Now that we have tools to find vast numbers of voids in the universe, we can finally ask…well, if we crack em open, what do we find inside?
The answer is a whole bunch of nothing. You probably could have guessed that from the same. But here’s the thing: for a good chunk of their volumes they’re not completely totally 100% dead and lifeless and empty. The analogy I like to use HERE are deserts. Sure, if you go out in a random desert you may not find a lot of rain or activity, but it’s not TOTALLY devoid of life. There are still, I don’t know, succulents and…small mammals, and… reptiles listen I’m not a biologist or an expert on biomes so I’m just winging it here. My point is that in a desert there’s still STUFF, just not a lot of it.
And if you take a picture of a void (or, more accurately, perform a deep galaxy survey WITHIN a void), we find that there’s still STUFF, just not a lot of it. We can see dim dwarf galaxies with thin threads of gas connecting them. We can’t directly see the dark matter in our observations, but when we build computer simulations of the universe and find voids THERE, we see entire mini-cosmic webs, with voids divided into subvoids divided into sub-sub-voids. Yes that does mean there’s a slight fractal character to the cosmic web which is really cool but not the point of today’s episode.
But still, even though the voids aren’t TOTALLY empty, they’re still pretty dang empty. A typical void will have somewhere around one fifth the average density of the universe, which doesn’t sound all that empty. But check this out. If you took all the stuff in the entire universe, every planet, star, galaxy, wedge of cheese, gas cloud, and even all the dark matter, and smeared it out into s uniform ooey gooey mess across its total observable volume, the entire 90-billion-plus light-years extent of it, you would end up with an average density of roughly only one single hydrogen atom per cubic meter.
A cubic meter is big. It’s about yay across. Imagine placing just one hydrogen atom in that entire volume. THAT’S what the universe is like ON AVERAGE. But the VAST majority of that stuff is crammed into very small volumes. I can assure you that the air your breathing is SLIGHTLY denser than 1 hydrogen atom per cubic meter. Now a typical cosmic void is only ONE FIFTH of that, so a volume five times bigger containing only one lonely hydrogen atom.
I don’t know about you, but to me, I consider that kind of empty.
So only 20% of that is pretty dang low, and that’s on AVERAGE. That INCLUDES the borders/boundaries of voids that butt up against walls and clusters and filaments. The boundaries of the voids are decidedly less voidy (out of necessity), like the edge of a desert that transitions to…uh…again not too familiar with biomes here…jungle seems wrong, as does ocean…let’s just call it not-desert).
But it IS possible to reach deep into the voids, just like it’s possible to reach deep into the deserts, and find truly lifeless portions. Like the Qattara depression in the deep Sahara, or the Empty Quarter of the Arabian desert, or Badwater basin in Death Valley.
There are deep regions within the voids, far from the walls and boundaries, far from any dwarf galaxies, far from any loose threads of gas, where there’s essentially nothing for up to millions of light-years. Heck, this even shows up in our dark matter simulations too. I mean yeah, sure, if you wait long enough you MIGHT see a random hydrogen atom wandering by, or a particle of dark matter zip on through, but you’d have to wait a really, really long time before the next one.
And I can’t help but wonder what it might be like to live inside a void. Imagine if we transported the solar system into one of these deep regions. Of course there would be no stars on the sky, but it would be even worse than that. There would be NOTHING on the sky. Just the sun, the moon, and the planets sitting against a completely blank canvas. It would take advanced telescopes to see even the NEAREST galaxy, and still it would only appear as a faint, dim smudge in the extreme distance. Which leads to a really intriguing thought: if somehow we arose to intelligence and civilization on a planet in the void, would we even develop astronomy? Yeah, we would invent telescopes and get close-up views of the planets, but with millions of light-years to our next nearest neighbor, would we ever both refining our technology? Would we ever discover cosmology, the expanding universe, the big bang?
Would we even know that the rest of the universe is out there?
When I stay up way too late at night, I sometimes wonder if we’re missing something ourselves, but I don’t like that thought all that much so when that happens I just switch to playing Minecraft.