There's something very magical about water and what happens to it when it freezes. I don't think there's anything else in the world, perhaps in our universe, that is quite like ice.

The principal reason it transforms is that water is a collection of molecules, H2O, every child learns that.And that bond has the property that as the bonds get stronger when you cool water, the ice expands.

Mainly, of course, if you're not an ice climber, where you really need ice, for most people ice is a damn nuisance. And we just can't wait for it to all melt.And it's always a remarkable fact that it takes so long to melt because the temperature of the air can be well above the freezing point, and the ice is still solid there. So for most people, that's the experience.

Amorphous forms [of ice], for example, are found naturally on comets, on asteroids, and the crystalline forms are found on Earth or at least could be made on Earth with enough pressure. Nothing else does this.

H2O it's a complicated, three-dimensional, charged object. And one can pack these things in many different ways, a little like playing the child's game of jacks, where those complicated little objects can be thrown together in all different ways.

I think the most remarkable thing about ice, in my opinion at least, is that it occurs in many, many, many different forms. Most solids occur in typically one or maybe two or three different forms, and ice has approximately 15 different crystal forms, as well as two forms that are called amorphous, which means without any shape at all.

Ice is remarkable in many ways. A simple experiment one can do at home is to add salt to an amount of water in different concentrations. For example, one can mimic the concentration of the ocean, or one can make it even saltier.