Truth and constructs

1 - Is "Truth" with a Capital T possible in science? How can we know if we've reached the truth in science? 2 - Can a field like psychology ever scientifically understand and explain an abstract construct? Are there certain areas of study/types of constructs that are that are easier to study than others? If so, why? 3 - For Mindfulness as a construct, do you believe we will be able to adequately define it in scientific psychological terms this semester? Why or why not?