The history of the Universe, as far back as we can see using a variety of tools and telescopes, out to the maximum present depth of SDSS. We are now up to SDSS-16, which can go all the way back to just ~3 billion years after the Big Bang, mapping out more than 2 million galaxies in the process. (SLOAN DIGITAL SKY SURVEY (SDSS))

Record-Breaking 3D Map Of The Universe Reveals Some Big Surprises

How quickly is it expanding today, and how does that expansion rate change over time?

What is the Universe made of? How quickly is it expanding today, and how does that expansion rate change over time? If we could know the answers to these questions, we’d understand both the past history and future fate of our Universe. Yet even with our best measurements of the Universe itself, different methods don’t give the same answer. Measuring the Big Bang’s leftover glow, the cosmic microwave background, gives us one set of answers, while measuring stars, galaxies, and supernovae gives us a different, incompatible answer. The discrepancy is, arguably, the biggest conundrum in modern cosmology.

But with more than two decades of data — and a detailed, 3D map of more than 2 million galaxies — the Sloan Digital Sky Survey might help us finally solve this cosmic mystery. These galaxies are spread out over more than 19 billion light-years in all directions, corresponding to more than 11 billion years of cosmic history in our expanding Universe. But what is it made out of? How quickly is it expanding today? What else have we learned, and what comes next for astrophysics? Here’s the remarkable story.