Theres one more thing that is often assumed, but "wrong" -- that there's some global time.

For example if you hear something like "did you know that aliens from Alpha Centauri see Earth as it was 2 years ago, as it's the time light from Earth takes to reach Alpha Centauri?". No they do not, because it would assume that there's some common "now" between Earth and Alpha C.

If we assume a common "now", it would lead to a whole bunch of paradoxes and errors, like "what was before the Big Bang?" (error in the question), or "where is the center of the Universe?", or "those faint red-shifted stars that we see as they were almost 13 billion years ago".

This is a sequel to the author's I Don't Understand Quantum Physics - https://news.ycombinator.com/item?id=50219666

Author: Prof. Douglas Ross of Southampton University - https://www.southampton.ac.uk/~doug/