PBS DIGITAL STUDIOS This episode is supported by the Great Courses Plus Richard Feynman called it the jewel of physics Of all of our mathematical descriptions of the universe, this one has produced the most stunningly precise results I'm talking about quantum electrodynamics - the first true quantum field theory Quantum mechanics is perhaps the most unintuitive theory ever devised And yet it's also the most successful in terms of sheer predictive power Simply by following the math of quantum mechanics, incredible discoveries have been made. It's wild success tells us that the mathematical description provided by quantum mechanics reflects deep truths about reality and by far the most successful, most predictive formulation of quantum mechanics is Quantum Field Theory It's the best description we have of the fundamental workings of reality. And the first part of quantum field theory that was derived, Quantum Electrodynamics is the most precise, most accurate of all. Quantum field theory, QFT describes all elementary particles as vibrational nodes in fundamental fields that exist at all points in space and time through the universe quantum electrodynamics - QED provides this description for one such field: the electromagnetic field. the pillars of QED are the description of the behavior of the EM field, and the description of the behavior of the electron by the Dirac equation. We covered the Dirac equation last time, and you really should watch that episode first if you haven't already. Now, before we start thinking about vibrating quantum fields, or even fields at all, let's talk about vibrations. knows that a stretched string vibrates with a certain frequency, when plucked. It also vibrates with an amplitude that depends on how hard you pluck it. A larger amplitude and/or a larger frequency means the vibration carries more energy. At any point in time, every point on a vibrating string, is displaced by some distance from its relaxed (or equilibrium) position. and that displacement changes over time, as the string oscillates back and forth. Guitar strings are 1-dimensional, but we can expand the analogy to any number of dimensions. In 2D, we have a membrane. Like a drum skin. Everywhere on the surface of a vibrating drum skin, there is a displacement from the flat equilibrium state in the up-down direction. The 3D analogy is harder to imagine. Every point in space, has some displacement in some imaginary extra direction. Analogous to, but not the same as a 4th dimension. For example, in a 3D room full of air, sound waves are oscillations in air density. That air density has an equilibrium value, which is just the average density, but in every point in the room, a soundwave can cause air density to oscillate: to higher and lower values. We describe air density as a field, because it has some value everywhere in the space of the room; and that's all a field is, some property that has some value throughout the space. Ok, let's go----quantum. And let's go back to the string. If this were a quantum mechanical guitar string, there's need to be a minimum amplitude for the vibration that depended on its frequency. No vibrations with amplitude smaller than that minimum could exist. And every larger vibration would have to be a whole number, an integer multiple of the smallest amplitude. This is exactly how light behaves. tells you that you can only have one fermion, so electron, quark,
gotta say I love these Space Time deep delves into cutting edge scientific theory. hard to grasp, but great that they don't go to absurd lengths to dumb it down beyond valuable meaning
Quantum field theory is a conspiracy made up by the bread company to sell more bread.
Sean Carroll has some very accessible chapters on Quantum Core Theory in his book "The Big Picture". It's been utterly enlightening as a layman who loves this stuff.
Having done QM at university and only covering schrodinger's equation, this video makes me really excited for the second QM module next year.
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