What is “proof”? What type of evidence crosses your personal threshold, and what should be the societal threshold?

This is perhaps a wider ontological question that many fields of study face (law, philosophy, medicine, etc), but I’d be intrigued to see how others define the word “proof,” and what criteria or standards should be included or expected when it comes to the bigger question of “are we alone?” How do you define that for yourself, and how should humanity define it on the whole for all of mankind? Do or should these differ? Should it be a “preponderance of the evidence” or a “beyond reasonable doubt” standard?

Personally I believe that there is such consternation around the topic and defining the term because on a deep level our own society and legal systems struggles with the same question.

Others have spoke to this point, but I think it’s also important to note the importance of “proof” being “self-evident.” In line with the “rational person standard” I believe that “proof” must be self-evident and easily observable and understood by the rational average adult person.

Personally, I believe in NHI and that we are not alone based on a preponderance of the evidence (video, sensor data, expert witnesses), but I’m not completely sold on it as I still maintain some reasonable doubt.

What is proof?