PBS Space Time
5 HN recommenders · recommended in 8 months, 2018–2026
13:02 · 1.1M views · May 16, 2018
PBS Space Time explains Noether's theorem: conservation laws such as energy and momentum are consequences of deeper symmetries. It also covers why those laws hold only under certain conditions.
HN commenters point to it as an approachable explanation of how symmetries give rise to conservation laws, including the story of Emmy Noether.
10 comments from Hacker News
I'd recommend the two episodes released right before the one about the black hole information paradox too. They set up for what is covered in the information paradox episode. "Why Quantum Information is Never Destroyed" - [LINK] "What Survives Inside A Black Hole?" - [LINK] Maybe the episode before those two also. I vaguely recall that something from the information paradox episode used something from that (and if I'm misremembering, it was still a neat episode): "Noether's Theorem and The Symmetries of Reality" - this video I have a question about the episodes you cited. They cover how beyond the event horizon space becomes time and time becomes space. They go over how that means that inside you can't go backwards in space for the same reason that out here in the normal universe you can't go backwards in time. You are doomed to only go forward, which inside means toward the singularity. (Much better than the ridiculous analogy often given that you can't get out of a black hole because the escape velocity equals or exceeds the speed of light. That's a ridiculous analogy because it only explains why you can't get out ballistically). But all their explanations used a simplified black hole in a spacetime with just 1 space dimension and 1 time dimension. We've actually got 3 space dimension. Does that mean that in a real block hole past the event horizon, you end up in a spacetime with 3 time dimensions and 1 space dimension? If so, does anything interesting happen due to having mor
TLDR: Do an experiment, then move 10 meters to the left (or rotate 90 degrees, or wait a few days) and do it again. The results don’t change, because the laws of physics don’t change. This realization alone is enough to produce conservation laws. Translational and rotational symmetries produce conservation of linear and angular momentum, and the time symmetry produces conservation of energy. Each symmetry you find leads to new physics. It's such an aha moment. PBS Space Time: this video
If you like reading about Wu from a woman in physics hidden in plain sight aspect you might like the story of Emmy Noether[0]. A mathematician who worked a few doors down from Einstein and produced era defining result in physics. The connection between symmetry and conservation. Noether's theorem to this day is one of the most profound holy shit moments in many physicists education. Her life was been cut tragically short. [0] this video
PBS Space Time has done a couple of episodes on Stationary Action and Noether's Theorem that are approachable by those not yet already exposed to Langrangians: [LINK] this video Sabine Hossenfelder also has a good episode on it: [LINK]
Things are conserved when there's a corresponding symmetry; this is Noether's Theorem.[1] I won't pretend to understand half that article, but here's a video[2] on it. [1]: [LINK] [2]: this video