The Hubble Space Telescope accumulated approximately 555 hours of exposure time to capture this Hubble eXtreme Deep Field image. The area shown represents a seemingly empty patch of sky about the width of a toothpick when held at arm’s length. The picture contains only two foreground stars . Every other object is a galaxy. The most distant galaxies’ light is reddened by the expansion of the universe. We’re seeing light that left them 13.2 billion years ago.
Paul Sutter is an astrophysicist at The Ohio State University and the chief scientist at COSI Science Center. Sutter is also host of Ask a Spaceman, RealSpace, and COSI Science Now.
Spoiler alert: The universe is flat. But there’s a lot of subtlety packed into that innocent-looking statement. What does it mean for a 3D object to be “flat”? How do we measure the shape of the universe anyway? Since the universe is flat, is that…it? Is there anything else interesting to say?
First, we need to define what we mean by flat. The screen you’re reading this on is obviously flat, and you know that the Earth is curved . But how can we quantify that mathematically? Such an exercise might be useful if we want to go around measuring the shape of the whole entire universe.
One answer lies in parallel lines. If you start drawing two parallel lines on your paper and let them continue on, they’ll stay perfectly parallel forever . That was essentially the definition of a parallel line for a couple thousand years, so we should be good.
Start at the equator and draw a couple parallel lines, each pointing directly north.
The opposite of the Earth’s curved shape is a saddle: on that surface, lines that start out parallel end up spreading apart from each other (in swanky mathematical circles this is known as “ultraparallel”).