Is it possible that protecting superposition and entanglement will be a fundamental problem for scaling quantum computing? I could imagine that beyond some point, each time you add an extra qubit the cost of shielding the computation goes up by a multiplicative factor.

Say the observable universe has something like 10^100 subatomic particles total. I believe that by current estimates, this is an upper bound.

A quantum computer with 350 qubits would have 2^350 states, or more states than the total number of subatomic particles in the universe. A single "NOT" operation on one of those qubits would, in constant time, change half of those states. I.e., the quantum computer would do way more work than there are particles in the observable universe. For every single one of its operations.

I just don't see how the universe will let nerds on some tiny little out-of-the-way planet get away with that.

QC demonstrably works for small numbers of qubits. I just wonder if it will ever scale to the point that large problems can be tackled with QC in a cost-effective manner.