Posts posted by tbain
Love the podcast... but this episode was painful! Christina was a great guest from a comedic perspective, but she got a lot of things just straight up wrong! It was like nails on a chalkboard hearing David and Kyle get excited about understanding something, when the explanation wasn't even close to correct.
Episode 50 — Gravity
in Professor Blastoff
Sorry for not posting more of an explanation after my initial criticism. I understand that is a bit of bad internet etiquette on my part but I was riled up after listening on my way home, and decided today was the day to begin posting. To be honest I planned to try and listen to it again and go through things in in detail, but haven't done so yet.
The first thing that really caused my ears to perk up while listening was Christina's explanation of the four forces. I don't recall the exact wording, but she says something like "the strong nuclear force is what's responsible for holding protons and neutrons together in the nucleus, and the weak nuclear force is responsible for holding together the quarks inside the protons and neutrons". This is just not true. The strong force is responsible for both of those phenomena. The traditional thing to cite, when explaining what the weak force is responsible for, is nuclear beta decay, but this is a rather esoteric topic itself so it doesn't come with much explanatory power.
I also had a hard time listening to her try and explain the incompatibility of quantum mechanics and gravity. Kyle asks something to the affect of "is the lack of gravity what makes quantum mechanics, quantum mechanics?" She fumbles around a bit saying something about quanta, and Plancks constant without ever really explaining what the issue is.
So, the standard model of particle physics (that she references a few times) is really two theories: Quantum Chromodynamics, which is the theory of the strong force, and (the un-cleverly named) Electroweak Theory, which is the theory of electricity ( and magnetism) and the weak force. These two theories are both Quantum Field Theories, or to just call them "Quantum Mechanics" is enough for my point. The formal mathematical description of these theories is complete, however, it's very difficult to carry out any practical calculation, and in practice everything is approximated (although these approximations can be extremely accurate, some of the best predictions in science in fact).
The theory of gravity on the other hand comes from Einsteins theory of General Relativity. It too is a "Field Theory", but not a quantum field theory. It explains gravity by positing that any mass or energy actually curves the space around it, and an object moving under the influence of gravity is actually just following the curvature of space, dictated by the distributed mass and energy. So, in general relativity the objects dictate the curvature of space, while also moving through this curved space, and the actual equations of the theory are like a feedback loop, both generating the curvature, and explaining how to move through the curvature.
Now people have been trying formulate a quantum theory of gravity since quantum mechanics came on the scene, but the problem is that quantum theories are already extremely hard to make calculate, and those calculations are done assuming the space around the particles is flat. Quantum field theories happen "in" space, where as general relativity actually changes the space. So far no one has been successful in combining these theories, and creating a quantum theory of gravity.
Luckily, as Christina does say, gravity is all but negligible except at the largest mass scales (planets, stars, galaxies etc.) and at these large mass scales, the quantum theories are negligible. However, things that are both massive and tiny (understanding the internal structure of a black hole for instance) would require a quantum theory of gravity.
Alright, maybe that was a bit much. And my first post not enough. I'll work on moderation.