As it turns out, the information density of a region of space is bounded by it's surface area, not its volume. If you try exceeding that bound, you collapse int

As it turns out, the information density of a region of space is bounded by it's surface area, not its volume. If you try exceeding that bound, you collapse into a black hole. This observation led to the idea of the Holographic principle in physics. Having said that, this is one of those areas that depends on a full understanding of quantum gravity, which we do not yet have, so I wouldn't call it settled science. In practical terms, if your argument ends with "otherwise, your computer would collapse into a black hole", you are considering technology far beyond anything we are currently capable of, so n^3 information density is still on the table for everyone except theoretical physicists.