Defying Gravity for Dummies

The Basics of Gravity

Everything has gravity. And by everything, I do literally mean everything. Sure, there are the obvious things like stars, planets and moons, but even much smaller things have gravity, like you, me, and the last doughnut in the packet (at least now you can blame physics when everyone gets mad!). The original wizard of gravity, Sir Isaac Newton, knew this when he explained in his law of universal gravitation:

"every particle attracts every other particle in the universe with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centres of mass"

Essentially, the more massive two objects are, the stronger the pull of gravity, and the further two objects are from each other, the weaker the attractive force will be. Makes sense so far. Earth's mass is overwhelmingly huge compared to everything else in our day to day lives that we don't randomly get stuck to buildings or cats on our commute to work. Maybe it also explains why long distance relationships are so difficult to maintain?

But Newton's law brings up another interesting point: gravitation influence is infinite. The attraction from the Earth's gravity will weaken as you get further away, but it never disappears. At least mathematically, anyway. We physicists are much smarter than mathematicians, and we know that at about 1.5 million kilometres from Earth the Sun's gravity takes over. But this means even if you're in space, gravity is still in the spotlight singing a power ballad.

Unfortunately this scuppers our plans of sticking our tongues out at Newton's fundamental force. How can we possibly defy gravity if it's everywhere? I mean, we can't all just wear a crown and come down in a bubble like Glinda, can we?

The Subtle Art of Zero-G

The best way to resist the force of gravity is to strap yourself onto a massive rocket filled with hundreds of tonnes of liquid fuel and oxygen and light the fuse. For anyone dreaming of finally refusing to let gravity bring them down for longer than one short day, you may want to forego launching vertically, and instead add a hefty chunk of horizontal velocity, or you may slightly resemble a comet pulled from orbit burning up in the atmosphere.

Here is where we need to once again turn to our favourite apple lover Isaac Newton, and his book Principia Mathematica. In it, he imagined a cannon firing cannonballs at varying speeds. The greater the speed, the further the cannonball travels. With enough speed, a ball travels so far that its landing point depends on the Earth’s curvature. With even more speed, the curve of its path will match that of the Earth’s surface. With no drag to slow it, the ball will continue to fall but never reach the ground, and hence it has achieved orbit

Remember earlier where you jumped to experience defying gravity for yourself?  As you began to fall back to Earth, you experienced a very brief example of weightlessness. And that's why astronauts are constantly floating around up there: to be in orbit is essentially just perpetually falling to Earth, but moving sideways fast enough to miss the ground. A continually falling spacecraft will experience everlasting zero-g, changing an astronaut's view of up and down for good.