 450, it says, in the first place, all the particles of Earth by reason of their weight and entertainment congregated in the middle and occupied the lowest positions. And there's another part in both. Well, basically, well, there's another particle that says something similar. And I think it kind of suggests that there is a center of the world or some sort of spherical spatial structure. But I think that also kind of contradicts what we heard earlier in class about how things fall parallel to each other rather than towards a center. So I thought that part was kind of confusing. It is. So first of all, they have an infinite spatial universe. So it's infinite in all directions. Now that is for sure. They don't have a limited cosmos like Aristotle does, where it's just a sphere or something. So already there's a problem. There can't be a center of something that's infinitely extended in every direction. So how could we, I mean, just immediately there's that problem of talking about a middle. Furthermore, this idea about atoms falling in parallel lines. And so you have this sort of laminated structure where everything is constantly falling downwards. Well, if everything is falling downwards, then again, how do they say there is any center? And also, how do they say there is any downwards? Because if it's infinite in all directions, what's the difference between up and down? Up and down means relative to some end point or beginning point. But if there isn't one, then downwards doesn't make any sense. So there's a couple of ways we use to get out of this. One thing we can do is have a conception where we have a kind of Cartesian grid with an x and a y axis. And we say that all the atoms all are falling at the same speed in the same direction downwards. And that means downwards relative to this grid, which we can place anywhere in the universe. Now, the idea of it collecting around a center, and what does that mean? First of all, in theory, that should imply that there is a spherical Earth. For example, I'll give you a simplified picture of Aristotle's cosmos, a sphere with a sphere in the center. The Earth is in the center. And downwards means in the direction towards the center. And that can go from any point on the circumference. So this is downwards. That's downwards, meaning towards the center. And up means away from the center. But that's not the Epicurean picture, because they don't have a spherical cosmos. And it's not even clear that they have a spherical conception of the Earth. So what we have to do here is talk about cosmic border states that somehow you have these vast regions of space. And then you get these that are full with atoms moving in all sorts of different directions. And these are relatively full. And then, but there's these vast void areas. There isn't actually a boundary here. It's just indicating that this is a void area that's free of these. Then there's a theory about how atoms falling into these kind of vortices end up swirling like this down towards the center of vortex. And so that's why it's thought to be down as it's sort of like a whirlpool heading down into it. And then down in the middle of this is where the heavy stuff gets collected. And there is a sort of centrifugal motion here where heavy bodies head towards the center and light bodies get thrown out towards the edge. And that's meant to account for the observable cosmos. It looks like heavy bodies are all here, like the ground we're standing on. And there's all these light bodies, like the stars and the sun and the moon up there. And we have to explain that. And we think that's all just motions of atoms and void. So we have this general view that atoms are all moving in the same direction. But they get caught up in vortices. And then there's some kind of physics of vortices. But although we need to use Lucretias to try to figure out details of Epicurean physics because of the loss of all the main Epicurean works, he is not always very clear with this. And so we get problems like this passenger calling our attention to.