Einstein (on love)
Einstein's 1933 letter question him as to whether being upside down was what caused people to fall in love, to which Einstein jotted the personal note: "Gravitation cannot be held responsible for people falling in love. [1] Right: An art.com picture frame of Einstein's famous 1933 personal scratch paper note about love and gravity. [3]
In theories of love, Einstein on love refers German-born physicist Albert Einstein’s jotted and or verbally stated views on the nature of love, falling in love, and first love, and or separation or divorce, one of which being his 1920s puzzled statement: “how on earth are you ever going to explain in terms of chemistry and physics so important a biological phenomenon as first love?”, the second being his 1933 personal note jotting “gravitation cannot be held responsible for people falling in love.”

Morgan incident
In the late 1920s at the California Institute of Technology, as recorded by Henry Borsook (1956), physical chemist Edwin Cohn asked American geneticist Thomas Morgan (1866-1945) what is research plans were? Morgan answer was: “I am not doing any genetics. I am bored with genetics. But I am going out to Cal Tech where I hope it will be possible to bring physics and chemistry to bear on biology.” Shortly after Morgan arrived at Cal Tech, Einstein visited the laboratory and posed almost the same question. Morgan answered similarly as before. In response, Einstein shook his head and said: [1]

“No, this trick won’t work. The same trick does not work twice. How on earth are you ever going to explain in terms of chemistry and physics so important a biological phenomenon as first love?”

The end of this statement has gone on to become a popular poster quote, in recent years, such as shown above.

Standing on their heads letter
During a visit to England in 1933, after having left Germany for good and just before going to the United States to take up his position at the Institute for Advanced Study in Princeton, N.J., Einstein received a letter from a correspondent described, by Einstein’s archives editors Helen Dukas and Banesh Hoffmann, as someone “whose knowledge of physics could hardly be sound”. The correspondent said that according to his understanding, the world moves so fast that it seems to be stationary. He went on to say, in all seriousness, that because of gravity a person on the spherical earth is sometimes upright, sometimes standing on his head, sometimes sticking out at right angles to the earth, and sometimes, as he put it, “at left angles”. He then asked if perhaps it was while upside down, standing on their heads, that people fell in love and did other foolish things? So far as is known, Einstein did not answer the man, but on it, in German, he scribbled the following words: [1]

“Falling in love is not the most stupid thing that people do—but gravitation cannot be held responsible for it.”

Females dorming together
A depiction of the McClintock effect: that females who react together or dorm in the same housing, eventually end up having synchronized menstrual cycles—and likewise synchronized mate selection windows, wherein the activation second of “falling in love”, possibly at first sight, becomes opportune.
In respect to gravitation and love, Einstein seems to have been off in logic a bit. To cite a simple disproof example, it is well known that female sexual heat and ovulation, for instance, is mediated by the lunar cycle: human females ovulate once per month in cycles; moreover, females who dorm together "cycle together", a phenomenon called the McClintock effect, named after American researcher Martha McClintock, who first described it in 1971) which is a gravitational phenomenon. In general, however, Einstein knew that human movement was controlled by "forces" an opinion he stated in 1929:

“Everything is determined … by forces over which we have no control. It is determined for the insect as well as the star. Human beings, vegetables, or cosmic dust—we all dance to a mysterious tune, intoned in the distance by an invisible piper.”

Commentary
What is strangely curious in discerning the above two anecdotes in unison is that it seems Einstein was toying around with, possibly, some unpublished, undocumented, or unspoken of ideas or thoughts or confusions about the nature of love, possibly that he grappling with or thought about in passing amusement. The strange part about this is that Einstein’s biggest intellectual mentor was Goethe: he kept a bust of Goethe in his study, and Goethe’s collected works, in a 52-volume set, took up the biggest portion of Einstein’s personal library. Therefore putting two and two together, it would seem logical that Einstein read Goethe’s self-defined best book: Die Wahlverwandtschaften (The Elective Affinities) or at least was aware of the concept of “wahlverwandtschaften”, the German-version of the “chemistry of love”, albeit described though a more complex theory taking into account interpersonal choices or elections being guided by forces “external to the system” as Goethe put it (1796).

It remains to be tracked down if Einstein read or was aware of Goethe’s Die Wahlverwandtschaften. If so, it would seem likely that Einstein, who published his first 30 papers in thermodynamics, would have known about German physicist Hermann Helmholtz’s 1882 paper “On the Thermodynamics of Chemical Processes” which proved, for the first time, that “affinities”, human, chemical or otherwise, are quantified by free energy change. Hence, had Einstein been able to put two and two together, he would have likely said to Morgan:

“No, you can’t trick me. The same trick does not work twice. To explain, in terms of chemistry and physics, so important a biological phenomenon as first love, you need to turn the discussion towards free energy [see: Note to chapter 6].”

He, oddly, did not say this. The reason he did not say this may be attributed to a combination of “not seeing the ships in the harbor” + “not seeing the forest amid the trees”, in the sense that his mind was solely focused on the thought experiment of attempting to run alongside a beam (tree) that he may have not seen the big picture, which amounts to connecting the different trees (Goethe + Helmholtz + Nernst + his own work) so to see the bigger forest and hence the elective affinities problem and hence may have not been aware of the chemical-version of Goethean philosophy, such as Arthur Schopenhauer was.

Lieserl love letter | Hoax
In circa 2015, a faked (Ѻ)(Ѻ) Einstein so-labeled newly unearthed (1980s) letter to his daughter Lieserl Einstein (1902-1903), began to surface (Ѻ), reporting Einstein as saying things like “love is gravity”, “love is god”, “love is a force that gives meaning to life”, etc.; none of which, however, are in accordance with his mindset or views. The hoaxer is someone trying to sell spirituality/new age ideas via artificial Einstein veneer.

See also
● Equation of love

References
1. Source: Kang, Manjit. (2002). Quantitative Genetics, Genomics, and Plant Breeding, (pg. 12). CABI Publishing.
2. (a) Dukas, Helen and Hoffmann, Banesh. (1979). Albert Einstein: the Human Side. New Glimpses into his Archives (pg. 56). Princeton University Press.
(b) Isaacson, Walter. (2007). Einstein (pg. 423). Simon and Schuster.
3. Einstein: Love (16” x 16” art print) – Art.com.

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