What would happen if every atom on earth was to simultaneously double in size?

The main question is unanswerable as it couldn't happen without fundamentally changing physics in some way. However, the other one is a lot more interesting.

On a large scale, one in ten atoms vanishing would decrease both the density and mass of most objects by 10%. This would also decrease their gravity by 10%, resulting in all orbits becoming significantly more (or less) eccentric. I imagine the changes would be enough to destabilize some solar systems, potentially causing planets to perturb each other's orbits until they collide or end up being ejected from the system.

The change in density also means that gravitationally bound objects that are held up by internal pressure (like planets and stars) would collapse slightly as their internals are re-compressed to their original density. The collapse would release a lot of energy, heating up planets significantly and (just guessing here) maybe causing a burst of fusion in stars as they're temporarily compressed past their equilibrium point.

All of that is pretty bad news for life on Earth, but the worst is what happens chemically. Some molecules are just going to become different molecules when one or more of their atoms disappears. Take water, for example; a water molecule has an 8.1% chance to become a hydrogen molecule, an 8.1% chance to become a (highly reactive) hydroxide ion, and a 0.9% chance to become a (highly reactive) single oxygen atom. 18% of nitrogen and oxygen molecules in the atmosphere would also become single atoms and promptly react violently. These molecular changes would instantly kill all life on Earth (and anywhere else). There's simply no possible way for an organism to survive so many reactive molecules being introduced throughout itself. Not to mention that all DNA would be irreparably damaged from the random deletions too.

I'm sure there are some other effects that I haven't thought of, but those are definitely the most noticeable ones.

That would result in an enormous outward pressure that would squash everything while heating it to extreme temperatures, resulting in near light speed expansion, and hurl almost all of the earth into space at extreme velocity. Instantly killing all life.

I like to pretend OP is God who is both very bored and still too lazy to do his own research before flipping a catastrophic switch, so he is outsourcing this research to humans.

Oh jeez, like a bunch of stuff, I bet.

Please do not adjust the scale in the devcommands. I'm not saying I'm having a great time here, but this is where I'm having a time.

Pretty sure you need to touch the fine structure constant to do so. And believe me, touching fundamental constant has a lot of side effects, for example semi conductors properties would change

It's difficult to say, because all the atoms suddenly doing that would mean that some basic laws of physics had changed, and since it isn't specified exactly how they've changed to produce this strange result it's hard to predict what might happen next.

But it seems a reasonably safe assumption that there would be a large explosion and then no more Earth.

We all die

Big brain time.

Big everything else time, too.

According to Internet, a big mess... (I asked Copilot...)

If atoms were to double in size, it would have profound consequences on the physical world as we know it. The size of an atom is determined by the space its electrons occupy around the nucleus. Doubling the size of atoms would mean that the electrons are further away from the nucleus, which would weaken the electromagnetic forces that hold atoms together.**

Here are some potential effects:

Chemical Bonding: The formation of chemical bonds could be significantly affected. Atoms might not be able to form multiple bonds, such as double or triple bonds, because the overlap of p orbitals would be less likely as they get farther apart.

Material Properties: The properties of materials would change drastically. For instance, metals might lose their conductivity because the delocalized electrons that allow for the flow of electricity would be too spread out. Biological Structures: The structures of proteins and DNA would be altered, potentially disrupting all biological processes. Enzymes might not function properly, and the basic mechanisms of life could fail. Physical Laws: The fundamental constants and laws that govern physical interactions would need to be redefined to accommodate the new atomic sizes. It’s important to note that this is a hypothetical scenario and not currently possible according to our understanding of physics. The size of atoms is a fundamental aspect of quantum mechanics and chemistry, and any change in atomic size would mean a change in the fundamental laws of nature.

I think the most important part of either question is that everyone would die.

The one in every 10 atoms, even randomly distributed, would kill all active enzymes in an organism, I would hypothesize. And break chromosomes and RNAs into small pieces. No more enzymes could be produced and therefore the nucleic acid couldn't be repaired.

I don't know if it would be enough to lyse cells immediately.

Are we talking about electron distance from nucleus doubling, or protons, neutrons and electrons doubling in size too?

Mercury would be solid at room temperature

Not a scientist, but my first assumption would be that everything on earth, but also earth itself will double in size, knock ourself around our nice orbit around the sun and kill everyone either flashly or coldly.

Ignoring that problem, or applying the effect to the entire universe, probably not much would happen.