Thursday, February 9, 2012
What makes something a cloud?
When you observe a cloud in the sky, it certainly seems like you're observing one thing--namely, the cloud. And yet, if you were to zoom in on it, you might not even notice the cloud. Instead you'd see lots of individual water droplets, some closer to the center of the cloud, some further away. If you look at the edges of the cloud, the water droplets are so spread out that some of them probably are not even part of the cloud in any meaningful sense. And yet there is no hard and fast point at which we'd say this droplet is part of the cloud--that one next to it is not. As a result, there are many groups of water droplets that have just as much claim to being that cloud as any other group of water droplets. It would seem, then, that there are many clouds. And yet it also seems that there is just one. What makes one group of water droplets qualify as that cloud, rather than another? Or is there no cloud at all?