Oh, man, is space big. I get upset thinking about it sometimes. It's just too big (then again, my general reaction to the largest living thing on the planet, the General Sherman Tree, was to get angry). But it's not that space is just so large, it's also that it's so empty. And that is what I'm here to talk about today.

The visible universe is about 93 million light-years from one side to the other. That means we can see about 46 million or so light-years in any given direction, if we look hard enough (you'd need impossibly good eyes, though, or you could just use a really powerful telescope and also be in space because the atmosphere really gets in the way of seeing that far). Most of that space is empty. Sure, there are an estimated 2x10²³ stars (that's 200 sextillion, or 200,000,000,000,000,000,000,000), and that seems like a lot, but a star doesn't take up that much space (well, they're huge, but not huge enough to make any kind of impact). In fact, the estimated amount of matter (that is, baryonic, visible matter) in the visible universe is 10⁵³kg. While that is 100,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 kg, or I-don't-know-the-word-for-that-number kilograms, that still pales in comparison to the amount of space in the universe. Let's be generous and say that all of the matter in the visible universe is Hydrogen (most of it is, realistically, anyway). Let's also say that you can clump it all together at Standard Temperature and Pressure, at which the density of Hydrogen is 0.09 g/L. That means that 1 kg of Hydrogen takes up 11111 Liters, or 11.111 cubic meters (m³). That's just about the volume that a standard commercial dump truck holds. Obviously, this is the reason we tend to compress Hydrogen to transport it. But, we're trying to be generous with how much stuff there is with the universe here, even though that stuff is almost always under more pressure or in a form that takes up less space when found naturally.

So if we gather together all our matter in the visible universe, make it all hydrogen, and clump it all at STP (Standard Temperature and Pressure), it will take up about 1.1x10⁵⁷ Liters, or 1.1x10⁴⁵ cubic kilometers, or about 1,312,144.4 cubic light-years. Let's be super generous and round that to 1.5 million cubic light-years. That sounds like a lot, right? Well, remember, I said that the visible universe had a radius of 46 million light-years? Yeah, space is much, much bigger.

The volume of the visible universe (using the formula for the volume of a sphere: 4/3 * pi * r³) is about 4x10²³ cubic light-years (actually slightly larger, but we're trying to be generous to matter, here). That's 400,000,000,000,000,000,000,000, or 400 sextillion cubic light-years. That's huge. That's mind-boggling. That's so far beyond angry-about-a-giant-sequoia huge that I can't even fathom it. So let's try to put this whole matter-to-space ratio into a better perspective.

[REDACTED DUE TO INCORRECT MATH]

This is absolutely mad. I've been figuring out these comparisons as I write this, and it's making my head hurt to try to process it. Space is too big, and way too empty. Next week I need to write about something more reasonable, like time travel.