 Hey everyone, Rivi here. Welcome to the next part of the course, which is on Einstein's theory of special relativity. Now for this section, I really recommend that you work together in groups, you know, watch the lectures together, discuss the problems, whenever someone gets confused, pause it and have a talk about it, because this style of learning, where you're having to explain things in your own words and consider questions that you might not have thought about yourself, is really one of the most efficient ways to go about learning. Okay, let's get started. Suppose it's a nice, calm, windless day, and you decide to go for a walk. Now it's lovely, but it's getting late, so you decide to jog home. And as you do so, you'll start to feel a breeze across your face, caused by you running through the air. And if you were to get onto a bike and pedal really, really fast, you'd feel a really strong wind on your face, even though it's a windless day. Now there's nothing really strange about this, but if you were to tell the story to a snail, you would blow its mind, because you see a snail never really goes fast enough to see this. And this idea that you could see wind on a windless day, just by going really fast, would be incredible. Even though to us it's just, you know, whatever, that's how the world works. Special relativity is like that. All our lives, we've been living like the snail, you know, never going anywhere near the speed of light. And if we did, we'd see all sort of strange effects. Time would slow down, space would get warped, and all sorts of other crazy things would happen. And we're going to have a look at this over the next few videos.