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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?

#581

Post by hoseja »

ajkjk wrote: post #265
pjungwir wrote: post #68

Quantum 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?

I'm an amateur, but I have been investigating this for myself for a long time and mean to write up a blog post when I have it all settled to my satisfaction. That's not ready yet, but I think I can give you an explanation that is more acceptable than the usual ones (including the other comments here: because it appears to have angular momentum, because it appears to have a two-component complex number that is affecte…

Interesting you mention "knot". What do you think of an utterly unfounded intuition that elementary particles are "knots", actually topological ones, on fields?

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

#584

Post by infogulch »

gnu-nobody wrote: post #568
TJSomething wrote: post #539

Earlier quoted context omitted.

Additionally, many problems are can be converted to matrix operations, like graph algorithms. Note that matrix multiplication takes O(n^2) time with a quantum computer, but O(n^2.807) time on a classical computer.

> but O(n^2.807) time on a classical computer Optimizing matrix multiplication for classical computers is an open research problem, and according to wikipedia there are algorithms with O(n^2.37) running time. Also according to wikipedia, it is not proven that matrix multiplication can't be done in O(n^2).

Ah yes, we may as well add NP-completeness to this thread.

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

#585

Post by Erlich_Bachman »

sooheon wrote: post #573
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…

Why isn't the MWI another form of hidden variables (a supremely non-parsimonious one at that), where the hidden variable is which of the many worlds you happen to inhabit?

An awesome question. That is exactly what I have been wondering without being able to put it into words, and this is core of why the MW seems completely uselsess to me as a scientific theory. (As a philosophical one-maybe? But science?)

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

#586

Post by traK6Dcm »

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…

The short answer: What exactly the "price" shown on the exchange website is depends on the exchange. Typically it's the last trade price or the mid price (average of best bid and offer). There really is no such thing as a single "price" because the price will depend on the quantity and direction you are transacting in.

Long answer: You need to understand how the Limit Order Book works. I wrote up something about this here [1]. It also goes into different definitions of price.

> If a very low-volume stock is listed at $4, and then I offer to buy a share for $100, does the NYSE suddenly start listing its price at $100?

If you trade actually absorbs the order book and pushes the asks to $100 then yes, that could be case depending on the exchange, but I'm not sure about NYSE specifically. Most likely that could never happen due to various hidden order types and HFT market makers though.

[1] https://www.tradientblog.com/2020/03/understanding-the-limit...

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

#587

Post by [deleted] »

dandare wrote: post #578

The cosmic inflation. Yes, the universe is smooth but how is that enough to justify this unimaginable expansion? There seem to be no proof or possible experiment yet the scientific community apparently accepted this theory with its abrupt start and abrupt end, only secondary to the big bang itself in its scale and energy.

[deleted]

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

#588

Post by traK6Dcm »

badpun wrote: post #543
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…

What happens if the stock sees almost no volume of trades, and we have a situation where the lowest sell is at $90 and highest buy at $100 (i.e. both parties are overgenerous)? Does the stock exchange make them split the difference, i.e. makes the trade at $95?

If someone wants to buy at $100 and someone else wants to sell at $90 it depends on who came first. To really answer this question, you need to understand the difference between market maker and taker and you need to understand how the limit order book [1] works.

Assume there are no other orders in the order book.

Scenario 1: Seller submits a limit sell order for $90. Since there are no buyers, this order goes into the book. Then a buyer submits a limit buy order for $100. The order would be filled at $90 (the best ask) and the buyer only pays $90. Here, the seller is the maker and the buyer is the taker.

Scenario 2: Buyer submits a limit buy order for $100. Since there are no sellers, this order goes into the book. Then a seller submits a limit sell order for $90. The order will be filled at $100 (the best bid) and the seller gets $100. Here, the buyer is the maker and the seller is the taker.

Market makers are responsible for setting prices and providing liquidity. If you want to understand this in more detail, check out this post [1] I wrote up a while ago.

[1] https://www.tradientblog.com/2020/03/understanding-the-limit...

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

#589

Post by skocznymroczny »

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 looked briefly at QCs and I understood them as kind of a machine that doesn't try every possible solution. It is in every possible solution, and then you can somehow "lock it" in the state that is the solution to your problem. Kind of like NP problems are hard to find a solution but easy to verify a solution.

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

#590

Post by dandare »

How a single hormone can regulate so many different things. Looking at Wikipedia, a single hormone like progesterone which is apparently one molecule regulates a plethora of effects. How is this implemented? As a coder, if I had to use one variable to simultaneously regulate 10 different things I would go crazy.
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