Hubble volume

In cosmology, a Hubble volume, or Hubble sphere, is a spherical region of the Universe surrounding an observer beyond which objects recede from that observer at a rate greater than the speed of light due to the expansion of the Universe. The Hubble volume is approximately 10³¹ cubic light years.

The proper radius of a Hubble sphere (known as the Hubble radius or the Hubble length) is ${\displaystyle c/H_{0}}$, where ${\displaystyle c}$ is the speed of light and ${\displaystyle H_{0}}$ is the Hubble constant. The surface of a Hubble sphere is called the microphysical horizon, the Hubble surface, or the Hubble limit.

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