Time may seem like one of the most predictable, dependable measures we've got. But despite the reliable tick, tick, tick of your wristwatch, time doesn't always flow at the same rate. Einstein's theories say that time varies depending on things like gravity and acceleration, so that time moves more slowly the further into an object's gravity you go. That means that the center of the Earth must be younger than its surface. According to a 2016 study, it is — by more than we ever believed.in 2016, a team of Danish physicists decided they should probably check the math. Nothing against Feynman, of course. " ... just because someone has become famous, this person is evidently not necessarily right on all matters," the authors write in their study, which was published in the European Journal of Physics. "Feynman himself would most likely have agreed with this and he would probably not have fallen for his own miscalculation."
The physicists performed a back-of-the-envelope calculation and found that, due to the effects of physics (and not, say, geological processes), the Earth's core is in fact 2.5 years younger than its surface.This isn't just a mathematical abstraction. The effects of time dilation actually affect things you use every day. Take GPS maps, for example. GPS satellites orbit the Earth at 12,500 miles up (20,117 km), which is considerably further out in Earth's gravity well than everything on its surface is. That means that time moves faster for GPS satellites than it does for clocks here on Earth.The one snag in this factoid is that satellites are also moving at 8,670 miles per hour (13,953 kph), and acceleration slows time down. That means time isn't as fast for satellites as it would be if they were stationary. But these two effects don't cancel each other out entirely — gravity has a bigger effect on the satellites than speed does. As a result, clocks on GPS satellites run a few nanoseconds slower than clocks here on Earth.