The Universe in a Glass of Ice Water

A photo of ice in water.

Ah, summertime! Warm weather, sunny days, and glasses of ice water on the table – er, I mean, the coaster, Mom. Really! Those crystalline cubes clinking against the glass, cooling all they touch and slowly, slowly disappearing into the background.

Incredibly, the science of ice water has a lot in common with the science of stars, including our own warmth-providing star the Sun. Let's look a little more deeply.

Ice water has an interesting property. Once the ice and water mixture reaches a particular temperature (which happens to be the freezing point, 32 degrees Fahrenheit), that temperature does not change as long as the ice cubes are still there. Instead of the heat from the room and the table (I mean the coaster, Mom!) going into raising the temperature of the ice water, all that heat goes into melting the ice cubes. Until those cubes have completely disappeared, the temperature holds steady at 32° F. In a sense, the ice cubes act as a barrier to change until they're gone. That, in fact, is exactly why we use ice cubes, and not just chilled water, to cool our drinks.

OK, now consider a star like the Sun. The Sun is a balancing act. Gravity is constantly pulling in on the Sun, trying to get it to contract. The temperature of the Sun counteracts this pulling. This high temperature pushes the Sun outward, achieving a between temperature and gravity. The diameter of the Sun is a perfect balance between the temperature pushing out and the Sun's own gravity pulling in.

What does this have to do with ice cubes? Well, stars have an interesting way of creating heat. They do so by changing one thing into another in a process called nuclear fusion. In the Sun, about four billion kilograms (nine billion pounds if measured on Earth) are changed into energy every second! That's about the same as around ten thousand 747 airplanes changed totally into energy every second, every day for billions of years!

All this matter turning into energy produces the outward-flowing heat that keeps the Sun's diameter the same despite the Sun's own crushing gravity. How does the Sun turn matter into energy? Deep inside the Sun, atoms of hydrogen slam into one another. If they are moving fast enough, for hydrogen atoms can stick together, turning into a single atom of helium. A single helium atom, however, weighs a bit less than four hydrogen atoms added together.

Think about what would happen if this hydrogen to helium transmutation wasn't possible. The Sun would keep collapsing, opposed only by the little bit of heat the hydrogen atoms could generate as they run into one another. And no more summer days for us on Earth. But the conversion of hydrogen to helium acts as a barrier to the collapsing Sun by releasing the heat to stop the collapse.

The hydrogen-to-helium transmutation, then, has a lot in common with the ice-to-water transformation in your glass of ice water. In both cases, the transformation acts as a barrier, holding things steady for as long as the hydrogen – or the ice – last. Next time you're enjoying a cold glass of ice water, think about the Sun, our nearest star, and the heat-releasing transmutations that make that ice water taste so good. All right, Mom, I'll use a coaster! Sheesh!

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