First principle reasoning in real life examples.
Ask HN: What scientific phenomenon do you wish someone would explain better?
81–90 of 839 posts
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#82Flight. Apparently "air flows faster on the top side of the wing, lowering the pressure" is an incomplete explanation; I even heard we don't completely understand why it works (?!?).
Flight is EXACTLY like swimming except in air and without any component of floating. You're welcome.
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#83I find most explanations of the Equivalence Principle that lies at the foundation of General Relativity to be very lax. To wit, the idea is that you cannot distinguish whether you are in an accelerated frame or in a gravitational field; alternatively stated, if you’re floating around in an elevator you don’t know whether you’re freefalling to your doom or in deep sideral space far from any gravitational source (thoug…
You're right that this is glossed over in popular explanations, but the point you make is exactly the starting point for all formal courses and textbooks.
The first part of the argument is that for single point particles falling, the effect of gravity is the same for all particles. This suggests that we should model gravity as something intrinsic to spacetime itself, rather than as a field living on top of spacetime, which could couple to different particles with different strengths.
The second part of the argument, which is what you point out, is that gravity can have nontrivial tidal effects. (This had better be true, because if all gravitational effects were just equivalent to a trivial uniform acceleration, then it would be so boring that we wouldn't need a theory of gravity at all!) This suggests that whatever property of spacetime we use to model gravity, it should reduce in the Newtonian limit to something that looks like a tidal effect, i.e. a gradient of the Newtonian gravitational field. That leads directly to the idea of describing gravity as the curvature of spacetime.
So both parts of the argument give important information (both historically and pedagogically). Both parts are typically presented in good courses, but only the first half makes it to the popular explanations, probably out of simplification.
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#84Flight. Apparently "air flows faster on the top side of the wing, lowering the pressure" is an incomplete explanation; I even heard we don't completely understand why it works (?!?).
I've been informed that I'm part of the problem. Comment removed, sorry for the trouble, folks!
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#85Measure theory.
This is a very good playlist: https://www.youtube.com/playlist?list=PLBh2i93oe2qvMVqAzsX1K...
Starts from basic concepts and builds up a nice overview.
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#86Earlier quoted context omitted.
Is there really no intuitive way to communicate the answer to that question without needing 10 years of grad math? I find that to be somewhat hard to believe
No, there is no intuitive way to communicate it. The theorem has taken >350 years to prove, which makes it clear that the proof is not some intuition that was somehow missed by hundreds of people for centuries. Fermat's Last Theorem (book) by Simon Singh is the source to check out if you're interested in the details of how it eluded mathematicians and a general idea of how the problem was solved, without getting too…
Thanks for the recommendation good sir!
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#87Bell's theorem. It somehow proves that quantum physics is incompatible with local hidden variables, but I could never see an understandable explanation (for me at least) of just how it works.
Minute Physics and 3brown1blue did a two part collab that simplifies some of it down to a counting problem that'd be suitable for grade school.
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#88The LIGO detector. I've never heard a logical explanation for it. If your explanation is that gravitational waves stretch and squash spacetime so light takes different amount of time to bounce from an emitter back to a measurer, then you don't have even a slight understanding of how it works. If your explanation doesn't involve higher spatial dimensions (not time) then you don't understand it. If you haven't even considered higher spatial dimensions when explaining LIGO then you shouldn't even try for the incorrect explanation above because you don't have any of the pieces of the puzzle.
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#89I find most explanations of the Equivalence Principle that lies at the foundation of General Relativity to be very lax. To wit, the idea is that you cannot distinguish whether you are in an accelerated frame or in a gravitational field; alternatively stated, if you’re floating around in an elevator you don’t know whether you’re freefalling to your doom or in deep sideral space far from any gravitational source (thoug…
> you’d see them move closer because of tidal effects dictated by the fact that they’re each falling towards the earth’s centre of gravity, and therefore at (very slightly) different angles.
This point isn't raised anywhere because it's mostly a pedantic point that has nothing to do with the thought experiment. You shouldn't try and decompose thought experiments literally, otherwise you'll get caught up in unimportant details like this. Just assume the elevator is close enough to the earth such that the field lines are effectively parallel, or better yet, just pretend the elevator is in an infinite plate field.
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#90The LIGO detector. I've never heard a logical explanation for it. If your explanation is that gravitational waves stretch and squash spacetime so light takes different amount of time to bounce from an emitter back to a measurer, then you don't have even a slight understanding of how it works. If your explanation doesn't involve higher spatial dimensions (not time) then you don't understand it. If you haven't even con…
> If your explanation is that gravitational waves stretch and squash spacetime so light takes different amount of time to bounce from an emitter back to a measurer, then you don't have even a slight understanding of how it works.
Well, I'll bite. I'm a physicist and I understand LIGO. What's your alternative explanation?