The answer is science. Making an observation, creating a hypothesis, performing experiments, testing the hypothesis and accepting, rejecting or modifying the hypothesis based on the results, and then repeating the experiment — this whole process is called the scientific method.
You can have confidence in a theory or hypothesis when you see the same experiment lead to the same results, over and over again – regardless of who is performing the experiment. The more times the same results are produced, the more trust and confidence you can have that they are results you can rely on.
The key question is, are the same results reproduced when someone else performs the experiment? This is the guideline we have used on this website to choose what articles and sources to reference, to back up the information we’ve provided you on this site. Please check the citations page for the answers to the questions on this site. Note the wide variety of sources we’ve drawn from, across long periods of time from around the globe. Read the methods the authors used and see for yourself what you think.