Theories of the universe's origin include:

1. **Big Bang Theory**: Proposes that the universe began from an extremely hot and dense point approximately 13.8 billion years ago and has been expanding ever since. It is supported by evidence such as cosmic microwave background radiation and the observed expansion of galaxies.

2. **Steady State Theory**: Suggests that the universe has always existed in a constant state, with new matter continuously created to maintain its density as it expands. This theory has largely been replaced by the Big Bang Theory due to observational evidence.

3. **Inflationary Theory**: An extension of the Big Bang Theory, it proposes that the universe underwent an exponential expansion during its earliest moments, smoothing out irregularities and explaining the uniformity observed in the cosmos.

4. **Multiverse Theory**: Suggests that our universe is one of many universes within a larger multiverse, each with different properties and origins. This theory explores possibilities beyond our observable universe.

These theories aim to explain the origin and evolution of the universe, each contributing to our understanding of cosmology.