The question of the farthest place from Earth is complex, fundamentally intertwined with the finite speed of light. When astronomers look out into the cosmos, they are simultaneously looking back in time because the light from distant objects takes billions of years to reach us. This means the concept of “farthest” is not a simple measure of current physical separation, but rather a blend of distance, history, and the immense age of the universe. The maximum distance we can observe is limited by the age of the cosmos itself, approximately 13.8 billion years, which sets the boundary of what light has had time to traverse.
The Farthest Specific Objects
The current record holders for the most distant individual structures are typically galaxies or quasars discovered by powerful instruments like the James Webb Space Telescope (JWST). These objects are measured by the time their light has traveled to Earth, which is called the “look-back time.”
One of the most distant confirmed galaxies is JADES-GS-z14-0, observed as it existed only about 290 million years after the Big Bang. The light from this galaxy has traveled for over 13.5 billion years to reach us, offering a direct view into the epoch known as Cosmic Dawn. Its existence so early in the universe challenges previous theories about how quickly massive, bright galaxies could form. The detection of such faint and distant objects relies heavily on cosmological redshift, which indicates their extreme distance.
The Edge of Observable Space
The farthest theoretical limit to what we can ever see is defined by the Cosmological Horizon, which marks the boundary of the observable universe. This horizon represents the maximum distance light could have traveled to reach us since the Big Bang began. Although the universe is approximately 13.8 billion years old, the edge of the observable cosmos is not 13.8 billion light-years away.
The difference arises because the fabric of space itself has been expanding during the entire time the light was traveling. Objects that emitted light 13.8 billion years ago are now calculated to be at a current physical distance of about 46.5 billion light-years. This theoretical maximum distance defines a sphere around us beyond which no information, even light, has had time to cross the intervening space.
The Most Distant Light Source
The true farthest light we can detect is not from an individual star or galaxy but from the pervasive glow known as the Cosmic Microwave Background (CMB) radiation. The CMB is residual heat left over from the Big Bang, representing a time when the entire universe was a hot, opaque plasma. It is the oldest and most distant radiation that can be directly observed.
This light originated about 380,000 years after the Big Bang, during the “era of recombination.” This occurred when the universe finally cooled enough for protons and electrons to combine and form the first neutral atoms. Before this event, the dense plasma scattered photons continuously, making the universe opaque. Once neutral atoms formed, the photons were free to stream across space, marking the point where the universe became transparent.
The CMB light we receive today comes from the “surface of last scattering,” a spherical shell in the early universe. This light has been traveling for over 13.7 billion years. Its wavelength has been stretched dramatically by the expansion of space, shifting its energy from visible light to the microwave part of the spectrum.
Measuring Cosmic Distance
The immense distances to these farthest objects are not measured with a ruler but are primarily determined using the concept of cosmological redshift. Redshift is the stretching of light waves as they travel through expanding space, causing the light to shift toward the red end of the electromagnetic spectrum. The greater the observed redshift value, the faster the object is receding and the farther away it is.
Redshift is the central tool of Hubble’s Law, which links the velocity of a distant galaxy to its distance from us. Astronomers measure the redshift of a galaxy’s light to calculate its “look-back time”—the time the light spent traveling to Earth. This look-back time is distinct from the object’s “co-moving distance,” which is the calculated physical distance to that object in the present day, accounting for the entire history of cosmic expansion.