A science (in a somewhat broader definition of the word) is a decipline focusing on facts that are based on testable and falsifiable evidence. So...you might be disinclined to post anything that is not testable or falsifiable such as astrology, religion, et hoc genus omni. Mathematics (though similar to science) is not in the scientific domain.
Other than that I am sure topics ABOUT science are acceptable (such as ethics, non-testable theory -- such as the string theory, and viewpoints about science, the scientific community, discoveries, etc.)