Space Is Curved!
Today is the 49th anniversary of the Apollo 11 lunar landing. On July 20, 1969, Neil Armstrong and Buzz Aldrin touched down in the Sea of Tranquility in their spaceship Eagle, and became the first humans in history to travel to the surface of another world.
The Moon. The little yellow dot shows the approximate location where the Eagle landed on July 20, 1969. (However, certain conspiracy theorists contend the moon landings were faked, and the Eagle actually "landed" at the site shown in the picture below.)
Anyway, today seemed like an especially fitting day to discuss another one of my keenest interests: SPACE! Space (or "space-time" if you prefer) is a simply fascinating realm that contains many exotic features, such as the rings of Saturn, the Oort Cloud, dark matter, dark energy, galaxies, quasars, and (a personal favorite) supermassive black holes! (Readers, the underlined links take you back to previous blog posts from THE MAIN THING dealing in more detail with a particular (ha ha) "spacial" feature.)
Now another completely mesmerizing feature of space is—get ready because this is really going to blow your mind—it's CURVED! That's right, friend, space is all curved up like nobody's business!
A skeptical reader: "Will, that doesn't seem right. Are you sure space is curved? If you're mistaken about this curvature of space thing, I can't overemphasize the gravity of your error!"
Ha Ha! Ironically, skeptical reader, gravity's exactly how we know space is curved! Please look at the illustration below from NASA. Let's think of space as like a giant soft mattress, and stars and planets and other space objects that have mass as heavy bowling balls. If there's no space bowling ball nearby, the mattress of space lies pretty much flat. But if a massive bowling ball is placed on the soft mattress of space, you get an indentation (or curve) in the mattress underneath the bowling ball.
See? Earth's mass causes curvature of the space nearby, like a bowling ball placed on a soft mattress. That curvature is actually the Earth's gravity! The satellite is held in orbit because its orbital velocity is balanced with the curvature of local space caused by Earth's gravity. Isn't that interesting?
Now consider a small marble rolling along the mattress of space near the bowling ball. (And you have to bear in mind there's no friction along the mattress of space to slow down the marble.) As the marble gets close to the bowling ball, its path starts to bend in that direction. That bending is the attractive force of gravity acting across curved space!
If you're learning about the curvature of space for the first time, you might be pretty shook up right now. Maybe you should take the rest of this historic 49th anniversary off. Maybe watch a Disney movie?