Everything everywhere in the universe is falling—even you.
You might think you’re sitting on a chair, reading this article, but you’re not. You’re falling toward the center of Earth. It’s just that you have no distance left to fall. This creates the illusion of being still. If everything everywhere in the universe is falling then nothing is still. Not even you on your chair.
Being stationary is an illusion. It’s a convenient one, but it’s like a magician’s trick, it hides reality from us.
Einstein proposed that gravity is the warping or distorting of spacetime by a massive object. The consequence of this simple insight is that space (and time) are not flat. Far from being empty, space is lumpy. Bumpy. It’s curved everywhere by gravity.
We’ve all seen astronauts floating in outer space, like on the International Space Station. We say they’re weightless. We used to call this zero gravity. Now it’s referred to as microgravity, but even that’s not entirely correct.
The International Space Station orbits about 250 miles above Earth, roughly 400 kilometers up. What would happen if I could build a tower that reached 250 miles into the sky? What if the Burj Khalifain, the world’s tallest building, had an elevator that took you to an observation deck at the same altitude as the International Space Station? What would you see? What would you feel? Would you be weightless like the astronauts? Would you be in microgravity?
Most people think the answer is yes. If astronauts are floating around up there, then why wouldn’t I float as well?
The answer is astonishing. You’d weigh less, but not by much. You certainly wouldn’t be floating around. Your feet would be firmly on the floor of the observation deck.
At sea level, Earth’s gravity is 9.8 meters per second squared—meaning if you drop something, it’s going to fall almost ten meters in the first second (ignoring wind resistance for a moment). That’s about 32 feet.
On top of our hypothetical super-high Burj Khalifain, at an altitude of 400km, Earth’s gravity has reduced as we move away from the planet, but it’s still astonishingly strong. It’s 8.7 meters per second, or about 28 feet.
But what about our astronauts in microgravity. Yeah, they’re not really in microgravity. They’re experiencing the same 8.7 meters per second acceleration down toward the center of Earth as I am standing on a tower 400 kilometers high.
The reason they’re floating is they’re falling. Remember. Everything everywhere in the universe is falling toward something. Earth is falling around the Sun. The Sun is falling around the Milky Way. Our galaxy is falling around the Great Attractor. Yep, the entire Milky Way is moving at well over a million miles an hour toward a super-cluster containing 10,000 galaxies the size of Andromeda.
And here you are sitting on a chair reading an article. It’s an illusion. We’re all falling. It’s just that most of us are falling along with a rather large mass we like to call Earth.
Going back to the observation deck on our imaginary Burj Khalifain, we’re looking for the International Space Station. Only there’s a problem. It’s not floating in space. It’s in orbit. And that means it’s falling. And it’s falling at five miles a second. It’s falling so fast it never reaches the ground.
Here it comes.
Blink and you’ll miss it as it whizzes by at five miles a second.
The Hitchhikers Guide to the Universe describes flight as…
…an art… [that] lies in learning how to throw yourself at the ground and missDouglas Adams
This is true of orbits as well.
In 1687, Sir Isaac Newton was inventing modern physics and he wondered how far a cannonball could go if the army kept increasing the amount of gunpowder behind the shot. He knew Earth was a sphere. He realized that with each increase in distance, the cannonball would slowly disappear over the horizon.
Our modern concept of orbits was born when he realized that at a certain speed, his cannonball would keep falling. It would be moving so fast that it would fall around Earth rather than back to it.
And that’s what’s happening to our astronauts and satellites. They’re moving so fast sideways, that when they fall back toward Earth, they miss the entire planet.
The next time you see a rocket launch at night, watch how it moves in an arc, curving until it’s going sideways.
Look at how the rocket clears the lower atmosphere and then races sideways. Why does it do that? Because getting into space is one thing. Staying there is another. Gravity is still strong up there, right? Remember, it’s 8.7 meters per second squared at 400 kilometers in altitude. So our rockets have to race sideways until they’re going fast enough to fall around Earth rather than falling back to Earth.
Astronauts floating in space are no different to you or me floating as an airplane hits turbulence and plummets a few hundred feet in a couple of seconds, or if we’re falling on a rollercoaster at the fairground, or falling while bouncing on a trampoline. The only difference is astronauts have mastered the art of missing the ground.
It seems Tom Petty was right—we are free-falling.