Smyslov_Fan wrote on 08/23/07 at 12:49:45:
MNb, I hope you'll be able to shed some light on the possibilities, but the papers I've read from mathematicians is that we can only guess at the magnitude of the possible moves and positions. Is that your understanding too?
Yes. Alas I don't know what "grondtal" is in English and it is not in my dictionary. I hope you still will follow my argument.
The simple approach is just to estimate. 20 moves per ply is probably too high; 15 may be too low. Then we also have to estimate the average length of the game until mate, say 60 moves (frankly I am not sure at all). Then you get 15^120. I suspect that this estimation is too low.
The uncertainty because of the different stages might not be that big. The rook and the queen get a lot of more freedom in the endgame and this may compensate for the lower number of pieces. Moreover we can correct with a random effect survey. The formula gets a little more complicated, but will not change essentially. Let us say, that the three stages all last 20 moves. Then you get a^40 * b^40 * c^40, simplified to (a*b*c)^40. A, b and c are the average amount of options in each stage per ply.
The effect of transpositions is far more difficult to incorporate in my opinion.
@Willempie: the mass of the earth is 6*10^24 kg. The mass of a watermolecule (consisting of 3 atoms) is about 30*10^-27. Dividing gives about 10^50 atoms. It may be three times more, but that does not really matter; such is the nature of exponential numbers.
This is probably too high, as the earth also consists of heavier atoms like iron.
A better approach though is to start with the model of the expanding/contracting universe mentioned by Udav and Markovich. This depends on the total mass (which causes gravity according to Newton). Alas there is a big uncertainty here (see the subject of dark mass). Also we must assume, that 80% (might be somewhat more or less) of the mass consists of Hydrogenatoms and 20% (idem) of Helium. With the same calculation as described above we can estimate the number of atoms in the universe.
Note: don't call physics and mathematics "exact" sciences ever again! It is so often just clever guesswork.