I remember reading about this a while back. Its an observation that under the right circumstances hot water may freeze faster than water which is cooler. It sounds intuitively crazy and with a basic knowledge of physics the first impulse is to say this is impossible, but it is in fact a well documented phenomena that has been reproduced in labs around the world.

what I wasn’t aware of was the story of the modern discovery of this effect by a high school student after which it is named.

Anyway, if the world hasn’t ended and you’re looking for something to do check it out at THIS LINK. The story and the reaction of the scientists and teachers just goes to show that those of us who claim to be critical thinkers need a reminder now and then not to let our thinking become dogma. Most things that seem impossible really are but every now and then there is a flaw in our thinking.

This was common knowledge when I was growing up.  When you think about it, it’s obvious that heating water would drive out the dissolved air, so that its freezing point should be just a tad lower.  But it doesn’t have a lot of practical value because, let’s face it how often is it vital to you if your ice cubes freeze a few minutes earlier? 

The concept clearly isnt new although it is by no means intuitive.  Even experts cant agree on the exact mechanism by which this odd phenomena occurs ( ie. 70°C water freezing faster than 30°C water). Most people who were not familiar with this phenomena would assume it was not possible. What was interesting is how certain the experts were of its impossibility when the high school student mentioned his observation.

It just points out that while logic and rationality are important we need to have a sense of humility because we rarely have a complete understanding of things. I actually deal with this issue a lot in medicine. There is so much we still don’t understand about the human body and yet time and again people propose a treatment that may sound good with a basic understanding of human physiology, yet more often than not the treatment doesn’t work as expected because we don’t have all the pieces to the puzzle, we don’t fully understand how the machine works.

The point being, a truly rational person needs to understand what they don’t understand and have the humility to admit it.

Right you are.  I think it was Aristotle who said, “Before we can command Nature, we must first learn to obey it.”  Or something to that effect.

And there’s a cool line from a Terry Pratchet novel, “The way I see it, logic is only a way of being ignorant by the numbers.” 

I just rediscovered this coincidentally a few days before you posted this. I know that here in Canada, (I’m in Saskatchewan), it seemed like a common thing for our mother’s to do but didn’t have an explanation for. I learned that it was because of this Mpemba Effect and that the rumour just got around from there. I also got the impression that cold water boils quicker than hot water. I later thought that this was one of those old wives tales and started boiling my water using hot water instead to do it quicker. I learned later though that the real reason for boiling water with cold water was due to the fact that the hot water boilers contained lead and other contaminants from the boiler itself for which I didn’t think of. I’m not sure if this still holds true for all modern boilers or if it was just due to older ones, but now I boil water in cold just in case. (I know that regular heating boilers are usually made with metals including lead. I’m guessing that if the new boilers for how water distribution still contain them, it would have to do with the welding.

The Mpemba Effect is interesting. I won’t put hot water in ice trays though regardless because it seems that the humidity created would only contribute to build-up of frosting.

I think the only thing important here is that knowing some simple laws of nature do not suffice for explaining phenomena in vivo.

BTW the German Wikipedia article is much longer, and accentuates the correct explanations:

1. A part of the hotter water evaporates, so there is less water to freeze than in the colder water.
2. Hot water has lost his dissolved gases. Dissolved gases lower the freezing point of water, so the colder water with more gases in it will freeze at a lower temperature than the water without.
3. Calcium Carbonate solubility decreases with temperature. So at higher temperature it leaves the solution by turning into small particles in the water. This also makes the freezing point slightly higher, and the particles functions as condensation points for the freezing of water, speeding up freezing process.

When two hermetically closed containers are used in which distilled water cannot evaporate and gases cannot get out of the solution the effect does not occur anymore.

It is true: the effect warns us for quick conclusions, by omitting details that can be important. Simple science believers also tend to fast and simple conclusions, just as their theistic counterparts. Scientists are humans too.