[SapphireSun]

I talked to a dude who made an interesting point about quantum computers. Quantum computations rely on particles behaving in a "quantum manner" in order for Shor's algorithm to reduce the big O complexity in factoring integers. However, at a certain size, you won't be able to entangle all the particles because there will be so many they'll start to behave like a macro material.

If true, this implies that quantum methods will only work up to a certain key size. Above that, you could run quantum computers in parallel, but now you're scaling your efficiency linearly instead of super-linearly, so hopefully having a huge (maybe impractically huge?) key size would be a sufficient defence. I understand that RSA gets substantially slower with larger keys though, so maybe it wouldn't be practical even if the key fits easily in memory.

I'm not an expert in physics or security, but I'd love for a physicist or cryptographer to comment as I thought that was a really intriguing argument.