The human being recognizes a deep sense of freedom in his actions and therefore free will is a fundamental component of the humanities, the social sciences and, in more general terms, of the central institutions of society. Without free will, subjectivity, rationality, and responsibility are empty notions. But the scientific interpretation of reality, which has been evolving throughout history, has provided arguments against that free will. We can go back to the fourth century BC, when Epicurus tried to reconcile our apparent freedom to act with Democritus’ idea that the world is made up of atoms that move according to immutable laws.
Laplace, in the eighteenth century, pushing Newtonian mechanics to the limit, manifested causal determinism through the well-known thought experiment called Laplace’s demon: if some hypothetical ultra-intelligent being, or demon, could somehow know the position of each atom in the universe in an instant of time, together with all the laws that govern its interactions, he could predict the future in its entirety.
According to this view, which is held by many scientists today, the existence of free will is denied. Everything, absolutely everything we see around us: rocks, plants, animals, as well as all the tissues that make up the human body, including our own brain, is made up of quarks and electrons.
The behavior of particles and fields when interacting causally leads to the formation of atoms. The interaction of atoms causally leads to the formation of molecules that, in turn, lead to more complex systems that reach up to machines or ecosystems, and human beings.
To understand the human mind we need to start by understanding the underlying physics: particles and fields. From this point of view, causality is an entirely bottom-up process. The behavior of particles and fields dictates the behavior of atoms and molecules which, in turn, dictates the behavior of cells, and so on. Hence the term “upward causation”.
As particle physics is considered totally deterministic, it leads us to conclude that our thoughts, what we are thinking at this precise moment, were already predetermined from the beginning of the universe, since it would depend on the physical variables of those particles at the initial moment of the universe.
Quantum uncertainty does not break the deterministic chain either
However, Heisenberg’s uncertainty principle indicates that events at the smallest scales are genuinely random, which would preclude speaking of determinism transmitted to higher scales.
Nevertheless, it is a widely held opinion that randomness at quantum levels should not have any effect at the level of classical physics, because all that fuzziness it produces should be absorbed or averaged out in the system and not passed on to higher levels, for so the behavior of the system at classical levels can still be considered deterministic.
There are even those who claim, like Sabine Hossenfelder, that there are hidden variables that are the reason why we cannot predict the result of quantum measurements. Hossenfelder calls free will “logically incoherent nonsense”.
Downward Causation Introduces Indeterminacy
But another way of thinking has developed in the last 30 years that gives rise to the existence of free will. There is a common view that the world is divided into stratified “levels” of organization; and to the existence of “upward causation” we must add what has been called “downward causation”, which starts from the idea that higher levels of complexity allow genuinely new qualities.
Science journalist John Horgan puts it this way: “What humans can do is not merely a more complex version of what amoebas can do — in turn supposed to be a more complex version of what electrons can do. Greater complexity can involve genuinely new qualities” . The quantity and variety of studies carried out in this field allow us to affirm that top-down causality is not a rare and suspicious form of causality, but rather is omnipresent in physical and biological systems alike.
Downward causation in biology is necessary, as organisms need to adapt to the environment. The environment sends information to the organism and the organism changes its structure or its behavior, or both.
In biological contexts, information is an independently existing entity that systems transmit, acquire, assimilate, decode, and manipulate; and, in so doing, generate meaning.
Life is information, it is coding: DNA is an indispensable element of life. And this information does not come from the particles that make up matter; information is something real but it is not something physical, it is not made up of particles. DNA can encode any protein structure without physics determining the result, so we no longer speak of physics but of biology, with different rules.
These downward causation processes introduce randomness, a feature present in molecular biology. This is how George Ellis explains it in his article From Chaos to Free Will , which takes into account Peter Hoffmann’s conclusions in his book The Ratchet of Life: How Molecular Machines Extract Order from Chaos in which he states that, at molecular scales, the processes at work forget initial data due to billions on billions of collisions between molecules every second, it is what microdeterminism avoids in practice.
Likewise, it is based on the ideas exposed by Raymond Noble and Denis Noble in their paper Harnessing stochasticity: How do organisms make choices, in which they conclude that molecular randomness gives cellular mechanisms the option of choosing the outcomes they want and discarding the ones they don’t.
This power of choice allows physiological systems, such as the heart and brain, to function in a way that is not enslaved by lower-level interactions, but instead chooses preferred interaction outcomes from a multitude of options. This is not conclusive proof of the existence of free will, but at least it opens a way for it to exist.
Understanding the mind-brain relationship
To understand how an abstract entity like information produces a causal effect on biology, on the human brain, Ellis has suggested looking at how things happen in a computer, which is something we do know well. It is not about comparing the functioning of the brain with that of a computer, that does not make sense, but simply to perceive how an abstract entity can influence biological behavior.
In a digital computer we can observe different levels: at its basic level there are a series of logic gates, transistors linked by wires, assembled with a keyboard and a screen, and so on. At the lowest level, the electrons flow through the gates in a particular way and that is what controls what happens on the screen. This constitutes the hardware, which does nothing until it is loaded with a program. What the same hardware does is completely different depending on the software that is loaded. The hardware, by itself, does not determine what happens. What determines it is the program it runs. And here it is necessary to consider what is the nature of a computer program: it is an abstract entity.
It is not a physical thing, even if it is physically contained on a CD or any other similar medium. The abstract logic of the program is transferred to all the layers of structure: there is the machine language, there is the assembly language, there is the language of the operating system, there is the high-level language, and what is key here is that there is a logic in the computer program.
The exact same logic is present at all levels, but it is represented differently with different rules, and at the lower level it is converted to instructions on the gate and converted to electronic states on the gates. The computer program is something abstract, but does it have causal power? Yes, it makes things happen. The abstract entities are driving the physics at the lower level. Physics is not controlling what happens.
We are a long way from understanding how the brain works. And there is a great diversity of theories to explain the meaning of it. But numerous philosophers and neuroscientists have been corroborating throughout the 20th century Descartes’ vision of a separation between the mind and the brain. In the list of philosophers who have abounded and perfected this thesis are Karl Popper or Richard Swimburne and, in the field of scientific research, the Nobel Prize-winning neuroscientists Charles Sherrington and John Eccles stand out, as well as other recognized ones such as Benjamin Libet or Wilder Penfield.
Neuroscientist Roger Sperry, a researcher at the California Institute of Technology and Nobel Prize in Medicine in 1981 for his studies of the specialized functions of the human brain, was not so categorical, but he did state: “Our interpretation of the facts tends to return to mind its former privileged position over matter, because it shows that mental phenomena transcend those of physiology and biochemistry”. 
Communicator and neuroscientist Caroline Leaf sums up what science tells us about the mind and the brain: “The mind works through the brain, but it is separate from the brain. The mind uses the brain, and the brain responds to the mind. The mind also changes the brain. People choose their actions—their brains do not force them to do anything. Yes, there would be no conscious experience without the brain, but experience cannot be reduced to the brain’s actions. Your mind is how you, specifically, experience life. It is responsible for how you think, feel and choose.” 
And going back to Ellis’s reasoning: “There is the mind and the brain, and the mind inhabits the brain… or thoughts, thoughts inhabit the brain and thoughts are not physical things. Thoughts are abstract things that are represented in physical form.
The end of determinism
Many centuries have passed in which scientific knowledge seemed to indicate, contrary to human sensation, the impossibility of the existence of free will. And this as a consequence of the idea that the human being and his brain is made up of material particles that are themselves deterministic. But the development of biology and the study of downward causality, in recent years, has given way to a new way of understanding how the introduction of non-deterministic information produces effects in the mind and brain, allowing the existence of free will.
Bioethics Observatory- Institute of Life Sciences
Catholic University of Valencia
 Kevin Mitchell, Escaping Flatland – when determinism falls, it takes reductionism with it, 2020
 Ibid. 2
 Sara Green, Robert Batterman, (PDF) Making sense of top-down causation: Universality and functional equivalence in physics and biology, 2021
 Pharoah, M., Causation and Information: Where Is Biological Meaning to Be Found? | SpringerLink, Biosemiotics 13, 309–326 (2020)
 George Ellis, Here’s why so many physicists are wrong about free will | Aeon Essays, 2020
 Peter M. Hoffmann, Life’s Ratchet: How Molecular Machines Extract Order from Chaos, 2012 Basic Books QH506.H636
 Raymond Noble and Denis Noble, Harnessing stochasticity: How do organisms make choices?, Chaos 28, 106309 (2018)
 Ibid 5
 Caroline Leaf, A Neuroscientist Explains The Difference Between The Mind & Brain | mindbodygreen, 2021
 Ibid 5