Physically, what are bitcoins?

Physically, what are bitcoins?

...

Data. Thus electronic impulses.

just bits (but that's just a representation), bitcoins aren't real objects they're mathematical solutions to equations.

this undergrad thinks that maths is not real

Nothing, physically.

However bitcoins are "minted" by brute forcing a random sequence of data, that when hashed with the current block data, yields a hash with a certain number of zeros at the start of it. A hash function basically takes some kind of text as input and transforms it to some random garbeldy-gook as output, except it does so in a repeatable way that a particular input will always map to the same seemingly random output. Now because you can't predict what that seemingly random output will look like, miners have to add random bits of data to the block they're try to mint over and over again, trying to find a combination of the random data that produces the output they're looking for. This brute forcing takes a lot of computational resources, and the first person to find a piece of random data that makes the block hash to a string of text with enough leading zeros gets to mint that block (which they inserted their bitcoin address into while they were minting it) and keep the payout.

Bulletproof atoms.

Isn't it possible for someone to generate a keypair (public and private) that is already in use and has a balance on it?

My head hurts.

Physically, what is you bank account?