Brazilian probes foundations of the Universe with experimental metaphysics – 09/29/2024 – Science
The word “metaphysics” is seen in many academic circles as something of a dirty word — something that refers to unverifiable speculations and assumptions that transcend observable reality. But a growing group of academics is beginning to explore eminently metaphysical questions through experiments —material or mental— in order to try to uncover the most elementary foundations of nature.
One example of this group of committed researchers is the Brazilian physicist Eric Cavalcanti, now at Griffith University, in Australia. He defines himself today as an “experimental metaphysician”, and his objective is to try to understand the limit of the possible behind the theories that today help to describe what we understand as reality, quantum mechanics and general relativity.
Cavalcanti gained notoriety with an article published in Nature Physics in 2020, in which he presented a thought experiment demonstrating that three basic pillars that apparently manifest themselves in nature cannot be true at the same time: “non-superdeterminism” (roughly speaking, something such as the rejection of the notion that all events in the Universe are entirely predetermined), “locality” (the fact that events only occur through local interactions, and the range of these interactions is limited by the speed of light) and the “absolutism of observed events” (the essential notion of reality, that is, that all events in the Universe are valid for everyone, although observers may disagree about the moment or place in which they occur). In his view, it is something that helps explore what is behind the foundations of physics, and what may or may not be logically consistent in them.
There is no doubt that there is something to explore. On the one hand, general relativity brings the notion that time and space fundamentally depend on the observer; on the other hand, quantum mechanics seems to treat reality as probability and allows for difficult-to-understand phenomena, such as quantum entanglement, in which particles have their quantum states intertwined in such a way that, when you mess with one, you instantly affect the other — yet that it is at great distances, in what Albert Einstein classified as “a ghostly action at a distance”. The phenomenon appears to be at odds with the locality, as it does not appear to obey the speed of light limit for interactions between particles. What does all this really mean about reality? Cavalcanti and his colleagues in this field try to explore this by devising ways to test assumptions underlying theories.
The objective is to go beyond what has been done over the last few decades, in which natural philosophers conceived interpretations for these quantum phenomena — or even adopted the stance that there is nothing to be explained, and we just have to accept that the limit of knowledge is that of the theory itself, the so-called “Copenhagen interpretation”, led by the pioneer of quantum physics Niels Bohr.
Experimental metaphysics seeks to explore the panorama of possible interpretations in a neutral way, trying to eliminate alternatives and, in doing so, get closer to the foundations that underpin what we call reality.
Next, a conversation with Cavalcanti.
You started as a biophysicist and then moved to quantum mechanics, to understanding the fundamental workings of the Universe. Why did this transition happen?
I started doing research in biophysics during my undergraduate studies at PUC-Rio, as a scientific initiation. After my master’s degree, I wasn’t feeling motivated to continue on the same experimental path. I passed a competition for a position as a Technologist at the National Nuclear Energy Commission. It was in my free time at the Cnen library that I found books by researchers like Roger Penrose and David Deutsch, who talked about the foundations of quantum mechanics, from completely different points of view. It was then that I realized that these questions about fundamentals —which, I had been told at the time of graduation, were not questions that were more objects of research—, not just high-caliber researchers like Penrose (who went on to win the Nobel Prize for his work black hole theorists) and Deutsch (one of the founders of quantum computing) were immersed in them, as if defending diametrically opposed positions! I also had exposure to very interesting ideas about the foundations of mathematics, quantum information, and a new universe of physical and philosophical questions opened up to me. It was then that I felt that I had found my “calling”, and decided to do a PhD in the foundations of quantum mechanics. The University of Queensland, in Australia, was an ideal place for this.
His field is described as experimental metaphysics.
It is not possible to do physics without metaphysics. What can be done is physics without paying attention to the metaphysical assumptions implicit in one or another point of view. But it is more interesting to be aware of these premises, to bring them to the surface. Even to open up opportunities to explore alternatives.
For much of the 20th century, quantum mechanics was embraced by most physicists with the Copenhagen interpretation. Does experimental metaphysics seek to break this paradigm? Do you feel that it has been gaining ground since you published your doctoral thesis on it in 2007?
Research in the area of fundamentals is really gaining more space and respect. Partly because it is following the growth of research in quantum information, which especially in recent years is receiving increasing investment. Many are realizing that fundamentals research, such as the quantum entanglement experiments aimed at violating Bell’s inequalities, which won the Nobel Prize in 2022, in part drove the development of quantum information and computing, which are now beginning to generate technological results. But experimental metaphysics seeks more than breaking the paradigm of the Copenhagen interpretation. The aim is to try to explore the panorama of interpretations or theories, in a philosophically informed way. The questions are like: What sets of hypotheses about reality are internally consistent, and consistent with experiments? The objective is to eliminate errors, and understand the alternatives that remain. It’s not about finding another “pet interpretation” to become the new dogma. In this sense, although experimental metaphysics has “metaphysics” in its name, it seeks not to take metaphysical positions as unquestionable.
His most celebrated work, published in Nature Physics in 2020, presents a thought experiment that demonstrates that three basic pillars that apparently manifest themselves in nature cannot be true at the same time: “non-superdeterminism”, “locality” and “absolutism of the observed events.” The first would be related to quantum mechanics, and the other two come from relativity. Wouldn’t confirming that all three cannot be real at the same time indicate that the theories are irreconcilable? Would it be the proclamation of the death of unification efforts or the search for a theory of quantum gravity?
Not the death proclamation, but it implies that, one, if the inequalities are not violated, quantum mechanics is not universally applicable, or, two, if they are violated, it is difficult to avoid some kind of conflict with relativity — unless possibly with some form of retrocausality or superdeterminism (which are neither part of quantum mechanics nor relativity). But note that this does not mean the death of the search for unification. On the contrary, it indicates the possible directions of unification. It means that some basic principle of one or another theory will have to be violated in their unification.
Returning perhaps to the more epistemological approach of the Copenhagen interpretation, could it be that the problem of the paradox between three characteristics mentioned in your 2020 article that manifest themselves in nature, but never at the same time, is not in the world but in the limitations imposed by our understanding ? As Neil deGrasse-Tyson says, the universe is under no obligation to make sense to us.
I think this kind of idea is unnecessary defeatism. In the same way, we could say that we did not evolve to understand almost anything that science has discovered. Evolution has not equipped us with the means to fly into space and see that the Earth is round, but science has given us the knowledge to achieve this. Evolution has not equipped us to travel at near-light speed and directly understand that time is relative, to see atoms with the naked eye, it has not equipped us with lives of billions of years to experience the expansion of the cosmos since the Big Bang. But we understand all this now, because evolution has equipped us with intelligence. And with it we can now understand natural evolution itself and even begin to tame it with genetic engineering. Of course, “the universe is under no obligation” to do anything. But given that we understand all these things, the argument that we are unable to understand some phenomenon just because evolution has not equipped us with some special faculty for visualizing that phenomenon doesn’t hold much water for me.
This, finally, leads to what seems to me to be a central point of the discussion: the importance of the observer. Quantum mechanics dictates that reality essentially depends on the observer, without whom it remains probabilistic. It is the presence of the observer that converts the quantum into the classical.
This statement is itself based on a certain interpretation. In several interpretations, such as Everett’s or Bohmian, the “observer” itself does not have a special role, nor is there a conversion from quantum to classical, strictly speaking — the wave function never “collapses” in these interpretations. What happens is that they need to explain why the world seems classical, while in reality it would always be quantum.
But what qualifies as an “observer”? More conservative physicists often think that perhaps any interaction between particles capable of disturbing an entanglement could qualify as “observable.” Others dare to suggest that a conscious mind, carrying out experiments and interacting with its surroundings, is necessary as an observer. The old Einstein-Bohr discussion… What is your view on this issue?
My vision is to try to bring experimental data to this question. There is no consensus even on whether there actually is a collapse of the wave function, or just an apparent collapse, and if there is, there is no consensus on what the characteristics would be necessary for an observer to cause this collapse. Our experimental project is to try to carry out experiments with increasingly complex systems, with increasingly more characteristics of an “observer”. If at some point the existence of an observer causes an objective collapse, determining the end of the limit of applicability of quantum mechanics, we want to discover this experimentally.
To finish, a thought from those who lose sleep… What if the entire Universe is composed of an enormous web of quantum entanglements that, through our intervention as observers, undergo the collapse of their wave function and gain a “” realistic”, with past and future established instantly, without any respect for locality (itself the result of this collapse), becoming a super-deterministic reality as observed, and not before or after? What if there is such a Universe for each observer?
I don’t know if I understand exactly the metaphysical theory you are proposing here, but it seems to me that you are at the same time considering the possibility of wavefunction collapse, nonlocality, superdeterminism, and violation of the absolutism of observable events. If each of these possibilities is a difficult pill to swallow, the possibility you are describing seems to be taking not only the blue or the red pill — in the Matrix metaphor — but at the same time the blue, the red, and for good measure also one purple and one green!
