God Does Not Play Dice With The Universe
Let me start with explaining the title which is a famous quote by one of the most interesting professors at California Institute of Technology, Richard Feynman. Quantum mechanics is so counterintuitive that anyone claiming to fully understand it and grasp all the concepts I will explain later on, will certainly have overlooked some aspects of it. Einstein also referred to quantum physics as something that could not be possible due to something he said about God and the probabilistic nature of quantum mechanics. Note that Einstein was not religious and only used the word God as a way to express his thoughts.
Note that I will use quantum physics from now on, there is no distinction between quantum physics and quantum mechanics, they are one and the same. Let me take you on a journey through the enormous interesting world of quantum physics. I will not do any math at all, but explain to you in layman terms and just the English language to help you gain insight into things like the double-slit experiment, singularities, quantum entanglement and much more. A lot of you have heard about Schrödinger’s cat, but what exactly does it portray, I will guide you through some thought experiments and real-world quantum experiments. My goal is to open up your mind to the strange quantum world and let you be baffled by it. If you are done reading this through, you can certainly impress people at parties.
Classical Physics vs Quantum Physics
The distinction between classical physics and quantum physics couldn’t be more clear. You can think of it this way, you can ask certain questions to classical physics and it will give the same predictable answer every time, if you ask it questions it doesn’t understand, it will say it is a bad question. Let’s say we go on a road trip and we would like to know when we will be at our next stop which is 100 kilometers further. If we are traveling at a speed of 100 kilometers per hour we will get there in exactly one hour. If you ask this very simple question to classical physics, it will always give the same answer, classical physics is deterministic. Our good guy Newton figured this all out which is rather crazy if you think of it. He also wrote the Principia Mathematica in 1687, which is the very basis of all classical physics. Ok, enough about the unfathomable knowledge of Newton and off to quantum physics superstars with names like Dirac, Schrödinger, Heisenberg and Hawking. I will not go further in all of the accomplishments of these gentlemen, but I felt it was needed to put them in the spotlight.
Quantum physics is one of the strangest things physicists came across, which Einstein emphasizes with his famous phrase “God does not play dice”. Einstein is referring to the probabilistic nature of quantum physics. If you ask a question to quantum physics, it doesn’t respond with a definite answer, it answers with a probability of multiple answers. If you ask it where an electron is when you know the speed of it, just like we did with classical physics, it will answer with a certain probability that it is somewhere and another probability that it is somewhere else. Before we dive a little deeper into one of the most profound experiments in quantum physics, the double split experiment, we are going to look at the most famous thought experiment about quantum physics which is Schrödinger’s cat.
Schrödinger’s Cat
As you’ll notice, all things about quantum physics don’t make sense, that’s the fun part, allow yourself to think different.
If we look at Schrödinger’s cat and If you get the point of the image above, you’ll notice the “&”-sign in “DEAD & ALIVE”. The thought experiment goes as follows, you have a cat which is in a sealed box (you can’t see anything through it) with some sort of explosive or poisonous gas which has a probability of 50% to go off and kill the poor cat and a probability of 50% to malfunction on detonation and spare the cat. If we think of this box, we must acknowledge that the cat is BOTH dead and alive at that time, that is, until we open the box. It exists in a superposition of both dead and alive. You must understand that this is merely a thought experiment, we know that the cat can’t be alive and dead at the same time, that is the point. This thought experiment shows us what’s happening in the quantum world and how counterintuitive it is. This is exactly what happens in quantum physics, we have a probability to find a particle in a certain place, sometimes it is here and sometimes it is there, it is until we observe the particle that it finds a deterministic position. Just like if we open the box, we can see that the cat is still there or not. If we don’t measure the state of the system we want to measure, the system as a whole exists in all possible outcomes. This shows that this cat can be both alive and dead, how unlikely as it seems. It illustrates quantum physics on a macro level, so applied to the real-life big world. These quantum rules govern quantum physics but are hard to grasp and to say the least, counterintuitive. Quantum rules applied to the macro world don’t make a lot of sense, that’s why we generally don’t understand or don’t want to understand what is really happening in front of our noses.
We now understand why quantum mechanics seems so weird to us, it doesn’t really make sense if we apply quantum rules to macro physics. This is what makes quantum physics so hard to grasp and acknowledge, hence the meaning of the title of this post.
Double-Slit Experiment
Now what was the first encounter with quantum physics and how did anyone stumble upon it. Hold your horses, this experiment is fundamental to understand quantum mechanics and all other phenomena I am going to explain. The double-slit experiment goes something like this, look at the image below on the right, I will go through it step by step. The image on the left will follow after I explained the one on the right.
On the right image, the first thing you see on the left is an electron gun, it shoots electrons, electrons are small particles. In the middle on the left you have an object with two slits in the middle, hence the double-slit experiment and on the far right you have some detector screens. You should immediately see what’s wrong and see that the detector screens do not contain 2 nice distributions of shot electrons that you’d expect. Another thing you’ll notice is that the distributions of shot electrons on the detector screen is not constant, you have more electrons landing on the middle of the screen than on the edges.
If we now look at the image to the left we have a light bulb that is emitting a bunch of electrons and we pretend that this stream of electrons is a wave to make us think about the nature of those particles. You can also imagine this in a real-life scenario when you drop something in a pool, it creates a ripple effect in the form of waves, if you put the same object which was used to block out electrons in the water, you’ll get the result you see on the detector screens. Waves cancel each other out en reinforce themselves as they meet with each other after they exit the object with the double slits. This is how the experiment works and a particle-wave duality is what emerges from it.
Particle-Wave Duality
Those 2 images show us that if we shoot electrons, which are particles, that they will behave like a wave. We can’t deny what we measure, we can’t deny what we see and we can’t deny what we observe. This is how it is, it doesn’t matter how strange we think it is, this is how the universe works and it goes way beyond what we, as a small species on a little planet floating in space, think. We can thus conclude that particles also behave like waves. The quantum world exhibits both characteristics of particles as waves. Accept this fact and don’t start fighting this idea, embrace it and continue on this quantum world journey. What follows this observation is the collapse of the probability wave function of the particle when we try to observe it and measure where it resides. Remember that the exact location of a particle is governed by a probabilistic wave, it has probabilities to be somewhere or to not be somewhere at the same time, it is only when we observe and measure that the final state of the particle will settle and the probability wave will collapse.
Collapse Of The Probability Wave
So alright, the quantum world is probabilistic, it acts like both a particle and a wave and particles can be in a superposition state where they represent all of their possible states at once. Now what will happen if we want to measure the location of a particle, what will happen with the probability wave of that particle, the wave will collapse and converge into 1 point which will have a probability of 0% or 100% of finding the particle there. This is where our classical physics world meets the quantum world, the quantum world exists in all possible states until observed, this inevitably makes you wonder about the true nature of the reality we live in.
Now that we know what quantum physics is about, let me introduce some of the weirdest, most hard to grasp quantum observations. Quantum physics does very strange things, but unmistakably does the most interesting things. Nothing is exciting following Newton’s laws of gravity and see an apple fall from a tree, let’s be honest. Here is where the fun begins!
Heisenberg’s Uncertainty Principle
The uncertainty principle of Heisenberg states that the more precise you measure the position of a particle, the more uncertain its speed becomes and vice versa. So it is possible to exactly measure the position of a particle or the speed of the particle, but you can’t know both at the same time. To understand this further, we need to dive deeper into how we measure and observe things. Measuring something requires some measurement device and that measurement device needs to shoot particles towards the object in order to catch it again. The same thing happens when we have a speeding gun, you aim it at the thing you want to measure the speed from, this gun sends out particles that bounce off the object and thus some measurement can occur. Let’s say we do this with very small particles like an electron, if we shoot particles at an electron, this electron will be bounced away by the sheer energy we push into it, even the slightest amount will increase the momentum of the particle extensively. This makes it obvious that we can’t know the position and speed at the same time because we alter the momentum when measuring.
Quantum Entanglement
Einstein called it “spooky action at a distance” and that’s indeed what it is. Quantum entanglement builds on the fact that you can entangle 2 particles with each other and influence how one particle reacts when you interact with the other. Electrons have properties like ‘spin’, which denotes the angular momentum of the electron, so in which way there are spinning. With quantum entanglement, you have 2 electrons entangled at the same moment in time and space and afterward distanced from each other, if you now interact with one and change the spin of one particle, the other particle changes its spin to be the opposite of the other electron. How strange that this may seem, it has been tested and observed. No matter how far apart you put these 2 particles, they are linked with a mysterious force and no one has a clue what it is and how it works. Einstein was right, it certainly is spooky action at a distance.
Singularities
There are 2 known singularities out there, one when spacetime gets so bend it tears itself apart in the center of a black hole and the other when everything started with a big bang. Let us zoom in on the spacetime singularity first.
spacetime singularity
Spacetime is a construct thought of by Einstein and shows that space and time are intricately woven together. So if you make a dent in space, you also make a dent in time. Look closely at the next image, you’ll see that if you put a heavy object like a star on spacetime, it will curve and as a result, it will bend and slow time with it. Time goes by faster away from those dents in spacetime, dents in spacetime slow downtime. This is also called time dilation and will be important to explain our spacetime singularity.
If spacetime bends too much it will create an infinite dent and time will cease to exist in the center of this dent. Massive objects like black holes create these infinite dents, other stellar heavyweights like neutron stars also create massive dents but not at the extent that spacetime itself breaks down and with it the mathematics that govern our world, these are called singularities. Nothing is what it seems anymore and no one knows exactly how to glue the mathematics together and come up with a coherent set of mathematical rules which govern and explain these phenomena.
big bang singularity
There is also the big bang singularity. This is the infinitely stretched point in spacetime where everything was so densely packed together into one infinitely small point. All of the mass you see around you today was once concentrated into this point. This singularity shares the same properties of the spacetime singularity, this is that mathematics breaks down and nothing we know of can make sense of how and what this could and should have been.
TL;DR
Alright, we’ve made it! You got yourself through some thought experiments, along with some weird quantum phenomena and some real-life world experiments. You are a quantum physics expert now! Ok, no not really, but you’ll hopefully have gained some more insight in the wondrous and mysterious quantum world. I hope you’ve enjoyed discovering and learning about it as much as I did when I was writing this.
