[subroutine]

I'm not sure they would be able to infer the board has 64 squares. They can't see the board, and can only see the locations of the starting pieces and location of the first move. The center of the board could be anything - 300 hexagons, a spin-wheel, series of mouse traps, etc.

Here's my interpretation of what they see pre- and post- opening move...

PRE: https://i.ibb.co/s6WnPNV/Chess.png

POST: https://i.ibb.co/7pg7GHW/Chess1.png

[tiborsaas]

This is a fun one, thanks for the illustration.

If you analyse 5000 board configurations you can deduce with a high certainty that there are 64 fields the pieces can be on.

The pressing question is then why can some pieces move only diagonally or only in one direction or any.

In the case of chess, going after the why question is pointless, but obviously that wouldn't satisfy any scientist: It works because someone decided that it should work like this.

Could it work with different rules? The alien scientist then probably opt for a positive answer calling for a multiverse of chess rules :)

[subroutine]

In keeping with the original authors description, the aliens can only see the opening move. I'm confused - how could they determine there are 64 fields (nb: I only know the very basics of chess)?

If they could view entire matches, it seems a trivial task to acquire a complete understanding of the underlying game, no?

[tiborsaas]

Oh sorry, I missed that part. But according to the rules of chess a random valid opening should cover all fields on the table so at least you'd know the layout. Pawns can move one or two fields.

Knowing only the first move would limit understanding heavily, that's true.