Everything in the universe can be said to belong in one of two different categories: stuff and things. Now, stuff and things are very different, and I’ll do my best to explain why below (and how the difference between them leads to the state of our universe as we know it).
Stuff is, well, stuff. If you get some stuff and you put it on some other stuff, you just have more stuff. Boom! That’s that for now; there’s nothing else to it.
Things are a little bit more complicated, but not by a lot. See, things are things, and if you try to put one thing where another thing is, you obviously can’t because they’re two different things. Simple enough.
When you were a child, this was explained in chemistry class (probably while you were sleeping) and in time-travel fiction (while you should have been studying for chemistry) using the following common-sense rule: No two things can occupy the same space at the same time.
But what’s actually pretty funny is that the “real” version of this is much simpler in principle:
No two things can be the same thing.
That’s it! It’s obvious; if two things were the same thing, then why would they be two things? They’d just be one thing, and then all of that same kind of thing would just be one big collective thing, and that would just be stuff. Capisce? Here’s a simple (read: made in Paint) visual comparison to help solidify what I mean.
With this in mind, it’s time to move away from the world of philosophical abstraction and actually mention examples of stuff and things in our universe.
Electrons & Atomic Structure (or Things on Things)
At the elementary level, practically everything is a thing; electrons, protons, neutrons, and everything made out of them (which is essentially, well, everything).
What’s actually very interesting about things is that the simple, essentially philosophical statement I made in the previous section about thingness is directly responsible for the existence of chemistry as we know it. I’ll show how & why below, but first I need to explain what makes an electron its own thing.
The first thing we need to know is that a single electron doesn’t exist as some tiny ball, but as a probability cloud with some specific shape; this is why it was important to generalize our common-sense statement about things not being in the same place & time since, technically, every electron exists practically everywhere in the universe at the same time. So now, that property of the electron we’d call its “location” can be replaced by a property we’ll call “cloud shape” or shape.
The other property that makes a single electron “its own thing” (that’s relevant to us) is a property called spin. Spin is tricky (it deserves its own post), but all you need to know is that it’s a property an electron has and that there are two possible values of it. In fact, if electrons all had name-tags that said either Harry or Bob instead of having spin, chemistry as we know it (sort of) would still exist. Go ahead, name them!* I’ll take the approach of painting a Harry electron blue and a Bob electron red in my illustrations, and say that our electrons now have names instead of spin.
*Just don’t feed them or you’ll have to absorb them.
The whole reason I bring these properties up is to explain why our atoms look the way they do. See, thanks to their names, electrons can indeed exist in the same place at the same time (a.k.a. have the same shape) as long as they have different names; because that means they’re still different things!
With that out of the way, consider the following two atoms in two different universes, one in which electrons are things (our own) and one in which electrons are stuff. Here’s what hydrogen would look like:
Nothing seems different there. The simplest (a.k.a. lowest-energy) shape an electron can have around the nucleus is just spherical, and both electrons here take that same shape. Here’s what lithium would look like:
Now we’re getting somewhere. Once both Harry & Bob electrons exist in that first shape in our atom, you can’t pile on another electron without it possessing a different shape because the extra electron would be identical to either Harry or Bob, and would therefore not be a different thing. This is why chemistry teachers say things like “The first electron shell holds 2 electrons”, and why the first row of the periodic table only has 2 elements. For lithium to form, what then winds up happening is that the extra electron would have to change its shape to get bound to the nucleus (with a little energy boost), and that’s exactly what the extra Harry electron in our lithium illustration does.
In contrast, stuffium-3 doesn’t need each electron to be individual things, and so allows all of them pile up indistinguishably in that lowest-energy sphere shape.
Now here’s what carbon would look like:
Completely different! The trend is evident; our electron-thing atoms seem to obtain spatial structure when we pile up electrons, while different elements of stuffium look exactly the same since we can just pile up electrons indefinitely in that lower-energy sphere shape. In carbon, we’ve already filled out that second spherical shape we saw in lithium with another Harry and Bob, and so we see the two extra Harrys forced to take on some funky non-spherical shapes. (Two ovals on the same axis are the same electron). Note that you can always distinctly identify every electron in our atoms, while stuff-electrons have no individual “identity” to speak of.
A stuffium universe would be drastically different to ours; there is no energetic barrier to the formation of heavier elements such as iron (ahem, stuffium-26), and most of these elements would exist in even denser polyatomic molecular forms. The abundant presence of these heavier elements and molecules leads gravity to form galaxies much quicker than they began to form in our universe, and most nebulae would rapidly collapse into massive, dense planets. Black holes would be a common sight, and with chemistry changing completely, it’s unclear if stars could even exist. Cool beans!
Light & Gravity (or Stuff and Some Other Stuff)
Now there’s not a lot of different kinds of stuff in the universe, but here’s a big one: Light is stuff! This is actually pretty intuitive, as I’m sure you’ve noticed that light doesn’t really behave like most things (pardon the pun) you’ve seen before. For one, clearly unlike things, you can essentially pile up “identical” light indefinitely just like the stuffium electrons above*. In fact, piling up identical light and then emitting it is precisely the definition of a laser.
*Eventually, piling up extremely large amounts of light creates things out of stuff, but that’s way out of our league here.
Gravity, or more accurately what causes it, is also stuff. This is actually a bit of a mind-boggler, since we haven’t really discovered the stuff that causes gravity; but we know for sure that it has to be stuff because gravity just wouldn’t be gravity if it wasn’t. Sadly there’s not much more to say about gravitational stuff at the moment, but we’re working on it.
At the risk of complicating things even more, scientists have actually discovered ways to make things behave like stuff! For example, in certain materials, you can actually trick every available electron (all ~10^23 of them) into piling up into the same material-wide shape, leading to some extremely strange phenomena.
Anyways, before I finish off this post, I should probably reveal the scientific names for things and stuff; now you can brag that you know what the second part of that whole “Higgs boson” hullabaloo means! (Admittedly, Higgs stuff doesn’t sound as interesting).