Why can science-fiction writers talk about the possible impacts of new science and technology in ways actual scientist cannot

you need to include the text. we have no idea what you are referring to

well basically since ima beginner people will answer any subject "right away"and if you get more points you could ask more questions or if you answer someone's question you get points

sentence lenght varies according to word choice.you select which word to use and that will require to use other expressions that collocate with the word chosen.sentence length will vary   according to the choice of words you make to express your ideas.