What is the Universe? Is there only one universe? Why is it expanding?

The Universe is the entire collection of all matter and energy, including all galaxies, stars, planets, and other forms of matter and energy.

It is believed that there is only one Universe, as it is impossible to observe anything outside of it.

The Universe is expanding due to the force of gravity, which causes the space between galaxies to stretch out.

This expansion is driven by dark energy, a mysterious force that is still not fully understood.

Examples of galaxies in the Universe include the Milky Way and Andromeda galaxies.

Stars are formed within galaxies, and they are the source of light and heat in the Universe.

Planets, asteroids, and comets orbit stars, with the Solar System being an example of this.

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