'If finally we look back at that idea of [Ernst] Mach [1838-1916], we shall realize that it comes as near to the orthodox dogma of the Upanishads as it could possibly do without stating it expressis verbis . The external world and consciousness are one and the same thing.'
Source, in full
Schrödinger, Erwin. My View of the World. Cambridge: Cambridge UniversityPress, 1964. quoted from Malhotra, R., & Infinity Foundation (Princeton, N.J.). (2018). Being different: An Indian challenge to western universalism.