Einstein's Third Paradise, an article by Prof. Gerald Holton (Physics, Harvard), tells a little story of the influence that Spinoza had had on Einstein's methods and attitudes throughout his life and work. One needs to read the entire article to get a better picture, but here are the more relevant excerpts:
On his belief in God.
In 1929, Boston's Cardinal O'Connell branded Einstein's theory of relativity as "befogged speculation producing universal doubt about God and His Creation," and as implying "the ghastly apparition of atheism." In alarm, New York's Rabbi Herbert S. Goldstein asked Einstein by telegram: "Do you believe in God? Stop. Answer paid 50 words." In his response, for which Einstein needed but twenty-five (German) words, he stated his beliefs succinctly: "I believe in Spinoza's God, Who reveals Himself in the lawful harmony of the world, not in a God Who concerns Himself with the fate and the doings of mankind." The rabbi cited this as evidence that Einstein was not an atheist, and further declared that "Einstein's theory, if carried to its logical conclusion, would bring to mankind a scientific formula for monotheism." Einstein wisely remained silent on that point.
On the evolution of religion.
In the evolution of religion, he remarked, there were three developmental stages. At the first, "with primitive man it is above all fear that evokes religious notions. This 'religion of fear' . . . is in an important degree stabilized by the formation of a special priestly caste" that colludes with secular authority to take advantage of it for its own interest. The next step – "admirably illustrated in the Jewish scriptures" – was a moral religion embodying the ethical imperative, "a development [that] continued in the New Testament." Yet it had a fatal flaw: "the anthropomorphic character of the concept of God," easy to grasp by "underdeveloped minds" of the masses while freeing them of responsibility. This flaw disappears at Einstein's third, mature stage of religion, to which he believed mankind is now reaching and which the great spirits (he names Democritus, St. Francis of Assisi, and Spinoza) had already attained – namely, the "cosmic religious feeling" that sheds all anthropomorphic elements. ...
On the source of his devotion to his work.
In another of his essays on religion, Einstein points to a plausible source for his specific formulations: "Those individuals to whom we owe the great creative achievements of science were all of them imbued with a truly religious conviction that this universe of ours is something perfect, and susceptible through the rational striving for knowledge. If this conviction had not been a strongly emotional one, and if those searching for knowledge had not been inspired by Spinoza's amor dei intellectualis, they would hardly have been capable of that untiring devotion which alone enables man to attain his greatest achievements."
On the importance of Spinoza to him.
He had written an introduction to a biography of Spinoza (by his son-in-law, Rudolf Kayser, 1946); he had contributed to the Spinoza Dictionary (1951); he had referred to Spinoza in many of his letters; and he even had composed a poem in Spinoza's honor. He admired Spinoza for his independence of mind, his deterministic philosophical outlook, his skepticism about organized religion and orthodoxy... In other pages of Ethics, Einstein could read Spinoza's opposition to the idea of cosmic purpose, and that he favored the primacy of the law of cause and effect – an all-pervasive determinism that governs nature and life – rather than "playing at dice," in Einstein's famous remark. And as if he were merely paraphrasing Spinoza, Einstein wrote in 1929 that the perception in the universe of "profound reason and beauty constitute true religiosity; in this sense, and in this sense alone, I am a deeply religious man."
Much has been written about the response of Einstein's contemporaries to his Spinozistic cosmic religion. For example, the physicist Arnold Sommerfeld recorded in Schilpp's volume that he often felt "that Einstein stands in a particularly intimate relation to the God of Spinoza." But what finally most interests us here is to what degree Einstein, having reached his Third Paradise, in which his yearnings for science and religion are joined, may even have found in his own research in physics fruitful ideas emerging from that union. In fact there are at least some tantalizing parallels between passages in Spinoza's Ethics and Einstein's publications in cosmology – parallels that the physicist and philosopher Max Jammer, in his book Einstein and Religion (1999), considers as amounting to intimate connections. For example, in Part I of Ethics ("Concerning God"), Proposition 29 begins: "In nature there is nothing contingent, but all things are determined from the necessity of the divine nature to exist and act in a certain manner." Here is at least a discernible overlap with Einstein's tenacious devotion to determinism and strict causality at the fundamental level, despite all the proofs from quantum mechanics of the reign of probabilism, at least in the subatomic realm.
There are other such parallels throughout. But what is considered by some as the most telling relationship between Spinoza's Propositions and Einstein's physics comes from passages such as Corollary 2 of Proposition 20: "It follows that God is immutable or, which is the same thing, all His attributes are immutable." In a letter of September 3, 1915, to Else (his cousin and later his wife), Einstein, having read Spinoza's Ethics again, wrote, "I think the Ethics will have a permanent effect on me."
I wonder what Einstein could have told us about his thoughts on Spinoza's "face of the whole universe"?