I Do Understand Relativitysouthampton.ac.uk
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".
I don’t have knowledge on these topics beyond some YouTube videos, but if you entangled two particles and then transported one to Alpha Centauri, wouldn’t you have a common “now” if you were able to transmit data between them?
Entanglement (more correctly, wave-function collapse) cannot be used to transmit information. So there is a "spooky action at a distance", but there is no faster than light communication.
I find it's easier to understand if you assume that every entangled particle already "knows" what state it will be at the moment of entanglement. In theory it's called "hidden variables". John Stewart Bell has proven that there's no local hidden variables, but noone said about global variables. For example, in Superdeterminism it's all easy and clear.
PS: Physicists thet reject Superdeterminism only for philosophical reasons, there's no scientific reasons to reject it.
Suppose we observe an alien in Alpha C. The alien has (in our observation) its own observation instruments directed at us. What does the alien (in our observation) observe? Modulo possibly more carefully formulating ”directed at us”, is this a well-posed question? If so, what is the answer?
>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?".
I've always thought of this as true, and I don't understand why it isn't?
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/