Three researchers were awarded the 2022 Nobel Prize in Physics for their ground-breaking work in understanding quantum entanglement, one of nature’s most puzzling phenomena. The most basic definition of quantum entanglement is that, regardless of their distance from one another or the object separating them, aspects of one particle in an entangled pair rely on aspects of the other particle. These particles might be electrons or photons, for instance, and one aspect might be the way they are behaving, like whether or not they are “spinning” in one direction or another.

The peculiarity of quantum entanglement is that, even if two particles are millions of light years distant, when you measure one of them, you immediately know something about the other. This strange instantaneous connection between the two particles appears to violate a fundamental law of the cosmos. The phenomena is referred to as “spooky activity at a distance” by Albert Einstein. I have spent the majority of the last two decades conducting experiments that are based on quantum physics, therefore I have come to terms with its peculiarities. Physicists can now integrate quantum phenomena into their understanding of the world with an exceptional level of assurance because to improved precision and dependability of instruments as well as the work of this year’s Nobel laureates, Alain Aspect, John Clauser, and Anton Zeilinger.

Even still, there was disagreement among scientists over the reality of quantum entanglement up until the 1970s. Who would dare challenge the great Einstein, who himself questioned it? And with good cause. To solve this issue once and for all, new experimental technologies and daring researchers were required. It’s critical to first comprehend quantum superposition in order to fully appreciate the unsettling nature of quantum entanglement. The concept of quantum superposition holds that particles can be in several states at once. When a measurement is made, it appears as though the particle chooses one of the superposition’s states.

For instance, many particles contain a property termed spin, which is measured as either “up” or “down” depending on the analyzer’s orientation. A particle, however, exists in a superposition of spin up and spin down until you measure its spin. Each condition has a probability associated with it, and a large number of measurements can be used to forecast the typical result. These probabilities determine the possibility of a single measurement going up or down, but this probability is unpredictable in and of itself.

Despite being extremely strange, quantum mechanics has been proven to accurately represent physical reality by mathematics and a large number of experiments. The quintessential architects of quantum mechanics who created the theory in the 1920s and 1930s were aware of the unsettling nature of quantum entanglement because of the fact of quantum superposition. You simply divide a system into two where the sum of the components is known in order to produce entangled particles. One can, for instance, divide a particle with spin zero into two particles whose spins must be opposite each other and whose sum is zero. In a 1935 publication, Albert Einstein, Boris Podolsky, and Nathan Rosen present a thought experiment meant to show how quantum entanglement appeared to contradict a fundamental law of the universe.

David Bohm is credited with coming up with a condensed version of this thought experiment that takes the decay of the pi meson into account. The electron and positron that are created when this particle decays have opposite spins and are travelling away from one another. So, if the measured spin of the electron is up, the measured spin of the positron can only be down, and the opposite is true. Even if the particles are billions of miles distant, this is still true. If the observed spin of the positron were always down and the measured spin of the electron were always up, this would be acceptable. However, until it is measured, each particle’s spin has both an up and a down component due to quantum mechanics. The quantum state of the spin can only “collapse” into either up or down when the measurement takes place, instantly collapsing the other particle into the opposing spin. This seems to imply that the particles communicate with one another through a method that travels at a speed faster than light. But nothing can move faster than the speed of light, in accordance with the principles of physics. There must be a limit to how quickly one particle’s measured state can predict another particle’s condition beyond the edge of the universe, right?

In the 1930s, physicists—including Einstein—proposed a variety of alternate explanations for quantum entanglement. They postulated that a particle’s condition before to measurement was determined by some unidentified characteristic they called hidden variables. But at the time, neither technology nor a definition of a precise measurement existed that could be used to determine whether or not hidden variables needed to be added to quantum theory. Prior to the 1960s, there were no hints as to the solution. Brilliant Irish physicist John Bell, who passed away before receiving the Nobel Prize, came up with a plan to determine whether the idea of hidden variables made sense. The equation Bell created, now known as Bell’s inequality, is only and exclusively true for hidden variable theories; it is not necessarily true for quantum mechanics. Thus, local hidden variable theories can be disregarded as a possible explanation for quantum entanglement if Bell’s equation is proven to be unsatisfied in a real-world experiment.

The Bell inequality was tested for the first time in the experiments of the 2022 Nobel laureates, particularly those of Alain Aspect. Instead of pairs of an electron and a positron, as in many thought experiments, entangled photons were employed in the trials. The findings definitively disproved the hypothesis of hidden variables, a puzzling property that would dictate in advance the states of entangled particles. These combined experiments, along with numerous more that followed, have supported quantum mechanics. Over very long distances, objects can be connected in ways that classical physics before quantum mechanics cannot explain. Furthermore, there is no issue with special relativity, which bans communication faster than the speed of light. The correlation of observations across great distances does not prove that the particles are communicating information. The phenomenon does not allow information to be transmitted faster than the speed of light between two parties measuring entangled particles. Physicists are still looking into the potential uses of quantum entanglement and conducting research on it today. Although quantum mechanics can predict a measurement’s probability with astonishing accuracy, many scientists still doubt that it fully captures reality. But one thing is certain. There is still a lot to be said about the enigmatic field of quantum mechanics.