Why does hot water sometimes freeze faster than cold—a 2300 year old question

The Mpemba effect is when hot water freezes more quickly than cold water and the question as to why was first posed, as far as we know, by Aristotle. 2300 years later we’re still looking for the answer and the UK’s Royal Society of Chemistry (RSC) has decided to pose the question to two different audiences in the hope of finally getting a solution. Brian Emsley in his June 26, 2012 posting on the Guardian Science Blogs describes the RSC’s open contest for £1000,

The Royal Society of Chemistry has decided enough is enough. In an attempt to nail the matter once and for all, we’re asking the public to come up with a convincing explanation of a phenomenon that defeated Aristotle, Francis Bacon and René Descartes. To win the £1,000 prize, you will need to make a convincing case and employ some creative thinking.

The deadline for public entries is 30 July [2012] …

You can go here to the Hermes organization website to submit your solution.

For those with any lingering questions about the competition for the general public, the June 26, 2012 RSC news release provides more information including a list of prominent theorists who have also puzzled over the question,

  • Aristotle agonized over it fruitlessly in the fourth century BC
  • Roger Bacon in the 13th century used it to advocate the scientific method in his book Opus Majus
  • Another Bacon, Francis, wrote in his 1620 Novum Organum, that “slightly tepid water freezes more easily than that which is utterly cold” but could not explain why
  • Descartes was defeated by it in the 17th century AD
  • Even perplexed 20th and 21st century scientists and intellectuals have swarmed over it without result

Now the Royal Society of Chemistry is offering £1000 to the person or team producing the best and most creative explanation of the phenomenon, known today as The Mpemba Effect.

Competition judges will be looking for an outside-the-box, inventive submission. In addition, the format of the submission should be creative and eye-catching.

Any medium or technology can be employed to make the case, including articles, illustrations or even film.

Submissions can be based on, and reference, existing research. The winning submission will be scientifically sound, and arresting in presentation and delivery.

The public has four weeks to crack the case …

Then, according to the RSC news release,

… a group of the world’s brightest young science brains take on the challenge in London as one aspect of a special science communications meeting entitled Hermes 2012.

The sharpest international postgraduate science students will travel to England from around the globe to participate in the Hermes 2012 event.

The Royal Society of Chemistry is sponsoring this visit to the UK of the hand-picked young scientists, who will gather at Cumberland Lodge in Windsor Great Park.

The organisers of Hermes 2012, based at Imperial College, chose the opening weekend of the Olympic Games for the academic event to underline the global nature of the meeting, with its temporary, multi-national community of high-achievers.

A highlight of the Windsor event will be a team attempt to produce videos to explain various scientific phenomena, which will include The Mpemba Effect.

Good luck!

Hermes, by the way, was the Greek god associated with messages and communication, as well as, sports, literature, and athletics, (from the Wikipedia essay) [Note: I have removed footnotes and links],

Hermes was the herald, or messenger, of the gods to humans, sharing this role with Iris. A patron of boundaries and the travelers who cross them, he was the protector of shepherds and cowherds, thieves, orators and wit, literature and poets, athletics and sports, weights and measures, invention, and of commerce in general.

While the effect had been observed a number of times, it wasn’t considered a serious scientific question (from the RSC news release),

The problem has been around for millennia, with philosophers such as Aristotle and Descartes pondering over it.

“But this effect was reintroduced into the scientific world in 1968 by Erasto Mpemba, a young inquisitive student in Tanzania during a lab session.

“Erasto questioned a teacher on why ice cream froze more quickly when it was boiled, and was quickly told that he was wrong and had probably imagined it. It was only when the teacher performed the experiment himself that he noticed this unusual phenomenon.

“Since the discovery of the effect, scientists have been trying to find out why the phenomenon occurs but remain divided as to what the answer is. It seems that there are lots of possible answers but a conclusive explanation hasn’t been produced yet.

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