Google to test ulta high-speed broadband network

I wonder how much faster internet can get? I thought speed of light would be pretty much at the limit.

The speed of light determines latency, transfer rates depend on sending information as either very short bits, or parallel.

There are limits on the length of bits due to signal quality (signal to noise ratio needs to be good enough) and the number of parallel signals you can send also depends on quality. Consider radio waves... you can pick up several different stations on your radio if you tune to different frequencies, but none of them are very close together or they interfere. You can use similar tricks to increase the amount of content through a cable.