Wednesday, April 7, 2010

Atoms are mostly empty space

The universe is weird. Those of you who don't believe this just haven't looked closely enough.

For a very long time, it was thought that the smallest building block of all matter was the atom. The very name "atom" comes from a Greek word which means "uncuttable" or "indivisible", and we already know that's no longer true. Not only can it be divided (sometimes with spectacularly devastating results), but the atom itself is comprised of many smaller components.

The study of these smaller components (known as subatomic particles, appropriately) is called particle physics, and the science of how they interact is called quantum mechanics. It's all pretty intimidating. I'm no expert in the field; my math skills are barely on par with my son's, who is a fourth grader. But I do find some of the information pretty fascinating.

Very Small is as Weird as Very Large
Possibly weirder. We've all heard stuff about the theory of general relativity, which is used to describe things that happen on the very large scale of the universe, things that seem to violate some of the rules of classical physics. Well, guess what? When you get small enough, many of those rules seem to go out the window as well.

I'm not going to try and define this stuff here. If you're looking to my blog to learn about particle physics, you're screwed. There are plenty of places online to learn from better resources... although I'd be happy to Google that for you. But in any case, be aware that things happen at a subatomic level that don't seem to apply to the rest of the universe, and vice-versa. Instead of delving into all that, let's just talk about some fun facts. I like fun facts. They're fun.

This is an atom. It's small, but now we know that it's not the smallest thing.

The atom is mostly made of space in between particles.
As per the title of this post, the atom is a lot of nothing. Since everything is made of atoms, we sure have a lot of emptiness around us! It's true, though. To understand this, you have to be aware of a few components that make up the atom. Atoms have a nucleus made of protons and (with the one exception of hydrogen) neutrons which makes up 99.9% of its mass, and is surrounded by a cloud of electrons. How much empty space is in between? If the proton of a hydrogen atom was the size of a marble, the nearest electron would be two miles away. In between? A whole lot of nothing. What holds them together? That gets complicated. Let's just call it an "energy force field", where the negative charge of the electron is bound to the positive charge of the proton in the nucleus via electromagnetic force (another interesting topic you might want to study at some point).

So most things are made of space? Why can't I walk through walls, then?
And why aren't you falling through the chair you're sitting in right now? Well, it's pretty simple: that empty space is hard to get into. The electrons are cruising around the nucleus very, very quickly. Think of it this way: there is a lot of space between cars barreling down a busy freeway, but you probably wouldn't want to run across it. Also like a multi-lane freeway, even if you made it past one layer of electrons, there are often several layers (or shells) of orbiting particles, so you'd have to be really lucky to get through all of them. If you want to look at it purely theoretically, it's actually not impossible to walk through a wall... just very, very improbable that you'll "miss" each of the billions and billions of electrons of every atom between you and the other side.

This magnet is levitating over supercooled liquid nitrogen. Why? As Shakespeare wrote, "There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy."

Compounding the matter is that the force that holds these particles together is pretty powerful. Think about the power needed to split an atom. It's probably more than you have in your body. And then, the atoms themselves bond to other atoms to form molecules. These things are tough to separate. However, if you want to try running full speed at a wall in the off-chance you'll make it through, don't let me stop you. But do have your medical insurance paid first.

So, everything is made of these little particles, eh?
Well, uh... sort of. Sometimes they seem like particles in that they have mass. But other times, they act like waves of energy. That's an important concept to grasp, since it applies to, well, everything in the universe: see wave-particle duality. This topic came up when people were trying to figure out what light was. Is it an energy wave? A stream of particles? The current theory says it's both, and so is everything else.

A light shines on a thin plate with two parallel slits cut in it, and the light passing through the slits strikes a screen behind them. If light is a wave, then the light waves pass through both slits to interfere. But at the screen, the light is always found to be absorbed as though it were made of discrete particles, called photons. Both answers are right.

Why are these things called "elementary particles"?

Because they're not made of anything smaller. Yeah, I know: we used to think that about the atom, and we were wrong. But we now have the technology to prove this stuff with empirical evidence that can be known via direct observation. What we don't really know for sure is how and why they behave as they do. We have theories that hopefully someday will be proven (or disproved) which will really help us have a better understanding of this universe in which we live. There aren't very many elementary particles, as it turns out. There are fermions (12 different kinds of quarks and leptons), and number of bosons that we probably haven't finished discovering or proving yet. Everything in the entire universe is made of this stuff... you, me, your computer, the sun, your house cat, the tree outside your window, the sky, the Doritos you just snacked on... everything.

What is "string theory"?
This shit is really complex. It's not something I can boil down to a cute sentence or two. String theory is an idea that what we observe in particle physics is only one aspect of many dimensions (between 10 and 26, per current theories). It would help explain some of the behavior of particles that don't line up with the general laws of physics. The problem is that by definition, it seems unprovable. I guess we'll wait and see.

One reason this stuff is so hard to understand: it's, like, really small. You have macroscopic level, molecular level, atomic level (protons, neutrons, and electrons), subatomic level (electrons), even smaller subatomic level (quarks), and then string level.

What is gravity? And why are you mentioning it here?
You probably have some understanding of gravity. Like, if you trip, it's more likely that you'll fall down, as opposed to up. You're standing on a planet that has quite a bit of mass, at least compared to you. And things with more mass attract things with less mass. Actually, to be accurate, all things with mass attract all other things. To a very minute degree, the Earth is also falling up at you. Anyway, there are only four known fundamental forces... "fundamental" because they can't be described via other interactions. Those four are electromagnetism, strong interaction, weak interaction, and gravitation. At a quantum (subatomic) level, we've observed that there are aspects to gravitation that don't seem to fit the same rules that apply to large items like stars, planets, and so on. The attempt to reconcile these incongruities will hopefully result in something called the theory of everything. I like that name. If you really want to keep yourself busy, just ponder the entire list of unresolved problems in physics. Fun stuff.

Everything in the universe attracts everything else. But the way large objects display gravitation is different than what we see at the subatomic level. This is a problem.

All of this is confusing.
Yes. It is. But at some point, it's the study of this stuff that will not only allow a better understand of what's around us, but might lead to things like time travel, or faster-than-light travel, or the exploration of other dimensions that we can't even conceptualize now. It could be cool.

Why are you writing about this?
I don't know. I do things that I feel like doing when I feel like doing them. I'm glad I usually don't need a reason for much of what I do, since I rarely stop to think of justification for it.

Why should I care about any of this?
You don't really need to. Life has existed here on Earth for about 3.5 billion years, and humans have existed in the current form for about 200,000 years. For nearly all of that time, no one had any idea about this stuff, and yet lived presumably happy lives. But ultimately, the reason you should know about this is because you can. It's one of the only things that makes you unique in the animal kingdom, this capability to understand extraordinarily complex topics. But a house cat seems to be able to enjoy himself without ever worrying about what the universe is made of and how it works, and you can too. It's all up to you.

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