Expanding Water...

Is water is the only liquid that expands when it freezes? Yes.

Water is most dense at 4 degrees Celcius. That's why lakes freeze at the top and you would never find frozen pockets of ice at the bottom of the sea - the pressure would force it to be in the liquid state.

All substances expand when you heat them, as the particles vibrate more the average space between them increases. Water is no exception, but it's only when it freezes that the strange stuff happens:

Science bit: "The reason water expands when frozen is the crystalline structure that forms, and the strong O-H bonds. The hydrogen atoms have a very strong attraction for the unbonded electrons in the nearby molecules. In an ice crystal, each oxygen atom has it's own 2 electrons, and grabs hold of 2 more electrons from the water molecule next door. And so they crystallize into a big hexagon shape, which takes up more space than the same molecules do when the water is in liquid form. An ice crystal's form is called a 'network structure.' Same molecules, but takes up more space."

Source: http://en.allexperts.com/q/Science-Kids-3250/water-expand-freezer.htm

We can never really be sure of anything...

How I Heard About This: I heard this quote from Einstein many years ago at university - I was reminded of it the other day by a friend.
Main Source: http://www.rockportinstitute.com/resources_transform.php
Topic: Philosophy/Science

Details: Part of the my physics degree was the study of the Philosophy of Science. One thing that did upset a few members of our class was the idea that whatever equations or theories we come up with, they are just one possibility, and can never really be proven "right". Even Newton's laws of motion, although amazingly accurate at predicting the motions of the planets, break down when you look at very small subatomic particles.

According to Prof. Steven Hawking, often when well respected theories are called into doubt by experimental findings - the accuracy of these readings (or indeed sometimes the characters of the scientists) are called in question before the theory is re-assessed. People put a lot of their faith in Science and in some ways it has become very much like a religion, the only thing that makes this religion so powerful is that it can often make very accurate predictions about the future. In our degree we were discouraged from thinking that this is the only answer, and one scientist I met some time ago said to me "the more I learn about science, the more I know there has to be a god."

Regardless as to whether there is a god, we should understand that we cannot ever really know what is going on, and anything we do "know" already is just one interpretation of many possible truths.

Here is what I consider to be Einstein's greatest contribution to science:

"In our endeavor to understand reality we are somewhat like a man trying to understand the mechanism of a closed watch. He sees the face and the moving hands, even hears its ticking, but he has no way of opening the case. If he is ingenious he may form some picture of a mechanism which could be responsible for all the things he observes, but he may never be quite sure his picture is the only one which could explain his observations. He will never be able to compare his picture with the real mechanism and he cannot even imagine the possibility of the meaning of such a comparison."

- ALBERT EINSTEIN, 1938