How large is the universe? | Brian Cox

Key Concepts

• Milky Way Galaxy: Our home galaxy, containing 200-400 billion stars.
• Andromeda Galaxy: The nearest large galaxy to the Milky Way, 2.5 million light-years away.
• Light-year: A unit of distance; the distance light travels in one year.
• James Webb Space Telescope: An instrument used to observe galaxies near the edge of the observable universe.
• Cosmic Microwave Background (CMB) Radiation: Remnant radiation from the early universe, emitted 380,000 years after the Big Bang.
• Observable Universe: The portion of the universe from which light has had time to reach us.
• Expansion of the Universe: The ongoing increase in the distance between distant galaxies.

Galactic and Universal Scale

The video begins by establishing our position within the Milky Way galaxy, a vast collection of stars estimated to contain between 200 and 400 billion suns. The galaxy spans approximately 100,000 light-years in diameter. A light-year is defined as the distance light travels in one year, serving as a crucial unit for measuring astronomical distances.

Neighboring Galaxies and Distance Measurement

Moving beyond our galaxy, the discussion shifts to the Andromeda galaxy, our closest large galactic neighbor. Located 2.5 million light-years away, the light we currently observe from Andromeda began its journey before the emergence of humans on Earth. This highlights the immense timescales involved in observing distant objects. The video emphasizes that observing these distant galaxies is made possible by instruments like the James Webb Space Telescope, which allows us to detect light that has travelled for over 13 billion years.

The Edge of the Observable Universe & Cosmic Microwave Background

The furthest detectable objects are located near the edge of the observable universe. The light from these objects has taken approximately 13 billion years to reach us. However, the universe has been expanding during this time. The most distant light we can detect is the Cosmic Microwave Background (CMB) radiation. This radiation originated 380,000 years after the Big Bang and has been travelling for roughly 13.8 billion years.

Expansion and the Radius of the Observable Universe

A key point is made regarding the expansion of the universe. While the CMB radiation has travelled for 13.8 billion years, the location from which that radiation originated is now approximately 46 billion light-years away due to this expansion. This leads to an apparent radius of the observable universe of around 92 billion light-years. However, the video clarifies that this is not the true radius of the universe, but rather the limit of what we can currently observe.

The Potential Infinity of the Universe

The video concludes by stating that the universe, as far as our current measurements allow us to determine, may be infinite in extent. The speaker acknowledges the difficulty in conceiving of such a scale, stating that it is “genuinely inconceivable.” This emphasizes the limitations of human comprehension when dealing with the vastness of the cosmos.