Another question, this time related to quantum mechanics: If all matter is made of electrons, and electrons can be present in multiple places at the same time, then why do humans, which are also made of electrons and protons, not have the ability to be present in multiple places at the same time?
That's a wrong notion you've got there. Electrons cannot be present in multiple places at the same time. It has one position at one point in time. But HUP states that such a position cannot be determined with absolute precision because it is not possible to determine both position and velocity with absolute certainty for an electron. Visualise this. Say you have two kinds of balls, tennis balls(photons) and footballs(electrons). Suppose you have to measure the position and velocity of a football using a tennis ball. How'd you go about it? One way to go about is, to throw the tennis ball in your hand with a known velocity towards the football, that way, when it comes back, you again measure the tennis ball's velocity and time it took to come back. Thereby you are able to calculate the position and velocity of the football too. Right?
But here's the catch.
By the time you've caught the tennis ball, the football has already moved from its previous position.
Why?
Because the tennis ball imparted some of its energy to the football and changed its inertia. So, the football isn't present at many places, it's just present in someplace you're not sure/certain of. Thus, the uncertainty.
Similarly when a photon strikes an electron, the photon imparts some energy to it and the electron assumes a new position. Thus, there is an uncertainty in the position of the electron by the time you've detected the photon. The uncertainty is a function of the energy in the photon.
This, in brief is HUP; Heisenberg's Uncertainty Principle.
As for quantum phenomenon not being observable in macro scale, the answer is very clear. The results of classical mechanics and quantum mechanics are congruent on the macro scale. Meaning, when a large number of quantum units are involved, the whole system behaves in a manner similar to classical dynamics. hence, humans cannot be present in multiple places at the same time.
The Uncertainty Principle is fantastic.
I never completely understood it when I studied physics....it leads to mind-boggling conclusions like for example that an electron under observation is everywhere at the same time, yet nowhere in particular. It only exists at a single point once we "look" at it. So our act of observation is what makes the electron "exist".
No, precisely speaking, the act of observation does not make the electron 'exist' per se. We are just uncertain how it exists. Through observation, it has been found that electrons are able to behave both like waves and like matter. Therefore, without observation, we cannot say with certainty in what form an electron is at a definite point in time.
Yup. I admire that principle too. It prevents achievement of perfection in measurement and observation. It's the universe's way of telling sapient lifeforms, "Bitch please".
I believe the "electrons at multiple locations" phenomenon you refer to, has something to do with a double slit experiment. And if I remember right, when the electron is observed, it appears to pass through one slit, if not observed , it passes through both slits. Though I'm not sure why.
Maybe
@Dovah knows something.
The double slit experiment only shows that the light has the property of wave nature. Young's double slit experiment has not much to do with electrons. But yes, you can look up the Davisson and Germer experiment, that one deals with electrons.
No, the electron does not pass through one or both slits. It simply means that electrons act both as waves and as matter. When the electrons are detected, the matter properties are exhibited. When it passes through the slits, the wave properties.
Source: High-school Physics. Resnick, Haliday and Walker: Fundamentals of Physics.
I think you re right. 
