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Will quantum 3D printers create entire universes one day?

The Science of Can and Can’t, a recently published book by Oxford theoretical physicist Chiara Marletto, discusses the concept of the Universal Constructor. We asked her if this could be the future of 3D printing.

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As industry analysts in additive manufacturing, we strive to forecast the evolutionary trends of 3D printing technologies across a time period that extends five or 10 years. As journalists, sometimes we venture farther into the future, trying to imagine what will happen in fifty or one hundred years. What if we looked beyond that, without a preset time limit? Then we would need to speak with a scientist to understand what ultimately can and cannot happen. And that is what we did when we had the unique opportunity to interview Chiara Marletto, Research Fellow at the Physics Department at the University of Oxford.

Professor Marletto is a theoretical physicist, and her studies focus on Quantum Theory of Computation, Information Theory, Thermodynamics, Condensed-Matter Physics and Quantum Biology. She just published a book titled The Science of Can and Can’t, which is based on her recent research harnessing a recently proposed generalization of the quantum theory of information—Constructor Theory—to address issues at the foundations of the theory of control and causation in physics.

Chiara Marletto, Research Fellow at Wolfson College, University of Oxford and author of The Science of Can and Can’t.

In the book, she also explores the concept of the Universal Constructor, which could represent the ultimate evolution of today’s 3D printers. “It is not the main part of the book—Professor Marletto says—however it is the inspiring principle for the Science of Counterfactuals – Science of Can and Can’t – that is commonly referred to as ‘Constructor Theory’, that is the theory of the universal constructor.”

But what exactly is a Universal Constructor? And how does it relate to today’s 3D printers? One possibility that comes to mind is something like the “replicator” described in the fictional Star Trek series, which is a machine that assembles objects at an atomic level. In some ways it is. The Universal Constructor was proposed as a theoretical model by physicist and mathematician John von Neumann in the 1950s to generalize the idea of the universal Turing machine, that is, the universal computer. “A universal computer is a machine that can be programmed to perform any computation that is physically possible—Marletto explains—the Universal Constructor on the other hand is a machine that can perform any transformation – not just computations – that is physically allowed. In particular, von Neumann devised it to emulate the behavior of cells, which can self-reproduce.”

One element that the Universal Constructor does share with 3D printers—which is also one of the defining characteristics of the Universal Constructor—is that it could make a replica of itself, something that inspired the early RepRap 3D printing movement and continues to define 3D printers even at the highest industrial levels: the ability to make parts for new printers.

Another key concept is that the Universal Constructor requires not only energy and/or raw materials but also knowledge, which—Professor Marletto explained—is a particular type of information contained in a software program, that must be given as input to the universal computing machine and also to the Universal Constructor so that they can perform the desired computation. The next question is: if we had enough of all these elements (energy/materials and knowledge) could we make a 3D printer that can make anything?

“We do not currently have a complete theory of the Universal Constructor,” says Professor Marletto, “so, your question does not have a precise answer. Much depends on the resources available in the universe, and on other aspects of our physical laws. However, we can say that there is no physical law that prevents creation in a Universal Constructor.” In other words, the laws of physics as we understand them today allow for the creation of a machine that can produce anything: the fact that doing this is incredibly complex with our current technological capabilities does not mean it is impossible as it would be, for example, to create perpetual motion machines, which are prevented by the principle of conservation of energy.

“For example—Professor Marletto adds—the theory of thermodynamics tells us that there is no limit to the construction of arbitrarily accurate heat engines, and we would like to generate such a prediction for the Universal Constructor as well. We would really like to have, when the theory of the Constructor is completed, a series of physical principles that indicate whether it is possible to have a Universal Constructor, and also what are the transformations that are in its repertoire.”

While we don’t know if 3D printers can ultimately evolve into Universal Constructors, there is nothing in physics that says they can’t. Either way, it may be possible to imagine an evolutionary process that takes us from today’s early 3D printers to a machine that can build anything. Professor Marletto agrees: “The final realization of a Universal Constructor will require the creation of imperfect constructors, which are not universal but have the ability to construct approximate constructors that work slightly better than the previous generation. This mechanism – of how imperfectly replicating organisms can create a better version from time to time, which then takes over – is already described in Charles Darwin’s theory of natural selection. A similar mechanism occurs in the context of technological evolution within our civilization, which proceeds gradually. Think of the evolution of computing machines, starting from Turing’s theoretical proposal.

The fact that the most optimized shapes produced by 3D printers often replicate “natural forms” such as lattices and fractals may be another key element that indicates they will evolve: not only do they replicate natural forms but they may eventually also replicate natural processes such as self-reproduction and natural selection. Today’s 3D printers are evolving in terms of size and speed but also in terms of precision. As resolutions become more and more precise, the assembly of matter at the most basic scale cannot escape the complexities of quantum mechanics. While most 3D printers today work with voxels of 10 to 100 microns, some can already go into the nanometer scale. And quantum effects can already come into play.

“Spontaneous quantum effects are usually confined to the atomic or subatomic scale,” Professor Marletto points out. “However, there are technologies that allow us to induce quantum effects on mesoscopic scales. For example, consider the interferometry expressions concerning complex molecules such as fullerenes. There are no limits set by quantum theory regarding the scale at which quantum effects can be used to improve the efficiency of a classical physical process. Think for example of the case of quantum biology – where the possibility is studied that living beings use quantum effects to function more efficiently. It is certainly possible to imagine ways of using quantum effects also within the Universal Constructor.”

Even before getting into quantum effects, 3D printers have to deal with physics at the macroscopic scale and its limitations all the time. For example, in terms of heat management, mechanical movements, in the physics of powders and liquids or in the physics of energy sources such as lasers and infrared radiation. Can Constructor Theory and the Science of Can and Can’t provide a practical framework to address some of these challenges as well?

Professor Marletto thinks so. “The laws of constructor theory are, like all laws of basic physics, universal—she confirms. “Therefore they apply to elementary systems such as particles, and also to aggregates of elementary particles which are becoming more and more complex – hence also to objects such as computers or living organisms.” Reading the Professor’s book, one does get the impression that Constructor Theory could help to broaden the horizons of creativity and innovation particularly in an innovation-rich and rapidly evolving industrial segment such as additive manufacturing, which continues to cross boundaries.

Another practical aspect to consider as 3D printing continues to advance is process simulation (and monitoring). Industrial 3D printers produce enormous quantities of digital data that need to be handled by increasingly powerful computers. Professor Marletto agrees that this may be an ideal task for the universal quantum computers of tomorrow. “The Universal Constructor technology—when it is implemented—will make use of a quantum universal computer to manage data and perform computations necessary for the constructor to function,” she explains.

Babbage’s Analytical Engine was a Universal Classical Computer. The question of whether a Universal Constructor can exist is of great interest in Constructor Theory.

Having the opportunity to discuss the evolution of 3D printing technology in terms of theoretical physics was truly inspiring. While we are certainly still at the very beginning of the evolution of 3D printing, and still far from a complete understanding of Constructor Theory, it appears clear that there are many common elements to be explored. As 3dpbm is actively working with Sarah Goerke at Women in 3D Printing to favor inclusion and gender equality in the AM industry, I should say that it was also refreshing to speak about these topics with a brilliant woman scientist, in a world of theoretical physics that is also generally male-dominated.

“I think it’s about the changing times,” Professor Marletto concludes. “In my opinion, the choices of work and study (both for men and for women) are largely determined by the culture and society in which we live. I expect that with the evolution (I hope for the better) of our costumes there will be an evolution of the choices that will go hand in hand. We will see what it will lead to. I am confident.”

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