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Noether's Theorem and The Symmetries of Reality

Noether's Theorem and The Symmetries of Reality

PBS Space Time
5 HN recommenders · discussed 2018–2026
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About this video

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.

Why it appears in the archive

HN commenters point to it as an approachable explanation of how symmetries give rise to conservation laws, including the story of Emmy Noether.

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From the Hacker News discussion

ben509 · 2020-01 · rec

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]: [VIDEO]

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tzs · 2021-05 · rec

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" - [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

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michelpp · 2022-08 · rec

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] [VIDEO] Sabine Hossenfelder also has a good episode on it: [LINK]

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psychphysic · 2023-03 · rec

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] [VIDEO]

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twiceaday · 2025-02 · rec

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: [VIDEO]

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geon · 2018-05 · reference

> if you're saying conservation of momentum can be violated, or conservation of energy can be violated, then basically all of modern physics would have to be wrong. Conservation is not a fundamental law, but an emergent property of a deeper principle called Noether's Theorem: [LINK] [VIDEO] And it is constantly violated.

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igravious · 2018-05 · reference

The section of the video dealing with Noether's Theorem and The Symmetries of Reality actually ends at t=594s :/ so just the main link is needed: [VIDEO] If one or another of these so-called fundamental laws is being apparently broken by the EmDrive then that would make it a very very unusual object. Consequently there would need to be repeatable verifiable evidence that it does so and at least the beginnings of a theory as to how in fact this breakage is occurring–Noether's theorem notwithstanding.

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stcredzero · 2018-05 · reference

Yes the actual laws of physics can't be broken Conservation laws should be considered more as powerful analysis tools than as foundations of reality. So more Newtonian gravity than Relativity. In fact, you can regard Newtonian orbital mechanics as elaborations on conservation of energy and momentum. Conservation laws themselves have an underlying principle: [VIDEO] Another analogy: Conservation laws are like Euclidian geometry. On the scale of building a cabinet or an office building, Euclidian geometry rules! On intergalactic scales, it simply fails. So too, with the conservation of energy. If someone tries to sell you a perpetual motion or over unity machine, it is pretty rock solid. But if you're going to try to make some kind of cosmological argument using conservation of energy, that's just plain facepalm territory there. (Some HNer actually reported me for using <facepalm> in response to conservation of energy in a cosmological argument.)

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