Pop science journalists toss around words like prove when chronicling scientific discoveries. I often wonder what exactly they mean by this, and what readers must think. I fear that both journalist and reader attribute a certainty to scientific statements that is unjustified and unjustifiable.
Regardless of what is actually evoked by the word prove, let’s use the mathematical definition below for the sake of drawing distinctions. To prove a statement means to establish its truth beyond possibility of retraction. Proving a statement is true means it can never later be proved false.*
With this definition, no statement about the universe has ever been, or could ever be, proved. Every scientific statement could conceivably be retracted one day. Provable statements only appear in formal worlds like logic and pure mathematics.
Now, one can propose a mathematical model of some biological process and then prove statements about that model, but it is impossible to prove that those statements are true about the actual biological process that we observe in nature. Even if observations and experiments repeatedly point to the same conclusion, this does not guarantee that someday a new observation won’t call it into question.
Similarly, we cannot prove that any historical event actually occurred. What we commonly refer to as a fact is not a statement that can be proved. Though overwhelmingly likely, new evidence could call any historical fact into question.
In fact, this limitation makes science more interesting. Scientists are free to question the assumptions and conclusions of previous generations. They can develop better mechanisms for experimentation and observation. They can use their intellect to analyze the evidence and theorize. This process is not a proof, but it is honest work toward uncovering truths about the universe.
The problem is that non-scientists do not always understand this limitation. Read the comments section of any popular science article about physics or evolutionary biology. You will find commenters with unwavering faith in the ability of science to prove assertions about physical reality. But no. All science can do is formulate hypotheses, obtain and arrange evidence, and make arguments based on the evidence.
Some may be troubled by the unprovability of science. I am not. To me it means that we all retain legitimate free will when interpreting the universe. Obviously, some theories are much more likely than others. But we still have the freedom to reason and draw conclusions based on evidence, and science can never compel us to concede this freedom.
*Assuming the proof is valid. Furthermore, not all true formal statements can be proved. However, it is still the case that there exist formal statements for which there exist valid proofs. My point is that this is not the case for scientific statements.