Parth G's video: The Universe Exists Because of Identical Particles

The universe as we know it, can only exist if certain particles are absolutely identical to each other (assuming also that quantum mechanics is correct...) Here's a talk I did recently (huge thanks to Reading School for inviting me) discussing this rather interesting concept. We started by considering the structure of atoms. We know that each atom has protons and neutrons in a nucleus, and electrons surrounding this nucleus. The electrons are arranged in shells and orbitals. But why is that? To answer that, we need to look at quantum mechanics. Quantum mechanics is basically the study of very small objects, such as particles that make up atoms. And because quantum mechanics is not very intuitive, it says that particles behave in rather strange ways. When we do an experiment to find where a particle is, it's not always going to be where we expect it. However we can work out the probability that we'll find our particle at a given point in space each time we are about to try and measure its position. So instead of working with pesky, difficult to track particles, we work with a wave function. A wave function is a mathematical function that changes smoothly over time, and tells us something about our particle. Most commonly, it tells us the probability of us finding our particle at different points in space. To find this probability, we square our wave function. This means that the square of the wave function is a directly measurable quantity, since we can repeat the experiment and work out the probability of each experimental result for a future experiment. So why deal with the wave function at all, and why not with the square of the wave function? Well that's because the wave function itself contains information that is lost when squaring. We also look at the wave functions of multi-particle systems. We understand how the probability of each experimental result changes if we swap two particles. For identical particles, the probability does not change because we cannot tell them apart. If this is true for all possible experimental results, then these particles are said to be "indistinguishable". There are two flavors of indistinguishable particles: bosons and fermions. Electrons happen to be fermions. We see how two fermions with the same spin state can never be found in the same orbital state. In other words, for every orbital in an atom, there can only be two electrons in it - one with spin up, and one with spin down. This is known as the Pauli Exclusion Principle. And it's because of this principle that atoms are arranged the way they are - with electrons being found in shells and orbitals (rather than all being in the same low-energy state). And it's the atomic structure that enables basically all of chemistry to occur through covalent and ionic bonding, and so on. Which means that the universe as we know it, made up of atoms, would not exist if electrons were not indistinguishable fermions. Neat right? I really enjoyed giving this talk, pitching it at a level that I felt comfortable explaining to a live audience. This inevitably meant cutting out on some not-very-important but technically correct details. So please let me know if I cut out too much! Thanks again to Reading for inviting me, and to the wonderful students who were so attentive and asked genuinely insightful questions. Thanks for watching, please do check out my links: MERCH - https://parth-gs-merch-stand.creator-spring.com/ INSTAGRAM - @parthvlogs PATREON - patreon.com/parthg MUSIC CHANNEL - Parth G Music CRICKET PAGE (TikTok, Instagram, YouTube) - @cricketinaminute Here are some affiliate links for things I use! Quantum Physics Book I Enjoy: https://amzn.to/3sxLlgL My Camera: https://amzn.to/2SjZzWq ND Filter: https://amzn.to/3qoGwHk