Since I have introduced this term I had always a bad conscience. But at that time I could see no other possibility to deal with the fact of the existence of a finite mean density of matter. I found it very ugly indeed that the field law of gravitation should be composed of two logically independent terms which are connected by addition. About the justification of such feelings concerning logical simplicity it is difficult to argue [emphasis added]. I cannot help to feel it strongly and I am unable to believe that such an ugly thing should be realized in nature.

In other words, the original motivation no longer existed, and Einstein felt that aesthetic simplicity was violated, so he did not believe that nature required a cosmological constant. Did he think then that this was his “biggest blunder”? Unlikely. Yes, he was uncomfortable with the concept, saying as early as 1919 that it was “gravely detrimental to the formal beauty of the theory.” But general relativity definitely allowed for the introduction of the cosmological term, without violating any of the fundamental principles on which the theory had been founded. In this sense, Einstein knew that this was not a blunder at all even before the more recent discoveries concerning the cosmological constant. The experience gained in theoretical physics since Einstein’s time has shown that any term allowed by the basic principles is likely to be necessary. Reductionism applies to the fundamentals, not to the specific form of the equations. The laws of physics thus resemble the rules in the Arthurian novel The Once and Future King by the English author T. H. White: “Everything that is not forbidden is compulsory.”

To conclude, it is virtually impossible to prove beyond any doubt that someone did not say something. Still, my best guess, based on the entire body of evidence, is that while Einstein may have had a “bad conscience” about the introduction of the cosmological constant, especially since he missed the chance to predict the cosmic expansion, he never actually called it “the biggest blunder” that he “had ever made.” That part was, in my humble opinion, almost certainly Gamow’s own hyperbole. Amusingly, in an article entitled “Einstein’s Greatest Blunder,” University of Manchester astronomer J. P. Leahy commented, “It is just as well that Einstein made his remark to Gamow, otherwise Gamow would have been severely tempted to make it up.” My conclusion is that Gamow probably did make it up!

You may wonder why this particular quip by Gamow has become one of the most memorable pieces of physics folklore. The answer, I believe, is threefold. First, people in general, and the media in particular, love superlatives. News in science is always more appealing when it involves “the fastest,” “the farthest,” “the biggest,” or “the first.” Einstein, being human, erred many times, but none of his other mistakes created such headlines as his so-called biggest one. Second, Einstein has become the embodiment of genius—the man who purely by his intellectual powers discovered the workings of the universe. He was the scientist who demonstrated that pure mathematics could discover what it creates and also create what it discovers. It has been said about the ancient Greeks that they found the universe a mystery and left it a polis (city-state). From the perspective of modern cosmology, this aphorism fits Einstein even better. (Figure 36 shows my favorite picture of Einstein.) The fact that even such a scientific powerhouse is fallible is both fascinating and a wonderful lesson in humility—and in how science truly progresses. Even the most impressive minds are not flawless; they merely pave the way for the next level of understanding. The third reason for the popularity of the cosmological constant, sometimes called the most famous fudge factor in the history of science, is that it has proven to be the ultimate diehard. Like drug dealer Pablo Escobar and Russian mystic Grigory Rasputin, the cosmological constant has been incredibly hard to kill, even though Einstein denounced it eighty years ago. What’s more, not only has this ostensible “blunder” refused to die, but in the past decade it has become the very center of attention. What was it that gave the cosmological constant its nine lives, and why was it thrown into the limelight again?