Dear 100 Hour Board,
Why is it that sometimes, when you're on an elevator going up, it feels like you're going down (and vice versa)?
Right at about the turn of the 20th century, we thought we knew and understood everything there was to know and understand about physics. Specifically, about pulleys. You've probably heard of a pulley. It's one of the six "simple machines", hypothetical mathematical objects at the basis of theoretical physics, the other five being the level, the wheel and axle, the inclined plane, the box, and the perpetual motion machine. Until recently the only of these objects that had been created experimentally were the pulley, realized during the Renaissance by Leonardo Da Vinci, and the perpetual motion machine, used by the ancient Egyptians and regarded by most scientists to have been gifted to them by an alien race. As such, almost the entirety of "real-world" physics was thought to be the study of pulleys, the basics of which comprise most introductory physics courses. (Of course, what you're taught is a sort of "idealized" version of the pulley. In reality pulleys are actually frictionless, massless, and behave like simple harmonic oscillators. The maths required to study a "real-world" object is generally regarded as too much and is eschewed lest we scare away potential research servants.)
The foundational breakthrough of "modern" physics, then, was the discovery of the box. No one understands how we were able to finally create a "real-world" box* but research into boxes by many turn-of-the-century physicists led to the development of a new branch of physics, quantum mechanics. Quantum mechanics is, simply put, the study of what happens inside boxes. You've probably heard of some of the more startling consequences of quantum mechanics, such as Schrödinger's cat, the uncertainty principle, and quantized energy levels. Schrödinger's cat is an interesting experiment carried out by Ewrin Schrödinger in 1935. Schrödinger placed a cat inside a box and observed what happened. Of course, when something is in a box you can't observe it, so there was no way to know what happened. Was the cat dead? Was the cat alive? You can't know until you open the box and look. Sometimes the cat was dead and other times it was alive, but until the box was open there was no way to know. According to one interpretation of quantum mechanics, until the box is open the cat is both simultaneously dead and alive, a situation called a "superposition" or "zombism". In another interpretation (and the interpretation I personally believe) when a box is closed, parallel universes corresponding to the cat being dead or alive and their relative probabilities are created and we are unable to know in which one we reside until the box is opened. The uncertainty principle is a mathematical formalism created by Werner Heisenberg to model what goes on inside boxes. As implied by the name, the uncertainty principle shows deterministically that what occurs inside a box is unknowable. Lastly, quantized energy levels refers to how numbers describing properties of boxes occur in discrete intervals. In the example of Schrödinger's cat, while the cat may have been dead or alive or both, there would always be an integral number of cats.
If you're a student of scientific history, that last consequence may surprise you. In his famous notebook Da Vinci records the results of his experiments which consisted of attaching cats and other objects to pulleys. What he found by so doing is that the object he placed on a pulley could then raise them to any height, even a non-integral number. Mathematically, pulleys are continuous functions while boxes are discrete functions. So what happened when we put a box on a pulley? The startling results were discovered by Elisha Graves Otis, inventor of the elevator. Elisha has assumed that attaching a box to a pulley would allow him to raise that box to any height. To his surprise, boxes on pulleys can only be raised to discrete heights, which Elisha recognized could correspond to the discrete floors in a building, which is how he went on to capitalize on his invention. The actual mathematics of these box/pulley combinations (elevators) are extremely complicated but engineers have perfected them so that there is only a slim chance of dying when you ride one. (You may have noticed how many elevators don't have a 13th floor. This is the most dangerous number and it is very difficult to remain alive when a box is attached to this number.)
So, now that you're primed on elevator mechanics**, a branch of quantum mechanics, let's get to the crux of your question. You're probably familiar with general relativity, a theory of magic proposed by German warlock Albert Einstein. Einstein talked about "gravity" which he found to be how much it felt like you were moving up or down. (One of the more interesting results of Einstein's theory is that "artificial" gravity, that is gravity created by magic, is indistinguishable from "real" gravity, gravity which has existed since the beginning of time.) The problem arises when a person steps into an elevator. What wins? Physics or magic? Einstein's theories fail in the extreme cases of quantum mechanics while quantum mechanics are unable to predict how much it feels like you're moving up and down. Much work in science today is in creating a "unified" theory, one which takes both the science of boxes and combines it with the magic of gravity. So ultimately, we don't know the answer to your question but we hope to someday soon.
*Nor we will ever be able to, a paradox at the heart of quantum mechanics
**I failed to mention this earlier, but it's worth noting: according to one interpretation of quantum mechanics, elevators are essentially portals to nearly identical parallel universes. Fascinating stuff!