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The universe is mind-boggling vast. The diameter of the observable universe is estimated to be about 93-billion light years across. With just our eyes, we can generally only see a few thousand light years of distance, although there are some objects we can see that are much further away.

The farthest object you can see with the naked eye is the Andromeda Galaxy located 2.5-million light years away, yet it is only visible if there is little to no light pollution. In order to see farther into space, we must rely on telescopes. How far can we see using the most powerful telescopes?

Before explaining the farthest distance we can see, it is important to know how big the universe is. As was already stated, the observable universe is estimated to be around 93-billion light years across. However, that number may seem contradictory as the universe itself is only 13.8-billion years old.

How can we see beyond 13.8-billion light years if light hasn’t had enough time to reach our eyes? Since the universe is expanding, and the speed of light is finite, we see objects as they were rather than as they are. A galaxy that is, say, one-billion light years away, is actually now located at a much further distance due to the expansion of space.

We simply see the galaxy as it was one-billion years ago, yet it has traversed a tremendous amount of distance since then. When astronomers account for the expansion of space, they end up with the estimated size of the universe being 93-billion light years.

To simplify things, a better way of thinking of distance is to view it as how far back in time we can see. That is to say, how close to the Big Bang can we see?

Until the launch of the James Webb Space Telescope (JWST) in 2021, the Hubble Space Telescope was the record holder for farthest visible distance in space. Although Hubble is smaller than some Earth-based observatories, it is able to see the universe in much higher detail due to the fact that it is in space, where it does not have to deal with any sort of atmospheric distortion.

Although no longer the most powerful telescope, Hubble is still able to see the universe as it was a mere 500-million years after the Big Bang. The image (see above) used for this stop on our journey is the Hubble Ultra Deep Field (UDF). The UDF is one of the deepest views of the visible universe to date; certainly it was the deepest when it was originally created in in 2003-2004.

There are approximately 10,000 galaxies in this view, which is a sort of "core sample" of a very narrow patch of sky near the constellation Fornax. The smallest, reddest galaxies in the image, of which there are about 100, are among the most distant known objects!

The UDF (see below) looks back approximately 13 billion years (approximately between 400 and 800 million years after the Big Bang). Galaxies that existed in that time period would be very young and very different in structure and appearance than the grand spirals we see nearby today.

The JWST is now the most powerful telescope ever built, and it is able to see the universe as it was only 200-million years after the Big Bang. That means that the JWST is able to piece together an additional 300-million years of cosmic history compared to Hubble.

The JWST will be able to study some of the first galaxies to form after the Big Bang (see above). The farthest physical distance we can see is the Cosmic Microwave Background Radiation (CMBR). The CMBR can be thought of as the echo of the Big Bang, as it is the leftover radiation from the birth of the universe.

The CMBR itself is the farthest possible distance humans can see as it represents the moment that the universe became transparent to light. Although light did exist before the CMBR, gas and dust were simply too dense for light to escape and traverse space.

The CMBR formed only 380,000 years after the Big Bang, and so we are seeing the universe prior to the formation of even the first stars. This radiation was emitted by matter that has, in the intervening time, mostly condensed into galaxies, and those galaxies are now calculated to be about 46 billion light-years from Earth.

Large-scale structure Sky surveys and mappings of the various wavelength bands of electromagnetic radiation have yielded much information on the content and character of the universe's structure. The organization of structure appears to follow a hierarchical model with organization up to the scale of superclusters and filaments.

Stars are organized into galaxies, which in turn form galaxy groups, galaxy clusters, superclusters, sheets, sheets, walls and filaments, which are separated by immense voids, creating a vast foam-like structure sometimes called the "cosmic web" (see below).

Since the early 1980s, more and more structures have been discovered. For example, in 1987, Robert Brent Tully identified the Pisces–Cetus Supercluster Complex, the galaxy filament in which the Milky Way resides. It is about 1 billion light-years across.

That same year, an unusually large region with a much lower than average distribution of galaxies was discovered, the Giant Void, which measures 1.3 billion light-years across. On January 11, 2013, another large quasar group, the Huge-LQG, was discovered, which was measured to be four billion light-years across, the largest known structure in the universe at that time.

In November 2013, astronomers discovered the Hercules–Corona Borealis Great Wall, an even bigger structure twice as large as the former. Some caution is required in describing structures on a cosmic scale because they are often different from how they appear.

Gravitational lensing can make an image appear to originate in a different direction from its real source, when foreground objects curve surrounding spacetime and deflect passing light rays.

Most distant objects The most distant astronomical object identified (as of August of 2024) is a galaxy classified as JADES-GS-z14-0 (see below), discovered by NASA's James Webb Space Telescope in the constellation Fornax. The galaxy is about 1,600 light-years across and is very luminous.

In 2009, a gamma ray burst, GRB 090423, was found to have a redshift of 14.32, which indicates that the collapsing star that caused it exploded when the universe was only 290 million years after the Big Bang.

Reference: Observable universe. (2024, December 18). In Wikipedia. https://en.wikipedia.org/wiki/Observable_universe Ptak, A. (2020). The Farthest Visible Reaches of Space. National Aeronautics and Space Administration. Remple, A. (2022). How Far Can Humans See In Space? WorldAtlas.

About Coram Deo

Coram Deo — before the face of God. This blog reflects on Scripture, world events, science, music, psychology, and the human mind — always through the lens of Christian faith. All of life is lived before the face of God.