I’m late to the discussion, but I hope I can clear up a common confusion.
According to Einstein’s relativity theories, the ultimate speed limit for travelling through space is the speed of light. No particle can travel faster than 299792.458 km/sec.
The expansion of space, however, is an entirely different thing, and it can’t even be measured in the same units. A speed is a ratio of distance divided by time, whereas space expansion is a ratio of speed divided by time. The current expansion rate of space in the universe is roughly 70 kilometres per second per million parsecs (a parsec is a distance greater than 30,000,000,000,000 km). This means that any two objects in the universe that are one million parsecs apart are being separated by the expansion of space by a relative speed of 70 km/sec, whereas any two objects that are two million pc apart are being separated at 140 km/sec, three million parsecs apart are being separated at 210 km/sec, etc. Another way of thinking about it is to say that every million parsec length of space everywhere is getting 70 km longer every second. The ratio of 70 km/sec per million parsecs is the same ratio all throughout the universe. It is that ratio— not any specific speed— that is increasing at an accelerating pace, and Einstein’s relativity theories set no restriction on how large that ratio may grow.
Darrin Bell and Theron Heir