Quantum Physics
Why is the Universe not Real (LOCALLY)?
You may have heard about the 2022 Nobel Prize in Physics awarded to physicists who experimentally confirmed that our Universe is “not Locally Real”. This led to some sensational misinterpretations like Universe is not “Real”, Universe is a ”Simulation” etc.., probably because the term, “Locally”, got lost in fine print. While these are far from foregone conclusions of these experiments, our Universe is indeed Not Locally Real.
In order to understand this discovery, we need to understand what Physicists mean by “Local” and “Real”.
What is “Local”?
Local simply means that nothing in the Universe can travel faster than the speed of Electromagnetic Waves (e.g. Light) and thereby no matter or force or information can be transmitted from one point in space to another, faster than this speed. This is derived from the special theory of relativity. For instance, if NASA wants to increase the speed of the Mars Rover by pressing the accelerate button here on Earth, it will take at least 3 mins for the electromagnetic wave (radio) signal to reach the Rover and for it to accelerate. There is no breaching this law, anywhere in the universe.
What is “Real”?
The concept of “Real” is quite intuitive. In the case of any macroscopic object, like a football, a planet or a star would be considered “Real” because they Exist at a Specific Location in space at a Specific Point in Time, with a Specific Momentum, Energy etc. In Classical physics, Location in space & time, Momentum, Energy etc are considered to be Deterministic and Objective properties of an object regardless of whether the object is being Observed by someone or not. Hence they were considered “Real”.
What does Quantum physics tell us about Reality?
According to Classical Physics, sub-atomic particles (Electrons, Protons, Neutrons, and more) which are the fundamental building blocks of all matter in our universe were considered to be Real in the same sense as macroscopic objects.
However in mid-1920s, Physicists Lois De Broglie and subsequently Erwin Schrodinger developed the foundational theories of Quantum Physics which postulated that the sub-atomic particles DO NOT Exist at a Specific point in space at a specific time, DO NOT have a specific momentum or direction of SPIN, until they are “Observed” (I’ll define what “Observed” means in a bit). They postulated that the Location, Momentum, Spin and Energy are NOT Deterministic properties of sub-Atomic Particles. Rather, the sub-atomic particles exist as a Probabilistic Wave, until the moment they are “Observed”. When Observed, the wave function collapses into particles with Deterministic Location, momentum and Spin. In other words, they are NOT “Real”, until observed.
How to interpret this Probabilistic Wave nature of sub-atomic particles?
How do we interpret this? The above image represents a possible Wave function to determine the Location of an electron. One interpretation of Quantum Physics is that the electron has a higher probability of existing all the Points in space corresponding to the Wave Peaks and progressively lower probabilities of existence at points down the slope of the Wave and 0% chance of existing at Points corresponding to the trough of the Wave. It does NOT mean that parts of a Single Electron physically exists in all possible locations simultaneously NOR does it mean that a Single electron is somehow Smeared all over the place like peanut-butter jelly with more lumps concentrated at a few points.
In terms of Electron’s angular SPIN, the electron has a certain probability of Spinning Up and a certain probability of Spinning Down. While it is technically wrong to visualize electron spinning like a top or a ball, because it is a point particle and points do not have a central axis around which it can Spin. But, for the sake of easy understanding think of Spin Up as spinning Right to Left and Spin Down as Left to Right.
Essentially, before being observed, the sub-atomic particles exist merely as a Probabilistic Wave function with certain probabilities of existing in all possible locations with all possible momentum and all possible spins. This is state is called Quantum Superposition. However, when Observed, the wave function collapses into a particle with definite location, momentum , spin etc.
Understanding Quantum Superposition with an analogy.
Quite fuzzy, isnt it? Think of it as an outcome of the Football game between Argentina and France. There was a certain probability of France winning vs Argentina winning , based on the quality of the team, manager, recent form etc. Likewise, the final score at the end of 90 mins could have been 0–0, 1–0,0–1, 1–1, 2–0, 2–1.. and so on, based on certain factors. When the final whistle is blown we know the exact state of the Outcome. However, until then, all out these outcomes are possible, each with different probabilities. With time, the probabilities of each of these outcomes changes as well. In Quantum mechanics, this probabilistic state of multiple possibilities is called Quantum Superposition.
What does “Observing” a sub-atomic particle mean?
In case of a macroscopic object like a football or moon, we observe the object when any Electromagnetic wave ( e.g. Light) or Sound wave bouncing off the Object reaches us. In case of Sub-Atomic particles , truth be told, we don’t really have a universally accepted definition of what constitutes “Observation” or “Measurement” of a particle. This is called the Measurement problem. However, in experimental physics, all it takes for the wave function of a sub-atomic particle to collapse is physical interaction with other particles. certain other particles bouncing off it is a simplistic way of thinking about it.
Some, including prominent physicists like Neil Bohr, Von Neuman and Eugene Wigner have argued that Observing really involves a Conscious being observing or measuring an electron via a measuring device. However, there has been no conclusive evidence that proves the role of Consciousness or Intent in collapsing the wave function. Nor has there been evidence Rejecting the role on Consciousness. If you think about it, it is quite difficult to separate the Intent to measure which is an essential precursor to the actual Measurement.
Einstein’s Reservations and Quantum Entanglement Paradox
Now this fuzzy wavy nature of particles before being observed was not accepted by many Physicists in the early days, including Einstein. In 1935 Einstein and his colleagues Boris Podolsky and Nathan Rosen (E-P-R) wrote a paper disputing the “Non-Real” nature of the Quantum world (i.e. Sub-Atomic world) , as derived by Quantum Physics. Einstein was particularly bothered by this because this violated the principle of “Locality” as implied by Special Relativity, in a specific scenario called Quantum entanglement.
A common analogy used to explain entanglement is a pair of Gloves. Now, lets say you take the left and right gloves and put them in a sealed box and ship them to different destinations. One Glove is sent to Alice who is an Astronaut stationed in Mars. Another is sent to Bob who is a scientist at a Research lab here on Earth. Let’s say Alice opens the box and finds that she has the right glove. Then she instantaneously knows that Bob has the left glove. Her knowledge is updated instantaneously even though it should take at least 3 Minutes for information to be transmitted from Earth to Mars.
Two Sub-Atomic particles are considered entangled when their Spins are perfectly correlated in opposite direction. Let’s say we have a device that can generate entangled electrons at a point in space that is exactly equidistant from Earth and Mars. We fire two entangled electrons , one towards Earth and one towards Mars. We have placed detectors in Earth and Mars to measure their Spin when they reach their destination. If one electron is detected to have Spin Up, then its entangled twin will instantaneously end up with Spin Down regardless of how many times you run this experiment.
Now, in the case of Gloves the package to Mars always contained the right glove and the Earth package contained left. While this property of the glove was hidden until the package was opened, it was Deterministic. The boxes never had a probability of containing either left or right, through its journey. However, in case of entangled electrons, both the electrons were in a Super-positioned state of both Spin Up and Spin Down. The electron which was observed first, ended up with a certain Spin which instantaneously influenced its twin electron’s Spin, regardless of the distance between them. This is what Einstein called Spooky action at a distance.
How could the second electron know the Spin of its entangled Twin and then “choose” the opposite Spin, instantaneously? E-P-R argued that the electrons were always had a deterministic Spin ( one Spinning up and other Spinning down) , from the moment they were generated in the lab. Going back to Glove experiment, the type of Glove ( i.e. Left or Right) in each of the boxes were pre-determined. Likewise, Einstein argued that the properties of electrons like Location, Spin and Momentum are always encoded as Hidden Variables, even before they are Observed and therefore “Real” in nature as opposed to “Probabilistic”.
The scientific debates about Real (Deterministic) vs Non-Real (Probabilistic) nature of the world lasted for a couple of decades, led by Einstein on the Deterministic side and Neil Bohr on the Probabilistic side. Einstein famously stated that God does not play dice.
How did Quantum Physics finally win the debate?
This seemed like a catch 22 puzzle until 1965 when John Bell, a theoretical Physicist working at CERN published an approach to ascertain whether Quantum world was Real or Probabilistic. Bell’s theorem was the basis for the 2022 Nobel Prize winning Physicists, Alain Aspect, John Clauser and Anton Zeilinger, who experimentally confirmed that the “Non-Real” nature of the Quantum world.
Let me explain the intuition behind Bell’s theorem with a slightly modified version of the thought experiment developed by Professor Brian Greene (Columbia University). Again, we have our entangled electron generator at an equidistant point between Earth and Mars. It fires entangled electrons one towards Earth and the other towards Mars. We have a detector placed in Mars and Earth to “Observe” these electrons when they reach the respective destinations. The property of the electron we measure is the Spin of the electrons (i.e. Up Spin or Down Spin). Now, the only difference between now and the previous thought experiment is that detectors in Earth and Mars can chose to detect the Spin along any 3 of the cartesian Axis ( i.e. X-Axis, Y-Axis or Z-Axis).
Yes, according to Quantum Physics, sub-atomic particles have the probabilities of Spinning up or Down along every possible axis, before being observed. I know it can be “head spinning” and practically impossible to imagine a ball spinning along multiple axis simultaneously.
Let’s ASSUME that Einstein’s view of “Real / Deterministic” world is True. Therefore, the electron Spins across all 3 Axis are already have a Specific Spin even before they are “Observed” by the detectors. It is NOT in this probabilistic state of all possible Spins. Given these electrons are entangled, by definition they have opposite Spins , along a given axis. However, note that entangled electrons can have same spin across different axis. For instance, along X-Axis, the entangled electrons will have opposite spins (i.e. Up-Down or Down-Up). However, along X-Axis and Y-Axis, entangled electrons can have the same spins or opposite spins (i.e Up-Up or Down-Down or Up-Down or Down-Up).
In the first version of the experiment, as indicated in above image, lets say that the Earth bound electron has specific spins of Up-Down-Up along X-Y-Z Axis respectively. Consequently, its Mars bound twin will have Down-Up-Down spins in the respective axis. You fire multiple entangled electron pairs with the above configuration The detectors in Earth and Mars can randomly chose the Axis along which they want to measure the Spin, every time electron hits the detector. The below matrix depicts the possible combination of measurements that will be detected when each electron pairs reach their respective detectors.
You can notice that there are 5 out of 9 possible combinations (i.e. 55%) where opposite Spins are detected.
Now, lets consider another version of the experiment where the Earth bound electron has specific spins of (Up-Up-Up) along X-Y-Z Axis respectively. The Mars bound will have opposite spins along the respective axis. Again, you fire multiple entangled electron pairs with the above configuration and the detectors randomly pick any axis to measure the spin.
The below matrix depicts the possible combination of measurements that will be detected when each electron pairs reach their respective detectors. Now, you see that all 9 out of 9 possible combinations (100%) where opposite spins are detected.
You can run any number of versions of the experiment with different configurations of Spin for the Earth vs Mars electrons twins (e.g. Up-Up-Down vs Down-Down-Up, Down-Up-Down vs Up-Down-Up etc…). As long as the Spins are Deterministic even before being Observed, you SHOULD find Opposite Spin combination in AT LEAST 55% of the measurements. This essential criteria for a deterministic world is called Bell’s inequality.
But, guess what. When the actual experiments were run by, not one , but 3 above mentioned Physicists independently, they Observed Opposite Spins only about 50% of the time. In these actual experiments, both detectors were in Earth of course. An they used Photons, instead of electrons.
Thanks to John Bell, Alain Aspect, John Clauser and Anton Zeilinger, we now definitively know that if the Universe is Local, then it cannot be Real.
However, these findings DO NOT rule out the possibility that Universe is
- Non-Local and Real — i.e. Sub-atomic particles have deterministic properties even before being Observed and are able to “communicate” instantaneously regardless of the distance. Hence, Real and Non-Local at Quantum level.
- Non-Local and Non-Real — Sub atomic particles only exist as a Probabilistic wave function before being observed and are able to “communicate” instantaneously regardless of the distance.
Given the sub-atomic particles are not locally real, does that mean we are not locally real either? Do we not exist unless somebody sees us. Technically, the answer is yes. We are not Locally Real either. However, at the macroscopic level, the Probabilistic nature of matter is too hard to detect. However, to understand the intuition behind this, we need to delve into Heisenberg’s uncertainty principle and Quantum decoherence. I’ll leave this for my subsequent blog.
