Tuesday, September 5, 2017

Water, water everywhere (but beware which sort you drink)

One of my longtime favorite novels is Kurt Vonnegut's Cat's Cradle, in which a major plot element is "ice nine." This is a form of H2O, not naturally occurring in nature, that's crystalline at room temperature. A seed crystal of ice nine turns all regular water in which it is in contact to more ice nine. Bear in mind that we are about 90 percent water. Quite the unique doomsday device ...

Highly recommended
Today's post isn't a book review (although I highly recommend Cat's Cradle; we're talking about one of Vonnegut's best). The book came to mind because of what is our topic: the recent real-world discoveries of new forms of H2O).

On the liquid side: "Physicists Discover Two Low-Temperature Forms of Liquid Water: A Stockholm University-led team of physicists has discovered two low-temperature phases of liquid water with large differences in structure and density." Sort of the opposite of ice nine, which is solid at an unexpectedly high temperature.

The takeaway: 

"When we think of ice it is most often as an ordered, crystalline phase that you get out of the ice box, but the most common form of ice is amorphous, that is disordered, and there are two forms of amorphous ice with low and high density. The two forms can interconvert and there have been speculations that they can be related to low- and high-density forms of liquid water.

Not ice nine (fortunately)
“We found that water can exist as two different liquids at low temperatures (minus 234 degrees Fahrenheit, or minus 148 degrees Celsius) where ice crystallization is slow,” said Anders Nilsson, professor in chemical physics at Stockholm University, and senior author of the paper reporting the results in the Proceedings of the National Academy of Science."

And on the solid side, we have "To make hot ice, take one diamond and vaporise with a laser: Creating an exotic state of water that may exist on other planets is a high-pressure job." ("Vaporise" is not a typo... this article is from Cosmos, an Aussie zine.) The takeaway here:

"Using an enormously powerful laser to vaporise diamond, a team of American researchers have blasted water into “hot ice”, an exotic crystalline state in which water may exist on Saturn’s moon Titan and on planets beyond our solar system."

A bonding exercise ...
And before I call it a post, let's make a small detour to a measurement of the proton -- which is, after all, the nucleus of two of the three atoms in a water molecule.

One of the things I love about (most) science is that nothing is ever quite settled. I don't mean thereby that random people should randomly disbelieve aspects of what scientists currently think has been proven. Rather, I mean that everything we believe we understand is -- quite properly -- subject to re-verification, and that sometimes new measurement techniques and/or new insights about old observations lead to surprises. As in "Is the proton lighter than we thought?" Short answer: maybe. Slightly longer answer: it seems so, but the evidence to that effect is not at a level of statistical significance physicists consider convincing.

"The most precise measurement ever of the mass of the proton suggests that the particle is a tiny bit lighter than the current accepted value. Although the difference is less than one part in 10 billion, it has a statistical significance of 3σ."

 "σ," the lower-case Greek letter sigma, is shorthand for what statisticians call a "standard deviation." When dealing with normal (bell curve) distributions of measurements, three σ of confidence is about 99.7%. Confidence at the three-σ level is considered highly suggestive -- but not compelling. Physicists generally insist upon six σ, or 99.99966% confidence, before accepting a conclusion.

And with that, I'm off for a cold drink, ideally free of ice nine.

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