The Universe consists of three principles: Space-time, forms of Energy, including Momentum and Matter, and physical laws that relate them.
Universe may be considered as separate soap bubbles (disconnected space-time), in which the observers living in one soap bubble cannot interact with those on another soap bubbles. Each soap bubble of space-time is denoted as universe. Actually our particular space-time is denoted as universe, just as we call our moon the ‘moon’. The separate universes are thought to be connected via worm holes created by Black Holes.The entire collection of these separate space-times is called Multiverse.
Matter in the universe is thought to be organized in strands or strings, a tiny structure.
The universe is everything within our connected space-time that could have a chance to interact with us and vice versa. According to the general theory of relativity, some regions of space may never interact with ours even in lifetime of the universe, due to finite speed of light and the ongoing expansion of space. For example, radio messages sent from earth may never reach some region of space, even if the universe would live forever; Space may expand faster than light can traverse it. The universe is immensely large and possibly infinite in volume. The region visible from earth (the observable universe) is a sphere with radius of about 47 billion light years.