The PDF that Sidhartha shared previously is now available as a book for $15 USD:
https://www.amazon.com/gp/product/171810040X
The Hollow Earth: And the Special Earth Core Theory (S.E.C.T) Paperback – August 10, 2018
The Hollow Earth and the Special Earth Core Theory details an approach of thought which seeks to validate alternative physics of the electromagnetic and occult principles for the Earth.