Ask HN: What scientific phenomenon do you wish someone would explain better? • Hacker News Board

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

#511

Post by punnerud » Mon, Apr 27, 2020, 6:44 AM UTC

Buttons840 wrote: post #497

Flight. How can a plane fly when it's thrust to weight ratio is less than one? It's like, if you can produce 10 pounds of thrust, who would look at that and say "ah ha, we can use this to keep a 100 pound machine miles in the air indefinitely"? I understand flight from a mathematical point of view. I've actually read a few books on the subject, and I could explain how flight works to someone. However, I'm still fishi…

The 10 pounds trust is used to overcome the airodynamic friction, when the plane is in high speed. Because the "way" around the wing is longer on one side compared to the other this create a lower pressure on one side, and higher on the other. This pressure both lift and push the plane up. If there was zero friction you would hold the plane up with zero thrust ;)

I build this at school, using the same principle: https://no.wikipedia.org/wiki/Sivilingeni%C3%B8r#/media/Fil:...

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

#512

Post by mongol » Mon, Apr 27, 2020, 6:45 AM UTC

AareyBaba wrote: post #401

IAmEveryone wrote: post #360

Earlier quoted context omitted.

I studied bioinformatics and found the standard textbook, Albert's "Molecular Biology of the Cell"[0] to be one of the most captivating books I've read. It's like those extremely detailed owners' manuals for early computers, except for cells. The amount of complexity is just absolutely insane. My favourite example: DNA is read in triplets. So, for example, "CAG" adds one Glutamine to the protein it's building[1]. The…

"The distance from brain to leg is too long, for example, to accurately control motion from "central command" As a dancer, I have been fascinated by that fact. It means that dancers do not dance to the beat as they hear it - it takes too much time for the sound to be transformed by the ear/brain into an electrical pulse that reaches your leg. Instead, all dancers have a mental model of the music they dance to that is…

I guess the same must apply to a soccer player, except instead the mental model is about the trajectory of the ball.

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

#513

Post by dnautics » Mon, Apr 27, 2020, 6:46 AM UTC

satori99 wrote: post #239

changoplatanero wrote: post #188

Earlier quoted context omitted.

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.

this segment is not the worst, but the full version of inner life of the cell is terrible. Because they cheated, by reversing highly symmetrical processes, for example:

https://www.youtube.com/watch?v=B_zD3NxSsD8&t=3m17s

The artistic director has a ted talk where he talks about how beautiful biological processes are, and it's like no, man, you made it look that way.

If you want a really fantastic video that captures just how messy and random it is I recommend the wehi videos, like the one on apoptosis, where the proteins look way more derpy than the secret life of the cell: https://www.youtube.com/watch?v=DR80Huxp4y8 There's a couple of places where they have a hexameric protein where things magically snap into place, but I give them a pass because the kinetics on that are atrociously slow. Let's just say for the sake of a short video the cameraman happened to be at the right place at the right time.

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

#514

Post by superfrank » Mon, Apr 27, 2020, 6:47 AM UTC

grecy wrote: post #468

alasano wrote: post #380

Earlier quoted context omitted.

If you see a single share price listed, that is the price of the last sale that occurred. Now that can either mean that someone bought a share that someone else was selling or that someone was selling a share to someone who was offering to buy. The shares are listed as a series of buy and sell orders in what's called an order book. If the price a share was sold at was 100$ and you think it will go a bit lower, you co…

How does it work with futures? My understanding is that I buy a contract for 100 shares at a future date of my choice. So let's say stock XYZ is currently trading at $20, and I buy a futures contract for $100 for Jan 1st 2021. I don't have enough money sitting around to buy those 100 shares, so let's say XYZ is trading at $200 by Jan 1st 2021, That means I have a contract where I can buy 100 of them at $100 and immed…

What you're describing is more like options, but futures and options both work in a similar way to what you described, but futures have an underlying commodity that you have an obligation to take possession of (such as barrels of oil) options on the other hand give you the right to buy the underlying stock, but you have no obligation to do so.

So if I have a futures contract for 1000 barrels of oil for $10 a piece, when that expires, no matter what the price of oil, $10000 will be taken out of my account and someone will contact me to come pick up those barrels (there's some nuance here, but let's ignore that)(funny story about this at the bottom). If I have an 10 options contracts for 1000 shares of stock XYZ at $10 a share and XYZ is at $9 a share, I can just let the contract expire worthless.

From here on out, I'm going to talk about options, because it's closer to what you are asking.

> I don't have enough money sitting around to buy those 100 shares, so let's say XYZ is trading at $200 by Jan 1st 2021, That means I have a contract where I can buy 100 of them at $100 and immediately sell them for $200, so in theory it's a $10k profit.... but because I don't have enough money to actually do that, do I just sell my future for something close to 100* $200 (because someone with enough money will buy it and do the actual trade?)

Contracts are exercised after hours. If you don't have the money you will usually collect the shares and be put in a margin call (you owe your broker money) and then the shares will be sold first thing the next day to cover the margin call. Some brokers will try and sell your contract for you before the end of the day the contracts expire if you don't have the money. So you may only get $9950 or something for your contract and it will be sold to someone else a few hours before the market closes.

> What happens if it's already well over $100 long before Jan 1? Can I just set a price and sell it whenever I want like a can with a regular share?

Yes, the contract itself cost money and can be bought or sold.

This isn't a perfect analogy, but think of the contract like a coupon. If I have a coupon for to buy a TV for $100 and the cheapest anywhere is selling that TV is for $200. That coupon has an intrinsic value of $100.

The analogy breaks down, because in the real world, you probably couldn't get $100 for that coupon. You'd probably get slightly less than the price difference. With options on the other hand, you usually pay slightly more than the price difference, because of the volatility of the underlying. Basically, someone might pay you $105 for that coupon because they think they the TV price will go up and they can sell it to someone next week for $110.

========

* As a side note, when people were saying oil prices went negative last week, it's because the May futures contracts were about to expire. Basically, it was the second to last day people could trade the contracts before they had to take delivery of the oil and, since so few people are using oil right now, many of the places where people would normally store oil are full. Since you can't just dump oil down the drain, people holding oil contracts were willing to pay other people to take over the contracts so they didn't have to take delivery of the oil.

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

#515

Post by TrackerFF » Mon, Apr 27, 2020, 6:53 AM UTC

robertakarobin wrote: post #370

If I buy a stock, does the price at which I agreed to buy it become the new share price on the stock exchange? Every article on "Where do stock prices come from?" seems to just talk at a high level about supply and demand. But where does the price come from at a nitty-gritty level? Is it an average of all existing offers or something? Do different exchanges and stock-ticker websites have different formula for calcula…

I think the other answers have been good at explaining HOW stock prices are determined at the exchange, but if you're wondering WHY someone would say "That stock is worth $xx.xx", then that's a more complicated question, with equally complicate answers.

At the very lowest level, it could be gut feelings from a potential buyer. They see electric cars more frequently, combustion engines going out of fashion, and simply wonder "Hey, why does that [electric car company] trade so low, when they'll probably be market leaders in 5/10/15 years?", or conversely, "Hey, why does that [petroleum] company trade so high, oil prices are shot, and the industry will lose relevance in 10/20/30 years"

On a higher level, some potential buyer will look at the companies financial statements, and figure out if the share price is too high / low for how the company is performing, from a financial standpoint. This is called "fundamental analysis", and you can easily find step-by-step analysis reports of such on various companies.

But the market is one big hodgepodge of beliefs, with probably thousands of different rationales behind their prices, and motives for sales / purchases.

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

#516

Post by dnautics » Mon, Apr 27, 2020, 6:54 AM UTC

mncharity wrote: post #369

satori99 wrote: post #239

Earlier quoted context omitted.

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.

Oh my that facepalm dreadful. Thank you! That gives me a new high-water mark for misleading biomolecular visualization computer graphics content. Snagged a copy. When most everything is unmoving, it's "obvious"... well no, not to students, but... there's no pretense of doing anything other than stitching together an extremely selective set of "snapshots", to tell a completely bogus narrative of smooth motion. Here it…

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

#517

Post by Buttons840 » Mon, Apr 27, 2020, 6:54 AM UTC

AngryData wrote: post #244

tomp wrote: post #116

Earlier quoted context omitted.

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.

Flat wings can and do fly just fine, they are just a bit less efficient. The teardrop shape and camber/cupping underneath just make the winds more efficient at slicing through the air without creating as much turbulence and drag.

My understanding is that "less efficient" here mean that flat wings have, specifically, less desirable stall behavior. Flat wings will stall more easily than an appropriate shaped "teardrop" wing.

A "stall" happens when the wing is no longer directing air downwards (and thus not providing lift), and is instead just chopping up in the air into turbulent chaos without any consistent direction.

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

#518

Post by rocqua » Mon, Apr 27, 2020, 6:57 AM UTC

knzhou wrote: post #390

bollu wrote: post #377

Earlier quoted context omitted.

> it should reduce in the Newtonian limit to something that looks like a tidal effect, i.e. a gradient of the Newtonian gravitational field. Can you please explain to me how you went from"looks like a tidal effect in the Newtonian limit" to "a gradient of the Newtonian Graviational field"?

"Tidal effects" are defined in terms of having different gravitational fields in one place than another (i.e. the tidal bulge near to the moon occurs because the moon's field is stronger there).

That's not quite true, as illustrated by the tidal bulge opposite the moon.

Tidal forces occur much more due to the difference in the direction of gravity than due to the difference in magnitude.

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

#519

Post by unexaminedlife » Mon, Apr 27, 2020, 6:59 AM UTC

Sort of trying to piggy-back on this thread in hopes someone with knowledge will be able to share it.

I've been having conversations about viruses recently and in those conversations / thought experiments I keep coming back to a point someone made to me.

Someone this person knows, with extensive medical expertise, explained that the "membrane" of the cell contains a ridiculously large number of unique types of proteins.

Understanding, in vague terms, how viruses penetrate cells the question I pose is "is this true because each of those proteins has a unique and distinct function in the cell membrane? Or is it more a matter of scale and utility?" In other words, does the observation simply indicate that our bodies are not as perfect as we'd like to think they are and the body's process for creating / repairing cells is more a utilitarian function where the "rules" of cell construction are extremely flexible such that these molecules are constructed in various ways where our cells are using materials available to them at the time?

If this is the case it starts to make a lot of sense to me at a molecular level why certain people tend to be more susceptible to contracting certain diseases. Could a lot of it really just come down to diet, along with probably a hint (or more) of DNA's interaction with those proteins we're providing to our bodies? And to what extent does each of those play a role? DNA and the proteins.

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

#520

Post by cyphar » Mon, Apr 27, 2020, 7:00 AM UTC

elorant wrote: post #502

cyphar wrote: post #488

Earlier quoted context omitted.

You can't, it's a fundamental aspect of quantum mechanics (measuring any entangled system collapses it because you've forced the system into a state by measuring it). The idea is that you structure the QC system such that the computation is done using entangled states, but when it comes to measuring the qubits (to get the result of the computation) the state is such that you'll get meaningful results. This means the…

OK but this implies that you'll have to know beforehand what a result will look like. Which kind of beats the purpose of a general purpose computational device.

No it doesn't. You know that the result of the computation for an individual qubit will be either 0 or 1 (otherwise it would be useless -- measuring only gives you one bit of information), so you construct the system such that after the computation is done each qubit will be aligned with the |+z> or whatever axis. The key point is that you have to be clever about how you construct the system for a given QC algorithm, not that you cannot do arbitrary computations using the system.