|A 2010 image (Ѻ) of Aristotle-Mpemba effect, by James Brownridge, who has conducted 100s of Mpemba effect experiments, who believes the effect has to do with impurities in the water.|
Since the 1960s, scientists have proffered dozens of theories to explain the effect, such as: evaporation, convection, frost, supercooling, latent heat of condensation, solutes, thermoconductivity, and supercooling.
In 2010, James Brownridge published a theory, which argued that the effect had something to do with impurities in the water.
In 2013, scientists at Nanyang Technical University, Singapore, argue that the covalent bonds in hot water are contracted (shortened) and the hydrogen bonds are stretched (longer), and that this structure allows the water to release energy faster, thereby reaching the freezing state quicker. (Ѻ) 
The hot-begets-cold-quicker phenomenon was first recorded by Greek philosopher Aristotle in circa 350BC: 
“The fact that water has previously been warmed contributes to its freezing quickly; for so it cools sooner. Hence many people, when they want to cool hot water quickly, begin by putting it in the sun.”
In c.1265, English philosopher Roger Bacon is said to have experimentally tested the phenomenon. 
In c.1461, Giovanni Marliani, an Italian physician-physicist, in a debate over how objects cooled, confirmed that hot water froze faster than cold, in an experiment where he had taken four ounces of boiling water, and four ounces of non-heated water, placed them outside in similar containers on a cold winter day, and observed that the boiled water froze first; Marliani was, however, unable to explain this occurrence. 
Thinkers such as Rene Descartes and Francis Bacon had also noticed this phenomenon. Bacon, commented, for example, in his 1620 Novum Organum, that “slightly tepid water freezes more easily than that which is utterly cold”.
|A 1979 clipping summary of the Mpemba effect by the journal of Physics Education of Great Britain. |
In 1963, a circa thirteen-year-old African student named Erasto Mpemba, in the United Republic of Tanzania, was making ice cream at school, which he did by mixing boiling milk with sugar. He was supposed to wait for the milk to cool before placing it the refrigerator, but in a rush to get scarce refrigerator space, put his milk in without cooling it. To his surprise, he found that his hot milk froze into ice cream before that of other students. He asked his physics teacher for an explanation, but was told that he must have been confused, since his observation was impossible.
Mpemba believed his teacher at the time. But later that year he met a friend of his who made and sold ice cream in Tanga town. His friend told Mpemba that when making ice cream, he put the hot liquids in the refrigerator to make them freeze faster. Mpemba found that other ice cream sellers in Tanga had the same practice.
Later, when in high school, Mpemba learned Newton's law of cooling, which describes how hot bodies cool, but does not explain the effect he observed. Mpemba asked his teacher why hot milk froze before cold milk when he put them in the freezer. The teacher answered that Mpemba must have been confused. When Mpemba kept arguing, the teacher said "All I can say is that is Mpemba's physics and not the universal physics" and from then on, the teacher and the class would criticize Mpemba's mistakes in mathematics and physics by saying "That is Mpemba's mathematics" or "That is Mpemba's physics." But when Mpemba later tried the experiment with hot and cold water in the biology laboratory of his school, he again found that the hot water froze sooner. This was done while he was elementary (or junior high school) student in in Form 3 of Magamba Secondary School, Tanzania. After passing his O-level examinations, he became a student at Mkwawa Secondary (formerly High) School, Iringa, Tanzania.
In high school, the school headmaster invited physicist Denis Osborne, from the University College in Dar Es Salaam, to their conference on "Physics and development of Tanzania," in which he gave a lecture on physics. After the lecture, Mpemba asked him the question:
“If you take two similar containers with equal volumes of water, one at 35°C (95°F) and the other at 100°C (212°F), and put them into a freezer, the one that started at 100°C (212°F) freezes first. Why?”
The question resulted in the eruption of laughter from the student audience, along with ridiculed by his classmates and teacher. Osborne said that he could not think of any explanation, but would try the experiment later. When back in his laboratory, he asked a young technician to test Mpemba's claim. The technician later reported that the hot water froze first, and said "But we'll keep on repeating the experiment until we get the right result." However, repeated tests gave the same result, and in 1969 Mpemba and Osborne wrote up their results. 
The 1969 article stimulated such debate among teachers, pupils, and the general public, particular on the issue that an unknown teenage African school boy can, in a sense, overthrow or rather throw an experimental wrench in Newton’s law of cooling, in such a way as to affront the world science community.
In 1979, the phenomenon had been christened the ‘Mpemba effect’ by the journal of Physics Education of Great Britain. 
|A 2013 power point depiction of a "Social Mpemba effect" in respect to the rate of "social cooling", i.e. solidification into the new social order, in respect to "hot wars" vs "cold wars" by American electrochemical engineer Libb Thims, presented at UPESW 2013 |
See main: Social Mpemba effectAs applied to social affairs, the Mpemba effect, in regards to orderings of human molecules (people) in societies, should predict that a “hot society” should cool faster, i.e. solidify into order faster, than a “cool society”.
This is evidenced by the fact that the “Cold War”, between Russia and America, lasted 44 years, from 1947 to 1991, whereas traditional “Hot Wars”, such as WWI (1914-1918) or WWII (1939-1945), tend to last on average about 5.5 years, in other words the “cooling process” to the new social order (frozen water) from the old social order, occurs much faster if the collective societies are heated (liquid water) first.
The repercussions of this would be that a hot war may, theoretically, would, in the long term, result in solidified order or a state of stable peace faster than would a cold war. Historically, French anthropologist Claude Levi-Strauss was the first to distinction between “cold” and “hot” societies; though it is doubtful that he ever considered the Mpemba effect in this respect.
In 2013, Libb Thims, at UPESW 2013, presented an outline of the social implications of the Mpemba effect. 
1. Shachtman, Tom. (1999). Absolute Zero and the Quest for Absolute Cold (pgs. 17, 28). Mariner Books
2. Jeng, Monwhea. (1998). “Can Hot Water Freeze Faster than Cold Water?”, Department of Physics, University of California.
3. Clagett, Marshall. (1967). "Giovanni Marliani and Late Medieval Physics" (pgs. 72, 79, 94). AMS press.
4. Cucic, Dragoljub. (2009). “Paradoxes of Thermodynamics and Statistical Physics” (abs), Arxiv.org, Dec 09.
5. Mpemba, Erasto B.; Osborne, Denis G. (1969). "Cool?". Physics Education (Institute of Physics) 4: 172–175.
6. (a) Mpemba, E. B.; Osborne, D. G. (1979). "The Mpemba effect". Physics Education (Institute of Physics) 14: 410–412.
(b) Barnes, Barry. (1985). About Science (pg. 61). Oxford: Blackwell.
(c) Bourguet, Marie-Noelle, Licoppe, Christian, Sibum, Heinz O. (2002). Instruments, Travel, and Science (pg. 279). Psychology Press.
7. Graves, Dan. (1996). Scientists of Faith: Forty-Eight Scientists and Their Christian Faiths (pg. 24). Kregel Resources.
8. Thims, Libb. (2013). “Econoengineering and Economic Behavior: Particle, Atom, Molecule, or Agent Models?” (video, 1:33-min) (article, 40-pgs) (PowerPoint, 36-slides), Key speaker talk delivered at the University of Pitesti Econophysics and Sociophysics Workshop (UPESW) / Exploratory Domains of Econophysics News (EDEN V) (organizer: Gheorghe Savoiu). University of Pitesti, Pitesti, Romania, Jun 29.
9. Zhang, Xi. (2013). “O:H-O Bond Anomalous Relaxation Resolving Mpemba Paradox” (co-authors: Yongli Huang, Zengsheng Ma, Chang Q Sun) (pdf), ArXiv.
● Fuente, Pedro. (2008). “Mpemba physics” (Spanish → English), Arxiu del Blog.
● Mpemba effect – Wikipedia.