You'll travel nearly a trillion miles in your lifetime

[soso]

You'll travel nearly a trillion miles in your lifetime, even if you never leave home. Here's how.

By Paul Sutter

published about 2 hours ago

Everything in the universe is moving, and fast.

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The arch of Milky Way shining bright above Lut (Dasht-e Lut) desert, in Kerman, Iran. (Image credit: Miguel Claro)

Whether you're a frequent jet-setter or a couch potato, you travel much more than you think.

In fact, that would be true even if you were to stay perfectly motionless your entire life. So how far, on average, does a person travel in their lifetime? The answer depends on whether you consider Earth as your vehicle.

As for distance on Earth's surface, the typical human will travel 30,000 to 50,000 miles (50,000 to 80,000 kilometers) in their lifetime, though some globe-trotters will go much farther. Considering most people accumulate the majority of this mileage from commutes and quick errands, that's an impressively large distance — enough to circumnavigate the globe at least once.

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But as large as it is, that number pales in comparison to the motion we get simply by hitching a ride on Earth. Our planet spins on its axis. And because Earth is mostly solid, it rotates as a single rigid body, meaning that everywhere on the planet experiences the same angular speed and everyone travels a full circle every 24 hours.

But if you were to stand on the north or south geographic poles, you wouldn't actually travel anywhere; you would just spin around and around. Those on the equator, however, get a tremendous amount of linear speed thanks to this rotation — roughly 1,000 mph (1,600 km/h).

Most people don't live on the equator, however, so we can say that the average human is constantly traveling at roughly 930 mph (1,500 km/h). (As we will see, precision doesn't really matter here.) When you add that up over a roughly 80-year life span, each person travels around 600 million miles (1 billion kilometers) in their lifetime.

That's a tremendous leap above the travel we do on Earth's surface, but we're just getting warmed up. In addition to rotating, Earth orbits the sun. That orbit is an ellipse, which causes our planet to occasionally move more quickly or slowly depending on its distance from the sun. But on average, Earth's orbital speed is about 19 miles per second (30 km per second).

That's about 600 million miles (1 billion km) every year. So over a lifetime, each of us travels roughly 50 billion miles (80 billion km) — which, again, dwarfs the distance we travel due solely to the rotation of our planet.

But Earth is not the only object in motion in the universe. The sun travels in a long, lazy orbit around the center of the Milky Way galaxy. One of these "galactic years" takes roughly 230 million Earth years to complete. To put that into perspective, life first arose on Earth around 17 galactic years ago, and in only 25 more galactic years, the sun will die.

Compared with these enormous galactic scales, a human lifetime is barely perceptible, with the sun barely inching along its orbit. But on a human scale, it's almost incomprehensible; due to the motion of the sun orbiting the center of the Milky Way, each of us will travel around 370 million miles (600 billion km) in our lifetime.

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And it doesn't stop there. Our entire galaxy is in motion, too. All galaxies are, on average, flying away from each other, but that's due to the expansion of the universe. On top of that expansion, each galaxy has some motion of its own — something astronomers dub "peculiar velocity." For example, the Milky Way is on a collision course with our nearest neighbor, the Andromeda galaxy. The mutual gravitational attraction is enough to overwhelm the general expansion of the universe, and in about five billion years, these galaxies will begin to merge.

On top of that, both the Milky Way and Andromeda are headed toward the Virgo cluster, a massive cluster of galaxies about 65 million light-years away. Beyond that, the Virgo cluster and its surrounding galaxies are all headed toward the Great Attractor, which is the center of our supercluster, called Laniakea.

Astronomers can calculate the combined motion of these gravitational influences by observing the cosmic microwave background (CMB), which is composed of radiation released when our universe cooled from a plasma state when it was only 380,000 years old. It completely soaks the universe and is the same to one part in a million across the entire sky.

Any motion in the universe will be visible in the CMB. Light in the direction we're headed in will get Doppler-shifted to higher frequencies (blueshift), and light in the direction we're moving away from will be shifted to lower frequencies (redshift). By measuring this shift, astronomers can calculate our total velocity through the universe, and those measurements give a number of around 390 miles per second (630 km per second).

When you add that up over an 80-year life span, it gives you a total movement of 930 billion miles (1.5 trillion km). Even if you never leave home, you will still travel that enormous distance — that's quite an accomplishment!