7:19 PM
silentbob14
So I've been learning quantum mechanics for some time now and I can say that it's a charming subject. It's hard to find another part of physics which makes you panic and adore it at the same time. So that's why I decided to create these simple lessons of the basics of quantum mechanics.
I tried to study quantum mechanics by myself a couple of times in the past and what I found out was that it is really hard to find good lessons, lectures or books about the basics online. I mean you can easily find good e-books about the whole philosophical part of quantum mechanics, which explain the basic principles, but hardly give you the real taste of the subject with whole the maths part of it. On the other hand, you can find a lot of hardcore stuff, like lectures and videos which require you to know the subject at a very high level. So as you can see it's really hard to come up with some real basic quantum mechanics with all the appropriate maths for a beginner. So I decided to make these basic lessons that give you all the basic stuff you need.
So firstly let's look at some basic information about quantum mechanics: Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic scales, the so-called quantum realm. In advanced topics of quantum mechanics, some of these behaviors are macroscopic and only emerge at very low or very high energies or temperatures. The name, coined by Max Planck, derives from the observation that some physical quantities can be changed only by discrete amounts, or quanta, as multiples of the Planck constant, rather than being capable of varying continuously or by any arbitrary amount. For example, the angular momentum, or more generally the action, of an electron bound into an atom or molecule is quantized. While an unbound electron does not exhibit quantized energy levels, an electron bound in an atomic orbital has quantized values of angular momentum. In the context of quantum mechanics, the wave–particle duality of energy and matter and the uncertainty principle provide a unified view of the behavior of photons, electrons and other atomic-scale objects.
So let's start easily. At the heart of quantum mechanics there is the famous Heisenberg uncertainty principle. This principle appears in all parts of quantum mechanics so it's important to know it by heart and get it out of the way early.
Heisenberg uncertainty principle:
So what does this mean? It means that the product of the uncertainty in position of a particle and momentum must always be higher than some constant quantity, which is h bar/2, where h bar= h/2pi (Planck constant). This means, that if you try to detect a particle you can only do it with a certain precision. For instance, if you detect it's position with a very small uncertainty then you will have a very big uncertainty in momentum of the particle.
Now this is very strange, because we are so used to the "fact" that we know the position of anything very accurately. And now suddenly we realise that when it comes to microscopic world, we can't even find the exact position of the particle. But this is just the beginning of the whole strangeness of the quantum world.
But why can't we detect particles position or moment with a big precision? Well it's mostly because of the way we detect particles. Long story short, we detect a particle by shooting a photon at it (a particle of light). However, a photon also has some momentum and as strange as it sounds you can simply "knock" a particle away with a photon. Also, if you want to find out the position of a particle with a high precision, you must use a high frequency light wave (a high energy photon, where the energy of a photon E is given by E=hf, where h- Planck constant and f- frequency) which naturally has a bigger momentum, which causes a particle to be knocked away at a high velocity. This is exactly what causes the uncertainty in the momentum.
Now if this looks strange to you then don't worry. I mean the whole world was in shock when quantum mechanics was established. One of the most shocking things was the collapse of the Newtonian determinism. This is an idea that if you know enough information about a particle, you can calculate it's position and velocity in the future, that is if you have enough information you can tell the future. You can imagine how shocked the world of science was when after a couple of hundread years suddenly they realised that you can't actually tell the particle's position and momentum with an exact precision (thus you can't tell the future of a particle with an exact precision). Long story short, the world went upside down in the beginning of the XX century - particles became wave - particle probability waves, nothing was certain anymore, electrons decided to show up at two different places at one time, other particles started to travel back in time and so on. Whole hell broke through in the world of science back in those days. All of these crazy things brought to the world of science by the quantum mechanics can really cause headaches, but hey don't worry, it can be explained in a very elegant way. But we'll look at it next time.Thanks for reading!
PS. I'm not an expert of quantum mechanics, so if you notice any mistakes feel free to tell me. Thanks!
I tried to study quantum mechanics by myself a couple of times in the past and what I found out was that it is really hard to find good lessons, lectures or books about the basics online. I mean you can easily find good e-books about the whole philosophical part of quantum mechanics, which explain the basic principles, but hardly give you the real taste of the subject with whole the maths part of it. On the other hand, you can find a lot of hardcore stuff, like lectures and videos which require you to know the subject at a very high level. So as you can see it's really hard to come up with some real basic quantum mechanics with all the appropriate maths for a beginner. So I decided to make these basic lessons that give you all the basic stuff you need.
So firstly let's look at some basic information about quantum mechanics: Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic scales, the so-called quantum realm. In advanced topics of quantum mechanics, some of these behaviors are macroscopic and only emerge at very low or very high energies or temperatures. The name, coined by Max Planck, derives from the observation that some physical quantities can be changed only by discrete amounts, or quanta, as multiples of the Planck constant, rather than being capable of varying continuously or by any arbitrary amount. For example, the angular momentum, or more generally the action, of an electron bound into an atom or molecule is quantized. While an unbound electron does not exhibit quantized energy levels, an electron bound in an atomic orbital has quantized values of angular momentum. In the context of quantum mechanics, the wave–particle duality of energy and matter and the uncertainty principle provide a unified view of the behavior of photons, electrons and other atomic-scale objects.
So let's start easily. At the heart of quantum mechanics there is the famous Heisenberg uncertainty principle. This principle appears in all parts of quantum mechanics so it's important to know it by heart and get it out of the way early.
Heisenberg uncertainty principle:
So what does this mean? It means that the product of the uncertainty in position of a particle and momentum must always be higher than some constant quantity, which is h bar/2, where h bar= h/2pi (Planck constant). This means, that if you try to detect a particle you can only do it with a certain precision. For instance, if you detect it's position with a very small uncertainty then you will have a very big uncertainty in momentum of the particle.
Now this is very strange, because we are so used to the "fact" that we know the position of anything very accurately. And now suddenly we realise that when it comes to microscopic world, we can't even find the exact position of the particle. But this is just the beginning of the whole strangeness of the quantum world.
But why can't we detect particles position or moment with a big precision? Well it's mostly because of the way we detect particles. Long story short, we detect a particle by shooting a photon at it (a particle of light). However, a photon also has some momentum and as strange as it sounds you can simply "knock" a particle away with a photon. Also, if you want to find out the position of a particle with a high precision, you must use a high frequency light wave (a high energy photon, where the energy of a photon E is given by E=hf, where h- Planck constant and f- frequency) which naturally has a bigger momentum, which causes a particle to be knocked away at a high velocity. This is exactly what causes the uncertainty in the momentum.
Now if this looks strange to you then don't worry. I mean the whole world was in shock when quantum mechanics was established. One of the most shocking things was the collapse of the Newtonian determinism. This is an idea that if you know enough information about a particle, you can calculate it's position and velocity in the future, that is if you have enough information you can tell the future. You can imagine how shocked the world of science was when after a couple of hundread years suddenly they realised that you can't actually tell the particle's position and momentum with an exact precision (thus you can't tell the future of a particle with an exact precision). Long story short, the world went upside down in the beginning of the XX century - particles became wave - particle probability waves, nothing was certain anymore, electrons decided to show up at two different places at one time, other particles started to travel back in time and so on. Whole hell broke through in the world of science back in those days. All of these crazy things brought to the world of science by the quantum mechanics can really cause headaches, but hey don't worry, it can be explained in a very elegant way. But we'll look at it next time.Thanks for reading!
PS. I'm not an expert of quantum mechanics, so if you notice any mistakes feel free to tell me. Thanks!
