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Ask HN: What scientific phenomenon do you wish someone would explain better?

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Re: Ask HN: What scientific phenomenon do you wish someone would explain better?

#231

Post by stevebmark »

knzhou wrote: post #104
stevebmark wrote: post #102

Earlier quoted context omitted.

I have no idea how it works, I don't have an explanation, I just know the one spouted by people doesn't make sense

Well, if you're uncomfortable with LIGO, you're in good company. Once a whole decade went by in physics where people couldn't agree if it would work in principle or not. And it is true that a lot of common explanations are bad (e.g. "it's just a ruler" is not complete by itself because "why doesn't the light get stretched too?"). Nonetheless, today we have a variety of independent explanations. Maybe you'll find this…

Thank you for this link. I read it once and think I've gotten more of the picture and I'm going to re-read it to see if I can get more. What's baffling to me is everyone who has tried to explain the LIGO detector doesn't even realize this question exists. I've independently thought this question and when people start explaining LIGO to me, and I take the time to spell out the question, they realize they don't understand LIGO either.

If light is emitted at a constant wavelength independent of the stretching of the universe, doesn't that imply light is traveling through a higher spatial dimension, otherwise the emitter itself would be stretched with the universe and we'd never be able to observe differences in the speed of light? If I understand this paper, once light is emitted, it's "stuck" to space and will stretch along with it. But if the emitter wavelength stays constant doesn't that imply it's waving through a higher dimension?

Re: Ask HN: What scientific phenomenon do you wish someone would explain better?

#232

Post by ad404b8a372f2b9 »

elgfare wrote: post #194
arkanciscan wrote: post #173

Quantum Computers. Not like I'm five, but like I'm a software engineer who has a pretty decent understanding of how a classical turing machine works. I can't tell you how many times I've heard someone say "qubits are like bits except they don't have to be just 1 or 0" without providing any coherent explanation of how that's useful. I've also heard that they can try every possible solution to a problem. What I don't u…

I recommend Computerphile's videos https://www.youtube.com/playlist?list=PLzg3FkRs7fcRJLgCmpy3o... . I had the same "problem" as you. What finally made me feel I sort of cracked it was those videos. The way I think of it now is: They let you do matrix multiplication. The internal state of the computer is the matrix, and the input is a vector, where each element is represented by a qubit. The elements can have any val…

I don't know if it's accurate (because I never understand anything I read about it) but this is the most concise and clear explanation I've read on this subject to date. Thank you!

Re: Ask HN: What scientific phenomenon do you wish someone would explain better?

#233

Post by plun9 »

elgfare wrote: post #182

The mathematics of training a neural network. I understand how they work once trained, but that you can train them almost seems too good to be true.

You likely understand minimizing a continuously differentiable function. Now, you are minimizing a continuously differentiable error function (which measures the difference between the output of your hypothesis function and actual data), with respect to adjustable weights and biases that determine the value for the neurons going from one layer to the next. The complexity is in that the hypothesis function is a composition of many functions due to the layering, and there usually are a large number of neurons. However, you are basically doing the same thing many times.

Re: Ask HN: What scientific phenomenon do you wish someone would explain better?

#234

Post by refurb »

LVB wrote: post #209

Genetics. I still have no intuition for how combining my wife’s and my DNA has resulted in children with traits from both of us. My brain always tries to imagine interleaving two binaries and hoping for a resulting program that works a bit like the two sources, which it of course wouldn’t.

The analogy works if each binary way laid out the same - the first MB is eye color, the 2nd MB was hair color, etc. Each segment of code is also duplicated.

When you produce sex cells, you body splits the code randomly. The cell might contain the first copy for hair color, but the 2nd copy for eye color. This happens in both the sperm and eggs.

Then when they combine you have a full set of genetic data again, but it’s a random selection of 50% of you DNA.

The fun part is that the code itself determines which copy is dominant. Your offspring has a copy of your eye color data, and your wife’s.

Added on that is that the two copies combine to produce the outcome. Depending on the code, the dad’s copy might dominate, or the mother’s, or the both of them can produce yet a 3rd outcome.

Re: Ask HN: What scientific phenomenon do you wish someone would explain better?

#235

Post by abdullahkhalids »

lpellis wrote: post #37

Bell'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.

The short answer is this. Suppose thread OP gave you and I a box each. Each box has a some knobs to choose some settings, and if one chooses a setting and presses the GO button, a number pops up on the screen. We go far away from each other so that, due to the finite speed of light, it takes quite a while for any information to travel between the boxes. We do this, because we don't want the boxes to communicate live, even though thread OP might have recorded the same data into the memory drive of both boxes.

Then we choose some settings and press GO and record whatever number pops up. We do this many times so we each have a nice frequency chart. Now Bell proved that if you live in a local hidden variable universe, the correlations between these numbers is upper bounded, no matter how you choose settings on the boxes. Then, he also gave a prescription for choosing the settings, such that if you live a in quantum universe, the correlations between these numbers will be higher than the upper bound.

The rest is mathematics, which cannot really be simplified without leaving the reader unsatisfied.

Re: Ask HN: What scientific phenomenon do you wish someone would explain better?

#236

Post by aazaa »

Sort of meta, but I always shudder when someone says that science has "proven" something.

What sets science apart from most other methods of seeking answers is its focus on disproof. Your goal as a scientist is to devise experiments that can disprove a claim about the natural world.

This misconception rears its head most prominently in discussions at the intersection between science and public policy. Climate change. How to handle a pandemic. Evolution. Abortion. But I've even talked to scientists themselves who from time to time get confused about what science can and can't do.

The problem with believing that science proves things is that it blinds its adherents to new evidence paving the way to better explanations. It also leads to the absurd conclusion that a scientific question can ever really be "settled."

Re: Ask HN: What scientific phenomenon do you wish someone would explain better?

#237

Post by na85 »

skanga wrote: post #223

Can anyone explain disc loading and solidity in a propeller and if there are any equations governing them?

Disc Loading is just the force on the actuator disc (such as a rotor, in which case the force is the weight of the vehicle the rotor holds aloft) divided by the swept area (pi times r squared).

It's used when discussing propulsive efficiency, as it's a proxy measurement for how much "work" each blade is doing. Because propeller/rotor blades are just high-aspect wings, if you have high disc loading your blades are at a high lift coefficient which means they'll be incurring lots of lift-induced drag which increases your power requirements.

Solidity in the same context refers to the amount of volume within an actuator disk that's occupied by actual solid material. If you have a 4-bladed rotor and you move to a 5-bladed rotor, all else equal, you've increased your solidity.

There are many many equations, and as most things in fluid mechanics you can get as deep into the weeds as you want. As a starting point, have a look at the wiki article for Blade Momentum Theory[0]

[0] - https://en.wikipedia.org/wiki/Momentum_theory

Re: Ask HN: What scientific phenomenon do you wish someone would explain better?

#238

Post by sloaken »

Avogadro constant - I can accept the number, if someone can show me how, over a hundred years ago, without having every really seen a molecule, this number could be derived. Obviously no one ever sat there and counted them but I find it hard to believe, they could have decided this without being able to see it.

Re: Ask HN: What scientific phenomenon do you wish someone would explain better?

#239

Post by satori99 »

changoplatanero wrote: post #188
knzhou wrote: post #143

Earlier quoted context omitted.

The issue with these animations is that they're getting rid of all the thermal noise. In reality, single proteins are flying around the whole length of the cell many times a second, just from their thermal motion. And when processes like DNA transcription happen, they're not like a regular conveyor belt -- a fraction of the time the machine will even accidentally run steps in reverse ! However, if any of this were sh…

just once i would like to see the realistic animation though even if it's impossible to understand

https://www.youtube.com/watch?time_continue=42&v=uHeTQLNFTgU

This comes close -- It shows the jittery thermal motion of this tiny machinery, instead of nice smooth glides.

Re: Ask HN: What scientific phenomenon do you wish someone would explain better?

#240

Post by kubanczyk »

ShamelessC wrote: post #192
kubanczyk wrote: post #145

Earlier quoted context omitted.

Well, I'd recommend to read the whole series. It's not so bad as it sounds. There are so many steps from where you are to appreciating the utter weirdness of Bell's experimental result. Not the weirdness of any theory (or an interpretation, which Many Worlds actually is) but of the basic experimental result. If you are properly amazed by it, rejecting MWI or any crazy-ish borderline-conspiracy theory seems suddenly a…

To be clear, I don't reject Many Worlds at all and in fact consider it a promising candidate due to it sort of "falling out" of the Schrodinger's equations taken literally unless you add complexity. But the fact remains that it is impossible to prove and it is conveniently well equipped to handle this situation. I'd prefer an argument that presupposes the Copenhagen interpretation as that is when my intuition fails.

If experimenters disprove Many Worlds, they've also disproved Copenhagen. These are exactly the same equations after all.

Theoreticians choose very different mindsets about the same equations, which (they say) somehow create them grounds to form various new hypotheses. As far as I know neither approach was very fruitful so far in terms of new science, so people try multitude of others.

What I've meant to say above, I have much trouble using Copenhagen to understand Bell's experiment. MWI fits the bill here for me.

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