Jan 9, 2021
Everything you thought you knew about physics is a lie
Imagine this. You’re sitting under a tree when all of a sudden an apple hits you on the head. Then something strikes you; why is it that apples fall from trees. It’s gravity! You’re brilliant, and you’ve just figured *all* there is to physics. Hmmm, not quite.
Ok, maybe not everything you know is a lie! But when we think about physics, it’s usually classical physics, which is able to describe everything around us fairly well. But when we get into quantum physics, which studies things even smaller than atoms, things become super interesting, and I think more of us should learn about this!
But before we start, I want to show you a quote:
I think I can safely say that nobody really understands quantum mechanics. –Richard Feynman, famous physicist and Nobel laureate
It’s a bit of a discouraging quote, especially coming from someone who’s dedicated their life to studying this stuff. Isn’t it?
Regardless of what Feynman said, I think we should at least try to understand some of it! So today, I’m attempting to give you a small glimpse into the magical world of quantum physics or quantum mechanics as if you’re a 5-year-old. Okay, maybe a pretty smart 5-year-old, but you get the point!
So What’s Quantum Physics, Really?
Let’s start with a simple question, “why?” Why is it that just subatomic particles use the laws of quantum mechanics (that you’ll learn about below!) and not us? I mean, isn’t physics just physics?
Well, according to Dr. Baird, an Assistant Professor of Physics at West Texas A&M University, if we wanted to see the awesome quantum effects on a larger scale, for example at our scale, we would need everything around us to act like waves but in an organized fashion. And this doesn’t often happen so all of those random waves basically cancel each other out and make the effects unnoticeable at our level. (Keep in mind that this is definitely an oversimplification!)
Sounds a little complicated, but let’s use this rough analogy to help us better understand: the reason we don’t see the effects of quantum mechanics on our scale is similar to how we don’t notice the Earth spinning at almost 1000 miles an hour! Of course, it’s happening (otherwise there’d be no night or day 🌙) but it’s unnoticeable to us. This is pretty similar to how quantum mechanics is happening but we just don’t notice it.
The Bare Bone Basics
It’s the explanation for how everything works at a subatomic level. That means when you go even smaller than an atom, which is what we thought was the building block of life for thousands of years. We used to think of atoms as LEGO blocks that couldn’t be broken down any further and made of everything we know and love.
Now we know that there are particles even smaller and to describe them we use quantum physics, or quantum mechanics (they mean the same thing).
So how do these particles act? To put it super simply, the particles are both waves and exact points, and they don’t have exact positions but instead are governed by probability. Wait, that doesn’t sound very simple…
What Even Are Subatomic Particles?
Let’s break it down together! If you’ve ever taken physics (which you likely haven’t as a 5-year-old), you would have been told that subatomic particles (remember those are the particles that are even smaller than atoms) are just that: particles.
Particles are small objects that are localized — that means they’re in one specific spot at a certain time. Let’s use an analogy to help! Imagine particles as small bouncy balls. At any point in time, they can only be in one spot.
But when you go subatomic, things start getting weird. Those particles that we thought acted super predictably and simply, don’t anymore.
You can think of these subatomic “particles” as slinkies! The analogy here isn’t perfect but it’s super helpful. If you throw your slinky with a lot of force, there’s a high chance of it stretching super far away, and a very small chance of it barely stretching, and staying right near you.
To put it in more scientific terms, it’s all dependant on probability and not certainty.
But where do the waves come in? Well, there’s this super awesome theory that subatomic particles behave as both waves and particles. (Remember that in science, a theory is actually backed by proof and widely accepted!) Mind blown 🤯
The Best of Both Worlds: Wave-Particle Duality!
Let’s go back to our bouncy ball and slinky. To avoid confusion, I’ll call our subatomic particles, subatomic objects from now on.
In some ways, subatomic objects act like a bouncy ball, or like a certain point in space. We’ll talk about an experiment by our favourite physicist, Einstein, that’ll help us better picture this.
But in other ways, subatomic objects are like waves, kind of like a slinky. If we want to find the position of the object, or where it is, and its momentum, a measurement of mass that is moving, we need to treat these objects like waves.
This is called (fancy word alert!) wave-particle duality. If we break up the words, the term makes a lot of sense. Here, duality means there are two states, two ways the object can act. So all it’s saying is that subatomic objects act as both waves and particles.
They’re Waves: The Double Slit Experiment
It’s definitely time for an example to help us wrap our mind around this. Let’s first talk about the idea that subatomic objects act like waves! Let’s turn to a super famous experiment, called the double slit experiment.
Imagine we have a wall with two slits and another wall behind it. We start shooting electrons at the wall. You’d expect to see a pattern form of two lines of electrons right behind the slits right?
Well, not so fast! What actually ends up happening is that we get several lines on the back wall. Can you guess why that is?
It’s in the same pattern as how waves would act. The waves cause something called an interference pattern when they “overlap” that causes a pattern where there are more electrons in several strips. Take a look down below to see what I mean!
They’re Particles: The Photoelectric Effect
That’s pretty cool and all, but then how are these subatomic objects like particles? Aren’t they just waves? That’s exactly what physicist thought about light for a while. Then came along Albert Einstein with his photoelectric effect experiment.
He wanted to show that light actually moved like quanta, little packets of energy. And so that’s what he did, using some good ol’ metal and light. He shined different amounts and types of light on metal and looked at how electrons (those are a type of subatomic object) left the metal.
If in fact, light traveled in waves, increasing the intensity of light would mean that the electrons would leave faster! But that’s not what happened. Increasing the intensity only increased the number of electrons that left.
What’s more, red light wasn’t able to get the electrons to leave, no matter the intensity of the light or the length of time it was shone on the metal. Without getting into wavelengths and all that, I’ll just let you know that if light just traveled in waves this wouldn’t be true!
We’re All Made Of Just 3 Things
Remember these guys from way at the beginning of the article?
Well, they’re about to become pretty important! I’ve been calling anything smaller than an atom, a subatomic object since the beginning. But it’s time to dig deeper!
I also mentioned that we used to think atoms were the smallest building blocks of life that couldn’t be broken down anymore, and that turns out to be wrong. Right now, we know there are things that are even smaller.
Let’s first zoom into the atom!
We see three particles, electrons, protons and neutrons. As far as we know, electrons are an elementary particle. This means, they probably can’t be broken down any further.
But we can zoom in even more into protons and neutrons. Oh look it’s our friends again! They’re called quarks. The green ones facing up are up quarks and the ones facing down are down quarks. Know that they don’t actually look like this in real life but right now their arrow-like shapes and faces are helpful to us for understanding them!
So now we have a list of elementary particles that looks like this:
It’s looks a little empty don’t you think? Woah how’d you know? There’s still another elementary particle called a neutrino. It’s a small particle that we haven’t studied as much as electrons or quarks because they rarely interact with things in the universe.
That’s why we’re all essentially made of the same three things, electrons, up quarks and down quarks, though billions and billions of neutrinos are passing through us right now!
But we’re not quite done yet! For no good reason (that we understand), there are two other categories of elementary particles. They get increasingly more massive. So think of the far left column below as the youngest siblings, the middle column as the middle siblings, and the far right one as the oldest siblings!
It’s good to know that we don’t see those middle and oldest siblings very often because they’re very unstable, meaning they decay (or get destroyed) super quickly!
Let’s Do Some Math!
Now that you know some basics, I think it’s time you graduated to some math! Let’s pretend you’re all grown up and no longer 5 years old. If you don’t feel up to it, that’s okay but you’ll be missing out on lots of fun!
Let’s take a look at the Schrödinger equation! It’s one of the most important equations in quantum mechanics and it’s similar to Newton’s laws of motions for classical physics but for the quantum world.
In simple terms, the equation helps determine the form of the probability waves that govern the motion of subatomic particles. It can also help with other quantities like momentum. Remember how I mentioned that the movement of particles is probabilistic when we got quantum.
Yes, the equation looks scary. Yes, this is a simplified version. And yes, we’ll understand at least what each of the symbols mean together (maybe not ∂ because that would slightly derail us but otherwise, we’ll get there!)
Let’s take a look at our H with a hat on top: it’s called the Hamiltonian operator. Basically, it operates on the system that takes into account the total energy in the system (the system’s the portion of the universe that we’re studying). This means both the kinetic energy and potential energy.
See, that wasn’t so bad! Next up is psi or Ψ. It represents the wave function. Think of it as the state that the system is in. It helps give us the probabality of finding a particle in a specific point in space.
We’re already on to the next side of the equation where we meet i. Don’t be scared by it; it just stands for the √(-1). Why an i? Without getting too deep into it, it’s because this is an imaginary number. You can read more here!
Then we come to another good ol’ number, known as Planck’s constant, and represented by the symbol called h-bar. What this constant actually is, is beyond the scope of this article, but just think of it as something similar to π. It does represent something very important but knowing that it’s a constant is good enough for us right now.
Then we get to what might look like the scariest part yet. Well, we know what Ψ is from before and t just stands for time. What’s the other weird symbol, ∂? This article isn’t about derivatives so to really understand it, read this awesome, but succinct explanation by Luboš Motl here. Just think of it as how fast something changes with respect to time!
We Did It!
Hey, looks like it’s the end of the article! Thanks for coming along on this wild journey and I hope you learned a thing or two. I wanted to mention that there are so so so many more concept to cover, from quantum field theory to the measurement problem. If you’re thirsty for some more quantum mechanics knowledge, check out this YouTube playlist I put together of some of the best, most interesting videos I found.
And if you’ve made it this far, you deserve a joke 😉
Quantum physics has its ups and downs…
But it all quarks out in the end
TL;DR
- Quantum physics and quantum mechanics provides an explanation for how everything works at a subatomic level– that’s when we got even smaller than an atom
- The field relies a lot on probability and waves 🌊
- The wave-particle duality tells us that subatomic objects act like both particles and waves: to find their approximate position and momentum we treat them like waves. But like we saw in the photoelectric effect experiment, they also act as little packets of energy, or quanta
- We don’t see the effects of quantum mechanics at our level (larger than subatomic) because everything around is has random waves that cancel each other out (read more here!)
- The smallest, indivisible building blocks of the universe are the elementary particles, but we’re basically just made of electrons, up quarks, and down quarks
Hey there 👋 Parmin here; I’m a 15 y/o student studying stem cells at The Knowledge Society 🧪 Everyday, I aspire to uncover the secrets of biology and learn something new! Make sure to follow me on Medium to hear about every new article I post, connect with me on LinkedIn, or contact me at parminsedigh@gmail.com! Also subscribe to my monthly newsletter to learn about every cool, new thing I’m working on ✍️
