"How do you know that other people are self-aware and not just very sophisticated computers?"
Until the day I meet a life-like android (or read that someone invented a life-like android), I will assume that all beings who appear to be self-aware, ARE actually self-aware human beings.
"lets say you had a box with something inside that gave answers to your questions, how could you ever tell if the thing in the box was self-aware?"
This sounds like a good definition of a Forum.
I type-out a question.
I send it to the Physics Forum.
Later, my computer screen comes back with an answer.
Certainly the answer could be self-generated by a computer program.
If the answer was clear and on-point, I wouldn't care if it came from a human (or not).
"If it's impossible [to tell the difference] then what's the point of talking about making computers that are self-aware if you can never prove that they are or are not?"
If I had a computer that was self-aware, it would be a simple matter to prove that it existed:
Input a question, and it outputs an answer.
Prove to a bystander that there is no external connection to a modem.
This will convince most people that the computer, itself, has output the answer.
If some scientist was still skeptical, I might show him the schematic of my design, and explain how my computer works. Then he would methodically go through the computer, attempting to hunt-down the secret modem. At some point, he would be convinced. Soon thereafter, I will win the Nobel Prize, and this will help convince the rest of the world that I have (indeed) created a self-aware computer.
It is impossible for a human to live in a Vacuum.
There is a Vacuum between the Earth and moon.
Therefore, what's the point of a Space program.
There is impossible ... and then there is IMPOSSIBLE.