Empty Space for Dummies Like Me
Full of empty space
Ever gaze out into the cosmos in wonder at just how much stuff must be out there? Immediately on the tails of that thought might come the conclusion that there's an awful lot more empty space out there than there is stuff. If you're having a tough time falling asleep, consider thinking on a few different levels how empty the universe really is. I've spent many a sleepless night contemplating just how ridiculously vacuous both the tiny scale and the immensely large scale are. You and I are, after all, mostly empty space, when it comes down to it. Let's get started!
Space: the brain's frontier
The scale of the atom
Let's start with the world of the very tiny: the scale of the atom itself. If you'll recall elementary and middle school, you probably either built a representation of the interior workings of the atom with styrofoam and wire coat hangers (a "mobile"), or you saw a similar model drawn in your science books. Well, this model is utterly, completely wrong, and terribly misleading (thanks, public education!). The scale of the atom is nothing whatsoever like a softball orbited by a golf ball a foot away.
A far, far more accurate analogy in terms of how much volume each component takes up and how much space is in between them is that of a mosquito in the center of a football field for the nucleus (the mosquito) and the orbiting electrons (the bleachers). Everything else inside the atom is just nothingness. Of course, quantum mechanics suggests that even nothing isn't necessarily empty, but that's another story entirely; for our purposes, we're going to simplify things so you can understand this concept considerably better (and, hopefully, fall alseep!).
I first heard this analogy from professor Richard Muller, who was one of the first YouTube physics lecturers to have his classes available online. Here's one of Muller's excellent basic lectures (the entire course is available on Youtube for free!).
Our solar system is wide open
The scale of the solar system is remarkably similar to the scale within the atom. You could fit literally a million earths inside the sun, and the space in between the earth and the sun (93 million miles, or 8 light seconds) is enough to fit around 12,000 earths (that is not a typo!). The earth is around 8000 miles across, and you can just divide 93 million by eight thousand.
Is the fact that the atom and the solar system are so similar in scale a cosmic coincidence, or is this just the way things are made up, macroscopic and microscopic alike? I don't know, but examining some other phenomena may give us some clues.
The moon is much, much closer to the earth - about 240,000 miles, so you could fit about 30 earths in between that space. That's a lot less than the distance from the earth to the sun, but it's still a whole lot more than most people probably think when they consider models, mobiles, and drawings of the earth-moon system.
Again, I'm drawn back to those styrofoam mobiles we all likely made as kids, and how very, very wrong they are.
What's the most fun to think about?
Even more immense spaces
Here's where the scale similarities really start to break down. Our sun has a diameter of just under a million miles, which sounds like a lot, but when compared to the spaces between stars, it's virtually nothing. You can take my word for it, or you can read one of my other thought experiments where I did the math in my head, but either way, the distance between stars is unimaginably immense.
If the sun and its nearest neighbor star were mosquitoes, they'd be a whopping 90 miles apart in order to scale correctly. That's something to really stop and think about the next time you're gazing out into the night sky! Washington, DC and Richmond, VA are about 90 miles apart. I could grab a mosquito in Richmond, then squish it (because, well, mosquitoes suck), and jump in my car, drive to DC, find another mosquito, and squish that one, too. That would be how far apart the nearest star is to the sun, if the sun was mosquito sized. Wow.
Bordering on the absurd
If the distance between stars is mind-bending, then the scale between galaxies is absurdly stupid. The universe itself looks a lot like a giant web when you watch simulations, but consider how well you can see individual galaxies and galaxy clusters. That’s because there is SO MUCH space in between galaxies and galaxy clusters.
While our nearest stars are four light years away, the nearest galaxies are in the range of hundreds of thousands of light years. This is so stupendously far that light has been traveling ever since our ancestors were first walking on two legs, or figuring out how to use language. Beyond that, outside of our local group, the distance to the next galaxies is in the many millions of light years (and, in some cases, in the range of a billion light years at a stretch).
That's a whole lot of empty space!
And it’s getting even more ridiculous. The spaces between the galaxies is expanding faster and faster, thanks to our new friend dark energy. As stupendously far apart as the galaxies are from one another, on average, they're getting further and further apart, and the distance is not only growing all the time, but they're accelerating!
We are not only made of empty space, but we're surrounded by it on all imaginable scales, from the microscopic to the macroscopic. As empty as the atom is (remember the mosquito in a football field analogy), the solar system is every bit as empty, and the galaxy contains even more empty space! The spaces between the galaxies are almost unimaginably vacuous, and they're getting more and more empty all the time! Think about how empty everything is the next time you're falling asleep, and how very important the role of empty space is.