The Universe Cares About How Fast You — Yes, You — Travel

NPR's resident physicist and commentator, Adam Frank, reflects on how your velocity — how quickly you move — affects how you experience life.

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We've been getting occasional light advice from NPR blogger and physicist Adam Frank. His mantra more or less is: Make friends with science and it will transform the ordinary into the extraordinary. Today, Adam's thoughts about how your speed affects the way you experience life. Or as he would prefer to say: your velocity.

ADAM FRANK: Velocity is just the distance you cover in the time it takes to cover that distance. Now, that might seem technical but actually you've been thinking this way your whole driving life. For example, Buffalo is about 60 miles away from where I live in Rochester. That means if I hop in my car and keep the speedometer - or better yet the speed-o-meter - fixed at 60 miles an hour, I'll get there in how long? Right, an hour.

But this easy road trip familiarity with velocity and space and time obscures something remarkable. The high speeds we travel everyday are something radically new for human beings. Before the mid-1800s and the invention of trains, pretty much no one ever moved as fast you travel in the slow lane of a highway. But you clock 65 miles an hour without blinking an eye. So why does that matter?

Well, gobbling up huge distances in short times has allowed us to create crazy new ways of being human that never existed before. Things like eating fresh fruit from thousands of miles away, or having long-distance romances with someone who lives on an entirely different coast.

But this thing with velocity, it can get even weirder. When we eventually get to high enough velocities, we're going to find it's not just society that changes but physics itself.

Your great-great-grand pappy's head might have spun right off if he roared through the sky at 500 miles per hour. But that's no big deal for you, it's just a plane trip. But it would be your head that would be spinning if you had a direct experience of moving close, as we learned from Albert Einstein's mind-bending Theory of Relativity. That's because Al understood that velocity is really not just about measurements of space and time. Instead velocity is what sets the behavior of space and time if you're traveling fast enough.

So, imagine for a second a pair of twins. Now imagine that one of twins climbs aboard a space ship. She blasts off and travels at 99.5 percent of light speed for a round trip into deep space and back. Using the clocks and calendars on her spaceship, she measures her travel time to be three years. Then she lands back on Earth and goes looking for her sister. But when they meet, she finds her Earth-bound twin is not three years older but 30 years older. While only three years have past for the space-traveling sister, 30 years have passed on Earth.

How is this possible? Well, Einstein realized that the flow of time for the space-traveling twin and the flow of time for the Earth-bound twin were not the same. Yeah-yeah-yeah, I know. That seems crazy but it's been proven a zillion times in laboratories all around the world: The relative flow of time between people moving relative to each other depends on their relative speed.

The reason you don't see this difference in everyday life because it only becomes noticeable when you travel close to the speed of light, which is 670 million miles per hour.

So yes, velocity matters, a lot. That's because there are so many different ways to experience this world of wonders we find ourselves in. And much of it depends on the space you cover in the time you have.

SIEGEL: Adam Frank spends his time teaching physics at the University of Rochester and blogging at NPR.org.

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