By the same argument, it's mathematics because John Conway was a mathematician, and it's physics because Ulam and Von Neumann were physicists.
https://fr.wikipedia.org/wiki/Turtles_All_the_Way_Down
https://en.wikipedia.org/wiki/Doctor_of_Philosophy
https://en.wikipedia.org/wiki/Wikipedia:Getting_to_Philosoph...
https://xefer.com/2011/05/wikipedia
https://snap.stanford.edu/class/cs224w-2013/projects2013/cs2...