium or a virus; the clouds in the sky; the waves in the ocean; the fluid, molten rock in the glowing interior of our planet. Their dominion extends even beyond what actually happens in the universe to encompass what can, and cannot, be made to happen. Whatever the laws of physics forbid cannot be brought about-no matter how hard one tries to realise it. No machine can be built that would cause a particle to go faster than the speed of light, for instance. Nor, as I have mentioned, could one build a perpetual motion machine, creating energy out of no energy-because the laws of physics say that the total energy of the universe is conserved.

 

The laws of physics are the primary explanation for that natural tendency for things to be impermanent. The reason for impermanence is that the laws of physics are not especially suited for preserving things other than elementary components. They apply to the primitive constituents of matter, without being specially crafted, or designed, to preserve certain special aggregates of them. Electrons and protons attract each other-it is a fundamental interaction; this simple fact is the foundation of the complex chemistry of our body, but no trace of that complexity is to be found in the laws of physics. Laws of physics, such as those of our universe, that are not specially designed, or tailored, to preserve anything in particular, aside from that elementary stuff, I shall call no-design laws. Under no-design laws, complex aggregates of atoms, such as rocks, are constantly modified by their interactions with their surroundings, causing continuous small changes in their structure.

 

From the point of view of preserving the structure, most of these interactions introduce errors, in the form of small glitches, causing any complex structure to be corrupted over time. Unless something intervenes to prevent and correct those errors, the structure will eventually fade away or collapse. The more complex and different from elementary stuff a system is, the harder it is to counteract errors and keep it in existence. Think of the ancient practice of preserving manuscripts by hand-copying them. The longer and more complex the manuscript, the higher the chance that some error may be performed while copying, and the harder it is for the scribe to counteract errors-for instance, by double-checking each word after having written it.

 

Given that the laws of physics are no-design, the capacity of a system to maintain itself in existence (in an otherwise changing environment) is a rare, noteworthy property in our universe. Because it is so important, I shall give it a name: resilience.

 

That resilience is hard to come by has long been considered a cruel fact of nature, about which many poets and writers have expressed their resigned disappointment. Here is a magisterial example from a speech by Prospero in Shakespeare’s Tempest:

 

Our revels now are ended. These our actors,

 

As I foretold you, were all spirits, and

 

Are melted into air, into thin air:

 

And like the baseless fabric of this vision,

 

The cloud-capp’d tow’rs, the gorgeous palaces,

 

The solemn temples, the great globe itself,

 

Yea, all which it inherit, shall dissolve,

 

And, like this insubstantial pageant faded,

 

Leave not a rack behind. We are such stuff

 

As dreams are made on; and our little life

 

Is rounded with a sleep.

 

Now, those lines have such a delightful form and rhythm that, on first reading, something important may go unnoticed. They present only a narrow, one-sided view of reality, which neglects fundamental facts about it. If we take these other facts into consideration, we see that Prospero’s pessimistic tone and conclusion are misplaced. But those facts are not immediately evident. In order to see them, we need to contemplate something more than what spontaneously happens in our universe (such as impermanence, occasional resilience, planets, and the cloud-capped towers of our cities). We shall have to consider what can, and cannot, be made to happen: the counterfactuals-which, too, as I said, are ultimately decided by the laws of physics.

 

The most important element that Prospero’s speech neglects is that even under no-design laws, resilience can be achieved. There is no guarantee that it shall be achieved, since the laws are not designed for that; but it can be achieved because the laws of physics do not forbid that. An immediate way to see this is to look around a bit more carefully than was possible in Shakespeare’s time. There are indeed entities that are resilient to some degree; even more importantly, some are more resilient than others. Some of them very much more. These are not, contrary to what proverbs and conventional wisdom might suggest, rocks and stones, but living entities.

 

Living things in general stand out as having a much greater aptitude to resilience than things like rocks. An animal that is injured can often repair itself, whereas a rock cannot; an individual animal will ultimately die, but its species may survive for much longer than a rock can.

 

Consider bacteria, for example. They have remained almost unchanged on Earth for more than three billion years (while also evolving!). More precisely, what has remained almost unchanged are some of the particular sequences of instructions that code for how to generate a bacterium out of elementary components, which are present in every bacterial cell: a recipe. That recipe is embodied in a DNA molecule, which is the core part of any cell. It is a string of chemicals, of four different kinds. The string works exactly like a long sequence of words composed of an alphabet of four letters: each word corresponds roughly to an instruction in the recipe. Groups of these elementary instructions are called ‘genes’ by biologists.

 

It is the particular structure, or pattern, of bacterial DNA that has remained almost the same over such a long time. In contrast, during the same period, the arrangement and structure of rocks on Earth have profoundly changed; entire continents have been rearranged by inner movements taking place underneath the Earth’s crust. Suppose some aliens had landed on Earth early in prehistory, collected DNA from certain organisms (say, blue-green algae), and had also taken a picture of our planet from space; and that they were to come back now to do the same. In the pictures of the planet, everything would have changed. The very arrangement of continents and oceans would be utterly different. But the structure of the DNA from those organisms would be almost unchanged. So, after all, certain things in our universe, like recipes encoded in DNA, can achieve a rather remarkable degree of resilience.

 

The other element that Prospero’s speech disregards is that living entities can operate on the environment, transform it, and (crucially) preserve the ability to do so again and again, thus leaving behind much more than ‘a rack’. The Earth still bears the signs of bacterial activity from a billion years ago (for instance, in the form of fossil carbon). Plants have caused a dramatic change in the composition of the atmosphere by releasing gaseous oxygen as a side effect of converting the sun’s light into chemical energy via photosynthesis. Humans, too, are capable of transforming the environment in a wide set of conditions. Contrary to Prospero’s view, palaces, temples, and cloud-capped towers can achieve resilience-because they are products of civilisation. Humans can restore them by following a blueprint-or rather, again, a recipe-of how they were initially built, guaranteeing that they will endure much longer than their constituent materials. In principle, a 3-D printer provided with such a recipe could reconstruct from scratch any ancient palace that happened to be completely destroyed.

 

The human life span may be still constrained, but technology has already extended it well beyond that of our ancestors. By changing the naturally occurring environment, human civilisation is tentatively improving and growing. We now have the knowledge to produce warm (or cooled) houses, powerful medications, efficient transport on Earth and even into space, and tools to save ourselves labour, to lengthen our lives and make them more enjoyable. We have majestic works of art and literature, music, and science. Those very words in Prospero’s speech are an example of our literary heritage, and they have therefore survived-together with countless other wondrous outputs of human intellectual activity. So, rather than fading away, this pageant we have set up, which sustains us, has been under way for centuries. The rest of life’s show on Earth has endured even longer, for billions of years.

 

Of course, the resilience of our civilisation is constantly threatened by severe problems, which crop up as we try to move forward. Some of them, such as global warming and fast-spreading pandemics, are in fact a by-product of the very progress I have described. These problems present considerable challenges and could easily wipe out several aspects of the progress we have made. But the point I would like to focus on here is this: it is possible to take steps to solve those issues, no matter how serious they appear; and the laws of physics do not forbid still greater improvement. They do not guarantee improvement or resolution, but nor do they forbid it: resilience and further progress, by addressing problems such as the climate crisis, are both possible. The laws of physics, expressed as counterfactuals, offer a chance for improvement. By contemplating what is possible in the universe, in addition to what happens, we have a much more complete picture of the physical world. Prospero’s gloomy conclusion is therefore partial and profoundly misguided. It was nothing more than an unreal nightmare.

 

These reflections suggest that the recipe in certain DNA patterns is much more resilient than stone; and that the elements of our civilisation for which there exists an analogous recipe, such as medicine, science, and literature, can be more resilient still. So, under no-design laws, a high degree of resilience seems to require there to be recipes of a particular kind. What kind? And what are such recipes made of, exactly?

 

The answer has to be constructed gradually and requires a digression about recipes. First, let’s understand how recipes can be created under no-design laws of physics. After all, as I said, the only things that these laws preserve ‘for free’ are certain elementary particles and chemicals; one therefore has to understand how those recipes can have come about at all, out of elementary things that know nothing about recipes of such complexity.

 

I shall start with the recipes coded in the pattern of living cells’ DNA. It is now well understood how those have come about. Darwin’s theory of evolution explains how living entities and their stupendous biological adaptations-such as the snout of a dog, the fins of a dolphin, or the wings of a bee-have come about in the absence of a designer, under no-design physical laws. Now, each biological adaptation of a given animal is coded for somewhere in the recipe embodied in the DNA of that animal. What Darwin’s theory tells us is how the recipes coding for complex biological adaptations can have come about without being explicitly designed. This will be key to understanding what the recipes are made of.

 

As is often the case with deep theories, grasping exactly what problem Darwin’s theory addresses requires some excavation. The problem was stated with great clarity by the theologian William Paley a few decades before Darwin’s breakthrough. Living things are so perfectly orchestrated that they seem to have been the output of an actual design process-such as that which produces a car in a factory-directed towards a purpose. They have the ‘appearance of design’, just like cars or smartphones or a watch. If you are walking along the beach and you suddenly see a watch on the ground, you may be guessing that some designer must have assembled it. But at the dawn of our planet’s history there was no designer, factory, or intentional design process that could create living things: only elementary components of matter, served in the form of an amorphous bubbling soup, and nothing more. So how can living entities, and the resilient recipes coding for the biological adaptations in their structure, have come about in the absence of a designer?

 

What Darwin discovered, and what Paley could not quite see, is that there is no need for any intentional design process: biological adaptations in animals can be created out of elementary components of matter, such as simple chemicals, via a nonpurposeful process called natural selection. That process needs only enough time and elementary resources, such as simple chemicals and so on. It is an undirected mechanism, and yet it can produce purposeful complexity, starting from scratch under laws of physics that are simple and no-design themselves.

 

There are two key concepts in Darwin’s powerful explanation (as it is understood today). One is that of a replicator-whose key role in evolution has been exposed with superb clarity by Richard Dawkins in the celebrated book The Selfish Gene. Think of the bacterial example again. Each instruction in the recipe to build a bacterium is embodied in a particular pattern of a portion of bacterial DNA; that portion is called a ‘gene’. Now, genes have a special property. Every time the bacterium cell self-reproduces and creates a new instance of itself, each gene’s pattern gets replicated, or copied, accurately; then the rest of the new cell is constructed by executing the recipe in the DNA. Since they are capable of being replicated, those patterns are called ‘replicators’. Incidentally, their replication is a step-wise, ‘letter-by-letter’ process, similar to that used by monastic scribes to copy the content of ancient manuscripts; and it can be error-corrected via a similar method, which in bacteria is implemented by the cell once the replication has happened. In this way, the structure of bacterial DNA has survived for long: by being copied from generation to generation and potentially preserved for a much longer time than the bacterium’s life span thanks to error-correction enacted by the cell. It is interesting that what’s passed on from generation to generation, via replication, is the particular pattern that codes for a gene, or an elementary instruction: every time it is copied it changes its physical support, while retaining all its properties as a pattern. It is the same as what happens to the sequence of words copied by the scribes: the ink and bits of parchment embodying those words change, but the copied words are, if no typos occur, the same as those in the source manuscript. Patterns with this particular counterfactual property, that of being copiable from one physical support to another while retaining all their defining properties, are a special case of ‘information’-of which I shall give a precise explanation (based on counterfactuals) in chapter 3.

US

Additional information

Dimensions	0.6900 × 5.2300 × 7.9300 in
Author	Chiara Marletto
Imprint	Penguin Books
ISBN-13	09780525521945
ISBN-10	0525521941
Audience	General / adult
BISAC	PHI004000, SCI075000
Subjects	gifts for science lovers, technology books, science books for adults, philosophy books, math books for adults, physics books for adults, physics book, quantum gravity, science teacher gifts, math books, scientific theories, physics problems, quantum computers, the science of can and can't, the science of can and cant, chiara marletto, counterfactuals, philosophy, nerdy gifts, quantum, popular science, physics books, SCI075000, science books, computers, ai, artificial intelligence, stem, physics, research, technology, science, PHI004000