It was by observing supernovae back in the late 1990s that Reiss and other scientists discovered the universe was not only expanding but also doing so at an increasing rate, estimated expansion at 73.4 kilometres a second every megaparsec, or 3.26 million light years or 255,000 kilometres (160,000 miles) per hour, according to a Harvard-Smithsonian statement.

Measuring cosmic microwave background radiation, which can look much farther back in time to around 300,000 years after the Big Bang, suggests the universe is expanding at a significantly slower rate -- around 67 kilometres per megaparsec.