Ernst Mach (February 18, 1838 – February 19, 1916) was an Austrian physicist and philosopher, noted for his contributions to physics such as the Mach number and the study of shock waves. As a philosopher of science, he was a major influence on logical positivism and through his criticism of Newton, a forerunner of Einstein's relativity.
1.) R. S. Cohen; Raymond J. Seeger (1975). Ernst Mach, Physicist and Philosopher. Springer. p. 158. ISBN 978-90-277-0016-2. "And Mach, in personal conviction, was a socialist and an atheist."
2.) Gregory Scott Charak (2007). Between Soul and Precision: Ernst Mach's Biological Empiricism and the Social Democratic Philosophy of Science. ProQuest. p. 94. ISBN 9780549129738. "Both make explicit claims against the pseudo-problems generated by materialism, and although Mach the atheist would have no gripe with “irreligion” per se, as a pacifist and a socialist he was indeed an ardent proponent of “peace."
3.) Helge Kragh (2004). Matter And Spirit In The Universe: Scientific And Religious Preludes To Modern Cosmology. OECD Publishing. p. 55. ISBN 9781860944697. "The Austrian positivist physicist and philosopher Ernst Mach was nominally a Catholic, but in reality he was an atheist and strongly opposed to Christian doctrines."