Some scientist say the brain has a power of several petaflops, so if you use this, I guess the design of stockfish was way less efficient.
You can't really compare things to cpu years, it doesn't make sense. Power consumption would be a better metric I think.
A more fair comparison would be use as much computation needed for training but for runtime, use equal wattage hardware.
E.g 20W of cpu in mobile phone running stockfish to 20W of GPU in nvidia TX2 running AlphaZero to 20W human brain.
Are you using some kind of conversion factor from TPUs to CPUs? If so, what is it? And is it valid to do that?
You could convert the amount of time it took to render an hour's worth of gameplay from 1 GPU-hour to 50 CPU-days (or whatever), but is that really meaningful?
Yes, it needs a boatload of very simple compute (8 bit operations), the kind that CPUs are not even close to ideal at providing economically.
In that time I figure they used the equivalent of about 1000 cpu-years. Imagine the things we'll be able to achieve as we can do more and more computation in less and less time.