In The Field

Cool time keeping

Tick tock tick tock—the sound of an atomic clock that loses a second once every 3 billion years.

But why do we need such an accurate clock? On Saturday Nobel Prize-winning physicist William Phillips mesmerized the crowd speaking about atomic clocks at the World Science Festival event Einstein, Time and the Explorer’s Clock. This wasn’t a normal session. The standing room only auditorium was buzzing with the excitement and impatience of kids not yet in their teens. And Phillips was no regular speaker, equally awing kids and adults.

First a little science: atomic clocks are important because, among other things, our GPS system relies on them. Location is determined by calculating signal delay between the GPS and at least four satellites orbiting Earth. The more accurate the time keeping pieces, the more accurate the positioning data. The physics and mechanics of atomic clocks are complex, suffice to say that the atomic clocks Phillips works on at the NIST rely on slowing down the movement of the atoms (at times I craved a little more explanation).

And here comes the science experiments: how do you slow down atoms? Well a little (or alot) of liquid nitrogen can help answer that question. To start, Phillips poured liquid nitrogen on to the stage. The floor is burning hot compared to nitrogen, he explained, so we get the “steam”.

He put 2-3 good breaths into an orange balloon and eased it into a bucket of liquid nitrogen.

He dipped a carnation into a jar of liquid nitrogen and shattered it.

And back to the balloons: 2-3 good breaths into a pink balloon and that went into the same bucket.

He filled a plastic water bottle with liquid nitrogen, tightened the cap and placed a trashcan over it—this, he told the giggling kids, is a cautionary tale.

Again to the balloons, a red one this time; all in all six balloons eased into the bucket.

We were distracted by a demonstrations of how magnets can be used to slow down atoms when KABOOM! Remember the bottle-trashcan? It exploded and the trashcan went straight up into the air (though Phillips never explained the physics of why). Delight all around!

And the balloons? Finally the bucket was opened: out came pancake shaped balloons—this time with an explanation of what happened.

It was amazing how the jittery kids calmed down after all that to sit through another 15 minutes of how and why this cooling works in the lab. “Cool” science redefined.


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