Right now, we use a raster logo instead of a vector logo.
For those who don't know, a raster is an image made of pixels. If you zoom enough, you'll see the image become pixelated (as is the case with our logo). Vector graphics don't become pixelated when you zoom into them, and they'll always remain crisp.
Almost every SE site uses vector logos because they look nicer. An example of a vector graphic is this:
Feynmann diagram is from Wikipedia, courtesy of user Joel Holdsworth under the Creative Commons Attribution 2.5 Generic license. Modified by changing the color and trimming the gluon spiral. Logo based on Physics SE's logo, copyright of Stack Exchange Inc.; no infringement intended.
I made this in a few minutes. Notice how it does not pixelate when you zoom in. Not to mention, the current logo shows up blurry for a lot of larger displays. Shouldn't we update our design to have better quality?
PS: If you decide to use the logo I made, please give attribution to the creator of the Feynmann diagram, as per the Creative Commons license.