What do scientists assume about the universe

There are many things that they assume, the assumption that it is expanding, it is more than 13 billion years old

The universe happened with a big bang, is a theory suggested by Stephen hawking an Astro scientist. According to scientists the universe is expected to get crunched, freeze or get ripped, that how it would end or probably start again with a bang.

There is also a theory of Multiverse, which means parallel universe, universe above universe or many universe.