The Cosmic Microwave Background Radiation. Image credit: NASA

What Shape Is The Universe?

  • The universe is either flat, hyperbolic, or spherical
  • The shape of the universe is dependent upon the curvature of space
  • The shape of the universe will determine whether space is finite or infinite

Most of the objects we can see in space, such as stars and planets, are spherical, yet does this also apply to the universe as a whole? Is the universe also spherical, or is it some other shape? There are three possible shapes of the universe: flat, hyperbolic, and spherical. The shape of the universe is dependent upon its curvature. Zero curvature means flat, negative curvature means hyperbolic, and positive curvature means superficial. Which of these three shapes describes our universe?

How The Shape Of The Universe Is Determined

Shapes of space
The three possible shapes of the universe, dependent upon the value of curvature. NASA

Determining the shape of the universe is no easy task. After all, the universe is unimaginably gigantic, and so determining its shape is difficult. In order to determine the shape of the universe, scientists must calculate the distance to the farthest regions of space we can see, and then determine the curvature along that distance. The farthest we can physically see is the Cosmic Microwave Background Radiation (CMBR), at over 13.7 billion light years away. The CMBR is the oldest known light in the universe, and as far as we know, it is the first form of light after the Big Bang. Thus, the CMBR is the maximum possible distance we can see. 

To determine the curvature of space, scientists must draw a gigantic triangle. The base of the triangle is the Earth’s Earth's orbit around the sun, while the two lines connected to the base are the distance to the CMBR. By knowing the size of Earth’s orbit and the distance to the CMBR, scientists can determine the curvature of these lines. By calculating the curvature, scientists can then determine the shape of the universe depending whether the curvature is negative, positive, or zero. 

Although the exact shape of the universe is still widely debated among scientists, observations of the CMBR have revealed that our universe has a curvature of zero, meaning that the universe is flat. However, do not think of a flat universe as being as flat as a sheet of paper. Rather, a flat universe is still three dimensional. Furthermore, the universe could be so large that any attempts to determine its shape are pointless. After all, a large universe that has curvature will appear indistinguishable from one that does not, assuming it’s large enough. 

Is The Universe Infinite? 

The shape of the universe determines whether or not the universe is finite or infinite in its expanse. To describe the topography of space, scientists use the term boundedness to describe the size of the universe. For example, a universe that has no bounds is infinite, while a universe that has boundaries would be finite. Whether the universe has boundaries or not is dependent upon its shape. For example, a spherical universe would be compact and have boundaries, so it would be finite. Meanwhile, a flat universe can either be infinite or finite. If the universe is actually flat, as most data suggests, space can either be infinite or finite. 

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