Dear Dr. Universe: What if gravity pulled up, instead of down? -Kyle, Cedar Lake, IN
Our universe would look so different, Kyle. You might not recognize it even if you could be here to see it. Unfortunately, there probably wouldn’t be a whole lot to see.
I learned about this from Washington State University professor and physicist Matthew McCluskey, who studies the material world. He explained how gravity pulls together dust, gas, and little particles floating around space to make massive clumps of matter that form stars and planets.
For example: planet Earth. Every particle in the Earth is pulling on you at this very moment–every single one.
You can jump really high despite that. McCluskey said this is because gravity is a wimpy force, an oddball compared to other forces of nature. Even a weak force can still add up to pull us toward the Earth’s center and keep us grounded.
If gravity pulled us up toward the sky, it would mean that gravity repelled. It would push objects away from each other.
Watching this happen from out in space, you could see everything not bolted down to Earth–buildings, desks, homework, cats–start to lift off and drift into space. Then, you could see the surface of the earth start to fall away. He thinks your question sounds like a good idea for a science fiction story.
There isn’t any place with zero gravity, but when you’re falling it feels as if there is no gravity. As you may already know, or as any astronaut can tell you, you can live without gravity. Gravity isn’t what keeps our guts together.
“In everyday physics, the most important forces besides gravity are electricity and magnetism,” McCluskey said. “Atoms are bound together into molecules via the electric force. So, that’s what keeps ordinary-sized objects like humans together.”
If gravity reversed on the Sun, McCluskey said he’d be scared because it is the only thing keeping the sun together. Nuclear fusion, inside the sun, pushes outward. Without gravity, the sun would explode.
In fact, gravity from the Sun is pulling on all the planets. The Sun has a bigger mass so it’s exerting the strongest gravitational pull in the solar system. Thankfully, our planet is also moving sideways so it won’t fall into the Sun.
McCluskey doesn’t believe gravity will ever reverse, though. Gravity has behaved the same way for billions of years.
And just imagine a universe where gravity was always pushing things away. There wouldn’t be a natural world to ask questions about, or inquisitive people like you to ask them. Matter would never clump together to form planets or stars. It would be a universe of dust.