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Why Is Relativity Hard? | Special Relativity Chapter 1

Hi, this is Henry, and this is the first in a series of videos about special relativity This is definitely not an academic course, but it’s going to be a more in-depth and developed exploration of a single topic than a typical standalone minute physics video. I’ve been greatly inspired and heckled to do this by my friend Grant Sanderson of Three Blue One Brown who set the standard for this kind of thing with his excellent series series’es? on calculus and linear algebra. So, special relativity. Special relativity is one of the most popularly famous ideas in physics It’s the thing that Einstein figured out about the speed of light and space and time and e equals mc-squared It changed our understanding of the universe and its core ideas are accessible in principle to anyone who understands some basic algebra and geometry You don’t even need to know calculus And yet in spite of this special relativity is one of the subjects in physics that confuses the most people and in many cases turns them away from physics altogether I think in part This is because special relativity is not quite a big enough subject to ever get its own full class in physics departments you might see classical mechanics or quantum mechanics or electromagnetism or intro to general relativity on a course syllabus But it’s surprisingly rare to see special relativity Even though relativity is an essential building block upon which most of the rest of modern physics depends Special relativity is typically relegated to just a few days squeezed into the beginning or end of other physics courses. However, the more important reason special relativity confuses so many people is that it’s almost always introduced confusingly with lots of complicated algebraic equations with Delta X’s and Delta X Prime’s and square roots Which sometimes you divide by and sometimes you multiply by and all the while you’re scrambling to figure out where in all this symbol logical mess they’re hiding a supposedly mind-blowing insight about the fundamental nature of space and time Special relativity doesn’t have to be that way. And I think the complicated explanations have only survived this long because they’re how Einstein did it. But he was a professional physicist climbing an intellectual mountain up its steepest face. And I don’t think that we should require everyone who learns about special relativity now to have to follow the same path Einstein did Especially not now that we have super beautiful and simple geometric ways of explaining it Essentially we figured out afterwards that there’s a much easier way to climb the mountain than what Einstein did, a way that you could probably even figure out on your own, given the right prompting. And it’s that fundamentally beautiful simple geometric way to understand space and time that I want you to leave with after watching this series of videos. If all goes well, hopefully you’ll gain some intuition for what special relativity really is, why it works why it’s right, and why all those paradoxes you’ve probably heard about aren’t paradoxical at all. They’re just easy confusions to stumble into when you’re attacking things with an army of square roots This is going to require some mental effort from your end. There’s a very real mathematical sense in which learning special relativity is kind of like living your entire life thinking the earth is flat And then learning that the earth is actually round. A round Earth isn’t actually that complicated of a thing to picture I mean, it’s just a ball But trying to get used to that idea, to really take it in and figure out how your day-to-day experiences on this flat seeming surface of the earth– how they fit into this new round earth idea– that would certainly take some mental effort. It is, though, a totally different kind of mental effort from plugging lots of numbers into complicated square root formulas and ultimately, much more worthwhile I mean you probably have a pretty good intuition about round Earth concepts, like what happens if you just keep walking east and what’s the shape of the Earth’s shadow on the moon without having to do complicated calculations in spherical polar coordinates. In fact we’re gonna take this analogy to the extreme. Just like a globe is a really useful hands-on visual way to explore what it means for the earth to be round because a globe comes with roundness built-in, I’ve designed and had built a hands-on space-time globe that has special relativity built in. It’s not quite as simple as a globe globe because special relativity is a little weirder than roundness But the thing I like about this machined aluminum space-time globe is that it’s a physical manifestation of the intuition that I hope you develop for special relativity. We’re going to use it to gain a hands-on understanding of the twins paradox, length contraction, and time dilation, why nothing can go faster than light, and much more. I hope to see you in the next video And while you’re waiting for the next special relativity video to come out you might want to check out this video’s sponsor: a site full of interactive quizzes and mini courses on physics and math. As you’ve probably heard me say before, if you want to understand physics deeply, you really have to think through ideas and solve problems yourself and Brilliant offers a great way to do just that– either by learning a new topic, like neural networks practicing problem solving in an area you already know, like algebra or solving tricky puzzles, like this one. If you decide to sign up for premium access to all of their courses and quizzes, you can get 20% off by going to Again, that’s, which lets Brilliant know you came from here
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