In two recent posts I discussed the question posed as to why there is something other than nothing and whether the question was even meaningful. The difficulty of showing that something does not exist is not confined to questions about the universe as a whole, it even applies to individual entities where you think it might be easier.
I got a text from a person I know and attached to it was a video of what looked like an organism consisting of the head and tail of a fish and, in between, the torso of a human being with arms behind its back and three pairs of breasts. This looked like it had been forwarded multiple times on social media and this person asked me if I thought it was real. I replied that it is safe to assume that anything seemingly bizarre that floats around the internet, and is not cited to a reputable news source along with supporting evidence, is a hoax. I did not tell him it was impossible that it was real because such a level of certainty implies omniscient knowledge on my part. But it is possible to be effectively certain that some things do not exist if one follows the logic of science.
On a recent episode of This American Life, they had a segment on investigations into Unidentified Aerial Phenomena (UAP) that were formerly referred to as UFOs. Although investigations showed that the ones that could be studied had mundane explanations like weather balloons, reflections off surfaces, camera-introduced effects and the like, it will never be possible to convince believers that extraterrestrial (ET) are not visiting us because new examples are continuously brought up. So in the debate over whether ETs are visiting us or not, it seems like the only possible definitive answer will be an affirmative one (if ETs were to actually make contact with us) while a definitive negative answer would forever remain elusive because however many cases are debunked, believers would never cease to have new cases to be investigated and thus could never ‘lose’ the argument. That seeming lack of ability to conclusively rule out the existence of an entity applies to any and all entities however absurd, like the fish-human hybrid sent to me, which is why we also have never-ending ‘debates’ about the existence of the Loch Ness monster, the Yeti, ghosts, vampires, and the like.
And yet, in science, we seem to be able to definitively say that some entities do not exist. We have done so with the aether, phlogiston, N-rays, etc. The ability to do so is a major part of the reason for science’s success since it prevents us from wasting time interminably debating the existence of spurious entities. The reason we can do so in science but not with things like UAPs is not because the entities in science are fundamentally different from things like UAPs but because in science we use the logic of science that includes decision rules that allow us to make definitive judgments. These decision rules depend upon the nature of the assertion (whether it is an existence claim or a universal claim) and where the corresponding burden of proof lies.
If someone makes an existence claim of an entity, the default position is nonexistence and the burden of proof is on that person to provide a preponderance of evidence in support of existence of that entity. Failure to do so implies nonexistence. For a universal claim (that, say, all electrons have the same mass), the default position (once some evidence in support of the claim is established) is that the claim is valid and the burden of proof is on the person challenging the claim to provide a preponderance of evidence that there is an exception to it. Failure to do so implies that the claim is valid. That is how scientific laws (which are universal claims) are established, because of the lack of credible evidence of a violation.
This logic and rules have close parallels with the reasoning used in the legal world to arrive at verdicts. It is the use of those rules that enables us to say with extremely high degrees of confidence that some things do not exist and that some laws always hold. This is why scientists tend to be skeptical of all supernatural claims, including the existence of gods, because there has never been a preponderance of evidence in favor of the claim.
The interesting thing is that scientists absorb the logic of science and the associated decision rules largely unconsciously during their training and practice and hence are often not explicitly aware that they are using them. This does not cause any problems within the world of science since all practitioners share the same implicit worldview but can result in frustration when they engage with the general public that does not share them. If people explicitly recognize the decision rules used in science and use them to adjudicate issues of existence and nonexistence of all entities, it is straightforward to conclude (with the same degree of certainty that the aether does not exist) that UAPs, ghosts, vampires, and gods do not exist either, thus saving us all a lot of time.
This has implications that extend well beyond things like UAPs which are, after all, fairly trivial matters. It has much more significant consequences when it comes to major issues such as climate change, the efficacy of vaccines, the dangers of smoking, and so on. Skeptics in these areas use the general ignorance of scientific logic to sow doubt as to the reliability and robustness of the scientific consensus in those areas. While they are perfectly happy to enjoy the tremendous benefits that science has provided, they are quite willing to jettison the very reasoning that science uses to obtain those successes when it leads to conclusions that are uncongenial to them for whatever reason. It is very important for public policy (especially in this age of anti-science sentiment) that we increase public awareness of the decision making rules used in science, and use them consistently, in order to make better policy decisions.
The argument that I have sketched out here is developed more fully in my book THE GREAT PARADOX OF SCIENCE: Why its conclusions can be relied upon even though they cannot be proven (Oxford University Press 2019).