My Encounters with A. Einstein

I met Einstein for the first time twenty-nine years ago. He had come to Brussels to attend the Solvay Congress of 1927. Walking through the avenues of the Leopold park, he spoke to me about an article regarding the expansion of the universe, passed almost unnoticed, which I had written the previous year and a friend had him read. After some favorable technical observations, he concluded by saying that from the point of view of physics it seemed to him absolutely abominable.

In an attempt to prolong the conversation, Auguste Piccard, who accompanied him, invited me to get into the taxi with Einstein, who needed to pay a visit to his laboratory at the University of Brussels. In the taxi I spoke about the recessional velocity of nebulae [we now know galaxies, ndt] and I had the impression that Einstein was not very informed about astronomical phenomena. At the university, the meeting took place completely in German and to my great surprise I heard myself presented as “Herr Lemaître”; I admired the interferometer, just returned from an ascent in a hot-air balloon, and I signed, after Einstein, the university’s gold book.

I saw Einstein again four years later in California at the university in Pasadena. Speaking to me about the doubts that arose in his mind about the inevitability, under certain conditions, of the zeroing of the radius of the universe, Einstein proposed a very simplified model of the universe to me, for which I had not the slightest difficulty to calculate the tensor energy. This occasion taught me a lot about his way of thinking and his way to truncate indecision by making a decision based on a good selection of examples. He concluded that the loophole he had thought of did not work.

I had many conversations with Einstein in that period, generally during walks, and almost always, then as afterwards, on the theme of the cosmological constant “lambda”, that he had cleverly introduced in his equations, but with which he was never satisfied and was trying to retract.

Some journalists had understood that we spoke about “little lambda”, which they enjoyed transforming into the “little lamb” that, so to speak, always followed us in our wanderings.

Speaking one day of this unitary theory that he incessantly pursued and for which he felt, at the time, a passing discouragement, he told me that it was a difficult problem whose chances of success were minimal and therefore it was better that someone who did not need to think further about making a career worked on it.

When I spoke to him about my ideas on the origin of cosmic rays, he reacted vivaciously: “Have you spoken about it to Millikan?”, but when I spoke to him about the primeval atom, he stopped me: “No, that no, that suggests creation too much.”

The following year, I met Einstein again in Belgium and took part, together with De Donder and Rosenfeld, in the cycle of conferences that he held in Brussels. I paid him a brief visit in the city of Le Coq. He loved to speak about his activities in that period and said: “I discovered sur le Coq [the rooster, in French, ndt]”.

At that time I still smoked and one day I offered him a cigarette; he refused it, but then, changing his mind, he took the cigarette and began to cut it lengthwise and put the tobacco into his pipe. He explained to me that he needed to be wary of the tobacco and whatever else he could smoke every day; I gave him the opportunity to commit a small infraction to his regime.

Naturally he didn’t miss recommencing on other occasions.

It is to this time that the anecdote of the quadruped dates back. In one of his presentations, Einstein, whose French was more than acceptable, was embarrassed in translating the German word Vierbein, extension to four of the usual word, trihedron, dreibein. As it was impossible to say ‘tetrahedron’, professor De Donder, one of the pioneers of the theory of relativity, suggested to him without hesitation the word ‘quadruped’, which amused us very much afterwards. Later, as Einstein spoke English, I was able to hear him speak about ‘quadruped’, not without causing some surprise.

Finally, in 1935, I visited Einstein again, for the last time, at Princeton and he told me, “Your mobility is remarkable.” I was too relativistic to not draw some conclusions on that about Einstein himself, but I refrained from any comment.

In the same period, the occasion presented itself to me to organize a meeting between a few professors of the Institute, to which Einstein came to present the research he was conducting at that time, which he had not yet spoken about. The theory was rather bizarre and was received with considerable coldness. I had the impression of senility being rumored.

In reality, it was one of the most interesting events. Einstein had embarked on a dead-end road following a communication received by letter from his friend Silberstein, a well-known scholar of relativity. He wrote him that he had found a solution to the equations on gravitation, where two point singularities harmonized themselves with each other. According to the approach of Einstein, such a situation radically excluded the most natural way of conducting his research and led him onto imaginative roads.

A short time later, he let Silberstein publish his solution and it was then that one could recognize the claw of the old lion in the masterly way in which he dismantled the subtle paradox of Silberstein and demonstrated a line of immobile singularities, which played the role of a rod linking the two masses, preventing them in a completely natural way from precipitating towards each other.

One day discussing the Dirac equation, which is the origin of semiconductors and spinors, he told me, “The equation of Dirac – it is an authentic miracle.” Naturally I resumed the discussion concerning the cosmological constant and for a moment I had the impression of being able to stump him: “Still,” he told me, “if you manage to demonstrate that the cosmological constant is not zero, it would be important.”

I also managed to make him clarify that in the article he had written in 1932, in collaboration with De Sitter and in which he spoke about a Euclidean space, and therefore infinite, he had in view a very large radius of space but not really infinite. This makes it possible to distinguish Einstein from those who, like Milne, have found it possible to reconcile a homogenous cosmology with an infinite space. Thanks to the cosmological constant, the argument publically closed with some contributions to the fine book Albert Einstein philosopher and scientist, which was presented to him in 1949 on the occasion of his seventieth birthday and in which he had agreed to raise and respond to criticisms.

No more than others, on subjects much more dear to his heart (I refer to Born, Pauli, Heitler, Bohr), was I able to convince him, or, I must admit, to grasp his thinking in a more precise fashion.

That book is an important document for the history of science. Maybe it shows that, even in a scientist who maintained prodigious activity until the end, old age still altered a bit the wonderful balance of his great period. Perhaps some faculties age faster than others, perhaps the critical spirit survived in Einstein, even if exacerbated, when the creative genius began to fade? It became difficult for him to follow exactly, to the end, the narrow path passing the same distance from both pitfalls lurking in every type of scientific research: the shortsighted positivism that cannot go beyond experience and the dreamy idealism that loses touch with it.

Maybe the pitfall of Einstein’s old age was the tirelessly pursued dream of a perfect theory, which led him to discard anything that did not fit with the aesthetic ideal he had conceived.

The cosmological constant can be compared to those iron rods that escape in all directions of a concrete construction. They are undoubtedly superfluous and inadmissible in a completed construction, but they are indispensable if the construction must later attach to others and become an element of a broader synthesis.