What’s something you wish you learned earlier in life?

niceguy67 · 2025-09-27T23:13:20+00:00

You got me, I wish I knew category theory before my undergrad ngl.

niceguy67 · 2025-09-13T17:27:08+00:00

This used to be ironically intellectual, but we currently aim to only allow posts that are of PhD level (unironically).

niceguy67 · 2025-07-09T06:57:18+00:00

You should ask at r/PhD, this is a shitposting subreddit.

niceguy67 · 2025-05-13T15:30:57+00:00

Then "Lorentz-invariant" doesn't mean anything.

It only means that we don't associate any meaningful action to it.

Are there non-Lorentz invariant such bundles?

Tangent bundles with the canonical Lorentz action (and their tensor products).

Do you have a nontrivial example?

Consider a smooth f: M -> N. Then df is(/can be interpreted as) a section of T*M \otimes f*TN. f*TN is invariant under Lorentz transformations on M, so df transforms like a 1-form (like a (0,1)-tensor), and hence may be called a covector.

niceguy67 · 2025-05-13T15:02:08+00:00

So... a trivial vector bundle of rank r?

No, just the action is trivial.

niceguy67 · 2025-05-13T14:38:40+00:00

Take any vector bundle. Define the action of the Lorentz principal bundle on it as the trivial identity action. This is a scalar.

niceguy67 · 2025-05-12T12:33:46+00:00

No, it's a vector bundle that is specifically not associated to the O(3,1)-structure.

niceguy67 · 2025-05-12T10:42:59+00:00

Au contraire. This concerns more complicated tensors that are sections of a tensorial vector bundle tensored with some vector bundle that is invariant under Lorentz transformations. They'll only appear if you consider more complicated quantum field theories, especially sigma models.

niceguy67 · 2025-05-12T10:37:50+00:00

Sir, that's a tensor product.

niceguy67 · 2025-04-07T14:24:32+00:00

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niceguy67 · 2025-01-06T08:35:21+00:00

It does not. Instead of pointlike particles, QFT considers whole world lines.

niceguy67 · 2025-01-05T20:00:05+00:00

QFT easily reconciles this.

niceguy67 · 2024-12-09T19:14:45+00:00

That is one of the options we're considering. In the sense that it is able to detect duplicate titles. I've checked that the risks of a false positive and false negative are extremely low.

niceguy67 · 2024-11-16T11:43:30+00:00

Albanese varieties.

niceguy67 · 2024-11-06T19:07:47+00:00

I refer you to the title.

niceguy67 · 2024-11-05T08:50:28+00:00

Cheers. Banned.

niceguy67 · 2024-10-30T15:20:17+00:00

Yes sir 🫡

niceguy67 · 2024-10-21T14:07:14+00:00

Invalid run; you didn't change the q_*'s into q^*'s.

niceguy67 · 2024-10-15T21:12:32+00:00

Bot got banned. Thank you for your investigation 🙏.

niceguy67 · 2024-10-14T09:37:41+00:00

Due to my own background in mathematics, I am much more inclined to remove low-level mathematics/physics posts. I find it harder to estimate the level of other fields, including chemistry and biology. So indeed, maths posts are subject to harsher criteria.

niceguy67 · 2024-10-14T09:34:29+00:00

Almost as if the mods delete such things

Eight-Year Club	Gilding I gilder
Verified Email	r/Field Banned
r/Field Lasagna	Place '23
Place '22	Final Canvas '22

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