It will not happen. It is already known what happens when both sides play without error,
Quantum computers will not change that.
It is not at all sure that quantum computers will ever be useful for chess.
But even if in the future they are better than today's best chess engines that will not change the fundamental truth about chess.
The truth is the truth regardless of who knows it or who does not know it.
#6854
The factor 10^20 must come from quantum computing.
60 years from now computers with transistors will look just as obsolete as the 1945 ENIAC computer with vacuum tubes looks now.
There is likely to be a paradigm shift. Silicon-based semiconductor integrated circuits have had a good run.