Typically, the Nobel Prize in physics is given to scientists who make sense of nature—those whose discoveries make the universe more understandable. However, the 2022 Nobel Prize in Physics was awarded to three physicists who demonstrated that the universe is even stranger than previously believed. John Clauser, Alain Aspect, and Anton Zeilinger are this year’s physics Nobel laureates. They are jointly responsible for a series of ingenious experiments that proved quantum mechanics’ most bizarre prediction to be accurate. It’s the prediction that Einstein refused to accept: the notion that two quantum systems can be entangled, meaning they can influence each other instantaneously over any distance. This “spooky action at a distance,” as Einstein described it, appears to contradict his own theory of relativity, which states that no causal influence can travel faster than the speed of light. Clauser and Aspect accomplished a rare feat: they proved Einstein wrong, while Zeilinger significantly advanced our understanding and practical application of the quantum entanglement phenomenon.
Certainly, we’ve discussed quantum entanglement a few times in the past, but today I’d like to discuss the series of brilliant experiments honored by this year’s Nobel. Let’s begin with a straightforward thought experiment. One of the balls is black, while the other is white. You close your eyes, jumble the balls, and place each one in a box of the same size. The first box is placed in a rocket and sent to the moon, while the second box remains on Earth. While this box is closed, there is a 50/50 chance that the ball on the moon is black or white. You immediately learn the color of the moon’s ball upon opening the box. Did you make information travel faster than the speed of light? Obviously not; the information regarding the colors of the balls was always present with the balls; you simply learned which was which. Imagine that these are quantum balls with “quantum” colors that are entangled. Not only do we not know which is which until the box is opened, but the colors of the balls are fundamentally undefined according to quantum mechanics. Until a measurement is taken, each ball exists in a state of superposition, where it could be black or white. The opening of the box forces the observed ball to select a color state, thereby compelling the ball on the moon to select the opposite. As soon as you make your observation, the ball on the moon transitions from a superposition state to a defined state, indicating that your influence appears to travel faster than light.
These “quantum balls” may be any subatomic or molecular particle, and their entangled properties may be spin, momentum, or any other quantum property. But why must we accept this bizarre interpretation? Is there a significant difference in the experiment’s outcome if the color of the balls is specified at the start or when the box is opened? Why suggest this entanglement and superposition nonsense? Quantum mechanics in its standard form dictates this. The wavefunction, which changes based on the Schrödinger equation, is what defines a quantum system. The joint wavefunction of two entangled objects doesn’t show their individual values, only how they relate to each other. They acquire specific values only when observed, at which point the wavefunction “collapses.” For our quantum balls to always be aware of their own color, there would need to be information outside of their wavefunction. There are different ways to look at quantum mechanics that allow for this hidden information. These ways are called “hidden variable theories” as a group. Einstein thought that there must be such hidden information, while others, like Neils Bohr, insisted that the wavefunction told the whole story of a quantum system. In nearly every scientific argument, physicists support Einstein. But quantum mechanics was just too successful in this case, and Neils Bohr pushed hard for his Copenhagen interpretation. It became the standard, and for a while, it was bad for your career to question the standard, like by doing research on hidden variable theories. David Bohm received the most criticism for his pilot wave theory. John Stuart Bell was another heretic with hidden variables.
This Irish physicist did not necessarily believe in them, but he did not accept the Copenhagen interpretation without rigorous testing. And he also realized that it was possible to reveal the existence of hidden information without actually measuring it or even testing a particular theory of hidden variables. If you wish to see exactly how this works, we have discussed these Bell tests previously. In brief, Bell developed his Bell theorem in 1964, which demonstrates that there should be a particular statistical relationship between the measured properties of entangled particles if the particles themselves hold information about their internal states, and a different statistical relationship if these properties are actually determined at the time of measurement. In particular, the so-called Bell inequality is satisfied if the particles contain hidden variables and is violated otherwise. Finally, there was a real test we could use to check for concealed variables. John Clauser, one of our 2022 Nobel laureates, conducted the initial Bell test in 1969. Why then did it take five years? Bell tests are extremely difficult to perform. They necessitate the production of entangled states, which must be manipulated and measured without disturbing the extremely delicate correlation between the particles. In addition, to conduct a Bell test was to question the status quo, making it difficult to garner support for the substantial effort required. Clauser describes the time when he pitched his experiment idea to Richard Feynman, who promptly threw him out of his office.
Evidently, Feynman considered it pointless because standard quantum mechanics was demonstrably accurate. Clauser and his student Stewart Jay Freedman did not allow themselves to be deterred. They were going to conduct a brilliant experiment that they had devised. It went as follows: A beam of calcium atoms was blasted through the intense light of an arc lamp. This light excited electrons in calcium atoms to a higher energy level, which they then returned to, with photons carrying away the lost energy. One of the possible electron transitions resulted in the production of two photons and occurred between two states with zero quantum spin. The quantum version of angular momentum is spin. Due to the fact that the spin of the atom did not change during this transition, in order to maintain angular momentum, the pair of photons required a total spin of zero, which corresponds to opposite circular polarizations. Standard quantum mechanics states that these polarizations are undefined until they are measured, at which point they will always be opposite. In contrast, hidden variable theories permit the polarization of photons to be determined at the time of their creation. Clauser and Freedman could conduct a Bell test if they measured these polarizations by passing both photons through polarizers.
Bell inequality was convincingly violated in their experiments, indicating that quantum mechanics functioned precisely as predicted and that there were no hidden variables, exactly as Feynman had instructed. However, the case was not yet closed. John Bell himself noted that hidden variables could still exist despite what the Bell test indicated. The outcome of a quantum measurement is dependent on the method of measurement; in this experiment, the orientation of the polarizers determined the polarizations to which the experiment was sensitive. Bell’s theorem assumes that the choice of measurement is completely independent of the process of particle creation. In Clauser’s experiment, however, the polarizers remained in place throughout the duration of the experiment. Prior to the production of entangled photons, their orientation was already determined. What does it matter if this orientation influences the polarization direction of photons at the time of their creation? Then the photons may have carried hidden information about the eventual measurement direction the entire time and conspired to make quantum mechanics appear standard, even if they contained actual hidden variables. To close this loophole, it would be necessary to set the direction of measurement after the photons have been produced.
In case you were unaware, photons travel very quickly. However, if you are a brilliant experimentalist, “extremely challenging” is your bread and butter. The second laureate is now introduced: Alain Aspect. Aspect’s apparatus was very similar to Clauser’s, consisting of a beam of calcium atoms excited by light—a laser instead of an arc lamp this time. However, the primary distinction lies in the polarizers. To change the measurement direction of a polarizer, it must be rotated, which is difficult to do faster than a photon can travel across an optical bench. Aspect discovered a method to randomize measurement direction without repositioning the polarizers. The secret was to utilize a transducer. In this case, a piece of quartz bends the path of light differently depending on whether or not it is vibrating, and that vibration can be activated or deactivated by an electric current. This implies that our entangled photons could be sent to different polarizers based on the state of an electrical switch—a switch that could be turned on and off rapidly and randomly in the brief time between the photon’s creation and arrival at the transducer. All of this indicates that photons cannot know how they will be measured at the time of their creation, which, as you may recall, was the potential flaw in Clauser and Freedman’s experiment. Alain Aspect’s experiment also violated the Bell inequalities, dealing another blow to hidden variable theories. So, did Aspect eliminate the last loophole?
There are two ways to violate the Bell inequalities without making quantum entanglement as spooky as Einstein feared. However, these methods are still eerie, albeit in different ways. First, as previously stated, what if the choice of measurement is not independent of the creation of entangled particles? By making this choice after the particles were created, Aspect’s experiment appeared to eliminate this possibility. Suppose, however, that the random number generator was not truly random. In any case, signals could have traveled to both the calcium atom and the random number generator as a result of a shared influence, causing them to conspire to violate Bell inequalities. This concept is known as “superdeterminism,” which essentially asserts that the particles are not only correlated with each other but also with the random number generator or the physicist selecting the measurement direction, so the universe is ultimately compelled to always conceal the existence of hidden variables. Now that we’ve discussed superdeterminism in the past, you can decide for yourself whether or not this concept is reasonable. But John Bell did not believe it to be plausible. However, even without superdeterminism, another loophole exists. It is possible to use Bell’s theorem to rule out the existence of local hidden variables. Local means that it has been ruled out that the secret information about the entangled particle states resides in the particles themselves.
However, it is still possible that the global wavefunction of the entangled particles contains hidden variables. Clauser and Aspect’s experiments ruled out the existence of local hidden variables, which may indicate that they ruled out locality rather than concealed information. Einstein loathed the idea that any violation of locality implies that some sort of influence travels faster than light. In one way or another, our Nobel laureates have revealed an unfamiliar universe to the majority of people. Okay, what about Anton Zeilinger, our third Nobel laureate? Clauser and Aspect’s research centered on testing the fundamentals of quantum mechanics and gaining a better understanding of what its quirkiness reveals about the world. However, their efforts also produced very practical outcomes. They and others like them improved our ability to create and manipulate quantum states that are entangled. and Zeilinger utilized them effectively. His demonstration of quantum teleportation may be his claim to fame. This phenomenon occurs when a quantum state is transferred from one particle to another via an intermediary particle that is entangled with both particles. We will save the amazing details for later. Quantum teleportation and the ability to move quantum information around are crucial for quantum computers, which is the most important fact to understand at the moment. Zeilinger is responsible for a number of advances in entanglement manipulation, which he has applied to the development of quantum cryptography and quantum computers. This is a rare Space-Time episode in which both Einstein and Feynman are incorrect. Einstein, because the quantum world is indeed quite spooky in one way or another.
And while Feynman was correct that Clauser would never disprove standard quantum mechanics, he was incorrect that Clauser shouldn’t even try. because science only advances when its theories are pushed to their breaking point. Whether they break or not, we learn something, and we may discover technologies that will be useful in ways nobody could have anticipated. Our improved knowledge of quantum entanglement has brought us very close to the era of quantum computing and quantum cryptography. All because a small number of scientists were willing to challenge the status quo and search for the hidden secrets of space and time. Before we move on to the comments, two items: It is once again that time of year when we ask you to participate in the annual PBS Digital Studios audience survey. The space-time audience has always been fantastic at completing surveys, and we hope this trend continues. By doing so, you can help us determine what new shows should be created and what topics they should cover. It will only take a few minutes, but it is of great importance to us. The entire network dives deeply into the data, which provides us with tremendous insights into your thoughts. The description contains a link. Many thanks in advance! As usual, we’d like to thank all of our Patreon supporters, but today I’d like to highlight Aleksander Henry Sajewski. Alek died at a young age, but according to all accounts, he was a true scientist throughout his entire life. When he entered college, he immersed himself in astrophysics and the sciences and emerged as a professional chemist and ALK staff scientist. He was such an avid admirer of the mysteries of physics and space that he named his pet hamster Sputnik and his pet fish Quark.
Therefore, Alek, on behalf of everyone at Space Time, we would like to thank you for the light you have brought to science and your community. We hope you discover serenity among the stars. Today we’ll be discussing the last two episodes. There was the one about photographing distant planets using the Sun’s gravitational field as a lens. The individual then solved the entire Lagrangian equation from the standard model of particle physics. Let’s begin with the gravitational lens of the sun. Antoine Micard raised an important issue: how do spacecraft send messages back to Earth? After all, it’s difficult to track Voyager’s faint signals, and the gravitational lens has a focal range at least four times greater than Voyager. This is a significant technological challenge, especially considering that we will be attempting to transmit actual images as opposed to merely numerical measurements and status updates. By the time these things launch, however, it will have been at least half a century since Voyager, so the technology of the power source, storage, and transmission will have advanced significantly. In addition, it may be possible to use the solar sails that propelled these crafts to their current position as antennae, which would aid. Vaka has two excellent inquiries. What is the maximum range of this method? Which planets should we investigate first? In terms of what planets can be brought into focus by the sun’s gravitational field, there is no real limit. In theory, it is possible to observe planets in other galaxies.
The actual limitation is the amount of light received, which would be insufficient beyond a certain distance. I was unable to locate a direct calculation, but the NASA report I referenced uses 100 LY as their canonical number, so I believe the implication is that this works on scales of hundreds of light years, but not many thousands of light years. Which planets do we examine first? Numerous planets of Earth’s mass orbiting sun-like stars are discussed in the report. Possibly, if we can find planets with other similarities to Earth, such as a similar age system and abundance of heavy elements, or gas giants in the outer solar system, But beyond that, it could be a matter of chance. Several of you commented that you appreciated the thorough explanation of the Standard Model Lagrangian, even if you couldn’t necessarily follow the math. In all honesty, this is a relief. Since that episode was somewhat experimental, There is no way to explain such a complicated equation in 10 minutes; it takes several years of coursework to even come close to being able to use the standard model Lagrangian to perform real calculations. The purpose of this excerpt was to give you a taste of the book’s contents and perhaps serve as a springboard for further research. Therefore, I am pleased and relieved that you found it useful in this manner. A few of you wondered if the ghosts in the Lagrangian of the standard model might be an indication of new physics beyond the standard model.
Perhaps, but I am uncertain. With a more refined formulation of the theory, I believe it is more probable that ghosts could be eradicated. Perhaps they are comparable to the fictitious spaces that appear when selecting a coordinate system with dimensions that extend beyond the physical universe. For instance, there are black hole coordinate systems that appear to imply alternate universes beyond the singularity; however, this is most likely just an artifact of overextending the mathematics. On the other hand, my analogy, which has nothing to do with particle physics, demonstrates that I am not a particle physicist. Quantum field theory, however, has a large number of problematic features that must be removed manually, such as the various infinities that must be manually renormalized. The equations then function flawlessly, indicating that the infinities do not belong to or represent anything physical. Nonetheless, it would be preferable if this content could be eliminated without these hacks. If you recite the complete Lagrangian equation three times in front of a mirror, particle ghosts will appear, according to 05TE. I tried it, and it worked. As you reach the end of the final Higgs kinetic term, the scene multiplies as the hermitian conjugate separates from the rest of reality and regresses into an infinite number of imaginary universes.
