Evidence

In science, everything has to be supported by evidence – no evidence,  no scientific theory.
Hyperspace is an example of science fiction as there is no evidence that faster than speed of light travel is possible. In the future, if this becomes possible then it will be science fact as there will be evidence to support it.
When writing a scientific paper e.g. dissertation, nothing that cannot be supported by evidence should be included.
Evidence comes from one of two sources:

1. Things that other people have discovered
2. Things you have discovered during your research