Imagine learning for the first 18 years of your life that the earth is flat. All through elementary school in high school, you grow up hearing about the flat earth we live on and doing boring Flat Earth physics homework. And then if you're lucky enough, you get to college and psych for the first time they show you a globe and say sorry for lying, the Earth is actually round. Well, this is unfortunately, exactly what we do with gravity. 1. You probably learned that objects attract each other based on their mass. So you probably grew up thinking that light can't possibly be affected by gravity because light is massless. I know I did. Well guess what? The source of gravity is not mass, its energy and momentum, which lights certainly has, of course, regular matter does too. So not only does light to get bent passing by a star or planet or black hole, but light attract to the planet or star or black hole in return. To be sure it's only a very, very small amount, but a small amount is not zero. Anyway, the point is that Newton's law of gravitation is just an approximation. Good enough to get us to the moon, but not perfect. 2.special relativity ,General relativity is better. Speaking of the moon You've probably also learned that if a sheep is moving two miles per hour relative to a train, and that train is moving two miles per hour in the same direction relative to the ground, then the sheep is moving four miles per hour relative to the ground, two miles per hour plus two miles per hour equals four miles per hour, right? False experiments in special relativity have confirmed that velocities don't simply add together. And so the sheep will, in fact, be moving very, very ever so slightly slower than four miles per hour relative to the ground. And the formula that correctly predicts this deviation from just adding the velocities is v one plus v two divided by one plus v one times v two over c squared. It's not a very big effect. But then again, the earth looks pretty flat, doesn't it? But the earth isn't flat. If I walk 10,000 kilometers away from my cat, and you continue on walking 10,000 kilometers more, you're not 20,000 kilometers away from my cat, you're just 12,750 kilometers away. In fact, the farthest on earth you can get from anything on earth is 12,750 kilometers. It's the earthly distance limit that we normally call it the diameter of the earth. And similarly when you try to add to Vulcan Together, there's a cosmic speed limit of 300 million meters per second. That is the speed of light. So just because to our eyes the earth looks flat velocities looked like they simply add together and lights looks like it doesn't attract gravitationally. Is that an excuse to mislead ourselves and our children about the true nature of things.