Quantum Physics - Overview

In this episode, we present a non-technical introduction to the intriguing world of quantum physics. 

Grasping its fundamental concepts is essential, for in many respects, quantum physics and Vedanta share and speak the same language. 

The focus of this episode is to highlight the essential and key aspects of quantum physics. 

Do contact us if you have any questions. 

Transcript

Hello and welcome to Science Meets Vedanta - a space where we explore the fundamental principles of Vedanta and unravel the profound intersections between scientific inquiry and ancient wisdom. I'm Jayant Kapatker, the author of the book - Science Meets Vedanta.

Drawing from the insights in this book, each week we’ll explore a variety of topics designed to help you understand the essential teachings of - Vedanta. Along the way, we’ll highlight valuable lessons that science can gain from Vedantic wisdom, so stay tuned! 

In today’s episode, we present a non-technical introduction to the intriguing world of quantum physics. Grasping its fundamental concepts is essential, for in many respects, quantum physics and Vedanta share and speak the same language. The focus of this episode is to highlight the essential and key aspects of quantum physics. 

Physics, in its vastness, can be traced along two main paths: Classical Physics and Quantum Physics.

Classical Physics: The Age of Newton

The story of classical physics begins with Isaac Newton, whose profound insights and groundbreaking laws laid the foundation for centuries of scientific exploration. Newton’s laws did not focus on atomic level objects but on macro-objects that we see around us. These laws, however, were so powerful and accurate that for a long time, physicists regarded the universe as a colossal, clockwork mechanism. Within this view, the motions of planets and all visible matter could be charted with certainty, allowing scientists to predict celestial movements with remarkable precision. Such was their confidence that many believed the universe’s secrets had been revealed, and little remained to be discovered.

The Quantum Leap: A New Era in Physics

But the dawn of the twentieth century brought a paradigm shift. As explorers of physics turned their gaze inward, probing the mysteries of atomic and subatomic particles, they encountered phenomena that defied the well-worn rules of Newtonian mechanics. The classical framework unraveled at these minuscule scales, revealing its limitations. To grapple with the perplexing behavior of matter and energy at the molecular, atomic, and even tinier levels, a new branch of physics emerged: quantum physics.

Quantum physics seeks to illuminate the strange, counterintuitive behavior of matter and energy at the smallest scales imaginable. Over the coming sections, we will explore the revolutionary discoveries and ideas that define quantum physics—a journey quite different from the predictable clockwork of Newton to the quantum world.

Light Is a Wave

In 1805, Thomas Young provided compelling evidence that light behaves as a wave through his renowned double-slit experiment. In this setup, a beam of light illuminated a barrier marked with two parallel slits. Beyond the barrier, a photographic plate captured the resulting light pattern. If light consisted solely of particles, the plate would reveal just two distinct bands corresponding to the slits. Instead, Young observed multiple alternating bands of light and dark—an interference pattern characteristic of waves combining and canceling each other out. This striking experiment demonstrated that light, when passing through the two slits, interferes with itself, confirming its wave-like nature. Today, you can find numerous videos on YouTube explaining the double-slit experiment and its fascinating implications. If you get a chance, you must watch these videos. 

Light as a Particle

A century later, in 1905, Albert Einstein challenged the wave-only view by investigating the “photoelectric effect.” In this experiment, when light shines upon a photoconductive metal, electrons are emitted from the metal’s surface. Einstein realized that this effect could only be explained if light acts as discrete packets of energy—later called photons. Each photon carries a packet of energy, behaving like a particle rather than a continuous wave. For this groundbreaking insight, Einstein received the Nobel Prize in Physics in 1921. Thus, light not only exhibits the attributes of a wave but can also behave as a stream of energy particles, deepening our understanding of the nature of light.

Matter Is Both Wave and Particle

The nature of matter is far more mysterious than it appears at first glance. Light, for instance, behaves both as a wave and a particle—a concept well established in physics. But in 1923, a bold idea was proposed by a French doctoral student, Louis de Broglie. He asserted that this dual character was not unique to light; instead, everything in the universe—ranging from you and me to planets, cars, and even the tree outside your window—possesses both wave-like and particle-like properties.

According to de Broglie’s hypothesis, every living or non-living thing is not merely a particle with mass and position, but also has an associated wavelength. This was a revolutionary leap in our understanding of reality. Remarkably, in 1927, experimental evidence confirmed de Broglie’s theory, establishing that all ‘matter’ exhibits this duality. For his groundbreaking insight, de Broglie was awarded the Nobel Prize in 1929, making him the only person to receive this honor for a doctoral thesis.

But how can we truly comprehend that everything around us is both matter (a particle) and non-matter (a wave)? The notion seems counterintuitive. When you look at the tree outside your window, it is undeniably there—a distinct, tangible object. It is a particle. So, when does this tree behave like a wave? Is it ever a wave at all? The de Broglie theory suggests it must be, or else the theory would not hold true. Let’s try to unravel this puzzle.

Suppose you are seeing a tree in front of you. You observe this tree, so it must be a particle – a physical tree. Imagine turning your back on the tree. Is it still a physical tree? Can you even be certain it exists in the way you perceive it? Without seeing it you cannot be sure - perhaps the tree has become a wave. This way of thinking can be extended to all objects in the universe, living or non-living, near or far. Suppose you’re having a conversation with a friend. While you’re face to face, your friend seems completely like a particle - physical being. But as soon as you leave the room and cannot see him, does your friend transform into a wave? When you return and see him again, do they revert to being a particle? This may sound bizarre, but such paradoxes lie at the heart of quantum physics.

You might even ask your friend, “Were you a wave while I was gone?” They might laugh or think you’re joking, but out of politeness, they’ll likely insist they were always a particle. Perhaps your friend would turn the question back to you: “I didn’t see you when you left. Were you a wave until you came back and I saw you again?” It’s a reasonable question! While you were apart, both of you could, in some quantum sense, consider the other as a wave.

These thought experiments imply something profound: Anything in your direct experience appears as a particle, but outside your presence—unobserved—it may exist as a wave. Your observation seems necessary for something to appear as a particle. This is an important implication of de Broglie’s theory.

But can something truly be both a wave and a particle at the same time? Or must it be one or the other, depending on whether it is being observed? If the tree is a particle when you see it, can it simultaneously be a wave? Science has yet to provide a clear answer. Here’s something to ponder: if an object is a particle, where does the wave nature reside? Is the wave an intrinsic part of space and time, or does it inhabit some other realm entirely?

De Broglie’s theory raises more questions than answers. The mysteries of how matter can be both wave and particle continue to challenge and fascinate scientists. We would be discussing these issues in the coming episodes. 

Schrodinger’s Wave Function

Just as Newton’s laws of motion are foundational to classical physics, Erwin Schrödinger’s wave function lies at the heart of quantum physics. Let’s break down what this means in simple terms.

1. What Is Schrödinger’s Wave Equation?

Schrödinger’s equation is a mathematical formula that describes how physical systems behave. In every case, there are two main parts: the “observing system” - the observer or measuring device and the “observed system” - the wave part of the object being studied. According to the wave-particle duality proposed by de Broglie, everything in the universe behaves both like a particle and a wave. Schrödinger’s equation specifically describes the wave aspect of these objects. We are interacting with its “wave function”—the mathematical description of its wave-like behaviors.

2. Standing Waves, Not Traveling Waves

Schrödinger’s equation only describes “standing” waves, not “traveling” waves. A traveling wave is what you see when you throw a stone in a pond, and the ripples move outward. In contrast, a standing wave bounces back and forth in a confined space, like the vibration of a guitar string or echoes between the walls of a room. Electrons in atoms act like standing waves because they are restricted within the boundaries of the atom. For us to observe these standing waves, the system needs to be enclosed in some way.

3. A Universal Equation for all standing waves

Schrodinger’s wave equation is a generic equation which represents all the possible standing wave functions in the universe. The main variables of Schrodinger’s wave equation are time and energy. If you input the correct variables for a particular observed system, Schrodinger’s wave equation will represent that wave function. If you input the energy variables of the electron wave, Schrodinger’s equation will represent the electron wave function over time. Understanding the energy structure of electrons, photons, molecules, and other micro-objects is simpler. Macro-objects have more complex wave functions and are much more difficult to understand. In conclusion, we may say that Schrodinger’s wave equation is applicable in every wave function, both simple and complex. The only limitation is that science still does not understand the input variables needed for the complex waves representing macro-objects like you and me, or cars and planets.

4. From Wave Function to Probability

You can convert Schrodinger’s wave function into a probability wave function by squaring the wave function. The probability wave function contains all the possible outcomes. There could be unlimited possibilities. To explain this, the famous “Schrodinger’s cat” example is given. A cat is enclosed in a box which contains a vial of poison attached to an atomic trigger. The atomic trigger can randomly trigger the poison vial. If the poison vial breaks, the cat will be dead. One is never sure if the cat is dead or alive at any given time. As per the probability function yielded by Schrodinger’s equation, the cat could be dead or alive, and it could also be half dead or half alive, one-third dead or two-thirds alive, and all the other different possible mixes of ratios between dead and alive. It has many possibilities. All these possibilities are within the cat wave function. 

5. The Role of Observation: Collapse of the Wave Function

A critical aspect of Schrödinger’s equation is the “observing system.” When an observer interacts with the observed system—say, by opening the box to check on the cat—the wave function instantly “collapses” to just one of the possible outcomes. If you see the cat alive, all other probabilities disappear in that instant. Before observation, the cat exists as a mixture of possibilities; after observation, only one reality remains.

This collapse only happens in the presence of an observing system. Without an observer, the physical system remains in its wave-like state, holding all possibilities at once. Once observation occurs, the system “chooses” one outcome.

6. The Chain of Observation

Another important aspect of the physical system for Schrodinger’s wave equation is the observing system. When this observing system interacts with the observed system at any given time, the wave function of the observed system collapses to only one of the logical possibilities at that given time. In the example of Schrodinger’s cat, if you open the trapdoor to see the cat, the cat will be alive or dead. If it is found alive, all the other possibilities become zero. In other words, when the observing system interacts with the observed system, the wave collapses to one of the possibilities for that given time, and then all the other possibilities have a zero chance of occurring. Till the trapdoor is opened, the cat is in a waveform with infinite possibilities. When the door is opened by the observing system, the cat wave collapses into being alive, and then all the other possibilities become zero.

Here is a direct hint that the wave function only collapses in the presence of an observing system. If there is no observing system, the observed system will continue to be a wave function. Before interacting with an observing system, the observed system is a wave, and the moment after interacting with the observing system, the observed wave function collapses to become a particle.

If you take the broader viewpoint, you will realize that the photographic plate in the double-slit experiment itself is matter, and therefore it also has a wave function. So, what observing system collapses the wave function of the photographic plate? The logical answer would be your eyes. But the eye is also matter and therefore it also has a wave function. So, what observing system collapses the wave function of the eye? The answer would be your brain. But the brain also is matter and therefore it also has a wave function. So, what observing system collapses the wave function of the brain? I think that at this point, science has come to the end of the road; it cannot explain what or which observing system collapses the wave function of the brain. What is this ultimate observing system which finally collapses all the wave functions. This is an unanswered mystery of quantum physics.  

In summary, Schrödinger’s wave function is a powerful tool that describes the strange, probabilistic nature of the quantum world. It reveals a universe where outcomes remain uncertain until observed, and where the act of observation itself shapes reality.

This episode has offered an introduction to the realm of quantum physics, shedding light on its foundational concepts. Yet, it has also unveiled many unresolved questions—such as the very nature of waves, the ultimate observing system. In future episodes, we will journey further into these profound mysteries, guided by the timeless insights of Vedanta to enrich and deepen our understanding.

We hope today’s episode has sparked your curiosity about quantum physics. If you’d like to dive deeper, visit our blog at Vedanta and science.com or find my book, Science Meets Vedanta, on Amazon. Be sure to subscribe so you won’t miss upcoming episodes. If you enjoyed this episode, please share it with your family and friends. 

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