Entropy. Sometimes you read that it's a measure of randomness; sometimes, information. Aren't randomness and information opposites?
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Ask HN: What scientific phenomenon do you wish someone would explain better?
111–120 of 839 posts
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#112When two particles get closer, their mutual gravitational attraction increases. As the distance approaches zero, the force approaches infinity. In the limit of d -> 0, the energy released -> infinity. Obviously at some scale the notion of a point mass breaks down, but even quantum theory would be problematic if we think of a wave function as describing a probability distribution, wouldn't it? What's the "official" story on this?
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#113Flight. 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 (?!?).
It directs air moving horizontally downwards, by conservation of momentum the wing must get additional upwards momentum, called lift.
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#114When I hear explanations like “space is expanding like the surface of a balloon” it’s always confusing. Because a surface is an object, separate from anything on it, but space is the thing we’re all embedded in, so we’re like drawings on the balloon. If space is expanding why aren’t the radii of fundamental particles and their orbits and molecules also expanding? And if that were the case we couldn’t notice space exp…
> If space is expanding why aren’t the radii of fundamental particles and their orbits and molecules also expanding? And if that we’re the case we couldn’t notice space expanding.
> Does space only expand somewhere else? Only between me and the Andromeda galaxy, and not _within_ me and the Andromeda galaxy? How would it know to do that?
If you start with expanding space in general relativity, and then carefully take the limit where you get back to Newtonian gravity, then it just corresponds to a classical force, specifically a very tiny force that weakly pulls everything apart, growing with distance.
This doesn't expand small objects, because they're rigid. It's the same reason that I can't make my laptop get bigger by gently pulling on the ends. On the other hand, it would pull apart two independent, noninteracting objects (such as the Milky Way and Andromeda).
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#115Entropy. Sometimes you read that it's a measure of randomness; sometimes, information. Aren't randomness and information opposites?
Let me give an analogy and then a solution to your paradox.
Temperature. Sometimes you read that it's a measure of warmth; sometimes cold. Aren't hot and cold opposites?
Yes, hot and cold are opposites, but in a way they give the same kind of information. That's also true for information and randomness. Specifically, little randomness means more (certain) information.
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#116Flight. 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 (?!?).
It directs air moving horizontally downwards, by conservation of momentum the wing must get additional upwards momentum, called lift.
That can't be the explanation, otherwise wings wouldn't need to be curved - flat wings could fly, as long as they're tilted to redirect the air.
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#117Quantum spin. Electrons aren't really spinning, right? But why do we call it spin? I know it has something to do with angular momentum. What are the possible values? Is it a magnitude or a vector? Is there a reason we call it "spin" instead of "taste" or some other arbitrary name? How do you change it? What happens to it when particles interact?
> Electrons aren't really spinning, right?
Correct.
> But why do we call it spin?
Because it is a physical quantity whose units are those of angular momentum, and we have to call it something.
> What are the possible values?
+/- h/4pi where h is Planck's constant. (It is usually written has h-bar/2 where h-bar is h/2pi.)
> Is it a magnitude or a vector?
It's a vector that always points in a direction corresponding to the orientation of the apparatus you use to measure it.
> Is there a reason we call it "spin" instead of "taste" or some other arbitrary name?
Yes. See above.
> How do you change it?
You can change an electron spin by measuring it along a different axis than the last time you measured it. The result you get will be one of two possible values. You can't control which one you get.
> What happens to it when particles interact?
Their spins become entangled.
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#118Fourier Transforms. I'd wish I had a intuitive understanding of how they work. Until then I'm stuck with just believing that the magic works out.
The best way to understand the Fourier transformations is to think of them as change-of-basis operations, like we do in linear algebra. Specifically a change from the "time basis" (normal functions) to the "frequency basis" (consisting of a family of orthonormal functions).
Here is the chapter on Fourier transforms from my linear algebra book that goes into more details: https://minireference.com/static/excerpts/fourier_transforma...
As for the math, there really is no other way to convince yourself that sin(x) and sin(2x) are orthogonal with respect to the product int(f,g,[0,2pi]) other than to try it out https://live.sympy.org/?evaluate=integrate(%20sin(x)*sin(2*x... Try also with sin(3x) etc. and cos(n*x) etc.
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#119I would like to understand how cellular biology processes actually work. Like, how do all the right modules and proteins line up in the right orientation every time? Every time I watch animations, it seems like the proteins and such just magically appear when needed and disappear when not needed [0]. Sometimes it's an ultra-complex looking protein and it just magically flys over to the DNA, attaches to the correct spot, does it's thing, detaches, and flies away. Yeah right! As if the protein is being flown by a pilot. How does it really work?
Re: Ask HN: What scientific phenomenon do you wish someone would explain better?
#120Bell'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.
I recommend this book:
https://www.amazon.com/Quantum-Non-Locality-Relativity-Metap...
If you don't want to read a whole book then I recommend this article:
https://kantin.sabanciuniv.edu/sites/kantin.sabanciuniv.edu/...
but the book will give you a much deeper understanding.