WAS EINSTEIN WRONG?

In October 2022, The Nobel Prize for Physics for awarded to a trio of scientists - Alain Aspect from Université Paris-Saclay in France, John Clauser from J.F. Clauser & Associates in the US, and Anton Zeilinger from University of Vienna in Austria - for their revolutionary work in Quantum Mechanics.

But what did they do?

Well... they basically proved Einstein wrong. Yes, you read that right! They proved the fuzzy-haired mega-genius of Physics wrong!

To understand how this, seemingly impossible feat, we might have to travel back a couple of decades to where it all began - during the period of The Great Einstein - Bohr Debate.

The Great Einstein - Bohr Debate

The Einstein-Bohr debates took place during a time of total chaos and confusion in the physics world. During a time when no one knew what the heck was going on in the universe - The Quantum Universe to be precise - including Physics giants like Einstein and Bohr. You see when things start to get really small, the laws of the real world or the laws of classical mechanics start to become non-existent and things get really weird. In simple words, particles smaller than atoms don't behave or exist in the same way as something like a tennis ball.

Let me build on this through an example beautifully explained by PBS Space Time in their video about Quantum Entanglement. Imagine you buy two balls - one black and one white, place them in two identical boxes and shuffle them so that you don't know which box contains which ball. Later on, you call your friend, give him one of the boxes and kick him out to another galaxy. Now the probability of the ball being black/white in both of the boxes is 50%. Say you open the box on Earth and learn that the color of the ball is white, so intuitively, the color of the ball your friend found must be black. But does this mean the information of you discovering the color of the ball traveled faster than the speed of light to the other ball and caused it to turn black the moment your friend opened the box? Obviously not! The color of both the balls was already set in both the boxes the moment you kicked your friend to another galaxy with his box.

Pretty intuitive right? Hold your horses, it's gonna get spooky from here

Let's say you bring back your poor friend to Earth and repeat the experiment but this time using quantum balls with entangled quantum colors. Repeat the same steps and kick your friend again to another galaxy. You might be thinking "well what's the difference? the balls are just smaller, we're gonna end up with the same result!" Umm... not exactly.

According to Bohr, Quantum Mechanics states that we don't only know which ball is which until the box is opened but the colors of balls before opening the box are fundamentally undefined, i.e. they are in a superposition of states. In simple language, the color of the balls is not already "set" the moment you kick your friend away but keeps switching between all of its possible states which in this case is white or black until a measurement or observation is made. When you open your box it forces the observed ball to "choose" a color state which then instantaneously forces the ball in the other box situated in another galaxy to choose the opposite. These quantum particles could be anything from a photon to an electron and their quantum property can be anything from color, spin, momentum, or any other entangled property. This is known as Quantum Entanglement which states that two particles like a pair of electrons or photons with a common source are connected and affect each other even if they are light-years apart.

The Copenhagen Interpretation further goes on to explain that such quantum systems are described by something called a wave function. The wave function encompasses all the possible states of the entangled particle pair. Now, if any measurement or observation is made on any one particle, it "collapses" the wave function and instantaneously influences the other particle's measurements regardless of the distance between them. In our example, the wave function collapses when either you or your friend opens the box and makes an observation.

Ok, what the fuc... Don't worry, even Einstein's reaction was somewhat similar.

Einstein called this peekabo universe of Bohrs, for a lack of better words, BS.

He strongly believed in objective reality that is independent of our measurement or observation of it. According to him, things cannot just appear and disappear or change their state automatically between intervals of looking at it and not looking at it. At the day time, we cannot observe the moon but does that mean that moon does not exist during that time? Of course not. It's there regardless of whether we see it or not.

To challenge Bohr’s peekaboo universe, Einstein along with Boris Podolsky ad Nathen Rosen released a famous paper titled the EPR Paradox. In this paper, the trio, through a thought experiment, tried to highlight that Quantum Mechanics is either incomplete at its best or completely wrong at its worst. The line of reasoning they provided for this was that in order for the peekaboo reality to make sense, you had to abandon a concept that was arguably the backbone of physics at the time, locality. Locality is a pretty intuitive concept that explains that anything in the universe is only affected by its immediate surrounding and that the chain of cause and effect cannot travel faster than the speed of light. Also, this was the fundamental foundation of his most famous theory – The Theory of General Relativity. So… there was a bit of money on the line.

For Bohr’s understanding of quantum entanglement, the information between the quantum pair of particles had to travel faster than the speed of light to influence one another instantaneously regardless of the distance between them. This idea violated both locality and causality because how the heck would a photon a million light years away instantaneously affect the quantum properties of my underwear?

Einstein and friends disagreed with this idea very strongly and thought that everything is the universe must be real, physical, and defined by knowable quantities. This is what he called a Deterministic Universe. The trio further went on to propose that for the quantum balls to “know” their color the whole time and not randomly switch between all their possible states, there would need to be some “extra” information in the wave function. This information is contained in what is called the “Hidden Variables”. The Hidden Variable Theory states that there exist some (possibly unobservable) quantities in the quantum system that “decide” the state of the quantum pairs at the moment of their creation. This allowed for information to not travel faster than the speed of light and thus preserve locality.

So, Einstein won right?

Even though no one was able to come up with a counterintuitive argument against Einstein’s EPR paper, Bohr still had more people believing his Copenhagen Interpretation because Quantum Mechanics was strong and Bohr was very determined in pushing his ideas forward.

The debate kind of lost its momentum but only until the entry of the Irish Physicist John Stewart Bell, in 1964.

Bell The Savior

John S. Bell was a physicist from CERN who decided to finally settle this increasingly confusing debate and help choose a side at last. He worked on what was later called The Bell Theory. In his quest to settle the Einstein-Bohr debate, he came up with the Bell Inequalities that would allow for an experimental test to take place that would finally prove if there existed hidden variables or not. The scientific specifications of the Bell test are beyond the scope of this article but the underlying idea was that these Bell Tests would demonstrate a specific statistical correlation if Einstein’s deterministic universe theory was correct and another if Bohr’s peekaboo universe theory was correct. In simplified language, the bell inequality would be true if the hidden variables are "deciding" the state of the entangled quantum particles at the beginning of their creation and violated otherwise. This groundbreaking discovery of Bell’s is one of the main reasons behind the success of the 2022 Nobel Prize Winners.

However, the task of proving a physics giant like Einstein wrong is no easy feat and was extremely difficult as no one believed in them. Clauser recalls the time when he ran into Richard Feynman’s office with, what he considered to be, a revolutionary idea and was famously kicked out for doubting the functioning of Quantum Mechanics.

Ok enough of twaddling, let’s jump on the coal-and-ice of this article.

The 2022 Nobel Trio

The most famous extension of the Bell Theory is the CHSH inequality by Clauser, Michael Horne, Abner Shimony, and Richard Holt published in 1969. Their theorem made the Bell theorem to be practically testable.

To understand this groundbreaking discovery that caused the 2022 trio to win the Nobel Prize, let me introduce you to a very simple concept called the Photon.

A photon is what light is made up of. Just as the screen that you’re staring at right now is made up of atoms, the fundamental particle of light is called the photon. This photon has a characteristic property called polarization that basically describes how a photon moves through space. It can either have horizontal polarization i.e. it only moves side to side or vertical polarization where it only moves up and down or anything in between as displayed in the GIF.

Now if you pass unpolarized photons (photons moving in all directions) through a horizontal polarizer (allows only horizontally polarized photons to pass), only the photons that are horizontally polarized will be able to pass through it and vice versa. But now if you place a vertical polarizer after the horizontal polarizer, nothing will be able to pass through it because all polarization angles had been blocked.

In the first Bell Test, performed by Clauser and his student Stuart Freedman in 1972, two entangled photons of opposite polarizations were emitted and passed through two different polarizers. Now Bohr’s peekaboo theory states that the polarization of the photons is undefined until an observation is made on one of them while Einstein states that their respective polarization is set the moment they’re created by hidden variables.

Ready for the climax?

*drumroll please*

Clauser and Freedman, through this Bell Test, found that the Bell Inequality was strongly violated and that there did not exist anything like hidden variables that would enable the entangled pair to have set a specific polarization at the time of their creation. This proved that the Universe is not locally “real” and Einstein’s deterministic view is false. However, it was not that easy to completely debunk Einstein’s work. Clauser’s experiment still had some loopholes that allowed for hidden variables to still exist.

This is where Alain Aspect comes into the picture, he corrected the flaws in the experiment, polished it a bit, and used excited photons with a more complex system of polarizers and lenses that would change their orientation every billionth of a second. So, once more, the experiment was proved to be in favor of Bohr and Quantum Mechanics.

You may think this would be enough to prove Einstein wrong. But guess what? You are wrong again. The slimmest of loopholes like super determinism in the experimental setup remained. However, this was only until 2017 when Anton Zeilinger along with his team closed the final loopholes at the University of Vienna by using the colors photons emitted from stars hundreds of years ago. This would erase any illusion caused by the experimental setup because for there to be any conspiracy that was creating the illusion of entanglement, it would have had to begin centuries before the starting of the experimenters. Ultimately, these indefatigable physics wizards managed to jump through the hoops and do the impossible - prove both Einstein and Feynman wrong!

But wait! Does this mean that information does travel faster than the speed of light?

To this question, almost every physicist together answers NO. This is because at the heart of the Copenhagen Interpretation lies the inherent randomness. So even if you measured one of the quantum entangled particle’s property and realize that the other particle pair must possess the opposite property, it is not until we verify the property of the second particle. Therefore, information does not travel faster than light and Einstein’s Theory of General Relativity remains unscathed.

So What?

Ok so what? This is just some boring physics theory. How does it have any impact on our day to day lives?

We had once used our knowledge of classical mechanics to build machines and factories that caused the industrial revolution to take place. Now with the knowledge of Quantum Entanglement, Zeilinger was responsible for advances in manipulating entanglement which forms the backbone of Quantum Computing. This discovery could very well lead to the Quantum Revolution in the future where Quantum Computers will, by a large amount, massively outperform the classical computers of the present.

But what does a Quantum Computer even mean?

It is a type of computer that only exists when you look at it. Relax, it was a joke!

In all seriousness, Quantum Computers harness the principles of Quantum Mechanics and possess enormous process power that can allow sensors to detect things with greater precision than one can currently imagine. Moreover, as per Scientific American, a quantum Internet could enable secure communication, clock synchronization, quantum-sensor networks, and access to remote quantum computers in the cloud.

The difference between regular and quantum computers is that regular computers make computations based on 1s and 0s – the binary system whereas quantum computers are based on quantum superpositions. In such computers, the possibility of either a 1 or a 0 until measured allows for more complicated calculations with extreme precision.

The development of the Quantum Internet has already begun and we already have the initial versions of quantum computers like The Micius satellite up and working.

All in all, this long discussion proves one thing:

Physics is not so useless and boring after all.