Not quite in the same vein, but there are graffiti in various places:

https://eeggs.com/items/9064.html

And, I'm told, on a PCB of Beagle2's avionics there's "We come in pieces".

<such trenchant wit>

I didn’t know our moon casts shadows that far away.

I know it’s not our moon

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Yea We are so Gullible as a species..No one will ever be able to see this for themselves..I'm more of a hands on see in person kinda guy..lmfao..

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It's hard to overstate how far ahead of anyone else SpaceX is. Honestly don't know if I can recall a similar situation in an industry

Thats what my butt looks like if i shine a light through my cheeks

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Imagine you're in a crowded mall and suddenly The Rock shows up and he's signing autographs and taking selfies with anyone who asks. You're at the edge of the crowd trying to take a video but people are just neck-and-neck crowding with each other and it's impossible for you to see him. You can pan the camera around and see the rest of the mall fine, but the closer you get to The Rock the more people are in the way. That's what taking a picture of the center of our galaxy is like, and the dark stuff in this image is all the crap that's blocking our shot.

Looks like the intro to Resident Evil paused mid-frame. Cool pic either way.

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I hope so too.

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Now I just heard the Milky Way is actually the Androneda galaxy colliding with our galaxy, the Milky Way

Now I just heard the Milky Way is actually the Androneda galaxy colliding with our galaxy, the Milky Way

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I think the biggest variable people downplay is the extreme youth of the universe. The universe has not been able to harbor baryonic, carbon-based life for all that long since it requires at least the second generation of stars to develop. Somebody has to be first and it very well could be us.

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You were on to the right track; you just want to think about it in terms of what's happening at an atomic level. To get as close as possible to the actual physical diameter of a hydrogen atom, you'd want to imagine a situation where the hydrogen atoms were all physically in contact with each other. This doesn't happen in a gas, but it does happen (more or less) in a liquid.

The density of liquid hydrogen is going to vary based on external pressure, but let's start with sea level pressure just to give ourselves a benchmark. The density of liquid hydrogen is 70.85 g/L. I don't even bother doing the calculation with Avogadro's number here; I just asked Google "70.85 g/L = ? amu/nm^3" and it converted grams to atomic mass units and it converted liters to cubic nanometers just fine. The result? The density of liquid hydrogen is 42.67 amu/nm^2. We know that a single hydrogen molecule has a mass of 2 amu, so this suggests that a single hydrogen molecule in a liquid occupies a space of 0.047 cubic nanometers. Solving gives us a radius of 0.26 nanometers. So we can say confidently that a single diatomic hydrogen molecule MUST be small enough to fit within a sphere that has a diameter of 0.52 nanometers.

So how small does that make a single hydrogen atom? Well, you can look up the bond length of diatomic hydrogen and find that it is 74 picometers, or 0.074 nanometers. Covalent bond length is the distance between bonded nuclei, given intersecting electron clouds. So the diameter of a single hydrogen atom must be less than 0.45 nanometers. We're now well within an order of magnitude of the actual size.

Can we do better? Yes, we can, by looking once more at what's actually happening at an atomic level. Think about a ball pit: there's a lot of empty space between the actual individual balls. Being (essentially) spheres, hydrogen molecules don't pack into each other perfectly; they leave space in between each other. How tightly can you pack spheres together? This is a well-studied problem. In a perfectly hexagonal offset lattice, spheres can be packed with an average density (relative to the space between them) of π/3*2^0.5 or ~0.7405. That would be if the hydrogen molecules were arranged in a perfect crystalline structure. Unfortunately, hydrogen molecules are nonpolar so they don't have any intermolecular electromagnetic forces to align them that way; they will be packed randomly. This is called a random close pack and mathematicians have found that such irregular packings will produce a density of 0.64 or thereabouts.

What does this tell us? Well, if the density of liquid hydrogen is measured at 42.67 amu/nm^2, but the molecules are only packed to a volumetric density of 0.64, then 36% of that volume is going to be empty space. So the actual density of an individual hydrogen molecule is 66.7 amu/nm^2 or 0.03 cubic nanometers per molecule. This gives me a radius of 0.193 nanometers. Subtract the bond length and I get a diameter of 0.238 nanometers for a single hydrogen atom.

The actual size of an atom is known as the van der Waals radius. The van der Waals radius of a hydrogen atom is 1.09 angstroms or .109 nanometers. So the actual physical diameter of a hydrogen atom is 0.218 nanometers.

So our approach got us within 10% of the real number. Not bad!

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