Quantum Debates

Written By: Arman Momeni

Introduction:

Quantum theory was the result of physicists’ confusion surrounding the behaviour of atoms. Atoms behave unlike any component of familiar matter, and physicists concluded that atoms did not make intuitive sense when compared to the laws of the universe. Quantum mechanics comprises a section of mechanics that deals with the mathematics, motion, and function of subatomic particles, denoting the strict yet confusing rules surrounding the manner of matter and light on the atomic scale. Just like any field of science, however, understanding and formulating a cohesive theory for quantum mechanics was not a simple task. Many scientists, including Schrödinger, Heisenberg, and Einstein went head-to-head, attesting that their interpretation of the quantum realm was the correct one. This article from Science ReWired takes you through the lens of multiple physicists, elucidating their perspective on the new-found branch of science: quantum mechanics. Welcome to quantum debates!

*Disclaimer: the text utilized is not verbatim to what the physicists have said, rather a summary of their points of view at a given time.

Einstein:

There is a common misconception that Einstein opposed quantum mechanics, stating that “God does not play dice,” but this statement is simply not true. Einstein, in fact, was one of the founding fathers of a quantum theory of nature, working with Planck to quantize light. Einstein discovered that light existed in clear, discrete units called photons. Einstein came up with the initial quantum hypothesis that would complement the wave-theory of light, and provide light with a particle-wave duality. This particle-wave duality was eventually attributed to all particles.

Einstein did have an objection to the field of quantum theory, but he didn’t go against the theory as a whole, he simply went against the idea that quantum mechanics was a “complete” theory. He believed that quantum mechanics had the potential to satisfy his detailed representation of nature.

Einstein’s theory for a particle-wave duality of light, however, was not looked upon with admiration. Based on the previous ideas of mechanics, one could not have a particle be both a wave and a particle without running into serious mathematical problems. One of Einstein’s greatest skeptics was Henri Poincaré:

            Poincaré: What mechanics are you using?

            Einstein: No mechanics.

Poincaré wasn’t a skeptic of Einstein for the sake of opposing his theory. He was willing to change the laws of physics, but there was a condition: the new laws had to have a form that he could grasp and must have a description that persists through the equations of nature from state to state. Eventually, however, Poincaré reluctantly surrendered the fight, losing to Einstein.

Poincaré: I tried the calculation that related to changing the theory in the format I believed would be the most useful. They led me to a negative result. A hypothesis that involves quantising light may be the only one that can explain phenomena in nature.

Bohr:

A year after the Solvay conference and the disagreements between Einstein and Poincare, Niels Bohr took up the idea of the quantum iteration of light. Bohr was a trailblazer, proposing a radical idea.

Bohr: What if electrons’ orbits did not obey classical electrodynamics? What if electrons were actually located in stationary states? States that were not disrupted the way classical electrodynamics would be.

Maybe the electrons radiated energy away from the nucleus, eventually falling into it. What if an electron went down to a lower orbit, meaning it changes its energy? What if that energy is emitted as a photon, a quantized packet of light?

Einstein: Bohr, can your idea explain the so-called Balmer lines, the spatial distribution of light. If it can Bohr, you may be the father of one of the greatest discoveries.

Louis de Broglie: Bohr, your idea seems like it is present in the face of desperation. You have no explanation of why these orbits stand the way they do. I propose a thought experiment.

If electrons are like waves and waves can only constructively interfere in whole number oscillations, then maybe I have a solution. I may have a proposal as to why stationary states act the way they are.  

Let’s look at an analog system: a sound pumped around a tube. Let’s look at the way the waves create interference and construction patterns, it only happens when they are in multiples of whole numbers.

Bohr, one of the most remarkable features of your proposed atom is that electrons of certain momenta are quantized and can only be found in certain sections of the atom. It can have an energy level of 1 or 2 or 3, but it cannot have an energy level of 2.627362.

This is much like how waves work, thus it seems that the idea of electrons having a wave structure must be accepted. If there are a whole number of wavelengths that can fit around the Bohr orbit, then it reinforces itself, and the system works. If it’s not in whole numbers, well, then the system kills itself.

This was just the start, however. Quantum theory continued to become more elaborate, and new scientists developed novel ideas for explaining the obscure behavior of atoms.

Heisenberg:

With Werner Heisenberg, we move beyond medieval quantum theory, the complicated theory of electrons in stationary states, and welcome the true beauty and arbitrary behaviour of particles.

Heisenberg was an enthusiastic, conservative character, differing much from the likes of Erwin Schrödinger, who we will discuss in the next section.

Heisenberg: I was recounting Bohr’s model, the model of a stationary state, but I came across an interesting stipulation. I can take an array of numbers and actually calculate the possibility of an electron jumping from one whole-number orbit to another. And not just in a linear pattern, but big jumps, like from orbit 1 to 5; my numbers can calculate that possibility.

Heisenberg began to understand how electrons could hop from orbit to orbit, but he never discussed how they actually got there. Heisenberg followed the strict instructions and postulates presented by Bohr.

Bohr: I forbid it. Any discussion surrounding what happens between orbit to orbit is irrelevant. It’s not possible to track the movement the same way we would track the movement of a classic particle.

Heisenberg: So, I’ll work around that. I will simply codify my numbers into a measure of position or momentum. But wait! When I measure the first momentum, the position is not the same as what I had measured before measuring the momentum. AND when I measure the first position, the measured momentum is no longer the same as my original measurement.

Bohr: Heisenberg, that does not make much sense. In classical physics, if I were to roll a ball, the order at which I measure the momentum and position would make no difference on the values.

Heisenberg: Empirical principles differ greatly from that of the quantum world Bohr.

Heisenberg began to show that you could never get an exact position and an exact momentum at the same time. When you measured the momentum it disturbed its position, and when you measured the position, it disturbed the momentum.

It is important to note that because quantum particles act as waves, they pertain both a position and a momentum. However, it is impossible to measure the exact position and momentum of a particle at the same time. A wave is not in one exact location, but it spreads out over time. If one wanted to measure position they would be focused on a specific part of the wave, whereas if one wanted to measure speed they would be focused on the entirety of its movement. Therefore, you can’t measure the two values simultaneously, as the means of measurement are inconsistent with each other. This is the famous uncertainty principle, which was created by Werner Heisenberg in 1927 and explains why one can never be accurate about the position and speed of a particle. While this may seem irrelevant to the visible world, the uncertainty principle applies to anything that moves in a wavelike pattern (water, roller coaster, etc.).

Schrodinger:

While Heisenberg was focused on the particle nature, Schrödinger wanted to know about waves.

Schrödinger: Waves are quite confusing. I want to make them as clear as possible. I want a pictorial understanding of what goes on in the quantum world.

Schrödinger, however, was also set into an existential crisis because of quantum mechanics.

Schrödinger: Do I exist? Does a world exist beside me? Do I cease to exist on bodily death? I want to combine philosophy and science. Rather, I want to use science to answer questions regarding philosophy. I want to understand the world much closer to what Einstein was striving for rather than Heisenberg. We need a concrete, cohesive understanding of the world we cannot view, the world we cannot touch.

Schrödinger’s questions lead to arguments…

Schrödinger: Bohr, what do quantum jumps denote. Your theory is nonsensical. You claim that an electron is in a stationary state of an atom, yet it does not radiate. You provide no explanation. How can you possibly label your so-called incredible phenomenon as purely arbitrary?

Bohr: Schrödinger, you may be right. In fact, you are right, but how does that disprove my theory. The only thing your statements prove is that we cannot visualize the jumps, it doesn’t mean they’re non-existent.

Schrödinger: But Bohr, as soon as we allow ourselves to change the picture and state that electrons are waves of matter rather than particles, everything looks different.

Bohr: Your point of view is rather optimistic Schrödinger. Problems do not simply disappear because we change the picture to waves. The problems are simply translated, transformed into an entity elsewhere.

Schrödinger’s ability to redefine the picture and look at electrons as waves allowed for significant mathematical clarity and simplicity. Schrödinger made enormous leaps in the world of quantum theory, but he was stubborn.

Bohr: Schrödinger, you cannot simply label these jumps as a discontinuity.

Schrödinger: If we are still going to put up with quantum jumps, then I am sorry I ever had anything to do with quantum theory.

Bohr: The scientific community, however, is very thankful. If it wasn’t for your wave mechanics, we would still have a very abstract view of particles.

By treating particles as waves, Schrödinger discovered some problems regarding the probabilities of waves, which welcomed the concept of quantum superposition.

Quantum superposition elucidates the idea that particles do not have a coherent state until they are observed. This means that a particle that is observed as red may be in a state where it is both red and blue before it is observed. It’s a confusing stipulation, but is in fact accurate when applied to the world of quantum mechanics.

In order to fully understand the ideas in the world of quantum mechanics, one must differentiate their understandings of the quantum world with that of the everyday world. In our world, positions, momentums, and other quantities are always well-defined. If you were to look at a fire hydrant, it will be red, and it will have been red before you were to look at it; if you were to look at the pavement, it will be grey, and it will have been grey before you were to look at it. These empirical principles still stand and are not falsified by superposition. Schrödinger’s theory exists as its own separate set of rules that apply to particles, such as electrons or photons (the smallest unit of a specific phenomenon).

Our current understanding of particle physics portrays particle behaviors as mathematically wave-like, and as there are so many particles within our universe, these particle waves will eventually overlap, combine, and build complex patterns that cannot simply be measured as an absolute value. The simplest way of thinking of superposition is as a function that can have two answers: one positive and one negative. For example, in the function x^2 = 9, x can be -3 and 3. The world of quantum mechanics is all about probabilities and lacks the absolutes of our known world.  

However, the idea of quantum superposition made Schrödinger uneasy. Schrödinger thought of quantum superposition using a thought experiment, which is famously known as Schrödinger’s cat.

Let’s presume you are a cruel cat owner. You place your mischievous cat Milton in a box and shut it with a lid. Inside of the box you also place a radioactive substance that controls a vial of poison. The radioactive substance has a 50% chance of radioactive decay and is connected to a Geiger counter that will instantaneously release the poison upon decay, ergo killing Milton.

According to the standard rules of probability, when you open the box, there is an equal probability that Milton is either dead or alive. Such rules of probability should remain the same even when the lid is closed; a 50% chance that the cat in the box is dead, and a 50% chance that the cat in the box is alive. This scenario makes sense, the probabilities are accurate, and your cat Milton, can either be alive OR dead. However, if one were to scale down this thought process all the way to the world of quantum mechanics, they would find that the scenario does not hold true. According to quantum superposition, until you open the box, your poor Milton is considered to be both alive AND dead. Schrödinger, in fact, was so revolted by his thought experiment that he decided to abandon physics all together and pursue the route of biological sciences.

Finale:

If you were hoping for an ending where one physicist slashed the rest and entered his rightful throne as the king of quantum mechanics, you may be disappointed.

One of the most noteworthy characteristics of quantum mechanics is that there are many different answers and interpretations. Sometimes we think of particles as particles, which yields several answers, but sometimes we think of particles as waves, which yields a new set of answers AND problems. There is a duality between particle-like and wave-like things and it is not something one can get around. Scientists don’t fully understand the world of quantum science. As stated above, quantum mechanics was the reason Schrödinger switched career paths as a whole. Quantum mechanics is an extremely abstract field of physics, and there is still so much to be uncovered by scientists and theorists as a whole. There is a lot of controversy in the field of quantum mechanics as well, just like in the 20th century, scientists fail to agree on and understand several topics within quantum physics, such as how gravity works when it is applied to the subatomic level.

Quantum Mechanics is a field that leaves a lot of doors open for future discoveries and provokes everyday people to formulate controversial paradoxes just like Schrödinger did with his cat. The important lesson to be learned from the quantum battles, however, is that there can be several different perspectives when looking at phenomena. While all the scientists held dramatically different views, they were all right with respect to their perspective on certain characteristics and behaviours. Quantum mechanics teaches us to stand our ground and be confident in what we believe is right, even if someone attests we’re wrong.