No signal can travel faster than light, hence there is a maximum distance (called the particle horizon) beyond which nothing can be detected, as the signals could not have reached us yet. It refers to the physical limit created by the speed of light itself. The word observable in this sense does not refer to the capability of modern technology to detect light or other information from an object, or whether there is anything to be detected. Every location in the universe has its own observable universe, which may or may not overlap with the one centered on Earth. That is, the observable universe is a spherical region centered on the observer. Assuming the universe is isotropic, the distance to the edge of the observable universe is roughly the same in every direction.

There may be 2 trillion galaxies in the observable universe, although that number was reduced in 2021 to only several hundred billion based on data from New Horizons. The observable universe is a ball-shaped region of the universe comprising all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time, because the electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion.

Acronis true image big sur