I live in Australia, how is it that Stack Exchange is so fast without using any CDN?

I had a look at the Stack Exchange Servers:

https://meta.stackexchange.com/questions/10369/which-tools-and-technologies-are-used-to-build-the-stack-exchange-network

Seems they only have two data centres with 11 servers. There's no mention of CDN, which I presume is not possible since they are using server side html rendering (ASP.Net).

Yet, I feel like they are as fast as google (which has a gazillion servers). How is this possible?

They do use CDN. It's at the moment Fastly: https://www.fastly.com/network-map.

Read Nick's blog series Stack Overflow: A Technical Deconstruction. Stack Exchange is a traditional architecture of a few racks of on premise servers behind a CDN. As said several times in that series, "performance is a feature", a fanatical focus of operations on being fast. Most requests hit a global CDN. Web servers requests are probably cached in memory - caching dynamic content is absolutely possible. Actual database hits are optimized to the point where they wrote custom ORM software. Even the slow path from halfway around the world can seem pleasantly fast when performance is a feature.

Although they both employ speed focused people, Google and Stack Exchange's scale is wildly different. Google tries to index all information ever, and rent out enough compute to be one of the largest clouds. Stack Exchange is a few TB of popular Q&A information. SE definitely punches above its weight in terms of search engine influence and my personal preference. Partly due to being fast, partly due to growing communities that actually answer questions.