In Big Bang cosmology, the observable universe consists of the galaxies and other matter that we can in principle observe from Earth
in the present day, because light (or other signals) from those objects
has had time to reach us since the beginning of the cosmological
expansion. Assuming the Universe is isotropic,
the distance to the edge of the observable universe is roughly the same
in every directionâ€”that is, the observable universe is a spherical
volume (a ball)
centered on the observer, regardless of the shape of the Universe as a
whole. The actual shape of the Universe may or may not be spherical.
However, the portion of it that we (humans, from the perspective of
planet Earth) are able to observe is determined by whether or not the
light and other signals originating from distant objects has had time
to arrive at our point of observation (planet Earth). Therefore, the
observable universe appears from our perspective to be spherical. Every
location in the Universe has its own observable universe which may or
may not overlap with the one centered around the Earth.