# How scientists can slow down time

There are things about theoretical and mathematically-proven physics that are difficult to see in practice, but of those things ... there is one that is no longer simply theoretical, we can actually DO it. Einstein's Theory of Special Relativity states that the faster something travels, the slower time appears to move relative to a stationary observer.

To test the time dilation part of the TSR massive experiments had to be conducted. In 1971, the Hafele (ha-fi-la) and Keating Experiment flew four atomic clocks on airplanes going around the world and compared the time-shift from those clocks to the atomic clock at the National Observatory in Washington, D.C., and JUST like Einstein predicted the airborne clocks were going SLOWER.

Think about it. When you're on an airplane, you're aging slower than your Mom. Unless of course, she's on the airplane too ... as long as we're thinking about it, time dilation theory says airline pilots might be aging slower than their ground crews ... think about it. Not a lot slower, mind you, but slower.

Once we started going to space, time dilation became a thing we actually had to deal with. GPS satellites, for example, are 20,000 km up going 14,000 km/hour. So, relative to an observer on the ground, the GPS satellites are going to lose about 7 microseconds per day! It doesn't seem like a lot, but knowing PRECISELY what time it is, is extremely important for measuring your exact location on the planet. If they let this go unchecked GPS would fail, so they have to correct for Special Relativity, just so you can find the nearest Shake Shack.

Usually, before now, scientists used mathematics or space travel to test these out-there theories. Special relativity says, the faster you go, the slower time goes. If you travelled a year at 95% the speed of light; you'd age one year, and people on Earth would age 3.2 years! But if you were going 50% the speed of light it would only be 1.15 years. The effect get's stronger as you go faster.

A German study published this week has shown you can create the time dilation effect in the lab! Which is HUGE news for physics. The experiment, published in Physical Review Letters, explains how these German scientists used a heavy ion storage ring to accelerate charged lithium particles to almost 40 percent the speed of light. A storage ring is sort of like the ghost containment box in Ghostbusters, but for charged particles.

Once the ions were traveling at top speed, the scientists shot two laser lights at them, one in front and one behind, and then measured the light absorption rate. Think of it like sonar or radar, they're measuring the amount of energy that comes back.

Because they had two lasers and the speed of light is constant -- they could use the Doppler effect to figure out the time dilation those ions were experiencing. If you want to read a full explainer, check out Ars Technica.

The reason this is so huge, is because we don't have to measure the changes on spacecraft, or use assumptions related to the movement of planets or astronomical bodies. On top of that, it verifies, yet again, that Einstein was right, and the Standard Model of Physics is accurate.

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