Episode 136: Introduction to General Relativity
The Science of Everything Podcast
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The Different Directions of a Spear
The idea is simply that if you go from being at the North Pole to pointing a spear out in front of you then walking all the way to the equator now the spear is pointing in different direction. It doesn't look like there's any change locally but actually it has been because they've moved on a curved surface. In what looked locally like we were just sort of moving in a straight line actually it turns out we were curving and something was bending right that the spear is now pointing in a different direction. We have to find a way of describing his motion along that path in a way that can subtract out the effect of the curvature as we don't want to describe how space
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