[...] when a learned man is presented with any statement in an ancient author, the one question he never asks is whether it is true. He asks who influenced the ancient writer, and how far the statement is consistent with what he said in other books, and what phase in the writer's development, or in the general history of thought, it illustrates, and how it affected other writers.Is this how we perceive the writings of ancient scientists? In their historical context? Were they not striving to attain an absolute truth about the universe, or only a truth bound-up in the milieu of their era and Kuhnian paradigms? The latter would be true if one adopted the philosophy of evolutionism, viz., as Sartre said in his Existentialism is a Humanism lecture, "that man first of all exists, encounters himself, surges up in the world—and defines himself afterwards," irrespective of a guiding authority for judging truth. This conception of man is untrue since we do not invent truth and arbitrarily assign it a meaning ourselves; an objective, unchanging Reality exists outside ourselves in which is unified all truth into an infinitely simple Unity. This Reality is God, and only God gives us our meaning and dignity.
—C. S. Lewis, The Screwtape Letters
Four years after Sartre's lecture, Pope Pius XII wrote Humani Generis saying this about existentialism and how it leads to "false science":
Such fictitious tenets of evolution which repudiate all that is absolute, firm and immutable, have paved the way for the new erroneous philosophy which, rivaling idealism, immanentism and pragmatism, has assumed the name of existentialism, since it concerns itself only with existence of individual things and neglects all consideration of their immutable essences. [...] [The] Teaching Authority [of the Church] is represented by them [e.g., the existentialists] as a hindrance to progress and an obstacle in the way of science. [...] [And] [t]hese and like errors, it is clear, have crept in among certain of Our sons who are deceived by imprudent zeal for souls or by false science.So, existentialism "concerns itself only with existence of individual things and neglects all consideration of their immutable essences." What scientists would reject, e.g., that the fundamental nature of proton seconds after the Big Bang is entirely different than it is now? Sure, physical constants could change over time, but unless there is some immutable kernel—such as the rational soul is for a human—you cannot have a coherent understanding of nature thus neither a coherent science. A proton a thousand years ago could be what we now call a unicorn.
Maintaining Catholic values amidst a culture so opposed to these values is the biggest challenge today facing not only scientists but everyone. Myriads of conflicting ideologies inundate us, and existentialists see the Catholic faith as just one of many seemingly equally true belief systems that man invented. Yet, man did not invent the Catholic Church, the most trustworthy, true, and immutable religion. God Himself, the immutable Word Incarnate, founded it out of love for us. Thus, the Catholic faith is a steady rock in the torrential sea of ideologies on which we can find hope, deepen our faith, and ultimately be charitable to both neighbor and God.
Those who seek a "Grand Unified Theory" of the universe ultimately seek to know God, who "became all things to all men" (1 Cor. 9:22) to "give testimony to the truth" (Jn. 18:37) so we can "have the unction from the Holy One, and know all things." (1 Jn. 2:20).