Cosmology is one of those fields where I suspect we'll always be finding things that don't match with theory because we can never know nor replicate the initial

Cosmology is one of those fields where I suspect we'll always be finding things that don't match with theory because we can never know nor replicate the initial state of the Universe. There's also a lot of fundamental questions we don't have answers on. For example: - What does space expanding actually mean? Is space stretching or is new space being created? If so, what is the mechanism for that? - Is time a fumdanental property of the Universe or is it an emergent property? - What are the fundamental intereptations of quantum mechanics [1]? And so on. The cosmic microwave background is our earliest yet observation from the Universe. Before this the Universe was really too dense and hot for radiation signatures to survive. Interestingly, we may be able to peak even earlier than that with the cosmic neutrino background [2]. But there are a ton of things about the early Universe's formation and expansion we will probably never know and will only be able to guess at with models that will always break at a certain point. [1]: https://www.southampton.ac.uk/~doug/quantum_physics/interpretation.pdf https://www.southampton.ac.uk/~doug/quantum_physics/interpre... [2]: https://en.wikipedia.org/wiki/Cosmic_neutrino_background https://en.wikipedia.org/wiki/Cosmic_neutrino_background