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

Here are things that I consider to be defining properties of human consciousness:

a) The ability to observe an instance of a multidimensional universe, each instance a mapping of a point moving along a continuous trajectory whose direction is constrained by the arrow of time (i.e., increasing entropy)

b) the ability to impart a force to change the direction that trajectory follows

First thing, propellers are wings, they work using exactly the same aerodynamic principles, except the "lift" goes sideways. And airliners use propellers (called fans here), the "jet" part of their engines only provide a fraction of the total thrust.

Now why not use a propeller pointing directly straight down? Well, you just made a helicopter. Helicopters are great, but they are not as fast as airplanes, the main reason is that as it goes forward, one part of the rotor is advancing and the other is retreating, this causes a whole lot of difficulties that doesn't appear when the propeller is mounted sideways.

Now propellers aren't the only way of producing thrust. There are jet engines, but these require significant airspeed in order to be efficient, and you usually have much more airspeed horizontally than vertically.

You can have rocket engines, which are great if you want to get really high, really fast, but they have to carry their own reaction mass, which is impractical in most situation.

Also you can use buoyancy as a form of "thrust", you now have an airship. Efficiency-wise, it is unbeatable. Unfortunately airships are big and slow and not very suited to modern requirements.

As you can see, there is absolutely nothing preventing us from thrusting downwards, it is just that airfoils are very efficient.

Back to your first question: how can 100 pounds of thrust keep a 1000 pound aircraft in the air. Without going into details, it is the same idea as a lever or gearbox (mechanical advantage). We rarely think of it this way for the wings of an airplane, but for propellers, it is a more apt comparison. A variable pitch on a propeller is like a gearbox for your car, and as seen earlier, propellers work exactly like wings.

As for what "thrust" is, it is really just a force, often shown together with with drag, lift and weight, it is provided by the engine. But in the end, there is nothing special about thrust, you can reorganize your forces anyway you want using simple vector math. For example gliders don't have thrust, and they still fly, taking advantage of updrafts.

You'd think, but of course we know that not to be the case. It's hard to pinpoint the exact reason though. Sure we know time and space are rather special, but its hard to say exactly why.

In the end though I reckon the most obvious reason is that speed is a property that directly corresponds to energy, therefore for each region of space to have a well defined energy (which is required for e.g. general relativity) every region of space needs to have a well defined distribution of speeds.

I suppose this does leave open a small loophole, as you can easily correlate speed with position in order to get a distribution that is uniform in both (but correlated). But this goes against our assumption that the universe is uniform everywhere (which might turn out to be false, but so far it's holding up well).

The best way to earn in my opinion is to start with small simple projects and build up from there. It can be a strange concept to get used to if you have a longtime background in synchronous programming (like I had too). I finally wrapped my head around it when picturing the programming flow as getting another direction - perpendicular to the normal vertical flow (I prefer to think in terms of geometry ...).

Japronto does not seem to be under active development any more, but async programming is definitely the way to go in order to squeeze the most performance out of the hardware at ones disposal.

I put down some thought round this that tracks my own journey to understanding the concept (sorry if this is too basic for you, take it or leave it, and please note that I'm not an expert by a long shot).

It's not guaranteed that you have the same way of picturing things, but here goes: programs normally run in one direction, executing one line at the time from top to bottom (vertically). But one or more of those 'vertical' commands may send the computer off in a horizontal direction too (async calls), that have a 'horizontal' chain of commands.

The problem that I (and I think many with me) have had a hard time grokking at first is that the 'vertical' flows continue immediately after having issued a 'horizontal'(async) call. The computer doesn't wait for the async call to come back. To do something after the async call has finished you have to tack a new call onto the result of the async call in the 'horizontal' chain of events, previously often leading to what was called 'callback hell' in Nodejs programming.

Not sure about PHP but one may get round the problem of callback hell in the JavaScript world by using async/await and promises which mimics synchronous programming, i.e. program flow in the 'vertical' direction is actually halted until the async calls return a result. Personally I find that this adds another level of abstraction that sometimes may make things even more difficult to understand and debug. I prefer wrapping async calls in some queue construct instead (which takes care of the chaining of consecutive async calls), works for me.

In short, synchronous commands are automatically 'chained' top to bottom in code, asynchronous commands have to be chained manually after the completion of each async bloc of code. I believe multi-threaded process programming is just a more advanced case of async calls that often need to be 'orchestrated', i.e. coordinated in a way that simple async calls usually don't need. But all types of async programming comes with some special issues, of which race-conditions is maybe the most common, i.e. when several async processes are trying to change the value of a shared asset in an ad-hoc manner.

and that had never happened to you in your other trips?