There’s a lot of not much in Space

A while ago I drove from Denver to Fort Worth, and I was impressed. See, there’s a lot of not much in eastern Colorado. It’s pretty much the same in western Oklahoma except there’s less not much because there’s less of Oklahoma – but Texas has way more not much than anybody.

That gives Texas not much to brag about, but they do the best they can, bless their hearts.

What got me started on this rant was a a pair of astronomical factoids Katherine Kornei wrote in the Nov 2014 Discover magazine.

“If galaxies were shrunk to the size of apples, neighboring galaxies would be only a few meters apart….”
“If the stars within galaxies were shrunk to the size of oranges, they would be separated by 4,800 kilometers (3,000 miles).”

Apple orangeSo there’s a lot of not much between galaxies, but a whole lot more not much, relatively speaking, within them. I just measured an apple and an orange in my kitchen. They’re both about the same size, 3 inches in diameter, so I have no idea why she chose different fruits – perhaps she wanted to avoid comparing apples and oranges.

Anyway, if you felt like doing the galaxy visualization you could put two apple galaxies on the floor about 12 feet apart and then line up about 50 apples between them. A fair amount of space for more galaxies.

To see inside a galaxy you could put one orange star in Miami FL, and its on-the-average nearest orange neighbor in Seattle WA. Then you could set out a long skinny row of just about 63 million oranges in between. Oh, and on this scale the nearest galaxy would be about 2 billion miles (or 43 quadrillion oranges) away. Way more not much inside a galaxy than between two neighboring ones.

So if we squeeze all those apples and oranges together we’d get rid of all the empty space, right?

Not by a long shot. Nearly all those stars are balls of very hot gas, which means they’re made up of atoms crossing empty space inside the star to collide with other atoms. Relative to the size of the atoms, how much empty space is there inside the star?

Matryoshkii 1For example, every chemistry student learns that 6×1023 molecules of any gas take up a volume of 22.4 liters at normal Earth temperature and pressure. For a single-atom gas like helium that works out to about 22 atom-widths between atoms.

Now think about emptiness inside the Sun. If it’s a typical star (which it is) and if all of its atoms are hydrogen (which they mostly are) and if the average density of the Sun (1408 kg/m3) applied all the way down to the center of the Sun (which it doesn’t), and if we believe NASA’s numbers for the Sun (hey, why not?), then the average density works out to about 0.7 atom-widths between neighbors.

So no empty space to squeeze out of the Sun, eh? Well, actually there is quite a lot, because those atoms are mostly empty space, too.

OK, I cheated up there about the Sun, because virtually all of the Sun’s atoms have been dissociated into separated electrons and nuclei. The nucleus is much smaller than than its atom – by a factor of 60,000 or so. Think of a grape seed in the middle of a football field.

To sum it upward, we’ve got a set of Russian matryoshka dolls, one inside the next. At the center is a collection of grape seeds, billions and billions of them, each in their own football field. The football fields are all balled into a stellar orange (or maybe an apple), but there are billions of those crammed into a galactic apple (or maybe an orange) that’s about ten feet away from the nearest other piece of fruit.

As Douglas Adams wrote in Hitchhiker’s Guide to The Galaxy,

“Space … is big. Really big. You just won’t believe how vastly, hugely, mindbogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space…”

The thing to realize is that the function of all that space is to keep everything from being in the same place. That’s important.

~~ Rich Olcott


2 thoughts on “There’s a lot of not much in Space

  1. As a native Texan, raised in the flat and farm-filled greater panhandle area, I can only nod at your description. As you know, we are frequently and vocally proud of “not much” in the Lone Star State. 😉


    • Hi, Jonpaul. I remember being on a plane that had to make an emergency landing in Lubbock. As I looked around at all the flat not-much around us I wondered, “Landing here’s no problem, but how the heck did he even find this place?”


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