Veritasium
3 HN recommenders · recommended in 4 months, 2025
27:40 · 14M views · Apr 14, 2025
Veritasium explores why energy is not conserved in general relativity, using Emmy Noether's theorem linking symmetries to conservation laws. Physicists interviewed explain energy loss in an expanding universe.
Recommended as high-quality physics communication and as an introduction to Noether and energy non-conservation in cosmology.
5 comments from Hacker News
Rather than turning to shit, I think the internet may be getting more diverse stuff in general. More good stuff and more shit. As an example of anti-shit I watched Veritasium "The Biggest Misconception in Physics" this video yesterday and thought wow this is good. Much better than the physics lectures I had at Cambridge Uni.
The typical example people use to illustrate that energy isn't conserved is that photons get red-shifted and lose energy in an expanding universe. See this excellent Veritasium video [0]. But there's a much more striking example that highlights just how badly energy conservation can be violated. It's called cosmic inflation. General relativity predicts that if empty space in a 'false vacuum' state will expand exponentially. A false vacuum occurs if empty space has excess energy, which can happen in quantum field theory. But if empty space has excess energy, and more space is being created by expansion, then new energy is being created out of nothing at an exponential rate! Inflation is currently the best model for what happened before the Big Bang. Space expanded until the false vacuum state decayed, releasing all this free energy to create the big bang. Alan Guth's book, The Inflationary Universe, is a great book on the topic that is very readable. [0] this video
reminds me of this video I found the other day this video if I'm understanding correctly the implications of Emily Noether's work, its an absolute travesty that she isn't famous in the same breath as Einstein and Feynman. Yet this video was the first time I had even heard of her.
The most recent Veritasium video touched on this — Emmy Noether worked under Hilbert and made significant contributions to general relativity, worked at University of Göttingen (Jewish, and first woman professor) until 1933. this video
> Energy and momentum are always conserved in EVERY physical process. Veritasium recently claimed otherwise this video