As I understand it, the surface of the earth is commonly bombarded by muons (and lots of them).

Surface muons are used for imaging the Egyptian pyramids, among other things:

https://www.nature.com/articles/d41586-018-05254-2

Neutrons are much more dangerous, as they will readily be absorbed by atomic nuclei when moving slowly enough, and can form unstable isotopes that might decay by alpha/beta/gamma radiation.

Neutron radiation must be at much lower levels than surface muon bombardment.

Yes - phosphenes can be caused by cosmic rays and other sufficiently energetic sources. Astronauts see such sparkles when they're not shielded. And such cosmic ray interactions are a mutagenic factor in changes to DNA, resulting in cancer and evolution.

A neuron in the brain is subject to orders of magnitude more noise, from chaotic factors like blood oxygenation, signaling molecules, aging...

For our actual conscious experience though, there's some evidence that we're very noise tolerant. I can't find the paper now, but one recently just came out showing that at certain parts of the brain you won't even notice an electric shock.

>For our actual conscious experience though, there's some evidence that we're very noise tolerant.

I have a disorder that's very relevant to this, it's called visual snow syndrome. It's poorly understood but the current theory is that the brain has a fair amount of internal noise which is suppressed by a filtering mechanism but in some people this filtering mechanism fails, making the brain's internal noise becomes consciously perceptible. It looks like a badly tuned analogue TV for the most part with lots of static (hence the disorder's name), although other things like haloes around objects and geometric patterns appearing in textures like bricks are common too. Less fun is the permanent headache, sensory overload issues, and often a whole host of other neurological issues.

It's one of those unfortunate cases where medical professionals palmed it off for decades as patients making it up for attention. I was personally told as a teenager to "try and imagine it away" by a neurologist which of course was utterly useless advice, and I was also given antidepressants at one point which made it infinitely worse, wouldn't wish that experience on my worst enemy. Fortunately I ended up in the care of a neurologist who finally recognised what it was and gave me a formal diagnosis after doing some scans to make sure it wasn't a brain tumour or something equally unpleasant. It turns out that although nothing shows up on a normal MRI scan, if you do an fMRI scan of brains like mine you can actually see the differences that cause the brain's noise to leak into your consciousness. Weird stuff.

>geometric patterns appearing in textures

Is it similar to the kinds of visuals a person using psychedelics might experience?

Yes, in fact visual snow has quite an overlap in symptoms with HPPD experienced by some chronic users of psychedelics! It was even sometimes misdiagnosed as HPPD in the past, although that theory was discounted as the vast majority of visual snow patients don't have a history of psychedelic use (I was far too much of a nerd to be dropping acid aged 14/15 when I contracted the disorder!). For me the appearance of these visuals is triggered by closely repeating patterns such as bricks, tiles, striped or chequered shirts, chessboards, that sort of thing. It makes reading a bit difficult sometimes too, I really struggle with dense typography like newsprint for example so I usually read on a Kindle with the line spacing and font size set quite high.

I definitely think psychedelics have a role to play in understanding these dysfunctions of the visual system, although unfortunately my country (the UK) has a very unenlightened view when it comes to banning things and firing chief scientific advisors when they point out that there's no real scientific justification for prohibitionism. Vernon Dursley is apparently the target voter for both major parties!

Probably. Given that nanometer scale CMOS is and thermal neutrons trigger the primary failure mechanism, BTI.

The brain operates with amazing error rates and low bandwidth because it can "refresh reality data" from expected results coded over a lifetime.

Most visual illusions, logical fallacy, etc. come from the heuristic of this process. We are NOT that smart. And part of the trick is we can convince ourselves that we nominally are despite that fact!

Visit some museeum, exhibition, laboratory, hack space with a https://en.wikipedia.org/wiki/Cloud_chamber and make up your own mind? :-)