- One of the greatest mysteries in quantum mechanics is whether physical reality exists independently of the observer.
- New research from Brazil provides strong evidence that there may be mutually exclusive, but complementary physical realities in the quantum realm.
- Future research into the great quantum debate could make us super disruptive quantum technologies— and probably surprising answers to the world’s greatest mysteries.
Does reality exist, or does it take shape as a observer measures it† Similar to the age-old riddle of whether a tree makes a sound when it falls into a forest without anyone around to hear it, the above question remains one of the most tantalizing in quantum mechanics, the branch of science that deals with the behavior of subatomic particles on a microscopic level.
In a field where intriguing, almost mysterious phenomena such as “quantum superposition” dominate – a situation in which someone particle can be in two or even ‘all’ possible places at once – some experts say that reality exists outside of your own consciousness and there is nothing you can do to change it. Others argue that “quantum reality” can be a form of Play-Doh that you mold into different shapes with your own actions. Now scientists at the Federal University of ABC (UFABC) in Brazil’s São Paulo metropolitan area are fueling the suggestion that reality may be “in the eye of the observer.”
In their new research, published in the journal Communication physics in April, scientists in Brazil attempted to verify the “principle of complementarity” proposed by famed Danish physicist Niels Bohr in 1928. There is that objects have certain pairs of complementary properties that are impossible to observe or measure at the same time, such as energy and duration, or position and momentum. For example, it doesn’t matter how you set up an experiment where a few electronsit is impossible to study the position of both quantities at the same time: the test will illustrate the position of the first electron, but at the same time obscure the position of the second particle (the complementary particle).
“God Does Not Play Dice”
To understand how this principle of complementarity relates to objective reality, we have to dive back in history, about a century ago. In 1927, a legendary debate took place in Brussels between Bohr and the celebrated German-born theoretical physicist Albert Einstein during the fifth Solvay conference (the most important annual international conference in physics and chemistry†
Before the eyes of 77 other brilliant scientists, all gathered in the Austrian capital to discuss the burgeoning field of quantum theory, Einstein insisted that quantum states had their own reality, independent of how a scientist reacted to them. Bohr, meanwhile, championed the idea that quantum systems can only allow their own reality to be defined after the scientist sets up the experimental design.
“God doesn’t play dice,” Einstein said.
“A system behaves like a wave or a particle, depending on the context, but you can’t predict what it will do,” Bohr argued, pointing to the concept of wave-particle duality, who says that matter can appear as a wave at one moment and as a particle at another, an idea that the French physicist Louis de Broglie first released in 1924.
The “principle of complementarity”
It was not long after the conclusion of the 1927 Solvay Conference for Bohr to publicly articulate its complementarity principle. In the coming decades, the controversial Bohr concept would be tested and retested to the bone. One of those who experimented with the principle of complementarity was the American theoretical physicist John Archibald Wheeler.
Wheeler tried to rethink Thomas Young’s 1801 double slit experiment in the properties of light in 1978 experiment with two slits involves shining a light on a wall with two parallel slits. As the light passes through each slit, on the other side of the divider, it bends and overlaps with the light from the other slit, interfering with each other. That means no more straight lines: the graph pattern that emerges at the end of the experiment is a interference pattern, meaning the light moves in waves. In essence, light has both a particle and a wave character, and these two natures are inseparable.
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Wheeler had his device switch between a “wave measuring device” and a “particle measuring device” after the light had already traveled through most of the machine. In other words, he made a delayed choice between whether the light had already propagated as a wave or a particle, and found that even after the choice was delayed, the principle of complementarity was not violated.
However, more recent studies† who tried to apply the quantum superposition principle to the delayed choice experiment, saw the two possibilities coexist (just like two waves may overlap on the surface of a lake). This suggested a hybrid wave-like and particle-like behavior within the same device, contradicting the complementarity principle.
Quantum-driven reality
The Brazilian scientists also decided to design a quantum-driven reality experiment.
“We used nuclear magnetic resonance techniques similar to those used in medical imaging,” Roberto M. Serraa researcher in quantum information science and technology at UFABC who led the experiment says: Popular mechanics† Particles such as protons, neutrons and electrons all have nuclear spin, which is a magnetic property analogous to the orientation of a needle in a compass† “We manipulated these nuclear spins of different atoms in a molecule using a type of electromagnetic radiation. In this setup, we created a new interference device for a proton nuclear spin to investigate wave and particle reality in the quantum realm,” explains Serra.
“This new setup produced exactly the same observed statistics as previous quantum delayed choice experiments,” Pedro Ruas Diegueznow a postdoctoral researcher at the International Center for Theory of Quantum Technologies (ICTQT) in Poland, who was part of the study, tells Popular mechanics. “In the new configuration, however, we were able to link the result of the experiment to the way waves and particles behave in a way that confirms Bohr’s complementarity principle,” continues Dieguez.
The main conclusion of the April 2022 study is that physical reality in the quantum world is made of mutually exclusive entities that do not contradict each other, but complement each other.
This is a fascinating result, experts say. “The Brazilian researchers have devised a mathematical framework and associated experimental configuration with which to test quantum theory, especially understanding the nature of complementarity by studying the physical realism of the system,” Stephen Holleran associate professor of physics at Fordham University, says: Popular mechanics†
It is a study that emphasizes the long-standing saying from iconic American quantum physicist and Nobel laureate Richard Feynman: “If you think you understand quantum mechanics, you don’t understand quantum mechanics,” says Holler. “There is a lot to learn about the theory and researchers are continuing to make strides in understanding even the basics, which is especially important as we enter the era where quantum devices and computers are beginning to spread.”
Dieguez is delighted. “The fact that a material particle can behave like a wave and light can behave like a particle, depending on context, is still one of the most intriguing and beautiful mysteries of quantum physics,” he says.
Paradoxically, this inherent “strangeness” of quantum mechanics can prove quite useful: “The more we unravel quantum mechanics, the more we are able to deliver disruptive quantum technologies that include their classical counterparts, quantum computers, quantum cryptography, quantum sensors, and quantum thermal devices.” says Serra.
That reality can be in the eye of the observer is a very peculiar aspect of physical reality in the quantum domain, and the mystery itself shows no signs of abating, both researchers agree.
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