Ancient cultures like the Chinese and the Greeks looked up at the sky in awe and racked their brains to figure out just what was going on up there. They made remarkable breakthroughs, but things really ramped up in the 20th and 21st centuries as technology advanced. Some of those discoveries might be unfathomable to the non-scientists out there, but they’re certainly real.

### Curved Space

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The idea that space can be flat or curved is strange and maybe not even believable, but alas, it is true.

Albert Einstein realized the space around gravitating objects is curved, which accounts for things like orbits (more on that next). One way to determine whether space is flat or curved is by testing Euclidean geometry in these spaces. This is geometry performed by Euclid, a mathematician from Ancient Greece that wrote up all the formulas you learned in high school geometry.

For example, in Euclidean geometry, a triangle’s angles add up to 180 degrees. Not in curved space. It’s because the curvature of the straight lines (what an oxymoron) causes the angles to be bigger. You could draw a triangle with three 90-degree angles.

Think about that for a minute.

### The Not Force Of Gravity

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Remember in high school physics when you learned Isaac Newton’s Three Laws of Motion? And the force of gravity? Force is mass times acceleration, or 9.8 m/s2? Forget it. Almost.

Newton was not completely wrong with his laws about gravity; however, he wasn’t completely right. Turns out, in his formulas, you could theoretically get answers, like the potential for infinite gravity, that just don’t add up, and Albert Einstein saw that. He then came up with his own equations that answered questions about gravity that Newton’s equations couldn’t. This is how we get curved space, which causes the phenomenon of gravity.

Imagine space as a rubber sheet. Now stick a bowling ball, representing Earth, on it. You should be seeing a curve in the rubber around the Earth. Keeping this in mind, if you were to roll a smaller, lighter ball (the Moon) at the edge of that curved rubber, it would get caught in the curvature of the rubber (gravity) and go in circles, or orbit around the Earth. This is how gravity works according to Einstein.

The big takeaway here? Gravity is not a force, so forget high school physics. Only that part, anyway.

### Einstein’s Theory Of Relativity

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Einstein’s theory of relativity is a complicated one, so hang on to your hats, boys and girls. This one plays in with curved space and gravity not being a force, but it is by far its own animal.

On larger scales, as an object moves from an observer, time slows down to that observer. For instance, if you hold a clock in front of you, the seconds will tick like normal. Move that clock farther away, and those seconds and minutes, to your perspective, will slow down. They don’t really slow down, but they look like it.

This goes for all kinds of things, like aging and light. If you hold a blue light in front of you, it will look blue, but as it moves farther and farther away, it will start to look red because red has a longer wavelength. This is also why the pitch of sound, like when you hear a train horn, changes. As it gets closer, the wavelengths shrink, so the frequency and the pitch go up. As it goes away, the wavelengths get longer, and the frequency and pitch drop.

On Earth, these relative differences are very subtle, almost negligible, which is why Newton’s laws are used and taught in school. They serve their purpose just fine on Earth, except in one respect: Global Positioning Systems.

GPS devices use Einstein’s Relativity to function properly. Time at the satellites above Earth pass slower, to us, than it really does, and for the satellites, time moves faster down here, due to Earth’s gravity. These time differences are great enough that they would completely throw off your travel time. To make sure we get to where we’re supposed to be, GPS devices rely on Einstein’s time.